共查询到20条相似文献,搜索用时 140 毫秒
1.
本文计算了准周期原胞超晶格中横弹性波的体和面模式的色散关系,导出了用传输矩阵表述的动力学格林函数,并用以计算了热涨落的谱密度。结果表明由于系统对于垂直于超晶格轴的平面不存在反映对称性,当表面截取在原胞内F_m个不同的界面上时(F_m是Fibonacci数)半无限样品的横声子表面谱呈现F_m种截然不同的形式。 相似文献
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用分子束外延生长了23周期的GexSi1-x/Si超晶格,用计算机控制的衍射仪(CuKa辐射)测量了X射线衍射曲线,共观察到13级超晶格结构的衍射峰。超晶格的周期和Ge平均含量可以根据考虑折射修正的布喇格定律得出。用光学多层膜反射理论分析衍射曲线可以确定超晶格的结构参数,第2级衍射峰与第一级峰的强度比对应于超晶格两种材料的相对厚度变化非常灵敏,通过比较实验和计算的I2/I1值,可以确定Si,GexSi1-x层的厚度以及合金组份x。用光学多层膜反射理谁计算得到的衍射曲线与实验曲线趋于一致。
关键词: 相似文献
7.
利用微区Raman散射技术研究了MOCVD-GaxIn1-xAsyP1-y/InPDBRs结构的晶格振动。在InP衬底上生长的与InP晶格匹配的四元合金Ga0.4In0.6As0.85P0.15中包含三种主要的振动模式,分别归属于类InAs、类GaAs和类GaInP。随着Ga0.4In0.6As0.85P0.15与InP交替生长构成的DBRs结构周期数增加,Raman散射谱中三种振动模式的谱线线型发生明显变化,类InAs振动强度不变,谱线窄化,峰值位置向低频方向移动,类GaAs和类GaInP振动强度逐渐减弱。同时类InAs与类GaAs振动强度比增大。Raman散射研究中声子的限制效应表明多层结构生长过程中界面存在非完整晶态。 相似文献
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V. I. Kadushkin 《Russian Physics Journal》1998,41(5):468-471
The anomalous shift in the maxima of the Shubnikov—de Haas transverse magnetoresistance oscillations in AlGaAs(Si)/GaAs with
2D electrons oriented in the [110] direction with respect to [{ie468-1}10] in large magnetic fields is explained by the formation
of a lateral superlattice with an increase of the effective mass (m[110]* > m[{ie468-2}]*).
Ryazan State Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 5, pp. 79–82, May, 1998. 相似文献
12.
J. Yoshida K. Kishino D. H. Jang S. Nahm I. Nomura A. Kikuchi 《Optical and Quantum Electronics》1996,28(5):547-556
A mechanism for self-organization of GalnP strained quantum wires in (GaP)
m
/(lnP)
m
short-period binary superlattice (SPBS) is discussed. To elucidate the self-organization mechanism, GalnP/AllnP compressively strained multi-quantum-wire (CS-MQWR) lasers were fabricated, changing the superlattice monolayer numberm in (GaP)
m
/(lnP)
m
SPBS active layers. The self-organization occurred form>1.2, determined from transmission electron microscopy images and from the anisotropic TM/TE polarization ratio in electroluminescence, i.e. an anisotropic dipole moment.The mechanism by which quantum wire axes were selected to the
direction is discussed in terms of the anisotropy in adatom diffusion between [011] and
directions. To confirm this, (GaP)1.2/(lnP)1.2 SPBS layers were grown on GaAs (100) substrates misoriented towards the [011] direction, on which the [011] adatom diffusion is suppressed. Enhanced quantum wires self-organization by substrate misorientation was observed, showing that anisotropic diffusion played an important role.The mechanism modelling of the lateral compositional modulation is discussed considering the initial growth of films largely mismatched to bottom crystals. The lateral compositional modulation is supposed to be related to GaP wire-like nuclei induced by large strain energy in the first GaP layer growth in (GaP)
m
/(lnP)
m
SPBSs.GalnP/AllnP CS-MQWR lasers with lowJ
th values of 257 A cm–2 were obtained atm=1.5. 相似文献
13.
W.L. Bloss 《Solid State Communications》1982,44(3):363-367
The collective plasmon modes of s semiconductor superlattices consisting of alternating layers of electrons and holes or alternating layers of electrons with different densities are investigated. For wells widely separated in space, such that Bloch wavefunction overlap between wells is negligible, we find optical-like and acoustical-like plasmon modes propagating along the superlattice direction. Perpendicular to the superlattice direction, the acoustic mode (ω~q″) recently observed by Olego and Pinczuk8 is found to be split into two acoustic branches. 相似文献
14.
J. Bremer 《Solid State Communications》1983,47(11):881-884
A method of calculating the effect of self-absorption in X-ray emission spectra and which is suitable for non-adiabatic excitation processes is presented. The Fermi-level EF and the “true” profile of the electron-excited (20–40keV) CuKβ2,5 band are determined. A deviation from the calvulated one-electron spectrum in the energy interval [-12 eV, -7 eV] below EF is interpreted as a result of plasmon formation and Auger broadening. A pronounced disagreement is found also in the range [-1 eV, + 10eV]. Above EF, a part of the intensity may be due to incomplete electron relaxation. 相似文献
15.
V. V. Klochkov F. Kh. Karatayeva R. A. Shaikhutdinov B. I. Khairutdinov M. -A. Molins M. Pons 《Applied magnetic resonance》2002,22(3):431-438
Variable temperature two-dimensional nuclear Overhauser enhancement experiment (2-D NOESY) is used to extract the rate constants and cross-relaxation rates that contribute to the same cross-peaks in NOESY spectra. Rate constants (k AB) and cross-relaxation rates (R AB) for two-site spin systems are related to the ratio between the cross-peak and diagonal peak integrals (F) by the expression:R AB -k AB = (1/2τ m)ln[(1 -F)/(1 +F)], where τm is the mixing time. As a model, we investigated the exchange processes in a system of dimer calix[4]arenes of C4v symmetrical configuration with guest inclusion (benzene or benzene-d6), where the measurement of exchange processes is hindered by the presence of strong nuclear Overhauser enhancement between protons in adjacent aromatic rings in the cone conformation of the calix[4]arene. 相似文献
16.
J. Kramář 《Czechoslovak Journal of Physics》1965,15(3):190-200
This article deals with the calculation of the influence of the magnetic field upon the electric current of a thermionic converter presupposing the approach to conditions in a low-pressure cesium converter. The distribution of the starting velocities of the emitted electrons is considered firstly as independent of the angle from the perpendicular to the emitter plane, and secondly according to the cosine law.The magnetic field effect from the converter current is calculated and compared with the calculations in the papers by Schock [1] and Block [2]; the effect of the external magnetic field is verified by measurements on a solar thermionic converter prototype.Symbols
F=I/I
0
factor of current reduction from magnetic field effect
-
¯F
value of factorF (when the magnetic field is not constant)
-
I [A/m2]
density of collector current (real current influenced by magnetic field)
-
I
0 [A/m2]
theoretical density of collector current (in ideal case equals electron emission current)
-
T
e
[°K]
electron gas temperature; assumed equal to emitter temperatureT
E
[°K]
-
B[Wb/m2]
magnetic induction (field)
-
D[m]
distance from emitter to collector
-
R[m]
radius of electrodes, emitter and collector
-
r[m]
variable radius in the limits 0 toR
-
V [m/s]
random velocity of electron
-
v
xz
[m/s]
component of the vectorV inx-z plane
-
v
m
=2kT
E
/m
most probable velocity in the velocity distribution according to Maxwell and Boltzmann
-
w-v
xz
/v
m
relatively expressed electron velocityv
xz
-
the angle of any vectorV
-
[m]
radius of circular electron path
-
n [m–3]
number (density) of electrons with certain value of random velocity
-
n
0 [m–3]
total electron number (density)
-
n
1 [m–3]
number of electrons returned to emitter by means of magnetic field
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N
0 [m–2s–1]
total flow of thermionic electrons emitted from a unit surface
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N
1 [m–2s–1]
partial flow of electrons returned to emitter
-
P=N
1/N0
relatively expressed flow of electrons returned to emitter (whenB = const.)
-
¯P
mean value ofP (whenB const.)
-
F
cos,
,P
cos,
values asF,¯F,P,¯P in case of velocity distribution according to cosine law
-
m=9·107×10–31 [gk]
electron mass
-
e=1·60×10–19 [C]
electron charge
-
k×1·38×10–23 [J/grad]
Boltzmann's constant
-
0
1·257×10–6 [H/Vs] permeability of vacuum 相似文献
17.
W.L. Bloss 《Solid State Communications》1983,48(10):927-931
The collective plasmon excitations of a superlattice are investigated in both the classical and quantum limits. Using a model that is applicable to superlattices whose constituent layers are either semiconductor- semiconductor, semiconductor-metal, or metal-metal, we show that the surface plasmon interface modes of each layer (slab) couple via the long range Coulomb interaction into two bands of plasmons with dispersion along the superlattice axis. Results for plasmon dispersion are presented for the classical limit (de Broglie wavelength less than the layer width) where the response is treated via a solution of Maxwell's equations using the bulk 3-D dielectric constant to describe each intervening layer. These results are compared to the plasmon dispersion in the quantum regime where the wave-vector frequency dependent dielectric constant of the superlattice is calculated taking into account quantization effects (subband structure). The relationship between the modes in both limits is derived. 相似文献
18.
This paper describes the development of surface morphology of thin InSn(90/10), In, Sn and Cr films, deposited on unheated glass substrates by d.c. magnetron sputtering, with the film thickness. The experiments show that the surface morphology of metallic films with low melting pointsT
m[InSn(90/10)–150°C, In–156.6°C, Sn–231.8°C] and that with high melting pointT
m [Cr–1875°C] strongly differ. InSn(90/10) and Sn films with thickness greater than about 30 nm and also In films with even lower thickness of about 20 nm have a rough surface, milky color and matt appearance. On the contrary, Cr films of the same thickness have a smooth and shiny surface. It is due to a large difference in normalized temperaturesT/T
m for low-T
m films [Sn–0.59, In–0.70, InSn(90/10) –0.71] and for high-T
m films [Cr–0.14] deposited at low temperatures close to room temperature (RT). High values of the ratioT/T
m>0.5 clearly indicate that just the low melting point materials can crystallize at low temperatures close to RT. A crystallization of lowT
m films results in rough surface, milky color and matt appearance of these films.This work was supported in part by the Grant Agency of Czech Republic under Grant No. 202/93/0508. 相似文献
19.
P. Steiner R. Courths V. Kinsinger I. Sander B. Siegwart S. Hüfner C. Politis 《Applied Physics A: Materials Science & Processing》1987,43(1):75-79
Ultrathin-layer (AlAs)
m
(GaAs)
m
superlattices withm = 1, 2, and 3 were grown by molecular beam epitaxy and characterized by x-ray diffraction and photoluminescence measurements. The appearance of distinct satellite peaks around the Bragg reflections demonstrate the formation of high-quality layered crystals. The observed luminescence shows a maximum at 2.033 eV form = 3, and the emission energy decreases form = 2 andm = 1 as well as for them = 4 superlattice. This result for the monolayer superlattice is in good agreement with recent theoretical calculations, and it shows that the (AlAs)1(GaAs)1 superlattice represents a new artificial semiconductor material with novel electronic properties.On leave from Mitsubishi Electric Corp., Central Research Laboratory, Amagasaki, Hyogo 661, JapanOn leave from Institute of Semiconductors, Academia Sinica, Beijing, PR China 相似文献
20.
The distinction between avalanche and tunneling breakdown in one-sided abrupt junctions is made on the basis of a new, simple expression for the tunneling breakdown field strengthF t. It is shown thatF t [V/cm] depends upon the temperatureT [K], the reduced tunneling effective massm eff + /m o and the semiconductor energy band gapE g [eV] according to the following equation $$F_t = 1.76 \cdot 10^6 \cdot \left( {\frac{T}{{300}}} \right) \cdot \left( {\frac{{m_{eff}^ + }}{{m_0 }} \cdot E_g } \right)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} [V/cm].$$ Using published calculations for the avalanche breakdown voltage, the result is applied to the semiconductors Ge, Si, GaAs and GaP at 300 K and InSb at 77K. 相似文献