Name: electron channeling contrast imaging for rapid iii-v heteroepitaxial characterization
Uploaded: 2015-07-17T14:00:00
Description: Watch this Scientific Journal Video about Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization at JoVE.com

This work was supported by the Department of Energy under the FPACE program (DE-EE0005398), the Ohio State University Institute for Materials Research, and the Ohio Office of Technology Investments&#8217; Third Frontier Program.

This protocol was written with an assumption that the reader will have a working understanding of standard SEM operation. Depending upon the manufacturer, model, and even software version, every SEM can have significantly different hardware and/or software interfaces. The same can be said with respect to the internal configuration of the instrument; the operator must be cautious and observant when following this protocol, as even relatively small changes in sample size/geometry, sample orientation (tilt, rotation), and w...

<ol>
	<li>Zaefferer, S., Elhami, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theory+and+application+of+electron+channelling+contrast+imaging+under+controlled+diffraction+conditions.">Theory and application of electron channelling contrast imaging under controlled diffraction conditions.</a> Acta Mater. 75, 20-50 (2014).</li><li>Crimp, 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.+Scanning+electron+microscopy+imaging+of+dislocations+in+bulk+materials,+using+electron+channeling+contrast.">A. Scanning electron microscopy imaging of dislocations in bulk materials, using electron channeling contrast.</a> Microsc. Res. Tech. 69 (5), 374-381 (2006).</li><li>Joy, D. C., Newbury, D. E., Davidson, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electron+channeling+patterns+in+the+scanning+electron+microscope.">Electron channeling patterns in the scanning electron microscope.</a> J. Appl. Phys. 53 (8), R81-R122 (1982).</li><li>Williams, D. B., Carter, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Transmission Electron Microscopy: A Textbook for Materials Science. , (2009).</li><li>Picard, Y. N., 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=Future+Prospects+for+Defect+and+Strain+Analysis+in+the+SEM+via+Electron+Channeling.">Future Prospects for Defect and Strain Analysis in the SEM via Electron Channeling.</a> Micros. Today. 20 (2), 12-16 (2012).</li><li>Naresh-Kumar, G., 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+Nondestructive+Analysis+of+Threading+Dislocations+in+Wurtzite+Materials+Using+the+Scanning+Electron+Microscope.">Rapid Nondestructive Analysis of Threading Dislocations in Wurtzite Materials Using the Scanning Electron Microscope.</a> Phys. Rev. Lett. 108 (13), 135503 (2012).</li><li>Naresh-Kumar, G., 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=Electron+channeling+contrast+imaging+studies+of+nonpolar+nitrides+using+a+scanning+electron+microscope.">Electron channeling contrast imaging studies of nonpolar nitrides using a scanning electron microscope.</a> Appl. Phys. Lett. 102 (14), 142103 (2013).</li><li>Kamaladasa, R. J., 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=Identifying+threading+dislocations+in+GaN+films+and+substrates+by+electron+channelling.">Identifying threading dislocations in GaN films and substrates by electron channelling.</a> J. Microsc. 244 (3), 311-319 (2011).</li><li>Picard, Y. N., 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=Nondestructive+analysis+of+threading+dislocations+in+GaN+by+electron+channeling+contrast+imaging.">Nondestructive analysis of threading dislocations in GaN by electron channeling contrast imaging.</a> Appl. Phys. Lett. 91 (9), 094106 (2007).</li><li>Picard, Y. N., 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=Electron+channeling+contrast+imaging+of+atomic+steps+and+threading+dislocations+in+4H-SiC.">Electron channeling contrast imaging of atomic steps and threading dislocations in 4H-SiC.</a> Appl. Phys. Lett. 90 (23), 234101 (2007).</li><li>Picard, 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=Epitaxial+SiC+Growth+Morphology+and+Extended+Defects+Investigated+by+Electron+Backscatter+Diffraction+and+Electron+Channeling+Contrast+Imaging.">Epitaxial SiC Growth Morphology and Extended Defects Investigated by Electron Backscatter Diffraction and Electron Channeling Contrast Imaging.</a> J. Electron. Mater. 37 (5), 691-698 (2008).</li><li>Wilkinson, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+strain+distributions+in+partially+relaxed+In0.2Ga0.8As+on+GaAs+using+electron+channelling+contrast+imaging.">Observation of strain distributions in partially relaxed In0.2Ga0.8As on GaAs using electron channelling contrast imaging.</a> Philos. Mag. Lett. 73 (6), 337-344 (1996).</li><li>Wilkinson, A. J., Anstis, G. R., Czernuszka, J. T., Long, N. J., Hirsch, P. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electron+Channeling+Contrast+Imaging+of+Interfacial+Defects+in+Strained+Silicon-Germanium+Layers+on+Silicon.">Electron Channeling Contrast Imaging of Interfacial Defects in Strained Silicon-Germanium Layers on Silicon.</a> Philos. Mag. A. 68 (1), 59-80 (1993).</li><li>Carnevale, S. D., 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+misfit+dislocation+characterization+in+heteroepitaxial+III-V/Si+thin+films+by+electron+channeling+contrast+imaging.">Rapid misfit dislocation characterization in heteroepitaxial III-V/Si thin films by electron channeling contrast imaging.</a> Appl. Phys. Lett. 104 (23), 232111 (2014).</li><li>Kvam, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interactions+of+dislocations+and+antiphase+(inversion)+domain+boundaries+in+III&#8211;V/IV+heteroepitaxy.">Interactions of dislocations and antiphase (inversion) domain boundaries in III&#8211;V/IV heteroepitaxy.</a> J. Electron. Mater. 23 (10), 1021-1026 (1994).</li><li>Grassman, T. J., 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=Control+and+elimination+of+nucleation-related+defects+in+GaP/Si(001)+heteroepitaxy.">Control and elimination of nucleation-related defects in GaP/Si(001) heteroepitaxy.</a> Appl. Phys. Lett. 94 (23), 232106 (2009).</li><li>Grassman, T. J., 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=Nucleation-related+defect-free+GaP/Si(100)+heteroepitaxy+via+metal-organic+chemical+vapor+deposition.">Nucleation-related defect-free GaP/Si(100) heteroepitaxy via metal-organic chemical vapor deposition.</a> Appl. Phys. Lett. 102 (14), 142102 (2013).</li><li>Volz, K., 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=GaP-nucleation+on+exact+Si(001)+substrates+for+III/V+device+integration.">GaP-nucleation on exact Si(001) substrates for III/V device integration.</a> J. Cryst. Growth. 315 (1), 37-47 (2011).</li><li>Beyer, A., 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=GaP+heteroepitaxy+on+Si(001):+Correlation+of+Si-surface+structure,+GaP+growth+conditions,+and+Si-III/V+interface+structure.">GaP heteroepitaxy on Si(001): Correlation of Si-surface structure, GaP growth conditions, and Si-III/V interface structure.</a> J. Appl. Phys. 111 (8), 083534 (2012).</li><li>Touloukian, Y. 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> Thermal Expansion: Nonmetallic Solids. , (1977).</li><li>Yamaguchi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dislocation+density+reduction+in+heteroepitaxial+III-V+compound+films+on+Si+substrates+for+optical+devices.">Dislocation density reduction in heteroepitaxial III-V compound films on Si substrates for optical devices.</a> J. Mater. Res. 6 (2), 376-384 (1991).</li><li>Nemanich Ware, R. J., Gray, J. L., Hull, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+a+nonorthogonal+pattern+of+misfit+dislocation+arrays+in+SiGe+epitaxy+on+high-index+Si+substrates.">Analysis of a nonorthogonal pattern of misfit dislocation arrays in SiGe epitaxy on high-index Si substrates.</a> J. Appl. Phys. 95 (1), 115-122 (2004).</li><li>Ghandhi Ayers, S. K., Schowalter, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystallographic+tilting+of+heteroepitaxial+layers.">Crystallographic tilting of heteroepitaxial layers.</a> J. Cryst. Growth. 113 (3-4), 430-440 (1991).</li><li>Yamane, T., Kawai, Y., Furukawa, H., Okada, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+of+low+defect+density+GaP+layers+on+Si+substrates+within+the+critical+thickness+by+optimized+shutter+sequence+and+post-growth+annealing.">Growth of low defect density GaP layers on Si substrates within the critical thickness by optimized shutter sequence and post-growth annealing.</a> J. Cryst. Growth. 312 (15), 2179-2184 (2010).</li><li>Jimbo Soga, T., Umeno, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dislocation+Generation+Mechanisms+For+GaP+On+Si+Grown+By+Metalorganic+Chemical-Vapor-Deposition.">Dislocation Generation Mechanisms For GaP On Si Grown By Metalorganic Chemical-Vapor-Deposition.</a> Appl. Phys. Lett. 63 (18), 2543-2545 (1993).</li><li>Weidner, A., Martin, S., Klemm, V., Martin, U., Biermann, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stacking+faults+in+high-alloyed+metastable+austenitic+cast+steel+observed+by+electron+channelling+contrast+imaging.">Stacking faults in high-alloyed metastable austenitic cast steel observed by electron channelling contrast imaging.</a> Scripta Mater. 64 (6), 513-516 (2011).</li></ol>

An accelerating voltage of 25 kV was used for this study. The accelerating voltage will determine the electron beam penetration depth; with higher accelerating voltage, there will be BSE signal coming from greater depths in the sample. The high accelerating voltage was chosen for this system because it allows for visibility of dislocations that are far from the surface of the sample, buried at the interface. Other types of defects/features may be more or less visible at different accelerating voltages depending on the ty...

Detailed characterization of crystalline defects and microstructure is a vitally important aspect of semiconductor materials and device research since such defects can have a significant, detrimental impact on device performance. Currently, transmission electron microscopy (TEM) is the most widely accepted and used technique for detailed characterization of extended defects &#8211; dislocations, stacking faults, twins, antiphase domains, etc. &#8211; because it enables the direct imaging of a wide variety of defects with ample spatial resolution. Unfortunately, TEM is a fundamentally low-throughput approach due to lengthy sample preparation times, which can lead to significant delays and bottlenecks in research and development cycles. Additionally, the integrity of the sample, such as in terms of the as-grown strain state, can be altered during sample preparation, leaving the opportunity for adulterated results.
Electron channeling contrast imaging (ECCI) is a complementary, and in some cases a potentially superior, technique to TEM as it provides an alternative, high-throughput approach for imaging the same extended defects. In the case of epitaxial materials, samples need little to no preparation, making ECCI much more time efficient. Additionally advantageous is the fact that ECCI requires only a field-emission scanning electron microscope (SEM) equipped with a standard annular pole-piece mounted backscatter electron (BSE) detector; forescatter geometry can also be used, but requires slightly more specialized equipment and is not discussed here. The ECCI signal is composed of electrons that have been inelastically scattered out of the in-going channeled beam (electron wave-front), and through multiple additional inelastic scattering events, are able escape the sample back through the surface.1 Similar to two-beam TEM, it is possible to perform ECCI at specific diffraction conditions in the SEM by orienting the sample so that the incident electron beam satisfies a crystallographic Bragg condition (i.e., channeling), as determined using low-magnification electron channeling patterns (ECPs);1,2 see Figure 1 for an example. Simply, ECPs provide an orientation-space representation of incident electron beam diffraction/channeling.3 Dark lines resulting from low backscatter signal indicate beam-sample orientations where Bragg conditions are met (i.e., Kikuchi lines), which yields strong channeling, whereas the bright regions indicate high backscatter, non-diffractive conditions. As opposed to Kikuchi patterns produced via electron backscatter diffraction (EBSD) or TEM, which are formed via outgoing electron diffraction, ECPs are a result of incident electron diffraction/channeling.
In practice, controlled diffraction conditions for ECCI are achieved by adjusting the sample orientation, via tilt and/or rotation under low magnification, such that the ECP feature representing the well-defined Bragg condition of interest &#8211; for example, a [400] or [220] Kikuchi band/line &#8211; is coincident with the optic axis of the SEM. Transitioning to high magnification then, because of the resultant restriction of the angular range of the incident electron beam, effectively selects for a BSE signal that ideally corresponds only to scattering from the chosen diffraction condition. In this manner it is possible to observe defects that provide diffraction contrast, such as dislocations. Just as in TEM, the imaging contrast presented by such defects is determined by the standard invisibility criteria, g &#183; (b x u) = 0 and g &#183; b = 0, where g represents the diffraction vector, b the Burgers vector, and u the line direction.4 This phenomenon occurs because only diffracted electrons from planes distorted by the defect will contain information about said defect.
To date, ECCI has predominantly been used to image features and defects near or at the sample surface for such functional materials as GaSb,5 SrTiO3,5 GaN,6-9 and SiC.10,11 This limitation is the result of the surface-sensitive nature of the ECCI signal itself, wherein the BSE that make up the signal come from a depth range of about 10 &#8211; 100 nm. The most significant contribution to this depth resolution limit is that of broadening and damping of the in-going electron wave front (channeled electrons), as a function of depth into the crystal, due to the loss of electrons to scattering events, which reduces the maximum potential BSE signal.1 Nonetheless, some degree of depth resolution has been reported in previous work on Si1-xGex/Si and InxGa1-xAs/GaAs heterostructures,12,13 as well as more recently (and herein) by the authors on GaP/Si heterostructures,14 where ECCI was used to image misfit dislocations buried at the lattice-mismatched heteroepitaxial interface at depths of up to 100 nm (with higher depths likely possible).
For the work detailed here, ECCI is used to study GaP epitaxially grown on Si(001), a complex materials integration system with application toward such areas as photovoltaics and optoelectronics. GaP/Si is of particular interest as a potential pathway for the integration of metamorphic (lattice-mismatched) III-V semiconductors onto cost-effective Si substrates. For many years efforts in this direction have been plagued by the uncontrolled generation of large numbers of heterovalent nucleation related defects, including antiphase domains, stacking faults, and microtwins. Such defects are detrimental to device performance, especially photovoltaics, due to the fact that they can be electrically active, acting as carrier recombination centers, and can also hinder interfacial dislocation glide, leading to higher dislocation densities.15 However, recent efforts by the authors and others have led to the successful development of epitaxial processes that can produce GaP-on-Si films free of these nucleation related defects,16-19 thereby paving the way for continued progress.
Nonetheless, because of the small, but non-negligible, lattice mismatch between GaP and Si (0.37% at RT), the generation of misfit dislocations is unavoidable, and indeed necessary to produce fully relaxed epilayers. GaP, with its FCC-based zinc blende structure, tends to yield 60&#176; type dislocations (mixed edge and screw) on the slip system, which are glissile and can relieve large amounts of strain through long net glide lengths. Additional complexity is also introduced by the mismatch in GaP and Si thermal expansion coefficients, which results in an increasing lattice mismatch with increasing temperature (i.e., &#8805; 0.5% misfit at typical growth temperatures).20 Because the threading dislocation segments that make up the remainder of the misfit dislocation loop (along with the interfacial misfit and the crystal surface) are well known for their associated non-radiative carrier recombination properties, and thus degraded device performance,21 it is important to fully understand their nature and evolution such that their numbers can be minimized. Detailed characterization of the interfacial misfit dislocations can thus provide a substantial amount of information about the dislocation dynamics of the system.
Here, we describe the protocol for using an SEM to perform ECCI and provide examples of its capabilities and strengths. An important distinction here is the use of ECCI to perform microstructural characterization of the sort typically performed via TEM, whereas ECCI provides the equivalent data but in a significantly shorter time frame due to the significantly reduced sample preparation needs; in the case for epitaxial samples with relatively smooth surfaces, there is effectively no sample preparation required at all. The use of ECCI for general characterization of defects and misfit dislocations is described, with some examples of observed crystalline defects provided. The impact of invisibility criteria on the observed imaging contrast of an array of interfacial misfit dislocations is then described. This is followed by a demonstration of how ECCI can be used to perform important modes of characterization &#8211; in this case a study to determine the GaP-on-Si critical thickness for dislocation nucleation &#8211; providing TEM-like data, but from the convenience of an SEM and in significantly reduced time frame.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Sirion Field Emission SEM</td>
			<td>FEI/Phillips</td>
			<td>516113</td>
			<td>Field emission SEM with beam voltage range of 200 V - 30 kV, equipped with a backscattered electron detector</td>
		</tr>
		<tr>
			<td>Sample of Interest</td>
			<td>Internally produced</td>
			<td>N/A</td>
			<td>Synthesized/grown in-house via MOCVD</td>
		</tr>
		<tr>
			<td>PELCO SEMClip</td>
			<td>Ted Pella, Inc.</td>
			<td>16119-10</td>
			<td>Reusable, non-adhesive SEM sample stub (adhesive attachment will also work)</td>
		</tr>
	</tbody>
</table>

electron channeling contrast imaging for rapid iii-v heteroepitaxial characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities &#8211; high spatial resolution and richness of microstructural data &#8211; with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

The GaP/Si samples for this study were grown by metal-organic chemical vapor deposition (MOCVD) in an Aixtron 3&#215;2 close-coupled showerhead reactor following the authors&#8217; previously reported heteroepitaxial process.17 All growths were performed on 4 inch Si(001) substrates with intentional misorientation (offcut) of 6&#176; toward [110]. All ECCI imaging was performed on as-grown samples with no further sample preparation whatsoever (aside from cleaving to yield approximately 1 cm x 1cm pieces for lo...

Watch this Scientific Journal Video about Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization at JoVE.com

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

electron-channeling-contrast-imaging-for-rapid-iii-v-heteroepitaxial

Research

JoVE Journal

Engineering

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization.

The fabrication process and experimental characterization techniques relevant to single-electron pumps based on silicon metal-oxide-semiconductor quantum dots are discussed.

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by ...

Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve the solar conversion efficiency of a concentrated photovoltaic system. The proposed system will also lower the solar cell cost in the concentrated photovoltaic system by replacing the expensive tandem solar cells with the cost-effective single junction solar cells. The structures and the parameters of high contrast gratings for the dispersive elements were numerically optimized. The large-area fabrication of high contrast gratings was experimentally demonstrated using nanoimprint lithography and dry etching. The quality of grating material and the performance of the fabricated device were both experimentally characterized. By analyzing the measurement results, the possible side effects from the fabrication processes are discussed and several methods that have the potential to improve the fabrication processes are proposed, which can help to increase the optical efficiency of the fabricated devices.

The fabrication of high contrast gratings as the parallel spectrum splitting dispersive element in a concentrated photovoltaic system is demonstrated. Fabrication processes including nanoimprint lithography, TiO2 sputtering and reactive ion etching are described. Reflectance measurement results are used to characterize the optical performance.

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve ...

Use of a Multi-compartment Dynamic Single Enzyme Phantom for Studies of Hyperpolarized Magnetic Resonance Agents

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due to fundamental constraints imposed by the hyperpolarized state, exotic imaging and reconstruction techniques are commonly used. A practical system for characterization of dynamic, multi-spectral imaging methods is critically needed. Such a system must reproducibly recapitulate the relevant chemical dynamics of normal and pathological tissues. The most widely utilized substrate to date is hyperpolarized [1-13C]-pyruvate for assessment of cancer metabolism. We describe an enzyme-based phantom system that mediates the conversion of pyruvate to lactate. The reaction is initiated by injection of the hyperpolarized agent into multiple chambers within the phantom, each of which contains varying concentrations of reagents that control the reaction rate. Multiple compartments are necessary to ensure that imaging sequences faithfully capture the spatial and metabolic heterogeneity of tissue. This system will aid the development and validation of advanced imaging strategies by providing chemical dynamics that are not available from conventional phantoms, as well as control and reproducibility that is not possible in vivo.

A multi-compartment dynamic phantom is used to simulate some biology of interest for metabolic studies using hyperpolarized magnet resonance agents.

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due ...

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications ...

Characterization of Anisotropic Leaky Mode Modulators for Holovideo

Holovideo displays are based on light-bending spatial light modulators. One such spatial light modulator is the anisotropic leaky mode modulator. This modulator is particularly well suited for holographic video experimentation as it is relatively simple and inexpensive to fabricate1-3. Some additional advantages of leaky mode devices include: large aggregate bandwidth, polarization separation of signal light from noise, large angular deflection and frequency control of color1. In order to realize these advantages, it is necessary to be able to adequately characterize these devices as their operation is strongly dependent on waveguide and transducer parameters4. To characterize the modulators, the authors use a commercial prism coupler as well as a custom characterization apparatus to identify guided modes, calculate waveguide thickness and finally to map the device's frequency input and angular output of leaky mode modulators. This work gives a detailed description of the measurement and characterization of leaky mode modulators suitable for full-color holographic video.

This work describes fabrication and characterization of anisotropic leaky mode modulators for holographic video.

Holovideo displays are based on light-bending spatial light modulators.  One such spatial light modulator is the anisotropic leaky mode modulator.  This ...

Electrochemical Etching and Characterization of Sharp Field Emission Points for Electron Impact Ionization

A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. The results of studies in which the etching current and the molarity of the NaOH solution used in the etching process were varied are presented. The investigation of the geometry of the tips, by imaging them with a scanning electron microscope, and by operating them in field emission mode is also described. The field emission tips produced are intended to be used as an electron beam source for ion production via electron impact ionization of background gas or vapor in Penning trap mass spectrometry applications.

A method for electrochemically etching field emission tips is presented. Etching parameters are characterized and the operation of the tips in field emission mode is investigated.

A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. ...

Single-Digit Nanometer Electron-Beam Lithography with an Aberration-Corrected Scanning Transmission Electron Microscope

We demonstrate extension of electron-beam lithography using conventional resists and pattern transfer processes to single-digit nanometer dimensions by employing an aberration-corrected scanning transmission electron microscope as the exposure tool. Here, we present results of single-digit nanometer patterning of two widely used electron-beam resists: poly (methyl methacrylate) and hydrogen silsesquioxane. The method achieves sub-5 nanometer features in poly (methyl methacrylate) and sub-10 nanometer resolution in hydrogen silsesquioxane. High-fidelity transfer of these patterns into target materials of choice can be performed using metal lift-off, plasma etch, and resist infiltration with organometallics.

We use an aberration-corrected scanning transmission electron microscope to define single-digit nanometer patterns in two widely-used electron-beam resists: poly (methyl methacrylate) and hydrogen silsesquioxane. Resist patterns can be replicated in target materials of choice with single-digit nanometer fidelity using liftoff, plasma etching, and resist infiltration by organometallics.

We demonstrate extension of electron-beam lithography using conventional resists and pattern transfer processes to single-digit nanometer dimensions by ...

A Rapid Method for Modeling a Variable Cycle Engine

The variable cycle engines (VCE) that combine the advantages of turbofan and turbojet engines, are widely considered to be the next generation aircraft engines. However, developing VCE requires high costs. Thus, it is essential to build a mathematical model when developing an aircraft engine, which may avoid a large number of real tests and reduce the cost dramatically. Modeling is also crucial in control law development. In this article, based on a graphical simulation environment, a rapid method for modeling a double bypass variable cycle engine using object-oriented modeling technology and modular hierarchical architecture is described. Firstly, the mathematical model of each component is built based on the thermodynamic calculation. Then, a hierarchical engine model is built via the combination of each component mathematical model and the N-R solver module. Finally, the static and dynamic simulations are carried out in the model and the simulation results prove the effectiveness of the modeling method. The VCE model built through this method has the advantages of clear structure and real-time observation.

Here, we present a protocol to build a component-level mathematical model for a variable cycle engine.

The variable cycle engines (VCE) that combine the advantages of turbofan and turbojet engines, are widely considered to be the next generation aircraft ...

Method Development for Contactless Resonant Cavity Dielectric Spectroscopic Studies of Cellulosic Paper

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of data that can be obtained from an individual sample and renders it difficult to produce statistically relevant data for unique and rare materials. Resonant cavity dielectric spectroscopy is a non-destructive, contactless technique which can simultaneously interrogate both sides of a sheeted material and provide measurements which are suitable for statistical interpretations. This offers analysts the ability to quickly discriminate between sheeted materials based on composition and storage history. In this methodology article, we demonstrate how contactless resonant cavity dielectric spectroscopy may be used to differentiate between paper analytes of varying fiber species compositions, to determine the relative age of the paper, and to detect and quantify the amount of post-consumer waste (PCW) recycled fiber content in manufactured office paper.

A protocol for the non-destructive analysis of the fiber content and relative age of paper.

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of ...