Fabrication Of Crystals Research Articles

Spatial Segregation of Microspheres by Rubbing-Induced Triboelectrification on Patterned Surfaces.

Particle (monolayer) assembly is essential to various scientific and industrial applications, such as the fabrication of photonic crystals, optical sensors, and surface coatings. Several methods, including rubbing, have been developed for this purpose. Here, we report on the serendipitous observation that microparticles preferentially partition onto the fluorocarbon-coated parts of patterned silicon and borosilicate glass wafers when rubbed with poly(dimethylsiloxane) slabs. To explore the extent of this effect, we varied the geometry of the pattern, the substrate material, the ambient humidity, and the material and size of the particles. Partitioning coefficients amounted up to a factor of 12 on silicon wafers and even ran in the 100s on borosilicate glass wafers at zero humidity. Using Kelvin probe force microscopy, the observations can be explained by triboelectrification, inducing a strong electrostatic attraction between the particles and the fluorocarbon zones, while the interaction with the noncoated zones is insignificant or even weakly repulsive.

Ring-Patterned Perovskite Single Crystals Fabricated by the Combination of Rigid and Flexible Templates.

Regular microstructures can improve the electrical and optical characteristics of perovskite single crystals because of the removal of defects and grain boundaries. Microstructured single crystals are commonly fabricated by either rigid or flexible templates. However, rigid templates usually need surface treatment before crystal fabrication to create an antiadhesion layer, while flexible templates encounter difficulties in achieving a large area of uniform single crystals without any deformation. In this work, we present a facile and robust method to fabricate perovskite single crystals using rigid silicon pillars coated with flexible polymer solutions, in which surface treatment is avoided in the preparation process, and deformation is absent in the formed crystals. The method realized the fabrication of colorful concentric-ring patterns composed of nanoscale single crystals for the first time. In order to concisely control the preparation of the template, the Newton's ring phenomenon was used to value the droplet height because the number of rings changed with the optical path difference. A related digital simulation was performed to find the correlation of the Newton's ring pattern with the shape of the droplets. The simulated results were consistent with the experimental observations generally, indicating that the pattern could be controlled mechanically. Concomitantly, the resulting perovskite nanoscale single crystals formed a regular colorful concentric-ring pattern. By changing the design of the rigid templates, the parameters of the fabrication process, or the selection of the coating polymer solution, different ring-patterned single crystals were successfully prepared without surface treatment and deformation. The crystals have potential applications in lasers or photodetectors.

Enhanced Reduction of Thermal Conductivity in Amorphous Silicon Nitride-Containing Phononic Crystals Fabricated Using Directed Self-Assembly of Block Copolymers.

Studies have demonstrated that the thermal conductivity (κ) of crystalline semiconductor materials can be reduced by phonon scattering in periodic nanostructures formed using templates fabricated from self-assembled block copolymers (BCPs). Compared to crystalline materials, the heat transport mechanisms in amorphous inorganic materials differ significantly and have been explored far less extensively. However, thermal management of amorphous inorganic solids is crucial for a broad range of semiconductor devices. Here we present the fabrication of freestanding amorphous silicon nitride (SiNx) membranes for studying κ in an amorphous solid. To form a periodic nanostructure, directed self-assembly of cylinder-forming BCPs is used to pattern in the SiNx highly ordered, hexagonally close packed nanopores with pitch and neck width down to 37.5 and 12 nm, respectively. The κ of the nanoporous SiNx membranes is 60% smaller than the classically predicted value based on just the membrane porosity. In comparison, holes with much larger neck widths and pitches patterned by e-beam lithography lead to only a slight reduction in κ, which is closer to the classical porosity-based prediction. These results demonstrate that κ of amorphous SiNx can be reduced by introducing periodic nanostructures that behave as a phononic crystal, where the relationship between the smallest dimension of the nanostructure and the length scale of the mean-free paths of the dominant, heat-carrying phonons is critical. Additionally, changing the orientation of the hexagonal array of nanopores relative to the primary direction of heat flow has a smaller impact on amorphous SiNx than was previously observed in silicon.

Cross‐Sectional Investigation of Multihigh‐Energy Proton‐Implanted Single Crystalline Diamond

Comprehending the implantation‐related characteristic quantities of multihigh‐energy proton irradiation of diamond is of significant technological interest for sensing applications, fabrication of 3D photonic crystals, and color centers (e.g., NV− center)‐based quantum computing. Herein, proton‐projected ranges and defect distributions in the (010) plane (Y‐normal plane) of microwave plasma chemical vapor deposition (MPCVD)‐grown diamond irradiated with 0.5–2.0 MeV proton (H+ or molecular ions) in a nonchanneling (near [001], Z‐axis) direction, are experimentally measured via cross‐sectional optical microscopy and high‐resolution confocal Raman spectroscopy mapping. It is found that the projected ranges of the experimental findings and the simulation results indicate good consistencies, whereas there is considerable disagreement between them in regards to longitudinal straggling and lateral straggling. Based on the comparisons and analyses, a clear view of protons implanted in single crystalline diamond in the high‐energy range theoretically and experimentally is obtained.

Evaluating new fault‐controlled hydrothermal dolomitization models: Insights from the Cambrian Dolomite, Western Canadian Sedimentary Basin

AbstractFault‐controlled hydrothermal dolomitization in tectonically complex basins can occur at any depth and from different fluid compositions, including ‘deep‐seated’, ‘crustal’ or ‘basinal’ brines. Nevertheless, many studies have failed to identify the actual source of these fluids, resulting in a gap in our knowledge on the likely source of magnesium of hydrothermal dolomitization. With development of new concepts in hydrothermal dolomitization, the study aims in particular to test the hypothesis that dolomitizing fluids were sourced from either seawater, ultramafic carbonation or a mixture between the two by utilizing the Cambrian Mount Whyte Formation as an example. Here, the large‐scale dolostone bodies are fabric‐destructive with a range of crystal fabrics, including euhedral replacement (RD1) and anhedral replacement (RD2). Since dolomite is cross‐cut by low amplitude stylolites, dolomitization is interpreted to have occurred shortly after deposition, at a very shallow depth (<1 km). At this time, there would have been sufficient porosity in the mudstones for extensive dolomitization to occur, and the necessary high heat flows and faulting associated with Cambrian rifting to transfer hot brines into the near surface. While the δ18Owater and 87Sr/86Sr ratios values of RD1 are comparable with Cambrian seawater, RD2 shows higher values in both parameters. Therefore, although aspects of the fluid geochemistry are consistent with dolomitization from seawater, very high fluid temperature and salinity could be suggestive of mixing with another, hydrothermal fluid. The very hot temperature, positive Eu anomaly, enriched metal concentrations, and cogenetic relation with quartz could indicate that hot brines were at least partially sourced from ultramafic rocks, potentially as a result of interaction between the underlying Proterozoic serpentinites and CO2‐rich fluids. This study highlights that large‐scale hydrothermal dolostone bodies can form at shallow burial depths via mixing during fluid pulses, providing a potential explanation for the mass balance problem often associated with their genesis.

Fabrication of mullite nano ceramic through addition of long-chain carbohydrates

Compared to common coarse-grained ceramics, nano-scaled mullite ceramics exhibit unique microstructures and mechanical properties. However, fabrication of homogeneous and ultra-fine ceramic crystals still remains a major challenge. In this study, fine-grain mullite nanocrystals with uniform particle distribution have been successfully synthesized by addition of agarose, which is a long-chain carbohydrate to the precursor. The effect of length of the carbohydrate chain on the size of mullite crystals has been investigated. The results show that long-chain carbohydrate agarose results in smaller grain size of mullite crystals as compared with glucose. Moreover, nano-scaled mullite ceramics with high hardness (18.36 GPa) and fracture toughness values (3.7 MPa m1/2) were obtained owing to the high relative density and small grain size. The present work highlights its potential application as long-chain carbohydrate in producing high-performance nanoceramics.

Highly Efficient Fabricating Amorphous Photonic Crystals Using Less Polar Solvents and the Wettability‐Based Information Storage and Recognition

AbstractFacile and efficient fabrication of amorphous photonic crystals (APCs) with uniform and angle independent structural colors is highly desired due to their unique applications in non‐iridescent colors‐based displays, pigments, and sensors. Here, a solvent‐assisted colloidal assembly approach is reported to fabricate APCs with uniform and angle‐independent structural colors by the self‐assembly of polydopamine‐embedded silica particles in pentanol. The surface charge of the particle mediated by the polarity of solvent is demonstrated to be the key to control the particle arrangements and the angle dependency of the structural colors, which makes the fabrication more efficient, simple, and convenient compared to previous methods. Owing to the amorphous structures, the APCs show unique sensitivity to the variation of the refractive index contrast. Based on this unique sensitivity of APCs, an information storage‐recognition system is established by constructing different wettability between the information and background region. The information integrated with the color, the number, and the site of APCs of the system can be stored and recognized at dry and wetting state, respectively, and the switching of the storage‐recognition process is fully reversible. These findings provide new insights into the design, fabrication, and application of materials with non‐iridescent structural colors.

Transferable High-Quality Inorganic Perovskites for Optoelectronic Devices by Weak Interaction Heteroepitaxy.

Transferable semiconductors with superior light-emitting properties are important for developing flexible and integrated optoelectronics. However, finding such a qualified candidate remains challenging. Here, we report the fabrication of transferable high-quality CsPbBr3 single crystals on a highly oriented pyrolytic graphite (HOPG) substrate via weak interaction heteroepitaxy for the first time. Semi-quantitative kinetic analysis based on the classical nucleation theory well accounts for the van der Waals (vdW) epitaxial growth process of perovskite on the HOPG substrate. The density functional theory calculations illustrate the bonding nature of the interface and predict the Volmer-Weber growth mode in vdW epitaxy, which is consistent with our experimental observations. Importantly, the extremely weak vdW interaction between the perovskite and HOPG not only enables the high quality of the crystals but also endows them with the facile transferability to any foreign substrate by the mechanical exfoliation technique. Leveraging on the transferred CsPbBr3 single crystals, the low-threshold microlasers and monolithic perovskite light-emitting diode devices are demonstrated. Our results represent a significant step toward advanced optoelectronic devices relying on the emerging perovskite semiconductors.

LiInSe2 for Semiconductor Neutron Detectors

Lithium Indium Selenide (LiInSe2) is being developed for use as a room temperature semiconductor detector for thermal neutrons The material has been studied for a number of applications including nonlinear optics such as parametric oscillators, as anode material for lithium ion batteries, piezoelectrics, as a scintillation detector material and as a semiconductor detector material. The recent advances of the crystal growth, material processing and detector fabrication have led to semiconductor neutron detectors with up to 100 mm2 active area. The thermal neutron detection sensitivity and gamma rejection ratio (GRR) are comparable to 10atm, He-3 tubes of similar size. Synthesis, crystal growth, detector fabrication, and characterization are discussed.

One-dimensional Photonic Crystals Fabricated Using Stereolithographic Single Layer Assembly for the Terahertz Spectral Range

A polymer-based one-dimensional photonic crystal with a photonic bandgap in terahertz frequency range was designed and fabricated through stereolithography and was characterized using THz spectroscopy. The photonic crystal studied here consists of alternating compact and low-density layers. The compact layers were fabricated from fully polymerized polymethacrylate without any intentional internal structure. The low-density layers consist of sub-wavelength sized columns, where the volume density was selected to provide sufficient contrast between the dielectric functions of adjacent layers. The photonic crystal samples were fabricated in a single step using a commercial stereolithography system and polymethacrylate compatible with the system. Transmission spectroscopy in a range from 82 to 125 GHz was used to determine the THz spectral response of the sample. The transmission data were analyzed using stratified optical layer model calculations. A distinct photonic bandgap with a center frequency of 111 GHz was observed in the experimental transmission spectra. Bruggeman effective medium approximation was found to accurately describe the dielectric function of the low-density layers. An excellent agreement between the relevant model parameters and the corresponding design parameters was found, indicating the versatility of the approach for the fabrication of photonic crystals for the THz spectral range.

Optimal design and fabrication of ITO photonic crystal using e-beam patterned hydrogen silsesquioxane resist

In this work, the authors report the design and fabrication of photonic crystals of indium tin oxide (ITO) in the visible range. The structures have been obtained using e-beam lithography combined with inductively coupled plasma reactive ion etching in boron trichloride and chlore plasma. They have particularly studied the effect of the process parameters on the hole features. The triangular lattice configuration consisting of air holes radii of 110 nm with a lattice spacing of 290 nm was successfully transferred through the 300-nm-thick hydrogen silsesquioxane resist mask to the 150 nm-thick ITO layer, achieving smooth and vertical sidewalls. The optical characterization, using an end-fire coupling technique, confirmed the existence of a photonic bandgap over 600–800 nm, which is of a great interest to develop new functionalities based on ITO thin films for laser applications in the visible range.

Fabrication of Single Crystals through a µ-Helix Grain Selection Process during Electron Beam Metal Additive Manufacturing

Selective Electron Beam Melting (SEBM) is a powder bed-based additive manufacturing process for metals. As the electron beam can be moved inertia-free by electromagnetic lenses, the solidification conditions can be deliberately adjusted within the process. This enables control over the local solidification conditions. SEBM typically leads to columnar grain structures. Based on numerical simulation, we demonstrated how technical single crystals develop in IN718 by forcing the temperature gradient along a µ-Helix. The slope of the µ-Helix, i.e., the deviation of the thermal gradient from the build direction, determined the effectiveness of grain selection right up to single crystals.

Fabrication of GaN crystals with low threading dislocation density and low resistivity by thin flux growth in the Na-flux point seed technique

We investigated the electrical properties of low threading dislocation density (TDD) GaN crystals grown by the thin flux growth method in the Na-flux point seed technique for the first time. In addition, we attempted to fabricate GaN crystals with further lower TDD and curvature by using point seeds having a smaller diameter of 250 μm, compared to that from a previous study having a diameter of 1000 μm. As a result, the free carrier concentration was 1.1 × 1020 cm−3 with a resistivity of 9 × 10−4 Ωcm. Moreover, TDD in about 80% of the observation area was on the order of 103 cm−2 or less, and the radius of curvature of the GaN crystal was over 100 m for both a// and m//, due to the smaller-sized point seeds. These results suggest that low-TDD GaN crystals with low resistivity can be realized with this method, and Na-flux GaN crystals exhibit great performance as substrates of power devices.

Millimeter-Scale Hexagonal Boron Nitride Single Crystals for Nanosheet Generation

Development of next-generation two-dimensional (2D) transistors or photoelectronic devices is closely linked to advances in 2D materials. Because of its outstanding properties (insulating, stable, inert, transparent, isostructural to graphene, etc.), the hexagonal boron nitride (hBN) crystal, and in particular its exfoliated nanosheets form, is a choice material to fabricate sensors or plasmonic and photonic devices. However, a wide development of these heterostructures still suffers from a lack of large samples and in ample supply. In this context, we propose the fabrication of large exceptional quality hBN single crystals of more than few millimeters lateral size using the polymer route combined with a sintering process. The structural quality and compositional purity are retained after exfoliation and dry transfer of these freestanding boron nitride nanosheets (BNNSs) onto Si substrates. This developed method can be achieved under short and soft conditions and leads to BNNSs with lateral sizes of several hundreds of micrometers. This work paves the way for a wide use of BNNS for 2D material applications.

Lasing in low-dimensional single crystals of hexyl-substituted thiophene/phenylene co-oligomer

We report on the fabrication and characterization of low-dimensional single crystals of hexyl-substituted thiophene/phenylene co-oligomer, 5,5′-Bis(4′-n-hexyl-4-biphenylyl)-2,2′-bithiophene (BP2T-Hx). X-ray diffraction measurements of the single crystals reveal that BP2T-Hx molecules crystallize in a monoclinic form. Temperature dependence of photoluminescence (PL) decay profiles of the BP2T-Hx crystal results in a PL quantum yield of 39%. Above an excitation threshold of 262 μJ cm−2, amplified spontaneous emission is obtained in a disk-shaped crystal of BP2T-Hx based on the self-waveguiding effect of fluorescence light. Owing to two-dimensional light confinement supported by high group refractive index of 3.4 and high quality factor of 3800, the one-dimensional needle crystal with a cavity length of 70 μm realizes a Fabry–Pérot lasing at a threshold of 186 μJ cm−2 which is 29% lower than that of the disk-shaped crystal.

Advanced Materials for Heat Energy Transfer, Conversion, Storage and Utilization

Advanced Materials for Heat Energy Transfer, Conversion, Storage and Utilization

Material properties and device performance of CdSe radiation detectors

CdSe single crystals are considered as promising candidates for radiation detectors, however, the progress is limited by the fabrication of high-quality CdSe single crystals. Herein, we reported a CdSe-based radiation detector, exhibiting superior detection performance for α-particles and γ-rays. The FWHM of the X-ray rocking curve of CdSe (100) plane was determined to 0.03°. The as-grown CdSe single crystal exhibited a high room-temperature resistivity of 1.83×109Ω cm. Moreover, the detector exhibited an energy resolution of ∼13.22% and ∼11.21% for α-particles and γ-rays, respectively. The hole mobility-lifetime product (μτ(h)) in experimental of the detector up to 2.20 × 10−4 cm2 V−1 was reported by using the Hecht equation.

Mesophase transition of cellulose nanocrystals aroused by the incorporation of two cellulose derivatives

Cellulose nanocrystals (CNCs) per their twisting structure and high aspect ratio and charged surface property are increasingly receiving great attention in chiral photonic crystal and pigment fabrication. However, the cholesteric mesophases of CNCs is unstable and easily destroyed by the additives with high Mw. In this work, hydroxypropyl cellulose (HPC) and carboxymethyl cellulose (CMC) are incorporated into CNCs for a continuous mesophase transition monitoring. We investigated the effects of HPC and CMC on the properties of CNCs with respect to the morphology, mesophase, rheology, and structure-color properties. Our results showed that the addition of CMC (≥ 1 wt%) prevented the formation of a continuous cholesteric phase but resulting in a fast gelation due to the strong repulsion between CMC and CNCs. Alternatively, the cholesteric phase was well-preserved in the CNC/HPC in which HPC (< 10 wt%) served as an efficient tuner of phase transition, color hue and rheology properties.

Two-dimensional high-quality Ag/Py magnetoplasmonic crystals

We demonstrate a perspective approach for the fabrication of functional high-quality magnetoplasmonic crystals based on a 2D periodical perforated silver film covered by a thin layer of ferromagnetic metal (Permalloy). The wavelength-angular spectra of the 2D crystals reveal a large number of high-quality resonant features associated with the excitation of surface plasmon-polariton modes of various orders. Due to the presence of a ferromagnetic material on both plasmonic interfaces, pronounced magnetic effects are observed for all excitations and are influenced by the coupling between various modes. The suggested magnetoplasmonic crystal composition with high-quality resonant optical and magneto-optical properties gives perspective for the control over the light propagation as well as for sensor applications.

Preparation and properties of multi-effect potassium sodium niobate based transparent ferroelectric ceramics

Traditional transparent materials, including glasses and polymers, are chemically unstable and mechanically weak. Single crystals of some inorganic materials are also optically transparent, which are more stable than glasses and polymers. The fabrication of crystals, however, is relatively slow. Fortunately, transparent ceramics emerge as a promising candidate. Transparent ferroelectric ceramic is a kind of transparent ceramic with electro-optic effect, which also has excellent characteristics of conventional ceramics with excellent mechanical properties, resistance to high temperature, resistance against corrosion, and high hardness. Lead based transparent ferroelectric ceramic dominates this field for many years due to its superior electro-optic effect. Owing to the high toxicity of lead oxide, however, its development is significantly hampered. Therefore, it is greatly urgent to develop the lead-free transparent ferroelectric ceramics with excellent properties to replace the traditional lead based ceramics. In this paper, (K&lt;sub&gt;0.5&lt;/sub&gt;Na&lt;sub&gt;0.5&lt;/sub&gt;)&lt;sub&gt;0.94–3&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;Li&lt;sub&gt;0.06&lt;/sub&gt;La&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Nb&lt;sub&gt;0.95&lt;/sub&gt;Ta&lt;sub&gt;0.05&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; (KNLTN-La&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt;; &lt;i&gt;x&lt;/i&gt; = 0, 0.01, 0.015, 0.02) lead-free transparent ferroelectric materials are fabricated by the conventional solid state reaction method and ordinary sintering process. The dependence of microstructure, phase structure, optical transmittance and electrical properties of the ceramic on composition are systemically investigated. The transparent ferroelectric ceramic with relaxor-behavior is obtained at &lt;i&gt;x&lt;/i&gt; = 0.02. The optical transmittance of the ceramic near infrared region is as high as 60%. Meanwhile, the electrical properties of the ceramic at &lt;i&gt;x&lt;/i&gt; = 0.01 still maintains a relatively high level (&lt;i&gt;d&lt;/i&gt;&lt;sub&gt;33&lt;/sub&gt; = 110 pC/N, &lt;i&gt;k&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt; = 0.267). In addition, the Curie temperature for each of all the samples is higher than 400 ℃. These results suggest that this material might be a novel and promising lead-free material that could be used in a large variety of electro-optical devices.