Application of pulsed liquid-injection MOCVD to the growth of ultrathin epitaxial oxides for magnetic heterostructures

We illustrate the capabilities of pulsed-liquid injection metal–organic chemical vapor deposition in the nano-engineering of complex oxides with results obtained on (La_0.7Sr_0.3MnO₃/SrTiO₃)₁₅ (LSMO/STO) superlattices. Superlattices with ultrathin films of a few monolayers have been successfully prepared, as shown by synchrotron radiation diffraction experiments. Laue oscillations were observed between the satellite peaks, indicating a smooth upper surface. Sets of superlattices with varying LSMO or STO thickness were synthesized on different substrates (LaAlO₃, SrTiO₃, MgO). By varying the relative thickness of each compound and changing the substrate, the strain in the stackings could be changed.     

Fabrication of GaN/GaN:Mn core/shell nanowires and their photoluminescences

We report on the fabrication of GaN/GaN:Mn core/shell nanowires (NWs) using a two-step metalorganic chemcial vapor deposition (MOCVD) and chloride-based chemical vapor transport (CVT) process. Structural analyses indicated that the heterostructure NWs were single crystalline and exhibited a core/shell and lozenge structure. The photoluminescence (PL) of the core/shell NWs showed a peak at a center wavelength of 454 nm, which was red-shifted compared to those of GaN and GaN:Mn NWs. This outcome indicates the accumulation of excited carriers at the interfaces that would be helpful in developing novel magnetism in diluted magnetic GaN:Mn semiconductors.     

磁控溅射SiGe异质结的薄膜分析

膜层生长不均匀是制备SiGe异质结的研究热点。采用射频磁控溅射方法,通过不断改变溅射时的实验参数,寻找能使Ge纳米薄膜在Si基片上均匀生长的溅射实验条件。实验中,在不同时间条件下分别制备了三种纳米Ge薄膜,通过原子力显微镜对其微观形貌的分析扫描,可以观察到纳米薄膜生长过程中的四个典型阶段,发现Ge/Si的共度生长取得了较好的结果,为SiGe异质结的进一步制备研究奠定了一定的实验基础。     

Ge_xSi_(1-x)/Si异质结器件的研制现状

介绍了应变层Ge_xSi_(1-x)/Si异质结构的生长、材料特性及其在异质结双极晶体管(HBT)、双极反型沟道场效应晶体管(BICFET)、调制掺杂场效应晶体管(MODFET)、谐振隧道二极管、负阻效应晶体管(NERFET)、毫米波混合隧道雪崩渡越时间(MITATT)二极管和光电探测器等器件中的应用状况,并指出了其发展前景。     

Preparation and properties of the composite material silicon/polypyrrole–copper for electronic devices applications

The paper presents the results of the elaboration of new composites materials (Si/PPy–Cu) by incorporation of copper in polypyrrole films. Polymer films have been deposited on silicon electrode surfaces by electrochemical oxidation of the monomer in an organic solution. The incorporation of copper particles in the polymer film has first been conducted by the immersion of the modified electrode in a copper solution, thereafter; it has been reduced electrochemically in an aqueous solution to disperse metallic particles in the polymer film. The results obtained from cyclic voltammetry and impedance spectroscopy of the films before and after copper incorporation show differences in the electrochemical behavior of the modified films which suggest that Cu particles have been incorporated in the polymer. This has also been confirmed by the electrical resistivity, XRD, SEM and EDX measurements. For a possible application, current–voltage characteristics of the heterostructure devices (Si/PPy–Cu) have indicated a diode behavior similar of power semiconductor diodes.     

Oxide content optimized ZnS–ZnO heterostructures via facile thermal treatment process for enhanced photocatalytic hydrogen production

The ZnS–ZnO heterostructured photocatalysts are synthesized by thermal treatments of the ZnS materials at various thermal processing temperatures (150 °C – 550 °C) with controlling O₂ partial pressures (7.8 kPa – 33.8 kPa). The ZnS–ZnO composite structure shows much higher photocatalytic hydrogen production than those from the ZnS and ZnO pure substances. This phenomenon is mainly caused by effective charge separation between the photoexcited electrons and holes. The thermal oxidation of ZnS materials proceeds at temperatures higher than 500 °C. In addition to the thermal processing temperature, O₂ partial pressure is also chosen for an experimental variable in order to control the atomic composition minutely. The ZnS–ZnO photocatalyst composite fabricated at 500 °C under 16.9 kPa of O₂ partial pressure shows the highest hydrogen production rate of 494.8 μmol g⁻¹ h⁻¹ under 1 sun irradiation condition, and it is 37 times higher than that (13.5 μmol g⁻¹ h⁻¹) from the ZnS pure substance. At this optimized production rate, the Zn/S/O atomic compositions are measured as 45.9/46.9/7.2 (XPS) and 53.3/42.1/4.6 (ICP-AES), respectively.     

Crossover of magnetoresistance from positive to negative in La0.5Sr0.5CoO3 − σ/Si heterostructure

The magnetoresistance (MR) properties of a heterostructure fabricated by depositing a La_0.5Sr_0.5CoO_3 − σ film on an n-type Si substrate have been studied. The heterostructure exhibits a good rectifying behavior. A negative MR at T = 210 K and a positive MR at T = 300 K are observed for all bias currents whereas; for temperatures ranging from 240 to 280 K the MR changes from being positive to negative with the increase of the bias current. The observed behavior of the MR effect is discussed in terms of current-induced ferromagnetic spin order.     

Thermal properties of high-power diode lasers investigated by means of high resolution thermography

In the present work, thermal effects in high-power diode lasers are investigated by means of high resolution thermography. Thermal properties of the devices emitting in the 650 nm and 808 nm wavelength ranges are compared. The different versions of the heterostructure design are analyzed. The results show a lowering of active region temperature for diode lasers with asymmetric heterostructure scheme with reduced quantum well distance from the heterostructure surface (and the heat sink). Optimization of technological processes allowed for the improvement of the device performance, e.g. reduction of solder non-uniformities and local defect sites at the mirrors which was visualized by the thermography.     

Synthesis of Fe3O4 nanocubes anchored in MgCo2O4 nanoneedle arrays for flexible all-solid-state asymmetric supercapacitor

The design of novel heterostructure with multifunctional characteristics is of great technical significance for the development of new energy storage devices. However, the lower conductivity of metal oxides and the accumulation caused by irreversible phase transition after multiple cycles are the main reasons for the low specific capacitance and cycle life. Herein, we synthesized bimetallic oxide MgCo₂O₄ nanoneedles with a spinel structure, and firmly anchored Fe₃O₄ nanocubes on MgCo₂O₄ nanoneedles by ion-exchange strategy. Thanks to the constructed heterostructure of nanoneedles/nanocubes, the introduction of Fe₃O₄ effectively improves the electron transport path in MgCo₂O₄ during repeated charging and discharging, and increases the effective activation sites involved in electron transfer. As a result, a higher specific capacitance of 1648 F g^?1 at 1 A g^?1 and an ultra-long cycle life of 78.6% capacitance retention after 6000 continuous charge/discharge cycles are obtained. A flexible all-solid-state asymmetric supercapcitor assembled with MgCo₂O₄-Fe₃O₄ as positive electrode and AC as negative electrode can deliver an ultra-high energy density of 78 Wh kg^?1 and maximum power density of 1.2 kW kg^?1, as well as extraordinary capacitive retention of 75.2% after 10,000 cycles. These excellent properties reveal the potential and application value of MgCo₂O₄-Fe₃O₄ in the development of high-performance supercapacitors.     

Influence of van der waals heterostructures of 2D materials on catalytic performance of ZnO and its applications in energy: A review

Recently, photocatalysis has received huge attention in order to overcome energy crisis worldwide. Many semiconductors, potential schemes and hierarchies have come to light during past few decades to fabricate efficient catalysts however, among all these methods heterostructures have taken the world by surprise. With the advancement in post-graphene 2D materials, van der Waals heterostructures have come to light exploring enhancement in photocatalysis. During a very short period a number of ZnO-based van der Waal heterostructures have taken the limelight in the field of photocatalysis. First principles calculations and DFT approach towards the heterostructures of GeC, GaN, WSe₂, WS₂ and other layered 2D materials unleased a series of properties and facts for the provision of enhanced catalysis. Reduction in bandgap of ZnO has also been observed which widens the pathways towards visible light irradiation. However, energy applications of zinc oxide are also fascinating feature as it can serve as a photoanode to replace TiO₂. Whereas the famous hydrogen production, batteries and solar cells have also been fabricated by the use of this semiconductor.