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101.
With a high pressure gas target muonic F and S X-ray intensities in SF6 and H2+SF6 have been measured. It was found that the distribution of muons between sulphur and fluorine is not at all equal to the ratio of the atomic numbers Z. 相似文献
102.
For a gaussian broadband radiation field (multimode laser without phase-correlation) the bleaching behaviour of a homogeneously broadened two level system is investigated in dependence on the spectral width (δυ) of the field. Taking into consideration the coherent mode-interaction, originating from the nonstationary reaction of population inversion on the fluctuations of the radiation field, a decrease of the bleaching effect results as soon as the spectral width δυ becomes larger than ⊥1 = 1/T1 with T1 the longitudinal relaxation time of the molecular transition concerned. Neglecting this effect in the analysis of broadband bleaching measurements can result in the unjustified assumption of an inhomogeneous broadening of the spectral band under consideration, which has consequences on the magnitude of the molecular absorption cross-section derived from these measurements. 相似文献
103.
104.
M.?BiasiniEmail author R. D.?Gann L. N.?Pfeiffer K. W.?West X. P.A.?Gao B. C.D.?Williams J. A.?Yarmoff A. P.?MillsJr 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,47(2):305-314
The conductivity of an Al0.24Ga0.76As/GaAs
quantum well was studied as a function of the surface charge
generated by electron bombardment of the sample in the absence of
an externally applied surface electric field. Under a suitable
rate of electron irradiation, it was possible to completely shut
off the conductive channel, implying a surface density
. Light illumination quenches the
increase of the resistivity, apparently due to photoemission from
the metastable surface states. Upon turning off the electron
bombardment the surface charge on adsorbed layers of xenon and
water at 8 K decays in room temperature darkness with a lifetime
τ= 0.30 ±0.02 s. The average charging efficiency, is
μ0 ≃0.001. Surface charging is shown to be an effective
method for contactless gating of field effect devices. 相似文献
105.
We have investigated the integer quantum Hall plateau-to-plateau transition in two-dimensional electrons confined to AlxGa(1-x)As-Al0.33Ga0.67As heterostructures over a broad range of Al concentration x. For x between 0.65% and 1.6%, where the dominant contribution to disorder is from the short-range alloy potential fluctuations, we observe a perfect power-law scaling in the temperature range from 30 mK to 1 K with a critical exponent kappa = 0.42 +/- 0.01. 相似文献
106.
In this Letter we report on lateral diffusion measurements of excitons at low temperature in double quantum wells of various widths. The structure is designed so that excitons live up to 30 micros and diffuse up to 500 microm. Particular attention is given to establishing that the transport occurs by exciton motion. The deduced exciton diffusion coefficients have a very strong well width dependence, and obey the same power law as the diffusion coefficient for electrons. 相似文献
107.
Gao XP Boebinger GS Mills AP Ramirez AP Pfeiffer LN West KW 《Physical review letters》2005,94(8):086402
We have studied the temperature dependent phonon emission rate P(T) of a strongly interacting (r(s) > or =22) dilute 2D GaAs hole system using a standard carrier heating technique. In the still poorly understood metallic state, we observe that P(T) changes from P(T) approximately T5 to P(T) approximately T7 above 100 mK, indicating a crossover from screened piezoelectric (PZ) coupling to screened deformation potential (DP) coupling for hole-phonon scattering. Quantitative comparison with theory shows that the long range PZ coupling between holes and phonons has the expected magnitude; however, in the metallic state, the short range DP coupling between holes and phonons is almost 20 times stronger than expected from theory. The density dependence of P(T) shows that it is easier to cool low-density 2D holes in GaAs than higher density 2D hole systems. 相似文献
108.
We realize p- and n-type doping of the organic semiconductor zinc-phthalocyanine using a novel strong organic donor. This allows us to demonstrate the first stable and reproducible organic p-n homojunctions. The diodes show very high built-in potentials, attractive, e.g., for organic solar cells. However, the diode characteristics cannot be described by the standard Shockley theory of the p-n junction since the ideality factor strongly increases with decreasing temperature. We show that this behavior can be explained by deviations from the Einstein relation for disordered materials. 相似文献
109.
We use a scanning capacitance probe to image transport in the quantum Hall system. Applying a dc bias voltage to the tip induces a ring-shaped incompressible strip (IS) in the 2D electron system (2DES) that moves with the tip. At certain tip positions, short-range disorder in the 2DES creates a quantum dot island in the IS. These islands enable resonant tunneling across the IS, enhancing its conductance by more than 4 orders of magnitude. The images provide a quantitative measure of disorder and suggest resonant tunneling as the primary mechanism for transport across ISs. 相似文献
110.
B. Maennig J. Drechsel D. Gebeyehu P. Simon F. Kozlowski A. Werner F. Li S. Grundmann S. Sonntag M. Koch K. Leo M. Pfeiffer H. Hoppe D. Meissner N.S. Sariciftci I. Riedel V. Dyakonov J. Parisi 《Applied Physics A: Materials Science & Processing》2004,79(1):1-14
We introduce a p-i-n-type heterojunction architecture for organic solar cells where the active region is sandwiched between two doped wide-gap layers. The term p-i-n means here a layer sequence in the form p-doped layer, intrinsic layer and n-doped layer. The doping is realized by controlled co-evaporation using organic dopants and leads to conductivities of 10-4 to 10-5 S/cm in the p- and n-doped wide-gap layers, respectively. The photoactive layer is formed by a mixture of phthalocyanine zinc (ZnPc) and the fullerene C60 and shows mainly amorphous morphology. As a first step towards p-i-n structures, we show the advantage of using wide-gap layers in M-i-p-type diodes (metal layer–intrinsic layer–p-doped layer). The solar cells exhibit a maximum external quantum efficiency of 40% between 630-nm and 700-nm wavelength. With the help of an optical multilayer model, we optimize the optical properties of the solar cells by placing the active region at the maximum of the optical field distribution. The results of the model are largely confirmed by the experimental findings. For an optically optimized device, we find an internal quantum efficiency of around 82% under short-circuit conditions. Adding a layer of 10-nm thickness of the red material N,N-dimethylperylene-3,4:9,10-dicarboximide (Me-PTCDI) to the active region, a power-conversion efficiency of 1.9% for a single cell is obtained. Such optically thin cells with high internal quantum efficiency are an important step towards high-efficiency tandem cells. First tandem cells which are not yet optimized already show 2.4% power-conversion efficiency under simulated AM 1.5 illumination of 125 mW/cm2 . PACS 73.61.Ph; 78.30.Jw; 89.30.Cc 相似文献