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1.
Methods for Thickness Determination of SiC Homoepilayers by Using Infrared Reflectance Spectroscopy
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Infrared reflectance spectra have been widely used to measure layer thickness based either on calculation or on curve fitting, and two traditional methods for thickness determination have been studied. Considering the disadvantages of those two methods, we propose a new fitting model based on the fitting of the fringe order difference. In comparison with the measured results, the new fitting model shows its superiority not only for its stable and accurate results which have great agreement with the results from SEM, but also for its simple and quick fitting process. 相似文献
2.
C. Koimtzoglou V. Kostopoulos C. Galiotis 《Applied Physics A: Materials Science & Processing》2003,76(2):231-239
The micromechanics of tension–tension fatigue loading in model single-fibre composite geometries is investigated in this paper.
In an attempt to emulate the conditions encountered in full carbon fibre composites, the fibres were prestrained prior to
the curing process to ensure that they were free of high residual compressive stresses as a result of resin shrinkage. The
resulting specimens were grouped into two categories depending on the level of the initial fibre prestrain (case A low, case
B high). The cyclic load is designed to be well below the endurance fatigue limit of the polymer matrix (∼0.6%), and to have
a frequency low enough to avoid unwanted thermal post curing. Throughout the preparation procedure, as well as during fatigue
loading, the fibre stress (strain) was constantly monitored by means of laser Raman spectroscopy. The fibre axial stress distributions
at each fatigue step were converted to interfacial shear stress (ISS) distributions, from which important parameters such
as the maximum ISS the system can accommodate, the transfer length for efficient stress built-up and the length required for
the attainment of maximum ISS were obtained. The results showed that, up to 2×106 loading cycles, the main parameters which affected the stress transfer efficiency at the interface were the fibre fracture
process itself and the viscoelastic behaviour of the matrix material.
Received: 7 November 2001 / Accepted: 22 March 2002 / Published online: 5 July 2002 相似文献
3.
G. Martel A. Hideur C. Lefebvre C. Özkul M. Hage-Ali J.M. Koebbel 《Applied physics. B, Lasers and optics》2000,70(1):77-84
The photopyroelectric (PPE) method in a non-contact configuration was proposed to study water migration in starch sheets used
for biodegradable packaging. A 1-D theoretical model was developed, allowing the study of samples having a water profile characterized
by an arbitrary continuous function. An experimental setup was designed or this purpose which included the choice of excitation
source, detection of signals, signal and data processing, and cells for conditioning the samples. We report here the development
of an inversion procedure allowing for the determination of the parameters that influence the PPE signal. This procedure led
to the optimization of experimental conditions in order to identify the parameters related to the water profile in the sample,
and to monitor the dynamics of the process.
Received: 1 June 1999 / Final version: 13 March 2000 / Published online: 7 June 2000 相似文献
4.
M.L.W. Thewalt 《Solid State Communications》2005,133(11):715-725
Recent high resolution spectroscopic studies of excitonic and impurity transitions in high-quality samples of isotopically enriched Si have dramatically expanded our understanding of the effects of isotopic composition on the electronic properties of semiconductors. Prior to these studies on Si, the results for other semiconductors, focusing mainly on the isotopic dependence of the electronic band gap energy EG in the T→0 limit, could all be explained within the virtual crystal approximation (VCA), in which only the average isotopic mass was relevant. Remarkably, not only were the effects of isotopic randomness observable in natural Si (when compared to enriched 28Si), but the random isotopic distribution present in natural Si was found to be the true source of what had been thought of as ‘fundamental’ spectroscopic limits in Si, including the linewidths of bound exciton emission lines and impurity absorption transitions, and the ‘intrinsic’ acceptor ground state splitting. Many of these transitions are far narrower in highly enriched 28Si than in the most perfect natural Si, challenging existing spectroscopic methods, and opening up new possibilities for precision measurements, and for the observation of new physics. 相似文献
5.
A Novel Fully Depleted Air AlN Silicon-on-Insulator Metal--Oxide--Semiconductor Field Effect Transistor
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A novel fully depleted air A1N silicon-on-insulator (SOD metai-oxide-semiconductor field effect transistor (MOS- FET) is presented, which can eliminate the self-heating effect and solve the problem that the off-state current of SOI MOSFETs increases and the threshold voltage characteristics become worse when employing a high thermal conductivity material as a buried layer. The simulation results reveal that the lattice temperature in normal SOI devices is 75K higher than the atmosphere temperature, while the lattice temperature is just 4 K higher than the atmosphere temperature resulting in less severe self-heating effect in air A1N SOI MOSFETs and A1N SOI MOSFETs. The on-state current of air A1N SOI MOSFETs is similar to the A1N SOI structure, and improves 12.3% more than that of normal SOI MOSFETs. The off-state current of A1N SOI is 6. 7 times of normal SOI MOSFETs, while the counterpart of air A1N SOI MOSFETs is lower than that of SOI MOSFETs by two orders of magnitude. The threshold voltage change of air A1N SOl MOSFETs with different drain voltage is much less than that of A1N SOI devices, when the drain voltage is Mased at 0.8 V, this difference is 28mV, so the threshold voltage change induced by employing high thermal conductivity material is cured. 相似文献
6.
Carbon nanotubes (CNTs) are potential strain sensors due to their excellent mechanical and spectral properties. A new theoretical model of a CNT strain sensor is obtained by applying the polarized Raman properties of CNTs, which calculates the synthetic contributions of Raman spectra from the CNTs in random directions. By using this theoretical model, the analytic relationship between planar strain components and the Raman shift increment of uniformly dispersed CNTs is obtained, which is applicable for accurately characterizing the strain in random directions on the surface of a measured microsystem. 相似文献
7.
Study on surface modification of porous apatite-wollastonite bioactive glass ceramic scaffold 总被引:1,自引:0,他引:1
Bin Cao Ming Xue Guangda Li Weizhong Yang Qin Long Li Ji 《Applied Surface Science》2008,255(2):505-508
Chitosan (CS) was used to modify the surface of apatite-wollastonite bioactive glass ceramic (AW GC) scaffold to prepare AW/CS composite scaffold. The in vitro bioactivity of the AW/CS composite scaffold was investigated by simulated body fluid (SBF) soaking experiment. Cell growth on the surface of the material was evaluated by co-culturing osteogenic marrow stromal cells (MSCs) of rabbits with the scaffold. The results showed that the compressive strength of AW GC scaffold was improved dramatically after being modified by CS, whereas the mineralization rate was delayed. MSCs can attach well on the surface of the composite scaffold. 相似文献
8.
Te-Hua Fang Liang-Wen Ji Stephen D. Prior Kuan-Jen Chen Chun-Nan Fang 《Journal of Physics and Chemistry of Solids》2009,70(6):1015-397
In this work, we have investigated the photoluminescence spectra of europium-doped zinc oxide crystallites prepared by a vibrating milled solid-state reaction method. X-ray diffraction, scanning electron microscopy, luminescence spectra and time-resolved spectra analysis were used to characterize the synthetic ZnO:Eu3+ powders. XRD results of the powders showed a typical wurtzite hexagonal crystal structure. A second phase occurred at 5 mol% Eu2O3-doped ZnO. The 5D0-7F1 (590 nm) and 5D0-7F2 (609 nm) emission characteristics of Eu3+ appeared after quenching with more than 1.5 mol% Eu2O3 doping. The Commission Internationale d’Eclairage (CIE) chromaticity coordinates of a ZnO:Eu3+ host excited at λex=467 nm revealed a red-shift phenomenon with increase in Eu3+ ion doping. The lifetime of the Eu3+ ion decreased as the doping concentration was increased from 1.5 to 10 mol%, and the time-resolved 5D0→7F2 transition presents a single-exponential decay behavior. 相似文献
9.
Novel porous ZnO nanobelts were successfully synthesized by heating layered basic zinc acetate (LBZA) nanobelts in the air. The precursor of LBZA nanobelts consisted of a lamellar structure with two interlayer distances of 1.325 and 0.99 nm were prepared using a low-temperature, solution-based method. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and infrared spectroscopy are used to characterize the as-products. PL measurements show that the porous ZnO nanobelts have strong ultraviolet emission properties at 380 nm, while no defect-related visible emission is detected. The good performance for photoluminescence emission makes the porous ZnO nanobelts promising candidates for photonic and electronic device applications. 相似文献
10.
Haizheng Tao 《Solid State Communications》2006,137(8):408-412
Room temperature Raman scattering measurements of samples of the (1−x)GeS2-xIn2S3 (x=0.00-0.35) system have been conducted together with the FTIR transmission spectra of partial samples. Based on the Raman scattering and FTIR transmission spectra of the prepared defect spinel polycrystalline In2S3, the additional peaks at 306 and 245 cm−1 were ascribed to the local symmetric stretching vibration of InS4 tetrahedra and InS6 octahedra, respectively. According to the Raman scattering spectral evolution of the Ge-In sulfide glasses, the microstructure of the studied glasses was considered to be that S3Ge-GeS3 and S3In-InS3 ethane-like units originated from the sulfur deficient with the addition of In2S3 are homogeneously dispersed in a disordered polymer network formed by GeS4, InS4 tetrahedra and a small quantity of InS6 octahedra interconnected by sulfur bridges. 相似文献
11.
Determination of the Li/Nb ratio in lithium niobate by means of birefringence and Raman measurements
U. Schlarb S. Klauer M. Wesselmann K. Betzler M. Wöhlecke 《Applied Physics A: Materials Science & Processing》1993,56(4):311-315
Two optical methods for the determination of the Li/Nb ratio in lithium niobate (LiNbO3) are discussed. Data for the optical birefringence method are presented, they cover the entire composition range in which LiNbO3 can be fabricated and a wide spectral region. The line-widths of lattice modes have been measured by means of Raman scattering as a function of the Li/Nb ratio for single crystals with polished and rough surfaces. 相似文献
12.
Ferroelectric BaTiO3 nanocrystalline films (BTNFs) with the crystalline sizes of about 30 nm were grown on Pt/Ti/SiO2/Si substrates by a modified sol-gel method. Spectroscopic ellipsometry (SE) was used to characterize the films in the photon energy range of 1.5-5.0 eV with a five-phase layered model (air/surface rough layer/BaTiO3/interface layer/Pt). The optical properties in the transparent and absorption regions have been investigated with the Forouhi-Bloomer dispersion relation. With the aid of the structural and dielectric function models, the microstructure and electronic structure of the BTNFs can be readily obtained. It was found that the refractive index reaches the value of 2.20 in the transparent region. Based on the Sellmeier dispersion analysis, the single-oscillator energy is about 4.7 eV for the BTNFs. The long wavelength refractive index n(0) can be estimated to about 2.00 at zero point. The direct optical band gap energy approaches approximately 4.2 eV and Urbach band tail energy is 262±2 and 268±1 meV respectively with increasing crystalline size. A higher band gap observed can be owing to the known quantum confinement effect in the nanocrystalline formation and different fraction of amorphous and crystalline components. The theoretical analysis based on the effective mass approximation theory is well used to explain these experimental data. 相似文献
13.
Impurity centres in high purity silicon with ionization energies 38.32 and 40.09meV are observed by photothermal ionization spectroscopy measurements. Their typical shallow donor characteristics are approved by good agreement with theoretic evaluation under varying magnetic fields. The 2p0 state lifetime of one donor centres are more than 3 times longer than that of phosphorus in the same silicon sample. Compared to phosphorus which has been already successfully exploited to produce silicon-based THz radiations, this shallow donor centre has a pronounced enhancement on lifetime and quality factor of population inversion level. Hence, silicon with this donor centre would be a potential excellent candidate to develop improved silicon-based THz sources. 相似文献
14.
Raman spectra of phosphorous doped ZnSe are recorded from 9 to 300 K. In addition to TO mode at 208 cm−1 and LO mode at 253 cm−1, a new mode around 240 cm−1 is observed between 55 and 270 K. The spectra at lower and higher temperatures do not show the new mode. This new mode confirms that there is a reduction of (Se site) symmetry from Td to C3v when P substitutes for Se. This is due to Jahn Teller distortion. 相似文献
15.
Holger Lange María Machón Mikhail Artemyev Ulrike Woggon Christian Thomsen 《固体物理学:研究快报》2007,1(6):274-276
We investigated the influence of an epitaxially grown ZnS shell on the phonon spectra of CdSe nanorods of different sizes. The CdSe related Raman peaks shift with addition of a ZnS shell. The longitudinal optical phonon shifts slightly due to strain and the low‐energy shoulder shifts stronger, which can be explained within a model for surface optical phonons. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
16.
This paper reports a study of the application of chemical vapor-etching (CVE) for the rear surface and in the emitter of polycrystalline silicon (pc-Si) solar cells. The CVE technique consists of exposing pc-Si wafers to a mixture of HF/HNO3. This technique is used to groove the rear surface of the pc-Si wafers for acid vapors rich in HNO3 (HNO3/HF > 1/4), in order to realize rear-buried metallic contacts (RBMC) and the formation of a porous silicon (PS) layer on the frontal surface of the cell for volume ratio of HNO3/HF = 1/7. A significant increase of the spectral response in the long wavelength range was observed when a RBMC is formed. This increase was attributed to the reduction of the effective thickness of the base of the cells and grain boundary Al gettering. The achievement of a PS layer on the emitter of the pc-Si cells passivates the surface and reduces the reflectivity. The dark I-V characteristics of pc-Si cells with emitter-based PS show an important reduction of the reverse current together with an improvement of the rectifying behaviour. The I-V characteristic under AM1.5 illumination shows an enhancement of both short circuit current density and fill factor. The internal quantum efficiency is improved, particularly in the short wavelengths region. 相似文献
17.
Thin film composition spreads of Mg-Ni were deposited by co-sputtering on micromachined Si-cantilevers. The investigated compositions range from about Mg60Ni40 to about Mg80Ni20. Structural properties as well as mechanical stress before and after hydrogenation were measured with X-ray diffraction (XRD) and laser profilometry, respectively. The composition spreads were hydrogenated in a special pressure vessel, which allows measuring optically the hydrogen-induced deflection (stress-change) of 16 cantilevers as a function of hydrogen pressure and/or temperature. It was found that the hydrogen-induced stress is correlated with the composition and microstructure of the films. Highest hydrogen-induced stress changes were found for compositions close to the crystalline Mg2Ni phase. 相似文献
18.
The intrinsic and phosphorous (P)-doped hydrogenated amorphous silicon thin films were crystallized by laser annealing. The structural properties during crystallization process can be investigated. Observed redshifts of the Si Raman transverse optical phonon peak indicate tensile stress present in the films and become intense with the effect of doping, which can be relieved in P-doped films by introducing buffer layer structures. Based on experimental results, the established correlation between the stress and crystalline fraction (XC) suggests that the relatively high stress can limit the increase in XC and the highest crystalline fraction is obtained by a considerable stress release. At high laser energy density of 1250 mJ/cm2, the poorer crystalline quality and disordered structure of the film originating from the irradiation damage and defects lead to the low electron mobility. 相似文献
19.
N. Esser 《Applied Physics A: Materials Science & Processing》1999,69(5):507-518
Only recently Raman spectroscopy (RS) has advanced into the study of surface phonons from clean and adsorbate-covered semiconductor
surfaces. RS allows the determination of eigenfrequencies as well as symmetry selection rules of surface phonons, by k-conservation limited to the Brillouin zone-center, and offers a significantly higher spectral resolution than standard surface
science techniques such as high-resolution electron energy loss spectroscopy. Moreover, surface electronic states become accessible
via electron–phonon coupling. In this article the fundamentals of Raman scattering from surface phonons are discussed and
its potential illustrated by considering two examples, namely Sb-monolayer-terminated and clean InP(110) surfaces. Both are
very well understood with respect to their atomic and electronic structure and thus may be regarded as model systems for heteroterminated
and clean semiconductor surfaces. In both cases, localized surface phonons as well as surface resonances are detected by Raman
spectroscopy. The experimental results are compared with surface modes predicted by theoretical calculations. On InP(110),
due to the high spectral resolution of Raman spectroscopy, several surface modes predicted by theory can be experimentally
verified. Surface electronic transitions are detected by changing the energy of the exciting laser light indicating resonances
in the RS cross section.
Received: 7 April 1999 / Accepted: 25 June 1999 / Published online: 16 September 1999 相似文献
20.
In the comparison of damage modifications, absorption measurement and energy dispersive x-ray analysis, the effect of vacuum on the laser-induced damage of anti-reflection coatings is analyzed. It is found that vacuum decreases the laser-induced damage threshold of the films. The low laser-induced damage threshold in vacuum environments as opposed to air environments is attributed to water absorption and the formation of the O/Si, O/Zr sub-stoichiometry in the course of laser irradiation. 相似文献