Epitaxial TiC/SiC multilayers were grown by magnetron sputtering at a substrate temperature of 550 °C, where SiC is normally amorphous. The epitaxial TiC template induced growth of cubic SiC up to a thickness of ～2 nm. Thicker SiC layers result in a direct transition to growth of the metastable amorphous SiC followed by renucleation of nanocrystalline TiC layers.
The DC, RF and noise characteristics of InGaP/GaAs heterojunction bipolar transistors (HBTs) with different base layer widths and δ‐doped layer in the collector were investigated. Analysis of the RF and noise characteristics revealed that the high frequency noise of these HBTs is reduced due to cross‐correlation of shot noise sources and Coulomb blockade from accumulated charge. The measured noise performance is in a good agreement with the HICUM L2 compact model [M. Schroter, IEICE Trans. Electron. E88‐C , 1098 (2005)] when correlated shot noise sources with Fano factor for collector shot noise are included.
In this Letter we demonstrate that hydrogen‐terminated porous silicon (PSi) layers and powders can serve as highly efficient reductive templates for noble metal salts. The reduction results in metal nanoparticle (NP) formation in the pores of PSi. Gold NP formation has been monitored in‐situ by measuring the plasmon resonance response. Pt NPs, formed in the PSi matrix, were investigated by transmission electron microscopy and energy‐dispersive X‐ray analysis. Furthermore, hybrid Pt/PSi nanocomposites exhibit a high catalytic activity for CO oxidation.
Here, we demonstrate the synthesis of graphene on Ag foil by an atmospheric‐pressure (AP) chemical vapor deposition (CVD) process as tarnish‐resistant coating. Synthesis of a continuous graphene film on Ag foil is achieved using the solid camphor as carbon precursor in a gas mixture of Ar and H2. Tarnishing of the Ag surface through sulfidation is investigated with and without coating of the graphene film. It is observed that the bare Ag surface immediately reacts with sulfur vapor to turn black, whereas graphene coating passivates the Ag surface robustly and thereby restrains the sulfur reaction to preserve from tarnishing. Our findings show that a large‐area graphene film can be effectively grown on Ag surface by a CVD process as a tarnish and corrosion resistance barrier.
The metastability of the bixbyite‐ and corundum‐type In2O3 polymorphs up to 33 GPa (at room temperature) is shown. While compressed (in diamond anvil cells) and laser‐heated, both polymorphs undergo a phase transition to the Rh2O3‐II‐type structure (space group Pbcn, No. 60). The direct transition from bixbyite to Rh2O3‐II structure has not yet been observed for any other oxide.
We demonstrate by a Monte Carlo simulation that the reflection of quasi‐ballistically accelerated electrons at the interfaces of an In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As double‐heterojunction structure is able to generate current oscillations at frequencies in the THz range. The possibility of taking advantage of this mechanism to generate THz signals has been demonstrated in structures with well dimension close to the electron ballistic transport length in In0.53Ga0.47As.
Graphene, the two‐dimensional form of carbon presents outstanding electronic and transport properties. This gives hope for the development of applications in nanoelectronics. However, for industrial purpose, graphene has to be supported by a substrate. We focus here on the graphene‐on‐SiC system to discuss how the SiC substrate interacts with the graphene layer and to show the effect of the interface on graphene atomic and electronic structures.
We demonstrate the monolithic integration of a microstructured organic photodiode with a planar optical stripe waveguide. The manufacturing of this waveguide‐integrated organic photodiode is based on an UV photolithography process. The integration of photodiodes with optical waveguides represents an essential building block in the field of optoelectronic‐photonic integrated circuits.
Bi2Te3 doped p‐type Pb0.13Ge0.87Te samples were prepared by hot pressing. We report on very high power factor values of ～30 μW/cm K2 at 500 °C, as were determined from Seebeck coefficient and electrical resistivity measurements. From dilatometric characterization, the phase transition from the low temperature rhombohedral to the high temperature cubic NaCl structures, takes place at 373 °C. This transition is accompanied by a continuous and gradual change of the lattice parameters, as was observed by hot stage XRD, suggesting a good mechanical durability upon thermal cycling and operating in large thermal gradients.
The fabrication of titania nanostructures with hierarchical order of different structural levels is investigated. The nanostructures are prepared with a diblock‐copolymer assisted sol–gel process. By iterative spin‐coating of the solution onto silicon substrates a thin polymer‐nanocomposite film is deposited and transformed to purely anatase titania nanostructures via calcination. In total, this procedure is repeated three times on top of the substrate. The approach is monitored with grazing incidence small angle X‐ray scattering after each fabrication step. With scanning electron microscopy the final hierarchical structure is imaged. From the characterization different structural levels are clearly identified.
Angle‐resolved photoemission spectroscopy (ARPES) and X‐ray photoemission spectroscopy have been used to characterise epitaxially ordered graphene grown on copper foil by low‐pressure chemical vapour deposition. A short vacuum anneal to 200 °C allows observation of ordered low energy electron diffraction patterns. High quality Dirac cones are measured in ARPES with the Dirac point at the Fermi level (undoped graphene). Annealing above 300 °C produces n‐type doping in the graphene with up to 350 meV shift in Fermi level, and opens a band gap of around 100 meV.
The crystallization process of mechanically alloyed Fe75Zr25 metallic glasses is investigated by means of both thermo‐magnetization and in situ neutron powder thermo‐diffraction experiments in the temperature range 300–1073 K. It was found that the crystallization takes place in a two‐step process, involving firstly the appearance of metastable Fe and Fe2Zr crystalline phases between 880 K and 980 K, and a subsequent polymorphic transformation into Fe3Zr above 980 K. These findings explain the anomalous magnetization vs. temperature behaviour on heating–cooling cycles.
We report enhanced anomalous photovoltaic effects and switchable photovoltage generation in pure and Pr–Cr co‐doped BiFeO3 (BFO) nanotubes (NTs). Influence of metal doping on short circuit current, open circuit voltage, power conversion efficiency and fill factor are investigated. The power conversion efficiency of pure BFO NTs (～0.207%) is found to be enhanced by several orders of magnitude in comparison with the reported bulk effect. Pr‐doped NTs provide highest values of power conversion efficiency (～0.5%).
Metallic single‐walled carbon nanotubes (m‐SWCNTs) with excellent conductivity and transparency are considered to be eminent electrode materials. However, it still remains a challenge to separate m‐SWCNTs by their diameters. As reported in this Letter, by effective purification treatment of SWCNTs, we succeeded in achieving diameter separation of m‐SWCNTs using gel column chromatography. TEM and Raman characterizations revealed that metal catalysts and amorphous carbon on tube surfaces were largely reduced, which contributed to the diameter separation of m‐SWCNTs.
Osmium diboride has been known for some time as a low compressibility material and a superhard material. It is suitable for hard coating applications. It is also a superconductor below 2.1 K. Using first‐principles calculations, the author investigated the geometry of its Fermi surface (FS) and calculated the related physical quantities. The theoretical results are used to predict the frequencies of the Shubnikov–de Haas quantum oscillations. Comparison with recent measurements of the magneto‐resistance oscillations in osmium diboride is made.
We present experimental and theoretical evidence of the role played by the spin–orbit coupling in the electronic structure of a pseudomorphic Au monolayer on Nb(001) substrate. The bands found with the help of the angle‐resolved ultraviolet photoelectron spectroscopy (ARUPS) are compared with those obtained from ab initio self‐consistent calculations by the VASP and WIEN2k codes. The slab calculations are performed including geometric relaxation and using both the generalized‐gradient (GGA) and local‐density (LDA) approximations for the exchange–correlation energy. The dispersions and energy positions of the calculated bands agree with the experimentally determined band structure only if the LDA is used and the spin–orbit coupling is included. Therefore, both the structure relaxation and spin–orbit coupling are essential in understanding the electronic structure of the Au/Nb(001) system.
Electric control of magnetism is demonstrated in a multiferroic metal–organic framework with a perovskite structure. A moderate electric field of a few kV/cm applied during the cooling process is able to cause a large (more than 50%) change of the magnetization at low temperature. This significant magnetoelectric effect is ascribed to the electric field manipulation of orientation of hydrogen bonds that modify the superexchange interaction between metal ions.
We report on wet etching of photomodified regions in crystalline sapphire using KOH solution. Tightly focused femtosecond laser pulses (150 fs at 800 nm wavelength) were used to create void structures enclosed in an amorphised sapphire shell inside the bulk of a crystalline host. The diameter of the amorphous regions can be controlled by pulse energy and was typically 0.5–1.5 µm. The etching rate depends on the distance between adjacent irradiation spots, pulse energy, concentration of etchant and ultrasonic agitation.
