HFCVD法制备纳米晶态SiC及其室温下的光致发光

用热丝化学气相沉积(HFCVD)法以CH4和SiH4作为反应气体在Si衬底上制备了纳米晶态6H-SiC。为减小6H-SiC与Si衬底之间的晶格失配,在HFCVD系统中通过对Si衬底表面碳化处理制备了缓冲层,确立了形成缓冲层的最佳条件。采用扫描电镜、傅里叶红外吸收谱和X射线衍射等分析手段对样品进行了结构和组分分析。结果表明,在较低的衬底温度下所沉积的是晶态纳米SiC,纳米晶粒平均尺寸约为60nm,并在室温下观察到所制备的纳米SiC位于380～420nm范围内的短波可见光。研究和分析了碳化时间对发光峰及红外吸收峰位置的影响。     

HFCVD法制备纳米晶体碳化硅薄膜中氢流量对晶粒尺寸的影响

以甲烷、硅烷和氢气为反应气体,采用热丝化学气相沉积(HFCVD)法在单晶硅衬底上沉积纳米晶体碳化硅(SiC)薄膜.通过X射线衍射(XRD)和扫描电子显微镜(SEM)分别对SiC薄膜的晶体结构和表面形貌进行分析.实验发现氢气流量对碳化硅薄膜晶粒尺寸有很大影响,当氢气流量从10SCCM变化到300SCCM时,薄膜晶粒的平均尺寸将由较大的400 nm左右减小到40 nm左右.     

HFCVD法制备纳米晶体碳化硅薄膜中氢流量对晶粒尺寸的影响

以甲烷、硅烷和氢气为反应气体,采用热丝化学气相沉积（HFCVD）法在单晶硅衬底上沉积纳米晶体碳化硅(SiC)薄膜.通过X射线衍射(XRD)和扫描电子显微镜（SEM）分别对SiC薄膜的晶体结构和表面形貌进行分析.实验发现氢气流量对碳化硅薄膜晶粒尺寸有很大影响,当氢气流量从10SCCM变化到300SCCM时,薄膜晶粒的平均尺寸将由较大的400 nm左右减小到40 nm左右.     

Synthesis of silicon carbide films by combined implantation with sputtering techniques

Silicon carbide (SiC) films were synthesized by combined metal vapor vacuum arc (MEVVA) ion implantation with ion beam assisted deposition (IBAD) techniques. Carbon ions with 40 keV energy were implanted into Si(1 0 0) substrates at ion fluence of 5 × 10¹⁶ ions/cm². Then silicon and carbon atoms were co-sputtered on the Si(1 0 0) substrate surface, at the same time the samples underwent assistant Ar-ion irradiation at 20 keV energy. A group of samples with substrate temperatures ranging from 400 to 600 °C were used to analyze the effect of temperature on formation of the SiC film. Influence of the assistant Ar-ion irradiation was also investigated. The structure, morphology and mechanical properties of the deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindentation, respectively. The bond configurations were obtained from IR absorption and Raman spectroscopy. The experimental results indicate that microcrystalline SiC films were synthesized at 600 °C. The substrate temperature and assistant Ar-ion irradiation played a key role in the process. The assistant Ar-ion irradiation also helps increasing the nanohardness and bulk modulus of the SiC films. The best values of nanohardness and bulk modulus were 24.1 and 282.6 GPa, respectively.     

Morphology and properties of ZnO films obtained by repeated spin coating on porous silicon substrates

Layers of porous silicon (PS), multilayered ZnO films, and heterostructures based on them are obtained. The surface morphology, chemical and phase composition of the PS layers and ZnO films, and the transverse cleavage of ZnO–PS nanocomposite, are investigated via energy-dispersive X-ray spectral analysis (EDX), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The current–voltage characteristics of Al/Ag/p-Si(100)/PS/ZnO/Ag/Al and Al/Ag/p-Si(100)/PS/ZnO/SiC/Ag/Al heterostructures are studied.     

Growth and characterization of β-SiC films obtained by fs laser ablation

We achieved the growth of cubic silicon carbide (SiC) films on (1 0 0)Si substrates by pulsed laser deposition (PLD) at moderate temperatures such as 750 °C, from a SiC target in vacuum. The as-deposited films are morphologically and structurally characterized by scanning electron microscopy (SEM), conventional and high-resolution transmission electron microscopy (TEM/HRTEM). The morphology of deposited films is dominated by columns nucleated from a thin nanostructured beta silicon carbide (β-SiC) interface layer. The combined effects of columnar growth, tilted facets of the emerging columns and the presence of particulates on the film surface, lead to a rather rough surface of the films.     

Influence of radiofrequency power on compositional, structural and optical properties of amorphous silicon carbonitride films

The silicon carbonitride (SiCN) films were deposited on n-type Si (1 0 0) and glass substrates by the radiofrequency (RF) reactive magnetron sputtering of polycrystalline silicon target under mixed reactive gases of acetylene and nitrogen. The films have been characterized by energy dispersive spectrometer (EDS), atomic force microscope (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectrophotometer (UVS). The influence of RF power on the compositional, morphological, structural and optical properties of the SiCN films was investigated. The SiCN films deposited at room temperature are amorphous, and the C, Si and O compositions except N in the films are sensitive to the RF power. The surface roughness and optical band gap decrease as the RF power increases. The main bonds in the SiCN films are C-N, N-H_n, C-H_n, C-C, CN, Si-H and Si-C, and the intensities of the CN, Si-H and C-H_n bonds increase with increment of the RF power. The mechanisms of the influence of RF power on the characteristics of the films are discussed in detail.     

Crystallization and surface morphology evolution of erbium fluoride films on different substrates

Erbium fluoride (ErF₃) films were thermally deposited on Ge(1 1 1), Si(0 0 1) and copper mesh grid with different substrate temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the films. The structure of ErF₃ films deposited on germanium and silicon changed from amorphous to crystalline with increasing the substrate temperature, while the crystallization temperature of the films on silicon is higher than that of on germanium. The infrared optical properties of the films change greatly with the evolution of crystal structure. It is also found that the morphology of ErF₃ film on Ge(1 1 1) at 200 °C is modulated by the stress between the substrate and film. The SEM and TEM results confirmed that the ErF₃ films on copper mesh grid were crystalline even at 100 °C. Interestingly, the ErF₃ films show flower-like surface morphology when deposited on copper mesh at 200 °C. The crystallization temperature (T_c) of ErF₃ films on the three substrates has the relation which is which is induced by the wetting angle of ErF₃ films on different substrates.     

Silicon Carbide Nanoparticles Produced by CO2 Laser Pyrolysis of SiH4/C2H2 Gas Mixtures in a Flow Reactor

Pulsed CO₂-laser-induced decomposition of different mixtures of SiH₄ and C₂H₂ in a flow reactor has been employed to produce silicon carbide clusters and nanoparticles with varying content of carbon. The as-synthesized species were extracted from the reaction zone by a conical nozzle and expanded into the source chamber of a cluster beam apparatus where, after having traversed a differential chamber, they were analyzed with a time-of-flight mass spectrometer. Thin films of silicon carbide nanoclusters were produced by depositing the clusters at low energy on potassium bromide and sapphire windows mounted into the differential chamber. At the same time, Si and SiC nanoparticles were collected in a filter placed into the exhaust line of the flow reactor. Both beam and powder samples were characterized by FTIR spectroscopy. The close resemblance of the spectra suggests that the composition of the beam and powder particles obtained during the same run is nearly identical. XRD spectroscopy could only be employed for the investigation of the powders. It was found that CO₂ laser pyrolysis is ideally suited to produce silicon carbide nanoparticles with a high degree of crystallinity. Nanopowders produced from the pyrolysis of a stoichiometric (2:1) mixture of SiH₄/C₂H₂ were found to contain particles or domains of pure silicon. The characteristic silicon features in the FTIR and XRD spectra, however, disappeared when C₂H₂ was applied in excess.     

X-ray micro-computed tomography of beech wood and biomorphic C,SiC and Al/SiC composites

The microstructures of beech wood and of beech wood-derived carbon, silicon carbide (SiC), and an aluminum/SiC composite were studied using both scanning electron microscopy (SEM) and synchrotron X-ray micro-computed tomography (µCT). As opposed to traditional two-dimensional imaging techniques, the µCT data allowed nondestructive evaluation of relatively large sample volumes. Nondestructive three-dimensional data analysis led to the observation of microstructural features, such as varying pore-wall topographies not previously seen in SEM, calculations of the volume fraction of porosity and characterization of the interconnectivity of porosity in the SiC material.     

Amorphous silicon carbide thin films doped with P or B for the photoelectrochemical water splitting devices

Photoelectrochemical water splitting devices require semiconductor photoelectrode material fulfilling a number of primary requirements such as band gap, band edge alignment and corrosion resistance to electrolyte. Amorphous silicon carbide films, undoped and doped (P or B), were deposited on Si substrates by PECVD technology. The concentration of elements in the films was determined by RBS and ERD analytical method. Raman spectroscopy study of the SiC films were performed by using a Raman microscope and chemical compositions were analyzed by FTIR, before and after immersion of samples to aqueous pH 2.0 and pH 1.0 sulphuric acid electrolyte. Electrical properties of SiC films before and after immersion of samples to aqueous pH 2.0 and pH 1.0 sulphuric acid electrolyte were studied by measurement of the I–V characteristics on structure Al/SiC/Si/Al. Differences between Raman spectra, FTIR spectra and I–V characteristics before and after immersion to electrolyte are discussed.     

Initial study on the structure and photoluminescence properties of SiC films doped with Al

SiC films doped with aluminum (Al) were prepared by the rf-magnetron sputtering technique on p-Si substrates with a composite target of a single crystalline SiC containing several Al pieces on the surface. The as-deposited films were annealed in the temperature range of 400-800 °C under nitrogen ambient. The thin films have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results show that the introduction of Al into films hinders crystalline formation process. And with the increase of annealing temperature, more Si particles are formed in the films, which strongly affect the optical absorption properties. The photoluminescence (PL) spectra of the samples show two peaks at 370 nm and 412 nm. The intensities of the PL peaks are evidently improved after Al doped. We attribute the origin of the two PL peaks to a kind of Si-related defect centres. The obtained results are expected to have important applications in modern optoelectronic devices.     

The structure and optical properties of SiC film on Si (111) substrate with a ZnO buffer layer by RF-magnetron sputtering technique

We have fabricated a multiply layer SiC/ZnO on Si substrates using the RF-magnetron sputtering technique with the targets of a single crystalline SiC and a polycrystalline ZnO. The as-deposited films were annealed in the temperature range of 600–1000 °C under nitrogen ambient. We have observed a strong ultraviolet (UV) emission (370 nm) from the as-deposited SiC/ZnO film and an intense violet emission (412 nm) from the film annealed at high temperature (1000 °C) under nitrogen ambient. The SiC film quality and the PL intensities are considered to be strongly dependent on the crystalline quality of the ZnO buffer layer. With the increase of the annealing temperature, the crystalline quality of the ZnO buffer layer is improved, resulting in the improvement of the SiC film quality and the increase of the PL intensities. The thin films have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) to provide the evidences of photoluminescence (PL). We suggest that the UV emission could be attributed to the nanocrystal silicon particles, that the 395 nm band is related to ZnO buffer layer and has a great relation to the crystalline quality of the ZnO film, and that the violet emission is associated with the emission luminescence from 6H-SiC, which bears on the SiC film quality. The obtained results are expected to have important applications in modern optoelectronic devices.     

Crystallization kinetics of amorphous SiC films: Influence of substrate

The crystallization kinetics of amorphous silicon carbide films was studied by means of X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The films were deposited by radio frequency (r.f.) magnetron sputtering on glassy carbon and single crystalline silicon substrates, respectively. TEM micrographs and XRD patterns show the formation of nano-crystalline β-SiC with crystallite sizes in the order of 50 nm during annealing at temperatures between 1200 and 1600 °C. A modified Johnson-Mehl-Avrami-Kolmogorov (JMAK) formalism was used to describe the isothermal transformation of amorphous SiC into β-SiC as an interface controlled, three-dimensional growth processes from pre-existing small crystallites in the order of 10 nm. These pre-existing crystallites are formed in a transient process in the early stages of crystallization. For films deposited on the silicon substrate, the obtained rate constants of crystallite growth obey an Arrhenius behavior with an activation enthalpy of 4.1 ± 0.5 eV in accordance with literature data. Films deposited on glassy carbon show an increased stability of amorphous SiC films, which is reflected in smaller rate constants of crystallite growth of several orders of magnitude at low temperatures and a higher activation enthalpy of 8.9 ± 0.9 eV. A model is proposed, where the faster crystallization of films on silicon substrates can be explained with the presence of superabundant point defects, which diffuse from the substrate into the film and accelerate the incorporation of atoms from the amorphous into the crystalline phase.     

Positron annihilation in diamond,silicon and silicon carbide

Recent positron lifetime and doppler broadening results on silicon, diamond and silicon carbide are presented in this contribution. In as-grown Czochralski Si ingols vacancies are found to be retained after growth at concentrations typically around 3×10¹⁶/cm³. 10 MeV eleciron irradiation of variously doped Si wafers shows that only high doping concentrations well in excess of the interstitial oxygen concentration causes an increase in the amount of monovacancies retained.In porous silicon very long-lived positronium lifetimes in the range 40–90 ns are found. Polycrystalline diamond films contain various types of vacancy agglomerates but these are found to be inhomogeneously distributed from crystallite to crystallite. Electron irradiation of silicon carbide results in two vacancy-related lifetimes which are interpreted as resulting from carbon and silicon vacancies.Paper presented at the 132nd WE-Heraeus-Seminar on Positron Studies of Semiconductor Defects, Halle, Germany, 29 August to 2 September 1994     

Spatially resolved Raman spectroscopy evaluation of residual stresses in 3C-SiC layer deposited on Si substrates with different crystallographic orientations

Raman scattering studies were performed on hot-wall chemical vapor deposited (heteroepitaxial) silicon carbide (SiC) films grown on Si substrates with orientations of (1 0 0), (1 1 1), (1 1 0) and (2 1 1), respectively. Raman spectra suggested that good quality cubic SiC single crystals could be obtained on the Si substrate, independent of its crystallographic orientation. Average residual stresses in the epitaxially grown 3C-SiC films were measured with the laser waist focused on the epilayer surface. Tensile and compressive residual stresses were found to be stored within the SiC film and in the Si substrate, respectively. The residual stress exhibited a marked dependence on the orientation of the substrate. The measured stresses were comparable to the thermal stress deduced from elastic deformation theory, which demonstrates that the large lattice mismatch between cubic SiC and Si is effectively relieved by initial carbonization. The confocal configuration of the optical probe enabled a stress evaluation along the cross-section of the sample, which showed maximum tensile stress magnitude at the SiC/Si interface from the SiC side, decreasing away from the interface in varied rate for different crystallographic orientations. Defocusing experiments were used to precisely characterize the geometry of the laser probe in 3C-SiC single crystal. Based on this knowledge, a theoretical convolution of the in-depth stress distribution could be obtained, which showed a satisfactory agreement with stress values obtained by experiments performed on the 3C-SiC surface.     

SiC Nanostructures Toward Biomedical Applications and Its Future Challenges

The present work reviews current research activities for possible applications of silicon carbide (SiC) nanostructures. The main attention is devoted to emerging biomedical applications which can bring a boon for a healthy society. Highlights toward the widespread of SiC nanostructures in new fields of applications are reviewed and explained. This article surveys some of the recent work using SiC nanostructures in biomedical field, sensing, and energy harvesting including a review on nanostructure biocompatibility research to date.

The review article begins with an overview of the state of art of silicon carbide along with their behavior, properties, and applications of SiC in bulk, thin films, and nanoscale forms, respectively. The multidisciplinary applications of SiC nanostructures are also highlighted. Different applications elaborated are as follows: (1) biomedical/nanomedical applications, (2) nanoelectronics, (3) sensing applications, (4) energy harvesting, and (5) other emerging areas. The possibility for employing SiC nanostructures to be accomplished in upgrading the existing devices is suggested based on their properties. This article is concluded with some challenges for future applications.     

Polymer-precursor-derived (am-) SiC/TiC composites for resistive heaters in large volume multi-anvil high pressure/high-temperature apparatus

(Amorphous-)SiC/TiC composites for resistive tubular heaters in HP/HT experiments were obtained via a polymer-precursor process. A slurry consisting of a commercial SiC-precursor polymer (allylhydridopolycarbosilane, AHPCS) and TiC powder as conductive filler was applied to the inner walls of zirconia insulation tubes, using a centrifugation-casting method. Resistive coatings with homogeneous thickness of ～200 μm were obtained. The heaters were tested in octahedral multi-anvil assemblies at ～10 GPa with simultaneous recording of heating voltage and current. Up to a maximum temperature of ～1800°C they showed temperature vs. power characteristics reproducible from batch to batch, with resistance decreasing from 0.08 to 0.02 Ω during heating. Microstructural characterization using SEM/EDX was carried out on the recovered SiC/TiC composite material, as well as on pristine resistive heaters directly after coating and curing to 230°C, and after additional pyrolysis at 900°C in argon. In all cases, a stable composite microstructure of an interpenetrating network of TiC particles with either silicon carbide polymer precursor or an amorphous SiC phase were found. The composites were characterized by XRD and thermogravimetry. Further improvement of coating procedure and materials combination (precursor/filler/insulator substrate) may result in advanced coatings, operational well beyond 2000°C.     

Deposition of BN interphase coatings from B-trichloroborazine and its effects on the mechanical properties of SiC/SiC composites

Boron nitride thin films were deposited on silicon carbide fibers by chemical vapor deposition at atmospheric pressure from the single source precursor B-trichloroborazine (Cl₃B₃N₃H₃, TCB). The film growth and structure, as a function of deposition temperature, hydrogen gas flow rate, and deposition time, were discussed. The deposition rate reaches a maximum at 1000 °C, then decreases with the increasing of temperature, and the apparent activation energy of the reaction is 127 kJ/mol. Above 1000 °C, gas-phase nucleation determines the deposition process. The deposited BN films were characterized by Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of BN interphase on the mechanical properties of the unidirectional SiC fiber-reinforced SiC matrix (SiC/SiC) composites was also investigated. The results show that the flexural strength of SiC/SiC composites with and without coating is 276 MPa and 70 MPa, respectively, which indicates that BN interphase coating deposited from B-trichloroborazine precursor can effectively adjust the fiber/matrix interface, thus causing a dramatic increase in the mechanical properties of the composites.     

Structural and optical properties of a-Si1−xCx:H films synthesized by dc magnetron sputtering technique

Hydrogenated amorphous SiC films (a-Si_1−xC_x:H) were prepared by dc magnetron sputtering technique on p-type Si(1 0 0) and corning 9075 substrates at low temperature, by using 32 sprigs of silicon carbide (6H-SiC). The deposited a-Si_1−xC_x:H film was realized under a mixture of argon and hydrogen gases. The a-Si_1−xC_x:H films have been investigated by scanning electronic microscopy equipped with an EDS system (SEM-EDS), X-ray diffraction (XRD), secondary ions mass spectrometry (SIMS), Fourier transform infrared spectroscopy (FTIR), UV-vis-IR spectrophotometry, and photoluminescence (PL). XRD results showed that the deposited film was amorphous with a structure as a-Si_0.80C_0.20:H corresponding to 20 at.% carbon. The photoluminescence response of the samples was observed in the visible range at room temperature with two peaks centred at 463 nm (2.68 eV) and 542 nm (2.29 eV). In addition, the dependence of photoluminescence behaviour on film thickness for a certain carbon composition in hydrogenated amorphous SiC films (a-Si_1−xC_x:H) has been investigated.