Name: quantification of hydrogen concentrations in surface and interface layers and bulk materials through depth profiling with nuclear reaction analysis
Uploaded: 2016-03-29T13:00:00
Description: Watch this Scientific Journal Video about Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis at JoVE.co

We greatly appreciate M. Matsumoto for implementing the software that enables the automated measurement of NRA H depth profiles by remotely controlling the MALT accelerator parameters from the data acquisition PC. We thank K. Namba for skillfully performing Pd(110) sample preparations and NRA and TDS measurements at the BL-1E UHV system, and C. Nakano for technical assistance in the accelerator operation. The SiO2/Si(100) specimen is gratefully received as a courtesy of Z. Liu of NEC Corporation, Japan. This work is partially supported by Grants-in-Aid for Scientific Research (Grant numbers 24246013 and 26108705) of the Japan Society for the Promotion of Science (JSPS), as well as through a Grant-in-Aid for Scientific Research in Innovative Areas &#39;Material Design through Computics: Complex Correlation and Non-Equilibrium Dynamics&#39; from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

1. Planning of Experiments
<ol>
	<li>Identify the MALT accelerator beam line of interest depending on the measurement task (BL-1E for surface hydrogen, BL-2C for bulk or interfacial hydrogen). Contact the assisting scientist (currently M.W. or K.F.) to discuss details of the NRA measurements and their necessary preparations.</li>
	<li>Download a beam time application form and observe the submission deadline on the MALT website31. 
	Note: The MALT facility invites new project proposals each March and Sep...

<ol>
	<li>Lanford, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+for+hydrogen+by+nuclear-reaction+and+energy+recoil+detection.">Analysis for hydrogen by nuclear-reaction and energy recoil detection.</a> Nucl. Instrum. Methods Phys. Res. B. 66 ((1-2)), 65-82 (1992).</li><li>Lanford, W. A., JR, T. e. s. m. e. r., M, N. a. s. t. a. s. i. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nuclear+Reactions+for+Hydrogen+Analysis,+Chapter+8.">Nuclear Reactions for Hydrogen Analysis, Chapter 8.</a> Handbook of Modern Ion Beam Materials Analysis. , 193-204 (1995).</li><li>Wilde, M., Fukutani, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+detection+near+surfaces+and+shallow+interfaces+with+resonant+nuclear+reaction+analysis.">Hydrogen detection near surfaces and shallow interfaces with resonant nuclear reaction analysis.</a> Surf. Sci. Rep. 69 (4), 196-295 (2014).</li><li>Lanford, W. A., Trautvetter, H. P., Ziegler, J. F., Keller, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+precision+technique+for+measuring+concentration+versus+depth+of+hydrogen+in+solids.">New precision technique for measuring concentration versus depth of hydrogen in solids.</a> Appl. Phys. Lett. 28 (9), 566-568 (1976).</li><li>Ross, R. C., Tsong, I. S. T., Messier, R., Lanford, W. A., Burman, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+hydrogen+in+a-Si-H+films+by+IR+spectrometry,+N-15+nuclear-reaction,+and+SIMS.">Quantification of hydrogen in a-Si-H films by IR spectrometry, N-15 nuclear-reaction, and SIMS.</a> J. Vac. Sci. Technol. 20 (3), 406-409 (1982).</li><li>Suzuki, T., Konishi, J., Yamamoto, K., Ogura, S., Fukutani, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Practical+IR+extinction+coefficients+of+water+in+soda+lime+aluminosilicate+glasses+determined+by+nuclear+reaction+analysis.">Practical IR extinction coefficients of water in soda lime aluminosilicate glasses determined by nuclear reaction analysis.</a> J. Non-Cryst. Solids. 382, 66-69 (2013).</li><li>Wagner, W., Rauch, F., Bange, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Concentration+profiles+of+hydrogen+in+technical+oxidic+thin-films+and+multilayer+systems.">Concentration profiles of hydrogen in technical oxidic thin-films and multilayer systems.</a> Fresenius Z. Analyt. Chem. 333 (4-5), 478-480 (1989).</li><li>Wagner, W., Rauch, F., Ottermann, C., Bange, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In-depth+profiling+of+hydrogen+in+oxidic+multilayer+systems.">In-depth profiling of hydrogen in oxidic multilayer systems.</a> Surf. Interf. Anal. 16 (1-12), 331-334 (1990).</li><li>Wagner, W., Rauch, F., Ottermann, C., Bange, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+dynamics+in+electrochromic+multilayer+systems+investigated+by+the+N-15+technique.">Hydrogen dynamics in electrochromic multilayer systems investigated by the N-15 technique.</a> Nucl. Instrum. Methods Phys. Res. B. 50 (1-4), 331-334 (1990).</li><li>Hj&#246;rvarsson, B., Ryd&#233;n, J., Karlsson, E., Birch, J., Sundgren, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interface+effects+of+hydrogen+uptake+in+Mo/V+single-crystal+superlattices.">Interface effects of hydrogen uptake in Mo/V single-crystal superlattices.</a> Phys. Rev. B. 43 (8), 6440-6445 (1991).</li><li>Fukutani, K., Itoh, A., Wilde, M., Matsumoto, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zero-Point+Vibration+of+Hydrogen+Adsorbed+on+Si+and+Pt+Surfaces.">Zero-Point Vibration of Hydrogen Adsorbed on Si and Pt Surfaces.</a> Phys. Rev. Lett. 88 (11), 116101 (2002).</li><li>Ericson, J. E., Dersch, O., Rauch, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quartz+hydration+dating.">Quartz hydration dating.</a> J. Archaeological Sci. 31 (7), 883-902 (2004).</li><li>Wilde, M., Matsumoto, M., Fukutani, K., Aruga, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Depth-resolved+analysis+of+subsurface+hydrogen+absorbed+by+Pd(100).">Depth-resolved analysis of subsurface hydrogen absorbed by Pd(100).</a> Surf. Sci. 482-485 (Part 1), 346-352 (2001).</li><li>Wilde, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+sorption+by+Ti(0001)+single+crystal+surfaces.">Hydrogen sorption by Ti(0001) single crystal surfaces.</a> J. Vac. Soc. Jpn. 45 (5), 458-462 (2002).</li><li>Ohno, S., Wilde, M., Fukutani, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+insight+into+the+hydrogen+absorption+mechanism+at+the+Pd(110)+surface.">Novel insight into the hydrogen absorption mechanism at the Pd(110) surface.</a> J. Chem. Phys. 140 (13), 134705 (2014).</li><li>Fukutani, K., Wilde, M., Matsumoto, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nuclear-reaction+analysis+of+H+at+the+Pb/Si(111)+inter-face:+Monolayer+depth+distinction+and+interface+structure.">Nuclear-reaction analysis of H at the Pb/Si(111) inter-face: Monolayer depth distinction and interface structure.</a> Phys. Rev. B. 64 (24), 245411 (2001).</li><li>Wilde, M., Fukutani, K., Naschitzki, M., Freund, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+absorption+in+oxide-supported+palladium+nanocrystals.">Hydrogen absorption in oxide-supported palladium nanocrystals.</a> Phys. Rev. B. 77 (11), 113412 (2008).</li><li>Wilde, M., Fukutani, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Penetration+mechanisms+of+surface-adsorbed+hydrogen+atoms+into+bulk+metals:+Experiment+and+model.">Penetration mechanisms of surface-adsorbed hydrogen atoms into bulk metals: Experiment and model.</a> Phys. Rev. B. 78, 115411 (2008).</li><li>Okada, M., Nakamura, M., Moritani, K., Kasai, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dissociative+adsorption+of+hydrogen+on+thin+Au+films+grown+on+Ir(111).">Dissociative adsorption of hydrogen on thin Au films grown on Ir(111).</a> Surf. Sci. 523 (3), 218-230 (2003).</li><li>Okada, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reactivity+of+gold+thin+films+grown+on+iridium:+Hydrogen+dissociation.">Reactivity of gold thin films grown on iridium: Hydrogen dissociation.</a> Appl. Catal. A General. 291 (1-2), 55-61 (2005).</li><li>Okada, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reactive+gold+thin+films+grown+on+iridium.">Reactive gold thin films grown on iridium.</a> Appl. Surf. Sci. 246 (1-3), 68-71 (2005).</li><li>Ogura, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+adsorption+on+Ag+and+Au+monolayers+grown+on+Pt(111).">Hydrogen adsorption on Ag and Au monolayers grown on Pt(111).</a> Surf. Sci. 566-568 (Part 2), 755-760 (2004).</li><li>Fukutani, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interface+hydrogen+between+a+Pb+overlayer+and+H-saturated+Si(111)+studied+by+a+resonant+nuclear+reaction.">Interface hydrogen between a Pb overlayer and H-saturated Si(111) studied by a resonant nuclear reaction.</a> Surf. Sci. 377 (1-3), 1010-1014 (1997).</li><li>Fukutani, K., Iwai, H., Murata, Y., Yamashita, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+at+the+surface+and+interface+of+metals+on+Si(111).">Hydrogen at the surface and interface of metals on Si(111).</a> Phys. Rev. B. 59 (20), 13020-13025 (1999).</li><li>Wilde, M., Fukutani, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-temperature+growth+of+Au+on+H-terminated+Si(111):+Instability+of+hydrogen+at+the+Au/Si+interface+revealed+by+non-destructive+ultra-shallow+H-depth+profiling.">Low-temperature growth of Au on H-terminated Si(111): Instability of hydrogen at the Au/Si interface revealed by non-destructive ultra-shallow H-depth profiling.</a> Jpn. J. Appl. Phys. 42 (7B), 4650-4654 (2003).</li><li>Liu, Z., Fujieda, S., Ishigaki, H., Wilde, M., Fukutani, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current+Understanding+of+the+Transport+Behavior+of+Hydrogen+Species+in+MOS+Stacks+and+Their+Relation+to+Reliability+Degradation.">Current Understanding of the Transport Behavior of Hydrogen Species in MOS Stacks and Their Relation to Reliability Degradation.</a> ECS Transactions. 35 (4), 55-72 (2011).</li><li>Zinke-Allmang, M., Kalbitzer, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+method+to+determine+vibrational+energy+states+of+atomic+systems.">A novel method to determine vibrational energy states of atomic systems.</a> Z. Physik A. 323 (2), 251-252 (1986).</li><li>Zinke-Allmang, M., Kalbitzer, S., Weiser, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nuclear+reaction+spectroscopy+of+vibrational+modes+of+solids.">Nuclear reaction spectroscopy of vibrational modes of solids.</a> Z. Physik A. 325 (2), 183-191 (1986).</li><li>N, B. o. h. r. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> K. Dan. Vidensk. Selsk. Mat. -Fys. Medd. 18, (1948).</li><li>Rud, N., B&#248;ttiger, J., Jensen, P. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurements+of+energy-loss+distributions+for+6.5+MeV+15N+ions+in+solids.">Measurements of energy-loss distributions for 6.5 MeV 15N ions in solids.</a> Nucl. Instrum. Methods. 151 (1-2), 247-252 (1978).</li><li>Briggs, D., Seah, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy. , (1983).</li><li>Rieder, K. H., Baumberger, M., Stocker, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selective+Transition+of+Chemisorbed+Hydrogen+to+Subsurface+Sites+on+Pd(110).">Selective Transition of Chemisorbed Hydrogen to Subsurface Sites on Pd(110).</a> Phys. Rev. Lett. 51 (19), 1799-1802 (1983).</li><li>Dong, W., Ledentu, V., Sautet, P., Kresse, G., Hafner, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+theoretical+study+of+the+H-induced+reconstructions+of+the+Pd(110)+surface.">A theoretical study of the H-induced reconstructions of the Pd(110) surface.</a> Surf. Sci. 377-379, 56-61 (1997).</li><li>Wilde, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+H2-annealing+on+the+hydrogen+distribution+near+SiO2/Si(100)+interfaces+revealed+by+in+situ+nuclear+reaction+analysis.">Influence of H2-annealing on the hydrogen distribution near SiO2/Si(100) interfaces revealed by in situ nuclear reaction analysis.</a> J. Appl. Phys. 92 (8), 4320-4329 (2002).</li><li>Himpsel, F. J., McFeely, F. R., Taleb-Ibrahimi, A., Yarmoff, J. A., Hollinger, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microscopic+structure+of+the+SiO2/Si+interface.">Microscopic structure of the SiO2/Si interface.</a> Phys. Rev. B. 38 (9), 6084-6096 (1988).</li><li>Helms, C. R., Poindexter, E. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+silicon-silicon+dioxide+system:+Its+microstructure+and+imperfections.">The silicon-silicon dioxide system: Its microstructure and imperfections.</a> Rep. Progr. Phys. 57 (8), 791 (1994).</li><li>Briere, M. A., Wulf, F., Braunig, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurements+of+the+accumulation+of+hydrogen+at+the+silicon-silicon-dioxide+interface+using+nuclear+reaction+analysis.">Measurements of the accumulation of hydrogen at the silicon-silicon-dioxide interface using nuclear reaction analysis.</a> Nucl. Instrum. Methods Phys. Res. B. 45 (1-4), 45-48 (1990).</li><li>Ecker, K. H., Krauser, J., Weidinger, A., Weise, H. P., Maser, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nuclear+reaction+analysis+of+hydrogen+migration+in+silicon+dioxide+films+on+silicon+under+N-15+ion+irradiation.">Nuclear reaction analysis of hydrogen migration in silicon dioxide films on silicon under N-15 ion irradiation.</a> Nucl. Instrum. Methods Phys. Res. B. 161-163, 682-685 (2000).</li><li>Maser, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogen+migration+in+wet-thermally+grown+silicon+dioxide+layers+due+to+high+dose+15N+ion+beam+irradiation.">Hydrogen migration in wet-thermally grown silicon dioxide layers due to high dose 15N ion beam irradiation.</a> Microelectron. Eng. 48, 1-4 (1999).</li><li>Bugeat, J. P., Ligeon, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+ion+beam+bombardment+in+hydrogen+surface+layer+analysis.">Influence of ion beam bombardment in hydrogen surface layer analysis.</a> Nucl. Instrum. Methods. 159 (1), 117-124 (1979).</li><li>Wilde, M., Fukutani, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+non-resonant+background+in+hydrogen+depth+profiling+via+1H(15N,ag)12C+nuclear+reaction+analysis+near+13.35+MeV.">Evaluation of non-resonant background in hydrogen depth profiling via 1H(15N,ag)12C nuclear reaction analysis near 13.35 MeV.</a> Nucl. Instrum. Methods Phys. Res. B. 232 (1-4), 280-284 (2005).</li><li>Horn, K. M., Lanford, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Suppression+of+background+radiation+in+BGO+and+NaI+detectors+used+in+nuclear+reaction+analysis.">Suppression of background radiation in BGO and NaI detectors used in nuclear reaction analysis.</a> Nucl. Instrum. Methods Phys. Res. B. 45 (1-4), 256-259 (1990).</li></ol>

Figure 4 demonstrates the efficient distinction and quantitation of surface-adsorbed from bulk-absorbed hydrogen through 15N NRA at the example of a Pd(110) single crystal in the BL-1E UHV system. The high reproducibility of the surface H peak in the three profiles attests to the reliability of the in-situ UHV sample preparation and to the non-destructive nature of the NRA measurement. The quantitative agreement of the determined H coverage with the expected atomic saturation density ...

The ubiquity of hydrogen as an impurity or as a constituent of a vast variety of materials and the wealth of hydrogen-induced interaction phenomena make revealing the hydrogen distribution in the near-surface region and at buried interfaces of solids an important task in many areas of engineering and fundamental material science. Prominent contexts include studies of hydrogen absorption in storage and purification materials for hydrogen energy applications, fuel cell, photo-, and hydrogenation catalysis, hydrogen retention and embrittlement in nuclear and fusion reactor engineering, hydrogen-induced surfactant effects in epitaxial growth fabrication and hydrogen-related electrical reliability issues in semiconductor device technology.
Despite its omnipresence and simple atomic structure, the quantitative detection of hydrogen poses analytical challenges. As hydrogen contains only a single electron, otherwise versatile elemental analysis by electron spectroscopy is rendered ineffective. Common hydrogen detection methods through mass analytical, optical, or nuclear resonance techniques such as metallurgical fusion, thermal desorption, infrared absorption or NMR spectroscopy are principally insensitive to the depth location of hydrogen. This precludes, e.g., discriminating between surface-adsorbed and bulk-absorbed hydrogen which differ substantially in their physical and chemical material interactions, and their distinction therefore becomes increasingly important for the analysis of nanostructured materials that comprise small volumes and large surface areas. Hydrogen profiling by secondary ion mass spectroscopy, although providing depth-resolved quantitative H concentrations, is equally destructive to the analyzed target as metallurgical fusion, and sputtering effects may render the depth information obtained near the surface unreliable.
Nuclear reaction analysis with the narrow energy resonance (Eres) of the 1H(15N,&#945;&#947;)12C reaction at 6.385 MeV1-3, on the other hand, combines the advantages of non-destructive hydrogen quantitation with high depth resolution in the order of a few nanometers near the surface. The method determines surface H coverages with a sensitivity in the order of 1013 cm-2 (~1% of a typical atomic monolayer density). Hydrogen concentrations in the interior of materials can be assessed with a detection limit of several 1018 cm-3 (~100 at. ppm) and a probing depth range of about 2 &#956;m. The near-surface depth resolution is routinely 2-5 nm in surface-normal incidence of the 15N ion beam onto the analyzed target. In surface-grazing incidence geometries, the resolution can be enhanced further to values below 1 nm. See Ref. 3 for a detailed account.
These capabilities have proven 1H(15N,&#945;&#947;)12C NRA as a powerful technique to elucidate the static and dynamic behavior of hydrogen at surfaces and interfaces in a large variety of processes and materials3. Established by Lanford4 in 1976, 15N NRA was first used predominantly to quantitatively determine volume H concentrations in bulk materials and thin films. Among other purposes, the absolute hydrogen concentrations obtained through 15N NRA have been used to calibrate other, not directly quantitative, hydrogen detection techniques5,6. Also 15N NRA hydrogen profiling in targets with well-defined interfaces in layered thin film structures has been described7-10. More recently, much progress has been achieved in studying hydrogen in the near-surface region of chemically clean and structurally well-defined targets by combining 15N NRA with surface analytical ultra-high vacuum (UHV) instrumentation to prepare atomically controlled surfaces in situ for the H analysis3.
By quantifying the hydrogen coverage on single crystal surfaces, NRA has contributed significantly to the current microscopic understanding of hydrogen adsorption phases on many materials. 1H(15N,&#945;&#947;)12C NRA is furthermore the only experimental technique to directly measure the zero-point vibrational energy of surface-adsorbed H atoms11, i.e., it can reveal the quantum-mechanical vibrational motion of adsorbed H atoms in the direction of the incident ion beam. Through the capability of nanometer-scale discrimination between surface-adsorbed and bulk-absorbed H, 15N NRA can provide valuable insight into the hydrogen ingress through material surfaces, such as relevant to mineral hydration dating12 or for observing hydride nucleation underneath surfaces of H-absorbing metals13-15. High-resolution 15N NRA applications have demonstrated the potential to detect sub-monolayer thickness variations of adlayers16 and to distinguish surface-adsorbed from volume-absorbed hydrogen in Pd nanocrystals17. The combination with thermal desorption spectroscopy (TDS) allows for unambiguous identifications of H2 thermal desorption features and for the depth-resolved assessment of the thermal stability of adsorbed and absorbed hydrogen states against desorption and diffusion13,15,18. Due to its non-destructive nature and high depth resolution 1H(15N,&#945;&#947;)12C NRA is also the ideal method to detect hydrogen buried at intact interfaces, which allows for studying hydrogen trapping at metal/metal19-22 and metal/semiconductor interfaces16,23-25 and for tracking hydrogen diffusion in stacked thin film systems9. By directly visualizing hydrogen redistribution phenomena between interfaces of SiO2/Si-based metal-oxide-semiconductor (MOS) structures that relate to electrical device degradation, NRA has made particularly valuable contributions to device reliability research26.
The hydrogen detection principle in NRA is to irradiate the analyzed target with a 15N ion beam of at least Eres=6.385 MeV to induce the resonant 1H(15N,&#945;&#947;)12C nuclear reaction between 15N and 1H in the material. This reaction releases characteristic &#947;-rays of 4.43 MeV that are measured with a scintillation detector nearby the sample. The &#947;-yield is proportional to the H concentration in a certain depth of the target. Normalizing this signal by the number of incident 15N ions converts it into absolute H density after the &#947;-detection system has been calibrated with a standard target of known H concentration. 15N ions incident at Eres can react with hydrogen on the target surface. The concentration of buried hydrogen is measured with 15N ions incident at energies (Ei) above Eres. Inside the target material, the 15N ions suffer energy loss due to electronic stopping. This effect provides the high depth resolution, because the 1H(15N,&#945;&#947;)12C nuclear reaction resonance has a very narrow width (Lorentzian width parameter &#915; = 1.8 keV) and the stopping power of materials for 6.4 MeV 15N ranges between 1-4 keV/nm, so that the passage of the 15N ion through only a few atomic layers is sufficient to shift its energy outside the resonance window. Thus, the resonant reaction detects buried H at Ei &#62; Eres in a probing depth d=(Ei-Eres)/S, where S is the electronic stopping power of the analyzed material3.
By measuring the &#947;-yield while scanning the incident 15N ion energy in small increments, one obtains a nuclear reaction excitation curve that contains the density-depth distribution of hydrogen in the target. In this excitation curve (&#947;-yield vs. 15N energy), the actual H depth distribution is convolved with the NRA instrumental function that adds a predominantly Gaussian broadening and is the main limitation for the depth resolution3. At the surface (i.e., at Ei = Eres) the Gaussian width is dominated by a Doppler Effect due to zero-point vibration of the H atoms against the target surface.11,27,28 The yield curve of buried hydrogen detected at Ei &#62; Eres is affected by an additional Gaussian broadening component due to random 15N ion energy straggling inside the target. The straggling width increases in proportion to the square root of the ion trajectory length in the material 29,30 and becomes the dominant resolution limiting factor above probing depths of 10-20 nm.
To demonstrate a few very typical hydrogen profiling applications with 15N NRA, we here exemplarily describe (1) the quantitative evaluation of the surface H coverage and of the bulk-absorbed hydrogen concentration in a H2 exposed palladium (Pd) single crystal, and (2) the evaluation of the depth location and hydrogen layer densities at buried interfaces of SiO2/Si(100) stacks. The NRA measurements are performed at the MALT 5 MV van-de-Graaf tandem accelerator31 of the University of Tokyo, which delivers a highly stable and well-monochromatized (&#916;Ei &#8805; 2 keV) 15N ion beam of 6-13 MeV. The authors have developed a computer control system for the accelerator to enable automated energy scanning and data acquisition for hydrogen profiling. Reflecting the two different NRA measurement tasks presented by the above H profiling applications, the MALT facility provides two ion beam lines with specialized experimental stations: (1) a UHV surface analytical system with a single bismuth germanate (BGO, Bi4Ge3O12) &#947;-scintillation detector dedicated to the NRA quantitation of hydrogen surface coverages, to zero-point vibration spectroscopy, and to H depth profiling at atomically controlled single crystal targets in a unique combination with TDS; and (2) a high vacuum chamber equipped with two BGO detectors positioned very close to the target for increased &#947;-detection efficiency, providing for a lower H detection limit and faster data acquisition. This setup has no sample preparation facilities but allows for rapid sample exchange (~30 min) and thus for a higher throughput of targets for which a well-controlled surface layer is not an essential part of the analytical task, such as H profiling at buried interfaces or the quantitation of bulk H concentrations. At both beam lines, the BGO detectors are placed conveniently outside of the vacuum systems because the &#947;-rays penetrate the thin chamber walls with negligible attenuation.
<img alt="Figure 1" src="/files/ftp_upload/53452/53452fig1.jpg" /> 
Figure 1. NRA setup in the BL-1E UHV system. (A) Schematic top view into the BL-1E UHV system equipped with sputter ion gun, low energy electron diffraction (LEED), and Auger electron spectroscopy (AES) for the in-situ preparation of atomically ordered and chemically clean single crystal surface targets and combined NRA and TDS measurements with a quadrupole mass spectrometer (QMS) mounted on a linear translation stage. (B) Pd single crystal specimen attached on the sample holder of the cryogenic manipulator. <a href="https://www.jove.com/files/ftp_upload/53452/53452fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Figure 1 (A) illustrates the UHV system at beam line (BL)-1E, which is fully equipped for the in-situ preparation of atomically ordered single crystal surfaces and has a base pressure &#60;10-8 Pa to maintain surface cleanliness. To provide sample access for the surface-analytical tools, the 4&#34; BGO scintillator is placed on the 15N ion beam axis ~30 mm behind the target. The sample is mounted on a 4-axis manipulation stage for precise (x, y, z, &#920;) positioning and can be cooled with liquid nitrogen to ~80 K or with compressed He to ~20 K. Figure 1 (B) shows a Pd single crystal target mounted by spot-welded Ta support wires to a He compression cryostat. Quartz sheet spacers insulate the sample holder plate electrically from the cryostat body. This enables the incident 15N ion beam current measurement necessary for quantitative NRA and allows for electron bombardment heating from the tungsten filament on the backside of the sample holder. A type K thermocouple is spot-welded to the edge of the Pd specimen. A quartz plate attached on the manipulator axis above the sample is used to monitor the ion beam profile and for sample-beam alignment. Figure 2 (A) shows the setup at BL-2C with two 4&#34; BGO detectors arranged at 90&#176; with respect to the 15N beam with their front face no further than 19.5 mm apart from the beam axis. The sample holder (Figure 2 (B)) provides a simple clamping mechanism for quick sample exchange and allows for rotation of the sample around the vertical axis to adjust the 15N incidence angle.
<img alt="Figure 2" src="/files/ftp_upload/53452/53452fig2.jpg" /> 
Figure 2. NRA setup at BL-2C. (A) Schematic top view into the high vacuum chamber at BL-2C equipped with two BGO &#947;-detectors close to the target position. (B) Sample holder with a large chip target of SiO2/Si(100) clamped on. Fogging up this sample type with water vapor after the NRA analysis visualizes the spots that were irradiated by the 15N ion beam. <a href="https://www.jove.com/files/ftp_upload/53452/53452fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table>
	<tbody>
		<tr>
			<td>Pd single crystal&#160;</td>
			<td>SPL (Surface Preparation Laboratory), http://www.spl.eu/products.html, or any other suitable supplier</td>
			<td>Order made to specification</td>
			<td>Disk, 9 mm diam., (110) oriented, aligned to &#60; 0.5 degree or less, one side polished to &#60; 0.3 mm roughness, self-prepared specimen&#160;</td>
		</tr>
		<tr>
			<td>H2 gas</td>
			<td>Joutou Gas Corporation, Ltd., Japan, http://www.jyotougas.co.jp/item/gas.html</td>
			<td></td>
			<td>(99.9995%), or any other suitable supplier</td>
		</tr>
		<tr>
			<td>O2 gas</td>
			<td>Joutou Gas Corporation, Ltd., Japan, http://www.jyotougas.co.jp/item/gas.html</td>
			<td></td>
			<td>(99.99%), or any other suitable supplier</td>
		</tr>
		<tr>
			<td>Ar gas</td>
			<td>Joutou Gas Corporation, Ltd., Japan, http://www.jyotougas.co.jp/item/gas.html</td>
			<td></td>
			<td>(99.99995%), or any other suitable supplier</td>
		</tr>
		<tr>
			<td>Tantalum / Wire</td>
			<td>The Nilaco Corporation, http://nilaco.jp/en/order.php</td>
			<td>TA-411325</td>
			<td>(99.95%), 0.3 mm diam., or any other suitable supplier</td>
		</tr>
		<tr>
			<td>Alumel / Wire&#160;</td>
			<td>The Nilaco Corporation, http://nilaco.jp/en/order.php</td>
			<td>851266</td>
			<td>0.2 mm diam., or any other suitable supplier</td>
		</tr>
		<tr>
			<td>Chromel / Wire (Chromel)</td>
			<td>The Nilaco Corporation, http://nilaco.jp/en/order.php</td>
			<td>861266</td>
			<td>0.2 mm diam., or any other suitable supplier</td>
		</tr>
	</tbody>
</table>

quantification of hydrogen concentrations in surface and interface layers and bulk materials through depth profiling with nuclear reaction analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

Figure 4 shows near-surface NRA H profiles of H2-exposed Pd(110) measured in the BL-1E UHV system at a sample temperature of 90 K under a H2 background pressure of 1.33&#215;10-6 Pa. The 15N ion incidence energy has been converted into probing depth using the stopping power of Pd (S = 3.90 keV/nm). The open symbol profile was obtained after pre-exposing the Pd(110) sample to 2,000 L H2 at 145 K to induce abso...

Watch this Scientific Journal Video about Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis at JoVE.co

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

The overall goal of nuclear reaction analysis with the resonant 15 nH nuclear reaction is to measure the density of absorbed hydrogen atoms on solid surfaces, and to determine the concentration versus depth distribution of absorbed hydrogen in the volume of materials. Clarifying the hydrogen content on surfaces, in the near surface region, and at shallow interfaces of solids is a key question in many fields of fundamental material science and engineering. The main advantage of nuclear reaction analysis is that it reveals the concentration and depth location of hydrogen quantitatively, nondestructively, and with nanometer depth resolution.Hydrogen profiling with NRA supports research of hydrogen storage and purification materials. Fuel cell and hydrogenation catalysts, hydrogen retention and embrittlement, device fabrication and hydrogen-related reliability concerns in semi-conducted technology. In this video, we demonstrate a unique combination of NRA with surface science instrumentation for the quantification of a hydrogen-layered densities on atomically-controlled target surfaces and at shallow interfaces.These nuclear reaction analysis experiments take place at the University of Tokyo's MALT accelerator facility. Measurements of surface hydrogen are done on beam line 1E in this ultra-high vacuum chamber. This chamber has been loaded with a palladium 110 single crystal sample and is held at less than 10 nanopascals at room temperature.This top view schematic of the sample chamber gives an overview of the equipment layout. The nitrogen ion beam line including a deflector and a Faraday cup comes in at the left. In addition, there is an ion gun for sputtering as well as an input for hydrogen.The chamber is equipped to perform low energy electron diffraction and Auger electron spectroscopy for INC2 preparation of targets. The final two instruments are quadrupole mass spectrometer shown at the bottom of the schematic and a scintillation detection system at the right. The sample is held by a sample holder on an XYZ stage near the center of the chamber and can be viewed through a viewport.This picture provides an example of the sample holder with a sample that is currently in the chamber. Tantalum wires support a single crystal specimen. The holder also facilitates electrical and thermal measurements.Begin with cleaning the target surface in the chamber through sputtering and annealing. Operate the XYZ stage to position the sample in the center of the chamber. In addition, rotate the sample to properly align it.The sample should face the gas doser between the ion gun and the viewport. To fine adjust the angle, turn on the ion gun power supply. Adjust emission control to 20 milliamps.Observe the sample through the viewport while fine adjusting its angle. The goal is to have the mirror image of the ion gun filament visible on the sample surface. Once fine adjustment is complete, change the ion gun power supply setting for the beam energy to 800 electron volts.Next, at the bottom of the chamber, close the NEG pump gate valve. Use a variable leak valve to introduce 9 millipascal argon gas into the chamber. For sputter ion current reading, consult the digital tester connected between the sample and ground.Confirm that the current is around two microamps for the 10-minute duration of the sputter. Stop the sputtering by closing the variable leak valve and turning off the ion gun power supply. Continue preparations by bringing liquid nitrogen to the manipulator and adding about 100 milliliters to the cryostat.Stay at the manipulator to make electrical connections for annealing. Connect the filament heater lids to the heater power supply. Also, connect the thermocouple feedthrough to a digital tester to monitor the temperature.Ground the filament by connecting it to the chamber body. Finally, connect the sample contact to the bias voltage power supply. At this point, set up the high voltage power supply.Apply a sample bias of one kilovolt. Proceed to anneal the sample at 1, 000 Kelvin and oxidize it at 750 Kelvin. After annealing and oxidation, prepare to do low energy electron diffraction on the sample.Observe the diffraction pattern and look for a clear structure with bright spots and low background noise as in this example. Be prepared to repeat the sputtering, annealing, oxidation, and reduction steps as necessary. The next step is to align the nitrogen ion beam to the single crystal target for nuclear reaction analysis.Center the sample in the XY plane and adjust the Z position to the height of the mass spectrometer front aperture. Rotate the sample back to face the beam line. Next, lower the sample holder to put the beam profile monitor into position for nuclear reaction analysis.Set a camera on the window flange to transmit beam profile images to the control room. Return to the manipulator and remove all electrical contacts to the sample. After this, attach the sample current line.Now, prepare for introducing the ion beam. Set the electrostatic deflector voltage on the beam line to 8, 500 volts. Enter the control room to continue.There, switch the current integrator from standby mode to operate. This schematic represents a portion of the accelerator beam line before the ion beam is stirred to the different experiment beam lines. The experiment beam lines are also represented.There are four components that are important for this protocol. BM03 is a 90-degree sector magnet. It selects the ion beam energy during depth profiling.FC04 is a Faraday cup that can be inserted into the beam to read the ion beam current and prevent the beam from reaching the sample. MQ04 is a magnetic quadrupole lens used to focus the beam onto the sample. And BM04 is a bending magnet that directs the beam into the beam lines.Take steps to adjust the ion beam energy and direct the beam onto the target in the vacuum chamber. Set the MQ04 magnetic quadrupole lens, XCC and the YCC lens parameters to approximately focus the beam. Open the gate valves between the accelerator and the beam line and then open the Faraday cup, FC04.Use the monitor to observe the ion beam profile on the quart's plate in the target chamber. With this feedback, fine-tune the bending magnet, BM04 and the magnetic quadrupole lens settings. The goal is to obtain a well-focused ion beam in the center of the profile monitor plate.Close the Faraday cup and record the parameters before returning to the beam line. Back on beam line 1E, use the filament heater to flash heat the palladium sample to 600 Kelvin then set the filament heater to about 3.6 amps to maintain the sample temperature at 145 Kelvin. Isolate the chamber from the accelerator and NEG pump before exposing the sample to 2, 000 langmuirs of hydrogen at 145 Kelvin.Turn off the filament heater and when the temperature reaches 80 Kelvin, adjust the hydrogen background pressure to be one micropascal. Back in the control room, arrange for the nitrogen ion beam to have the desired starting energy. For this experiment, ensure that Faraday cup 04 registers a beam current of 10 to 20 nanoamps.Next, enter the parameters for the energy scan and the acquisition time into the control software before starting automated data acquisition. These are typical parameter values for BM03 to control the energy scan. Values are given for selecting the initial energy, the final energy, and the change in energy with each step.The acquisition time is 50 seconds. Measurements of bulk and interface hydrogen are done on beam line 2C. This manipulator has been removed from the beam line and is ready with a new sample in the sample holder.For these measurements, the sample is a thin film of silicon dioxide on a silicon 100 surface. With the sample aligned parallel to the transfer tube access, tighten the clamp screws to secure it in place. Retract the sample into the transfer tube and secure it with a locking screw.Move the manipulator to its position on the beam line and reinstall it on the gate valve. When the system is ready, lower the sample into position for the NRA measurement. As in this schematic, align the sample surface normal to the incident beam.Use a beam line camera and monitor for this purpose. At the manipulator head, connect the sample current line to the control room current integrator. Move to the control room to continue.Coursely align the beam by setting the bending magnet and the magnetic quadrupole lens parameters. Observe the beam profile on the profile monitor while further optimizing the parameters for beam transmission and keeping the profile on target. Next, set the BM03 parameter to determine the starting beam energy for the scan.At the computer, enter the desired parameters for the energy scan and start the automated scan of energy to acquire a depth profile. This near surface depth profile is from single crystal palladium that has had its 110 surface exposed to hydrogen gas. The experiment was performed in beam line 1E with a hydrogen background pressure of 1.3 micropascals.The bottom horizontal axis gives the nitrogen ion beam energy. The top axis provides a measure of the depth based on the stopping power of palladium. The open symbols correspond to an experiment with palladium that was pre-exposed in 100 seconds to 2, 000 langmuirs of hydrogen gas at 145 Kelvin.The data were taken at 90 Kelvin. The profile can be decomposed into a peak at depth zero in black and a plateau in blue. The area of the peak provides information on hydrogen surface density.In this case, the coverage is 1 1/2 hydrogens per surface palladium atom. The plateau reveals that hydrogen has been absorbed to a depth of at least 20 nanometers. The gray and black symbols are for experiments with no pre-dosage of hydrogen.These data were taken at 170 Kelvin. These plots represent data from a series of experiments with silicon dioxide on silicon performed in beam line 2C. As before, the ion energy is shown on the bottom axis.The depth along the top. The positions of the interface between the materials is indicated by a vertical dashed line. All profiles show two peaks indicating a non-uniform distribution of hydrogen including hydrogen just a few nanometers in front of the silicon oxide silicon interface.The experiments in this video demonstrate that the NRA technique can distinguish surface-absorbed and volume or interface-absorbed hydrogen in solid targets. NRA furthermore quantifies the hydrogen content at their respective depth locations without destroying the sample material. Please be aware that especially the temperature and pressure during hydrogen exposure, very critically influence the depth distribution of palladium-absorbed hydrogen.If these experimental parameters are changed, hydrogen profile is different from those shown in this video will likely result. After watching this video, you should have a good impression of how nuclear reaction analysis measurement is performed at MALT facility to quantitatively determine hydrogen densities on surfaces and in the interior of solid materials through nanoscale depth profile.

quantification-hydrogen-concentrations-surface-interface-layers-bulk

Research

JoVE Journal

Engineering

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do so is highly important in view of a number of applications in functional soft matter including electronics, biomedical engineering, and sensors. In the past, successful strategies to control the size and shape of supramolecular polymers typically focused on the use of templates2,3, end cappers4 or selective solvent techniques5. 
Here we disclose a strategy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing electrostatic repulsive interactions on the hydrophilic rim and attractive non-covalent forces within the hydrophobic core of the polymerizing building block, we manage to create small and discrete spherical objects6,7. Increasing the salt concentration to screen the charges induces a sphere-to-rod transition. Intriguingly, this transition is expressed in an increase of cooperativity in the temperature-dependent self-assembly mechanism, and more stable aggregates are obtained. 
For our study we select a benzene-1,3,5-tricarboxamide (BTA) core connected to a hydrophilic metal chelate via a hydrophobic, fluorinated L-phenylalanine based spacer (Scheme 1). The metal chelate selected is a Gd(III)-DTPA complex that contains two overall remaining charges per complex and necessarily two counter ions. The one-dimensional growth of the aggregate is directed by &pi;-&pi; stacking and intermolecular hydrogen bonding. However, the electrostatic, repulsive forces that arise from the charges on the Gd(III)-DTPA complex start limiting the one-dimensional growth of the BTA-based discotic once a certain size is reached. At millimolar concentrations the formed aggregate has a spherical shape and a diameter of around 5 nm as inferred from 1H-NMR spectroscopy, small angle X-ray scattering, and cryogenic transmission electron microscopy (cryo-TEM). The strength of the electrostatic repulsive interactions between molecules can be reduced by increasing the salt concentration of the buffered solutions. This screening of the charges induces a transition from spherical aggregates into elongated rods with a length &gt; 25 nm. Cryo-TEM allows to visualise the changes in shape and size. In addition, CD spectroscopy permits to derive the mechanistic details of the self-assembly processes before and after the addition of salt. Importantly, the cooperativity -a key feature that dictates the physical properties of the produced supramolecular polymers- increases dramatically upon screening the electrostatic interactions. This increase in cooperativity results in a significant increase in the molecular weight of the formed supramolecular polymers in water.

The goal of this experiment is to determine and control the size, shape and stability of self-assembled discotic amphiphiles in water. For aqueous based supramolecular polymers such level of control is very difficult. We apply a strategy using both repulsive and attractive interactions. The experimental techniques applied to characterize this system are broadly applicable.

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

Simultaneous Multi-surface Anodizations and Stair-like Reverse Biases Detachment of Anodic Aluminum Oxides in Sulfuric and Oxalic Acid Electrolyte

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental sciences and industrial applications owing to their periodic arrangement of nanopores with relatively high aspect ratio. However, the techniques reported so far, which could be only valid for mono-surface anodization, show critical disadvantages, i.e., time-consuming as well as complicated procedures, requiring toxic chemicals, and wasting valuable natural resources. In this paper, we demonstrate a facile, efficient, and environmentally clean method to fabricate nanoporous AAOs in sulfuric and oxalic acid electrolytes, which can overcome the limitations that result from conventional AAO fabricating methods. First, plural AAOs are produced at one time through simultaneous multi-surfaces anodization (SMSA), indicating mass-producibility of the AAOs with comparable qualities. Second, those AAOs can be separated from the aluminum (Al) substrate by applying stair-like reverse biases (SRBs) in the same electrolyte used for the SMSAs, implying simplicity and green technological characteristics. Finally, a unit sequence consisting of the SMSAs sequentially combined with SRBs-based detachment can be applied repeatedly to the same Al substrate, which reinforces the advantages of this strategy and also guarantees the efficient usage of natural resources.

A protocol for fabricating nanoporous anodic aluminum oxides via simultaneous multi-surfaces anodization followed by stair-like reverse biases detachments is presented. It can be applied repeatedly to the same aluminum substrate, exhibiting a facile, high-yield, and environmentally clean strategy.

After reporting on the two-step anodization, nanoporous anodic aluminum oxides (AAOs) have been widely utilized in the versatile fields of fundamental ...

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is known about the effects of high pressure hydrogen on the polymer sealing and barrier materials also found within these components. More study is required in order to determine the compatibility of common polymer materials found in the components of the hydrogen fuel delivery infrastructure with high pressure hydrogen. As a result, it is important to consider the changes in physical properties such as friction and wear in situ while the polymer is exposed to high pressure hydrogen. In this protocol, we present a method for testing the friction and wear properties of ethylene propylene diene monomer (EPDM) elastomer samples in a 28 MPa high pressure hydrogen environment using a custom-built in situ pin-on-flat linear reciprocating tribometer. Representative results from this testing are presented which indicate that the coefficient of friction between the EPDM sample coupon and steel counter surface is increased in high pressure hydrogen as compared to the coefficient of friction similarly measured in ambient air.

In Situ High Pressure Hydrogen Tribological Testing of Common Polymer Materials Used in the Hydrogen Delivery Infrastructure

A test methodology for quantifying tribological properties of polymers used in hydrogen infrastructure service is demonstrated and characteristic results for a common elastomer are discussed.

High pressure hydrogen gas is known to adversely affect metallic components of compressors, valves, hoses, and actuators. However, relatively little is ...

Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued development of nanocrystalline metals. Despite these efforts, the transition of these materials from the lab bench to actual applications has been blocked by the inability to produce large scale parts that retain the desired nanocrystalline microstructures. Following the development of a method proven to stabilize the nanosized grain structure to temperatures approaching that of the melting point for the given metal, the US Army Research Laboratory (ARL) has progressed to the next stage in the development of these materials - namely the production of large scale parts suitable for testing and evaluation in a range of relevant test environments. This report provides a broad overview of the ongoing efforts in the processing, characterization, and consolidation of these materials at ARL. In particular, focus is placed on the methodology used for producing the nanocrystalline metal powders, in both small and large-scale amounts, that are at the center of ongoing research efforts.

This paper provides a brief overview of the ongoing efforts at the Army Research Laboratory on the processing of bulk nanocrystalline metals with an emphasis on the methodologies used for the production of the novel metal powders.

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued ...

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...

Determining Tribocorrosion Rate and Wear-Corrosion Synergy of Bulk and Thin Film Aluminum Alloys

The increasing complexity and severity of service conditions in areas, such as aerospace and marine industries, nuclear systems, microelectronics, batteries, and biomedical devices, etc., impose great challenges on the reliable performance of alloys exposed to extreme conditions where mechanical and electrochemical attack co-exist. Finding ways for alloys to mitigate the combined attack of wear and corrosion (i.e., tribocorrosion) under such extreme conditions is thus highly critical for improving their reliability and service lifetime when used in such conditions. The challenge lies in the fact that wear and corrosion are not independent of each other, but rather work synergistically to accelerate the total material loss. Thus, a reliable method to evaluate the tribocorrosion resistance of metals and alloys is needed. Here, a protocol for measuring the tribocorrosion rate and wear-corrosion synergy of Al-based bulk and thin film samples in a corrosive environment under room temperature is presented.

Here, we present a protocol to measure the tribocorrosion rate and wear-corrosion synergy of thin film and bulk Al alloys in simulated sea water at room temperature.

The increasing complexity and severity of service conditions in areas, such as aerospace and marine industries, nuclear systems, microelectronics, ...

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Reduction of threading dislocation density (TDD) in epitaxial germanium (Ge) on silicon (Si) has been one of the most important challenges for the realization of monolithically integrated photonics circuits. The present paper describes methods of theoretical calculation and experimental verification of a novel model for the reduction of TDD. The method of theoretical calculation describes the bending of threading dislocations (TDs) based on the interaction of TDs and non-planar growth surfaces of selective epitaxial growth (SEG) in terms of dislocation image force. The calculation reveals that the presence of voids on SiO2 masks help to reduce TDD. Experimental verification is described by germanium (Ge) SEG, using an ultra-high vacuum chemical vapor deposition method and TD observations of the grown Ge via etching and cross-sectional transmission electron microscope (TEM). It is strongly suggested that the TDD reduction would be due to the presence of semicylindrical voids over the SiO2 SEG masks and growth temperature. For experimental verification, epitaxial Ge layers with semicylindrical voids are formed as the result of SEG of Ge layers and their coalescence. The experimentally obtained TDDs reproduce the calculated TDDs based on the theoretical model. Cross-sectional TEM observations reveal that both the termination and generation of TDs occur at semicylindrical voids. Plan-view TEM observations reveal a unique behavior of TDs in Ge with semicylindrical voids (i.e., TDs are bent to be parallel to the SEG masks and the Si substrate).

Theoretical calculation and experimental verification are proposed for a reduction of threading dislocation (TD) density in germanium epitaxial layers with semicylindrical voids on silicon. Calculations based on the interaction of TDs and surface via image force, TD measurements, and transmission electron microscope observations of TDs are presented.