Crystals — Open Access Journal

We present preliminary results on minority carrier traps in as-grown n-type 4H–SiC Schottky barrier diodes. The minority carrier traps are crucial for charge trapping and recombination processes. In this study, minority carrier traps were investigated by means of minority carrier transient spectroscopy (MCTS) and high-resolution Laplace-MCTS measurements. A single minority carrier trap with its energy level position at E_v + 0.28 eV was detected and assigned to boron-related defects. Full article

In this work, we effectuated the numerical simulations of the phase dynamics of an array of Josephson junctions taking into account the capacitive coupling between the neighboring junctions and the diffusion current in the stack. We observed that, if we increase the coupling and the dissipation parameters, the IV characteristic changes qualitatively from the IV characteristics studied before. For currents greater than the critical one, we obtained an additional branch in the IV characteristics. This branch is characterized by a lower voltage than the outermost one. Moreover, we obtained an additional charging of the superconducting layers in the IV region for currents greater than the critical one. We studied the time evolution of this charging by the means of Fast Fourier Transform. We proved that the charge density wave associated with this charging has a complex spectral structure. In addition, we analyzed the behavior of the system for different boundary conditions, appropriate to different experimental setups. Full article

The results presented in this paper, based on the powder X-ray diffraction technique followed by Rietveld analyses, are devoted to the mechanism of silver incorporation in biphasic calcium phosphates. Results were confirmed by SEM observation. Samples were synthesized via the sol-gel route, followed by heat treatments. Two incorporation sites were highlighted: Ca²⁺ replacement by Ag⁺ into the calcium phosphates (HAp: hydroxyapatite and β-TCP: tricalcium phosphate), and the other as metallic silver Ag° nanoparticles (formed by autogenous reduction). The samples obtained were thus nanocomposites, written Ag°/BCP, composed of closely-mixed Ag° particles of about 100 nm at 400 °C (which became micrometric upon heating) and calcium phosphates, themselves substituted by Ag⁺ cations. Between 400 °C and 700 °C the cationic silver part was mainly located in the HAp phase of the composition Ca_10−xAg_x(PO₄)₆(OH)_2−x (written Ag⁺: HAp). From 600 °C silver cations migrated to β-TCP to form the definite compound Ca₁₀Ag(PO₄)₇ (written Ag⁺: TCP). Due to the melting point of Ag°, the doping element completely left our sample at temperatures above 1000 °C. In order to correctly understand the biological behavior of such material, which is potentially interesting for biomaterial applications, its complex doping mechanism should be taken into consideration for subsequent cytotoxic and bacteriologic studies. Full article

: Spherical Fe₅₀Ni₅₀ alloy powders were fabricated via a novel route based on in-situ interface de-wetting between liquid Fe-Ni alloy and alumina. The obtained Fe₅₀Ni₅₀ alloy particles exhibit very good spherical shape according to SEM images. Furthermore, the cross-sectional SEM images show that there are no pores and bulk inclusions in the internal region of the spherical particles. The XRD results show a trace amount of the impurity alumina phase appearing in taenite phase. The size distribution agreed well with the SEM observation confirms that the alumina powders successfully segregated pre-alloy powders. As an incidental benefit, the surface alumina particles were treated as the electrical insulation coatings. The magnetic character shows that spherical Fe₅₀Ni₅₀ powders exhibit a good soft magnetic property even though with a slightly decreasing of saturation magnetization due to non-magnetic coatings. Our strategies provide a method to in-situ fabricate insulation coated Fe-Ni spherical alloy powders as magnetic powder core. Full article

Single crystals of PrNiO₃ were grown under an oxygen pressure of 295 bar using a unique high-pressure optical-image floating zone furnace. The crystals, with volume in excess of 1 mm³, were characterized structurally using single crystal and powder X-ray diffraction. Resistivity, specific heat, and magnetic susceptibility were measured, all of which evidenced an abrupt, first order metal-insulator transition (MIT) at ~130 K, in agreement with previous literature reports on polycrystalline specimens. Temperature-dependent single crystal diffraction was performed to investigate changes through the MIT. Our study demonstrates the opportunity space for high fugacity, reactive environments for single crystal growth specifically of perovskite nickelates but more generally to correlated electron oxides. Full article

Herein, we describe the synthesis and single crystal X-ray diffraction characterization of several Pb(II) complexes using Schiff base hydrazido-based ligands and different counterions (NO₃⁻, I⁻ and ClO₄). In the three complexes reported in this work, the lead(II) metal exhibits a high coordination number (n > 8) and thus it is apparently not involved in tetrel bonding interactions. Moreover, the aromatic ligands participate in noncovalent interactions that play an important role in the formation of several supramolecular assemblies in the solid state of the three Pb(II) complexes. These assemblies have been analyzed by means of Hirshfeld surface analysis and DFT calculations. Full article

The cubic intermetallic compound Sm${}_3$Co${}_4$Ge${}_{13}$ (space group $Pm\overline{3}n$) possesses a cage-like structure composed of Ge and displays an antiferromagnetic transition at $T_N\approx$ 6 K in magnetization, $M\left(T\right)$, specific heat, $C_p\left(T\right)$ and in thermal conductivity, $\kappa \left(T\right)$. The magnetic transition at $T_N$ is observed to be robust against applied magnetic fields up to 9 T. From the analysis of specific heat, a Sommerfeld coefficient $\gamma$ = 80(2) mJ/mol-Sm K${}^2$ is estimated. The magnetic entropy released at $T_N$ is estimated as lower than that of a doublet, R ln(2). A positive Seebeck coefficient is observed for the thermopower, $S\left(T\right)$. Photoemission spectroscopy reveals distinct electronic character of the near-$E_{\mathrm{F}}$ valence band states arising out of Co($3d$)-Sm($4f$) hybridization and Sm($4f$) electron correlation. The unusual field-independent features in magnetization, specific heat and electrical transport is an indication of the significant correlation between f and d wave functions. Full article

Ice cream is a complex multi-phase structure and its perceived quality is closely related to the small size of ice crystals in the product. Understanding the quantitative coarsening behaviour of ice crystals will help manufacturers optimise ice cream formulations and processing. Using synchrotron X-ray tomography, we measured the time-dependent coarsening (Ostwald ripening) of ice crystals in ice cream during cooling at 0.05 °C/min. The results show ice crystal coarsening is highly temperature dependent, being rapid from ca. −6 to −12 °C but significantly slower at lower temperatures. We developed a numerical model, based on established coarsening theory, to calculate the relationship between crystal diameter, cooling rate and the weight fraction of sucrose in solution. The ice crystal diameters predicted by the model are found to agree well with the measured values if matrix diffusion is assumed to be slowed by a factor of 1.2 due to the presence of stabilizers or high molecular weight sugars in the ice cream formulation. Full article

A 2.45 GHz microwave-plasma chemical-vapor deposition (MPCVD) reactor was designed and built in-house by collaborating with Guangdong TrueOne Semiconductor Technology Co., Ltd. A cylindrical cavity was designed as the deposition chamber and a circumferential coaxial-mode transformer located at the top of the cavity was adopted as the antenna. Two quartz-ring windows that were placed far away from the plasma and cooled by water-cooling cavity walls were used to affix the antenna to the cavity and act as a vacuum seal for the reactor, respectively. This design improved the sealing and protected the quartz windows. In addition, a numerical simulation was proposed to predict the electric-field and plasma-density distributions in the cavity. Based on the simulation results, a microwave-plasma reactor with TM₀₂₁ mode was built. The leak rate of this new reactor was tested to be as low as 1 × 10⁻⁸ Pa·m³·s⁻¹, and the maximal microwave power was as high as 10 kW. Then, single-crystal diamond films were grown with the morphology and crystalline quality characterized by an optical microscope, atomic force microscope (AFM), Raman spectrometer, photoluminescence (PL) spectrometer, and high-resolution X-ray diffractometer. It was shown that the newly developed MPCVD reactor can produce diamond films with high quality and purity. Full article

The ruthenium carbonyl compounds, Ru(bpy)(CO)₂X₂ (X = Cl, Br or I) act as neutral halogen bond (XB) acceptors when co-crystallized with 1,4-diiodotetrafluoro-benzene (DITFB). The halogen bonding strength of the Ru-X⋅⋅⋅I halogen bonds follow the nucleophilic character of the halido ligand. The strongest halogen bond occurs between the chlorido ligand and the iodide atoms of the DITFB. All three halogen bonded complexes form polymeric assemblies in the solid state. In Ru(bpy)(CO)₂Cl₂⋅DITFB (1) and in Ru(bpy)(CO)₂Br₂⋅DITFB (2) both halido ligands are halogen bonded to only one DITFB donor. In Ru(bpy)(CO)₂I₂⋅DITFB (3) only one of the halido ligands is involved in halogen bonding acting as ditopic center for two DITFB donors. The polymeric structures of 1 and 2 are isomorphic wave-like single chain systems, while the iodine complexes form pairs of linear chains attached together with weak F⋅⋅⋅O≡C interactions between the closest neighbors. The stronger polarization of the iodide ligand compared to the Cl or Br ligands favors nearly linear C-I⋅⋅⋅I angles between the XB donor and the metal complex supporting the linear arrangement of the halogen bonded chain. Full article

In this work, the resistive switching characteristics of resistive random access memories (RRAMs) containing Sm₂O₃ and V₂O₅ films were investigated. All the RRAM structures made in this work showed stable resistive switching behavior. The High-Resistance State and Low-Resistance State of Resistive memory (R_HRS/R_LRS) ratio of the RRAM device containing a V₂O₅/Sm₂O₃ bilayer is one order of magnitude higher than that of the devices containing a single layer of V₂O₅ or Sm₂O₃. We also found that the stacking sequence of the Sm₂O₃ and V₂O₅ films in the bilayer structure can affect the switching features of the RRAM, causing them to exhibit both bipolar resistive switching (BRS) behavior and self-compliance behavior. The current conduction mechanisms of RRAM devices with different film structures were also discussed. Full article

Topological insulators (TIs) have a bulk bandgap and gapless edge or surface states that host helically spin-polarized Dirac fermions. Theoretically, it has been predicted that gapless states could also be formed along dislocations in TIs. Recently, conductivity measurements on plastically deformed bismuth antimony (Bi_1−xSb_x) TIs have revealed excess conductivity owing to dislocation conduction. For further application of them, fundamental study on dislocations in TIs is indispensable. Dislocations controlled based on fundamental studies could potentially be useful not only for experimental investigations of the dislocation properties but also for diverse device applications. In the present study, Bi_1−xSb_x TI single crystals were fabricated by a zone-melting method. The crystals were plastically deformed at room temperature. The resultant dislocations were observed by transmission electron microscopy (TEM). It was found that high-density dislocations with the Burgers vector satisfying the condition for the formation of gapless states were successfully introduced. The dislocations were mostly of edge type with lengths on the order of more than a few micrometers. Full article

The crystal structure of the polymeric spin crossover compound Fe(3,4-dimethyl-pyridine)₂[Ag(CN)₂]₂ has been solved and its temperature dependence followed by means of single-crystal and powder X-ray diffraction. This compound presents a two-step spin transition with relatively abrupt steps centred at ca. 170 K and 145 K and a plateau at around 155 K. The origin of the two-step transition is discussed in light of these structural studies. The observations are compatible with a mostly disordered state between the two steps, consisting of mixing of high-spin and low-spin species, while weak substructure reflections in the mixed phase could indicate some degree of long-range order of the high-spin and low-spin sites. Full article

Van der Waals heterojunctions based on transition metal dichalcogenides (TMDs) show promising potential in optoelectronic devices, due to the ultrafast separation of photoexcited carriers and efficient generation of the photocurrent. Herein, this study demonstrated a high-responsivity photovoltaic photodetector based on a MoTe₂/MoSe₂ type-II heterojunction. Due to the interlayer built-in potential, the MoTe₂/MoSe₂ heterojunction shows obvious photovoltaic behavior and its photoresponse can be tuned by the gate voltage due to the ultrathin thickness of the heterojunction. This self-powered photovoltaic photodetector exhibits an excellent responsivity of 1.5 A W⁻¹, larger than previously reported TMDs-based photovoltaic photodetectors. Due to the high-efficiency separation of electron-hole pairs and ultrafast charge transfer, the light-induced on/off ratio of current switching is larger than 10⁴ at zero bias, and the dark current is extremely low (~10⁻¹³ A). These MoTe₂/MoSe₂ type-II heterojunctions are expected to provide more opportunities for future nanoscale optoelectronic devices. Full article

Conventional display applications of liquid crystals utilize thin layers of mesogenic materials, typically less than 10 µm. However, emerging non-display applications will require thicker, i.e., greater than 100 µm, layers of liquid crystals. Although electro-optical performance of relatively thin liquid crystal cells is well-documented, little is known about the properties of thicker liquid crystal layers. In this paper, the electro-optical response of dual-frequency nematic liquid crystals is studied using a broad range (2–200 µm) of the cell thickness. Two regimes of electro-optical switching of dual-frequency nematics are observed and analyzed. Full article

We show that topological interface mode can emerge in a one-dimensional elastic string system which consists of two periodic strings with different band topologies. To verify their topological features, Zak-phase of each band is calculated and reveals the condition of topological phase transition accordingly. Apart from that, the transmittance spectrum illustrates that topological interface mode arises when two topologically distinct structures are connected. The vibration profile further exhibits the non-trivial interface mode in the domain wall between two periodic string composites. Full article

This paper aims to understand the effect of local recrystallization (RX) on the low cycle fatigue fracture of a turbine-blade single crystal nickel-based superalloy. The fatigue life of the single crystal superalloy was evidently decreased by local recrystallization. In single crystal specimens, casting porosity is the preferential fatigue crack initiation site, which is followed by crystallographic crack propagation along one or several octahedral slip planes. For all RX specimens, fatigue cracks preferred to initiate from local recrystallized grains and propagated through the recrystallized grains in a transgranular manner, followed by crystallographic crack propagation in the substrate single crystal superalloy. Moreover, fatigue tests indicated that locally recrystallized specimens exhibited temperature dependent fracture modes, i.e., transgranular cracking dominated at 550 °C, whereas intergranular cracking was preferred at 850 °C. Evident oxidation of fracture surfaces and strength degradation of grain boundaries at 850 °C was evidenced by scanning electronic microscopic observations. The present study emphasized the need to evaluate the effect of recrystallization according to the working conditions of turbine components, i.e., the local temperature. Full article

With the growing demand for driving safety and convenience, Head-Up Displays (HUDs) have gained more and more interest in recent years. In this paper, we propose a HUD system with the ability to adjust the relative brightness of ambient light and virtual information light. The key components of the system include a cholesteric liquid crystal (CLC) film, a geometric phase (GP) liquid crystal lens, and a circular polarizer. By controlling the voltage applied to the GP lens, the contrast ratio of the virtual information light to ambient light could be continuously tuned, so that good visibility could always be obtained under different driving conditions. Full article

Low emissivity glass (low-e glass), which is often used in energy-saving buildings, has high thermal resistance and visible light transmission. Heavily doped wide band gap semiconductors like aluminum-doped zinc oxide (AZO) and tin-doped indium oxide (ITO) have these properties, especially after certain treatment. In our experiments, in-line sputtered AZO and ITO bilayer (AZO/ITO) films on glass substrates were prepared first. The deposition of AZO/ITO films was following by annealing in hydrogen/nitrogen (H₂/N₂) plasma with different N₂ flows. The structure and optical and electrical properties of AZO/ITO films were surveyed. Experiment results indicated that N₂ flow in H₂/N₂ plasma annealing of AZO/ITO films slightly modified the structure and electrical properties of AZO/ITO films. The X-ray diffraction peak corresponding to zinc oxide (002) crystal plane slightly shifted to a higher angle and its full width at half maximum decreased as the N₂ flow increased. The electrical resistivity and the emissivity reduced for the plasma annealed AZO/ITO films when the N₂ flow was raised. The optimum H₂/N₂ gas flow was 100/100 for plasma annealed AZO/ITO films in this work for low emissivity application. The emissivity and average visible transmittance for H₂/N₂ = 100/100 plasma annealed AZO/ITO were 0.07 and 80%, respectively, lying in the range of commercially used low emissivity glass. Full article