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The rapid development in information technologies necessitates rapid advancements of their supporting hardware. In particular, new computing paradigms are needed to overcome the bottleneck of traditional von Neumann architecture. Bottom‐up innovation, especially at the materials and devices level, has the potential to disrupt existing technologies through their emergent phenomena. As a new type of conceptual device, 2D ferroelectric field‐effect transistor (FeFET) is highly sought after due to its potential integration with modern semiconductor processes. Its low power consumption, area efficiency, and ultra‐fast operation provide an extra edge over traditional technologies. This review highlights recent developments in 2D FeFET, covering their device construction, working mechanisms, 2D ferroelectric polarization mechanism, multi‐functional applications and prospects. In particular, the combination of 2D semiconductor and ferroelectric dielectric materials for multi‐functionality applications is discussed. This includes non‐volatile memories (NVM), neural network computing, non‐volatile logic operation, and photodetectors. As a novel device platform, 2D semiconductor and ferroelectric interfaces are bestowed with a plethora of emergent physical mechanisms and applications. [ABSTRACT FROM AUTHOR]

Piezo‐assisted photocatalysis (namely, piezo‐photocatalysis), which utilizes mechanical energy to modulate spatial and energy distribution of photogenerated charge carriers, presents a promising strategy for molecule activation and reactive oxygen species (ROS) generation toward applications such as environmental remediation. However, similarly to photocatalysis, piezo‐photocatalysis also suffers from inferior charge separation and utilization efficiency. Herein, a Z‐scheme heterojunction composed of single Ag atoms‐anchored polymeric carbon nitride (Ag‐PCN) and SnO2−x is developed for efficient charge carrier transfer/separation both within the catalyst and between the catalyst and surface oxygen molecules (O2). As revealed by charge dynamics analysis and theoretical simulations, the synergy between the single Ag atoms and the Z‐scheme heterojunction initiates a cascade electron transfer from SnO2−x to Ag‐PCN and then to O2 adsorbed on Ag. With ultrasound irradiation, the polarization field generated within the piezoelectric hybrid further accelerates charge transfer and regulates the O2 activation pathway. As a result, the Ag‐PCN/SnO2−x catalyst efficiently activates O2 into ·O2−, ·OH, and H2O2 under co‐excitation of visible light and ultrasound, which are consequently utilized to trigger aerobic degradation of refractory antibiotic pollutants. This work provides a promising strategy to maneuver charge transfer dynamics for efficient piezo‐photocatalysis by integrating single‐atom catalysts (SACs) with Z‐scheme heterojunction. [ABSTRACT FROM AUTHOR]

Vapor-phase growth of large-area two-dimensional (2D) MoS2 nanosheets via reactions of sulfur with MoO3 precursors vaporized and transferred from powder sources onto a target substrate has been rapidly progressing. Recent studies revealed that the growth yield of high quality singlelayer (SL) MoS2 is essentially controlled by quite a few parameters including the temperature, the pressure, the amount/weight of loaded source precursors, and the cleanup of old precursors. Here, we report a dispersive growth method where a shadow mask is encapsulated on the substrate to 'indirectly' supply the source precursors onto the laterally advancing growth front at elevated temperatures. With this method, we have grown large-area (up to millimeters) SL-MoS2 nanosheets with a collective in-plane orientation on c-plane sapphire substrates. Regular ripples (~1 nm in height and ~50 nm in period) have been induced by laser scanning into the SL-MoS2 nanosheets. The MoS2 ripples easily initiate at the grain boundaries and extend along the atomic steps of the substrate. Such laser-induced ripple structures can be fundamental materials for studying their effects, which have been predicted to be significant but hitherto not evidenced, on the electronic, mechanical, and transport properties of SL-MoS2. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have received significant attention recently due to their unique properties such as a transition from indirect to direct band gap when thinned down to a monolayer and also valley-dependent photoluminescence. In addition, being a semiconductor with considerable mobility, it has been touted as a candidate in next generation electronics. However, a major hurdle to its implementation is the difficulty in producing large areas of these 2D TMDCs with well-defined thicknesses. In this review, we will first introduce the basic properties as well as the various synthesis methods of 2D TMDCs. Focus will be placed on recent advances in chemical vapor deposition (CVD) growth as they currently yield the largest areas. Obstacles present in CVD growth will be presented and existing solutions to them will be discussed in tandem with current characterization methods for evaluation of crystal quality. Through our presentation on the latest approaches to issues in CVD growth, we hope to present the readers a perspective on recent developments as well as providing an outlook on the future of CVD growth of TMDCs. [ABSTRACT FROM AUTHOR]

Artificial synapses in neuromorphic computing systems hold potential to emulate biological synaptic plasticity to achieve brain-like computation and autonomous learning behaviors in non-von-Neumann systems. 2D materials, such as graphene, graphene oxide, hexagonal boron nitride, transition metal dichalcogenides, transition metal oxides, 2D perovskite, and black phosphorous, have been explored to achieve many functionalities of biological synapses due to their unique electronic, optoelectronic, electrochemical, and mechanical properties that are lacking in bulk materials. This review features the current development in the state-of-the-art artificial synaptic electronic devices based on 2D materials. The structures of these devices are first discussed according to their number of terminals (two-, three-, four-, and multi-terminals) and geometric layouts (vertical, horizontal, hybrid). Since different 2D materials have been utilized to fabricate these devices, their underlying physical mechanisms and principles are further discussed, and their artificial neuron synaptic functionalities and performances are analyzed and contrasted. Finally, a summary of the current research status and major achievements is concluded, and the outlooks and perspectives for this emerging and vibrant field and the potential applications of these devices for neuromorphic computing are presented. [ABSTRACT FROM AUTHOR]

Abstract: Wedge indentation experiments are performed to study the time-dependent fracture behavior of silica-based low-k films, namely BlackDiamond® (BD) film and methysilsesquoxane (MSQ) film, both on Si substrate. Two wedge indentation tests, load-holding and varying-loading-rates tests, are performed in this study. It is found that the chemical structure of the low-k films greatly influences the crack growth during the load-holding and varying-loading-rates tests. For the MSQ/Si system, continuously increasing indentation load to above the critical load (>2mN) is required for crack growth; while for the BD/Si system, spending excessive period of time at below the critical load (<7.5mN) is leading to the initiation and propagation of interface and film cracks. The wedge indentation tests on BD/Si system at ambient environment show that time-to-failure decreases exponentially with holding load, and a linear relation exists between loading rate and the onset of time-dependent fracture. Supplying the indentation site with a water droplet, the time-to-failure reduces by at least one order of magnitude. Time-dependent fracture is also found to persist under inert environment. [Copyright &y& Elsevier]

Abstract: This paper presents further studies to determine the interface toughness of low-k films (black diamond (BD) film) using wedge indentation experiments and analysis. In addition, the effects of film thickness on the delamination mode are studied and an analysis methodology is proposed. The curvature of the delamination crack front is measured and compared for the films with different thicknesses, and this information is used to determine the critical buckling stress and the delamination mode: i.e. with or without buckling. For a thinner film with a straight crack front, there is greater likelihood of buckling delamination, while for a thicker film with a curved crack front buckling is less likely. Combining these results with those from a previous study, it is shown that the wedge indentation test is capable of accurately measuring the interface toughness of low-k films, and a pop-in event in the load–penetration curve can be used as an early indication of interface crack initiation. It is also found that the resistances to the initiation and propagation of the interfacial cracks for the porous methylsilsesquioxane (MSQ) and non-porous BD films are significantly different; this could be due to the fact that in the porous MSQ film, molecular bridges might provide an additional mechanism to resist interfacial delamination cracks. [Copyright &y& Elsevier]

Nano-additives reinforced Inconel 625 alloys were manufactured by laser powder bed fusion (LPBF), consisting of titanium carbide nanoparticles (TiC) and/or nickel-coated multi-walled carbon nanotubes ((Ni)MWCNT). Microstructural characterization revealed that respective structures of TiC and (Ni)MWCNT nano-additives were retained, while the (Ni)MWCNT experienced fragmentation into shorter segments after ball milling and LPBF. Compared to LPBF In625, the reinforced samples showed enhanced ultimate tensile strength, yield strength, and hardness, despite decreased elongation to failure. Nano-additives exert varying effects on the properties of the alloys. Individually, (Ni)MWCNT strengthens the alloy, and TiC plays an insignificant role; collectively, they strengthen the material to a higher degree, via refining the cell size and probably increasing dislocation density. • Two nano-additives, (Ni)MWCNT and TiC, were incorporated into In625 alloy. • The nano-additives were found to be along the boundaries of cellular structures. • Individually, (Ni)MWCNT strengthens the alloy, and TiC plays an insignificant role. • Collectively, they strengthen the material to a higher degree, via refining the cell size. [ABSTRACT FROM AUTHOR]

As an emerging member in 2D materials, pentagonal palladium diselenide (PdSe2) has interesting ambipolar charge transport behavior with high air‐stability and shows great potential in nanoelectronics and optoelectronics. Moreover, the puckered pentagon structure in PdSe2 results in an intrinsic low lattice thermal conductivity, which makes PdSe2 a superior material prospect for thermoelectric (TE) applications. However, its TE properties have yet to be experimentally demonstrated. Here, the TE transport in 2D PdSe2 with a low‐symmetry pentagonal lattice is probed for the first time. By thickness‐engineering, it is demonstrated that the TE property of PdSe2 can be effectively manipulated due to its sensitive dependence on the interlayer coupling originating from the special lattice structure. The TE performance can be largely enhanced benefiting from the high band convergence and quantum confinement in thinner PdSe2 flakes. A power factor as high as 1.5 mW m−1 K−2 can be achieved for a PdSe2 flake with a thickness of 5 nm. This work provides the first TE study on a pentagonal lattice as opposed to hexagonal lattices that dominate the 2D layered material family. The unique lattice structure with special interlayer interaction in PdSe2 opens up new pathways for TE applications, low‐dimensional electronics, and quantum devices. [ABSTRACT FROM AUTHOR]

The quasimetallic 1T′ phase 2D transition‐metal dichalcogenides (TMDs) consist of 1D zigzag metal chains stacked periodically along a single axis. This gives rise to its prominent physical properties which promises the onset of novel physical phenomena and applications. Here, the in‐plane electronic correlations are explored, and new mid‐infrared plasmon excitations in 1T′ phase monolayer WSe2 and MoS2 are observed using optical spectroscopies. Based on an extensive first‐principles study which analyzes the charge dynamics across multiple axes of the atomic‐layered systems, the collective charge excitations are found to disperse only along the direction perpendicular to the chains. Further analysis reveals that the interchain long‐range coupling is responsible for the coherent 1D charge dynamics and the spin–orbit coupling affects the plasmon frequency. Detailed investigation of these charge collective modes in 2D‐chained systems offers opportunities for novel device applications and has implications for the underlying mechanism that governs superconductivity in 2D TMD systems. [ABSTRACT FROM AUTHOR]

Structural and electrical characteristics of sputtered TiO2 gate dielectric on p-GaAs substrates have been investigated. It has been demonstrated that the introduction of thin aluminum oxynitride (AlON) layer between TiO2 and p-GaAs improves the interface quality. X-ray photoelectron spectroscopy and transmission electron microscopy results show that the AlON layer effectively suppresses the interfacial oxide formation during thermal treatment. The effective dielectric constant value is 1.5 times higher for the TiO2/AlON gate stack compared to directly deposited TiO2 on p-GaAs substrates, with a comparable interface state density. The capacitance-voltage (C-V), current-voltage (I-V) characteristics, and charge trapping behavior of the TiO2/AlON gate stack under constant voltage stressing exhibit an excellent interface quality and high dielectric reliability, making the films suitable for GaAs based complementary metal-oxide-semiconductor technology. [ABSTRACT FROM AUTHOR]

This article presents studies on using a wedge indentation technique to determine interfacial adhesion properties of low-k dielectric films, namely, methyl-silsesquioxane (MSQ) and black diamond (BD™)films, both on a Si substrate. Interfacial crack initiation and propagation processes in the MSQ/Si system are studied by using focused-ion-beam sectioning of the indentation impressions created by wedge tips with 90° and 120° of inclusion angles, respectively. Furthermore, the indentation induced stress is found to be proportional to the ratio of the indentation volume and the interface delamination crack volume for both plane strain and nonplane strain cases. With this analysis, the interface toughness of the MSQ/Si and BD/Si system, in terms of the strain energy release rate, is determined. The interface toughness for the MSQ/Si system is found to be a value of 1.89±0.28 J/m2 for the 90° wedge tip indentation and 1.92±0.08 J/m2 for the 120° wedge tip indentation. In addition, using the 120° wedge tip, the interface toughnesses of the BD films on the Si substrate with 200 and 500 nm thicknesses are found to be the values of 6.62±1.52 and 6.35±2.27 J/m2, respectively. [ABSTRACT FROM AUTHOR]

• Microencapsulated PCM and glass bubble as complementary passive cooling strategies. • Microencapsulated PCM and glass bubble coating system on mortar panels is developed. • Maximum surface reduction of 3.2 °C in a laboratory-based study. • Maximum ambient reduction of 7.0 °C in an outdoor-based study. As climate change intensifies in recent years, many are paying much attention to efficient energy-saving solutions to reduce the cooling load in buildings. In this work, a passive cooling strategy involving the incorporation of microencapsulated phase change material (MEPCM) and glass bubble (GB) into the paint and coating on mortar panels was investigated in the tropics. Results indicated that the integrated MEPCM-GB mortar panel consisting of 30% PCM and 20 % GB was found to have a maximum surface temperature and ambient temperature reduction of 3.2 °C and 7.0 °C in a laboratory-based and outdoor-based parametric study respectively. [ABSTRACT FROM AUTHOR]

Since the first isolation of graphene, new classes of two-dimensional (2D) materials have offered fascinating platforms for fundamental science and technology explorations at the nanometer scale. In particular, 2D transition metal dichalcogenides (TMD) such as MoS2 and WSe2 have been intensely investigated due to their unique electronic and optical properties, including tunable optical bandgaps, direct–indirect bandgap crossover, strong spin–orbit coupling, etc., for next-generation flexible nanoelectronics and nanophotonics applications. On the other hand, organics have always been excellent materials for flexible electronics. A plethora of organic molecules, including donors, acceptors, and photosensitive molecules, can be synthesized using low cost and scalable procedures. Marrying the fields of organics and 2D TMDs will bring benefits that are not present in either material alone, enabling even better, multifunctional flexible devices. Central to the realization of such devices is a fundamental understanding of the organic–2D TMD interface. Here, we review the organic–2D TMD interface from both chemical and physical perspectives. We discuss the current understanding of the interfacial interactions between the organic layers and the TMDs, as well as the energy level alignment at the interface, focusing in particular on surface charge transfer and electronic screening effects. Applications from the literature are discussed, especially in optoelectronics and p–n hetero- and homo-junctions. We conclude with an outlook on future scientific and device developments based on organic–2D TMD heterointerfaces. [ABSTRACT FROM AUTHOR]

Carbon nanotubes showing tensile strength up to 20 GPa and stiffness up to 1000 GPa, are the strongest fibers known to mankind, which has been proved to be an extraordinary filler for light metals such as aluminium and titanium metals and alloys. However, the efficiency of its reinforcement to hard metallic materials such as Nickel-based superalloys are still unknown and under developed in the current powder metallurgy research. This study focuses on the sintering and mechanical properties of carbon nanotube reinforced Inconel 625 superalloy. The carbon nanotube modified Inconel 625 powder was pressed with a polymer binder and sintered to achieve high density. The mechanical properties are measured and compared with non-reinforced counterparts to verify the efficiency of carbon nanotube reinforcement. The mechanism of such reinforcement will be discussed based on the optical image and nano-indentation analysis. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) was used for additive manufacturing multi-wall carbon nanotube (MWCNT) reinforced Inconel 625 composites. The MWCNTs were coated on Inconel 625 powder through molecular-level mixing. Compared to the SLM fabricated Inconel 625 sample, the composite sample showed significant improvement in ultimate tensile and yield strength with less elongation. Heat-treatment on the composite sample recovered its elongation to the level of pure Inconel 625 while maintaining its ultimate tensile strength but reducing its yield strength. The microstructures of the composite sample had a slightly faster cooling rate than the pure metallic sample during SLM fabrication. The electron backscatter diffraction graphs revealed the grain refinement induced by MWCNTS in the alloy matrix. The Raman spectra and TEM micrographs revealed the presence of MWCNT in the metal matrix after SLM fabrication. [ABSTRACT FROM AUTHOR]

Earth abundant materials based photoelectrochemical cells (PECs) are designed using aluminium alloyed iron silicide (FeSi(Al)) as auxiliary electrode, tungsten oxide (WO 3 ) and iron-oxide (Fe 2 O 3 ) as working electrodes for solar driven hydrogen (SH) production. Low temperature grown metallic α-phase and semiconducting β-phase FeSi(Al) are introduced as auxiliary electrode and hydrogen evolution performance is compared with commercially available platinum electrode. The β-phase FeSi(Al) electrode yields similar hydrogen evolution compared with platinum electrode and are highly stable in electrolyte solution. This study shows that the earth-abundant iron-silicide and cheap metal oxides based PEC cells provide great potential toward Pt-free devices for the development of sustainable and low cost PECs for large scale solar hydrogen production. [ABSTRACT FROM AUTHOR]

This work reports a unique in-grown structure of a NiFe-MMO/CNT hybrid catalyst. This structure creates larger interfacial area and strong interaction between the NiFe-MMO catalyst and the CNT, which could promote charge transfer at the interface, and hence improve conductivity. This leads to outstanding electrochemical performance for oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

We have synthesized crystalline MoS 2 thin films on Si substrates by thermal processing of molybdenum layers in sulfur vapor environment at elevated temperatures. The molybdenum layers were deposited at room temperature by magnetron sputtering. X-ray diffraction, Raman scattering spectroscopy, and transmission-electron microscopy characterizations revealed that the synthesized MoS 2 thin films are of hexagonal crystal with van der Waals layered structures that bended into bell-like domains. Amorphous SiO 2 layers have been observed not only at the MoS 2 /Si interface but also anomalously on top of the MoS 2 layer. Secondary ion mass spectroscopy has been employed to investigate the elemental depth profiles, which, together with the structural properties, provides evidence that the surface SiO 2 was grown out from its bottom layers rather than deposited from the growth environments. A mechanism based on solid-state reactions and atomic diffusions is introduced to explain the formation of the observed SiO 2 /MoS 2 /SiO 2 sandwich structures, which may have important consequences when fabricating and/or processing MoS 2 /Si heterostructures for electrical and optoelectronic applications. [ABSTRACT FROM AUTHOR]

Structural properties and solar cells performance of sputter grown sub-micrometer thick (~600 nm) Cu 2 ZnSnS 4 (CZTS) films are investigated for low cost and large scale photovoltaic deployment. The CZTS films are deposited using single quaternary stoichiometric target at room temperature. X-ray diffraction, micro-Raman spectroscopy, and scanning electron microscopy measurements were carried out to investigate the structural property and secondary phase formation. The intense phonon peak at 334 cm −1 in the visible Raman spectra confirms the deposition of single phase CZTS films. CZTS-based thin film solar cells show excellent performance with open circuit voltage ~600 mV and over all cell efficiency of ~3.07%, exhibiting commercial potential toward large scale fabrication of photovoltaic devices. [ABSTRACT FROM AUTHOR]

Growth of alpha phase aluminum alloyed iron silicide (α-phase FeSi(Al)) ternary alloy on silicon (Si) substrate at a temperature of 600 °C has been reported. The α-phase FeSi(Al) thin films are grown on Si substrate by using conventional sputter deposition and rapid thermal annealing (RTA) treatment. The transition temperature of α-phase FeSi 2 reduces to 600 °C through incorporating aluminum into the silicide films. Thickness of amorphous silicide layer and aluminum composition are very critical to grow highly texture α-FeSi(Al) layer at a lower temperature. The α-FeSi(Al) film shows a preferential orientation (001) after annealed at temperature of 600 °C through the formation of thin film epitaxial silicon at the interface. The α-FeSi(Al) films tends to show a polycrystalline nature with the increase on annealing temperature to 700 °C. The α-FeSi(Al) ternary alloy has high work function of ∼5.3 eV. The low temperature grown α-phase FeSi(Al) can be applied for renewable energy and electronic applications as an electrode. [ABSTRACT FROM AUTHOR]

The authors report on high quality TiO 2 epilayers grown on lattice-matched LaAlO 3 substrates by pulsed laser deposition. A prototype of metal–semiconductor–metal ultraviolet (UV) photodetector based on TiO 2 was fabricated by employing Au as the Schottky contact metal. The UV–visible transmittance spectrum of the TiO 2 epilayer and the spectral response of the photodetector reveal that the deposited anatase TiO 2 thin film exhibits excellent visible-blind UV characteristics with an optical bandgap of 3.25 eV. In addition, the fabricated photodetector exhibits a high UV-to-visible rejection ratio ( R 270 nm / R 400 nm ) of 10 5 while displaying a low dark current of 0.25 pA under 5 V bias and a high responsivity of 0.21 A/W, suggesting a potential application in UV photodetection. [ABSTRACT FROM AUTHOR]

Development of high quality p -type epitaxial gallium–arsenide (epi-GaAs) on germanium (Ge) with sub-nm surface roughness is much sought after for the next generation high speed transistors application. High quality zinc doped p -type epitaxial GaAs with surface roughness of ~0.87 nm was grown on Ge substrates at 675 °C. Thin Al 0.3 Ga 0.7 As buffer layer and un-doped GaAs of 300 nm thick were introduced to suppress the Ge defects and auto-doping into epi-GaAs layer. The material and optical properties of the p -type epi-GaAs/un-doped GaAs/Al 0.3 Ga 0.7 As/Ge structures were examined through PL and Raman analysis. The metal–oxide–semiconductor capacitor (MOSC) was fabricated using p -type epi-GaAs layer and atomic-layer-deposited Al 2 O 3 gate dielectric. The effective dielectric constant of the Au/Al 2 O 3 / p -epi-GaAs gate-stack is 5.9 and hysteresis voltage of 500 mV was observed. The epi-GaAs layer is p -type in nature with doping densities of 5×10 17 cm −3 . [ABSTRACT FROM AUTHOR]

Abstract: Thin film WO3 photoanodes were prepared by reactive sputtering in Ar and O2 gas mixtures of various flow rate combinations. Furnace annealed films were nanocrystalline monoclinic WO3 with (002), (020) and (200) plane orientations. Water oxidation in 0.33 M H2SO4 electrolyte under simulated solar illumination showed that photoanodes deposited in highest Ar and O2 flow rate combinations exhibited highest photocurrent of 4.1 mA cm−2 (at 1.3 V vs Ag/AgCl) compared to 3–3.8 mA cm−2 for photoanodes deposited in lower flow rate combinations. The higher photocurrents were ascribed to lower bulk resistivity and charge transfer resistance at the WO3/electrolyte interface. These photoanodes consisted of randomly oriented (002), (020) and (200) planes in contrast to the preferentially orientated (002) and (200) planes of photoanodes which were highly resistive with poorer photocurrent responses. These results were interpreted in terms of the effects of Ar:O2 flow rate combinations on the distribution of oxygen vacancies and formation of crystallographic shear planes in the sputtered films. [Copyright &y& Elsevier]

The applications of lanthanide-doped upconversionnanocrystals in biological imaging, photonics, photovoltaics and therapeutics have fuelled a growing demand for rational control over the emission profiles of the nanocrystals. A common strategy for tuning upconversion luminescence is to control the doping concentration of lanthanide ions. However, the phenomenon of concentration quenching of the excited state at high doping levels poses a significant constraint. Thus, the lanthanide ions have to be stringently kept at relatively low concentrations to minimize luminescence quenching. Here we describe a new class of upconversion nanocrystals adopting an orthorhombic crystallographic structure in which the lanthanide ions are distributed in arrays of tetrad clusters. Importantly, this unique arrangement enables the preservation of excitation energy within the sublattice domain and effectively minimizes the migration of excitation energy to defects, even in stoichiometric compounds with a high Yb3+ content (calculated as 98 mol%). This allows us to generate an unusual four-photon-promoted violet upconversion emission from Er3+ with an intensity that is more than eight times higher than previously reported. Our results highlight that the approach to enhancing upconversion through energy clustering at the sublattice level may provide new opportunities for light-triggered biological reactions and photodynamic therapy. [ABSTRACT FROM AUTHOR]

The impact of AlGaAs and AlAs buffer layers on the electrical properties of an epitaxial gallium–arsenide (epi-GaAs) metal–oxide–semiconductor capacitor (MOSC) was investigated. MOSC was fabricated by using atomic-layer-deposited \Al2\O3–\TiO2 (TiAlO) alloy gate dielectric and epi-GaAs layers. The epi-GaAs layer was grown on Ge substrates at 675 ^ \circ\C with and without buffer layer between epi-GaAs layer and Ge substrates. The TiAlO/epi-GaAs interface with an AlGaAs buffer layer allows realizing a high-quality interface between epi-GaAs layers and TiAlO dielectric, much sought after for high-speed transistor applications on a silicon platform. TiAlO dielectric is amorphous even upon annealing at 500 ^\circ\C and exhibits a sharp interface with epi-GaAs layers. The choice of AlGaAs over AlAs for a buffer layer was made based on the quality of resulting TiAlO/epi-GaAs surface passivation as evident through structural and electrical characteristics. Epi-GaAs with an AlGaAs buffer layer was found to improve the performance of the MOSC significantly through increase in accumulation capacitance and breakdown voltage. The interface state density, flatband voltage, frequency dispersion, and leakage current were decreased for the MOSC fabricated with an AlGaAs buffer layer. [ABSTRACT FROM AUTHOR]

This paper presents the study on the effect of low-\kappa stacked layer, chip pad design structures, and shift pad design of a large die size Cu/low-\kappa chip for improving assembly and reliability performance on organic buildup substrate flip chip ball grid array (FCBGA). Bump shear characterization has been performed on the integrity of different stacked layer and pad structure, supported by bump shear modeling analysis. Initial reliability testing was performed on assembled package to identify the best choice of design and finally implemented on the reliability test vehicle for verification. In addition, a potential chip crack problem due to excessive warpage in FCBGA with large die assembly is examined and a simple failure criterion is proposed. [ABSTRACT FROM PUBLISHER]

Keywords: 2D; field-effect transistors; palladium diselenide; pentagonal crystals; thermoelectric devices EN 2D field-effect transistors palladium diselenide pentagonal crystals thermoelectric devices 1 1 1 12/24/20 20201222 NES 201222 In article number 2004896, John T. L. Thong, Jing Wu, and co-workers investigate thermoelectric transport in novel 2D palladium diselenide (PdSe SB 2 sb ) with a low-symmetry pentagonal lattice. The high band convergence and quantum confinement through thickness engineering advance and broaden the applications of thermoelectric such as in soft robotics, health monitoring, and human-machine interfaces. 2D, field-effect transistors, palladium diselenide, pentagonal crystals, thermoelectric devices. [Extracted from the article]

In this work, we demonstrate that by using H2O based thermal atomic layer deposited (ALD) Al2O3 films, excellent passivation (emitter saturation current density of ∼28 fA/cm2) on industrial highly boron p+-doped silicon emitters (sheet resistance of ∼62 ࡎ/sq) can be achieved. The surface passivation of the Al2O3 film is activated by a fast industrial high-temperature firing step identical to the one used for screen printed contact formation. Deposition temperatures in the range of 100-300 °C and peak firing temperatures of ∼800 °C (set temperature) are investigated, using commercial-grade 5″ Cz silicon wafers (∼5 ࡎ cm n-type). It is found that the level of surface passivation after activation is excellent for the whole investigated deposition temperature range. These results are explained by advanced computer simulations indicating that the obtained emitter saturation current densities are quite close to their intrinsic limit value where the emitter saturation current is solely ruled by Auger recombination. The process developed is industrially relevant and robust. [ABSTRACT FROM AUTHOR]

Abstract: Differential Scanning Calorimetry (DSC) was used to study the effect of Al incorporation on the crystallization of β-FeSi2 film on SiO2/Si(100) substrate. An exothermic reaction pertaining to the crystallization of β-FeSi2, confirmed using X-Ray Diffraction, can be observed by heating a 1.2μm amorphous FeSi2 film in the DSC. Using Kissinger analysis, the activation energy of thin β-FeSi2 crystallization was determined to be 2.63±0.05eV. In this study, it was found that the activation energy for β-FeSi2 crystallization increases with Al incorporation by co-sputtering. Hall measurements show the Al incorporated β-FeSi2 to be P-type. [Copyright &y& Elsevier]

Interfacial reaction and the energy-band alignments of HfO2 films on p-GaAs substrate were investigated by using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It has been demonstrated that the alloying of HfO2 with Al2O3 (HfAlO) can significantly reduce native oxides formation and increases the valence-band offsets (VBOs) at HfO2/p-GaAs interface. In addition, the effects of Si interfacial passivation layer on band alignments have also been studied. VBO at HfO2/p-GaAs, HfAlO/p-GaAs, and HfO2/Si/p-GaAs interfaces were 2.85, 2.98, and 3.07 eV, respectively. [ABSTRACT FROM AUTHOR]

The interfacial characteristics and band alignments of high-k ZrO2 on p-GaAs have been investigated by using x-ray photoelectron spectroscopy and electrical measurements. It has been demonstrated that the presence of Si interfacial passivation layer (IPL) improves GaAs metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, and hysteresis. It is also found that Si IPL can reduce interfacial GaAs-oxide formation and increases effective valence-band offset at ZrO2/p-GaAs interface. The effective valence-band offsets of ZrO2/p-GaAs and ZrO2/Si/p-GaAs interfaces are determined to be 2.7 and 2.84 eV, while the effective conduction-band offsets are found to be 1.67 and 1.53 eV, respectively. [ABSTRACT FROM AUTHOR]

Neuromorphic computing, which emulates the biological neural systems could overcome the high‐power consumption issue of conventional von‐Neumann computing. State‐of‐the‐art artificial synapses made of two‐terminal memristors, however, show variability in filament formation and limited capacity due to their inherent single presynaptic input design. Here, a memtransistor‐based artificial synapse is realized by integrating a memristor and selector transistor into a multiterminal device using monolayer polycrys‐talline‐MoS2 grown by a scalable chemical vapor deposition (CVD) process. Notably, the memtransistor offers both drain‐ and gate‐tunable nonvolatile memory functions, which efficiently emulates the long‐term potentiation/depression, spike‐amplitude, and spike‐timing‐dependent plasticity of biological synapses. Moreover, the gate tunability function that is not achievable in two‐terminal memristors, enables significant bipolar resistive states switching up to four orders‐of‐magnitude and high cycling endurance. First‐principles calculations reveal a new resistive switching mechanism driven by the diffusion of double sulfur vacancy perpendicular to the MoS2 grain boundary, leading to a conducting switching path without the need for a filament forming process. The seamless integration of multiterminal memtransistors may offer another degree‐of‐freedom to tune the synaptic plasticity by a third gate terminal for enabling complex neuromorphic learning. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials and their corresponding van der Waals heterostructures have drawn tremendous interest due to their extraordinary electrical and optoelectronic properties. Insulating 2D hexagonal boron nitride (h-BN) with an atomically smooth surface has been widely used as a passivation layer to improve carrier transport for other 2D materials, especially for Transition Metal Dichalcogenides (TMDCs). However, heat flow at the interface between TMDCs and h-BN, which will play an important role in thermal management of various electronic and optoelectronic devices, is not yet understood. In this paper, for the first time, the interface thermal conductance (G) at the MoS2/h-BN interface is measured by Raman spectroscopy, and the room-temperature value is (17.0 ± 0.4) MW · m−2K−1. For comparison, G between graphene and h-BN is also measured, with a value of (52.2 ± 2.1) MW · m−2K−1. Non-equilibrium Green's function (NEGF) calculations, from which the phonon transmission spectrum can be obtained, show that the lower G at the MoS2/h-BN interface is due to the weaker cross-plane transmission of phonon modes compared to graphene/h-BN. This study demonstrates that the MoS2/h-BN interface limits cross-plane heat dissipation, and thereby could impact the design and applications of 2D devices while considering critical thermal management. [ABSTRACT FROM AUTHOR]

Two-dimensional layered semiconductors such as molybdenum disulfide (MoS2) at the quantum limit are promising material for nanoelectronics and optoelectronics applications. Understanding the interface properties between the atomically thin MoS2 channel and gate dielectric is fundamentally important for enhancing the carrier transport properties. Here, we investigate the frequency dispersion mechanism in a metal-oxide-semiconductor capacitor (MOSCAP) with a monolayer MoS2 and an ultra-thin HfO2 high-k gate dielectric. We show that the existence of sulfur vacancies at the MoS2-HfO2 interface is responsible for the generation of interface states with a density (Dit) reaching ~7.03 × 1011 cm−2 eV−1. This is evidenced by a deficit S:Mo ratio of ~1.96 using X-ray photoelectron spectroscopy (XPS) analysis, which deviates from its ideal stoichiometric value. First-principles calculations within the density-functional theory framework further confirms the presence of trap states due to sulfur deficiency, which exist within the MoS2 bandgap. This corroborates to a voltage-dependent frequency dispersion of ~11.5% at weak accumulation which decreases monotonically to ~9.0% at strong accumulation as the Fermi level moves away from the mid-gap trap states. Further reduction in Dit could be achieved by thermally diffusing S atoms to the MoS2-HfO2 interface to annihilate the vacancies. This work provides an insight into the interface properties for enabling the development of MoS2 devices with carrier transport enhancement. [ABSTRACT FROM AUTHOR]

We introduce a facile method to generate silicon nanostructures with superior anti-reflectance (AR) properties. These nanostructures possess the ideal tapered structure and aperiodic distribution required for low reflectance over a broad range of wavelengths. Consideration of effective medium theories might explain the behavior between structure and reflectance, and suggest the advantage of aperiodicity in affording the material broadband AR properties. We then implemented these nanostructures as photocathodes to drive the hydrogen evolution reaction in AM 1.5 illumination. These nanostructures showed a significant improvement in photoelectrochemical performance over their planar counterpart, with the best performances corresponding to nanostructures which possessed AR properties matching the solar spectrum output. [ABSTRACT FROM AUTHOR]