气态源分子束外延生长Ge_xSi_(1-x)/Si异质结合金

采用气态源分子束外延法成功地生长了ＧｅｘＳｉ１－ｘ／Ｓｉ异质结合金材料，所使用的气体分别是乙硅烷和锗烷。高能电子衍射被用于原位监控生长层的表面重构状态。在一定的生长温度下，ＧｅｘＳｉ１－ｘ合金组分ｘ取决于锗烷和乙硅烷的流量比。外延层的表面形貌与锗组分的大小、生长层的厚度及生长温度有关。结果表明，较大的锗组分和较高的生长温度利于由二维模式向三维模式转变的外延生长。

A novel immiscible high entropy alloy strengthened via L1_(2)-nanoprecipitate

The low-cost Fe-Cu,Fe-Ni,and Cu-based high-entropy alloys exhibit a widespread utilization prospect.However,these potential applications have been limited by their low strength.In this study,a novel Fe_(31)Cu_(31)Ni_(28)Al_(4)Ti_(3)Co_(3) immiscible high-entropy alloy(HEA)was developed.After vacuum arc melting and copper mold suction casting,this HEA exhibits a unique phase separation microstructure,which consists of striped Cu-rich regions and Fe-rich region.Further magnification of the striped Cu-rich region reveals that it is composed of a Cu-rich dot-like phase and a Fe-rich region.The aging alloy is further strengthened by a L1_(2)-Ni_(3)(AlTi)nanoprecipitates,achieving excellent yield strength(1185 MPa)and uniform ductility(~8.8%).The differential distribution of the L1_(2) nanoprecipitate in the striped Cu-rich region and the external Fe-rich region increased the strength difference between these two regions,which increased the strain gradient and thus improved hetero-deformation induced(HDI)hardening.This work provides a new route to improve the HDI hardening of Fe-Cu alloys.

Preparation of high-mechanical-property medium-entropy CrCoNi alloy by asymmetric cryorolling

In order to obtain good strength−plasticity synergy for a medium entropy alloy(MEA)CrCoNi,cold rolling,asymmetric rolling,cryorolling and asymmetric-cryorolling with subsequent annealing at different temperatures were conducted.The results showed that the asymmetric-cryorolled alloy achieved a high strength of over 1.6 GPa.After annealing at 1073 K,it retained a high strength of~1 GPa while the elongation reached nearly 60%.After annealing,the heterogeneous characteristics were formed in asymmetric-cryorolled samples,which were found to be more distinct than those of the samples subjected to asymmetric rolling.This resulted in the generation of high strength and ductility.

Effects of extrusion temperature on microstructure evolution and mechanical properties of heterogeneous Mg−Gd alloy laminates via accumulated extrusion bonding

The influence of extrusion temperature on microstructure and mechanical properties of heterogeneous Mg−1Gd/Mg−13Gd laminate prepared by accumulated extrusion bonding was investigated.The results reveal that the Mg−1Gd/Mg−13Gd laminate forms a significant difference in grain size between the successive layers when extruded at 330℃,and this difference gradually disappears as the extrusion temperature increases from 380 to 430℃.Besides,the growth rate of recrystallized grains in fine-grained layers is faster than that in coarse-grained layers.Moreover,the diffusion ability of Gd element increases with elevating extrusion temperatures,promoting the increase and coarsening of precipitates in fine-grained layers.Tensile tests indicate that the sample extruded at 380℃ has a superior combination of strength and ductility.This is mainly attributed to the synergy of the heterogeneous texture between coarse and fine-grained layers,hetero-deformation induced strengthening and hardening.The fine-grained layers facilitate the activation of prismaticáañslips,while coarse-grained layers make it easier to active basaláañand pyramidalác+añslips,especially for the sample extruded at 380℃.The activation of pyramidalác+añslips contributes to coordinating further plastic deformation.

Bacterial Cellulose Templated p-Co3O4/n-ZnO Nanocomposite with Excellent VOCs Response Performance

In this work,p-type Co3O4 decorated n-type ZnO(Co3O4/ZnO)nanocomposite was designed with the assistance of bacterial cellulose template.Phase composition,morphology and element distribution were investigated by XRD,SEM,HRTEM,EDS mapping and XPS.Volatile organic compounds(VOCs)sensing measurements indicated a noticeable improvement of response and decrease of working temperature for Co3O4/ZnO sensor,in comparison with pure ZnO,i.e.,the response towards 100 ppm acetone was 63.7(at a low working temperature of 180℃),which was 26 times higher than pure ZnO(response of 2.3 at 240℃).Excellent VOCs response characteristics could be ascribed to increased surface oxygen vacancy concentration(revealed by defect characterizations),catalytic activity of Co3O4 and the special p-n heterojunction structure,and bacterial cellulose provides a facile template for designing diverse functional heterojunctions for VOCs detection and other applications.

Electrochemically formed PtFeNi alloy nanoparticles on defective NiFe LDHs with charge transfer for efficient water splitting

Efficient and stable bifunctional electrocatalysts for water splitting is essential for producing hydrogen and alleviating huge energy consumption.Meanwhile,charge transfer engineering is an efficient approach to modulate the localized electronic properties of catalysts and tune the electrocatalytic performance.Herein,we tactfully fabricate PtFeNi alloys/NiFe layered double hydroxides(LDHs)heterostructure by an easily electrochemical way with a small amount of Pt.The experimental and theoretical results unravel that the charge transfer on the alloy clusters modulated by the defective substrates(NiFe LDHs),which synergistically optimizes the adsorption energy of the reaction intermediates.The electrocatalyst exhibits an ultra‐low overpotential of 81 and 243 mV at the current density of 100 mA cm^(–2) for hydrogen evolution and oxygen evolution,respectively.Furthermore,the overall water splitting indicates that PtFeNi alloys/NiFe LDHs presents an ultra‐low overpotential of 265 and 406 mV to reach the current density of 10 and 300 mA cm^(–2),respectively.It proves that the PtFeNi alloys/NiFe LDHs catalyst is an excellent dual‐function electrocatalyst for water splitting and promising for industrialization.This work provides a new electrochemical approach to construct the alloy heterostructure.The prepared heterostructures act as an ideal platform to investigate the charge re‐distribution behavior and to improve the electrocatalytic activity.

Bandgap-tunable lateral and vertical heterostructures based on monolayer Mo1-xWxS2 alloys

The fabrication of heterostructures of two-dimensional semiconductors with specific bandgaps is an important approach to realizing the full potential of these materials in electronic and optoelectronic devices. Several groups have recently reported the direct growth of lateral and vertical heterostructures based on monolayers of typical semiconducting transition metal dichalcogenides （TMDCs） such as WSe2, MoSe2, WS2, and MoS2. Here, we demonstrate the single-step direct growth of lateral and vertical heterostructures based on bandgap-tunable Mo1-xWxS2 alloy monolayers by the sulfurization of patterned thin films of WO3 and MoO3. These patterned films are capable of generating a wide variety of concentration gradients by the diffusion of transition metals during the crystal growth phase. Under high temperatures, this leads to the formation of monolayer crystals of Mo1-xWxS2 alloys with various compositions and bandgaps, depending on the positions of the crystals on the substrates. Heterostructures of these alloys are obtained through stepwise changes in the ratio of W/Mo within a single domain during low-temperature growth. The stabilization of the monolayer Mo1-xWxS2 alloys, which often degrade even under gentle conditions, was accomplished by coating the alloys with other monolayers. The present findings demonstrate an efficient means of both studying and optimizing the optical and electrical properties of TMDC-based heterostructures to allow use of the materials in future device applications.

Wavelength-tunable infrared light emitting diode based on ordered ZnO nanowire/Si1-xGex alloy heterojunction

A novel infrared light emitting diode （LED） based on an ordered p-n heterojunction built of a p-Si1-xGe/alloy and n-ZnO nanowires has been developed. The electroluminescence （EL） emission of this LED is in the infrared range, which is dominated by the band gap of Si1-xGex alloy. The EL wavelength variation of the LED shows a red shift, which increases with increasing mole fraction of Ge. With Ge mole fractions of 0.18, 0.23 and 0.29, the average EL wavelengths are around 1,144, 1,162 and 1,185 nm, respectively. The observed magnitudes of the red shifts are consistent with theoretical calculations. Therefore, by modulating the mole fraction of Ge in the Si1-xGex alloy, we can adjust the band gap of the SiGe film and tune the emission wavelength of the fabricated LED. Such an IR LED device may have great potential applications in optical communication, environmental monitoring and biological and medical analyses.