Ultra‐Fast Fabrication of <110>‐Oriented β‐SiC Wafers by Halide CVD

Φ80 mm‐diameter, highly <110>‐oriented β‐SiC wafers were ultra‐fast fabricated via halide chemical vapor deposition (CVD) using tetrachlorosilane (SiCl₄) and methane (CH₄) as precursors. The effects of deposition temperature (T_dep) and total pressure (P_tot) on the orientations, microstructures, and deposition rate (R_dep) were investigated. R_dep dramatically increased with increasing T_dep where maximum R_dep was 930 μm/h at T_dep = 1823 K and P_tot = 4 kPa, leading to a maximum of 1.9 mm in thickness in 2 h deposition. The <110>‐oriented β‐SiC was obtained at T_dep > 1773 K and P_tot = 1–4 kPa. Growth mechanism of <110>‐oriented β‐SiC has also been discussed under consideration of crystallographic planes, surface energy, and surface morphology.     

Fast preparation of (111)‐oriented β‐SiC films without carbon formation by laser chemical vapor deposition from hexamethyldisilane without H2

(111)‐oriented β‐SiC films were prepared by laser chemical vapor deposition using a diode laser (wavelength: 808 nm) from a single liquid precursor of hexamethyldisilane (Si(CH₃)₃–Si(CH₃)₃, HMDS) without H₂. The effects of laser power (P_L), total pressure (P_tot) and deposition temperature (T_dep) on the microstructure, carbon formation and deposition rate (R_dep) were investigated. β‐SiC films with carbon formation and graphite films were prepared at P_L ≥ 170 W and P_to ≥ 1000 Pa, respectively. Carbon formation strongly inhibited the film growth. β‐SiC films without carbon formation were obtained at P_tot = 400‐800 Pa and P_L = 130‐170 W. The maximum R_dep was about 50 μm·h^?1 at P_L = 170 W, P_tot = 600 Pa and T_dep = 1510 K. The investigation of growth mechanism shows that the photolytic of laser played an important role during the depositions.     

Effect of Pressure on Microstructure of <111>‐Oriented β‐SiC Films: Research via Electron Backscatter Diffraction

Scanning electron microscopy (SEM) and high‐resolution electron backscatter diffraction (EBSD) has been employed to study the microstructure development of <111 > ‐oriented β‐SiC films prepared by laser chemical vapor deposition (LCVD) with various total pressure (P_tot). The Surface morphology of films evolved from pyramids with sixfold symmetry to needlelike structure by increasing the P_tot. The EBSD results indicated that the higher P_tot (800 Pa) led to the lower neighbor‐pair misorientation and large in‐plane domains in β‐SiC films.     

High‐speed heteroepitaxial growth of 3C‐SiC (111) thick films on Si (110) by laser chemical vapor deposition

3C‐SiC (111) thick films were grown on Si (110) substrate via laser chemical vapor deposition (laser CVD) using hexamethyldisilane (HMDS) as precursor and argon (Ar) as dilution gas. The 3C‐SiC (111) polycrystalline films were prepared at deposition temperature (T_dep) of 1423‐1523 K, whereas the 3C‐SiC (111) epitaxial films were obtained at 1573‐1648 K with the thickness of 5.40 to 9.32 μm. The in‐plane relationship was 3C‐SiC [‐1‐12]//Si [001] and 3C‐SiC [‐110]//Si [‐110]. The deposition rates (R_dep) were 16.2‐28.0 μm/h, which are 2 to 100 times higher than that of 3C‐SiC (111) epi‐grown on Si (111) by conventional CVD. The growth mechanism of 3C‐SiC (111) epitaxial films has also been proposed.     

High Tunability in (111)‐Oriented Relaxor Pb0.8Ba0.2ZrO3 Thin Film with Antiferroelectric and Ferroelectric Two‐Phase Coexistence

Using a sol‐gel method Pb_0.8Ba_0.2ZrO₃ (PBZ) thin film with a thickness of ~320 nm was fabricated on Pt(111)/TiO_x/SiO₂/Si substrate. The analysis results of XRD, SEM, and dielectric properties revealed that this thin film is a (111)‐oriented nano‐scaled antiferroelectric and ferroelectric two‐phase coexisted relaxor. Calculations of dielectric tunability (η) and figure‐of‐merit (FOM) at room temperature display a maximum value of 75% at E = 560 kV/cm and ~236, respectively. High‐temperature stability (η > 75% and FOM > 230 at 560 kV/cm in the range from 300 to 380 K) and high breakdown dielectric strength (leakage current < 1 nA at 598 kV/cm) make the PBZ thin film to be an attractive material for applications of tunable devices.     

Preparation of highly oriented β-SiC bulks by halide laser chemical vapor deposition

Highly oriented β-SiC bulks with high hardness were fabricated by halide laser chemical vapor deposition (HLCVD) using SiCl₄, CH₄ and H₂ as precursors. The effects of total pressure (P_tot) and deposition temperature (T_dep) on the preferred orientation, microstructure, deposition rate (R_dep) and micro-hardness were investigated. The 〈110〉-oriented β-SiC bulks were obtained at low P_tot (2–4 kPa), non-oriented β-SiC bulks were obtained at mediate P_tot (6 kPa), and 〈111〉-oriented β-SiC bulks were obtained at high P_tot (10–40 kPa), exhibiting faceted, cauliflower-like and six-fold pyramid-like microstructure, respectively. The maximum R_dep of 〈111〉- and 〈110〉-oriented β-SiC bulks were 3600 and 1300 μm/h at, respectively. The activation energy obtained by the plot of lgR_dep-T_dep⁻¹ is 170 to 280 kJ mol⁻¹, showing an exponential relation with P_Si. The Vickers micro-hardness of β-SiC bulks increased with increasing P_tot and showed the highest value of 35 GPa at P_tot = 40 kPa with a complete 〈111〉 orientation.     

Crystallographic Orientation Dependence on Electrical Properties of (Bi,Na)TiO3‐based Thin Films

Orientation‐engineered (La, Ce) cosubstituted 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ thin films were epitaxially deposited on CaRuO₃ buffered (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.35 single‐crystal substrates by pulsed laser deposition. The ferroelectric, piezoelectric, dielectric, and leakage current characteristics of the thin films were significantly affected by the crystallographic orientation. We found that the (001)‐oriented film exhibited the best ferroelectric properties with remnant polarization P_r = 29.5 μC/cm² and coercive field E_c = 7.4 kV/mm, whereas the (111)‐oriented film demonstrated the largest piezoelectric response and dielectric permittivity. The bipolar resistive switching behavior, which is predominantly attributed to a combined effect of ferroelectric switching and formation/rupture of conductive filaments, was observed. The conduction mechanisms were determined to be ohmic conduction and Poole–Frenkel emission at high‐ and low‐resistance states, respectively, in all the films.     

Transparent highly oriented 3C-SiC bulks by halide laser CVD

Transparent and highly oriented 3C-SiC bulks were speedily fabricated at deposition temperature (T_dep) of 1623?K by halide laser chemical vapor deposition (HLCVD). The effect of total pressure (P_tot) on the optical transmittance, preferred orientation, microstructure, deposition rate (R_dep) and micro-hardness were investigated. The maximum R_dep of the transparent 3C-SiC reached 2450?μm/h at P_tot?=?10?kPa. With an increase in P_tot, the transmittance of 3C-SiC bulks increased firstly, and then decreased. At P_tot?=?10?kPa, 3C-SiC bulk, a highly <111>-oriented and low density of defects, showed the highest transmittance, greater than 55% in the wavelength range of 800–1100?nm. At P_tot?=?4?kPa and 20?kPa, 3C-SiC bulks showed much lower transmittance, in which contained poorly oriented grains and numerous defects. The Vickers micro-hardness of 3C-SiC bulks increased with increasing P_tot and showed the highest value of 34.8?GPa at P_tot?=?40?kPa.     

Highly (100)‐Oriented Bi(Ni1/2Hf1/2)O3‐PbTiO3 Relaxor‐Ferroelectric Films for Integrated Piezoelectric Energy Harvesting and Storage System

Highly (100)‐oriented 0.38Bi(Ni_1/2Hf_1/2)O₃‐0.62PbTiO₃ relaxor‐ferroelectric films were fabricated on Pt(111)/Ti/SiO₂/Si(111) substrates by introducing a lead oxide seeding layer. A moderate relative permittivity , a low dissipation factor (tan δ < 5%), and strong relaxor‐like behavior (γ = 0.74) over a broad temperature region were observed. The energy storage density of approximately 45.1 ± 2.3 J/cm³ was achieved for films with (100) preferential orientation, which is much higher than the value ~33.5 ± 1.7 J/cm³ obtained from films with random orientation. Furthermore, the PbO‐seeded films are more capable of providing larger piezoelectric response (~113 ± 10 pm/V) compared to the films without seeds (~85 ± 8 pm/V). These excellent features indicate that the highly (100)‐oriented 0.38Bi(Ni_1/2Hf_1/2)O₃‐0.62PbTiO₃ films could be promising candidates for applications in high‐energy storage capacitors, high‐performance MEMS devices, and particularly for potential applications in the next‐generation integrated multifunctional piezoelectric energy harvesting and storage system.     

Strong Near‐Infrared Photoluminescence Emission of (003)‐Oriented MgTiO3 Thin Films

In this study, ilmenite‐MgTiO₃ films were sputtered on p‐type Si(111) substrates and the extrinsic effects, such as grain size, crystallinity, and orientation of photoluminescence (PL) properties of the films are discussed. To reduce the effect of oxygen vacancies (act as shallow defects) on PL emissions in the films, oxygen (O₂) was introduced as the sputtering gas and the excitation light source (λ = 532 nm) which has a corresponding energy (hν = 2.33 eV) below the shallow defect states was used. In this study, intense near‐infrared (NIR) PL emission centered at 810.1 nm at room temperature can be observed when the MgTiO₃ thin films exhibit the preferred (003)‐orientation and accompanied by the presence of hexagon‐shaped grains. In this study, the experiment results reveal that the NIR emission intensity of MgTiO₃ films highly depend on crystal orientation and/or grain morphology.     

Intense Red Photoluminescence Emission of Sol–Gel‐Derived Nanocrystalline Mg2TiO4 Thin Films

In this work, undoped Mg₂TiO₄ thin films were fabricated on p‐type Si(111) substrates by the sol–gel method, and the red photoluminescence (PL) of the films is introduced and discussed. According to the experimental results, the red emission appears when the films have been thermally treated at higher temperatures, which have a long range and well‐organized crystalline arrangement. Furthermore, to have better realization of the red emission mechanism of Mg₂TiO₄ films, the optical band gap of Mg₂TiO₄ (E_g^Mg2TiO4) was estimated at ~3.7 eV; furthermore, 325 nm (corresponding energy, hν = 3.82 eV > E_g^Mg2TiO4) and 633 nm (corresponding energy, hν = 1.96 eV < E_g^Mg2TiO4) excited light sources were used to clarify the position of the defect levels. In addition, the influence of annealing atmospheres (O₂, air, and vacuum) on the red emission of our samples is also discussed. A significant variety of red emissions can be found between these annealing conditions: the red emission can be effectively enhanced by O₂ annealing, but weakened by vacuum annealing. Results reveal that the red emission of Mg₂TiO₄ thin films may be highly dependent on the completeness of the O–X–O (X = Mg, Ti) bonds.     

Structural study of β‐SiC(001) films on Si(001) by laser chemical vapor deposition

β‐SiC thin films have been epitaxially grown on Si(001) substrates by laser chemical vapor deposition. The epitaxial relationship was β‐SiC(001){111}//Si(001){111}, and multiple twins {111} planes were identified. The maximum deposition rate was 23.6 μm/h, which is 5‐200 times higher than that of conventional chemical vapor deposition methods. The density of twins increased with increasing β‐SiC thickness. The cross section of the films exhibited a columnar structure, containing twins at {111} planes that were tilted 15.8° to the surface of substrate. The growth mechanism of the films was discussed.     

High-speed epitaxial growth of SrTiO3 films on MgO substrates by laser chemical vapor deposition

Epitaxial (100) and (111) SrTiO₃ films were prepared on (100) and (111) MgO single-crystal substrates, respectively, using laser chemical vapor deposition. The effect of deposition temperature (T_dep) on the orientation and microstructure of the SrTiO₃ films was investigated. On the (100) MgO substrates, SrTiO₃ films showed a (111) orientation at a low T_dep of 1023 K. (100) SrTiO₃ films, which were epitaxially grown at T_dep=1123–1203 K, had dense cross sections and flat surfaces with rectangular-shaped terraces. On the (111) MgO substrates, (111) SrTiO₃ films were epitaxially grown at T_dep=983–1063 K; however, these films' orientations became random at high T_dep of 1063–1113 K. The (111) SrTiO₃ films consisted of columnar grains with triangular pyramidal caps. The deposition rates of the epitaxial (100) and (111) SrTiO₃ films were 13–25 and 18–32 μm h⁻¹, respectively, which is 5–530 times higher than those obtained by MOCVD.     

Enhanced Thermoelectric Properties in Cu‐Doped c‐Axis‐Oriented Ca3Co4O9+δ Thin Films

Highly c‐axis‐oriented Ca₃Co_4?xCu_xO_9+δ (x = 0, 0.1, 0.2, and 0.3) thin films were prepared by chemical solution deposition on LaAlO₃ (001) single‐crystal substrates. X‐ray diffraction, field‐emission scanning electronic microscopy, X‐ray photoelectron spectroscopy, and ultraviolet‐visible absorption spectrums were used to characterize the derived thin films. The solubility limit of Cu was found to be less than 0.2, above which [Ca₂(Co_0.65Cu_0.35)₂O₄]_0.624CoO₂ with quadruplicated rock‐salt layers was observed. The electrical resistivity decreased monotonously with increasing Cu‐doping content when x ≤ 0.2, and then slightly increased with further Cu doping. The Seebeck coefficient was enhanced from ~100 μV/K for the undoped thin film to ~120 μV/K for the Cu‐doped thin films. The power factor was enhanced for about two times at room temperature by Cu doping, suggesting that Cu‐doped Ca₃Co₄O_9+δ thin films could be a promising candidate for thermoelectric applications.     

Structural,Electrical, and Ferroelectric Properties of Nb‐Doped Na0.5Bi4.5Ti4O15 Thin Films

Ferroelectric Na_0.5Bi_4.5Ti₄O₁₅ (NaBTi) and donor Nb‐doped Na_0.5Bi_4.5Ti_3.94Nb_0.06O₁₅ (NaBTiNb) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates using a chemical solution deposition method. The doping with Nb⁵⁺‐ions leads to tremendous improvements in the ferroelectric properties of the NaBTiNb thin film. Room‐temperature ferroelectricity with a large remnant polarization (2P_r) of 64.1 μC/cm² and a low coercive field (2E_c) of 165 kV/cm at an applied electric field of 475 kV/cm was observed for the NaBTiNb thin film. The polarization fatigue study revealed that the NaBTiNb thin film exhibited good fatigue endurance compared with the NaBTi thin film. Furthermore, the NaBTiNb thin film showed a low leakage current density, which was 1.48 × 10^?6 A/cm² at an applied electric field of 100 kV/cm.     

Greatly enhanced photocurrent in inorganic perovskite [KNbO3]0.9[BaNi0.5Nb0.5O3‐σ]0.1 ferroelectric thin‐film solar cell

Inorganic perovskite [KNbO₃]_0.9[BaNi_0.5Nb_0.5O_3‐σ]_0.1 (KBNNO) ferroelectric thin films with narrow band gap (1.83 eV) and high room‐temperature remnant polarization (Pr = 0.54 μC/cm²) was grown successfully on the Pt(111)/Ti/SiO₂/Si(100) substrates by pulsed laser deposition. Ferroelectric solar cells with a basic structure of ITO/KBNNO/Pt were further prepared based on these thin films, which exhibited obvious external‐poling dependent photovoltaic effects. When the devices were negatively poled, the short‐circuit current and open‐circuit voltage were both significantly higher than those of the devices poled positively. This is attributed to enhanced charge separation under the depolarization field induced by the negative poling, which is superimposed with the built‐in field induced by the Schottky barriers at the interfaces between KBNNO and the two electrodes. When a poling voltage of ‐1 V was applied, the device showed a short‐circuit current as high as 27.3 μA/cm², which was by two orders of magnitude larger than that of the KBNNO thick‐film (20 μm) devices reported previously. This work may inspire further exploration for lead‐free inorganic perovskite ferroelectric photovoltaic devices.     

Eu‐Doped β‐SiAlON Phosphors: Template‐Assistant Low Temperature Synthesis,Dual Band Emission,and High‐Thermal Stability

A hard template route has been successfully developed for synthesis of β‐SiAlON:Eu phosphors at low temperatures. The synthesis utilizes mesoporous silica (SBA‐15) skeleton as an active Si source, combined with the carbothermal reduction and nitridation method. It has been shown that the additional driving force from high surface area and porosity of SBA‐15 enables β‐SiAlON:Eu (with compositions of Si_6?zAl_z?xO_z+xN_8?z?x: xEu, x = 0.010–0.200 and z = 1.000) phosphors to be formed as a dominant phase at low temperature of 1400°C. The resultant β‐SiAlON:Eu phosphor powders exhibit a typical rod‐like morphology and a well dispersed state. By tailoring the Eu²⁺ concentration in the phosphors, a continuous change in emission band can be realized, that is a blue emission dominated for low Eu²⁺ concentrations and a green emission dominated for high Eu²⁺ doping concentrations. Furthermore, the resultant phosphors exhibit a small thermal quenching up to high temperature of 250°C. Therefore, the developed method is beneficial to synthesize LED phosphors of oxynitride systems at lower temperatures.     

Microstructure and texture of polycrystalline 3C–SiC thick films characterized via EBSD

Cubic silicon carbide (3C–SiC) is an excellent protective film on graphite and has been fabricated via laser chemical vapor deposition (LCVD) with an extremely high deposition rate by our research group. To understand comprehensively its growth behavior, the polycrystalline 3C–SiC thick films with the preferred orientation of <111> and <110> were characterized by diverse measurements, especially electron back-scatter diffraction (EBSD). Along the growth direction of the <110>-oriented 3C–SiC, the microstructure changed from equiaxed grains to elongated grains with <111> orientation, and eventually the <110>-oriented columnar grains. The stacking faults in the <110>-oriented 3C–SiC could be marked as <11–20>-oriented 6H–SiC. On the other hand, in the <111>-oriented 3C–SiC films, the microstructure changed from mainly equiaxed grains to large columnar grains. The high-density stacking faults in <111>-oriented 3C–SiC films may lead to the identification of the nominal 2H, 4H and 6H polytypes by Raman spectra and EBSD. The (0001) planes of 2H-, 4H–SiC are perpendicular to the growth direction, while that of 6H–SiC are parallel.     

Synthesis,densification, and microstructure of TaC‐TaB2‐SiC ceramics

The usual way to prepare TaC‐TaB₂ ceramics by adding B₄C to TaC leads to formation of residual C, which degrades samples’ mechanical properties. To eliminate the residual C, we suggest incorporating Si together with B₄C into TaC ceramics, resulting in new ultrahigh‐temperature ceramics (TaC‐TaB₂‐SiC). Dense ceramics (>99%) with SiC volume fraction ranging from 15.86% to 41.04% were fabricated by reactive spark plasma sintering at 1900°C for 5 minutes. The formation of SiO₂‐based transient liquid phase was evidenced by the “film” in intermediate products, which can promote densification. The fine‐grained microstructure in final products was found to be associated with the in situ formed SiC, which impeded TaC and TaB₂ grains from coarsening by the pinning effect. Besides, ultrafine TaB₂ grains (~100 nm) produced during the reaction and then rearranged in liquid also contributed to grain refinement. Compared to TaC‐TaB₂(‐C) ceramics prepared from TaC and B₄C, the acquired composites exhibit better mechanical properties, due to their fine‐grained microstructures and the elimination of residual C.     

Synthesis and growth mechanism of single crystal β‐Si3N4 particles with a quasi‐spherical morphology

Single‐crystal β‐Si₃N₄ particles with a quasi‐spherical morphology were synthesized via an efficient carbothermal reduction‐nitridation (CRN) strategy. The β‐Si₃N₄ particles synthesized under an N₂ pressure of 0.3 MPa, at 1450°C and with 10 mol% unique CaF₂ additives showed good dispersity and an average size of about 650 nm. X‐ray photoelectron spectroscopy analysis revealed that there was no SiC or Si–C–N compounds in the β‐Si₃N₄ products. Selected‐area electron‐diffraction pattern and high‐resolution image indicated single crystalline structure of the typical β‐Si₃N₄ particles without an obvious amorphous oxidation layer on the surface. The growth mechanism of the quasi‐spherical β‐Si₃N₄ particles was proposed based on the transmission electron microscopy and energy dispersive X‐ray spectroscopy characterization, which was helpful for controllable synthesis of β‐Si₃N₄ particles by CRN method. Owing to the quasi‐spherical morphology, good dispersity, high purity, and single‐crystal structure, the submicro‐sized β‐Si₃N₄ particles were promising fillers for preparing resin‐based composites with high thermal conductivity.