Optoelectronic properties of single-crystalline GaInAsSb quaternary alloy nanowires

Bandgap engineering of semiconductor nanomaterials is critical for their applications in nanoelectronics, opto- electronics, and photonics. Here we report, for the first time, the growth of single-crystalline quaternary alloyed Ga0.75In0.25As0.49Sb0.51 nanowires via a chemical-vapor-deposition method. The synthesized nanowires have a uniform composition distribution along the growth direction, with a zinc-blende structure. In the photoluminescence investigation, these quaternary alloyed semiconductor nanowires show a strong band edge light emission at 1950 nm （0.636 eV）. Photodetectors based on these alloy nanowires show a strong light response in the near-infrared region （980 nm） with the external quantum efficiency of 2.0 × 104% and the responsivity of 158 A/W. These novel near-infrared photodetectors may find promising applications in integrated infrared photodetection, information communication, and processing.

NEW AMORPHOUS Al-La-Y-Ni(Fe)QUATERNARY ALLOYS WITH SUPERIOR STRENGTH AND DUCTILITY

The melt spun ribbons of Al-La-Y-Ni(Fe)quaternary alloys were prepared by a single- roller melt spinning technique in vacuum.Their amorphous nature,mechanical properties and tensile fracture surface morphology were investigated.The experimental results show that amorphous alloys with high strength and good ductility as well as good thermal stability can be achieved in Al-La-Y-Ni(Fe)system,when the alloy contains 85—90 at.-% Al and less than 10 at.-% La+Y.The maximum tensile fracture strength(σ_f) and microhardness(HV)are as high as 760 MPa and 294 DPN,respectively.The as- quenched ribbons can be bent 180 degree without fracturing.The dominant factors for formation of amorphous Al-La-Y-Ni(Fe)are the strong attractive interaction among Al, La,Y and a decrease of melting temperature.

Thermoelectric properties of quaternary Mg_2Sn_(0.4)Si_(0.6-x)Ge_x alloys

Quaternary alloys Mg2Sn0.4Si0.6-xGex （x=0, 0.02, 0.05, 0.08 0.1, and 0.2） were prepared using induction melting followed by hot-pressing. Relative densities of the sintered samples were over 97% of the theoretical values. Multiple phases were detected in the samples. It was found that the Seebeck coefficient was sensitive to the content of Mg2Ge and a maximum value of about 350 μV-K^-1 was obtained. The introduction of Ge increases the electrical conductivity and the thermal conductivity simultaneously. The mechanism of this phenomenon was discussed. A maximum dimensionless figure of merit, ZT, of about 0.28 was obtained for Mg2Sn0.4Si0.55Ge0.05 at 550 K.

Combinatorial Synthesis and High-Throughput Characterization of Microstructure and Phase Transformation in Ni-Ti-Cu-V Quaternary Thin-Film Library

Ni-Ti-based shape memory alloys(SMAs)have found widespread use in the last 70 years,but improving their functional stability remains a key quest for more robust and advanced applications.Named for their ability to retain their processed shape as a result of a reversible martensitic transformation,SMAs are highly sensitive to compositional variations.Alloying with ternary and quaternary elements to finetune the lattice parameters and the thermal hysteresis of an SMA,therefore,becomes a challenge in materials exploration.Combinatorial materials science allows streamlining of the synthesis process and data management from multiple characterization techniques.In this study,a composition spread of Ni-Ti-Cu-V thin-film library was synthesized by magnetron co-sputtering on a thermally oxidized Si wafer.Composition-dependent phase transformation temperature and microstructure were investigated and determined using high-throughput wavelength dispersive spectroscopy,synchrotron X-ray diffraction,and temperature-dependent resistance measurements.Of the 177 compositions in the materials library,32 were observed to have shape memory effect,of which five had zero or near-zero thermal hysteresis.These compositions provide flexibility in the operating temperature regimes that they can be used in.A phase map for the quaternary system and correlations of functional properties are discussed w让h respect to the local microstructure and composition of the thin-film library.

Structural,electronic,and magnetic properties of quaternary Heusler CrZrCoZ compounds:A first-principles study

Using the first-principles calculations,we study the structural,electronic,and magnetic properties along with exchange interactions and Curie temperatures for CrZrCoZ(Z=Al,Ga,In,Tl,Si,Pb)quaternary Heusler alloys.The results show that the CrZrCoZ alloys are half-metallic ferrimagnets,and their total spin magnetic moments,which are mainly carried by the Cr atom,obey the Slater-Pauling rule.Analysis of local density of states confirms that the exchange splitting between eg and t2g states leads to the formation of half-metallic gap.According to the calculated Heisenberg exchange coupling parameters,it is found that the Cr(A)-Cr(A)and Cr(A)-Zr(B)exchanges dominate the appearance of ferrimagnetic states in CrZrCoZ(Z=Al,Ga,In,Tl,Pb)alloys,and it is the Cr(A)-Zr(B)and Zr(B)-Zr(B)exchanges for CrZrCoSi alloy.Finally,we estimate the Curie temperatures of CrZrCoZ by using mean-field approximation,it is found that the CrZrCoZ(Z=Al,Ga,In,Tl,Pb)alloys have noticeably higher Curie temperatures than room temperature.So,we expect that the CrZrCoZ alloys are promising candidates in spintronic applications in future.

Microwave synthesis of single-phase nanoparticles made of multiprincipal element alloys

Metal nanoparticles of multi-principal element alloys(MPEA)with a single crystalline phase have been synthesized by flash heating/cooling of nanosized metals encapsulated in micelle vesicles dispersed in an oil phase(e.g.,cyclohexane).Flash heating is realized by selective absorption of a microwave pulse in metals to rapidly heat metals into uniform melts.The oil phase barely absorbs microwave and maintains the low temperature,which can rapidly quench the high-temperature metal melts to enable the flash cooling process.The precursor ions of four metals,including Au,Pt,Pd,and Cu,can be simultaneously reduced by hydrazine in the aqueous solution encapsulated in the micelle vesicles.The resulting metals efficiently absorb microwave energy to locally reach a temperature high enough to melt themselves into a uniform mixture.The duration of microwave pulse is crucial to ensure the reduced metals mix uniformly,while the temperature of oil phase is still low to rapidly quench the metals and freeze the single-phase crystalline lattices in alloy nanoparticles.The microwave-enabled flash heating/cooling provides a new method to synthesize single-phase MPEA nanoparticles of many metal combinations when the appropriate water-in-oil micelle systems and the appropriate reduction reactions of metal precursors are available.

Controllable optical emission wavelength in all-inorganic halide perovskite alloy microplates grown by two-step chemical vapor deposition

All-inorganic halide perovskites(IHP),CsPbX_(3)(X=Cl,Br,I)exhibiting efficient optical emissions within the spectral range of 410 to 730 nm are potential candidates for many optoelectronic devices.Anion alloying of these IHPs is expected to achieve tunable emission wavelength covering the entire visible spectrum.Here,we developed a two-step chemical vapor deposition(CVD)process for growing quaternary IHP CsPbX_(3)(X=Cl/Br and Br/I)alloys.By exploiting the fast diffusion of halide anions in IHPs,the alloy composition can be precisely controlled by the growth time of the respective layers once the growth of the individual ternary IHP is optimized.Hence complexities in the multi-parameter optimization in the conventional CVD growth of quaternary alloys can be mitigated.Using this process,we synthesized single crystalline,homogeneous and thermally stable CsPbCl3_((1−X))Br_(3x)and CsPbBr3_((1−X))I_(3x)perovskites alloy microplates and demonstrated continuously tunable emission covering the spectrum from 428 to 715 nm by varying the halide compositions in the alloys.These alloy microplates also exhibit room temperature amplified spontaneous emissions(ASE)along with strong photonic discharges from the microplate’s edges and hence are potentially useful as a gain medium as well as optical cavities for emissions with wavelengths covering the visible spectrum.