Name: use of sacrificial nanoparticles to remove the effects of shot-noise in contact holes fabricated by e-beam lithography
Uploaded: 2017-02-12T13:00:00
Description: Watch this Scientific Journal Video about Use of Sacrificial Nanoparticles to Remove the Effects of Shot-noise in Contact Holes Fabricated by E-beam Lithography at JoVE.com

Intel Corporation funded this work through grant number 414305, and the Oregon Nanotechnology and Microtechnology Initiative (ONAMI) provided matching funds. We gratefully acknowledge the support and advice of Dr. James Blackwell in all phases of this work. Special thanks go to Drew Beasau and Chelsea Benedict for analyzing particle positioning statistics. We thank Professor Hall for a careful reading of the manuscript and Dr. Kurt Langworthy, at the University of Oregon, Eugene, OR, for his help with E-beam lithography.

1. Derivatize and Characterize the Surface of the Silicon Wafers

<ol>
	<li>Clean the surface of wafers using Radio Corporation of America (RCA) cleaning solutions SC1 and SC2.</li>
	<li>Prepare SC1 and SC2 by volumetrically mixing the following chemicals: 
	SC1: H2O2:NH4OH:H2O = 1:1:5 v/v and SC2: H2O2:HCl:H2O = 1:1:5 v/v.
	<ol>
		<li>Immerse the wafer in SC1 for 10 min at 70 &#176;C, and then p...

<ol>
	<li>Moore, G. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cramming+more+components+onto+integrated+circuits.">Cramming more components onto integrated circuits.</a> Electronics. 38 (8), 114 (1965).</li><li>Moore, G. E., Allen, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lithography+and+the+future+of+Moore's+law.">Lithography and the future of Moore's law.</a> SPIE Proc.: Advances in Resist Technology and Processing XII. 2438, 2-17 (1995).</li><li>Rayleigh, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+theory+of+optical+images,+with+special+reference+to+the+microscope.">On the theory of optical images, with special reference to the microscope.</a> The London, Edinburgh, and Dublin Philosophical Magazine and J. Sci. 42 (255), 167-195 (1896).</li><li>Levenson, M. D., Viswanathan, N. S., Simpson, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improving+resolution+in+photolithography+with+a+phase-shifting+mask.">Improving resolution in photolithography with a phase-shifting mask.</a> IEEE Trans. Electron Devices. 29 (12), 1828-1836 (1982).</li><li>French, R. H., Tran, H. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immersion+Lithography:+Photomask+and+Wafer-Level+Materials.">Immersion Lithography: Photomask and Wafer-Level Materials.</a> Annu. Rev. Mater. Res. 39 (1), 93-126 (2009).</li><li>Borodovsky, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Complementary+Lithography+at+Insertion+and+Beyond.">Complementary Lithography at Insertion and Beyond.</a> , (2012).</li><li>Reiser, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Photoreactive Polymers: the Science and Technology of Resists. , (1989).</li><li>Brunner, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Why+optical+lithography+will+live+forever.">Why optical lithography will live forever.</a> J. of Vac. Sci. &amp; Technol. B: Microelectronics and Nanometer Structures. 21 (6), 2632-2637 (2003).</li><li>Tran, H., Jackson, E., Eldo, J., Kanjolia, R., Rananavare, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photochemical+reactivity+of+bis-carbamate+photobase+generators.">Photochemical reactivity of bis-carbamate photobase generators.</a> , 1683-1688 (2011).</li><li>Hallett-Tapley, G. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single+component+photoacid/photobase+generators:+potential+applications+in+double+patterning+photolithography.">Single component photoacid/photobase generators: potential applications in double patterning photolithography.</a> J. Mater. Chem. C. 1 (15), 2657-2665 (2013).</li><li>Krysak, M., De Silva, A., Sha, J., Lee, J. K., Ober, C. K., Henderson, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+glass+resists+for+next-generation+lithography.">Molecular glass resists for next-generation lithography.</a> Proc. SPIE: Advances in Resist Materials and Processing Technology XXVI. 7273, 72732N (2009).</li><li>Li, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bottom-up+assembly+of+large-area+nanowire+resonator+arrays.">Bottom-up assembly of large-area nanowire resonator arrays.</a> Nat Nano. 3 (2), 88-92 (2008).</li><li>Thiruvengadathan, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanomaterial+processing+using+self-assembly-bottom-up+chemical+and+biological+approaches.">Nanomaterial processing using self-assembly-bottom-up chemical and biological approaches.</a> Rep. Prog. Phys. 76 (6), 066501 (2013).</li><li>Tsai, H. Y., Zhang, Y., Oehrlein, G. S., Lin, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pattern+transfer+of+directed+self-assembly+(DSA)+patterns+for+CMOS+device+applications.">Pattern transfer of directed self-assembly (DSA) patterns for CMOS device applications.</a> Proc.SPIE Advanced Etch Technology for Nanopatterning II. 8865, 86850L-86850L (2013).</li><li>Hawker, C. J., Russell, T. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Block+Copolymer+Lithography:+Merging+&amp;#34;Bottom-Up&amp;#34;+with+&amp;#34;Top-Down&amp;#34;+Processes.">Block Copolymer Lithography: Merging &amp;#34;Bottom-Up&amp;#34; with &amp;#34;Top-Down&amp;#34; Processes.</a> MRS Bulletin. 30 (12), 952-966 (2005).</li><li>Lin, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-directed+self-assembly+of+nanoparticle/copolymer+mixtures.">Self-directed self-assembly of nanoparticle/copolymer mixtures.</a> Nature. 434 (7029), 55-59 (2005).</li><li>Cheng, J. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simple+and+Versatile+Methods+To+Integrate+Directed+Self-Assembly+with+Optical+Lithography+Using+a+Polarity-Switched+Photoresist.">Simple and Versatile Methods To Integrate Directed Self-Assembly with Optical Lithography Using a Polarity-Switched Photoresist.</a> ACS Nano. 4 (8), 4815-4823 (2010).</li><li>Wong, H. S. P., Bencher, C., Yi, H., Bao, X. Y., Chang, L. W., Tong, W. .. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Block+copolymer+directed+self-assembly+enables+sublithographic+patterning+for+device+fabrication.">Block copolymer directed self-assembly enables sublithographic patterning for device fabrication.</a> Proc. SPIE. 8323, Alternative Lithographic Technologies IV, (2012).</li><li>Chan, J. C., Hannah-Moore, N., Rananavare, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+Deposition+of+Tin+Oxide+and+Silver+Nanoparticles+Using+Microcontact+Printing.">Controlled Deposition of Tin Oxide and Silver Nanoparticles Using Microcontact Printing.</a> Crystals. 5 (1), 116-142 (2015).</li><li>Morakinyo, M. K., Rananavare, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reducing+the+effects+of+shot+noise+using+nanoparticles.">Reducing the effects of shot noise using nanoparticles.</a> J. Mater. Chem. C. 3 (5), 955-959 (2015).</li><li>Cui, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integration+of+Colloidal+Nanocrystals+into+Lithographically+Patterned+Devices.">Integration of Colloidal Nanocrystals into Lithographically Patterned Devices.</a> Nano Lett. 4 (6), 1093-1098 (2004).</li><li>Huang, H. W., Bhadrachalam, P., Ray, V., Koh, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-particle+placement+via+self-limiting+electrostatic+gating.">Single-particle placement via self-limiting electrostatic gating.</a> Appl. Phys. Lett. 93 (7), 073110-073113 (2008).</li><li>Ma, L. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrostatic+Funneling+for+Precise+Nanoparticle+Placement:+A+Route+to+Wafer-Scale+Integration.">Electrostatic Funneling for Precise Nanoparticle Placement: A Route to Wafer-Scale Integration.</a> Nano Lett. 7 (2), 439-445 (2007).</li><li>Richard Bowen, W., Filippov, A. N., Sharif, A. O., Starov, V. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+model+of+the+interaction+between+a+charged+particle+and+a+pore+in+a+charged+membrane+surface.">A model of the interaction between a charged particle and a pore in a charged membrane surface.</a> Adv. Colloid Interface Sci. 81 (1), 35-72 (1999).</li><li>Morakinyo, M. K., Rananavare, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Positional+control+over+nanoparticle+deposition+into+nanoholes.">Positional control over nanoparticle deposition into nanoholes.</a> , 1677-1682 (2011).</li><li>Keymeulen, H. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+the+x-ray+dose-dependent+glass+transition+temperature+of+structured+polymer+films+by+x-ray+diffraction.">Measurement of the x-ray dose-dependent glass transition temperature of structured polymer films by x-ray diffraction.</a> J. Appl. Phys. 102 (1), 013528 (2007).</li><li>Feng, B. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resist+Reflow+Method+for+Making+Submicron+Patterned+Resist+Masks.">Resist Reflow Method for Making Submicron Patterned Resist Masks.</a> US patent A. , (1977).</li><li>You, J. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Position+Shift+Analysis+in+Resist+Reflow+Process+for+Sub-50+nm+Contact+Hole.">Position Shift Analysis in Resist Reflow Process for Sub-50 nm Contact Hole.</a> Jpn. J. Appl. Phys. 48 (9), 096502 (2009).</li><li>Montgomery, P. K., Fedynyshyn, T. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resist+reflow+for+193-nm+low-K1+lithography+contacts.">Resist reflow for 193-nm low-K1 lithography contacts.</a> Proc. SPIE Advances in Resist Technology and Processing XX. 5039, 807-816 (2003).</li><li>King, W. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atomic+force+microscope+cantilevers+for+combined+thermomechanical+data+writing+and+reading.">Atomic force microscope cantilevers for combined thermomechanical data writing and reading.</a> Appl. Phys. Lett. 78 (9), 1300-1302 (2001).</li><li>Chuo, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+fabrication+of+nano-structured+quartz+stamps.">Rapid fabrication of nano-structured quartz stamps.</a> Nanotechnology. 24 (5), 055304 (2013).</li><li>Moreau, W. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Semiconductor Lithography: Principles, Practices, and Materials. , 419 (2012).</li><li>Chan, J. C., Tran, H., Pattison, J. W., Rananavare, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facile+pyrolytic+synthesis+of+silicon+nanowires.">Facile pyrolytic synthesis of silicon nanowires.</a> Solid-State Electron. 54 (10), 1185-1191 (2010).</li><li>Tran, H. A., Rananavare, S. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+characterization+of+N-+and+P-+doped+tin+oxide+nanowires.">Synthesis and characterization of N- and P- doped tin oxide nanowires.</a> , (2011).</li><li>Tran, H. A., Rananavare, S. B., Morris, J. E., Iniewski, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ch.+39,+Synthesis+and+Characterization+of+n-+and+p-Doped+Tin+Oxide+Nanowires+for+Gas+Sensing+Applications.">Ch. 39, Synthesis and Characterization of n- and p-Doped Tin Oxide Nanowires for Gas Sensing Applications.</a> Nanoelectronic Device Applications Handbook . , (2013).</li></ol>

Shot-noise (SN) in lithography is a simple consequence of statistical fluctuations in the number of photons or particles (N) arriving in a given nano-region; it is inversely proportional to the square root of a number of photons/particles:
<img alt="Equation 3" src="/files/ftp_upload/54551/eq3.jpg" />
where A and r are the area and the size of the exposed region, respectively. For example, when using an ArF 193-nm (6.4-eV) excimer laser to pattern ...

The exponential growth in computational power, as quantified by Moore&#39;s law1,2 (1), is a result of progressive advances in optical lithography. In this top-down patterning technique, the achievable resolution, R, is given by the well-known Raleigh theorem3:
<img alt="Equation 1" src="/files/ftp_upload/54551/eq1.jpg" />
Here, &#955; and NA are the light wavelength and numerical aperture, respectively. Note that NA = &#951;&#183;sin&#952;, where &#951; is the refractive index of the medium between the lens and the wafer; &#952; = tan-1(d/2l) for the diameter, d, of the lens, and the distance, l, between the center of the lens and the wafer. Over the last fifty years, the lithographic resolution has improved through the use of (a) light sources, including excimer lasers, with progressively smaller UV wavelengths; (b) clever optical designs employing phase-shift masks4; and (c) higher NA. For exposure in air (&#951; = 1), NA is always less than unity, but by introducing a liquid with &#951; &#62;1, such as water5, between the lens and the wafer, NA can be elevated above 1, thereby improving the resolution of immersion lithography. Currently viable paths to a 20-nm node and beyond include extreme UV sources (&#955; = 13 nm) or patterning techniques using complex double and quadruple processing of a multilayered photoresist6,7.
At nanometer-length scales, statistical fluctuations, caused by shot-noise (SN), in the number of photons arriving within a nano-region cause variation in the dimensions of lithographic patterns. These effects are more pronounced with exposure to high-energy EUV light and E-beams, systems that need orders of magnitude fewer photons/particles compared to normal optical lithography8. Supersensitive chemically amplified (with a quantum efficiency &#62;1) photoresists also introduce a chemical SN caused by a variation in the number of photoreactive molecules in exposed nanoregions9,10. Lower sensitivity photoresists that need longer exposures suppress these effects, but they also reduce throughput.
On the molecular scale, the contribution to line-edge roughness from the molecular size distribution inherent to the photoresist polymers may be reduced by using molecular resists11. An approach that is complementary to this top-down processing of nano-patterning is the use of bottom-up methods12,13 that rely specifically on the directed self-assembly (DSA) of diblock polymers14. The ability of these processes to direct nucleation and to create non-uniform spacing between desired patterns, such as holes or lines, remains challenging. The size distribution of molecular components15,16 also limits the scale and yield of fabrication17,18. Similar problems limit microcontact printing of nanoparticles in soft lithography19.
This paper presents studies of a new hybrid approach (Figure 1) that combines the classic top-down projection lithography with electrostatically directed self-assembly to reduce the effect of SN/line-edge roughness(LER)20. Positively charged amine groups on self-assembled monolayers (SAMs) of N-(2-aminoethyl)-11-amino-undecyl-methoxy-silane (AATMS) underlying the PMMA film are exposed after development. The negatively charged photoresist film of PMMA electrostatically funnels negatively charged gold nanoparticles (GNPs), capped with citrate,21-24 into SN-affected holes25. Re-flow of the PMMA photoresist engulfs predeposited nanoparticles in the film.
<img alt="Figure 1" src="/files/ftp_upload/54551/54551fig1.jpg" /> 
Figure 1: Schematic representation of the strategy to remove the effects of shot-noise and line-edge roughness for the patterning of contact holes using NPs of precise size. Here, the critical dimension (CD) is the desired diameter of the holes. The approach (step 1) begins with depositing a self-assembled monolayer (SAM) of silane molecule bearing positively charged amine groups on the oxide surface of a silicon wafer. Next, E-beam lithography is used to pattern the holes (steps 2 and 3) in PMMA photoresist film, the blue layer, which generates shot-noise, as illustrated in the inset SEM image. Lithography exposes amine groups at the bottom of the holes. Step 4 entails the aqueous phase deposition of controlled-size, citrate-capped (negatively charged) gold nanoparticles (GNPs) in lithographically patterned holes using electrostatic funneling (EF). In step 5, heating the wafer to 100 &#176;C, below the glass transition temperature of the PMMA, 110 &#176;C, causes the reflow of the photoresist around pre-deposited nanoparticles. Etching overlaid PMMA with oxygen plasma (step 6) exposes the GNPs, and subsequent wet-etching (iodine) of the exposed particles (step 7) creates holes corresponding to the size of the GNPs. When coupled with reactive-ion/wet-etching, it is possible to transfer the hole pattern in the photoresist to SiO2 (step 8)31. Reprinted with permission from reference20. <a href="http://cloudflare.jove.com/files/ftp_upload/54551/54551fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The electrostatic interaction between the oppositely charged GNPs and amine groups on the substrate prevents the displacement of the GNPs from the binding site. The reflow step maintains the relative location of the GNPs but erases the holes and the effects of SN/LER. Plasma/wet etching steps regenerate holes that have the size of the GNP. Reactive-ion etching transfers their pattern to SiO2 hard-mask layers. The method relies on using more uniformly sized nanoparticles than a patterned nanohole (NH), expressed as the standard deviation, &#963;, such that &#963;GNP &#60;&#963;NH. This report focuses on steps (4 and 5 described in Figure 1) involving the deposition of nanoparticles from dispersion and the reflow of the photoresist around them to assess the advantages and limitations of the method. Both steps are, in principle, scalable to larger substrates, requiring no extensive modification of the current flow of producing modern integrated circuits on chips.

<table border="0" cellpadding="0" cellspacing="0" width="700">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">AATMS (95%)</td>
			<td style="width:71px;">Gelest Inc.</td>
			<td style="width:89px;">SIA0595.0</td>
			<td style="width:167px;">N-(2-aminoethyl)-11-aminoundecyltrimethoxysilane&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Gold colloids (Ted Pella Inc.)</td>
			<td style="width:71px;">Ted Pella</td>
			<td style="width:89px;">15705-20</td>
			<td>Gold Naoparticles</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">hydrogen peroxide</td>
			<td style="width:71px;">Fisher Scientific&#160;</td>
			<td style="width:89px;">H325-100</td>
			<td>Analytical grade (Used to clean wafer)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:373px;">hydrochloric acid</td>
			<td style="width:71px;">Fisher Scientific&#160;</td>
			<td style="width:89px;">S25358</td>
			<td>Analytical grade</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Ammonium hydroxide</td>
			<td style="width:71px;">Fisher Scientific&#160;</td>
			<td style="width:89px;">A669S-500SDS</td>
			<td>Analytical grade (Used to clean wafer)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">hydrogen fluoride</td>
			<td style="width:71px;">Fisher Scientific&#160;</td>
			<td style="width:89px;">AC277250250</td>
			<td>Analytical grade(used to etch SiO2)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Toluene (anhydrous, 99.8 %)&#160;</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:89px;">244511</td>
			<td>Analytical grade (solvent used in Self Assembly of AATMS</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">&#160;Isopropyl alcohol (IPA)</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:89px;">W292907</td>
			<td>Analytical grade (Used to make developer)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">Methyl butyl ketone (MIBK)</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:89px;">29261</td>
			<td>Analytical grade(used to make developer)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">1:3 MIBK:IPA developer</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:89px;"></td>
			<td>Analytical grade (Developer)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">950 k poly(methyl methacylate (PMMA, 4 % in Anisole)</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:89px;">182265</td>
			<td>Photoresist for E-beam lithography</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:373px;">Purified Water : Barnstead Sybron Corporation water purification Unit, resistivity of 19.0 M&#937;cm</td>
			<td style="width:71px;"></td>
			<td style="width:89px;"></td>
			<td>Water for substrate cleaning</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Gaertner ellipsometer&#160;</td>
			<td>Gaertner</td>
			<td></td>
			<td>Resist and SAM thickness measurements</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:373px;">XPS, ThermoScientifc ESCALAB 250 instrument</td>
			<td style="width:71px;">Thermo-Scientific</td>
			<td style="width:89px;"></td>
			<td>Surface composition</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:373px;">An FEI Siron XL30</td>
			<td style="width:71px;">Fei Corporation</td>
			<td style="width:89px;"></td>
			<td>Characterize nanopatterns</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;">Zeiss sigma VP FEG SEM</td>
			<td style="width:71px;">Zeiss Corporation</td>
			<td style="width:89px;"></td>
			<td>E-beam exposure and patterning</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MDS 100&#160; CCD camera</td>
			<td style="width:71px;">Kodak</td>
			<td style="width:89px;"></td>
			<td>Imaging drop shapes for contact angle measurements</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">Tegal Plasmod</td>
			<td style="width:71px;">Tegal</td>
			<td style="width:89px;"></td>
			<td>Oxygen plasma to etch photoresist</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:373px;">I2</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:89px;">451045</td>
			<td>Components for gold etch solution</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:373px;">KI</td>
			<td style="width:71px;">Sigma Aldrich</td>
			<td style="width:89px;">746428</td>
			<td>Components for gold etch solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ellipsometer ( LSE Stokes model L116A);</td>
			<td style="width:71px;">Gaertner</td>
			<td style="width:89px;">L116A</td>
			<td>AATMS self assembled monolayer film thickness measurements</td>
		</tr>
	</tbody>
</table>

use of sacrificial nanoparticles to remove the effects of shot-noise in contact holes fabricated by e-beam lithography

Nano-patterns fabricated with extreme ultraviolet (EUV) or electron-beam (E-beam) lithography exhibit unexpected variations in size. This variation has been attributed to statistical fluctuations in the number of photons/electrons arriving at a given nano-region arising from shot-noise (SN). The SN varies inversely to the square root of a number of photons/electrons. For a fixed dosage, the SN is larger in EUV and E-beam lithographies than for traditional (193 nm) optical lithography. Bottom-up and top-down patterning approaches are combined to minimize the effects of shot noise in nano-hole patterning. Specifically, an amino-silane surfactant self-assembles on a silicon wafer that is subsequently spin-coated with a 100 nm film of a PMMA-based E-beam photoresist. Exposure to the E-beam and the subsequent development uncover the underlying surfactant film at the bottoms of the holes. Dipping the wafer in a suspension of negatively charged, citrate-capped, 20 nm gold nanoparticles (GNP) deposits one particle per hole. The exposed positively charged surfactant film in the hole electrostatically funnels the negatively charged nanoparticle to the center of an exposed hole, which permanently fixes the positional registry. Next, by heating near the glass transition temperature of the photoresist polymer, the photoresist film reflows and engulfs the nanoparticles. This process erases the holes affected by SN but leaves the deposited GNPs locked in place by strong electrostatic binding. Treatment with oxygen plasma exposes the GNPs by etching a thin layer of the photoresist. Wet-etching the exposed GNPs with a solution of I2/KI yields uniform holes located at the center of indentations patterned by E-beam lithography. The experiments presented show that the approach reduces the variation in the size of the holes caused by SN from 35% to below 10%. The method extends the patterning limits of transistor contact holes to below 20 nm.

Figure 2 shows an SEM image of 20-nm GNPs deposited in 80-nm diameter holes patterned in a 60-100 nm-thick PMMA film driven by electrostatic funneling. As observed by others22, the process resulted in about one particle per hole. The distribution of particles around the center of the holes was Gaussian (top right inset). Most holes (93%) contained one GNP, and 95% of these particles occurred within 20 nm of the center. Further optimization, discuss...

Watch this Scientific Journal Video about Use of Sacrificial Nanoparticles to Remove the Effects of Shot-noise in Contact Holes Fabricated by E-beam Lithography at JoVE.com

Use of Sacrificial Nanoparticles to Remove the Effects of Shot-noise in Contact Holes Fabricated by E-beam Lithography

Uniformly sized nanoparticles can remove fluctuations in contact hole dimensions patterned in poly(methyl methacrylate) (PMMA) photoresist films by electron beam (E-beam) lithography. The process involves electrostatic funneling to center and deposit nanoparticles in contact holes, followed by photoresist reflow and plasma- and wet-etching steps.

Nano-patterns fabricated with extreme ultraviolet (EUV) or electron-beam (E-beam) lithography exhibit unexpected variations in size. This variation has ...

The overall goal of this protocol is to remove the effect of shot-noise from lithographic patterns using nanoparticles and resist reflow techniques. This nanopatterning technique allows the removal of Shot-noise from extreme UV and E-Beam lithography's currently planned in fabricating advanced semiconductor devices, such as, micro-processors and memory chips. The main advantage of this technique is that the steps are easily implemented.In current semiconductor processing fabs, without extensive modification of existing duel sets. The implication of this technique extends toward our ability to craft sub-20 nanometer patterns because it will deduce dimensional fluctuation from optical and chemical shot-noise effect. Generally, individuals new to this method will struggle because it requires familiarity with bottom-up and top-down processing methods, such as, sub fact self assembly and projection lithography.Demonstrating the procedure will be Dr.Moshood Morakinyo currently at Intel. And he will be assisted by Srikar Rao, a Graduate student in my lab. To being the procedure, prepare SC-1 and SC-2 solutions for the RCA cleaning method.Immerse the silicon wafer in the SC-1 and SC-2 solutions in turn for 10 minutes each at 70 degrees Celsius. Rinse the wafer with deionized water after each immersion and then dry the wafer in a stream of Nitrogen gas. Next, soak the clean, dry silicon wafer in a 0.05 molar solution of AATMS in dry toluene at 80 degrees Celsius for 20 minutes to derivatize the wafer surface.Sonicate the wafer in toluene at room temperature for five minutes at 100 watts and dry the wafer with Nitrogen gas. Apply a photo-resist film of poly methyl methacrylate to the prepared wafer by spin coating. And then pattern holes in it with electron beam lithography.Prepare a suspension of citrate capped gold nanoparticles of a smaller diameter than the patterned holes. The GNP concentration may range from 5.7 times 10 to the 9th to 10 to the 12th nanoparticles per milliliter depending on the GNP size. To deposit GNPs in the patterned contact holes by immersion, soak the patterned wafer in the suspension for 24 to 48 hours, depending on the GNP size.Alternatively, to deposit GNPs by evaporation, first place the patterned wafer on the flat surface, spread drops of GNP suspension over the entire surface of the wafer. Keep the wafer on a hot plate at 30 to 35 degrees Celsius for 10 minutes to evaporate the solvent. After GNP deposition, ultrasonicate the wafer in a deionized water bath for 50 seconds at 100 watts.Dry the wafer with Nitrogen gas. To perform top-down scanning electron microscopy of the wafers, set the electron beam to the lowest possible acceleration voltage and current to reduce the damage to the photo resist film during imaging. Heat the wafer on a hot-plate at 100 degrees Celsius for three minutes to facilitate reflow of the PMMA photo resist around the deposited GNPs.Dry etch the wafer with Oxygen plasma for about 55 seconds to expose the GNPs in the contact holes without completely removing the PMMA film. Monitor the etching rate throughout the process to ensure that the PMMA film is not completely removed. Then, wet etch the GNPs for 10 minutes with a solutions of 1.0 grams of Iodine crystals and 4.0 grams of Potassium Iodide and 40 milliliters of deionized water to remove the GNPs from the film.Image the wafer with scanning electron microscopy. Calculate the hole centers, GNP displacement, particle count, particle density, and fill fraction from the SCM images before and after reflow and etching. Using this method, 20 nanometer GNPs were deposited in 80 nanometer holes patterned in a PMMA coated silicon wafer.The PMMA photo resist was heated to just below it's glass transition temperature to enable photo resist reflow around the GNPs, erasing the nano-hole patterns, created by electron bean lithography. After re-exposing the GNPs by dry etching, the GNPs were removed by wet etching, leaving 20 nanometer diameter holes in the PMMA film and the same arrangement as the original pattern. When the immersion deposition method was used, 93%of the holes were singularly occupied and 95%of the particles were deposited within 18 nanometers of the hole centers.The evaporation method resulted in many holes being occupied by multiple GNPs, indicating that the process requires further optimization. Extraction of the contribution of photo resist reflow on displacement of the 20 nanometer GNPs, indicated that the reflow process had a negligible effect on GNP positioning. The coefficient of variation of the 20 nanometer holes created by this method was determined to be about 9%which was comparable to the coefficient of GNPS size variation.This was roughly a six fold improvement over the predicted CV of electron beam lithography patterned 20 nanometer holes and about a 60%improvement over the predicted CV of the original 80 nanometer holes. Once mastered, this technique can be done in 24 hours if it is performed properly. While attempting this procedure, remember to use mono-dispersed nanoparticles and mild ultrasonication to remove loosely bound nanoparticles on the resist surface.Though this method has been demonstrated using E-Beam lithography, it can also be applied to other systems based on extreme UV, X-ray, or other high energy exposure systems. I developed this idea for this method during an Intel sponsored project on lithography. Now this technique provides a new approach to remove effects of shot-noise and line edge roughness in lithography.After watching this video, you should have a good understanding of how to deposit nanoparticles, reflow resist and etch nanoparticles to reduce shot-noise in nano fabrication.

use-sacrificial-nanoparticles-to-remove-effects-shot-noise-contact

Research

JoVE Journal

Engineering

Micropunching Lithography for Generating Micro- and Submicron-patterns on Polymer Substrates

Conducting polymers have attracted great attention since the discovery of high conductivity in doped polyacetylene in 19771. They offer the advantages of low weight, easy tailoring of properties and a wide spectrum of applications2,3. Due to sensitivity of conducting polymers to environmental conditions (e.g., air, oxygen, moisture, high temperature and chemical solutions), lithographic techniques present significant technical challenges when working with these materials4. For example, current photolithographic methods, such as ultra-violet (UV), are unsuitable for patterning the conducting polymers due to the involvement of wet and/or dry etching processes in these methods. In addition, current micro/nanosystems mainly have a planar form5,6. One layer of structures is built on the top surfaces of another layer of fabricated features. Multiple layers of these structures are stacked together to form numerous devices on a common substrate. The sidewall surfaces of the microstructures have not been used in constructing devices. On the other hand, sidewall patterns could be used, for example, to build 3-D circuits, modify fluidic channels and direct horizontal growth of nanowires and nanotubes.
A macropunching method has been applied in the manufacturing industry to create macropatterns in a sheet metal for over a hundred years. Motivated by this approach, we have developed a micropunching lithography method (MPL) to overcome the obstacles of patterning conducting polymers and generating sidewall patterns. Like the macropunching method, the MPL also includes two operations (Fig. 1): (i) cutting; and (ii) drawing. The "cutting" operation was applied to pattern three conducting polymers4, polypyrrole (PPy), Poly(3,4-ethylenedioxythiophen)-poly(4-styrenesulphonate) (PEDOT) and polyaniline (PANI). It was also employed to create Al microstructures7. The fabricated microstructures of conducting polymers have been used as humidity8, chemical8, and glucose sensors9. Combined microstructures of Al and conducting polymers have been employed to fabricate capacitors and various heterojunctions9,10,11. The "cutting" operation was also applied to generate submicron-patterns, such as 100- and 500-nm-wide PPy lines as well as 100-nm-wide Au wires. The "drawing" operation was employed for two applications: (i) produce Au sidewall patterns on high density polyethylene (HDPE) channels which could be used for building 3D microsystems12,13,14, and (ii) fabricate polydimethylsiloxane (PDMS) micropillars on HDPE substrates to increase the contact angle of the channel15.

A micropunching lithography approach is developed to generate micro- and submicron-patterns on top, sidewall and bottom surfaces of polymer substrates. It overcomes the obstacles of patterning conducting polymers and generating sidewall patterns. This method allows rapid fabrication of multiple features and is free of aggressive chemistry.

Conducting polymers have attracted great attention since the discovery of high conductivity in doped polyacetylene in 19771. They offer the advantages of ...

Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

Process of Making Three-dimensional Microstructures using Vaporization of a Sacrificial Component

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material fabrication techniques are able to mimic the complexity of these structures while maintaining scalability. The Vaporization of a Sacrificial Component (VaSC) process is able to do so. This process uses sacrificial fibers as a template to form hollow, cylindrical microchannels embedded within a matrix. Tin (II) oxalate (SnOx) is embedded within poly(lactic) acid (PLA) fibers which facilitates the use of this process. The SnOx catalyzes the depolymerization of the PLA fibers at lower temperatures. The lactic acid monomers are gaseous at these temperatures and can be removed from the embedded matrix at temperatures that do not damage the matrix. Here we show a method for aligning these fibers using micromachined plates and a tensioning device to create complex patterns of three-dimensionally arrayed microchannels. The process allows the exploration of virtually any arrangement of fiber topologies and structures.

The Vaporization of a Sacrificial Component (VaSC) process is used to fabricate microvascular structures. This procedure uses sacrificial poly(lactic) acid fibers to form hollow microchannels with precise 3D geometric positioning provided by laser micromachined guide plates.

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material ...

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Analyzing the Movement of the Nauplius 'Artemia salina' by Optical Tracking of Plasmonic Nanoparticles

We demonstrate how optical tweezers may provide a sensitive tool to analyze the fluidic vibrations generated by the movement of small aquatic organisms. A single gold nanoparticle held by an optical tweezer is used as a sensor to quantify the rhythmic motion of a Nauplius larva (Artemia salina) in a water sample. This is achieved by monitoring the time dependent displacement of the trapped nanoparticle as a consequence of the Nauplius activity. A Fourier analysis of the nanoparticle&#39;s position then yields a frequency spectrum that is characteristic to the motion of the observed species. This experiment demonstrates the capability of this method to measure and characterize the activity of small aquatic larvae without the requirement to observe them directly and to gain information about the position of the larvae with respect to the trapped particle. Overall, this approach could give an insight on the vitality of certain species found in an aquatic ecosystem and could expand the range of conventional methods for analyzing water samples.

Analyzing the Movement of the Nauplius 'Artemia salina' by Optical Tracking of Plasmonic Nanoparticles

We use optical tracking of plasmonic nanoparticles to probe and characterize the frequency movements of aquatic organisms.

We demonstrate how optical tweezers may provide a sensitive tool to analyze the fluidic vibrations generated by the movement of small aquatic organisms. A ...

Surface Enhanced Raman Spectroscopy Detection of Biomolecules Using EBL Fabricated Nanostructured Substrates

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules is reported. The entire sequence of relevant experimental steps is described, involving the fabrication of nanostructured substrates using electron beam lithography, immobilization of biomolecules on the substrates, and their characterization utilizing surface-enhanced Raman spectroscopy (SERS). Three different designs of nano-biological systems are employed, including protein A, glucose binding protein, and a dopamine binding DNA aptamer. In the latter two cases, the binding of respective ligands, D-glucose and dopamine, is also included. The three kinds of biomolecules are immobilized on nanostructured substrates by different methods, and the results of SERS imaging are reported. The capabilities of SERS to detect vibrational modes from surface-immobilized proteins, as well as to capture the protein-ligand and aptamer-ligand binding are demonstrated. The results also illustrate the influence of the surface nanostructure geometry, biomolecules immobilization strategy, Raman activity of the molecules and presence or absence of the ligand binding on the SERS spectra acquired.

We describe the fabrication and characterization of nano-biological systems interfacing nanostructured substrates with immobilized proteins and aptamers. The relevant experimental steps involving lithographic fabrication of nanostructured substrates, bio-functionalization, and surface-enhanced Raman spectroscopy (SERS) characterization, are reported. SERS detection of surface-immobilized proteins, and probing of protein-ligand and aptamer-ligand binding is demonstrated.

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules ...

Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step process that finishes with Negishi coupling. Negishi coupling is a cross-coupling process in which a chemical precursor is first lithiated, followed by transmetallation with ZnCl2. The resultant organozinc compound can be coupled to a dibrominated aromatic precursor to give the conjugated monomer. Polymer films can be prepared via electropolymerization of the monomer and characterized using cyclic voltammetry and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. Nanoparticles (NPs) are prepared via emulsion polymerization of the monomer using a two-surfactant system to yield an aqueous dispersion of the polymer NPs. The NPs are characterized using dynamic light scattering, electron microscopy, and UV-Vis-NIR-spectroscopy. Cytocompatibility of NPs is investigated using the cell viability assay. Finally, the NP suspensions are irradiated with a NIR laser to determine their effectiveness as potential materials for photothermal therapy (PTT).

A protocol is presented for the synthesis and preparation of nanoparticles consisting of electroactive polymers.

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step ...

Scanning SQUID Study of Vortex Manipulation by Local Contact

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual vortices is necessary in order to study how vortices interact with each other, with the lattice, and with other magnetic objects. Here, we present a protocol for vortex manipulation in thin superconducting films by local contact, without applying current or magnetic field. Vortices are imaged using a scanning superconducting quantum interference device (SQUID), and vertical stress is applied to the sample by pushing the tip of a silicon chip into the sample, using a piezoelectric element. Vortices are moved by tapping the sample or sweeping it with the silicon tip. Our method allows for effective manipulation of individual vortices, without damaging the film or affecting its topography. We demonstrate how vortices were relocated to distances of up to 0.8 mm. The vortices remained stable at their new location up to five days. With this method, we can control vortices and move them to form complex configurations. This technique for vortex manipulation could also be implemented in applications such as vortex based logic devices.

We present a protocol for manipulation of individual vortices in thin superconducting films, using local mechanical contact. The method does not include applying current, magnetic field or additional fabrication steps.

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual ...

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET+)) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET+ intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Here, we present a protocol for the in situ synthesis of gold nanoparticles (AuNPs) within the interlayer space of layered titanate films without the aggregation of AuNPs. No spectral change was observed even after 4 months. The synthesized material has expected applications in catalysis, photo-catalysis, and the development of cost-effective plasmonic devices.

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs ...