This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM release LLNL-JRNL-667016.

1. Resorcinol-formaldehyde (RF) Derived Graphene Aerogels
<ol>
	<li>Na2CO3 catalyzed carbon aerogel (11% solids, cRF)
	<ol>
		<li>In a 40 ml scintillation vial, add deionized water (7.1 ml) to resorcinol (0.625 g, 5.68 mmol) and mix on a vortex for 1 min. Crush large resorcinol pieces to powder using a mortar and pestle prior to water addition. Note that they may not completely dissolve until the next step.</li>
		<li>Add 37% formaldehyde solution (0.900 g, 11.4 mmol) to the resorcinol slurry and vortex for 1 min.</li>
		<li>Add sodium carbonate (0.003 g, 0.028 mmol) to the reaction mixture and vortex for 1 min.</li>
		<li>Transfer the reaction mixture to glass molds that can be sealed air tight (e.g., vial or glass slides that are separated by a silicone gasket) which define the shape of the resulting solid part.</li>
		<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
		<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically we perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.</li>
	</ol>
	</li>
	<li>Acetic acid catalyzed carbon aerogel (AARF)17
	<ol>
		<li>In a 40 ml scintillation vial, add deionized water (15 ml) to resorcinol (12.3 g, 0.112 mol) and mix on a vortex for 1 min. Crush large resorcinol pieces to powder using a mortar and pestle prior to water addition. Note that they may not completely dissolve until the next step.</li>
		<li>Add 37% formaldehyde solution (17.9 g, 0.224 mol) to the resorcinol slurry and vortex for 1 min.</li>
		<li>Add glacial acetic acid (0.44 g, 0.007 mol) to the reaction mixture and vortex for 1 min.</li>
		<li>Transfer the reaction mixture to glass molds that can be sealed air tight (e.g., vial or glass slides that are separated by a silicone gasket), which define the shape of the resulting solid part.</li>
		<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
		<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically we perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.</li>
	</ol>
	</li>
	<li>Carbon Additives to the RF precursor solution (CNT, GO)
	<ol>
		<li>Carbon nanotube/RF composite11
		<ol>
			<li>Suspend 1 wt% single-walled carbon nano-tubes in deionized water and thoroughly disperse using an ultrasonic bath (sonic power 90 W, frequency 40 kHz).</li>
			<li>Add resorcinol (1.235 g, 11.2 mmol), formaldehyde (1.791 g, 22.1 mmol), and sodium carbonate catalyst (5.95 mg, 0.056 mmol) to 1.5 g of the CNT dispersion.</li>
			<li>Transfer the reaction mixture to glass molds that can be sealed air tight (e.g., vial or glass slides that are separated by a silicone gasket), which define the shape of the resulting solid part.</li>
			<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
			<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.&#160;</li>
		</ol>
		</li>
		<li>Graphene oxide/RF composite12
		<ol>
			<li>Suspend 1 wt% graphene oxide (GO, 300-800 nm diameter) in deionized water and thoroughly disperse using an ultrasonic bath (sonic power 90 W, frequency 40 kHz).</li>
			<li>Add resorcinol (1.235 g, 11.2 mmol), formaldehyde (1.791 g, 22.1 mmol, 37% solution) and sodium carbonate catalyst (5.95 mg, 0.056 mmol) to 1.5 g of the GO dispersion.</li>
			<li>Transfer the reaction mixture to glass molds that can be sealed air tight (e.g., vial or glass slides that are separated by a silicone gasket) which define the shape of the resulting solid part.</li>
			<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
			<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Drying
	<ol>
		<li>Supercritical CO2
		<ol>
			<li>Prepare washed samples for drying with supercritical CO2 by exchanging the H2O solvent with acetone. Remove sample from water bath and place into bath containing clean acetone. Replace with fresh acetone two more times at 12 hr intervals.</li>
			<li>Load acetone-exchanged samples into a supercritical drying apparatus, filled with acetone and with circulating coolant at 12-15 &#176;C.</li>
			<li>Seal supercritical dryer and exchange with liquid CO2 until no acetone remains (4-24 hr depending on sample size, density, pore morphology, etc.).</li>
			<li>Shut off CO2 supply and raise temperature of circulating coolant to 55 &#176;C, while maintaining pressure in the supercritical dryer between 1,200-1,600 psi (80-110 bar). Hold at 55 &#176;C for 1 hr.</li>
			<li>Slowly vent CO2 (2-12 hr) while maintaining temperature of circulating coolant at 55 &#176;C. Remove samples.&#160;</li>
		</ol>
		</li>
		<li>Ambient drying (Xerogel)
		<ol>
			<li>Prepare washed samples for drying under ambient conditions by exchanging the H2O solvent with acetone. Remove sample from water bath and place into bath containing clean acetone. Replace with fresh acetone two more times at 12 hr intervals.</li>
			<li>Place acetone-exchanged samples on a clean surface (e.g., Teflon block). To slow the rate of solvent evaporation to prevent cracking and uneven shrinking, cover the sample with an inverted beaker of sufficient volume to provide plenty of headspace.</li>
			<li>Allow solvent to evaporate for (24-72 hr).&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Carbonization
	<ol>
		<li>Perform carbonization of the dried foams at 1,050 &#176;C under N2 atmosphere. Ramp from RT at a rate of 5 &#176;C/min, and hold at 1,050 &#176;C for 3 hr. Note that thin samples may need to be placed between two sheets of graphite paper (or other temperature stable, non-reactive material) with weight on top to prevent curling and &#8220;potato chipping.&#8221;</li>
	</ol>
	</li>
	<li>Activation
	<ol>
		<li>Activate an AARF carbon foam part (2 cm &#215; 3 cm &#215; 4 mm, 1.2 g) to generate 3D nanographene (3D-NG) under flowing CO2 (10 sccm) at 950 &#176;C for 5 hr.7</li>
	</ol>
	</li>
</ol>
2. Graphene Oxide Derived Graphene Macro Assemblies
<ol>
	<li>NH4OH catalyzed GO assembly
	<ol>
		<li>In a 40 ml scintillation vial, add deionized water (20 ml) to 400 mg single layer graphene oxide (GO, 300-800 nm diameter). Thoroughly disperse using an ultrasonic bath (sonic power 90 W, frequency 40 kHz) O/N.</li>
		<li>Add concentrated NH4OH solution (0.211 ml per g GO suspension).</li>
		<li>Transfer into glass molds that can be sealed airtight (e.g., vial or glass slides that are separated by a silicone gasket which defines the shape of the resulting solid part).</li>
		<li>Place the sealed molds into an 80 &#176;C oven and cure for 72 hr.</li>
		<li>After curing, remove the solid monoliths from the glass mold and wash with water to remove residual unreacted starting materials and catalyst. Typically perform 3 x 12 hr washes with fresh DI H2O. The material is now ready for drying.&#160;</li>
	</ol>
	</li>
	<li>Drying
	<ol>
		<li>Supercritical CO2
		<ol>
			<li>Prepare washed samples for drying with supercritical CO2 by exchanging the H2O solvent with acetone. Remove sample from water bath and place into bath containing clean acetone. Replace with fresh acetone two more times at 12 hr intervals.</li>
			<li>Load acetone-exchanged samples into a supercritical drying apparatus, filled with acetone and with circulating coolant at 12-15 &#176;C.</li>
			<li>Seal supercritical dryer and exchange with liquid CO2 until no acetone remains (4-24 hr depending on sample size, density, pore morphology, etc.). Complete exchange is indicated by cessation of acetone drips at the exhaust valve of the supercritical dryer.</li>
			<li>Shut off CO2 supply and raise temperature of circulating coolant to 55 &#176;C, while maintaining pressure in the supercritical dryer between 1,200-1,600 psi (80-110 bar). Hold at 55 &#176;C for 1 hr.</li>
			<li>Slowly vent CO2 (2-12 hr) while maintaining temperature of circulating coolant at 55 &#176;C. Remove samples.&#160;</li>
		</ol>
		</li>
		<li>Ambient drying (xerogel) 
		Note that thin samples may need to be placed between two sheets of Teflon (or other non-stick material) with weight on top to prevent curling and &#8220;potato chipping.&#8221;
		<ol>
			<li>Prepare washed samples for drying under ambient conditions by exchanging the H2O solvent with acetone. Remove sample from water bath and place into bath containing clean acetone. Replace with fresh acetone two more times at 12 hr intervals.</li>
			<li>Place acetone-exchanged samples on a clean surface (e.g., Teflon block). To slow the rate of solvent evaporation to prevent cracking and uneven shrinking, cover the sample with an inverted beaker of sufficient volume to provide plenty of headspace.</li>
			<li>Allow solvent to evaporate for (24-72 hr).&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Carbonization
	<ol>
		<li>Perform carbonization of the dried foams at 1,050 &#176;C under N2 atmosphere. Ramp from RT at a rate of 5 &#176;C/min, and hold at 1,050 &#176;C for 3 hr. Note that thin samples may need to be placed between two sheets of graphite paper (or other temperature stable, non-reactive material) with weight on top to prevent curling and &#8220;potato chipping.&#8221;</li>
		<li>Thermal anneal for highly crystalline GMA. Perform additional thermal annealing of carbonized foams at temperatures up to 2,500 &#176;C under He atmosphere. Ramp from RT at a rate of 100 &#176;C/min, and hold at elevated temperature for 1 hr.&#160;</li>
	</ol>
	</li>
	<li>Post-carbonization functionalization
	<ol>
		<li>Non-covalent anthraquinone functionalization (AQ-GMA)
		<ol>
			<li>Prepare a 3 mM solution of anthraquinone (AQ) in dry EtOH. Heat in a sealed vial at 75 &#176;C to ensure complete dissolution.</li>
			<li>Add hot AQ solution to GMA sample (~2 ml/mg of sample). Soak in a sealed vial for 2 hr at 75 &#176;C.</li>
			<li>Remove excess AQ solution from vial and allow sample to dry at 75 &#176;C O/N&#160;(vial cap off).&#160;</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

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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=Battery/supercapacitor+hybrid+via+non-covalent+functionalization+of+graphene+macro-assemblies.">Battery/supercapacitor hybrid via non-covalent functionalization of graphene macro-assemblies.</a> J. Mater. Chem. A. 2, 17764-17770 (2014).</li><li>Worsley, M. A., Charnvanichborikarn, 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=Toward+Macroscale,+Isotropic+Carbons+with+Graphene-Sheet-Like+Electrical+and+Mechanical+Properties.">Toward Macroscale, Isotropic Carbons with Graphene-Sheet-Like Electrical and Mechanical Properties.</a> Adv. Funct. Mater. 24 (27), 4259-4264 (2014).</li><li>Baumann, T. F., Worsley, M. A., Han, T. Y. -. J., Satcher, J. 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R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane-less+hydrogen+bromine+flow+battery.">Membrane-less hydrogen bromine flow battery.</a> Nat. Comms. 4, 1-6 (2013).</li><li>Zhu, C., Han, T. Y., Duoss, E. B., Golobic, A. M., Kuntz, J. D., Spadaccini, C. M., Worsley, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+compressible+3D+periodic+graphene+aerogel+microlattices.">Highly compressible 3D periodic graphene aerogel microlattices.</a> Nat Comms. 6, (2015).</li><li>Worsley, M. A., Shin, S. J., Merrill, M. D., Lenhardt, J., Nelson, A. J., Woo, L. Y., Gash, A. E., Baumann, T. F., Orme, C. 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The authors have nothing to disclose.

It is important to note that the procedures outlined here are only representative. Many adjustments are possible to tune materials for a specific application. For example, varying the starting material concentrations, while keeping resorcinol/formaldehyde (RF) ratio constant, can have an impact on the final material density. Catalyst loading can alter pore morphology, as a higher loading in the RF procedure leads to smaller primary particles and vice-versa. Activation time can play a role as well; at shorter activation t...

Since the isolation of graphene in 2004,1 interest in harnessing its unique properties has led to intense effort directed toward assembling graphene into three-dimensional, monolithic structures that retain the properties of individual graphene sheets.2-5 These efforts have been hampered by the fact that graphene itself is expensive and time consuming to produce and tends to aggregate in solution, which limits the scalability of materials based on graphene building blocks. Additionally, graphene assemblies are typically comprised of physical cross-linking interactions (e.g., van der Walls forces) between the individual graphene sheets, which are much less conductive and mechanically robust than chemical bond cross-links. Lawrence Livermore National Laboratory has been involved in the development of novel porous, low-density carbon materials since the 1980s.6 Several strategies have been identified to fabricate mass-producible graphene-based monolithic bulk materials from both low-cost polymer-derived carbon foams, which are called graphene aerogels (GAs),7 as well as by direct cross-linking of graphene oxide (GO) sheets, which are called graphene macro-assemblies (GMAs).8,9 These ultrahigh surface area bulk materials have high electrical and thermal conductivities, exceptional mechanical strength and elasticity, and tunable pore morphologies. GAs and GMAs have found utility in numerous applications including electrode materials in supercapacitors and rechargeable batteries, advanced catalyst supports, adsorbents, thermal insulation, sensors, and desalinization.10
The synthesis of graphene aerogels begins with sol-gel polymerization of an aqueous solution of resorcinol and formaldehyde to generate highly cross-linked organic gels. These gels are washed with water and acetone, then dried using supercritical CO2 and pyrolyzed in an inert atmosphere to give carbon aerogels with relatively low surface area and pore volume. Carbon aerogels are activated by controlled removal of carbon atoms under mild oxidizing condition (e.g., CO2) to form a cross-linked material composed of both amorphous carbon and graphite nanoplatelets, with higher surface area and open pore morphology.7 A unique advantage of the sol-gel synthesis is that GAs can be fabricated in a variety of forms, including monoliths and thin films, depending on the needs of the application. Carbon nanotubes11 and/or graphene sheets12 can be integrated into GAs by including these additives in the sol-gel precursor solution. This generates composite structures in which the additive becomes a part of the primary carbon network structure. Additionally, the GA framework can be functionalized after carbonization/activation either through modification of the aerogel surface or through the deposition of materials, for example catalyst nanoparticles, onto the framework structure.13
Graphene macro-assemblies (GMAs) are prepared by directly cross-linking suspended graphene oxide (GO) sheets, taking advantage of their inherent chemical functionality.9 GO sheets contain a variety of functional groups, including epoxide and hydroxide moieties, that can serve as chemical cross-linking sites. As in the GA preparation, assembled GMAs are supercritically dried to preserve the porous network, then pyrolized to reduce the chemical cross-links into conductive carbon bridges that provide structural support for the assembly. Due to the covalent carbon bridges between graphene sheets, GMAs have electrical conductivities and mechanical stiffness that are orders of magnitude higher than graphene assemblies formed with physical cross-linking. Additionally, GMAs have surface areas approaching the theoretical value of a single graphene sheet. Post-synthetic thermal treatment at elevated temperatures (&#62;1,050 &#176;C) can significantly improve the crystallinity of GMAs, leading to even higher conductivities and Young&#8217;s moduli as well as better thermal oxidation resistance.14 Post-synthetic chemical treatment of GMAs with redox-active organic molecules such as anthraquinone can enhance charge storage capacity in supercapacitor applications.15
The tunable material properties of GAs and GMAs are, in part, a result of carefully varying synthetic conditions such as reagent and catalyst concentrations, cure time and temperature, drying conditions, and carbonization/activation processes.16 This detailed video protocol aims to resolve ambiguities in the published methods, and to guide researchers attempting to reproduce the materials and conditions.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Single Layer Graphene Oxide</td>
			<td>Cheap Tubes</td>
			<td>n/a</td>
			<td>300-800nm XY dimensions</td>
		</tr>
		<tr>
			<td>single wall carbon nano tubes (SWCNTs)</td>
			<td>Carbon Solutions</td>
			<td>P2-SWNT</td>
			<td></td>
		</tr>
		<tr>
			<td>resorcinol</td>
			<td>aldrich</td>
			<td>398047-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>37% formaldehyde solution in water</td>
			<td>aldrich</td>
			<td>252549</td>
			<td></td>
		</tr>
		<tr>
			<td>acetic acid</td>
			<td>aldrich</td>
			<td>320099</td>
			<td></td>
		</tr>
		<tr>
			<td>ammonium hydroxide solution 28-30% NH3 basis</td>
			<td>aldrich</td>
			<td>320145</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium carbonate</td>
			<td>aldrich</td>
			<td>791768</td>
			<td></td>
		</tr>
		<tr>
			<td>anthraquinone</td>
			<td>aldrich</td>
			<td>a90004</td>
			<td></td>
		</tr>
		<tr>
			<td>Polaron supercritical dryer</td>
			<td>Electron Microscopy Sciences</td>
			<td>EMS 3100</td>
			<td>this is a representative model, any critical point dryer compatible with acetone should work</td>
		</tr>
	</tbody>
</table>

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.

The evolution of material composition and morphology during fabrication can be tracked in various ways including X-ray diffraction, Raman and NMR spectroscopy, electron microscopy, and porosimetry. For example, in the synthesis, pyrolysis, and CO2 activation of GAs, the conversion was followed by X-ray diffraction (XRD) (Figure 1E). The absence of the stacking-related (002) diffraction peak in the XRD pattern after activation (blue trace) indicates the transition from a structure containing gr...

Watch this Scientific Journal Video about Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies at JoVE.com

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

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. ...

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14.0K Views.  Lawrence Livermore National Laboratory. 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.

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

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

We discussed the synthesis of individual graphitic nanocups using a series of techniques including chemical vapor deposition, acid oxidation and probe-tip sonication. By citrate reduction of HAuCl4, the graphitic nanocups were effectively corked with gold nanoparticles due to the chemically reactive edges of the cups.

Nitrogen-doped carbon  nanotubes consist of many cup-shaped graphitic compartments termed as  nitrogen-doped carbon nanotube cups (NCNCs).  These ...

Development of a 3D Graphene Electrode Dielectrophoretic Device

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The protocol details the procedures to construct a versatile, reusable, multiple layer, laminated dielectrophoresis chamber. Specifically, six layers of 50 &#181;m x&#160;0.7 cm x&#160;2 cm graphene paper and five layers of double sided tape were alternately stacked together, then clamped to a glass slide. Then a 700 &#956;m diameter micro-well was drilled through the laminated structure using a computer-controlled micro drilling machine. Insulating properties of the tape layer between adjacent graphene layers were assured by resistance tests. Silver conductive epoxy connected alternate layers of graphene paper and formed stable connections between the graphene paper and external copper wire electrodes. The finished device was then clamped and sealed to a glass slide. The electric field gradient was modeled within the multi-layer device. Dielectrophoretic behaviors of 6 &#956;m polystyrene beads were demonstrated in the 1 mm deep micro-well, with medium conductivities ranging from 0.0001 S/m to 1.3 S/m, and applied signal frequencies from 100 Hz to 10 MHz. Negative dielectrophoretic responses were observed in three dimensions over most of the conductivity-frequency space and cross-over frequency values are consistent with previously reported literature values. The device did not prevent AC electroosmosis and electrothermal flows, which occurred in the low and high frequency regions, respectively. The graphene paper utilized in this device is versatile and could subsequently function as a biosensor after dielectrophoretic characterizations are complete.

A microdevice with high throughput potential is used to demonstrate three-dimensional (3D) dielectrophoresis (DEP) with novel materials. Graphene nanoplatelet paper and double sided tape were alternately stacked; a 700 &#956;m micro-well was drilled transverse to the layers. DEP behavior of polystyrene beads was demonstrated in the micro-well.

The design and fabrication of a novel 3D electrode microdevice using 50 &#181;m thick graphene paper and 100 &#181;m double sided tape is described. The ...

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene&#8217;s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene&#39;s electronic structure in the presence of a charged impurity.&#160;The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene&#8217;s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

This paper details the fabrication process of a gate-tunable graphene device, decorated with Coulomb impurities for scanning tunneling microscopy studies. Mapping the spatially dependent electronic structure of graphene in the presence of charged impurities unveils the unique behavior of its relativistic charge carriers in response to a local Coulomb potential.

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees ...

Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using visible light irradiation with plasmonic nanoparticles. The plasmonic nanoparticle is used to improve the reduction efficiency of GO. It only takes 30 min&#160;at RT by illuminating the solutions with Xe-lamp, the r-GO solutions can be obtained by completely removing gold nanoparticles through simple centrifugation step. The spherical gold nanoparticles (AuNPs) as compared to the other nanostructures is the most suitable plasmonic nanostructure for r-GO preparation. The reduced graphene oxide prepared using visible light and AuNPs was equally qualitative as chemically reduced graphene oxide, which was supported by various analytical techniques such as UV-Vis spectroscopy, Raman spectroscopy, powder XRD and XPS. The reduced graphene oxide prepared with visible light shows excellent quenching properties over the fluorescent molecules modified on ssDNA and excellent fluorescence recovery for target DNA detection. The r-GO prepared by recycled AuNPs is found to be of same quality with that of chemically reduced r-GO. The use of visible light with plasmonic nanoparticle demonstrates the good alternative method for r-GO synthesis.

A simple protocol for the preparation of reduced graphene oxide using visible light and plasmonic nanoparticle is described.

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using ...

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (&#181;PAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

The study demonstrates the growth of iridium oxide-reduced graphene oxide (IrO2-RGO) nanohybrid thin films on irregular and rough screen-printed carbon substrate through a green electrochemical synthesis, and their implementation as a pH sensor with a patterned paper-fluidic platform.

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use ...

Preparation of ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Piezoelectrical Nanogenerator by Using Preheating Hydrothermal

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we describe a one-step fabrication technique to synthesis freestanding ZnO nanorod/graphene/ZnO nanorod double heterostructure. The preparation of the double heterostructure is performed by using thermal chemical vapor deposition (CVD) and preheating hydrothermal technique. In addition, the morphological properties were characterized by using the scanning electron microscopy (SEM). The utility of freestanding double heterostructure is demonstrated by fabricating the piezoelectric nanogenerator. The electrical output is improved up to 200% compared to that of a single heterostructure owing to the coupling effect of the piezoelectricity between the arrays of ZnO nanorods on the top and bottom of graphene. This unique double heterostructure have a tremendous potential for applications of electrical and optoelectrical devices where the high number density and specific surface area of nanorod are needed, such as pressure sensor, immuno-biosensor and dye-sensitized solar cells.

One-step fabrication method for obtaining freestanding epitaxial double heterostructure is presented. This approach could achieve ZnO coverage with a higher number density than that of the epitaxial single heterostructure, leading to a piezoelectric nanogenerator with an increased output electrical performance.

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we ...

Strain Sensing Based on Multiscale Composite Materials Reinforced with Graphene Nanoplatelets

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are proposed to create the electrical network in this work: (a) the incorporation of the nanoplatelets into the epoxy matrix and (b) the coating of the glass fabric with a sizing filled with the same nanoplatelets. Both types of multiscale composite materials, with an in-plane electrical conductivity of ~10-3 S/m, showed an exponential growth of the electrical resistance as the strain increases due to distancing between adjacent functionalized graphene nanoplatelets and contact loss between overlying ones. The sensitivity of the materials analyzed during this research, using the described procedures, has been shown to be higher than commercially available strain gauges. The proposed procedures for self-sensing of the structural composite material would facilitate the structural health monitoring of components in difficult to access emplacements such as offshore wind power farms. Although the sensitivity of the multiscale composite materials was considerably higher than the sensitivity of metallic foils used as strain gauges, the value reached with NH2 functionalized graphene nanoplatelets coated fabrics was nearly an order of magnitude superior. This result elucidated their potential to be used as smart fabrics to monitor human movements such as bending of fingers or knees. By using the proposed method, the smart fabric could immediately detect the bending and recover instantly. This fact permits precise monitoring of the time of bending as well as the degree of bending.

The integration of conductive nanoparticles, such as graphene nanoplatelets, into glass fiber composite materials creates an intrinsic electrical network susceptible to strain. Here, different methods to obtain strain sensors based on the addition of graphene nanoplatelets into the epoxy matrix or as a coating on glass fabrics are proposed.

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are ...

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.

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 ...

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

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

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

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

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.