The authors thank M. Leboeuf for assistance with the AFM, W. Lee for the anodically textured aluminum master and the Swiss Federal Energy Office and the Swiss National Science Foundation for funding. A part of this work was carried out in the framework of the FP7 project "Fast Track" funded by the EC under grant agreement no 283501.

1. Mould Fabrication
We use our home-built nanoimprinting setup for the fabrication of the negative mould following Ref. 6, but any alternative nanoimprinting setup will work fine. Alternatively a functionalized polydimethylsiloxane (PDMS) mould might also work.
<ol>
 <li>Fabricate or buy a suitable master carrying the nanoscale pattern to be transferred. In principle, any master suitable for nanoimprinting will do the job. We use a textured ZnO layer on a glass sheet (Schott, AF32 eco, 41 mm x 41 mm x 0.5 mm) deposited as described in 3.1 as a master structure to illustrate the method.</li>
 <li>Apply an anti-adhesion layer on the master structure as described in 2.</li>
 <li>Clean a polyethylene naphtalate (PEN) sheet (Goodfellow, 82 mm x 41 mm x 0.125 mm) in an ultrasonic acetone bath for 2 min followed by an ultrasonic isopropanol bath for 2 more min. Rinse once more with isopropanol and blow dry with nitrogen.</li>
 <li>Deposit a sputtered Cr adhesion layer (5-10 nm) on the PEN sheet.</li>
 <li>Spin-coat the UV-curable resin (Microresist, Ormocer, 1-2 ml) on the PEN sheet at 5,000 rpm to get a uniform coverage.</li>
 <li>Perform a prebake for 5 min on a hot plate at 80 &deg;C to evaporate the solvent, improve film uniformity and adhesion to the PEN sheet.</li>
 <li>Use your nanoimprinting setup to stamp the master pattern into the UV-curable resin. Although not mandatory, we perform stamping under vacuum to prevent bubble inclusions by applying a homogenous pressure of 1 bar onto a flexible silicone membrane. In our setup, the silicone membrane separates the vacuum chamber into two sub-compartments. Pressure is generated by venting the upper compartment, while the lower compartment remains under vacuum. Venting pushes the flexible membrane towards the bottom initiating the stamping.</li>
 <li>Expose the resin to UV light to provoke the cross-linking reaction of the resin. We apply a moderate light intensity of 1.4 mW/cm2 at a wavelength of 365 nm provided by several LEDs. Exposure time through the PEN sheet is typically 15-20 min.</li>
 <li>Carefully demould by manually peeling the mould off the master structure.</li>
 <li>As the resin may undergo slight shrinkage during the deposition of the functional material, which may lead to spontaneous peeling, we perform a mild thermal post bake at 150 &deg;C during 6-8 hr in an oven with ambient atmosphere before further processing.</li>
</ol>
2. Anti-adhesion Layer
For successful demoulding, the anti-adhesion layer must be adapted to the materials and the pattern roughness. Generally rough patterns require low sticking coefficients. Low sticking coefficients on smooth patterns may lead to peeling of the functional material from the mould. High sticking coefficients on rough patterns may result in peeling of the resin from the PEN sheet during mould fabrication as the adherence of the resin to the master is stronger.
<ol>
 <li>Coat the mould (or master) with a sputtered chromium layer (5-10 nm) to promote the adhesion of the anti-adhesion agent. For smooth patterns we drop this step. In some cases the chromium layer may prevent the anti-adhesion agent to etch the master structure.</li>
 <li>Apply a small drop of anti-adhesion agent (Sigma-Aldrich, (1H, 1H, 2H, 2H-Perfluoroctyl)-trichlorsilane) on a glass slide. Put the glass slide together with the mould into a vacuum chamber and pump down. The anti-adhesion agent will evaporate and deposit as a molecular monolayer on the mould.</li>
 <li>Anchor the anti-adhesion agent via annealing during 1-2 hr at 80 &deg;C.</li>
</ol>
3. Material Deposition
We demonstrate here three deposition techniques suitable for material deposition to illustrate the versatility of nanomoulding. Other deposition techniques might also be applied. The third example describes the fabrication of a complete thin-film silicon solar cell.
<ol>
 <li>Chemical vapor deposition (CVD) of zinc oxide: Put the mould onto the heating plate of the CVD reactor heated to 180 &deg;C. Use a metal frame to avoid bending of the PEN mould during ZnO deposition. Close the reactor, pump down and allow thermalization. Admit the precursor gases (H2O and (C2H5)2Zn). In addition we dose small amounts of B2H6 for doping. The ZnO layer thickness is proportional to the deposition time. We use ZnO layer thicknesses of typically 1-5 &mu;m. Details on typical depositions parameters may be found in Ref. 7</li>
 <li>Physical vapor deposition (PVD)/sputtering of silver: Put the mould into the PVD system. Close the system and pump down. Admit argon process gas. Turn on the DC generator. The Ag layer thickness is again proportional to deposition time. We use Ag layer thicknesses of typically 1 &mu;m. Typical deposition parameters are an argon pressure of 5.5x10-3 mbar and a setup specific DC power of 250 W yielding a deposition rate of approximately 45 nm/sec.</li>
 <li>Plasma-enhanced chemical vapor deposition (PE-CVD): Deposit ZnO as in 3.1). Put the mold into the PE-CVD reactor heated to 200 &deg;C. Close the reactor, pump down and allow thermalization. Admit the precursor gases (SiH4 and H2). In addition we dose small amounts of B(CH3)3 and PH3 to achieve p- and n-type doping respectively. To increase the open-circuit voltage of the solar cells, we also use small amounts of CH4 and CO2 for the doped layers. After deposition of the p-i-n amorphous silicon solar cell stack, we deposit a ZnO backcontact as described in 3.1.</li>
 <li>Avoid excessive bending of the mould, as bending might cause peeling of the deposited layer.</li>
</ol>
4. Layer Transfer
We use glass slides (Schott AF32 eco, 41 mm x 41 mm x 0.5 mm) as final substrate. But other substrates, including metal foils or polymer sheets, could be used alternatively.
<ol>
 <li>Clean glass slides with acetone and isopropanol and blow dry with nitrogen.</li>
 <li>Spin-coat UV-curable resin (Microresist, Ormocer, 1-2 ml) on the glass slide at 5,000 rpm.</li>
 <li>Use your nanoimprinting setup to anchor the mould carrying the deposited layers onto the final substrate. As for stamping, we perform anchoring under vacuum by applying a homogenous pressure of 1 bar.</li>
 <li>Expose the resin to UV light to provoke the cross-linking reaction. We apply a moderate intensity of 1.4 mW/cm2 at a wavelength of 365 nm provided by several LEDs. Exposure time through the glass slide is only 1-3 min due to the higher UV transmission of glass compared to PEN.</li>
 <li>Demould by manually peeling the mould off the glass slide.</li>
</ol>
5. Sample Characterization
<ol>
 <li>Use your favorite morphological, electrical or optical technique to characterize the nanomoulded samples. Here we characterize our nanomoulded samples using scanning electron microscopy (SEM) and atomic force microscopy (AFM).</li>
</ol>

<ol>
	<li>Geissler, M., Xia, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Patterning:+Principles+and+Some+New+Developments.">Patterning: Principles and Some New Developments.</a> Advanced Materials. 16 (15), 1249-1269 (2004).</li><li>Guo, 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=Nanoimprint+Lithography:+Methods+and+Material+Requirements.">Nanoimprint Lithography: Methods and Material Requirements.</a> Advanced Materials. 19, 495-513 (2007).</li><li>Ahn, S. H., Guo, 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=Large-Area+Roll-to-Roll+and+Roll-to-Plate+Nanoimprint+Lithography:+A+Step+toward+High-Throughput.">Large-Area Roll-to-Roll and Roll-to-Plate Nanoimprint Lithography: A Step toward High-Throughput.</a> Application of Continuous Nanoimprinting. ACS Nano. 3 (8), 2304-2310 (2009).</li><li>Battaglia, C., Escarr&#233;, 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=Nanoimprint+Lithography+for+High-Efficiency+Thin-Film+Silicon+Solar+Cells.">Nanoimprint Lithography for High-Efficiency Thin-Film Silicon Solar Cells.</a> Nano Letters. 11, 661-665 (2011).</li><li>Battaglia, C., Escarr&#233;, 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=Nanomoulding+of+Transparent+Zinc+Oxide+Electrodes+for+Efficient+Light+Trapping+in+Solar+Cells.">Nanomoulding of Transparent Zinc Oxide Electrodes for Efficient Light Trapping in Solar Cells.</a> Nature Photonics. 5, 535-538 (2012).</li><li>Escarr&#233;, J., S&#246;derstr&#246;m, 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=High+Fidelity+Transfer+of+Nanometric+Random+Textures+by+UV+Embossing+for+Thin+Film+Solar+Cells+Applications.">High Fidelity Transfer of Nanometric Random Textures by UV Embossing for Thin Film Solar Cells Applications.</a> Solar Energy Materials &amp; Solar Cells. 95, 881-886 (2011).</li><li>Fa&#255;, S., Feitknecht, L., Schl&#252;chter, R., Kroll, U., Vallat-Sauvain, E., Shah, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rough+ZnO+layers+by+LP-CVD+process+and+their+effect+in+improving+performances+of+amorphous+and+microcrystalline+silicon+solar+cells.">Rough ZnO layers by LP-CVD process and their effect in improving performances of amorphous and microcrystalline silicon solar cells.</a> Solar Energy Materials and Solar Cells. 90, 2960-2967 (2006).</li><li>Zhao, X. -. M., Xia, Y., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+Three-Dimensional+Micro-Structures:+Microtransfer+Molding.">Fabrication of Three-Dimensional Micro-Structures: Microtransfer Molding.</a> Advanced Materials. 8, 837-840 (1996).</li><li>Hampton, M. J., Williams, S. S., 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=The+Patterning+of+Sub-500+nm+Inorganic+Oxide+Structures.">The Patterning of Sub-500 nm Inorganic Oxide Structures.</a> Advanced Materials. 20, 2667-2673 (2008).</li><li>Bass, J. D., Schaper, C. 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=Transfer+Molding+of+Nanoscale+Oxides+Using+Water-Soluble+Templates.">Transfer Molding of Nanoscale Oxides Using Water-Soluble Templates.</a> ACS Nano. 5 (5), 4065-4072 (2011).</li><li>Escarr&#233;, J., Nicolay, S., 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=Nanomoulded+front+ZnO+contacts+for+thin+film+silicon+solar+cell+applications.">Nanomoulded front ZnO contacts for thin film silicon solar cell applications.</a> , (2012).</li><li>Sontheimer, T., Rudigier-Voigt, E., Bockmeyer, M., Klimm, C., Schubert-Bischoff, P., Becker, C., Rech, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Large-area+fabrication+of+equidistant+free-standing+Si+crystals+on+nanoimprinted+glass.">Large-area fabrication of equidistant free-standing Si crystals on nanoimprinted glass.</a> Phys. Status Solidi. RRL. 5, 376-379 (2011).</li></ol>

No conflicts of interest declared.

Nanomoulding allows the transfer of nanopatterns on arbitrary functional materials. Comparison of the individual processing steps in Figure 1 and 2 reveals the close relationship between nanomoulding and nanoimprinting. The major difference between nanomoulding and nanoimprinting is the additional material deposition step in Figure 2e. The remaining process flow is identical. Nanomoulding can therefore be performed on any available nanoimprinting setup.
<p class="jov...

Nanopatterning has gained tremendous importance in many fields of nanotechnology and applied sciences. Pattern generation is the first step and may be accomplished by top-down approaches such as electron-beam lithography or bottom-up approaches based on self-assembly methods such as nanosphere lithography or block copolymer lithography 1. As important as pattern generation is pattern replication. Besides photolithography, nanoimprinting (Figure 1) has emerged as a promising alternative in particular suitable for high-throughput large-area nanoscale patterning at low cost 2-4. While photolithography requires a patterned mask, nanoimprinting relies on a prefabricated master structure. Pattern transfer from the master is commonly performed into a thermoplastic or a UV- or thermally curable polymer. However there are many cases, where it is desirable to transfer the pattern directly onto a functional material.
Here we describe a replication method based on nanomoulding and layer transfer (Figure 2) which we recently introduced in Ref. 5 to transfer nanoscale patterns onto functional zinc oxide electrodes. Our nanomoulding method can be easily implemented if a nanoimprinting setup is available. Nanomoulding offers the potential to be generalized to many other functional materials, materials stacks and even complete devices, provided that the mould material is chosen such that it is compatible with the material deposition process(es). As an example we present here nanomoulding of transparent conductive zinc oxide (ZnO) electrodes deposited by chemical vapor deposition (CVD) which find their application to enhance light trapping in solar cells 5.

<table border="1">
 <tbody>
 <tr>
 <td>Name of the Reagent</td>
 <td>Company</td>
 <td>Catalogue Number</td>
 <td>Comments (optional)</td>
 </tr>
 <tr>
 <td>Nanoimprinting resin</td>
 <td>Microresist</td>
 <td>Ormostamp</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>(1H, 1H, 2H, 2H-Perfluoroctyl)-trichlorsilane, anti-adhesion agent</td>
 <td>Sigma Aldrich</td>
 <td>448931-10G</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Glass slides</td>
 <td>Schott</td>
 <td>AF32 eco</td>
 <td>0.5 mm</td>
 </tr>
 <tr>
 <td>Polyethylene naphtalate (PEN) sheets</td>
 <td>Goodfellow</td>
 <td>ES361090</td>
 <td>0.125 mm</td>
 </tr>
 <tr>
 <td>(C2H5)2Zn</td>
 <td>Akzo Nobel</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Ag sputter target 4N</td>
 <td>Heraeus</td>
 <td>81062165</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>B2H6, SiH4, H2, B(CH3)3, PH3, CH4, CO2</td>
 <td>Messer</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 <td>EQUIPMENT</td>
 </tr>
 <tr>
 <td>Nanoimprinting system</td>
 <td>Home-built</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>LP-CVD system</td>
 <td>Home-built</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>PVD system</td>
 <td>Leybold</td>
 <td>Univex 450 B</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>PE-CVD reactor</td>
 <td>Indeotec</td>
 <td>Octopus I</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>SEM</td>
 <td>JEOL</td>
 <td>JSM-7500 TFE</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>AFM</td>
 <td>Digital Instruments</td>
 <td>Nanoscope 3100</td>
 <td>&nbsp;</td>
 </tr>
 </tbody>
</table>

nanomoulding of functional materials, a versatile complementary pattern replication method to nanoimprinting

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding combined with layer transfer enables the replication of arbitrary surface patterns from a master structure onto the functional material. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes. In particular we demonstrate the fabrication of patterned transparent zinc oxide electrodes for light trapping applications in solar cells.

Figure 3 summarizes some illustrative examples of nanomoulded structures. A ZnO master structure grown by CVD on glass is shown in (a). The corresponding nanomoulded ZnO replica is shown in (d). Comparison of the local height (g) and angle (j) histograms extracted from AFM images reveal the high fidelity of the nanomoulding process. Analogous results are shown for a one-dimensional grating fabricated by interference lithography (b,e,h,k) and anodically textured aluminum (c,f,i,l).
<p class="jo...

Watch this Scientific Journal Video about Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting at JoVE.com

Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes.

We describe a nanomoulding technique which  allows low-cost nanoscale patterning of functional materials, materials stacks  and full devices. Nanomoulding ...

nanomoulding-functional-materials-versatile-complementary-pattern

Research

JoVE Journal

Engineering

11.6K ビュー.  Ecole Polytechnique Fédérale de Lausanne (EPFL). 我々は、機能材料、材料スタックとフルデバイスの低コストのナノスケールのパターニングを可能nanomoulding手法を説明します。 Nanomouldingはどのナノインプリントセットアップで実行することができ、材料や成膜プロセスの広い範囲に適用することができます。

ビデオ: Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

Using Neutron Spin Echo Resolved Grazing Incidence Scattering to Investigate Organic Solar Cell Materials

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped crystallites. Neutrons are passed through two well defined regions of magnetic field; one before and one after the sample. The two magnetic field regions have opposite polarity and are tuned such that neutrons travelling through both regions, without being perturbed, will undergo the same number of precessions in opposing directions. In this case the neutron precession in the second arm is said to &#34;echo&#34; the first, and the original polarization of the beam is preserved. If the neutron interacts with a sample and scatters elastically the path through the second arm is not the same as the first and the original polarization is not recovered. Depolarization of the neutron beam is a highly sensitive probe at very small angles (&#60;50&#160;&#956;rad) but still allows a high intensity, divergent beam to be used. The decrease in polarization of the beam reflected from the sample as compared to that from the reference sample can be directly related to structure within the sample.
In comparison to scattering observed in neutron reflection measurements the SERGIS signals are often weak and are unlikely to be observed if the in-plane structures within the sample under investigation are dilute, disordered, small in size and polydisperse or the neutron scattering contrast is low. Therefore, good results will most likely be obtained using the SERGIS technique if the sample being measured consist of thin films on a flat substrate and contain scattering features that contains a high density of moderately sized features (30 nm to 5 &#181;m) which scatter neutrons strongly or the features are arranged on a lattice. An advantage of the SERGIS technique is that it can probe structures in the plane of the sample.

Progress has been made in utilizing spin echo resolved grazing incidence scattering (SERGIS) as a neutron scattering technique to probe the length-scales in irregular samples. Crystallites of [6,6]-phenyl-C61-butyric acid methyl ester have been probed using the SERGIS technique and the results confirmed by optical and atomic force microscopy.

The spin echo resolved grazing incidence scattering (SERGIS) technique has been used to probe the length-scales associated with irregularly shaped ...

Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many cases validated experimentally, for light weight or impact energy absorbing structures, as high surface area heat exchangers or electrodes, as implants to the body, and many more. Although great progress has been made in understanding their structure-properties relationships, the large number of different processing techniques, each producing material with different characteristics and structure, means that understanding of the individual effects of all aspects of structure is not complete. The replication process, where molten metal is infiltrated between grains of a removable preform material, allows a markedly high degree of control and has been used to good effect to elucidate some of these relationships. Nevertheless, the process has many steps that are dependent on individual &#8220;know-how&#8221;, and this paper aims to provide a detailed description of all stages of one embodiment of this processing method, using materials and equipment that would be relatively easy to set up in a research environment. The goal of this protocol and its variants is to produce metal foams in an effective and simple way, giving the possibility to tailor the outcome of the samples by modifying certain steps within the process. By following this, open cell aluminum foams with pore sizes of 1&#8211;2.36 mm diameter and 61% to 77% porosity can be obtained.

Replication is one of the processing techniques used for the production of porous metal sponges. In this paper one implementation of the method for the production of open celled porous aluminum is shown in detail.

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many ...

Preparation and Reactivity of Gasless Nanostructured Energetic Materials

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the balls. Among other applications, it is a versatile technique that allows for effective preparation of gasless reactive nanostructured materials with high energy density per volume (Ni+Al, Ta+C, Ti+C). The structural transformations of reactive media, which take place during HEBM, define the reaction mechanism in the produced energetic&#160;composites. Varying the processing conditions permits fine tuning of the milling-induced microstructures of the fabricated composite particles. In turn, the reactivity, i.e., self-ignition temperature, ignition delay time, as well as reaction kinetics, of high energy density materials depends on its microstructure. Analysis of the milling-induced microstructures suggests that the formation of fresh oxygen-free intimate high surface area contacts between the reagents is responsible for the enhancement of their reactivity. This manifests itself in a reduction of ignition temperature and delay time, an increased rate of chemical reaction, and an overall decrease of the effective activation energy of the reaction. The protocol provides a detailed description for the preparation of reactive nanocomposites with tailored microstructure using short-term HEBM method. It also describes a high-speed thermal imaging technique to determine the ignition/combustion characteristics of the energetic materials. The protocol can be adapted to preparation and characterization of a variety of nanostructured energetic composites.

This protocol describes the preparation of gasless nanostructured energetic materials (Ni+Al, Ta+C, Ti+C) using the short-term high-energy ball milling (HEBM) technique. It also describes a high-speed thermal imaging method to study the reactivity of mechanically fabricated nanocomposites. These protocols can be extended to other reactive nanostructured energetic materials.

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the ...

Energy Dispersive X-ray Tomography for 3D Elemental Mapping of Individual Nanoparticles

Energy dispersive X-ray spectroscopy within the scanning transmission electron microscope (STEM) provides accurate elemental analysis with high spatial resolution, and is even capable of providing atomically resolved elemental maps. In this technique, a highly focused electron beam is incident upon a thin sample and the energy of emitted X-rays is measured in order to determine the atomic species of material within the beam path. This elementally sensitive spectroscopy technique can be extended to three dimensional tomographic imaging by acquiring multiple spectrum images with the sample tilted along an axis perpendicular to the electron beam direction.
Elemental distributions within single nanoparticles are often important for determining their optical, catalytic and magnetic properties. Techniques such as X-ray tomography and slice and view energy dispersive X-ray mapping in the scanning electron microscope provide elementally sensitive three dimensional imaging but are typically limited to spatial resolutions of &gt; 20 nm. Atom probe tomography provides near atomic resolution but preparing nanoparticle samples for atom probe analysis is often challenging. Thus, elementally sensitive techniques applied within the scanning transmission electron microscope are uniquely placed to study elemental distributions within nanoparticles of dimensions 10-100 nm.
Here, energy dispersive X-ray (EDX) spectroscopy within the STEM is applied to investigate the distribution of elements in single AgAu nanoparticles. The surface segregation of both Ag and Au, at different nanoparticle compositions, has been observed.

The use of energy dispersive X-ray tomography in the scanning transmission electron microscope to characterize elemental distributions within single nanoparticles in three dimensions is described.

Energy dispersive X-ray spectroscopy within the scanning transmission electron microscope (STEM) provides accurate elemental analysis with high spatial ...

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

This video method describes the synthesis of high surface area, monolithic 3D graphene-based materials derived from polymer precursors as well as single layer graphene oxide.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. ...

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.

We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film ...

Standardized Method for Measuring Collection Efficiency from Wipe-sampling of Trace Explosives

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common procedure for collecting traces of explosives, and standardized measurements of collection efficiency are needed to evaluate and optimize sampling protocols. The approach described here is designed to provide this measurement infrastructure, and controls most of the factors known to be relevant to wipe-sampling. Three critical factors (the applied force, travel distance, and travel speed) are controlled using an automated device. Test surfaces are chosen based on similarity to the screening environment, and the wipes can be made from any material considered for use in wipe-sampling. Particle samples of the explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) are applied in a fixed location on the surface using a dry-transfer technique. The particle samples, recently developed to simulate residues made after handling explosives, are produced by inkjet printing of RDX solutions onto polytetrafluoroethylene (PTFE) substrates. Collection efficiency is measured by extracting collected explosive from the wipe, and then related to critical sampling factors and the selection of wipe material and test surface. These measurements are meant to guide the development of sampling protocols at screening venues, where speed and throughput are primary considerations.

Optimized sampling protocols and the development of new wipe materials can be facilitated by standardized measurements of collection efficiency from wipe-sampling. Our approach for sampling trace explosives uses an automated device to control speed, force, and distance during wipe-sampling followed by extraction of collected explosives.

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

A Fabrication and Measurement Method for a Flexible Ferroelectric Element Based on Van Der Waals Heteroepitaxy

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on high-density data storage and low-power consumption capabilities. However, the high-quality oxide based nonvolatile memory on flexible substrates is often constrained by the material characteristics and the inevitable high-temperature fabrication process. In this paper, a protocol is proposed to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica. The versatile deposition technique and measurement method enable the fabrication of flexible yet single-crystalline non-volatile memory elements necessary for the next generation of smart devices.

In this paper, we present a protocol to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica.

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on ...

Studying Large Amplitude Oscillatory Shear Response of Soft Materials

We investigate the sequence of physical processes exhibited during large amplitude oscillatory shearing (LAOS) of polyethylene oxide (PEO) in dimethyl sulfoxide (DMSO) and xanthan gum in water &#8212; two concentrated polymer solutions used as viscosifiers in foods, enhanced oil recovery, and soil remediation. Understanding the nonlinear rheological behavior of soft materials is important in the design and controlled manufacturing of many consumer products. It is shown how the response to LAOS of these polymer solutions can be interpreted in terms of a clear transition from linear viscoelasticity to viscoplastic deformation and back again during a period. The LAOS results are analyzed via the fully quantitative Sequence of Physical Processes (SPP) technique, using free MATLAB-based software. A detailed protocol of performing a LAOS measurement with a commercial rheometer, analyzing nonlinear stress responses with the freeware, and interpreting physical processes under LAOS is presented. It is further shown that, within the SPP framework, a LAOS response contains information regarding the linear viscoelasticity, the transient flow curves, and the critical strain responsible for the onset of nonlinearity.

We present a detailed protocol outlining how to perform nonlinear oscillatory shear rheology on soft materials, and how to run the SPP-LAOS analysis to understand the responses as a sequence of physical processes.

We investigate the sequence of physical processes exhibited during large amplitude oscillatory shearing (LAOS) of polyethylene oxide (PEO) in dimethyl ...