Two-dimensional, partially flexible polymers interacting with each other through the Onsager-like excluded-volume interaction are shown to exhibit a second-order, isotropic-nematic transition at a sufficiently high de...
Two-dimensional, partially flexible polymers interacting with each other through the Onsager-like excluded-volume interaction are shown to exhibit a second-order, isotropic-nematic transition at a sufficiently high density. The instability of the free energy under the influence of a nematic state is investigated and the critical density at which the isotropic-nematic phase transition takes place is determined analytically. It is shown that both second- and fourth-rank order parameters must be included in order to deduce a Landau expansion of the free energy.
A numerical solution is obtained for the generalized Onsager problem for the isotropic-nematic interface of rigid rods, which accounts for the biaxial effect that was ignored in previous calculations. It is found that...
A numerical solution is obtained for the generalized Onsager problem for the isotropic-nematic interface of rigid rods, which accounts for the biaxial effect that was ignored in previous calculations. It is found that the biaxial effect on interfacial tension is indeed weak, as previously expected. The biaxiality becomes significant only near the isotropic side of the interface.
Fermion mean-field solutions for the Heisenberg and the t-J models have been obtained by considering particle-hole correlations and carrying out the mean-field-theory calculations in momentum space. At half-filling th...
Fermion mean-field solutions for the Heisenberg and the t-J models have been obtained by considering particle-hole correlations and carrying out the mean-field-theory calculations in momentum space. At half-filling the solutions have mixed (s±d)-wave-like symmetry and have a lower ground-state energy than the s (uniform phase) and the d phases. On doping, the solutions with mixed s and d symmetry still have lower ground-state energy than the uniform phase. In the presence of doping, the density of states at the Fermi level in the mixed phases is depressed from its value in the uniform phase and is in good agreement with the experimental data.
The influence of a laterally inhomogeneous electrostatic potential of an adsorbate-covered surface on the resonant charge transfer in ion-surface scattering is investigated by means of the time-dependent Anderson-Newn...
The influence of a laterally inhomogeneous electrostatic potential of an adsorbate-covered surface on the resonant charge transfer in ion-surface scattering is investigated by means of the time-dependent Anderson-Newns Hamiltonian. The adsorbate-induced random modulation of the projectile orbital energy level is treated as a stochastic process, and its role in the charge transfer is evaluated analytically, in the Gaussian-process approximation, for low projectile speeds and low surface coverage by alkali atoms.
Non-hydrogenated amorphous silicon nitride (a-SiNx) films have been prepared using ion-beam-assisted reactive deposition and N2for the ion source gas. For a fixed ion beam voltage, a fixed Si deposition rate and a fix...
Non-hydrogenated amorphous silicon nitride (a-SiNx) films have been prepared using ion-beam-assisted reactive deposition and N2for the ion source gas. For a fixed ion beam voltage, a fixed Si deposition rate and a fixed substrate temperature, the N concentration in the film is determined by the ion beam current. At low N concentrations, the dark conductivities are dominated by hopping transport via the gap states. When the N content is increased, the gap state density is reduced and activated conductivities are observed. Room-temperature dark conductivities varying by ten orders of magnitude and optical bandgaps from 1.3 to 3.5 eV were obtained by changing the N concentration. Films with a ratioNN/NSiof N to Si content greater than 0.7 were photoconducting and this degraded slowly over time with exposure to a mercury light source. Since care was taken to eliminate H from these films and no H was detected in the films by infrared absorption, this would suggest that H may not be needed for the photoinduced degradation mechanism in a-SiNx. In addition, evidence is given that suggests sample polarization occurs and this could explain the photoconductivity fatigue observed.
Transport properties of antiferromagnetic superconductors with T(N) < T(c) have been investigated. Detailed numerical results are given for SmRh4B4 by using the following model. The paramagnetic phase (T(N) < T ...
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Transport properties of antiferromagnetic superconductors with T(N) < T(c) have been investigated. Detailed numerical results are given for SmRh4B4 by using the following model. The paramagnetic phase (T(N) < T < T(c)) is described by using Abrikosov-Gorkov theory of magnetic ions in an ordinary superconductor. In the AF phase (T less-than-or-equal-to T(N)), the effects of the molecular field H(Q)(T) and the elastic scattering of conduction electrons from spin fluctuations are included. Expressions for H(Q)(T) and the scattering rate from spin fluctuations have been derived. The aim has been to see if properties are enhanced or depressed by the AF ordering occurring below T(N). It is found that whereas the electronic thermal conductivity K(s), nuclear spin relaxation rate R(s), and the longitudinal ultrasonic attenuation alpha(s), are depressed by the AF ordering, the inverse of the magnetic penetration depth, [lambda(T)]-1, is enhanced below T(N). The effect of all types of impurities is included in the study. Theoretical results for K(s) and [lambda(T)]-1 agree with the experimental values for SmRh4B4 (experimental data for other properties are not available in literature). In the above, T(N) is the Neel temperature and T(c) is superconducting transition temperature.
a-Si:F and a-Si:F:H films have been prepared by ion-beam-assisted deposition using SiF4, SiH4+Ar, or SiF4+SiH4 as the gases for the ion source. Fluorine in a-Si eliminates some dangling bonds, increases the optical ga...
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a-Si:F and a-Si:F:H films have been prepared by ion-beam-assisted deposition using SiF4, SiH4+Ar, or SiF4+SiH4 as the gases for the ion source. Fluorine in a-Si eliminates some dangling bonds, increases the optical gap, and decreases the dark conductivity. The results are influenced mainly by the ion-beam energy used. The a-Si:F films do not exhibit an activated conductivity even up to 150-degrees-C, and no photoconductivity could be detected. However, film properties were significantly improved when a very small amount of H was added to the a-Si:F and much less than 1 at. % H produced films that were photoconducting and had activated conductivities. The properties of these a-Si:F:H are strongly dependent on both the fluorine concentration C(F) and the hydrogen concentration C(H). The deposition rate decreases with increasing SiF4 content in the source gas, and neither C(F) nor C(H) vary linearly with the change in the source gas ratio SiH4/(SiF4+SiH4). Hence, C(H) must be known and controlled in order to evaluate the effect of fluorine on the film's properties. By studying a series of a-Si:F:H samples containing the same C(H), it is noted that incorporating some F does improve the film's electrical properties. Annealing experiments suggest that an observed peak at 2100 cm-1 in the IR spectra of these a-Si:F:H films is not completely due to SiH2, as has been suggested by others.
TiO2 was prepared by the oxidation of TiCl4 at relatively low deposition temperatures using spray pyrolysis. For a fixed carrier gas (N2) flow rate, the substrate temperature is the critical parameter determining the ...
TiO2 was prepared by the oxidation of TiCl4 at relatively low deposition temperatures using spray pyrolysis. For a fixed carrier gas (N2) flow rate, the substrate temperature is the critical parameter determining the film properties. Films made near 595 K contain only the anatase phase, adhere well to the glass substrate, and have a relative optical transmission of about 75% (between 450 and 850 nm), the value one calculates for the non-absorbing anatase phase in this region. These films have an absorption edge characteristic of a direct gap semiconductor with allowed transitions and optical gaps of 3.5-3.7 eV, depending on the porosity. At higher substrate temperatures (above 635 K), the resulting films have a cloudy appearance and they contain both the rutile and the anatase modifications, confirmed by X-ray diffraction. Lower temperature substrates reduce the deposition rate and yield more porous films. For the pure anatase films, the dark conductivities are about one order of magnitude larger, and the photoconductivity is about one order of magnitude smaller when measured with the sample in air, than those observed when the sample is in a vacuum. When the samples are in a vacuum, the conductivities of the clear films increase by about two orders of magnitude (from about 10(-10) to about 10(-8) S cm-1) when illuminated with light from an electrically programmable read-only memory eraser (mercury light), which gives an intensity of about 30-mu-w cm-2 at the sample. The photoresponse has two parts;the fast portion rises in less than 1 s to 99% of its final value, followed by a small slow rise portion. The slow response, which is more pronounced in the decay process, is interpreted as being due to the presence of surface trapping states.
If the lineshape response of a Si(Li) detector is measured using monoenergetic x-rays provided by a monochromator, it must be convoluted by a Lorentzian of appropriate width in order to represent the lineshape encount...
If the lineshape response of a Si(Li) detector is measured using monoenergetic x-rays provided by a monochromator, it must be convoluted by a Lorentzian of appropriate width in order to represent the lineshape encountered in directly measured x-ray spectra. It is shown that the Lorentzian component is responsible for a significant fraction of low-energy peak tailing, a phenomenon usually attributed to detector imperfections.
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