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Two-dimensional van der Waals materials have rich and unique functional properties, but many are susceptible to corrosion under ambient conditions. Here we show that linear alkylamines n-CmH2m+1NH2, with m = 4 through 11, are highly effective in protecting the optoelectronic properties of these materials, such as black phosphorus (BP) and transition-metal dichalcogenides (TMDs: WS2, 1T'-MoTe2, WTe2, WSe2, TaS2, and NbSe2). As a representative example, n-hexylamine (m = 6) can be applied in the form of thin molecular monolayers on BP flakes with less than 2-nm thickness and can prolong BP's lifetime from a few hours to several weeks and even months in ambient environments. Characterizations combined with our theoretical analysis show that the thin monolayers selectively sift out water molecules, forming a drying layer to achieve the passivation of the protected 2D materials. The monolayer coating is also stable in air, H2 annealing, and organic solvents, but can be removed by certain organic acids. [ABSTRACT FROM AUTHOR]

Self-assembled InAs quantum dots (QDs) grown on different InxGa1-xAs/InP matrixes by metal-organic chemical vapor deposition with fast nucleation rate and atomic layer epitaxy in pure nitrogen ambient have been studied. It has been found that the InAs QD formation efficiency is enhanced when the dots are grown on the strained InxGa1-xAs/InP matrix compared with the dots grown on an unstrained InxGa1-xAs/InP matrix. By changing the indium composition x of the InxGa1-xAs barrier from 0.53 to 0.72, the 77 K photoluminescence (PL) emission wavelength of the InAs QD structures is redshifted by 220–300 nm. The transition energy of the InAs/InGaAs/InP QD structure has been calculated by using the eight-band k·p theory with consideration of the strain effect from QD’s upper InxGa1-xAs barrier layer. The calculated E1-HH1 transition energies agree with the measured PL emission peaks quite well. [ABSTRACT FROM AUTHOR]

Self-assembled InAs quantum dots (QDs) on GaAs grown by metal-organic chemical vapor deposition using tertiarybutylarsine as arsenic source in pure nitrogen ambient have been investigated in detail. Effects of the growth conditions, e.g., substrate temperature and inlet precursor flux, on the QD formations have been studied. A temperature window for growing high density (1.3×1010 cm-2) of QDs with the trimethylindium (TMIn) flow flux of 30 SCCM (SCCM denotes cubic centimeter per minute at STP) is observed from 440 to 460 °C. High density, >=1.3×1010 cm-2, of the QDs have been grown at higher temperature, 500 °C, with the higher TMIn flux of 75 SCCM, but the formed QDs are not very uniform. To improve the QD uniformity and density further, a two-step growth method has been proposed and investigated. Using the two-step growth method, the dot density achieves 30% higher than that of the QDs grown by using the normal Stranski-Krastanow growth method. The size of the QDs formed by the two-step growth is larger and more uniform. [ABSTRACT FROM AUTHOR]

The article looks at a study enhanced transport in transistor by tuning transition-metal oxide (TMOs) electronic states interfaced with diamond by enabling unprecedented surface charge doping efficiency. It mentions surface-doped diamond with TMOs has recently yielded record sheet hole concentrations and launched the quest for its implementation in microelectronic devices. It also mentions stoichiometry changes caused by typical transistor fabrication process and atomic layer deposition.

A facile strategy to prepare MoS2-MoO3 hybrid nanomaterials is developed, based on the heat-assisted partial oxidation of lithium-exfoliated MoS2 nanosheets in air followed by thermal-annealing-driven crystallization. The obtained MoS2-MoO3 hybrid nanomaterial exhibits p-type conductivity. As a proof-of-concept application, an n-type SiC/p-type MoS2-MoO3 heterojunction is used as the active layer for light-emitting diodes. The origins of the electroluminescence from the device are theoretically investigated. This facile synthesis and application of hybrid nanomaterials opens up avenues to develop new advanced materials for various functional applications, such as in electrics, optoelectronics, clean energy, and information storage. [ABSTRACT FROM AUTHOR]

A facile strategy to prepare MoS2-MoO3 hybrid nanomaterials is developed, based on the heat-assisted partial oxidation of lithium-exfoliated MoS2 nanosheets in air followed by thermal-annealing-driven crystallization. The obtained MoS2-MoO3 hybrid nanomaterial exhibits p-type conductivity. As a proof-of-concept application, an n-type SiC/p-type MoS2-MoO3 heterojunction is used as the active layer for light-emitting diodes. The origins of the electroluminescence from the device are theoretically investigated. This facile synthesis and application of hybrid nanomaterials opens up avenues to develop new advanced materials for various functional applications, such as in electrics, optoelectronics, clean energy, and information storage. [ABSTRACT FROM AUTHOR]

Abstract  InAs quantum dots (QDs) have been formed on GaAs (001) substrate by metal-organic vapor phase epitaxy (MOVPE) under the safer growth conditions: using tertiarybutylarsine (TBA) to replace AsH3 as the arsenic source and replacing hydrogen by pure nitrogen as the carrier gas. Effects of growth conditions on the QD formation have been investigated. It is observed that the wetting layer is stabilized with some material being transferred to form the QDs due to the strain relaxation process during the QD formation. Dot size dispersion becomes broader when the post-growth interruption is more than 20 s. Compared with normal one-step grown QDs, dot density increases greatly by 213% after employing two-step deposition for QD growth. This is explained by considering the indium-flux-dependent nucleation density at step 1 and kinetically self-limiting growth at step 2. The two photoluminescence (PL) emission peaks, 1.203 μm and 1.094 μm, from the two-step grown QDs are attributed to E1–HH1 and E1–LH1 transitions of the QDs, respectively. The measured results agree well with those received by an 8 kp theoretical calculation. The narrow PL linewidth of ~50 nm shows high quality of the QDs. This paves the way to develop safer MOVPE process, using TBA/N2 instead of AsH3/H2, to grow QDs for device application. [ABSTRACT FROM AUTHOR]

InAs mid-infrared emissive quantum dots (QDs) grown on a gradedInxGa1−xAs/InP matrix with more uniform size and higher dot density have been successfully prepared by lowpressure metal organic chemical vapour deposition (LP-MOCVD) under safer growth conditions.Low toxic tertiarybutylarsine and tertiarybutylphosphine sources were used to replace the hightoxic arsine and phosphine in the MOCVD growth. To improve the process safety further, inertialN2 instead of the normallyused explosive H2 was used as the carrier gas. Initially, by using a two-step growth method, uniform InAs QDs with a high dotdensity of 1.3 1010cm−2 have been successfully grown on a InGaAs/InP matrix. The emission wavelength of the QDs reaches>2.1m. The low temperature photoluminescence spectrum of the QDs grown by the two-stepgrowth has much narrower linewidth and higher intensity than that of the QDs grown byusing normal Stranski–Krastanow (S–K) and atomic layer epitaxy (ALE) growth methods. [ABSTRACT FROM AUTHOR]

The article presents a study on postchemistry of aqueous tetrathiafulvalene (TTF) microparticles and tetracyanoquinodimethane (TCNQ) microstructures. It states that TTF or TCNQ acetonitrile solution were added to water containing nonionic surcatant in the preparation of TTF or TCNQ microparticles and were observed through scanning electron microscopy (SEM) and x-ray diffraction. It concludes that organic particle offers an option in preparing novel organic microparticles.

Liquid methanol has the potential to be the hydrogen energy carrier and storage medium for the future green economy. However, there are still many challenges before zero-emission, affordable molecular H2 can be extracted from methanol with high performance. Here, we present noble-metal-free Cu--WC/W plasmonic nanohybrids which exhibit unsurpassed solar H2 extraction efficiency from pure methanol of 2,176.7 µmol g-1 h-1 at room temperature and normal pressure. Macro-to-micro experiments and simulations unveil that local reaction microenvironments are generated by the coperturbation of WC/W's lattice strain and infrared-plasmonic electric field. It enables spontaneous but selective zero-emission reaction pathways. Such microenvironments are found to be highly cooperative with solar-broadband-plasmon-excited charge carriers flowing from Cu to WC surfaces for efficient stable CH3OH plasmonic reforming with C3-dominated liquid products and 100% selective gaseous H2. Such high efficiency, without any COx emission, can be sustained for over a thousand-hour operation without obvious degradation. [ABSTRACT FROM AUTHOR]

First-step nucleation growth has an important impact on the two-step growth of high-quality mid-infrared emissive InAs/InGaAs/InP quantum dots (QDs). It has been found that an optimized growth rate for first-step nucleation is critical for forming QDs with narrow size distribution, high dot density and high crystal quality. High growth temperature has an advantage in removing defects in the QDs formed, but the dot density will be reduced. Contrasting behavior in forming InAs QDs using metal-organic vapor phase epitaxy (MOVPE) by varying the input flux ratio of group-V versus group-III source (V/III ratio) in the first-step nucleation growth has been observed and investigated. High-density, 2.5 × 1010 cm[?]2, InAs QDs emitting at>2.15 µm have been formed with narrow size distribution, [?]1 nm standard deviation, by reducing the V/III ratio to zero in first-step nucleation growth. [ABSTRACT FROM AUTHOR]

We investigate the ultralow-frequency Raman response of atomically thin ReS2, a special type of two-dimensional (2D) semiconductors with unique distorted 1T structure. Bilayer and few-layer ReS2 exhibit rich Raman spectra at frequencies below 50 cm-1, where a panoply of interlayer shear and breathing modes are observed. The emergence of these interlayer phonon modes indicate that the ReS2 layers are coupled and orderly stacked. Whereas the interlayer breathing modes behave similarly to those in other 2D layered crystals, the shear modes exhibit distinctive behavior due to the in-plane lattice distortion. In particular, the two shear modes in bilayer ReS2 are nondegenerate and clearly resolved in the Raman spectrum, in contrast to the doubly degenerate shear modes in other 2D materials. By carrying out comprehensive first-principles calculations, we can account for the frequency and Raman intensity of the interlayer modes and determine the stacking order in bilayer ReS2. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated metalorganic vapor phase epitaxy (MOVPE) growth of Al x In1−x P alloy using tertiarybutylphosphine (TBP) as the phosphorus source in pure N2 ambient. The effect of the substrate temperature on the aluminum composition of Al x In1−x P epilayers during the MOVPE growth has been studied. When the source flow rates were kept unchanged, the aluminum composition of the Al x In1−x P epilayer increased monotonically when the substrate temperature, T g, was raised from 580 °C to 660 °C during the growth. It became saturated when T g reached 660 °C and above. The crystalline quality of the grown Al x In1−x P epilayers has been investigated by X-ray diffraction and photoluminescence measurements. A linear relationship between the aluminum composition of the Al x In1−x P epilayer and TMAl/(TMAl+TMIn) source flow ratio has been obtained when grown at the optimized growth temperature of T g =630 °C. It has also been observed that the aluminum incorporation coefficient of Al x In1−x P epilayers decreased when the V/III source flow ratio was increased during the MOVPE growth. [Copyright &y& Elsevier]

Spontaneous CuPt ordering is observed in AlxIn1-xP layers grown by metal-organic vapor-phase epitaxy in pure nitrogen ambient with tertiarybutylphosphine as phosphorus precursor. Changes of the degree of ordering of the AlxIn1-xP epilayer versus annealing temperature have been investigated by using photoluminescence and transmission electron diffraction. The degree of ordering of the AlxIn1-xP layers is reduced after annealing the sample at a temperature higher than the sample growth temperature. It becomes completely disordered when the annealing temperature reaches 900 °C and above. [ABSTRACT FROM AUTHOR]