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1.
Rotational and vibrational population distributions have been determined for D2 molecules recombinatively desorbing from polycrystalline Pd surfaces by tunable vacuum-ultraviolet laser-induced fluorescence. In the temperature range 550 KT s 1050 K studied in this work a rotational temperature ofT rot 450 K was found, nearly independent of the surface temperature. Similarly, the vibrational temperature could be described by a value ofT vib1100 K, being always higher than the surface temperature.  相似文献   

2.
The electrical properties of a single crystal of KTiOPO4 was studied by impedance spectroscopy methods in the temperature range –100 to 100 °C. The complex resistivity decreases rapidly with increasing temperature, and resistivity dispersion begins at a temperature of TS=-80 °C. The complex resistivity was fitted to the superposition of two Cole-Cole-type relaxations. The low frequency relaxation is associated with the electrode/crystal surface, while the high frequency relaxation is interpreted as resulting from ion migration in the bulk. It is believed that high frequency relaxation is related to ionic hopping conduction, which arises mainly from the jumping of K+ ions. The activation energies associated with hopping conduction are Ea0.21 eV above TS and Ea0.11 eV below TS . PACS 77.22.-d; 77.22.Gm; 66.10.Ed; 77.84.-s; 66.30.Hs  相似文献   

3.
We discuss a heurisitic model of gravitational vacuum as a set of virtual, radiating planckeons, particles with Planck size (L) and mass (/cL). Combined with Dirac's large number hypothesis, this gives the minimum universe scale factor valuea min10–13 cm, the strong interaction length (a = L just whena=a min ). Taking this state as an initial one using standard quantum techniques, we consider particle creation by planckeons. Under some reasonable assumptions we obtain the present number of particles with nucleon mass close to observations,N 1080. A criterion for gravitational stability of particles is formulated and some applications of the corresponding mass formula are considered. In particular, Fermi's weak interaction constant is expressed in terms ofa andL and a finite value for the neutrino mass is obtained.  相似文献   

4.
An attempt to unify the scales of physical quantities is presented within the framework of a hypothesis about the existence of a family of black holes. There exists a scale characterized by parametersm x 4×1014 GeV and GUM 1/25 which may be identified with a scale for the grand unification.  相似文献   

5.
The nonlinear properties of a ferromagnet are studied. Many-time retarded Green's functions are used to obtain an expression for the cubic nonlinearity tensor with allowance for spatial dispersion of a uniaxial ferromagnet. The components due to the dipole-dipole interaction of the spins and also due to the anisotropy energy are found. A comparative analysis is made of the different components of the cubic nonlinearity tensor in both the nonresonance case and for various resonances, in particular when 0, 3 2w0, 2 0, 3 0 for the case in tripling of the frequency. Here, is the frequency of the incident wave and 0 is the frequency of uniform precession. It is shown that in the non-resonance case the largest components are those that are nonvanishing when no allowance is made for spatial dispersion; in the resonance cases the largest components are those due to the dipole-dipole interaction of the ferromagnetism spins.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 53–58, December, 1973.  相似文献   

6.
Generation of the second- and fourth-order harmonics of laser radiation is reported in Mg vapor at the forbidden 3s 21 S o–4s 1 S o transition. The conversion efficiency for the second-order harmonics has been measured to be 10–2% and for the fourth one 10–8%.  相似文献   

7.
The detailed temperature variation of the Mössbauer spectral intensity in Sn(CH3)4 displays a pronounced drop of the Debye temperature from D 96K below the transition temperature (T t 43K) to D 76K above it. The transition atT t is discussed in terms of recent INS and NMR results where increased motion of inequivalent CH3 groups has been observed around the temperatureT t .Supported by the U.S.-Israel Binational Science Foundation  相似文献   

8.
Self-avoiding random walks (SAWs) are studied on several hierarchical lattices in a randomly disordered environment. An analytical method to determine whether their fractal dimensionD saw is affected by disorder is introduced. Using this method, it is found that for some lattices,D saw is unaffected by weak disorder; while for othersD saw changes even for infinitestimal disorder. A weak disorder exponent is defined and calculated analytically [ measures the dependence of the variance in the partition function (or in the effective fugacity per step)vL on the end-to-end distance of the SAW,L]. For lattices which are stable against weak disorder (<0) a phase transition exists at a critical valuev=v * which separates weak- and strong-disorder phases. The geometrical properties which contribute to the value of are discussed.  相似文献   

9.
Thin films of zirconium silicate ZrxSi1-xO2 (with x=0.69), a material that has been suggested as a possible high-k dielectric, are deposited on silicon wafers by pulsed laser deposition (PLD) under different deposition and post-annealing conditions. The morphology and electrical properties of these films are characterized. It is shown that the films remain amorphous after an ex situ rapid thermal annealing (RTA) at temperatures as high as 800 °C. For the 6 nm thick film deposited at 300 °C in an O2 ambient with a N2 ambient post-RTA at 500 °C for 5 min, the equivalent oxide thickness (EOT) is 1.9 nm, as evaluated from capacitance-voltage (C–V) measurements. The samples prepared with the N2 ambient post-RTA show a slightly higher leakage current than that for samples annealed in the O2 ambient. For the films deposited in N2, the smallest EOT of 1.1 nm is obtained, and the films have fair electrical properties in spite of the high interface state density and relatively higher leakage. PACS 77.55.+f; 81.15.Fg; 81.40.Ef  相似文献   

10.
Magnetic transitions are described by the critical indices0,1/3,4/3 while some ferroelectric transitions appear to give0,R~1/2,1. It is pointed out that these two sets of values for the critical indices are allowed by the scaling laws and stability conditions near the phase transitions.The authors thank Prof. R. S. Krishnan for his encouragement and Mr. B. Viswanathan for some discussions. The financial assistance from DAE and CSIR is also acknowledged.  相似文献   

11.
The self-averaging properties of the conductanceg are explored in random resistor networks (RRN) with a broad distribution of bond strengthsP(g)g –1. The RRN problem is cast in terms of simple combinations of random variables on hierarchical lattices. Distributions of equivalent conductances are estimated numerically on hierarchical lattices as a function of sizeL and the distribution tail strength parameter . For networks above the percolation threshold, convergence to a Gaussian basin is always the case, except in the limit 0. Adisorder length D is identified, beyond which the system is effectively homogeneous. This length scale diverges as Dµ–v ( is the regular percolation correlation length exponent) when the microscopic distribution of conductors is exponentially wide (0). This implies that exactly the same critical behavior can be induced by geometrical disorder and by strong bond disorder with the bond occupation probabilityp. We find that only lattices at the percolation threshold have renormalized probability distributions in aLevy-like basin. At the percolation threshold the disorder length diverges at a critical tail strength µc as µ––z withz3.2±0.1, a new exponent.Critical path analysis is used in a generalized form to give the macroscopic conductance in the case of lattices abovep c.  相似文献   

12.
Conversion electron Mössbayer spectroscopy (CEMS) on three monolayers (ML) thick metastable fcc-Fe(001) films grown epitaxially on a Cu(001) substrate under different conditions shows that these films are characterized by a distributionP(B hf) of magnetic hyperfine fieldsB hf. The vast majority of57Fe nuclei experience relatively large hyperfine fields at low temperature. The temperature dependence of the most probable fieldB peak was found to follow aT 3/2 spin-wave law below 300 K. It is shown from the relative line intensities that preferential Fe spin orientation perpendicular to the film plane exists in films grown at 120 K, while preferential in-plane spin orientation is found for a growth temperature of 300 K. Coating a low-temperature grown Fe film by 2 ML of Cu(001) drastically reduces the hyperfine field, in contrast to the case of room-temperature grown Cu-coated films.Dedicated to Professor Ulrich Gonser on the occasion of his 70th birthday  相似文献   

13.
Self diffusion coefficients in supercooled orthoterphenyl (OTP) have been determined down toD t =3·10–14 m2s–1 using a1H-NMR technique applying static field gradients up to 53T m–1 In a range of more than two decades theD t values agree with those of photochromic tracer molecules of the same size determined by forced Rayleigh scattering down to the glass transition temperatureT g . A change of mechanism is found for translational diffusion atT c 1.2T g whereD t is proportional to the inverse shear viscosity –1 atT>T c butD t with =0.75 atT<T c . Rotational correlation times determined by2H-NMR stimulated echo techniques in deuterated OTP remain proportinal to –1 down toT g . Our results are discussed in relation with mode coupling theory and with models of cooperative motion at the glass transition.  相似文献   

14.
The properties of p-type ZnGeP2 [p0=(5–10)·1010 cm–3, 0=(2–5)·10–7 (·cm)–1], irradiated with H+ ions [E=5 MeV, Tirr=300 K, D=(1·1012–1.7·1016) cm–2] are studied. An increase in the resistivity (to grmax - 5·1011 ·cm) and subsequent reduction in for large currents of H+ ions ( - 9·108 ·cm for D - 1.7·1016 cm–2), is observed in irradiated crystals. The resistivity of irradiated p-type ZnGeP2 is found to be very sensitive to hydrostatic pressure [(4–5)·10–5 bar–1]. The annealing of radiation defects in the temperature interval (20–600) °C is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–93, October, 1991.  相似文献   

15.
In-depth stress distribution GaAs layers grown by Molecular Beam Epitaxy (MBE) on Si (001) has been studied by X-ray diffraction, photoluminescence and Raman spectroscopy. In order to determine the stress state at different distances to the interface GaAs/Si, layers of different thickness were prepared by chemical etching of the grown samples. We observe a non-uniform residual strain distribution through the GaAs on Si epilayer. Residual strain of thermal origin is larger in the highly defective region ( 0.4 m) near the GaAs/Si interface where we have found a non-elastic relation between measured in-plane (a ) and in growth direction (a ) lattice parameters. However, thermal strain is partially relaxed by formation of 107 cm–2 dislocations in the region of better crystalline quality near the external surface.  相似文献   

16.
The adsorption of H2 and D2 on a Rh (110) surface at 100 K leads to a sequence of ordered phases, among others 1×2 phases at H =0.5 and at H =1.5 which likely involve a partial surface reconstruction consisting of a small perpendicular displacement of Rh surface atoms. The structure of the adsorbate phases is strongly correlated with the binding energy of the adsorbed phases. Three H (D) binding states (1,2 and) are populated at saturation as determined by thermal desorption spectroscopy (TDS). Whereas the peak temperature of the state is invariant with the hydrogen isotope, the D 1 state appears at a 8 Klower and theD 2 state at a 5 Khigher temperature than the respective H states. Generally the D phases exhibit a better long-range order than the H phases. The rate of adsorption is identical for the first three adsorbed phases but D2 adsorbs appreciably faster in the 1×2–3H and the final l×1–2H phases.Zero point energy effects as well as a H coverage dependent local interaction model could account for the observed effects.  相似文献   

17.
We have studied the properties of an electron bubble close to the surface of liquid3 He, by using a Density Functional approach. We find that up to an electron-surface distanced 0 23 Åthe bubble is stable, while at smaller distances it becomes unstable and bursts. A potential energy barrier /K B 38°K for the thermal emission of electrons is obtained from our results, in agreement with experiments. Even when the electron-surface distance is larger thand 0, however, tunneling through the surface layer dominates the electron escape probability. Large deviations of the electron potential energy from its ideal value are found close to the surface. These deviations have a profound effect on the calculated decay rates of the tunneling curent, which are much smaller than those obtained previously and in semi-quantitative agreement with experiments.  相似文献   

18.
The effect of impurity-induced states on the long range order in a lamellar antiferromagnet (AF) is studied and the magnetic phase-diagram of a lightly doped La2–x Sr x CuO4 is proposed. It is shown that long range magnetic perturbations and the layered structure cause the shrinkage of AF domain on the phase diagram and lead to the reentrant AF transition. A nonmonotonous dependence of the correlation length 2D on temperatureT is obtained; the dependence 2D (x) is exponential for highT and 2D x 1/2 for lowT.  相似文献   

19.
ZnO nanorods grown by site-selective molecular beam epitaxy show current–voltage characteristics that are sensitive to the presence of hydrogen or ozone in the measurement ambient for temperatures as low as 112 °C for H2 or room temperature for O3. The sensitivity to hydrogen increases sharply with temperature and multiple nanorods contacted at both ends by ohmic electrodes show currents of 10-8 A at 200 °C and a differential current change of 18% when changing from a pure N2 ambient to 10% H2 in N2. The nanorods are able to detect small concentrations (3%) of O3 in O2, with changes in current of 10-7 A at 25 °C. The sensitivity was 21% for O3 at room temperature. The nanorods also show a strong response to above-band-gap illumination with ultraviolet light. PACS 81.05.Dz; 73.61.Ga; 72.80.Ey  相似文献   

20.
Magnetic cluster excitations in various physical systems (e.g., soliton bearing one-dimensional solids, metallic alloys, amorphous materials, small particle aggregates, magnetically ordered substances near TC, transition metal di-chloride graphite intercalation compounds, etc.) are described. Use of Fe-57 Mössbauer effect spectroscopy as a probe of the spin dynamics for inverse autocorrelation times between 107Hz to 1010 Hz is emphasized. Particular attention is given to systems which exhibit local or long range magnetic order and whose Mössbauer spectra must therefore be described by more than one autocorrelation (or dwell) time for fluctuations between different allowed hyperfine field directions on a given site.  相似文献   

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