This research was supported by the 1,000 Talents Program for Young Scientists of China, National Natural Science Foundation of China (Grant No. 51472164), the A*STAR Pharos Programme (Grant No. 152 70 00014), and facility support from the NUS Center for Advanced 2D Materials.

Caution: Some of the chemical agents and gases used in this work are toxic, carcinogenic, flammable, and explosive. Please use all appropriate safety practices when performing a vapor transport deposition including the use of engineering controls (fume hood) and personal protective equipment (safety glasses, professional protective masks, gloves, lab coat, full length pants, and closed-toe shoes).
1. Auto-Tune Function of Temperature Controller Parameters
NOTE: Before the synthesis of SnSe flakes, the heating system of the furnace needs to be calibrated by following the manufacturer&#39;s manual.
<ol>
	<li>Set 80% of the most commonly used temperature as the target temperature. Here, set 560 oC for 1 h and run the furnace.</li>
	<li>When the temperature approaches 560 oC, press the &#34;SET&#34; key for 2 s, note that the parameter &#34;HAL&#34; pops up, and press the &#34;SET&#34; key for 1 s to go next parameter.</li>
	<li>Continue to press the &#34;SET&#34; key. After &#34;Cont=3&#34; appears, set it as 2. The system starts the auto-tune function to work out the value for Int, Pro, and Lt, and then system will go to 3. When re-auto-tune is needed, set it as 2.</li>
</ol>
2. Pretreatment of Quartz Tubes and Ceramic Boats
NOTE: Before the synthesis of SnSe flakes, a high temperature cleaning process is required, where a new ceramic boat and a new quartz tube are pretreated.
<ol>
	<li>Position a new ceramic boat inside a new 1-inch diameter quartz tube. Place the 1-inch diameter quartz tube inside a horizontal tube furnace with a new 2 inch diameter quartz tube. Ensure that the both ends of the tubes are firmly fixed and supported.</li>
	<li>Close the furnace lid, and heat the tube furnace to 1,000 oC over 30 min.</li>
	<li>When the temperature at the center of the furnace approaches 1,000 oC, keep the furnace at 1,000 oC for 30 min. Then, gradually move the tube furnace from one end to the other to heat the whole length of the tube for cleaning the quartz tube wall and the ceramic boat.</li>
	<li>After this, allow the tube furnace to cool to room temperature by turning off the furnace. When the furnace has cooled to room temperature, open the furnace lid and take out the new ceramic boat and the new 1-inch diameter quartz tube, which can be used for the subsequent experiments.</li>
</ol>
3. Pretreatment SiO 2 /Si Substrates
<ol>
	<li>Cut the SiO2/Si wafer (300 nm thick SiO2 on heavily doped Si) (see Table of Materials) using a diamond scriber into an appropriate size (about 1.5 cm &#215; 2 cm) to be used as growth substrates.</li>
	<li>Clean the SiO2/Si substrates in acetone, isopropanol, and water, followed by a nitrogen blow dry.</li>
</ol>
4. Synthesis of Bulk Rectangular Shaped SnSe Flakes
<ol>
	<li>Place 0.010 g SnSe powder (see Table of Materials) in the clean ceramic boat. Place a clean SiO2/Si substrate (about 1.5 cm &#215; 2 cm) onto the ceramic boat, growth side facing the SnSe powder. Position the ceramic boat inside a clean 1-inch diameter quartz tube.</li>
	<li>Place the 1-inch diameter quartz tube inside a horizontal tube furnace with a 2-inch diameter quartz tube on the outside, and ensure that the ceramic boat is located upstream of the heating zone of the tube furnace. Tighten the flanges at both ends of the tube, and close the vent valve, which seals the 2-inch diameter quartz tube.</li>
	<li>Turn on the pump that connects to the quartz tube, pump the tube to a pressure of ~1&#215;10-2 mbar to remove air and moisture in the tube. After that pressure is achieved, turn off the pump.</li>
	<li>Then open the carrier gas valves, using the gas flow meter to control the gas flows. Introduce 40 standard cubic cm per min (sccm) Ar and 10 sccm H2 (purity: 99.9%) into the quartz tube until atmospheric pressure was achieved. Open the vent valves to allow a continuous flow of gas in the quartz tubes.</li>
	<li>Close the furnace lid and rapidly heat the tube furnace with a 35 oC per minute heating-rate.</li>
	<li>When the temperature at the center of the furnace approaches 700 oC, quickly move the tube furnace to position the SnSe powders at the center of the furnace. The SnSe powder will evaporate, and the bulk SnSe flakes will deposit on the SiO2/Si surface.</li>
	<li>After 15 min growth time, open the furnace lid to quickly cool the tube furnace to room temperature. Meanwhile, adjust the flow of Ar/H2 carrier gas to maximum, which will help to drive the unreacted gas or particles out of the tubes. When the growth process is completed, bulk SnSe flakes will be obtained on the surface of the SiO2/Si substrates.</li>
</ol>
5. Fabrication of Single-Layer Rectangular Shaped SnSe Flakes
<ol>
	<li>Place the as-grown bulk SnSe/SiO2/Si sample face up onto a new clean ceramic boat. Position the ceramic boat inside a new clean 1-inch diameter quartz tube.</li>
	<li>Put the 1-inch diameter quartz tube inside the horizontal tube furnace with a 2-inch diameter quartz tube, with the ceramic boat located upstream of the heating zone of the tube furnace. Tighten the flanges at both ends of the tube, and close the vent valve to seal the 2-inch diameter quartz tube.</li>
	<li>Turn on the pump that connects to the quartz tube, pump down the tube to a pressure of ~1&#215;10-2 mbar to remove air and moisture in the tube. After that is achieved, turn off the pump.</li>
	<li>Open the carrier gas valves, using the gas flow meter to control the gas flows. Introduce 50 sccm N2 (purity: 99.9%) into the quartz tube until atmospheric pressure is achieved. Open the vent valves to allow a continuous flow of gas in the quartz tubes.</li>
	<li>Close the furnace lid and rapidly heat the tube furnace to 700 oC in 20 min.</li>
	<li>When the temperature at the center of the furnace approaches 700 oC, quickly move the tube furnace to position the bulk SnSe/SiO2/Si sample at the center of the furnace.</li>
	<li>Maintain the furnace at 700 oC for ~5-20 min to complete the etching process. After that, open the furnace lid, and quickly cool the tube furnace to room temperature. Meanwhile, keep the flow of N2 gas to a maximum, which will help to drive the unreacted gas or particles out of the tubes. When the etching process is completed, observe the single-layer rectangular shaped SnSe flakes obtained on the surface of the SiO2/Si substrates. 
	NOTE: The etching gas and etching time are the main controlling factors in this process. The etching mechanism is investigated in reference 29, so see reference 29 for more details.</li>
</ol>

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We have nothing to disclose.

Here, the combination of a vapor transport deposition method and a nitrogen etching technique in an atmospheric pressure system is first reported. In this protocol, the critical steps are the section of the fabrication of single-layer SnSe flakes.
Although the bulk samples can be etched to form a high-quality single-layer sample, the thickness of the bulk samples should be uniform and the decomposition temperature of bulk samples should be higher than the etching temperature. The resulting sam...

Research into two dimensional (2D) materials has bloomed in recent years since the successful isolation of graphene, due to the possibility of 2D materials having superior electrical, optical, and mechanical properties over their bulk counterparts1,2,3,4,5. 2D materials show promising applications in optoelectronic and electronic devices6,7, catalysis and water splitting8,9, surface-enhanced Raman scattering sensing10,11, etc. The large family of layered materials which can be exfoliated into 2D materials show great diversity, ranging from the semi-metallic graphene to the semiconducting transition-metal dichalcogenides (TMDs) and black phosphorus (BP) to the insulating hexagonal boron nitride (h-BN). These materials and their heterostructures have been well studied in recent years, and have exhibited many novel properties and applications12. Other less studied, but equally promising 2D layered materials in the IIIA-VIA (GaS, GaSe, and InSe)13,14 and IVA-VIA (GeS, GeSe, and SnS)15,16,17 families have also recently received attention.
SnSe belongs to the IVA-VIA group and crystallizes in an orthorhombic structure, with the atoms arranged in the pnma space group and buckled within the layer, like the crystal structure of phosphorene. SnSe is a narrow gap semiconductor with a band gap of 0.6 eV, but is more well known for its more unique thermoelectric properties, as it is reported to have a very high ZT (thermoelectric figure of merit) value of 2.6 at 923 K18,19, which has been attributed to its unique electronic structure and low thermal conductivity. While bulk SnSe crystals are available commercially and can be grown by known methods, such as the Bridgeman-Stockbarger method20 or the chemical vapor transport method21, growing large sized few-layer and single-layer SnSe on dielectric substrates is more challenging. There are many substrates to support 2D material growth, such as highly oriented pyrolytic graphite (HOPG), mica, SiO2, Si3N4, and glass. Low-cost SiO2 dielectrics are the most commonly used substrate, as these allow the fabrication of field-effect transistors, where the dielectrics serve as part of the electrical back gate. In our experience, unlike graphene and TMDs, it is difficult to obtain few-layer or single-layer SnSe flakes by the micromechanical exfoliation method, as bulk SnSe has a high interlayer binding energy22 of 32 meV/&#197;2, which leads to thick layers, even along the edges of the exfoliated flakes. Therefore, to study the novel electronic properties of few layer and single layer SnSe, a new, simple, and low-cost synthetic method to prepare high quality large-sized single-layer SnSe crystals on insulating substrates is required, especially since SnSe has shown great promise as a candidate for thermoelectric applications for energy conversion in the low and moderate temperature range19.
Several researchers have developed methods to synthesize high quality SnSe crystals. Liu et al.23 and Franzman et al.24 used a solution-phase method to synthesize SnSe nanocrystals of different shapes, such as quantum dots, nanoplates, single crystalline nanosheets, nanoflowers, and nanopolyhedra using SnCl2 and alkyl-phosphine-selenium or dialkyl diselenium as precursors. Baumgardner et al.25 synthesized colloidal SnSe nanoparticles by injecting bis[bis(trimethylsilyl)amino]tin(II) into hot trioctylphosphine, and they obtained nanocrystals of ~4-10 nm in diameter. Boscher et al.26 used an atmospheric pressure chemical vapor deposition technique to obtain SnSe films on glass substrates using tin tetrachloride and diethyl selenide precursors with a tin tetrachloride ratio 10 larger than diethyl selenide, and their synthesized SnSe films were about 100 nm thick and silver-black in appearance. Zhao et al.27 used vapor transport deposition in a low vacuum system and synthesized single-crystal SnSe nanoplates on mica substrates and obtained square nanoplates of 1-6 &#181;m. However, obtaining single-layer SnSe crystals are not possible using these techniques. Li et al.28 successfully synthesized single-layer single-crystal SnSe nanosheets using a one-pot synthetic method with SnCl4 and SeO2 precursors. However, they were only able to obtain a lateral size of about 300 nm for their nanosheets. We have recently published our method to grow high quality, large-sized single-layer SnSe crystals which are phase pure29. This detailed protocol is intended to help new practitioners to grow other large-sized high-quality ultrathin 2D materials using this methodology.

<table><tbody><tr><td>SnSe powder</td><td>Sigma-Aldrich</td><td>1315-06-6</td><td>(99.999%) toxic, carcinogenic</td></tr><tr><td>Ar gas</td><td></td><td></td><td>explosive</td></tr><tr><td>H2 gas</td><td></td><td></td><td>flammable, explosive</td></tr><tr><td>SiO&lt;sub&gt;2&lt;/sub&gt;/Si wafer</td><td></td><td></td><td>300 nm thick SiO2 on heavily doped Si</td></tr><tr><td>Acetone</td><td>Sigma-Aldrich</td><td>67-64-1</td><td>toxic, flammable</td></tr><tr><td>Isopropanol</td><td>Sigma-Aldrich</td><td>67-63-0</td><td>flammable</td></tr><tr><td>Quartz tube</td><td>Dongjing Quartz Company, China</td><td></td><td></td></tr><tr><td>Ceramic boat</td><td>Dongjing Quartz Company, China</td><td></td><td></td></tr><tr><td>Optical microscope</td><td>Olympus, BX51</td><td></td><td></td></tr><tr><td>Atomic force microscopy</td><td>Bruker</td><td></td><td>Using FastScan-A probe type and ScanAsyst-air</td></tr><tr><td>Scanning electron microscopy</td><td>JEOL JSM-6700F</td><td></td><td></td></tr><tr><td>transmission electron microscopy</td><td>FEI Titan</td><td></td><td></td></tr><tr><td>Tube furnace</td><td>MTI Corporation</td><td></td><td></td></tr></tbody></table>

atmospheric pressure fabrication of large-sized single-layer rectangular snse flakes

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for applications in two-dimensional nanoelectronics devices. Although many methods to synthesize SnSe nanocrystals have been developed, a simple way to fabricate large-sized single-layer SnSe flakes remains a great challenge. Herein, we show the experimental method to directly grow large-sized single-layer rectangular SnSe flakes on commonly used SiO2/Si insulating substrates using a straightforward two-step fabrication method in an atmospheric pressure quartz tube furnace system. The single-layer rectangular SnSe flakes with an average thickness of ~6.8 &#197; and lateral dimensions of about 30 &#181;m &#215; 50 &#181;m were fabricated by a combination of vapor transport deposition technique and nitrogen etching route. We characterized the morphology, microstructure, and electrical properties of the rectangular SnSe flakes and obtained excellent crystallinity and good electronic properties. This article about the two-step fabrication method can help researchers grow other similar two-dimensional, large-sized, single-layer materials using an atmospheric pressure system.

Schematic diagrams of the experimental apparatus, optical images, atomic force microscopy (AFM) images, scanning electron microscopy (SEM) images, and transmission electron microscopy (TEM) images of the fabricated SnSe flakes are shown in Figure 1, Figure 2, and Figure 3. The optical images are performed by a traditional optical microscope. The eyepiece lens is 10X, and the objective lens is 20X, 50...

Watch this Scientific Journal Video about Atmospheric Pressure Fabrication of Large-Sized Single-Layer Rectangular SnSe Flakes at JoVE.com

Atmospheric Pressure Fabrication of Large-Sized Single-Layer Rectangular SnSe Flakes

A protocol is presented demonstrating a two-step fabrication technique to grow large-sized single-layer rectangular shaped SnSe flakes on low-cost SiO2/Si dielectrics wafers in an atmospheric pressure quartz tube furnace system.

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for ...

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Research

JoVE Journal

Engineering

8.1K Views.  Shenzhen University. Een protocol wordt gepresenteerd tonen een tweestaps fabricage techniek om te groeien groot formaat enkellaags rechthoekige gevormde SnSe goedkope SiO2/Si diëlektrica (wafers) in een systeem met luchtdruk kwarts buisjes oven vlokken.

Video: Atmospheric Pressure Fabrication of Large-Sized Single-Layer Rectangular SnSe Flakes

Origami Inspired Self-assembly of Patterned and Reconfigurable Particles

There are numerous techniques such as photolithography, electron-beam lithography and soft-lithography that can be used to precisely pattern two dimensional (2D) structures. These technologies are mature, offer high precision and many of them can be implemented in a high-throughput manner. We leverage the advantages of planar lithography and combine them with self-folding methods1-20 wherein physical forces derived from surface tension or residual stress, are used to curve or fold planar structures into three dimensional (3D) structures. In doing so, we make it possible to mass produce precisely patterned static and reconfigurable particles that are challenging to synthesize.
In this paper, we detail visualized experimental protocols to create patterned particles, notably, (a) permanently bonded, hollow, polyhedra that self-assemble and self-seal due to the minimization of surface energy of liquefied hinges21-23 and (b) grippers that self-fold due to residual stress powered hinges24,25. The specific protocol described can be used to create particles with overall sizes ranging from the micrometer to the centimeter length scales. Further, arbitrary patterns can be defined on the surfaces of the particles of importance in colloidal science, electronics, optics and medicine. More generally, the concept of self-assembling mechanically rigid particles with self-sealing hinges is applicable, with some process modifications, to the creation of particles at even smaller, 100 nm length scales22, 26 and with a range of materials including metals21, semiconductors9 and polymers27. With respect to residual stress powered actuation of reconfigurable grasping devices, our specific protocol utilizes chromium hinges of relevance to devices with sizes ranging from 100 &mu;m to 2.5 mm. However, more generally, the concept of such tether-free residual stress powered actuation can be used with alternate high-stress materials such as heteroepitaxially deposited semiconductor films5,7 to possibly create even smaller nanoscale grasping devices.

We describe experimental details of the synthesis of patterned and reconfigurable particles from two dimensional (2D) precursors. This methodology can be used to create particles in a variety of shapes including polyhedra and grasping devices at length scales ranging from the micro to centimeter scale.

There are numerous techniques such as photolithography, electron-beam lithography and soft-lithography that can be used to precisely pattern two ...

Chemistry

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10- nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

Various procedures are outlined to prepare atomically defined templates for epitaxial growth of complex oxide thin films. Chemical treatments of single crystalline SrTiO3 (001) and DyScO3 (110) substrates were performed to obtain atomically smooth, single terminated surfaces. Ca2 Nb3 O10- nanosheets were used to create atomically defined templates on arbitrary substrates.

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain ...

Fabrication of Large-area Free-standing Ultrathin Polymer Films

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films. Typically, ultrathin films are prepared using either sacrificial layers, which may damage the film or affect its mechanical properties, or they are made on freshly cleaved mica, a substrate that is difficult to scale. Further, the size of ultrathin film is typically limited to a few square millimeters. In this method, we modify a surface with a polyelectrolyte that alters the strength of adhesion between polymer and deposition substrate. The polyelectrolyte can be shown to remain on the wafer using spectroscopy, and a treated wafer can be used to produce multiple films, indicating that at best minimal amounts of the polyelectrolyte are added to the film. The process has thus far been shown to be limited in scalability only by the size of the coating equipment, and is expected to be readily scalable to industrial processes. In this study, the protocol for making the solutions, preparing the deposition surface, and producing the films is described.

We describe a method for the fabrication of large-area (up to 13 cm diameter) and ultrathin (as thin as 8 nm) polymer films. Instead of using a sacrificial interlayer to delaminate the film from its substrate, we use a self-limiting surface treatment suitable for arbitrarily large areas.

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films.  Typically, ultrathin films are prepared ...

Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent thermal evaporation, and it absorbs visible light strongly. However, for a long time the record power conversion efficiency of SnS solar cells remained below 2%. Recently we demonstrated new certified record efficiencies of 4.36% using SnS deposited by atomic layer deposition, and 3.88% using thermal evaporation. Here the fabrication procedure for these record solar cells is described, and the statistical distribution of the fabrication process is reported. The standard deviation of efficiency measured on a single substrate is typically over 0.5%. All steps including substrate selection and cleaning, Mo sputtering for the rear contact (cathode), SnS deposition, annealing, surface passivation, Zn(O,S) buffer layer selection and deposition, transparent conductor (anode) deposition, and metallization are described. On each substrate we fabricate 11 individual devices, each with active area 0.25 cm2. Further, a system for high throughput measurements of current-voltage curves under simulated solar light, and external quantum efficiency measurement with variable light bias is described. With this system we are able to measure full data sets on all 11 devices in an automated manner and in minimal time. These results illustrate the value of studying large sample sets, rather than focusing narrowly on the highest performing devices. Large data sets help us to distinguish and remedy individual loss mechanisms affecting our devices.

Tin sulfide (SnS) is a candidate material for Earth-abundant, non-toxic solar cells. Here, we demonstrate the fabrication procedure of the SnS solar cells employing atomic layer deposition, which yields 4.36% certified power conversion efficiency, and thermal evaporation which yields 3.88%.

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent ...

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 ...

Preparation of Liquid-exfoliated Transition Metal Dichalcogenide Nanosheets with Controlled Size and Thickness: A State of the Art Protocol

We summarize recent advances in the production of liquid-exfoliated transition metal dichalcogenide (TMD) nanosheets with controlled size and thickness. Layered crystals of molybdenum disulphide (MoS2) and tungsten disulphide (WS2) are exfoliated in aqueous surfactant solution by sonication. This yields highly polydisperse mixtures containing nanosheets with broad size and thickness distributions. However, for most purposes, specific sizes (in terms of both lateral dimension and thickness) are required. For example, large and thin nanosheets are desired for (opto) electronic applications, while laterally small nanosheets are interesting for catalytic applications. Therefore, post-exfoliation size selection is an important step that we address here. We provide a detailed protocol on the efficient size selection in large quantities by liquid cascade centrifugation and the size and thickness quantification by statistical microscopic analysis (atomic force microscopy and transmission electron microscopy). The comparison of MoS2 and WS2 shows that both materials are size-selected in a similar way by the same procedure. Importantly, the dispersions of size-selected nanosheets show systematic changes in their optical extinction spectra with size due to edge and confinement effects. We show how these optical changes are related quantitatively to the nanosheets dimensions and describe how mean nanosheets length and layer number can be extracted reliably from the extinction spectra. The exfoliation and size selection protocol can be applied to a broad range of layered crystals as we have previously demonstrated for graphene, gallium sulphide (GaS) and black phosphorus.

A protocol for the liquid exfoliation of layered materials to nanosheets, their size selection and size measurement by microscopic and spectroscopic techniques is presented.

We summarize recent advances in the production of liquid-exfoliated transition metal dichalcogenide (TMD) nanosheets with controlled size and thickness. ...

Fabrication of Magnetic Nanostructures on Silicon Nitride Membranes for Magnetic Vortex Studies Using Transmission Microscopy Techniques

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared on transparent membranes which are very fragile and difficult to manipulate. We present processes for the fabrication of samples with magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for Lorentz transmission electron microscopy and magnetic transmission x-ray microscopy studies. The samples are prepared on silicon nitride membranes and the fabrication consists of a spin coating, UV and electron-beam lithography, the chemical development of the resist, and the evaporation of the magnetic material followed by a lift-off process forming the final magnetic structures. The samples for the Lorentz transmission electron microscopy consist of magnetic nanodiscs prepared in a single lithography step. The samples for the magnetic x-ray transmission microscopy are used for time-resolved magnetization dynamic experiments, and magnetic nanodiscs are placed on a waveguide which is used for the generation of repeatable magnetic field pulses by passing an electric current through the waveguide. The waveguide is created in an extra lithography step.

A protocol for the fabrication of magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for transmission electron microscopy (TEM) and magnetic transmission x-ray microscopy (MTXM) studies is presented.

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared ...

Exfoliation and Analysis of Large-area, Air-Sensitive Two-Dimensional Materials

We describe methods for producing and analyzing large, thin flakes of air-sensitive two-dimensional materials. Thin flakes of layered or van der Waals crystals are produced using mechanical exfoliation, in which layers are peeled off a bulk crystal using adhesive tape. This method produces high-quality flakes, but they are often small and can be hard to find, particularly for materials with relatively high cleavage energies such as black phosphorus. By heating the substrate and the tape, two-dimensional material adhesion to the substrate is promoted, and the flake yield can be increased by up to a factor of ten. After exfoliation, it is necessary to image or otherwise analyze these flakes but some two-dimensional materials are sensitive to oxygen or water and will degrade when exposed air. We have designed and tested a hermetic transfer cell to temporarily maintain the inert environment of a glovebox so that air-sensitive flakes can be imaged and analyzed with minimal degradation. The compact design of the transfer cell is such that optical analysis of sensitive materials can be performed outside of a glovebox without specialized equipment or modifications to existing equipment.

A method for exfoliating large thin flakes of air sensitive two-dimensional materials and safely transporting them for analysis outside of a glovebox is presented.

We describe methods for producing and analyzing large, thin flakes of air-sensitive two-dimensional materials. Thin flakes of layered or van der Waals ...

Fabrication of Three-Dimensional Graphene-Based Polyhedrons via Origami-Like Self-Folding

The assembly of two-dimensional (2D) graphene into three-dimensional (3D) polyhedral structures while preserving the graphene's excellent inherent properties has been of great interest for the development of novel device applications. Here, fabrication of 3D, microscale, hollow polyhedrons (cubes) consisting of a few layers of 2D graphene or graphene oxide sheets via an origami-like self-folding process is described. This method involves the use of polymer frames and hinges, and aluminum oxide/chromium protection layers that reduce tensile, spatial, and surface tension stresses on the graphene-based membranes when the 2D nets are transformed into 3D cubes. The process offers control of the size and shape of the structures as well as parallel production. In addition, this approach allows the creation of surface modifications by metal patterning on each face of the 3D cubes. Raman spectroscopy studies show the method allows the preservation of the intrinsic properties of the graphene-based membranes, demonstrating the robustness of our method.

Fabrication of Three-Dimensional Graphene-Based Polyhedrons via Origami-Like Self-Folding

Here, we present a protocol for fabrication of 3D graphene-based polyhedrons via origami-like self-folding.

The assembly of two-dimensional (2D) graphene into three-dimensional (3D) polyhedral structures while preserving the graphene's excellent inherent ...

Fabricating van der Waals Heterostructures with Precise Rotational Alignment

In this work we describe a technique for creating new crystals (van der Waals heterostructures) by stacking distinct ultrathin layered 2D materials. We demonstrate not only lateral control but, importantly, also control over the angular alignment of adjacent layers. The core of the technique is represented by a home-built transfer setup which allows the user to control the position of the individual crystals involved in the transfer. This is achieved with sub-micrometer (translational) and sub-degree (angular) precision. Prior to stacking them together, the isolated crystals are individually manipulated by custom-designed moving stages that are controlled by a programmed software interface. Moreover, since the entire transfer setup is computer controlled, the user can remotely create precise heterostructures without coming into direct contact with the transfer setup, labeling this technique as &#8220;hands-free&#8221;. In addition to presenting the transfer set-up, we also describe two techniques for preparing the crystals that are subsequently stacked.

In this work we describe a technique that is used to create new crystals (van der Waals heterostructures) by stacking ultrathin layered 2D materials with precise control over position and relative orientation.

In this work we describe a technique for creating new crystals (van der Waals heterostructures) by stacking distinct ultrathin layered 2D materials. We ...

Atmospheric Pressure Fabrication of Large-Sized Single-Layer Rectangular SnSe Flakes

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