共查询到20条相似文献,搜索用时 31 毫秒
1.
研究了利用离子注入法得到的掺氮n-SiC拉曼光谱. 理论线形分析表明,与4H-SiC相比,6H-SiC中LO声子等离子体激元耦合模(LOPC模)拉曼位移随自由载流子浓度变化较小. 5145nm激发光下得到的电子拉曼散射光谱表明,k位处由1s(A1)到1s(E)的能谷轨道跃迁带来的拉曼谱6H-SiC中有四条,4H-SiC中有二条;高频6303及635cm-1处观察到的谱线被认为与深能级缺陷有关. 最后,利用纤锌矿型结构二级拉曼散射选择定则指认了6
关键词:
碳化硅
电子拉曼散射
轨道能谷分裂
倍频谱 相似文献
2.
M. Gutfleisch D.I. Shin T. Dreier P.M. Danehy 《Applied physics. B, Lasers and optics》2000,71(5):673-680
Laser-induced thermal gratings (LITG) were generated in mixtures of ethylene and ammonia in nitrogen using mid-infrared laser
radiation from a grating-tuned, low-pressure, pulsed (5 ms pulse width) CO2 laser, and read out with a continuous wave Nd:YLF laser. The LITG signal intensity was measured as a function of pressure
(0.1–2 MPa) and temperature (300–800 K, at 0.1 and 1 MPa) by tuning the laser to the accidental coincidences of the 10P(14)
and 10R(6) emission lines with molecular absorption transitions of C2H4 and NH3, respectively. Comparisons are made with theoretical predictions for the grating efficiency from a simple thermalization
model. A theoretical comparison of the temporal LITG signal response for three excitation pulse shapes – a delta function,
a realistic pulse, and a square wave is presented. Furthermore, it is shown that for NH3, most of the decrease of the LITG signal intensity with increasing temperature is due to the corresponding decrease in fractional
molecular absorption of the pump beam radiation. The diagnostic capabilities of the mid-infrared LITG experiment is demonstrated
for spatially resolved ethylene measurements with long laser pulses in a premixed stoichiometric CH4–air flame at atmospheric pressure.
Received: 17 March 2000 / Revised version: 23 March 2000 / Published online: 13 September 2000 相似文献
3.
Photoconductivity is observed in n-channel inversion Si MOSFETS at 4.2 K at infrared frequencies up to 700 cm?1. Two groups of sharp lines of opposite sign are observed in the regions of 300 and 650 cm?1 together with a continuum of transitions starting at ~ 350 cm?1. The sharp lines are interpreted as bound transitions from shallow neutral phosphorous donors and boron acceptors on either side of the depletion layer. The angular dependence of the Zeeman splitting of the sharp lines demonstrates that the normal 90° symmetry of the 100 surface is lifted for devices with thin metal gates due to the presence of a strong unixial stress component. 相似文献
4.
M. Wieland T. Wilhein M. Faubel Ch. Ellert M. Schmidt O. Sublemontier 《Applied physics. B, Lasers and optics》2001,72(5):591-597
A liquid jet of either nitrogen or argon of 20 μm diameter was exposed to intense laser fields with pulse durations between
70 fs and 250 ps, leading to intensities of 1016 W cm-2 and 1013 W cm-2, respectively. The emission of extreme UV light and soft X-rays shows the characteristic lines of hydrogen-like nitrogen
and carbon-like argon. For nitrogen the emitted photon flux at 250 ps was about two orders of magnitude higher than for 70 fs
pulses. A weak dependence on the laser polarization with respect to the liquid jet axis was found. The kinetic energy of the
emitted ions easily exceeded 100 keV for nitrogen and 200 keV for argon for a pulse duration close to 2 ps.
Received: 21 August 2000 / Revised version: 20 December 2000 / Published online: 22 March 2001 相似文献
5.
T. Ban H. Skenderovi S. Ter-Avetisyan G. Pichler 《Applied physics. B, Lasers and optics》2001,72(3):337-341
We present results of absorption measurements in a dense superheated cesium vapor generated in an all-sapphire cell using
a UV–violet light-emitting diode as a continuum source. Due to the very effective thermal destruction of Cs2 molecules, a number of diffuse and satellite bands appear around higher members of cesium principal series lines, which are
not easily visible in saturated cesium vapor. From the temperature dependence of the diffuse features we can distinguish short-range
singlet transitions from temperature-independent spectral features that stem either from a shallow lowest triplet state or
from the long-range photo association spectra of triplet or singlet Cs2 molecules. The limits of the present interpretation of the observed bands in the UV–violet spectral region are discussed.
Received: 25 May 2000 / Revised version: 20 September 2000 / Published online: 13 December 2000 相似文献
6.
The dielectric function data for CuGaSe2 and CuInSe2 have been modeled for both perpendicular (E⊥c) and parallel (E∥c) polarizations. We employ the modified Adachi’s model dielectric
function model with variable broadening. Variable broadening is accomplished by replacing the damping constant Γ with the
energy-dependent expression Γ(E), where the shape of the broadening function is determined by two adjustable model parameters.
In spite of one additional parameter per transition, this model requires fewer parameters than the conventional Adachi’s model
to achieve equal or better agreement with the experimental data. Our calculations give the relative rms errors for the real
and imaginary parts of the index of refraction, δn and δk, equal to 0.9% and 9.5% for CuGaSe2 (E⊥c), 0.8% and 7.3% for CuGaSe2 (E∥c), 1.1% and 3.0% for CuInSe2 (E⊥c), and 2.5% and 3.7% for CuInSe2 (E∥c), respectively.
Received: 10 July 2000 / Accepted: 10 July 2000 / Published online: 9 November 2000 相似文献
7.
U. V. Valiev J. B. Gruber D. K. Sardar B. Zandi I. S. Kachur A. K. Mukhammadiev V. G. Piryatinskaya V. Yu. Sokolov I. S. Edelman 《Physics of the Solid State》2007,49(1):91-98
The Zeeman effect in the 7 F 6 → 5 D 4 absorption band of the Tb3+ ion in the paramagnetic garnets Tb3Ga5O12 and Tb3Al5O12 was studied. The field dependences of the Zeeman splitting of some absorption lines are found to exhibit unusual behavior: as the magnetic field increases, the band splitting decreases rather than increases. Symmetry analysis relates these lines to 4f → 4f electron transitions of the doublet-quasi-doublet or quasi-doublet-doublet type, for which the field dependences of the splitting differ radically from the well-known field dependences of the Zeeman splitting for quasi-doublet-quasi-doublet or quasi-doublet-singlet transitions in a longitudinal magnetic field. 相似文献
8.
强磁场中的Cs原子有较大的超精细塞曼分裂,实验用频率可调谐的窄线宽半导体激光调谐到各超精细塞曼能级上进行光泵浦,利用稳态吸收谱方法研究了原子的光泵浦。表明基态超精细相互作用的碰撞修正项导致的驰豫跃迁是谱形状和电子自旋极化新特征的根缘。同时提出了强场下极化度的一种测量方法。 相似文献
9.
A. Brockhinke W. Kreutner U. Rahmann K. Kohse-Höinghaus T.B. Settersten M.A. Linne 《Applied physics. B, Lasers and optics》1999,69(5-6):477-485
Laser-induced fluorescence of OH (A 2Σ+, v’=1) was measured in hydrogen/oxygen and hydrogen/air/nitrogen flames using laser pulses of 80 psec duration. A 2D signal
acquisition scheme simultaneously employed wavelength, temporal, and polarization resolution. The signals emitted in different
rotational branches exhibit polarization-dependent intensities, depending on the rotational branch of the absorption line
used. It is possible to select experimental conditions such that rotational and vibrational relaxation as well as electronic
quenching can be monitored simultaneously. Advantages and limitations of the experimental approach are discussed. Numerical
simulations are presented of the LIF spectra affected by energy transfer.
Received: 29 March 1999 / Revised version: 14 June 1999 / Published online: 27 October 1999 相似文献
10.
C. Degenhardt M. Fiebig D. Fröhlich Th. Lottermoser R.V. Pisarev 《Applied physics. B, Lasers and optics》2001,73(2):139-144
The hexagonal rare-earth manganites RMnO3 (R = Sc, Y, Ho, Er, Tm, Yb, Lu) are a group of materials with an unusual combination of magnetic, electric and optical properties.
The electronic structure of these materials was studied by second harmonic (SH) spectroscopy in the range from 1.2 to 3.0 eV.
Faraday rotation and absorption spectra were measured in the range from 1.0 to 1.6 eV. Broad bands at ∼1.7 eV and ∼2.7 eV
are assigned to electronic transitions between Mn3+(3d4) levels. The SH spectra are discussed on the basis of a recently developed microscopic theory.
Received: 26 April 2001 / Published online: 18 July 2001 相似文献
11.
The electronic spectra of CrO2?4 ions embedded in cesium halide lattices show two well defined bands due to dipole allowed transitions along with some weak bands due to forbidden transitions. All the above bands are interpreted in terms of transitions within molecu ar orbital levels using the Ballhausen and Liehr scheme. It is observed that superposed on the electronic transitions there is a vibrational fine structure which arises due to the coupling between the electronic transitions and the totally symmetric stretching frequency of the ion. IR absorption spectrum of Analar grade CsI :CrO2?4 shows seven lines, whereas Specpure CsI :CrO2?4 shows five lines. The above spectra are interpreted on the basis of different local symmetries of CrO2?4 ions in the lattice. 相似文献
12.
D. Sarkisyan T. Becker A. Papoyan P. Thoumany H. Walther 《Applied physics. B, Lasers and optics》2003,76(6):625-631
An extremely thin cell (ETC) with the thickness of a Rb atomic vapor layer in the range of 100–300 nm was fabricated. It is
demonstrated that a simple laser-diode technique with a single resonant light beam is sufficient to observe separately all
of the atomic hyperfine transitions of the D
2 line of Rb (780 nm) and also allows us to measure the relative transition probabilities of the hyperfine transitions. The
onset of collisional self-broadening of the hyperfine transitions as the number density of atoms increases was studied. The
detrimental role of the atoms with slow longitudinal velocity in the sub-Doppler response of the Rb ETC is demonstrated by
studies in which the cell is tilted from normal incidence of the laser beam. It is also shown that using an ETC allows us
to resolve in a moderate external magnetic field the Zeeman splitting of the hyperfine transitions of the 87Rb D
1 transition F
g=1F
e=1,2.
Received: 19 February 2003 / Revised version: 4 April 2003 / Published online: 2 June 2003
RID="*"
ID="*"Corresponding author. Fax: +374/32-31172, E-mail: david@ipr.sci.am 相似文献
13.
The paper is devoted to the problem of the optical anisotropy of the rare-earth ions occupying low-symmetry positions in crystals. The crystal field multiplets arising from LSJ terms of Eu3+ and Tb3+ ions in the crystal field of calcium tungstate scheelite (CaWO4) are analyzed (S4 point symmetry). The selection rules, in particular, polarization rules for the allowed electric dipole optical transitions in the electronic shells of the Eu3+ and Tb3+ in CaWO4 host lattice are discussed. Special attention is paid to the study of the angular (polarization) dependence of the two-photon absorption that seems to be an effective tool for the understanding of the complicated optical pattern. The peculiarities of the anisotropy of the two-photon absorption prove to be specific for each allowed dipole transition in S4 symmetry center. 相似文献
14.
Metal-insulator-silver junctions are well suited to measure genuine surface optical excitations, especially electronic transitions
to the lowest unoccupied molecular orbitals (LUMO) of adsorbates on silver. This is demonstrated by the increase of internal
photoemission current after monolayer coverage with C2H4 (which has π*-LUMO) by a factor of about 2.5, but a missing change in the case of C2H6 (which has no π*-LUMO ).
Received: 26 November 1999 / Published online: 8 March 2000 相似文献
15.
Baranov PG Orlinskii SB de Mello Donegá C Schmidt J 《Applied magnetic resonance》2010,39(1-2):151-183
It is shown that high-frequency electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy are excellent tools for the investigation of the electronic properties of semiconductor quantum dots (QDs). The great attractions of these techniques are that, in contrast to optical methods, they allow the identification of the dopants and provide information about the spatial distribution of the electronic wave function. This latter aspect is particularly attractive because it allows for a quantitative measurement of the effect of confinement on the shape and properties of the wave function. In this contribution EPR and ENDOR results are presented on doped ZnO QDs. Shallow donors (SDs), related to interstitial Li and Na and substitutional Al atoms, have been identified in this material by pulsed high-frequency EPR and ENDOR spectroscopy. The shallow character of the wave function of the donors is evidenced by the multitude of ENDOR transitions of the 67Zn nuclear spins and by the hyperfine interaction of the 7Li, 23Na and 27Al nuclear spins that are much smaller than for atomic lithium, sodium and aluminium. The EPR signal of an exchange-coupled pair consisting of a shallow donor and a deep Na-related acceptor has been identified in ZnO nanocrystals with radii smaller than 1.5 nm. From ENDOR experiments it is concluded that the deep Na-related acceptor is located at the interface of the ZnO core and the Zn(OH)2 capping layer, while the shallow donor is in the ZnO core. The spatial distribution of the electronic wave function of a shallow donor in ZnO semiconductor QDs has been determined in the regime of quantum confinement by using the nuclear spins as probes. Hyperfine interactions as monitored by ENDOR spectroscopy quantitatively reveal the transition from semiconductor to molecular properties upon reduction of the size of the nanoparticles. In addition, the effect of confinement on the g-factor of SDs in ZnO as well as in CdS QDs is observed. Finally, it is shown that an almost complete dynamic nuclear polarization (DNP) of the 67Zn nuclear spins in the core of ZnO QDs and of the 1H nuclear spins in the Zn(OH)2 capping layer can be obtained. This DNP is achieved by saturating the EPR transition of SDs present in the QDs with resonant high-frequency microwaves at low temperatures. This nuclear polarization manifests itself as a hole and an antihole in the EPR absorption line of the SD in the QDs and a shift of the hole (antihole). The enhancement of the nuclear polarization opens the possibility to study semiconductor nanostructures with nuclear magnetic resonance techniques. 相似文献
16.
I. Sokólska 《Applied physics. B, Lasers and optics》2000,71(2):157-162
LaGaO3 crystals doped with Er3+ ions were grown by the Czochralski method and their optical properties were examined. The Er3+ energy levels have been determined from the low-temperature absorption and emission spectra. The results of Judd–Ofelt analysis
are presented and compared with experimental data. The emission cross sections are determined for the 4
I
13/2→4
I
15/2 (1.55 μm) and 4
I
11/2→4
I
13/2 (2.85 μm) transitions of erbium.
Received: 6 December 1999 / Revised version: 10 February 2000 / Published online: 27 April 2000 相似文献
17.
U. V. Valiev D. R. Dzhuraev S. I. Mukhamedkhanova N. M. Narzullaev V. Yu. Sokolov S. A. Rakhimov 《Russian Physics Journal》2008,51(6):593-600
The Zeeman effect is investigated in the green luminescence band corresponding to the 4f→4f radiative transition 5D4 → 7F5 of Tb
3+
ions in Tb
0.2
Y
2.8
A
l5
O
12
terbium-yttrium-aluminum garnet at the temperature T = 85 K. It is demonstrated that an external field causes not only the
Zeeman shifts of the resonant frequencies of radiative transitions in the luminescence spectra but also changes in the emission
line intensities caused by modification of the optical transition probabilities in the σ− and σ+ opposite circular polarization states. Special features of field dependences of the Zeeman effect for the emission lines
are qualitatively explained based on the results of numerical energy spectrum calculations for the 5D4 and 7F5 multiplets of the Tb
3+
ion in yttrium-aluminum garnet in the geometry of the longitudinal and transverse Zeeman effects. The possibility of nonequilibrium
population of sublevels of the (Γ1, Γ4) quasi-doublet state of the 5D4 multiplet with energy of ∼20585 cm−1 is demonstrated in an external magnetic field.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 38–45, June, 2008. 相似文献
18.
The measurement of relative intensities in CO2 combination bands spectrum is performed using wavelength modulation spectroscopy (WMS) and a DFB (distributed feedback) diode
laser operating at 1.6 μm. The diode laser is stabilized with an external Fabry–Pérot interferometer and absorption spectroscopy
is performed in a multipass gas cell. A spectrum containing spectral lines of both 13CO2 and 12CO2 isotopic species is recorded. The variation of laser power during frequency scanning and the line shape are taken into account
to accurately extract line intensities from experimental data. The isotopic concentration ratio is deduced from the intensity
ratio. Both ratios are measured with an accuracy of about 0.5% in pure CO2.
Received: 9 June 2000 / Published online: 8 November 2000 相似文献
19.
We have recorded the fluorescence excitation spectra of three heterocyclic compounds with a chain structure [BPO (2-phenyl-5-(4-diphenylyl)oxazole),
POPOP (1,4-di[2-(5-phenyloxazolyl)]benzene, and TOPOT (1,4-di[2-(5-n-tolyloxazolyl)]benzene] and the fluorescence spectra
of POPOP, under conditions where the molecules were cooled in an ultrasonic helium jet. A line structure is observed in the
spectra of POPOP and TOPOT; for the BPO molecules, whose configuration changes considerably during electronic excitation,
vibrational structure is apparent only in the low-frequency region of the excitation spectrum, and a diffuse spectrum is recorded
starting from ν
0
0
+ 200 cm−1. For all the compounds, in the spectra we recorded vibrations with frequencies up to 100 cm−1, arising due to the flexibility of the molecular structure. The rotational contours of the lines for the electronic and vibronic
transitions of the POPOP molecules (Trot = 10.5 K) and TOPOT molecules (Trot = 15 K) are structureless and bell-shaped. The degree of polarization of the fluorescence Pfl for the jet-cooled POPOP molecules for excitation of vibrations along the absorption band up to 2000 cm−1 above ν
0
0
is practically constant (∼8.4%) and matches Pfl for high-temperature vapors.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 728–734, November–December, 2006. 相似文献
20.
S. Heinz E. Berdermann F. Heine O. Joeres P. Kienle I. Koenig W. Koenig C. Kozhuharov U. Leinberger M. Rhein A. Schröter H. Tsertos The ORANGE Collaboration at GSI 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):55-61
We present new results from measurements and simulations of positron spectra, originating from 238U + 181Ta collisions at beam energies close to the Coulomb barrier. The measurements were performed using an improved experimental
setup at the double-Orange spectrometer of GSI. Particular emphasis is put on the signature of positrons from Internal-Pair-Conversion
(IPC) processes in the measured e+-energy spectra, following the de-excitation of electromagnetic transitions in the moving Ta-like nucleus. It is shown by
Monte Carlo simulations that, for the chosen current sweeping procedure used in the present experiments, positron emission
from discrete IPC transitions can lead to rather narrow line structures in the measured energy spectra. The measured positron
spectra do not show evidence for line structures within the statistical accuracy achieved, although expected from the intensities
of the observed γ-transitions ( E
γ∼ 1250-1600 keV) and theoretical conversion coefficients. This is due to the reduced detection efficiency for IPC positrons,
caused by the limited spatial and momentum acceptance of the spectrometer. A comparison with previous results, in which lines
have been observed, is presented and the implications are discussed.
Received: 27 April 2000 / Accepted: 14 September 2000 相似文献