Single Crystalline Materials Research Articles

The photoelectrochemical exploration of multifunctional TiO2 mesocrystals and its enzyme-assisted biosensing application.

Mesocrystals, as the assemblies of crystallographically oriented nanocrystals, have single-crystal-like atom structures and scattering features but with much higher porosity than single-crystalline materials, making them promising substitutes for conventional single crystals in photoelectrochemical application. As a proof-of-concept, a series of photoelectrochemical tests were investigated to understand the influence of the differences between them on photoelectrochemical activity. Expectedly, comparing with TiO2 single crystals, TiO2 mesocrystals demonstrated higher photoelectrochemical capability, which provides unique new opportunities for materials design in the fields of solar-energy conversion and catalysis. Therefore, an elegant photoelectrochemical biosensing platform was firstly developed by virtue of carbon nanohorns with outstanding electrical conductivity support multifunctional TiO2 mesocrystals to accelerate the transfer of photogenerated electrons, and then horseradish peroxidase was introduced through the immune recognition reaction for enzyme-assisted in situ generating CdS QDs. The multiplex amplification strategy successfully achieved the ultrasensitive detection of α-fetoprotein antigen. Promisingly, the successful application of multiplex amplification strategy affords a rational and practical consideration for the fabrication of new and high-performance photoelectrochemical sensing devices.

Spin-related thermoelectric conversion in lateral spin-valve devices with single-crystalline Co2FeSi electrodes

We demonstrate the conversion between a heat current and a spin current in Cu-based lateral spin valves (LSVs) with single-crystalline Co2FeSi (CFS) electrodes. We can observe the thermally induced spin injection from CFS into Cu resulting from the spin-dependent Seebeck effect, and the heat current generated by the spin-dependent Peltier effect can be detected even in the LSV structures. This study is an important step toward understanding heat-spin conversion in single-crystalline materials with various electronic band structures.

Evaluation of the Tauc method for optical absorption edge determination: ZnO thin films as a model system

One of the most frequently used methods for characterizing thin films is UV–Vis absorption. The near-edge region can be fitted to a simple expression in which the intercept gives the band-gap and the fitting exponent identifies the electronic transition as direct or indirect (see Tauc et al., Phys. Status Solidi 15, 627 (1966); these are often called “Tauc” plots). While the technique is powerful and simple, the accuracy of the fitted band-gap result is seldom stated or known. We tackle this question by refitting a large number of Tauc plots from the literature and look for trends. Nominally pure zinc oxide (ZnO) was chosen as a material with limited intrinsic deviation from stoichiometry and which has been widely studied. Our examination of the band gap values and their distribution leads to a discussion of some experimental factors that can bias the data and lead to either smaller or larger apparent values than would be expected. Finally, an easily evaluated figure-of-merit is defined that may help guide more accurate Tauc fitting. For samples with relatively sharper Tauc plot shapes, the population yields Eg(ZnO) as 3.276 ± 0.033 eV, in good agreement with data for single crystalline material.

Synthesis and structural characterization of new bismuth (III) nano coordination polymer: A precursor to produce pure phase nano-sized bismuth (III) oxide

A novel bismuth (III) nano coordination polymer, {[Bi (pcih)(NO3)2]⋅MeOH}n (1), (“pcih” is the abbreviations of 2-pyridinecarbaldehyde isonicotinoylhydrazoneate) were synthesized by a sonochemical method. The new nano-structure was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray powder diffraction, elemental analyses and IR spectroscopy. Single crystalline material was obtained using a heat gradient applied to a solution of the reagents. Compound 1 was structurally characterized by single crystal X-ray diffraction. The determination of the structure by single crystal X-ray crystallography shows that the complex forms a zig–zag one dimensional polymer in the solid state and the coordination number of BiIII ions is seven, (BiN3O4), with three N-donor and one O-donor atoms from two “pcih” and three O-donors from nitrate anions. It has a hemidirected coordination sphere. The supramolecular features in these complexes are guided and controlled by weak directional intermolecular interactions. The chains interact with each other through π–π stacking interactions creating a 3D framework. After thermolysis of 1 at 230 °C with oleic acid, pure phase nano-sized bismuth (III) oxide was produced. The morphology and size of the prepared Bi2O3 samples were further observed using SEM.

Quantitative experimental determination of the solid solution hardening potential of rhenium, tungsten and molybdenum in single-crystal nickel-based superalloys

The solid-solution hardening potential of the refractory elements rhenium, tungsten and molybdenum in the matrix of single-crystal nickel-based superalloys was experimentally quantified. Single-phase alloys with the composition of the nickel solid-solution matrix of superalloys were cast as single crystals, and tested in creep at 980°C and 30–75MPa. The use of single-phase single-crystalline material ensures very clean data because no grain boundary or particle strengthening effects interfere with the solid-solution hardening. This makes it possible to quantify the amount of rhenium, tungsten and molybdenum necessary to reduce the creep rate by a factor of 10. Rhenium is more than two times more effective for matrix strengthening than either tungsten or molybdenum. The existence of rhenium clusters as a possible reason for the strong strengthening effect is excluded as a result of atom probe tomography measurements. If the partitioning coefficient of rhenium, tungsten and molybdenum between the γ matrix and the γ′ precipitates is taken into account, the effectiveness of the alloying elements in two-phase superalloys can be calculated and the rhenium effect can be explained.

Magnetic materials. Tilt engineering of spontaneous polarization and magnetization above 300 K in a bulk layered perovskite.

Crystalline materials that combine electrical polarization and magnetization could be advantageous in applications such as information storage, but these properties are usually considered to have incompatible chemical bonding and electronic requirements. Recent theoretical work on perovskite materials suggested a route for combining both properties. We used crystal chemistry to engineer specific atomic displacements in a layered perovskite, (Ca(y)Sr(1- y))(1.15)Tb(1.85)Fe2O7, that change its symmetry and simultaneously generate electrical polarization and magnetization above room temperature. The two resulting properties are magnetoelectrically coupled as they arise from the same displacements.

Tilting toward two properties

Magnetic Materials Opposing electronic and symmetry constraints can make it difficult to combine some pairs of material properties in a single crystalline material. Magnetization and electrical polarization are such a pair, but their combination could be useful for applications such as magnetoelectric information storage. Pitcher et al. now show that careful design of chemical substitutions in a layered perovskite are both electrically polar and weakly ferromagnetic at temperatures up to 330 K. Science , this issue p. [420][1] [1]: /lookup/doi/10.1126/science.1262118

Indium oxide—a transparent, wide-band gap semiconductor for (opto)electronic applications

The present review takes a semiconductor physics perspective to summarize the state-of-the art of In2O3 in relation to applications. After discussing conventional and novel applications, the crystal structure, synthesis of single-crystalline material, band-structure and optical transparency are briefly introduced before focussing on the charge carrier transport properties. The issues of unintentional n-type conductivity and its likely causes, the surface electron accumulation, and the lack of p-type conductivity will be presented. Intentional doping will be demonstrated to control the electron concentration and resistivity over a wide range, but is also subject to compensation. The control of the surface accumulation in relation to Schottky and ohmic contacts will be demonstrated. In the context of scattering mechanisms, the electron mobility and its limits will be discussed. Finally, the Seebeck coefficient and its significance will be shown, and ferromagnetic doping of In2O3 will be critically discussed. With this overview most if not all ingredients for the use of In2O3 as semiconductor material in novel or improved conventional devices will be given.

Influence of Solid Solution Hardening on Creep Properties of Single-Crystal Nickel-Based Superalloys

Improving the creep resistance of the matrix by alloying with refractory elements is a major strengthening effect in nickel-based superalloy with rhenium as one of the most effective elements. In this work, the influence of rhenium on creep properties of single-phase single crystals with varying rhenium content and matrix-near composition is investigated. The use of single-crystalline material leads to very distinct results which are not deteriorated by grain boundary effects. So the strengthening effect can be solely attributed to the alloying element rhenium and is quantified for the first time. By comparing the creep strength of two matrix compositions with the corresponding single-crystal superalloys using the threshold stress concept, the potential of creep strengthening of the matrix in two-phase single-crystal alloys is quantified.

Microstructure-dependent deformation behaviour of bcc-metals – indentation size effect and strain rate sensitivity

In this work, the indentation size effect and the influence of the microstructure on the time-dependent deformation behaviour of body-centred cubic (bcc) metals are studied by performing nanoindentation strain rate jump tests at room temperature. During these experiments, the strain rate is abruptly changed, and from the resulting hardness difference the local strain rate sensitivity has been derived. Single-crystalline materials exhibit a strong indentation size effect; ultrafine-grained metals have nearly a depth-independent hardness. Tungsten as a bcc metal shows the opposite behaviour as generally found for face-centered cubic metals. While for UFG-W only slightly enhanced strain rate sensitivity was observed, SX-W exhibits a pronounced influence of the strain rate on the resulting hardness at room temperature. This is due to the effects of the high lattice friction of bcc metals at low temperatures, where the thermally activated motion of screw dislocations is the dominating deformation mechanisms, which causes the enhanced strain rate sensitivity. For the SX-materials, it was found that the degree of the indentation size effect directly correlates with the homologous testing temperature and thus, the material specific parameter of the critical temperature Tc. However, for the resultant strain rate sensitivity no depth-dependent change was found.

Sonochemical synthesis of tri-nuclear lead(II)-azido nano rods coordination polymer with 3,4,7,8-tetramethyl-1,10-phenanthroline (tmph): Crystal structure determination and preparation of nano lead(II) oxide

Preparation of rod-shaped nanostructure of a new 1D lead(II) tri nuclear coordination polymer containing the Pb2-(μ-N3)2 and Pb2-(μ-N3)(NO3) motifs [Pb3(tmph)4(μ-N3)5(μ-NO3)]n (1) where “tmph” is the abbreviation of 3,4,7,8-tetramethyl-1,10-phenanthroline, using a sonochemical method is described. The new coordination polymer is characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), elemental analysis and infrared spectroscopy. The single crystalline material is obtained using a heat gradient applied to a solution of the reagents. Single-crystal XRD analysis indicates three different lead(II) centers in the structure with coordination numbers of seven and eight with a holo and hemidirected coordination geometry. They also show that the chains interact with each other through π–π stacking interactions creating a 3D framework. PbO nanoparticles are obtained by thermolysis of 1 at 180°C with oleic acid as a surfactant. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirm formation of PbO particles around 10–20nm.

Multiferroic hexagonal ferrites (h-RFeO3,R=Y,Dy-Lu): a brief experimental review

Hexagonal ferrites ( h - RFeO3, R = Y , Dy - Lu ) have recently been identified as a new family of multiferroic complex oxides. The coexisting spontaneous electric and magnetic polarizations make h - RFeO3rare-case ferroelectric ferromagnets at low temperature. Plus the room-temperature multiferroicity and the predicted magnetoelectric effect, h - RFeO3are promising materials for multiferroic applications. Here we review the structural, ferroelectric, magnetic and magnetoelectric properties of h - RFeO3. The thin film growth is also discussed because it is critical in making high quality single crystalline materials for studying intrinsic properties.

Invited: Metal-Semiconductor-Metal Photocurrent Chip for Hydrogen Peroxide and Biomolecular Sensing with Chemiluminescence

Photodetectors are generally the most promising, representative and widely-used type of detectors, and the applications of photodetectors are quite extensively[1-3]. Basically photodetectors are made of photosensitive elements which are able to turn the light signal into electrical signal. Nowadays, the detecting wavelength region is very broad and can be classified into infrared, visible light and ultraviolet zone; furthermore, the applications of each region are manifold especially in visible light region. Additionally owing to the nature of fast responding speed, it promises photodetectors an advantageous future in biomedical sensing territory[4-5]. This study is focus on fabrication method of the flexible[6-8] photodetectors and application to biomolecule sensing through luminescence. The photosensitive element is based on single crystalline silicon semiconductor material which is treated with chemical etching process to achieve pliable characteristic[9]. Then, the metal-semiconductor-metal[10-14]structural flexible photodetectors are achieved after integrated with simple fabricating processes. In detail, the accomplished devices are handled with immobilization steps to fix the target enzyme which is able to catalyze the luminescent reaction (Fig.1). Owing to only extremely stable sensor for biomedical use, it is necessary to ensure the operation function at any crucial conditions. In this study, we provide a portable biomolecule sensor with outstanding flexible characteristic and high sensitivity and it exhibits illustrious stable consequence in various situations. Figure 1.Schematic diagram of immobilization process flow and luminescence detection.A pliable silicon chip measured under fifty micrometers in thickness is achieved through a simple method via alkaline etchant. The silicon chip with designed thickness is featured of great flexibility and relatively little fragility. A surface modification is applied to the flexible silicon chip with non-toxic and easy-arranged texturing solution from texturization process. Owing to anisotropic etching, the three-dimensional structure of pyramidal shape is constructed onto the chip surface. The reflectivity decreases advantageously in virtue of increasing roughness, and the final reflectivity is only one-fourth in comparison with original smooth chip surface due to formation of surface microstructure. The flexible MSM photodetectors are accomplished after mantling metal electrode with well-designed pattern. The semiconductor material we used is featured of high natural abundance and the manufacturing processes are considerably uncomplicated.In taking advantage of immobilization technique, the targeting enzyme is bound to photodetector devices and as-prepared devices are employed in optical sensing of luminescence which is catalyzed by the immobilized enzyme. This optical sensor exhibits great flexibility and remarkable durability and shows marvelous stability even in various stretching conditions. Furthermore, the photodetector devices are featured portable and cost-efficient. A novel application of this detector in healthcare field which is a significant issue nowadays is performed on available hair dye products. The examination is taken into consideration owing to the potential damage caused by hydrogen peroxide of which the main ingredient in hair dye products (Fig.2). For this interdisciplinary-technology-based device, the flexible optical sensor can be utilized in multiple regions and it can be integrated with promising instruments in virtue of great mechanical property. Figure 2.Hydrogen peroxide detections for hair dye samples through luminescence sensing by flexible MSM photodetectors.

Single crystal growth of TIMETAL LCB titanium alloy by a floating zone method

The methodology of single crystal growth of metastable β-Ti alloy TIMETAL LCB in an optical floating zone furnace is presented in this paper. Chemical compositions of both precursor material and single crystals were checked. It was found that the concentration of base alloying elements did not change significantly during the growth process, while the concentrations of interstitial elements O and N increased. DSC measurement determined that this concentration shift has a slight impact on ongoing phase transformations, as in the single-crystalline material peak associated with α phase precipitation moves by a few degrees to a lower temperature and peak attributed to diffusion controlled growth of ω particles shifts to a higher temperature. X-ray reciprocal space maps were measured and their simulation showed that the single crystal has a mosaic structure with mean size of mosaic blocks of approximately 60nm.

High-precision transfer-printing and integration of vertically oriented semiconductor arrays for flexible device fabrication

Flexible electronics utilizing single crystalline semiconductors typically require post-growth processes to assemble and incorporate the crystalline materials onto flexible substrates. Here we present a high-precision transfer-printing method for vertical arrays of single crystalline semiconductor materials with widely varying aspect ratios and densities enabling the assembly of arrays on flexible substrates in a vertical fashion. Complementary fabrication processes for integrating transferred arrays into flexible devices are also presented and characterized. Robust contacts to transferred silicon wire arrays are demonstrated and shown to be stable under flexing stress down to bending radii of 20 mm. The fabricated devices exhibit a reversible tactile response enabling silicon based, nonpiezoelectric, and flexible tactile sensors. The presented system leads the way towards high-throughput, manufacturable, and scalable fabrication of flexible devices.

In-plane thermal conductivity of sub-20 nm thick suspended mono-crystalline Si layers

We measure the thermal conductivity of a 17.5-nm-thick single crystalline Si layer by using a suspended structure developed from a silicon-on-insulator wafer, in which the Si layer bridges the suspended platforms. The obtained value of 19 Wm−1 K−1 at room temperature represents a tenfold reduction with respect to bulk Si. This design paves the way for subsequent lateral nanostructuration of the layer with lithographic techniques, to define different geometries such as Si nanowires, nanostrips or phononic grids. As a proof of concept, nanostrips of 0.5 × 10 μm have been defined by focused ion beam (FIB) in the ultrathin Si layer. After the FIB cutting process with Ga ions at 30 kV and 100 pA, the measured thermal conductivity dramatically decreased to 1.7 Wm−1 K−1, indicating that the structure became severely damaged (amorphous). Re-crystallization of the structure was promoted by laser annealing while monitoring the Raman spectra. The thermal conductivity of the layer increased again to a value of 9.5 Wm−1 K−1 at room temperature, below that of the single crystalline material due to phonon scattering at the grain boundaries.

Functionalizing Single Crystals: Incorporation of Nanoparticles Inside Gel‐Grown Calcite Crystals

Synthetic single crystals are usually homogeneous solids. Biogenic single crystals, however, can incorporate biomacromolecules and become inhomogeneous solids so that their properties are also extrinsically regulated by the incorporated materials. The discrepancy between the properties of synthetic and biogenic single crystals leads to the idea to modify the internal structure of synthetic crystals to achieve nonintrinsic properties by incorporation of foreign material. Intrinsically colorless and diamagnetic calcite single crystals are turned into colored and paramagnetic solids, through incorporation of Au and Fe3O4 nanoparticles without significantly disrupting the crystalline lattice of calcite. The crystals incorporate the nanoparticles and gel fibers when grown in agarose gel media containing the nanoparticles, whereas the solution-grown crystals do not. As such, our work extends the long-history gel method for crystallization into a platform to functionalize single-crystalline materials.

Using the Evolutionary Selection Principle in Selective Area Growth to Achieve Single-Crystalline GaN on SiO2

Conventional epitaxial techniques requires single crystalline substrates to form semiconductor material of desired material quality for device applications. The use of amorphous substrates, in many applications, provides an opportunity to consider new materials and designs, which can fundamentally alter the performance, functionality and/or cost limitations of many optoelectronic devices. Here, a growth process is described to achieve single crystalline GaN material on amorphous SiO2. The evolutionary selection principle in crystal growth is the basis of this technique, and the mechanism is described and analyzed in detail. It is expected that this process can be extended to other semiconductor and substrate combinations, allowing heterogenous integration with functional substrates to produce new classes of semiconductor devices.

A diffraction effect in X-ray area detectors

When an X-ray area detector based on a single-crystalline material, for instance a state-of-the-art hybrid pixel detector, is illuminated from a point source by monochromatic radiation, a pattern of lines appears which overlays the detected image. These lines are easily seen in scattering experiments with smooth patterns, such as small-angle X-ray scattering. The origin of this effect is Bragg reflection within the sensor layer of the detector. Experimental images are presented over a photon energy range from 3.4 to 10 keV, together with a theoretical analysis. The intensity of the detected signal is decreased by up to 20% on this pattern, which can affect the evaluation of scattering and diffraction experiments. The patterns can be exploited to check the alignment of the detector surface with the direct beam, and the alignment of individual detector modules with each other in the case of modular detectors, as well as for energy calibration of the radiation.

The role of cationic and anionic point defects in pulsed laser deposition of perovskites

Pulsed laser-deposited thin films often show properties that are less optimized compared to single crystalline materials, or thin films grown by molecular beam epitaxy. The main reasons include the high particle energies and the dynamics of the laser plasma. Furthermore, point defect engineering is difficult to achieve experimentally since the adjustable parameters show a complex interplay. Using the examples of the simple perovskite SrMoO3 and the double perovskite Sr2CrWO6 we discuss the role of cationic and anionic point defects, and how far they can be engineered during pulsed laser deposition.