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1.
The extensive polygonization of 200 nm rutile crystals in high-energy dry milling allowed to study the spectral properties of grain boundaries and adjacent microstrained crystalline matter. Changes in UV, VIS, NIR, IR and FIR spectra during milling were followed. For the UV absorption edge the value of unstrained rutile was retained while residual traces of anatase, intergrown with the rutile phase, continued to act as traps for photoinduced charges. The evolving broad absorption in VIS and NIR could be attributed to electrons weakly bound to defects in the packing of oxygen anions at the grain boundaries, which may relax to face-sharing Ti3+-O octahedra. Among the IR-active lattice vibrations, the narrow Eu(2) band showed a shift to higher frequencies by 15 cm−1 which is definitively not due to phonon confinement or Fröhlich surface modes but probably to coupling of the bulk phonon to a plasmon at the grain boundary. At the external surface of the polygonized primary particle, the regular atomic order is destroyed by milling so that hydroxylation is replaced by physisorption of H2O, as shown by IR and TG.  相似文献   

2.
Near-normal incident infrared reflectivity spectra of (100) MgAl2O4 spinel single crystal have been measured at different temperatures in the frequency region between 50 and 6000 cm^-1. Eight infrared-active phonon modes are identified, which are fitted with the factorized form of the dielectric function. The dielectric property and optical conductivity of the MgAl2O4 crystal are analysed. From TO/LO splitting, the effective Szigeti charges and Born effective charges at different temperatures are calculated for studying the ionicity and the effect of polarization. Based on the relationship between the (LO-TO)1 splitting, which represents the transverse and longitudinal frequencies splitting of the highest energy phonon band in the reflectivity spectrum, and the ionic-covalent parameter, the four main phonon modes are assigned. MgA1204 can be considered as a pure ionic crystal and its optical characters do not change with decreasing temperature, so it may be used as a suitable substrate for high-Tc superconducting thin films.  相似文献   

3.
Dark currents in a biased quantum well fabricated using Al0.27Ga0.73As/GaAs heterojunctions are calculated at two different temperatures including thermionic field emission currents arising from the electron scattering with phonons and plasmons. In the electron–phonon scattering process several modes due to heterojunctions such as the confined, half-space and interface longitudinal optic phonons are taken into account. It is found that the confined phonon scattering process results in maximum currents compared to those obtained in the half-space and interface scattering modes. However, the magnitude of the currents that resulted from the electron–plasmon scattering process is found to be higher than that found from the electron scattering with confined phonons. Comparison of the calculated dark currents with experiments shows that the thermionic emission currents due to phonon and plasmon assisted processes are essential to get better agreement with experiments than the previously employed bulk phonon scattering process.  相似文献   

4.
We report the first Raman investigation of the rutile material RuO2. The four allowed first-order Raman-active phonon modes have been observed and classified. Comparison is made with other rutile materials.  相似文献   

5.
Infrared Fourier transform spectroscopy has been used to investigate phonon and plasmon modes in Cd1-xHgxTe and CdTe thin layer on GaAs substrate. Attenuated total reflection (ATR) spectroscopy has been used to excite surface plasmon and phonon polaritons. The plasmon-LO phonon coupling modes in samples are studied by dispersion curve calculation for various carrier concentrations. There exist three branches of coupled modes in dispersion curve. For analysis of the far infrared polarized reflectivity spectra we employ the harmonic oscillator dielectiic function model and the Drude model for free carrier response. We find that the coupling modes dependent to the concentration of free carriers. Furthermore, the experimental data have been used to calculate carrier concentration, composition parameter, mobility of carrier, thickness of layer and gap energy.  相似文献   

6.
A first principles calculation of the lattice dynamical properties of rutile SnO2 has been performed using density functional perturbation theory at ambient and high‐pressure conditions to understand the pressure‐induced phase transition. The calculated zone centre phonon modes at ambient and high pressures have been compared with Raman scattering and infrared measurements. Full phonon dispersion curves and phonon densities of states and Raman intensities at high pressures are calculated and given for the first time in literature. The ferroelastic transition from the rutile to the CaCl2‐type structure was confirmed. It is clearly illustrated that the first transition is associated with macroscopic shear instability which arises from the strong coupling between elastic constants and softening of Raman active B1g mode. The observed pressure of phase transition in experimental measurements was reproduced more accurately than in previous calculations, and the difference between observed and calculated transition pressure is only of the order of 2%. The mode Grüneisen parameter is quantitatively as well as qualitatively different from the earlier reported values. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

7.
In this work polarized infrared Fourier transform spectroscopy is employed to study the electronic and optical properties of doped Ga1-xNxAs ternary alloy and GaN-Ga1-xNxAs MQW. We have analyzed the far infrared spectra of GaN-GaNAs MQW by using a simple macroscopic theory base on effective medium approximation model. The dispersion curve of coupled LO phonon- plasmon modes were calculated from the polarized infrared reflectivity data. The GaNAs layer shows two-mode behavior in the infrared spectral range, a GaAs-like and a GaN-like sublattices. We detect the transverse optic phonon of GaN sublattice around 475 cm-1. The origin of the sharp feature in p-polarization reflectivity about 300 cm-1 as well as the dip at LO phonon frequency of GaAs sublattice are due to Brewster mode. The Brewster mode is couple strongly to plasmon mode. Attenuated total reflection spectroscopy has been used to excite and investigate surface plasmon and surface polariton.  相似文献   

8.
The Raman spectra of single crystals of CrO2 and MoO2 have been studied from 77°K to 500°K for a comparison with the heavily damped phonon features in metallic VO2. The spectrum of MoO2 is very similar to that of monoclinic VO2 whereas CrO2 exhibits phonon spectra similar to rutile with no appreciable change at the ferromagnetic c curie temperature. The results are discussed with respect to the various models proposed for the semiconductor-to-metal transition in VO2.  相似文献   

9.
The local-density approximation is used to find the phonon dispersion relations, total and partial phonon density of states for TiO2 crystal of rutile structure. For that the Hellmann-Feynman forces were computed and direct method applied. Some thermodynamic quantities are also presented. Calculated results are analyzed and compared with the experimental neutron scattering and optic data. Good agreement has been achieved. A giant LO/TO splitting is observed for A2u and Eu modes.  相似文献   

10.
We present new measurements of infrared reflectivity of Cd3As2 at 15 K. One plasmon and eleven phonon characteristics are determined by the fitting process that reveals weak dipolar moments in the structure.  相似文献   

11.
Surface phonon and plasmon–phonon polariton characteristics of GaAs, Al x Ga1?x As/GaAs, and GaN/Al2O3 layered structures are investigated by means of terahertz radiation reflection spectroscopy. The strong resonant absorption peaks and selective emission of the THz radiation dependent upon the lattice composition and free electron density in these layered structures are experimentally observed and analyzed.  相似文献   

12.
Infrared Fourier transform spectroscopy has been used to investigate phonon, plasmon, surface polariton and plasma-longitudinal optical phonon coupling in highly donor doped multi quantum wells (GaAs/Al0.33Ga0.67As) and direct band gap n- type AlXGa1-XAs thin layer on GaAs substrate. Using different samples with different concentration of free carriers. The dispersion equation of coupling modes have been calculated by using the condition which the dielectric functions of samples are zero for longitudinal coupled modes and experimental papameters which have been obtained from the best fit p-polarized oblique incidence far infrared reflection spectra. In MQW samples, the free carriers confined to the well and carriers are quasi two dimensional. So, plasmon- LO phonon coupling occur in the well (GaAs). In n- type AlXGa1-XAs thin layer, the coupled modes consist of three branches of the high, intermediate and low frequency modes. Their frequencies depend on both concentration and alloy composition. To analyses the surface polariton modes we carry out attenuated total reflection (ATR) measurements. In order to support our assignment the magnetic field profiles and surface polariton dispersion curves have been calculated.  相似文献   

13.
Far infrared measurements give detailed information on the phonon and plasmon contributions to the dielectric response of p-doped GaAs–Al0.33Ga0.67As superlattices grown on (311) GaAs substrates. The measured spectra are in good agreement with theoretical spectra which take account of the optical response of confined optical phonon modes in the dielectric function of the short period part of the structures and the directional dependence of the plasma response in the wells of the MQW part of the samples. The effect of surface roughness was included in modeling. We also report some evidence of intersubband transitions of holes by far infrared transmission measurements at the Brewster angle.  相似文献   

14.
A continuum model is developed which describes the infrared absorption of interacting spheres very much smaller than the wavelength of light. A mode with uniform polarization inside the sphere is assumed responsible for the absorption. The frequency of this mode in a small isolated sphere can be greatly shifted from the bulk value due to the surface polarization charge. If the particles are not isolated, this frequency is also influenced by the dipolar interaction of neighboring particles. We find that it is possible to define an average dielectric function for a layer of small interacting, absorbing spheres which has the Lorentz form for either phonon or plasmon excitations. If both plasmon and phonon excitations are possible in the same particle, the absorption coefficient of the coupled system displays two resonances and an antiresonance.  相似文献   

15.
The magnetron sputtering of Ag nanoparticles onto ZnO nanorod arrays is studied. The lateral faces of the nanorods are coated with nanoparticles at a much lower density as compared to the flat faces at comparable sputtering times. The silver density is high on the edges of the lateral faces of the nanorods. The plasmon absorption in the synthesized arrays of nanorods coated with individual Ag nanoparticles is maximal at 450?C500 nm. The appearance of local plasmon excitations increases the intensity of the multiphonon processes with the participation of ZnO polar modes in Raman spectra. The cross section of resonance Raman scattering for A 1(LO) phonon overtones increases with the equivalent Ag film thickness.  相似文献   

16.
Size effects on the phonon modes have been unambiguously observed on single individual titanium dioxide (TiO2) nanowire using Raman spectroscopy. A template-free oxidation process using ethanol vapor was developed to control the growth and the density, length, and size distribution of the TiO2 nanowires. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction were used to characterize the morphology, crystalline phases and microstructures. Using a confocal laser probe, Raman spectroscopy revealed in the individual rutile TiO2 nanowire, the Eg, A1g vibration modes which are confined in the radial directions. Along the single-crystalline nanowire axis, the systematic size-dependent variations in the center-shift, broadening as well as the shape asymmetry of the Raman peaks can be well explained in terms of the phonon confinement model.  相似文献   

17.
Thin-film assemblies of magnesium fluoride/aluminium/BK7-glass (MgF2/Al/BK7) and rutile/aluminium/BK7-glass (TiO2/Al/BK7) are experimentally studied, both by a direct coupling of evanescent waves and by a coupling of guided waves into surface plasmon waves (SPWs). Anisotropic effects of the prism coupler as well as the MgF2 and the TiO2 films on the phase-matching condition are examined theoretically and experimentally. The dielectric function of the Al films is recovered from SPW experiments with an uncertainty <10%.  相似文献   

18.
杨昌虎  马忠权  徐飞  赵磊  李凤  何波 《物理学报》2010,59(9):6549-6555
采用溶胶-凝胶法在石英玻璃衬底上用旋涂法制备了未掺杂、掺杂钇和掺杂镧的TiO2薄膜样品,对样品在700—1100 ℃范围内进行退火处理,并对样品的拉曼光谱进行了分析.分析表明:随着退火温度的升高,未掺杂TiO2薄膜发生了从锐钛矿相经混相最终向金红石相的转换,掺杂钇和掺杂镧对TiO2薄膜的晶相转换起阻碍作用,掺杂镧的阻碍作用更强;稀土掺杂能使TiO2薄膜晶粒细化,并使晶粒内部应力增大从而阻碍晶格振动,掺杂镧比掺杂钇的效果 关键词: 2薄膜')" href="#">TiO2薄膜 稀土掺杂 拉曼光谱 溶胶-凝胶  相似文献   

19.
The far-infrared reflectivity spectra of CdTe0.97Se0.03 and CdTe0.97Se0.03(In) single crystals were measured at different temperatures. The analysis of the far-infrared spectra was carried out by a fitting procedure based on the dielectric function which includes spatial distribution of free carriers as well as their influence on the plasmon–phonon interaction. We found that the long wavelength optical phonon modes of CdTe1xSex mixed crystals exhibit a two-mode behavior. The local In mode at about 160 cm−1 is observed. In both sample, a surface layer with a low concentration of free carriers (depleted region) are formed.  相似文献   

20.
The vibrational properties of InN films with different strain have been studied using Infrared ellipsometry and Raman scattering spectroscopy. We have established a correlation between the phonon mode parameters and the strain, which allows the determination of the deformation potentials and the strain-free frequencies of the InN E1(TO) and E2 modes. The LO phonons and their coupling to the free-carrier plasmon excitations are also discussed in relation to the carrier concentration in the films.  相似文献   

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