Preparation Of Single Crystals Research Articles

Compensation of p-type doping in Al-doped 4H-SiC

One of the major challenges of 4H-silicon carbide (4H-SiC) is that the preparation of low resistivity p-type 4H-SiC single crystals lags seriously behind that of low resistivity n-type 4H-SiC single crystals, hindering the development of important 4H-SiC power devices such as n-channel insulated gate bipolar transistors. In particular, the resistivity of p-type 4H-SiC single crystals prepared through the physical vapor transport technique can only be lowered to around 100 mΩ cm. One of the key causes is the incomplete ionization of the p-type dopant Al with an ionization energy ∼0.23 eV. Another factor is the compensating effect. It cannot simply assume nitrogen (N) is the sole compensatory center, since the number of the compensating center is larger than the concentration of N doping. In this work, we systematically investigate the compensation of native defects and self-compensation in Al-doped 4H-SiC. It is found that the positively charged carbon vacancies (VC2+) are also the dominant compensating centers in Al-doped 4H-SiC. When the Al concentration is in the range of 1016–1019 cm−3, the concentration of holes is lower by one order of magnitude than the Al concentration because of the compensation of VC2+. As the Al concentration exceeds 1020 cm−3, the concentration of holes is only in the order of magnitude of 1019 cm−3 owing to the dominant compensation of VC2+ and supplementary self-compensation of interstitial Al (Ali3+). We propose that the passivation of VC2+ as well as quenching is effective to enhance the hole concentration of Al-doped 4H-SiC.

Growth Pattern Control and Nanoarchitecture Engineering of Metal-Organic Framework Single Crystals by Confined Space Synthesis.

The nanoarchitecture engineering of metal–organic frameworks (MOFs) is a fascinating but intellectually challenging concept that opens up avenues for both tailoring the properties of MOFs and expanding their applications. Herein, we report the confined growth of ZIF-8 single crystals in a three-dimensionally ordered (3DO) macroporous polystyrene replica and reveal that their growth patterns, morphologies, and nanoarchitectures can be highly engineered using the concentration of the precursor. Impressively, the favorable in situ confined growth enables the successful fabrication of 3DO sphere-assembled ZIF-8 single crystals or 3DO single-crystalline ZIF-8 sphere arrays when a low- or high-concentration precursor solution, respectively, is used as the feedstock. Furthermore, our strategy can be extended to the preparation of other 3DO MOF single crystals, including ZIF-67 and HKUST-1, with similar controllable hierarchical nanoarchitectures. With the successful preparation of a series of diameter-tunable ZIF-8 single-crystalline spheres, we further unravel their interesting size–performance relationship in the Knoevenagle reaction between benzaldehyde and malononitrile, wherein the smallest spheres show the fastest first-order reaction kinetics. This study not only develops a general strategy for engineering the nanoarchitectures of MOF single crystals but also provides fundamental knowledge of the mechanism for the growth of hierarchical single crystals under confined spaces.

Enhanced structure and electrochemical stability of single crystal nickel-rich cathode material by La2Li0.5Co0.5O4 surface coating

The emergence of single crystal nickel-rich cathode materials preparation offsets the poor cycle performance of traditional ternary cathode materials, with an efficient enhancement of the energy density. Despite all this, the stability of single crystal Ni-rich materials is still hard to fully meet the commercial requirements. We select La and Co elements for co-coating single crystal cathode materials by an efficient method, La2Li0.5Co0.5O4 coating layer with a thickness of about 5 nm is successfully formed on the single crystal nickel-rich samples. The coating layer effectively protect nickel-rich materials from the corrosion of electrolyte and retain a high Li-ion conductivity during charge/discharge processes. Besides, the part of residual lithium reacts with La and Co, forming La2Li0.5Co0.5O4 coating layer, and decorates the materials surface. Eventually, the single crystal NCM811 with 2 wt% La2Li0.5Co0.5O4 coating affords a terrific cyclic stability after 200 cycles. The capacity retention is 81.15% at 1 C with voltage range of 2.8–4.3 V, obtaining an 18% performance improvement compare with that of pristine material. Moreover, the rate performance and first charge/discharge efficiency are improved to a certain extent. The co-coating process with La and Co is a competitive approach to modify the performance of single crystal nickel-rich cathode materials and contribute to the commercial application of the NCM811 materials.

2D Covalent Organic Frameworks: From Synthetic Strategies to Advanced Optical-Electrical-Magnetic Functionalities.

Covalent organic frameworks (COFs), an emerging class of organic crystalline polymers with highly oriented structures and permanent porosity, can adopt 2D or 3D architectures depending on the different topological diagrams of the monomers. Notably, 2D COFs have particularly gained much attention due to the extraordinary merits of their extended in-plane π-conjugation and topologically ordered columnar π-arrays. These properties together with high crystallinity, large surface area, and tunable porosity distinguish 2D COFs as an ideal candidate for the fabrication of functional materials. Herein, this review surveys the recent research advances in 2D COFs with special emphasis on the preparation of 2D COF powders, single crystals, and thin films, as well as their advanced optical, electrical, and magnetic functionalities. Some challenging issues and potential research outlook for 2D COFs are also provided for promoting their development in terms of structure, synthesis, and functionalities.

High-pressure high-temperature industrial preparation of micron-sized diamond single crystals with silicon-vacancy colour centres

Negatively charged silicon-vacancy (SiV−) colour centres are considered to be promising room-temperature single-photon sources. The controlled preparation of high-grade industrial diamonds containing a certain amount of SiV− colour centres remains a significant technical challenge. Herein, micron-sized industrial-grade diamonds containing different concentrations of SiV− colour centres were prepared by adjusting the doping amount of Si powder under the pressure conditions of 5.0–5.2 GPa and temperatures of 1420–1500 °C. Al was used as the nitrogen getter in FeNiCo−C systems through the diamond film growth method (FGM). The results show that the intensity of the SiV− colour centres in synthesized diamond increases with increases in the Si doping amount. It has also been proved that nitrogen impurities inhibit the formation of SiV− colour centres in diamond. In addition, the diamond Raman peak positions exhibit a redshift (from 1330.88 cm−1 to 1329.55 cm−1), and an increase in the Raman full width at half maximum (FWHM) (from 4.78 cm−1 to 5.17 cm−1), indicating that Si enters the diamond lattice, but the diamond crystals still have a single sp3 structure. Our research provides a fast, efficient and low-cost method for the controlled batch preparation of industrial-grade diamond containing SiV− colour centres.

Growing MASnI3 perovskite single-crystal films by inverse temperature crystallization

Perovskite single-crystal films are promising candidates for high-performance perovskite optoelectronic devices due to their optoelectrical properties. However, there are few reports of single-crystal films of tin based perovskites. Here, for the first time, we realize the controllable growth and preparation of lead-free tin perovskite MASnI3 single crystals via inverse temperature crystallization (ITC) strategy with γ–butyrolactone (GBL) as solvent. The solubility characteristics of MASnI3 in GBL are clarified by quantitative analytical method. Highly repeatability experiments are further demonstrated using this unique solubility and ITC properties. Sequentially, using space limiting method, tin perovskite MASnI3 single-crystal thin films are fabricated with micron-scale thickness, which is highly desired for efficient tin perovskite solar cells. Our MASnI3 single-crystal thin films show typical single-crystalline features including strongly optical absorbance with sharp absorption edges, pure-phase x-ray diffraction patterns, and absence of Sn(IV) x-ray photoelectron spectroscopy. We believe that our findings will further broaden the application prospects of tin perovskite MASnI3 single crystals and cause a new upsurge in exploring the field of lead-free perovskite single-crystal growth.

High-Performance Photodetectors Based on the 2D SiAs/SnS2 Heterojunction.

Constructing 2D heterojunctions with high performance is the critical solution for the optoelectronic applications of 2D materials. This work reports on the studies on the preparation of high-quality van der Waals SiAs single crystals and high-performance photodetectors based on the 2D SiAs/SnS2 heterojunction. The crystals are grown using the chemical vapor transport (CVT) method and then the bulk crystals are exfoliated to a few layers. Raman spectroscopic characterization shows that the low wavenumber peaks from interlayer vibrations shift significantly along with SiAs’ thickness. In addition, when van der Waals heterojunctions of p-type SiAs/n-type SnS2 are fabricated, under the source-drain voltage of −1 V–1 V, they exhibit prominent rectification characteristics, and the ratio of forwarding conduction current to reverse shutdown current is close to 102, showing a muted response of 1 A/W under excitation light of 550 nm. The light responsivity and external quantum efficiency are increased by 100 times those of SiAs photodetectors. Our experimental results enrich the research on the IVA–VA group p-type layered semiconductors.

Crystallographic and computational investigations of structural properties in phenyl and methoxy‑phenyl substituted 1,4 dihydropyridine derivatives

Single crystal preparation of two 1,4-dihydropyridine (1,4-DHP) derivative molecules, namely, (i) 2,6-dimethyl-4-phenyl-1, 4-dihydro-pyridine-3, 5-dicarboxylic acid diethyl ester and (ii) 4-(4‑methoxy-phenyl)-2,6-dimethyl-1, 4-dihydro-pyridine-3, 5-dicarboxylic acid diethyl ester was done. Crystal structure solution and refinement of final R values converged to 0.0478 and 0.0466. Hirshfeld surface analysis mapped dnorm surfaces, shape index, curvedness and hydrogen bonding present in the molecules. These calculations established the relative contributions of the various intermolecular contacts to the total Hirshfeld surface area. Both the molecular structures were optimized and confirmed by Density Functional Theory (DFT) simulations in an implicit aqueous solvation environment. The molecular electrostatic potential (MEP) analysis elucidated the electrophilic and nucleophilic regions in the molecules to be the hydrogen attached to the nitrogen and the carboxyl oxygen atoms. Frontier molecular orbital analysis indicated the stability of these molecules while they appeared to be electrophilic in nature from the reactivity descriptors analysis.

Wafer-Scale Uniform Synthesis of 2D Transition Metal Dichalcogenides Single Crystals via Chemical Vapor Deposition

ConspectusTwo-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs), most with a formula of MX2 (M = Mo, W; X = S, Se, etc.), have emerged as ultrathin channel materials in next-generation electronics, due to their atomic thickness, tunable bandgap, and relatively high carrier mobility, etc. To propel their practical applications in integrated circuits, large-scale preparation of large-domain MX2 single crystals and single-crystal films is significantly important. Among all the synthetic methods, chemical vapor deposition (CVD) has shown great promise for the controllable syntheses of large-area uniform 2D materials with electronic-grade quality and reasonable cost. So far, intensive efforts have been devoted to the controllable growth of MX2 single crystals with large sizes, controlled thicknesses, fast growth rates, and unidirectional orientations. However, due to the complexity of the precursor species (mostly like solid powders) and their gradient feeding distributions along the gas flow direction, it is still a huge challenge to synthesize large-area MX2 samples with centimeter-scale uniformity, which inevitably hinders their practical applications in industry. More significantly, due to the noncentrosymmetric structures of MX2, antiparallel domains and twin grain boundaries usually evolved on most substrates (e.g., mica, C-sapphire). These defective grain boundaries usually exhibit metallic characteristics and serve as conducting channels, seriously impairing the electrical and optical properties of related devices.This review thereby focuses on the recent progresses on the CVD syntheses of large-scale uniform, large-domain MX2 flakes and single-crystal films, primarily on the single-crystal insulating substrates, amorphous insulating substrates and single-crystal metal substrates. Some promising growth strategies toward improving the thickness uniformity, domain size and crystal quality of MX2 are highlighted, through modulating the key parameters in the CVD processes, such as precursor type, substrate category/crystallinity or growth promoter. The key mechanisms that directing the uniform orientations of individual domains and their merging toward single-crystal films are also highlighted. Besides, the applications of the 2D MX2 in high-performance electronic devices are also discussed. Finally, the current challenges for the wafer-scale syntheses of MX2 single crystals and their applications are prospected. The potential opportunities in this field are also proposed in terms of the wafer-scale production and thickness control of 2D MX2, epitaxial growth of wafer-scale MX2 single-crystals, damage-free, and easy-processing transfer of wafer-scale MX2, as well as the high-performance electronics/optoelectronics based on wafer-scale MX2. We believe this review can provide a basic guidance for the controllable growth of wafer-scale MX2 single crystals, and inspire more researchers to design innovative synthesis routes to promote their practical applications in new-generation electronic devices.

Dzyaloshinskii-Moriya anisotropy effect on field-induced magnon condensation in the kagome antiferromagnet α−Cu3.26Mg0.74(OH)6Br2

We performed a comprehensive electron spin resonance, magnetization and heat capacity study on the field-induced magnetic phase transitions in the kagome antiferromagnet $\alpha-Cu_3Mg(OH)_6Br_2$. With the successful preparation of single crystals, we mapped out the magnetic phase diagrams under the $c$-axis and $ab$-plane directional magnetic fields $B$. For $B\|c$, the three-dimensional (3D) magnon Bose-Einstein condensation (BEC) is evidenced by the power law scaling of the transition temperature, $T_c\propto (B_c-B)^{2/3}$. For $B\|ab$, the transition from the canted antiferromagetic (CAFM) state to the fully polarized (FP) state is a crossover rather than phase transition, and the characteristic temperature has a significant deviation from the 3D BEC scaling. The different behaviors of the field-induced magnetic transitions for $B\|c$ and $B\|ab$ could result from the Dzyaloshinkii-Moriya (DM) interaction with the DM vector along the $c$-axis, which preserves the $c$-axis directional spin rotation symmetry and breaks the spin rotation symmetry when $B\|ab$. The 3D magnon BEC scaling for $B\|c$ is immune to the off-stoichiometric disorder in our sample $\alpha-Cu_{3.26}Mg_{0.74}(OH)_6Br_2$. Our findings have the potential to shed light on the investigations of the magnetic anisotropy and disorder effects on the field-induced magnon BEC in the quantum antiferromagnet.

Preparation and Characterization of Lithium Niobate Single Crystals Activated with Magnesium and Boron

Preparation and Characterization of Lithium Niobate Single Crystals Activated with Magnesium and Boron

Single Crystal Preparation and Luminescent Properties of Lu2O3:Eu Scintillator by Vertical Bridgman Method

AbstractEuropium‐doped lutetium oxide (Lu2O3:Eu) single crystal is grown by vertical Bridgman method for the first time. Correlated measurements of X‐ray diffraction, X‐ray fluorescence spectra, optical transmittance, photoluminescence excitation, photoluminescence (PL), PL decay, and X‐ray excited luminescence (XEL) spectra are performed. The transmittance of about 80% above 300 nm indicates that the crystal is of good optical quality. By measuring actual Eu3+ concentration, the effective segregation coefficient of Eu3+ in the Lu2O3:Eu crystal is calculated to be 0.75. In the PL spectrum, the dominant emission peaks at 612 and 630 nm originate from the 5D0→7F2 transitions of Eu3+ in C2 site. It is worth mentioning that several emission peaks between 575 and 605 nm mainly ascribe to the transitions of different 5D0 levels to the split 7F1 levels of Eu(C2) or Eu(C3i). PL decay spectra indicate the decay time of 612 nm emission can be determined about 1.0 ms. The decay curve of 582.6 nm emission can be fitted into triple components, and the 5.3 and 1.4 ms components are attributed to Eu3+(C3i) and Eu3+(C2), respectively. The XEL strongest emission of Lu2O3:Eu sample is around 612 nm with a bright red luminescence that matches silicon photodetectors sensitivity.

Research on Silicon Wafer Manufacturing Process and Physical Properties Testing Using High-Purity Polysilicon

The shape of a bare wafer is round, so it is called a wafer or a silicon wafer. It is the basis for the production of silicon semiconductor integrated circuits. The silicon wafer is cut from a large piece of semiconductor material silicon ingot. The high-purity polysilicon (its purity is up to 99.999999999%) is into a large single crystal, given the correct orientation and an appropriate amount of N-type or P-type doping, a silicon ingot is obtained through five-step crystal growth. Wafers (wafers) are then made from silicon ingots by more than eight processes. This paper investigates the single crystal silicon growth and wafer preparation process technology, and finally discusses the evolution of wafer size growth and changes in the development of the semiconductor industry chain.

Preparation of polyethylene oxide single crystals via liquid gating technology and morphology design strategy

A novel type of liquid gating technology has been developed to prepare a polyethylene oxide (PEO) single-crystal film, and the crystal growth was observed via atomic force microscopy. The self-seeding method has been widely used in the preparation of polymer single crystals, but the mechanism through which single polymer crystals are formed via the combination of liquid gating technology and the self-seeding method remains unclear. To elucidate the mechanism of this process, a series of experiments were conducted in which a dilute polymer solution was sprayed onto a mica substrate to form a single-crystal film through liquid gating technology to study the effect of the crystallization time on the morphology of a thiol PEO (mPEO-SH) crystal. Based on this research, it was found that liquid gating helps to prevent twinning during crystal growth. The combination of liquid gating and self-seeding technology thus provides a new strategy for polymer single-crystal growth.

Preparation of low cost NaCl single crystal for IR optical window applications

Preparation of low cost NaCl single crystal for IR optical window applications

Twisting of 2D Kagomé Sheets in Layered Intermetallics.

Chemical bonding in 2D layered materials and van der Waals solids is central to understanding and harnessing their unique electronic, magnetic, optical, thermal, and superconducting properties. Here, we report the discovery of spontaneous, bidirectional, bilayer twisting (twist angle ∼4.5°) in the metallic kagomé MgCo6Ge6 at T = 100(2) K via X-ray diffraction measurements, enabled by the preparation of single crystals by the Laser Bridgman method. Despite the appearance of static twisting on cooling from T ∼300 to 100 K, no evidence for a phase transition was found in physical property measurements. Combined with the presence of an Einstein phonon mode contribution in the specific heat, this implies that the twisting exists at all temperatures but is thermally fluctuating at room temperature. Crystal Orbital Hamilton Population analysis demonstrates that the cooperative twisting between layers stabilizes the Co-kagomé network when coupled to strongly bonded and rigid (Ge2) dimers that connect adjacent layers. Further modeling of the displacive disorder in the crystal structure shows the presence of a second, Mg-deficient, stacking sequence. This alternative stacking sequence also exhibits interlayer twisting, but with a different pattern, consistent with the change in electron count due to the removal of Mg. Magnetization, resistivity, and low-temperature specific heat measurements are all consistent with a Pauli paramagnetic, strongly correlated metal. Our results provide crucial insight into how chemical concepts lead to interesting electronic structures and behaviors in layered materials.

Preparation and Characterization of Lithium Niobate Single Crystals Doped with Zinc and Erbium

Preparation and Characterization of Lithium Niobate Single Crystals Doped with Zinc and Erbium

Synthesis of Wafer‐Scale Graphene with Chemical Vapor Deposition for Electronic Device Applications

AbstractThe first isolation of graphene opens the avenue for new platforms for physics, electronic engineering, and materials sciences. Among several kinds of synthesis approaches, chemical vapor deposition is most promising for the growth at wafer‐scale, which is compatible with the Si‐based electronic device integration protocols. In this review, the types, properties, and synthesis methods of graphene are first introduced. Many details of wafer‐scale graphene synthesis by chemical vapor deposition strategies are given, including the wafer‐scale single crystal metal and alloy preparation, roll to roll synthesis over Cu, roll to roll electrochemical transfer technique. Besides, the batch‐to‐batch synthesis are highlighted for direct graphene over dielectric substrates such as sapphire and Si/SiO2. The electronic transport and transparent conductance of the wafer‐scale graphene are compared with high‐quality single crystal. The progress and proof‐of‐the‐concept are briefly recalled in graphene‐based electronics such as transistors, sensors, integrated circuits, and spin transport valves. Eventually, the readers are provoked with the current challenges as well as the future opportunities.​

Two-dimensional halide perovskite single crystals: principles and promises

In the last few years, two-dimensional (2D) metal halide perovskites (MHPs) are gaining tremendous attention and are replacing their three-dimensional (3D) congeners rapidly. These next-generation halide perovskites can circumvent the limitations of the 3D MHPs such as stability and structural diversity. The incorporation of bulky organic cation can not only prevent the moisture penetration into the crystal lattice and thus providing greater stability but also expands the field of hybrid semiconducting materials by offering structural diversity. These unique features render even higher tuneability and improved photophysical properties and as a result intensive investigations have been made for 2D MHP–based polycrystalline thin films. However, single crystals based on two-dimensional halide perovskites are still emerging and have great potential for future device applications. Along with the hybrid halide perovskites, the all inorganic halide perovskites are also blossoming. In this review, we have discussed exclusively the development of hybrid as well as all inorganic two-dimensional halide perovskites. First, we have discussed the crystal structure of 2D perovskites. In the next section, different growth procedures reported for preparation of single crystals are discussed. We then highlight the effect of doping on single crystals and their optoelectronic properties. Finally, we discuss the current challenges and future perspectives to further develop 2D single crystals for their efficient use in various devices.

Erratum: “Preparation, thermoelectric properties, and crystal structure of boron-doped Mg2Si single crystals” [AIP Advances 10, 035115 (2020)

First Page