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1.
Jairo A. Cardona-Bedoya Alfredo Cruz-Orea Orlando Zelaya-Angel Julio G. Mendoza-Alvarez 《Journal of nanoparticle research》2008,10(3):519-523
GaNAs thin films were deposited on Corning glass substrates by radio frequency (r.f.) sputtering in molecular nitrogen ambient.
The stoichiometry in the GaNAs alloy was controlled by changing the nitrogen incorporation in the film during the growth process,
through the variation of the r.f. power in the range 30–80 watts which produced films with N concentrations in the range:
x = 0.85–0.90. The structural and optical properties of the GaNAs thin films were studied by X-ray diffraction (XRD), photoacoustic
(PA) and photoluminescence (PL) spectroscopies. XRD measurements show a broad diffraction band with a peak close to the (002)
diffraction line of the GaN hexagonal phase, and a slight shoulder at the position corresponding to the (111) GaAs cubic phase.
The PA absorption spectra showed a remarkable shift to higher energies of the absorption edge as the r.f. power decreases
corresponding to the films with higher N concentrations. Thermal annealing of the GaNAs films at temperatures of 450 °C produced
a GaAs nanocrystalline phase with grain sizes in the range 10–13 nm, as confirmed by the XRD measurements that showed a well-defined
peak in the (111) GaAs direction, and also by the PA spectra which showed an absorption band at energies around 1.45 eV due
to the quantum confinement effects. PL spectra of thermal-annealed GaNAs films showed a very intense emission at 1.5 eV which
we have associated to transitions between the first electron excited level and acceptor states in the GaAs nanocrystallites. 相似文献
2.
We report here high-pressure x-ray diffraction (XRD) studies on tellurium (Te) at room temperature up to 40 GPa in the diamond
anvil cell (DAC). The XRD measurements clearly indicate a sequence of pressure-induced phase transitions with increasing pressure.
The data obtained in the pressure range 1 bar to 40 GPa fit five different crystalline phases out of Te: hexagonal Te (I)
→ monoclinic Te(II) → orthorhombic Te (III) → Β-Po-type Te(IV) → body-centered-cubic Te(V) at 4, 6.2, 11 and 27 GPa, respectively. The volume changes across these transitions
are 10%, 1.5%, 0.3% and 0.5%, respectively.
Self consistent electronic band structure calculations both for ambient and high pressure phases have been carried out using
the tight binding linear muffin tin orbital (TB-LMTO) method within the atomic-sphere approximation (ASA). Reported here apart
from the energy band calculations are the density of states (DOS), Fermi energy (E
f) at various high-pressure phases. Our calculations show that the ambient pressure hexagonal phase has a band gap of 0.42
eV whereas high-pressure phases are found to be metallic. We also found that the pressure induced semiconducting to metallic
transition occurs at about 4 GPa which corresponds to the hexagonal phase to monoclinic phase transition. Equation of state
and bulk modulus of different high-pressure phases have also been discussed. 相似文献
3.
K.?Sudheendran M.?Ghanashyam?Krishna K.?C.?James?Raju 《Applied Physics A: Materials Science & Processing》2009,95(2):485-492
Bismuth Zinc niobate (Bi1.5Zn1.0Nb1.5O7) thin films were deposited by pulsed laser deposition (PLD) method on fused silica substrates at different oxygen pressures.
The structural, microwave dielectric and optical properties of these thin films were systematically studied for both the as-deposited
and the annealed films at 600°C. The as-deposited films were all amorphous in nature but crystallized on annealing at 600°C
in air. The surface morphology as studied by atomic force microscopy (AFM) reveals ultra-fine grains in the case of as-deposited
thin films and cluster grain morphology on annealing. The as-deposited films exhibit refractive index in the range of 2.36–2.53
(at a wavelength of 750 nm) with an optical absorption edge value of 3.30–3.52 eV and a maximum dielectric constant of 11
at 12.15 GHz. On annealing the films at 600°C they crystallize to the cubic pyrochlore structure accompanied by an increase
in band gap, refractive index and microwave dielectric constant. 相似文献
4.
Libin Mo Yongjun Chen Lijie Luo 《Applied Physics A: Materials Science & Processing》2010,100(1):129-134
ZnO films were deposited by RF magnetron sputtering at the substrate temperature of 120∼420°C. XRD measurements revealed the
improvement of crystalline quality and grain size of the films with substrate temperature. The dielectric function of the
films was determined by fitting the experimental transmission spectra with Tauc–Lorentz (TL) model and a single Lorentzian
oscillator (SLO) dispersion function in the energy range of 1∼5 eV. The optical properties of the ZnO films strongly depended
on the substrate temperature. The optical band gap and the Penn gap of the ZnO films increased with the substrate temperature.
The band gap of the ZnO films indicated a direct interband transition between the valence and conduction band, and the change
of the in-plane film stress promoted the enhancement of the band gap. These results of the optical properties of the ZnO films
might be very meaningful to the application in the window design in solar cells. 相似文献
5.
Effects of thermally induced anatase-to-rutile phase transition in MOCVD-grown TiO2 films on structural and optical properties 总被引:2,自引:0,他引:2
D.-J. Won C.-H. Wang H.-K. Jang D.-J. Choi 《Applied Physics A: Materials Science & Processing》2001,73(5):595-600
Titanium dioxide (TiO2) films with a thickness of 550 nm were deposited on quartz glass at 300 °C by metalorganic chemical vapor deposition. The
effects of post-annealing between 600 °C and 1000 °C were investigated on the structural and optical properties of the films.
X-ray diffraction patterns revealed that the anatase phase of as-grown TiO2 films began to be transformed into rutile at the annealing temperature of 900 °C. The TiO2 films were entirely changed to the rutile phase at 1000 °C. From scanning electron spectroscopy and atomic force microscopy
images, it was confirmed that the microstructure of as-deposited films changed from narrow columnar grains into wide columnar
ones. The surface composition of the TiO2 films, which was analyzed by X-ray photoelectron spectroscopy data, was nearly constant although the films were annealed
at different temperatures. When the annealing temperature increased, the transmittance of the films decreased, whereas the
refractive index and the extinction coefficient calculated by the envelope method increased at high temperature. The values
of optical band gap decreased from 3.5 eV to 3.25 eV at 900 °C. This abrupt decrease was consistent with the anatase-to-rutile
phase transition.
Received: 4 October 2000 / Accepted: 4 December 2000 / Published online: 23 May 2001 相似文献
6.
Polycrystalline Pb1−x
Sr
x
(Fe0.012Ti0.988)O3 (0.2≤x≤0.4) (PSFT) thin films have been grown on fused quartz substrates by metallo-organic decomposition technique. The grown films
were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), source meter and UV–Vis–NIR spectrophotometer
to determine the structural, microstructural, dc resistivity and optical properties. The XRD pattern confirmed that the PSFT
films has distorted tetragonal single phase, which close to cubic at higher Sr concentration. AFM analysis revealed that the
grains size reduces with increasing Sr concentration and their average values lies in the range of 26–9 nm. The higher values
of dc resistivity of PSFT nano grains indicate that the transmission of light occurs within these grains up to short wavelength.
The refractive index and the extinction coefficient were determined from the optical transmission spectrum in the wavelength
range of 200–1100 nm and compared with that theoretically calculated, when fitted to a single oscillator model. The values
of optical band gap were determined from Tauc’s extrapolation fitting and suggests that the transformation of electrons during
transmission of light through local states within Fermi gap. 相似文献
7.
B. Y. Man J. Wei C. Yang C. S. Chen M. Liu 《Applied Physics A: Materials Science & Processing》2009,96(4):827-831
ZnO buffer layers have been used to fabricate GaN thin films by using pulsed laser deposition on Si (111) substrates. c-axis GaN thin films were obtained by annealing in NH3 atmosphere at 950°C for 15 min. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and atomic force
microscopy (AFM) have been used for the characterizations of the crystalline quality, composition, and surface morphology
of the films. The annealing in ammonia (NH3) atmosphere markedly affects the preparation of GaN films and the least annealing time is 15 min under our experimental conditions.
The mechanism of the effects of the ZnO buffer layers was studied. In the beginning, Zn–O bonds are destroyed in the interface
of the films; a few O and Zn atoms depart from their positions, while N and Ga atoms fill in the empty positions and form
a hexagonal structure of a special component. Many bonds (such as Ga–O bonds, Zn–N bonds) existed then. The number of Zn–O
bonds decreases and the number of Ga–N bonds increases in the films with increasing of the annealing time. Many other bonds
(such as Ga–O bonds, Zn–N bonds) also decreased and more Ga–N bonds formed with annealing time increasing. After having been
annealed for 15 min under our experimental conditions, the quality of the hexagonal structure GaN films was markedly improved
by the destroying of the Zn–O bonds during high-temperature annealing. 相似文献
8.
N. Rücker 《Zeitschrift für Physik A Hadrons and Nuclei》1974,271(3):281-288
By simultaneous evaporation of LiI and Li onto a cooled substrate F centers can be produced in the hexagonal (78 K<T K <200 K) and amorphous (T K <78 K) phase of one and the same salt. In both modifications there exist two types of centers F and F*. The F* center differs from the cubic F center (T d -symmetry) by a nearby Frenkel defect. In hexagonal films the normal F band peaks at 2.58 eV, whereas the transitions of the F* center appear at 2.92 and 2.58 eV too. Polarized irradiation at 20 K causes a dichroic behaviour of the F* centers. Both types of centers can be transformed into one another photochemically. In the amorphous phase all transitions are shifted to lower energies by about 0.1 eV. After the phase change amorphous→hexagonal the absorption bands shift back by the same amount of energy. AboveT K =230 K the excess metal forms colloids. The absorption bands are due to colloidal centers embedded in the crystalline material (2.25 eV) and films adsorbed to the crystallites (3.1 eV), respectively. By annealing a particle growth can be observed. After electrolytic colouration cubic single crystals of LiI exhibit an absorption band peaking at 2.36 eV. However, it is not yet sure, if this band is allowed to be ascribed to F centers. 相似文献
9.
A low temperature synthesis of CdSe, HgSe and Cd0.5Hg0.5Se alloy thin films in cubic modification under similar set of conditions is presented. The method is based on chemical reaction
of complexed cadmium sulphate, mercuric nitrate or mixtures of both with sodium selenosulphate in aqueous ammonical medium
at 5 °C. The films were characterized by using XRD, Optical absorption, Electrical measurements AAS and EDAX techniques. The
films were found to be uniform, well adherent, dark red, nearly stoichiometric and polycrystalline in cubic form without trace
of any hexagonallity. The growth of film was found to occurs by ion by ion by ion nucleation. CdSe, HgSe and (CdHg)Se films
showed optical band gaps at 1.75 eV, 0.81 eV and 1.34 eV respectively. The electrical conductivity of (CdHg)Se alloy was found
to be of the order of 10−2 (Θcm)−1. The rate of increase of conductivity with temperature was found to reduce with the inclusion of mercury. Thermoelectric
study indicated the presence of n-type conduction mechanism for all the films.
Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003. 相似文献
10.
M. Modreanu J. Sancho-Parramon B. Servet C. Eypert A. Knowles M.-F. Ravet 《Applied Surface Science》2006,253(1):328-334
In the present paper, we investigate the effect of thermal annealing on optical and microstructural properties of HfO2 thin films (from 20 to 190 nm) obtained by plasma ion assisted deposition (PIAD). After deposition, the HfO2 films were annealed in N2 ambient for 3 h at 300, 350, 450, 500 and 750 °C. Several characterisation techniques including X-ray reflectometry (XRR), X-ray diffraction (XRD), spectroscopic ellipsometry (SE), UV Raman and FTIR were used for the physical characterisation of the as-deposited and annealed HfO2 thin films. The results indicate that as-deposited PIAD HfO2 films are mainly amorphous and a transition to a crystalline phase occurs at a temperature higher than 450 °C depending on the layer thickness. The crystalline grains consist of cubic and monoclinic phases already classified in literature but this work provides the first evidence of amorphous-cubic phase transition at a temperature as low as 500 °C. According to SE, XRR and FTIR results, an increase in the interfacial layer thickness can be observed only for high temperature annealing. The SE results show that the amorphous phase of HfO2 (in 20 nm thick samples) has an optical bandgap of 5.51 eV. Following its transition to a crystalline phase upon annealing at 750 °C, the optical bandgap increases to 5.85 eV. 相似文献
11.
Cadmium sulphide (CdS) thin films were prepared chemical bath deposition technique. The films were doped with copper using the direct method consisting in the addition of a copper salt in the deposition bath of CdS. The doped films were annealed in air, at 250, 300 and 350 °C, for 1 h. The deposition films were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis by X-rays (EDAX) and optical properties of CdS thin films before and after Cu doping. XRD analysis shows that the films are polycrystalline in nature with cubic crystalline structure. The various parameters such as crystallite size, micro strain and dislocation density were evaluated. SEM study shows that the total substrate surface is well covered by uniformly distributed spherical shaped grains. Optical transmittance study shows the presence of direct transition with band gap energy decrease 2.5–2.2 eV. 相似文献
12.
Pulsed-laser-induced transformation path of graphite to diamond via an intermediate rhombohedral graphite 总被引:3,自引:0,他引:3
The new phase transformation of hexagonal graphite to cubic diamond was experimentally produced without catalyst, using a
high-power pulsed laser. Interestingly, by the X-ray diffraction spectra, it was proved that this transition was not direct,
but through an intermediate rhombohedral phase. Furthermore, it is important that the rhombohedral phase, as the theoretical
transformation path of hexagonal graphite to cubic diamond, was first truly substantiated by our experimental results. The
transformation mechanism was suggested that diamond with hexagonal structure was obtained by the direct transforming of hexagonal
graphite to hexagonal diamond, and diamond with cubic structure was formed by the indirect transforming, i.e., hexagonal graphite
to rhombohedral graphite to cubic diamond.
Received: 7 February 2000 / Accepted: 28 March 2000 / Published online: 9 November 2000 相似文献
13.
Production and characterization of Nd,Cr:GSGG thin films on Si(001) grown by pulsed laser ablation 总被引:2,自引:0,他引:2
P.R. Willmott P. Manoravi K. Holliday 《Applied Physics A: Materials Science & Processing》2000,70(4):425-429
Nd,Cr:Gd3Sc2Ga3O12 (GSGG) thin films have been produced for the first time. They were grown on Si(001) substrates at 650 °C by pulsed laser
ablation at 248 nm of a crystalline Nd,Cr:GSGG target rod. The laser plume was analyzed using time-of-flight quadrupole mass
spectroscopy, and consisted of elemental and metal oxide fragments with kinetic energies typically in the range 10 to 40 eV,
though extending up to 100 eV. Although films deposited in vacuum using laser fluences of 0.8±0.1 J cm−2 reproduced the Nd,Cr:GSGG bulk stoichiometry, those deposited using fluences above ≈3 J cm−2 resulted in noncongruent material transfer and were deficient in Ga and Cr. Attempts to grow films using synchronized oxygen
or oxygen/argon pulses yielded mixed oxide phases. Under optimal growth conditions, the films were heteroepitaxial, with GSGG(001)[100]∥Si(001)[100],
and exhibited Volmer–Weber-type growth. Room-temperature emission spectra of the films suggest efficient non-radiative energy
transfer between Cr3+ and Nd3+ ions, similar to that of the bulk crystal.
Received: 1 October 1999 / Accepted: 15 October 1999 / Published online: 23 February 2000 相似文献
14.
V. B. Efimov A. N. Izotov A. A. Levchenko L. P. Mezhov-Deglin S. S. Khasanov 《JETP Letters》2011,94(8):621-625
The structure of ice samples formed in the decay of a water impurity gel at temperatures above 4 K and atmospheric pressure
has been examined. The X-ray diffraction analysis indicates that three phases coexist in the initial sample at temperatures
of 85–110 K. These phases are amorphous ice occupying up to 30% of the sample volume, cubic-phase ice I
c metastable at low pressures (∼60%), and normal hexagonal ice I
h (≤6%). The characteristic sizes of crystals of the cubic and hexagonal phases are about 6 and 30 nm, respectively. The amorphous
phase at annealing above 110 K is gradually transformed to the crystalline phase both cubic and hexagonal. This transition
is accompanied by two processes, including a fast increase in the sizes of cubicphase nanocrystals and the partial transition
of the cubic phase I
c to the hexagonal one I
h. Hexagonal ice I
h prevails in the bulk of the sample above 200 K. 相似文献
15.
Nita Dilawar Sharma Jasveer Singh Sugandha Dogra D. Varandani Himanshu Kumar Poswal S. M. Sharma A. K. Bandyopadhyay 《Journal of Raman spectroscopy : JRS》2011,42(3):438-444
The phase transformation in nano‐crystalline dysprosium sesquioxide (Dy2O3) under high pressures is investigated using in situ Raman spectroscopy. The material at ambient was found to be cubic in structure using X‐ray diffraction (XRD) and Raman spectroscopy, while atomic force microscope (AFM) showed the nano‐crystalline nature of the material which was further confirmed using XRD. Under ambient conditions the Raman spectrum showed a predominant cubic phase peak at 374 cm−1, identified as Fg mode. With increase in the applied pressure this band steadily shifts to higher wavenumbers. However, around a pressure of about 14.6 GPa, another broad band is seen to be developing around 530 cm−1 which splits into two distinct peaks as the pressure is further increased. In addition, the cubic phase peak also starts losing intensity significantly, and above a pressure of 17.81 GPa this peak almost completely disappears and is replaced by two strong peaks at about 517 and 553 cm−1. These peaks have been identified as occurring due to the development of hexagonal phase at the expense of cubic phase. Further increase in pressure up to about 25.5 GPa does not lead to any new peaks apart from slight shifting of the hexagonal phase peaks to higher wavenumbers. With release of the applied pressure, these peaks shift to lower wavenumbers and lose their doublet nature. However, the starting cubic phase is not recovered at total release but rather ends up in monoclinic structure. The factors contributing to this anomalous phase evolution would be discussed in detail. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
16.
M. Maus G. Ganteför W. Eberhardt 《Applied Physics A: Materials Science & Processing》2000,70(5):535-539
The electronic structure and especially the band gap of Sin clusters (n=3–45 atoms) is studied by photoelectron spectroscopy. Contrary to expectations of quantum confinement, almost
all clusters studied here have a band gap smaller than that of crystalline Si or even display a continuous (metallic) density
of states. We attribute this to covalent bond formation analogous to the reconstructions observed on single-crystal surfaces.
Additionally, for Si30 and Si33 a gap size of 0.6 eV (0.4 eV) is observed, supporting the prediction of stable, spherically symmetric structures of these
particular clusters.
Received: 18 November 1999 / Accepted: 24 November 1999 / Published online: 5 April 2000 相似文献
17.
The Zn1-xMgxO thin films were deposited on sapphire substrates by reactive electron beam evaporation deposition (REBED). The X-ray diffraction (XRD) measurement demonstrates that these films undergo phase transition from hexagonal to cubic with increasing the Mg concentration. Absorption coefficients at 532 nm of the samples were obtained from the absorption spectra. Using optical Kerr effect, the thirdorder susceptibilities of the ternary films over a wide range of Mg concentrations were determined. The magnitude of x(3) of the ternary Zn1-xMgxO films is order of 10-11 esu at λ = 532 nm. The sample with phase mixture of both hexagonal and cubic structures shows the largest third-order susceptibility. The difference observed in the magnitude of x(3) of Zn1-xMgxO films is attributed to the different microstructures of the ternary films, such as crystalline phase separation and crystal grains that enhance stimulated scattering. 相似文献
18.
K.-H. Shim M.C. Paek B.T. Lee C. Kim J.Y. Kang 《Applied Physics A: Materials Science & Processing》2001,72(4):471-474
Effects of thermal treatments on the electrical properties and microstructures of indium–tin oxide (ITO)/GaN contacts have
been investigated using a rf-magnetron sputter deposition followed by rapid thermal annealing. ITO films annealed at 800 °C
revealed Schottky contact characteristics with a barrier height corresponding to ITO’s work function of 4.62 eV. The evolution
of electrical properties of ITO/GaN contacts was attributed to the preferential regrowth of In2O3 (222)//GaN (0001) with an ideal metal–semiconductor Schottky contact. The feasible use of ITO/GaN as a transparent Schottky
contact would be realized by the enhanced regrowth of In2O3 at high temperature.
Received: 1 September 2000 / Accepted: 15 November 2000 / Published online: 28 February 2001 相似文献
19.
T. Palasyuk 《Solid State Communications》2005,133(7):481-486
High-pressure X-ray diffraction studies of gadolinum, holmium and lutetium trihydrides have been carried out in a diamond anvil cell up to 30 GPa at room temperature. A reversible structural phase transformation from the hexagonal to cubic phase has been observed for all the hydrides investigated. These results confirm our first discovery of the hexagonal to cubic phase transition in erbium trihydride published recently [T. Palasyuk, M. Tkacz, Solid State Commun. 130 (2004) 219. [1]]. The lattice parameters of the new cubic phases and the volume changes at transition points were determined for SmH3, GdH3, and HoH3. The parameters of the equation of state for all the hexagonal and cubic phases of the investigated compounds have been determined. 相似文献
20.
L. K. Orlov E. A. Shteinman N. L. Ivina V. I. Vdovin 《Physics of the Solid State》2011,53(9):1798-1805
The light-emitting properties of cubic silicon carbide films grown by vacuum vapor phase epitaxy on Si(100) and Si(111) substrates
under conditions of decreased growth temperatures (T
gr ∼ 900–700°C) have been discussed. Structural investigations have revealed a nanocrystalline structure and, simultaneously,
a homogeneity of the phase composition of the grown 3C-SiC films. Photoluminescence spectra of these structures under excitation of the electronic subsystem by a helium-cadmium
laser (λexcit = 325 nm) are characterized by a rather intense luminescence band with the maximum shifted toward the ultraviolet (∼3 eV)
region of the spectral range. It has been found that the integral curve of photoluminescence at low temperatures of measurements
is split into a set of Lorentzian components. The correlation between these components and the specific features of the crystal
structure of the grown silicon carbide layers has been analyzed. 相似文献