Sheet Of Atoms Research Articles

Transport through a monolayer-tube junction: Sheet-to-tube spin current

We develop a method to calculate the electron flow between an arbitrary atomic monolayer sheet and an arbitrary tube by expressing the corresponding sheet-tube tunneling matrix elements with those between sheets. We use this method to calculate the spin current from a monolayer silicene sheet with sublattice-staggered current-induced spin polarization to a silicene tube. The calculated sheet-to-tube spin current exhibits an oscillation as a function of the tube circumferential length because the Fermi points in the tube cross the Fermi circle in the sheet. Furthermore, the spin current with spin in the out-of-plane direction, which is absent in the sheet-sheet junction (including twisted sheets) with C3 rotational symmetry, appears in an oscillating form in the tube-sheet junction due to the broken C3 rotational symmetry. This is an example of the symmetry manipulation which realizes switching a particular component of the spin current.

Graphene via Microwave Expansion of Graphite Followed by Cryo-Quenching and its Application in Electrostatic Droplet Switching.

Monoelemental atomic sheets (Xenes) and other 2D materials offer record electronic mobility, high thermal conductivity, excellent Young's moduli, optical transparency, and flexural capability, revolutionizing ultrasensitive devices and enhancing performance. The ideal synthesis of these quantum materials should be facile, fast, scalable, reproducible, and green. Microwave expansion followed by cryoquenching (MECQ) leverages thermal stress in graphite to produce high-purity graphene within minutes. MECQ synthesis of graphene is reported at 640 and 800 W for 10 min, followed by liquid nitrogen quenching for 5 and 90 min of sonication. Microscopic and spectroscopic analyses confirmed the chemical identity and phase purity of monolayers and few-layered graphene sheets (200-12 µm). Higher microwave power yields thinner layers with enhanced purity. Molecular dynamics simulations and DFT calculations support the exfoliation under these conditions. Electrostatic droplet switching is demonstrated using MECQ-synthesized graphene, observing electrorolling of a mercury droplet on a BN/graphene interface at voltages above 20 V. This technique can inspire the synthesis of other 2D materials with high purity and enable new applications.

Scalable Fabrication of Quasi-One-Dimensional van der Waals Ta2Pt3Se8 Nanowire Thin Films via Solution Processing for NO2 Gas Sensing over Large Areas.

Solution-based processing of van der Waals (vdW) one- (1D) and two-dimensional (2D) materials is an effective strategy to obtain high-quality molecular chains or atomic sheets in a large area with scalability. In this work, quasi-1D vdW Ta2Pt3Se8 was exfoliated via liquid phase exfoliation (LPE) to produce a stably dispersed Ta2Pt3Se8 nanowire solution. In order to screen the optimal exfoliation solvent, nine different solvents were employed with different total surface tensions and polar/dispersive (P/D) component (P/D) ratios. The LPE behavior of Ta2Pt3Se8 was elucidated by matching the P/D ratios between Ta2Pt3Se8 and the applied solvent, resulting in N-methyl-2-pyrrolidone (NMP) as an optimal solvent owing to the well-matched total surface tension and P/D ratio. Subsequently, Ta2Pt3Se8 nanowire thin films are manufactured via vacuum filtration using a Ta2Pt3Se8/NMP dispersion. Then, gas sensing devices are fabricated onto the Ta2Pt3Se8 nanowire thin films, and gas sensing property toward NO2 is evaluated at various thin-film thicknesses. A 50 nm thick Ta2Pt3Se8 thin-film device exhibited a percent response of 25.9% at room temperature and 32.4% at 100 °C, respectively. In addition, the device showed complete recovery within 14.1 min at room temperature and 3.5 min at 100 °C, respectively.

The Rise of Xene Hybrids.

Xenes, mono-elemental atomic sheets, exhibit Dirac/Dirac-like quantum behavior. When interfaced with other 2D materials such as boron nitride, transition metal dichalcogenides, and metal carbides/nitrides/carbonitrides, it enables them with unique physicochemical properties, including structural stability, desirable bandgap, efficient charge carrier injection, flexibility/breaking stress, thermal conductivity, chemical reactivity, catalytic efficiency, molecular adsorption, and wettability. For example, BN acts as an anti-oxidative shield, MoS2 injects electrons upon laser excitation, and MXene provides mechanical flexibility. Beyond precise compositional modulations, stacking sequences, and inter-layer coupling controlled by parameters, achieving scalability and reproducibility in hybridization is crucial for implementing these quantum materials in consumer applications. However, realizing the full potential of these hybrid materials faces challenges such as air gaps, uneven interfaces, and the formation of defects and functional groups. Advanced synthesis techniques, a deep understanding of quantum behaviors, precise control over interfacial interactions, and awareness of cross-correlations among these factors are essential. Xene-based hybrids show immense promise for groundbreaking applications in quantum computing, flexible electronics, energy storage, and catalysis. In this timely perspective, recent discoveries of novel Xenes and their hybrids are highlighted, emphasizing correlations among synthetic parameters, structure, properties, and applications. It is anticipated that these insights will revolutionize diverse industries and technologies.

Nickel Nanoplates Enclosed by (111) Facets as Durable Oxygen Evolution Catalysts in Anion Exchange Membrane Water Electrolyzers

AbstractThe long‐term stability of Ni‐based catalysts, employed in the anode of anion exchange membrane water electrolyzers (AEMWE), has been a persisting concern. In this work, through a simple and powerful electrochemical anodization process, vertically aligned β‐NiOOH atomic sheets (vertical‐β‐NiOOH) grown on Fe‐doped Ni nanoplates (FeNi nanoplates) as a solution are offered. This innovative electrocatalyst demonstrates sustained stability of constant current density for over 120 d during the oxygen evolution reaction.The zero‐gap AEMWE cell harnessing the anodized FeNi nanoplates achieves a remarkable current density of 2.26 A cm−2 at 1.80 V with an energetic efficiency of 85.1%. It is anticipated that the electrochemically produced highly active, stable Ni‐based nanostructures demonstrate the potential in pushing the boundaries of AEMWE technology.

Improved photocatalytic activity of graphene oxide modified Ag-TiO2 for degradation of piroxicam-20 and dehydrogenation of methanol under light irradiation

BackgroundGraphene oxide (GO), an atomic sheet structure made of sp2-bonded carbon atoms with superior optoelectronic, and catalytic properties, has attracted much interest. Incorporating a carbon-rich material, onto metal-loaded TiO2 is reported to increase the photocatalytic properties of resultant composites. MethodsThis research aimed at the deposition of different amounts (1–5 wt.%) of GO using the ultrasonication method on bare TiO2 and Ag (3 wt.%)-TiO2 (AT3) and studied their influence on piroxicam-20 degradation under visible light and methanol dehydrogenation under UV light. The prepared composites' structural, optical, and morphological properties were characterized using XRD, DRS, HR-TEM, FE-SEM, and XPS. Significant findingsHRTEM analysis confirmed the existence of GO layers and spherical-shaped Ag nanoparticles deposited over the TiO2 surface. GO(5 wt.%)@Ag(3 wt.%)-TiO2 (G5@AT3) displayed better photodegradation efficiency (78 %) (k = 0.0082 min−1) under 120 min, and GO(1 wt.%)@Ag(3 wt.%)-TiO2 (G1@AT3) composite produced higher amount (427 mmol) of H2 from photocatalytic dehydrogenation of CH3OH under 5 h relative to TiO2 (2 mmol), AT3 (166 mmol) and GO(5 wt.%)@TiO2 composite (GT5) (11 mmol). HRMS analysis was performed to identify the piroxicam-20 degradation intermediates. Thus, this research provides a proactive strategy highlighting the cooperative effect of Ag and GO loading to improve the photocatalytic efficiency of TiO2 photocatalyst using both UV–visible light irradiation.

ELECTRON TRANSPORT IN GRAPHENE BASED NANOTRANSISTOR AND USE OF NEGATIVE CAPACITANCE FOR STEEPER SUB-THRESHOLD SLOPE

Graphene has demonstrated tremendous promise in recent years as a material that, in the future, could replace silicon-based materials because of its exceptional electrical transfer characteristics. The diffusive MOSFETs suffer from short channel effects caused by their shorter channels, however graphene has numerous unusual features. The strongest material yet tested, Graphene exhibits a significant and nonlinear diamagnetism, has great mobility at room temperature, a low atomic thickness, a high current density, and is almost transparent. A single sheet of carbon atoms organized in a hexagonal lattice makes up graphene, an allotrope form of carbon. It is a semimetal with little short channel effects overall and little overlap between the valence and conduction bands. The Graphene nanoribbon has been incorporated into the ballistic nanotransistor as its channel and differentiate it form the diffusive one.In this review , I have presented the report on the survey of Nanotransistor . It has been divided into three sections : (1) Ballistic transport in Nanotransistor (2) Modelling of GNRFET (Graphene Nano-ribbon FET) using NEGF (Non-equilibrium Greens function) (3) Using ferroelectric capacitance into FET to reduce its sub-threshold regime below 60 mV/decade.The purpose of this review is to understand charge carrier transport phenomenon in the Nanotransistor. This includes the description about the ballistic nanotransister and differentiate it form the diffusive one. The NEGF allows us to characterizing its transfer characteristics in the real lattice space.Also the Id-Vd, sub-threshold regime , log(Id)-Vg , transmission coefficient and their application to drastically enhance the device performance for low energy digital electronics are being studied and modeled. Furthermore, the negative capacitance due to FE (ferroelectric layer) in FET will enhance the switching speed of FET and reduce the sub-threshold swing (SS) below 60 mV/decade which is impossible in case of traditional MOSFET. Thus, improving ION/IOFF ratio for low power digital devices.

Free-standing 2D gallium nitride for electronic, excitonic, spintronic, piezoelectric, thermoplastic, and 6G wireless communication applications

Two-dimensional gallium nitride (2D GaN) with a large direct bandgap of ~5.3 eV, a high melting temperature of ~2500 °C, and a large Young’s modulus ~20 GPa developed for miniaturized interactive electronic gadgets can function at high thermal and mechanical loading conditions. Having various electronic, optoelectronic, spintronic, energy storage devices and sensors in perspective and the robust nature of 2D GaN, it is highly imperative to explore new pathways for its synthesis. Moreover, free-standing sheets will be desirable for large-area applications. We report our discovery of the synthesis of free-standing 2D GaN atomic sheets employing sonochemical exfoliation and the modified Hummers method. Exfoliated 2D GaN atomic sheets exhibit hexagonal and striped phases with microscale lateral dimensions and excellent chemical phase purity, confirmed by Raman and X-ray photoelectron spectroscopy. 2D GaN is highly stable, as confirmed by TGA measurements. While photodiode, FET, spintronics, and SERS-based molecular sensing, IRS element in 6G wireless communication applications of 2D GaN have been demonstrated, its nanocomposite with PVDF exhibits an excellent thermoplastic and piezoelectric behavior.

Synthesis, Characteristics and Applications of Graphene Composites: A Survey

Graphene is the name for a monolayer sheet of carbon atoms that are bonded together in a repeating pattern of hexagons. This sheet is only one atom thick. Monolayers of graphene stacked on top of each other. In this article, we have compared the characterization results of graphene and graphene oxide along with synthesis via different methods. A sigma bond connects each atom in a graphene sheet to its three closest neighbours and each atom also contributes one electron to a conduction band that covers the entire graphene sheet. Graphene when oxidized is called graphene oxide (GO) and is mostly used in photoelectric, materialistic, catalyst and energy fields due to its thermal, electrical and mechanical characteristics. It is also used in the field of medical science, drug delivery and biomedical applications. Graphene have been improved due to import of 3D printing technology. In last few years, graphene has taken the attention of most material science researchers due to its various applications. Graphene based polymers and nanocomposites are widely used in sensors, optoelectronics, magneto transport, automotive, biosensors, electronics and aerospace fields.

D-Wave Superconducting Gap Symmetry as a Model for Nb1−xMoxB2 (x = 0.25; 1.0) and WB2 Diborides

Recently, Pei et al. (National Science Review2023, nwad034, 10.1093/nsr/nwad034) reported that ambient pressure β-MoB2 (space group: R3¯m) exhibits a phase transition to α-MoB2 (space group: P6/mmm) at pressure P~70 GPa, which is a high-temperature superconductor exhibiting Tc=32 K at P~110 GPa. Although α-MoB2 has the same crystalline structure as ambient-pressure MgB2 and the superconducting critical temperatures of α-MoB2 and MgB2 are very close, the first-principles calculations show that in α-MoB2, the states near the Fermi level, εF, are dominated by the d-electrons of Mo atoms, while in MgB2, the p-orbitals of boron atomic sheets dominantly contribute to the states near the εF. Recently, Hire et al. (Phys. Rev. B2022, 106, 174515) reported that the P6/mmm-phase can be stabilized at ambient pressure in Nb1−xMoxB2 solid solutions, and that these ternary alloys exhibit Tc~8 K. Additionally, Pei et al. (Sci. China-Phys. Mech. Astron. 2022, 65, 287412) showed that compressed WB2 exhibited Tc~15 K at P~121 GPa. Here, we aimed to reveal primary differences/similarities in superconducting state in MgB2 and in its recently discovered diboride counterparts, Nb1−xMoxB2 and highly-compressed WB2. By analyzing experimental data reported for P6/mmm-phases of Nb1−xMoxB2 (x = 0.25; 1.0) and highly compressed WB2, we showed that these three phases exhibit d-wave superconductivity. We deduced 2Δm(0)kBTc=4.1±0.2 for α-MoB2, 2Δm(0)kBTc=5.3±0.1 for Nb0.75Mo0.25B2, and 2Δm(0)kBTc=4.9±0.2 for WB2. We also found that Nb0.75Mo0.25B2 exhibited high strength of nonadiabaticity, which was quantified by the ratio of TθTF=3.5, whereas MgB2, α-MoB2, and WB2 exhibited TθTF~0.3, which is similar to the TθTF in pnictides, A15 alloys, Heusler alloys, Laves phase compounds, cuprates, and highly compressed hydrides.

Comparing the Shielding Features of Graphene and Impregnated Activated Carbon with Selected Traditional Shielding Materials For Gamma-Rays

Graphene and carbon-based materials are widely used in daily life applications. The richness of optical and electronic properties has made them rapidly rising materials on the horizon of material science and condensed matter physics. Having the sheets of atoms stacked in disorganized manner makes activated carbon different from other forms of graphitic structures. The research about the shielding properties of reduced graphene oxide (RGO) and activated carbon for gamma-rays are very rare and active domain of study. Since the use of radioactive sources in different fields (nuclear industry, shielding materials, radiation biophysics and space research application, etc.) has been increasing expeditiously, the photon interactions with matter have gained importance in the world of material science technology. In this work, we review the basics of the impregnated activated carbon (AC) and RGO, as well as the relationship between the structures and the gamma shielding properties in terms of both quality and efficiency. XCom software and EGSnrc simulation code were used to obtain the theoretical values of various shielding parameters which are significantly important to be able to understand the shielding properties of AC and RGO for gamma-rays. We report the mass attenuation coefficients (μm), the half value layer (HVL), the tenth value layer (TVL), and the mean free path (MFP) values and compare them with other commonly used shielding materials like lead, borosilicate, concrete, and vermiculite. The calculated data showed that AC is very appropriate and consistent to be one of the candidates for shielding materials of gamma-rays even though the graphene is seen as inconsistent for such purpose.

Inter-quintuple layer coupling and topological phase transitions in the chalcogenide topological insulators

Driving quantum phase transitions in the 3D topological insulators offers pathways to tuning the topological states and their properties. We use DFT-based calculations to systematically investigate topological phase transitions in Bi2Se3, Sb2Se3, Bi2Te3 and Sb2Te3 by varying the ratio of lattice constants. This ensures no net hydrostatic pressure under anisotropic stress and strain and allows a clear identification of the physics leading to the transition. As a function of , all of these materials exhibit structural and electronic stability of the quintuple layers (QLs), and quasi-linear behavior of both the inter-QL distance and the energy gap near the topological transition. Our results show that the transition is predominantly controlled by the inter-QL physics, namely by competing Coulomb and van der Waals interactions between the outer atomic sheets in neighboring QLs. We discuss the implications of our results for topological tuning by alloying.

Wavelength‐Dependent Photocurrent Generation Efficiency in the Carbon Nanowall Films

Herein, the efficiency of generation of unipolar photocurrent pulses under action of obliquely incident nanosecond laser pulses is studied in carbon nanowall (CNW) films on silicon substrate depending on the direction of the wave vector and polarization of the laser radiation. The films consist of flake‐like graphite crystallites of nanometer thickness. Each of the crystallites comprises stacked graphene atomic sheets oriented mostly perpendicular to the substrate surface with random orientation in other directions. The angular and polarization dependencies of the longitudinal and transverse photocurrents at wavelengths of 266, 354.7, 532, and 1064 nm are measured. The longitudinal and transverse photocurrents are odd functions of the incidence angle, and, for a given angle of incidence, they are even and odd functions of the polarization azimuth, respectively. It is noteworthy that with the decrease in exciting radiation wavelength, the conversion coefficients of laser pulse power into longitudinal and transverse photocurrents increase and decrease, respectively. At wavelength of 266 nm, the transverse photocurrent changes its polarity, and the longitudinal photocurrent generated by s‐polarized radiation exceeds the p‐polarized radiation photocurrent. The obtained results are explained by morphology peculiarities of the CNW films and the surface photogalvanic effect photocurrent generation.

High-refractive index and mechanically cleavable non-van der Waals InGaS3

The growing family of two-dimensional crystals has been recognized as a promising platform for investigation of rich low-dimension physics and production of a variety of devices. Of particular interest are recently reported atomic sheets of non-van der Waals materials, which reshape our understanding of chemical bonds and enable heterostructures with novel functionality. Here, we study the structural and optical properties of ultrathin non-van der Waals InGaS3 sheets produced by standard mechanical cleavage. Our ab initio calculations reveal weak out-of-plane covalent bonds, responsible for the layered structure of the material. The energy required for isolation of a single layer is as low as ~50 meVÅ–2, which is comparable with the conventional van der Waals material’s monolayer isolation energies of 20–60 meVÅ–2. A comprehensive study of the structural, vibrational, and optical properties of the material reveals its wide bandgap (2.73 eV), high refractive index (>2.5) and negligible losses in the visible and infrared spectral ranges. These properties make it a perfect candidate for visible-range all-dielectric nanophotonics.

Transition Metal-Doped Boron Nitride Atomic Sheets with an Engineered Bandgap and Magnetization

Controlled doping of flat atomic sheets of boron nitride (BN) can in principle break charge and spin symmetries. In contrast to graphene that oxidizes at >500 °C, due to its high melting point (ca. 2700 K) and the electrically insulating nature (Eg ∼ 5.5 eV), BN presents strong material candidature for flexible magnetic memory chips that are functional even under fire. Here, we report the transition metal (Fe and Cr) doping of BN by microwave and solvothermal methods. X-ray photoelectron spectroscopy reveals ∼17% doping by microwave (800 W) and <11% doping by the solvothermal method. Cr or Fe doping brings the bandgap down to ∼3.6 or ∼2.0 eV, respectively, for the doped BN samples. Cr doping by microwave results in intrinsic ferromagnetic ordering evident from the high Curie point (∼380 K) in contrast to orbital-mediated magnetic ordering in solvothermal Cr-doped BN systems. Fe doping raises magnetization values in particular. Spin-polarized DFT band structure calculations suggest vivid spin asymmetry caused by doping, supporting our experimental findings on doped BN samples.

Photoinduced Rippling of Two-Dimensional Hexagonal Nitride Monolayers.

Inducing structural changes and deformation using noninvasive methods, such as ultrafast laser technology, is an attractive route to multiple optomechanical and optoelectronic applications. Here, we show how photon excitation could accumulate in-plane stress and induce long-wavelength ripples in two-dimensional (2D) materials. Numerical results based on first-principles calculations and a continuum model predict that long-range nanoscale rippling could emerge under photon excitation in hexagonal nitride single atomic sheets. The photosoftened transverse acoustic mode dominates the out-of-plane distortion of the sheet, and the resultant rippling pattern strongly depends on the boundary condition. We reveal that the wavelength and height of the ripple scale as I-1/3 and I1/6, respectively, where I is the incident light energy flux. Our findings based on multiscale theory and simulations elucidate the interplay between carrier excitation, phonon dispersion, and long-range mechanical deformations, which could find potential usage in flexible electronics and electromechanical devices.

Investigation of Arsenic Transient Enhanced Diffusion From Emitter Process at 550 °C Si:As RP-CVD Epitaxy Using Disilane Precursor

Reduced Pressure Chemical Vapor Deposition (RP-CVD) Epitaxy bellow 600 °C is studied for 3D sequential integration [1] where cyclic deposition is needed. Another approach can be useful with Si epitaxy at temperature bellow 600 °C : the deposition of amorphous Si on dielectric during non-selective epitaxy combined with solid phase epitaxy regrowth (SPER) to extend the monocrystalline area. Indeed, using temperature above 600 °C during non-selective epitaxy, a polycrystalline Si film is formed on dielectric. This technique has been used in heterojunction bipolar transistor for the non-selective base deposition [2] and can also be used to ensure a fully monocrystalline emitter.Si:As process has been developed at 550 °C using disilane (Si2H6) as Si precursor and Arsine (AsH3) for As precursor. At this temperature, disilane is mandatory to ensure a sufficient growth rate. The disilane process will be compared to a process of reference, using silane (SiH4) precursor at 620 °C. The As dopant concentration targeted is between 1x20 at.cm-3 and 5x20 at.cm-3. Finally, the dopant diffusion is controlled on non-productive Si(100) wafer (NPW), without pattern, by SIMS for both processes before and after thermal budget (720 °C, 1 h + high temperature Spike anneal) to simulate the thermal budget undergone by the emitter.Thanks to the ASTAR system [3] from NanoMEGAS, the crystal orientation and phase maps of the emitter are extracted for both processes (Fig 1.a). ASTAR system is based on the Automated Crystal Orientation Mappings technique used on a Transmission Electron Microscope (ACOM-TEM). With silane precursor, a poly-emitter is generated whereas the emitter is fully monocrystalline with disilane. The amorphous deposition coupled with SPER ensure a fully monocrystalline emitter. SIMS analysis have been performed and show abnormal diffusion of As with disilane process. To understand the causes of the diffusion, both Si:As processes have been reproduced on NPW by full sheet epitaxy. The abnormal diffusion is still observed with the disilane process (Fig 1.b). Compared to diffusion length extracted from [4] (19nm) the diffusion of As is enhanced. Moreover, As enhanced diffusion occurs for low temperature thermal budget (Fig. 1.c).Historically, defects generated from implantation are known to enhance the diffusion length of the dopant. This phenomenon is called Transient Enhanced Diffusion (TED) and it has been studied and observed from dopant implantation [5]. The implantations generate a supersaturation of interstitials defects (such as auto-interstitial) which enhance the dopant diffusion for low temperature thermal budgets. This is a transient effect because the enhanced diffusion occurs in a short time [5]. In our case, several anneal at 720 °C were applied on the disilane Si:As layer from 1 h to 24 h (Fig. 1.d). Most of the diffusion occurs after the annealing at 720 °C, 1 h. These results highlight the transient effect of the As diffusion using disilane process. With the disilane process, TED of As occurs. Indeed, enhanced diffusion of Arsenic appears only for low temperature annealing and the effect is also transient. Compared to implantation which generates defects during the bombardment, low temperature epitaxy generates defects when the growth rate is too high. The molecules from the gas phase are adsorbed on the surface and break down on atoms (called adatom). The adatoms diffuse on the surface to find a suitable site. During low temperature epitaxy, when the growth rate is too high, the adatom don’t have enough time to diffuse on a suitable site and generate defects.Finally, dopant profile analysis will be completed by atomic force microscopy (AFM) and sheet resistance measurement. The AFM will provide an evolution of the surface topography with the annealing. The sheet resistance, coupling with SIMS, will help to extract the deactivation of dopant. The causes of the TED from disilane process at 550 °C will be discussed and experimental results will be provided.[1] L. Brunet et al., IEEE International Electron Devices Meeting (IEDM), 2018[2] Holger Rücker and Bernd Heinemann, Semicond. Sci. Technology, 2018[3] A. Valery, Doctoral dissertation. Université Grenoble Alpes, 2017[4] S. W. Jones, "Diffusion in silicon". IC Knowledge LLC, 2008[5] S. C. Jain, et al., Journal of applied physics, 2002 Figure 1

Microwave Synthesized 2D Gold and Its 2D-2D Hybrids.

Xenes, i.e., monoelemental two-dimensional atomic sheets, are promising for sensitive and ultrafast sensor applications owing to exceptional carrier mobility; however, most of them oxidize below 500 °C and therefore cannot be employed for high-temperature applications. 2D gold, an oxidation-resistant plasmonic Xene, is extremely promising. 2D gold was experimentally realized by both atomic layer deposition and chemical synthesis using sodium citrate. However, it is imperative to develop a new facile single-step method to synthesize 2D gold. Here, liquid-phase synthesis of 2D gold is demonstrated by microwave exposure to auric chloride dispersed in dimethylformamide. Microscopies (AFM and high-resolution TEM), spectroscopies (Raman, UV-vis, and X-ray photoelectron), and X-ray diffraction establish the formation of a hexagonal crystallographic phase for 2D gold. 2D-2D hybrids of 2D gold have also been synthesized and investigated for electronic/optoelectronic behaviors and SERS-based molecular sensing. DFT band structure calculation for 2D gold and its hybrids corroborates the experimental findings.

Enhanced Photoelectrochemical Performance in Engineered Interface 2D Metal Sulfide Heterostructures for Water Splitting

Photoelectrochemical water splitting (PEC) is a viable solution for addressing future environmental and energy concerns. However, due to the high cost of photoelectrodes and the limitations of sluggish kinetics, practical applications are limited. To achieve that goal, effective solutions are still needed to create low-cost photoelectrodes suited for PEC. Transistion metal sulfides (TMS) materials have a high potential for use as photoelectrodes due to their favorable and impressive properties1. The photoactivity of TMS is typically unlimited due to low reflection at the grain boundary. The individual atomic thin sheets with higher surface area compared to bulk materials allow for faster diffusion of photoinduced charge carriers primarily due to the less interface between their grains. Their lower interfacial contact resistance enables enhanced charge dynamics and, as a result, improved electrochemical reaction kinetics. When compared to other TMS, CdS has a direct bandgap and excellent photoactivity. However, its toxicity and photocorrosion make it unsuitable for long-term practical use. WS2 is well-known layered transition metal sulfide that has a 2D molybdenite structure. It is non-toxic in acidic/neutral solutions that are chemically stable. It has been demonstrated to be more stable against oxidation and photo corrosion than CdS, which is extensively employed in photocatalysis2. However, because of the recombination of photoinduced charge carriers, pure WS2 exhibits relatively poor photocatalytic efficiency and stability. As a result, combining WS2 based photoactive nanomaterials with other suitable materials has helped overcome this challenge. Transistion metal sulfides with acceptable band structures for heterostructure construction with WS2 may enable breakthroughs in photocatalytic and photo-electrochemical processes.The primary focus of this work is to construct heterostructures by combining CdS and WS2 and to investigate their role as photoanodes of semiconductor materials in PEC water splitting. In this work, we have synthesised heterostructures using a facile solution-reaction method and Successive Ionic Layer Adsorption Reaction deposition (SILAR) technique which is intrinsically cost effective and scalable3. The heterostructure is characterised by XRD, SEM and TEM. We also studied the performance enhancement of this heterostructure using Linear sweep voltammetry and Electrochemical impedance spectroscopy. Pristine WS2 and CdS showed photocurrent densities of 3 μA cm-2 and 20 μA cm-2. However, heterostructures formation led to much improved photocurrents. Photocurrent densities of 151 μA cm-2 were observed for WS2/CdS heterostructures respectively at 1.23 V vs RHE. The enhanced improvement in photoelectrochemical performance in the case of the heterostructures could be due to the following factors: (a) the intimate interaction of this unique heterostructure improves adhesion and lowers the photoinduced charge transfer barrier; (b) increased light harvesting capability; and (c) improved charge dynamics of photoinduced charge carriers due to proper band alignment. The current study paves the way for further research into the creation of metal sulfide heterostructures that generate analogous photoelectrode materials.Keywords: Photoelectrochemical water splitting, metal sulfides, photoelectrodes.

Hierarchical Self-Assembly Pathways of Peptoid Helices and Sheets.

Peptoids (N-substituted glycines) are a class of tailorable synthetic peptidomic polymers. Amphiphilic diblock peptoids have been engineered to assemble 2D crystalline lattices with applications in catalysis and molecular separations. Assembly is induced in an organic solvent/water mixture by evaporating the organic phase, but the assembly pathways remain uncharacterized. We conduct all-atom molecular dynamics simulations of Nbrpe6Nc6 as a prototypical amphiphilic diblock peptoid comprising an NH2-capped block of six hydrophobic N-((4-bromophenyl)ethyl)glycine residues conjugated to a polar NH3(CH2)5CO tail. We identify a thermodynamically controlled assembly mechanism by which monomers assemble into disordered aggregates that self-order into 1D chiral helical rods then 2D achiral crystalline sheets. We support our computational predictions with experimental observations of 1D rods using small-angle X-ray scattering, circular dichroism, and atomic force microscopy and 2D crystalline sheets using X-ray diffraction and atomic force microscopy. This work establishes a new understanding of hierarchical peptoid assembly and principles for the design of peptoid-based nanomaterials.