The effects of many-body interactions in the static structure of dense gaseous krypton (for 0.9-2.1 rho(c), where rho(c) is the critical density) and xenon (for 2.2-2.6 rho(c)) were investigated in the momentum transf...
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The effects of many-body interactions in the static structure of dense gaseous krypton (for 0.9-2.1 rho(c), where rho(c) is the critical density) and xenon (for 2.2-2.6 rho(c)) were investigated in the momentum transfer range 4 less than or equal to Q less than or equal to 42 nm(-1), through comparisons of the measured structure factors S(Q) with those calculated through the MHNC-CRS integral equation by Reatto and Tau. One property investigated is the small increase in the effective atomic diameter with increasing density. While the observed variation, as determined through the position of the main diffraction maxima, is similar to that given by the inclusion of the Axilrod-Teller triple-diploe interaction in the calculation, further small deviations exist which indicate the need for additional many-body terms.
Dynamic light scattering is an established technique for measuring the average size and size distribution of particles in a suspension. The technique has the advantage of being fast and non-invasive, but it does requi...
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Dynamic light scattering is an established technique for measuring the average size and size distribution of particles in a suspension. The technique has the advantage of being fast and non-invasive, but it does require low particle concentrations. As well, dynamic light scattering results are often open to misinterpretation if one is unaware of the state of the sample and the method of data analysis. The following discussion reviews some of the basic concepts of dynamic light scattering and outlines some of the pitfalls that are often encountered in data interpretation. A modification of dynamic light scattering, diffusing wave spectroscopy, can be used to obtain approximate size information at higher particle concentrations. The fundamentals of this new technique are summarized.
Hexagonal ZnO films with different observed orientations were deposited on glass substrates at temperatures below 200-degrees-C by r.f. sputtering of a ZnO target using an oxygen and argon gas mixture. Orientations wi...
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Hexagonal ZnO films with different observed orientations were deposited on glass substrates at temperatures below 200-degrees-C by r.f. sputtering of a ZnO target using an oxygen and argon gas mixture. Orientations with the (002) planes of the crystallites parallel to the substrate, or with the (100) planes parallel to the substrate, or films in which the (101) peak is dominant in their X-ray diffraction spectra have been obtained by selecting the deposition parameters. The partial pressure of the oxygen in the sputtering gas, the distance between target and substrate, the substrate temperature during film nucleation and the input power each affect (to varying degrees) the observed crystallite orientation obtained. Polycrystalline ZnO films made in the presence of excess oxygen or at a high sputtering gas pressure tend to have the c axis parallel to the substrate and they exhibit a large photoresponse, while films sputter-deposited with a low partial pressure of oxygen tend to have the c axis perpendicular to the substrate and may have no detectable d.c. photoresponse. The availability of oxygen during sample preparation has a significant affect on the slow photoresponse of the resulting ZnO films.
Annealing ZnO films prepared by ion-beam-assisted deposition (IBAD) in air above 773 K can change the resistivity from almost-equal-to 10(-4) OMEGA cm to more than 10(6) OMEGA cm, changing the films from a highly dege...
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Annealing ZnO films prepared by ion-beam-assisted deposition (IBAD) in air above 773 K can change the resistivity from almost-equal-to 10(-4) OMEGA cm to more than 10(6) OMEGA cm, changing the films from a highly degenerate transparent material to a thermally activated semiconductor. No change in the transmission through the visible region of the spectrum (more than 90%) is observed but the optical band gap can change from almost-equal-to 3.41 to almost-equal-to 3.24 eV, as a result of a Burstein-Moss shift. However, for films that are not initially very transparent, the average transmission can be increased from almost-equal-to 28% to more than 85%. High temperature annealing increases the average size of crystallites by almost-equal-to 15%. After annealing, a large photoresponse is observed, with the conductivity increasing by more than a factor of 10(5) when the film is illuminated with UV light (almost-equal-to 4 x 10(16) photons cm-2 s-1). The rise and decay time constants are very large, indicating that previously reported surface structural changes occur. These constants strongly depend on the intensity of the light and the ambient gases present. Any true photoconductiity present appears to be very small. Encapsulating the free surface of a ZnO film with a layer of amorphous SiN(x) can help to stabilize the film, and it decreases the photoresponse time as well as the magnitude of the photoresponse.
Amorphous hydrogenated silicon germanium thin films with 20% Ge content (a-Si0.8Ge0.2:H) were deposited by ion beam-assisted deposition (IBAD), using SiH4 as the source gas. Moderate ion energies of similar to 125 to ...
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Amorphous hydrogenated silicon germanium thin films with 20% Ge content (a-Si0.8Ge0.2:H) were deposited by ion beam-assisted deposition (IBAD), using SiH4 as the source gas. Moderate ion energies of similar to 125 to 135 eV and an ion-to-atom ratio of similar to 1, produced samples with a reduced number of SiH2 and (SiH2)(n) bonding configurations, an increased hydrogen content and a decreased porosity compared with non-bombarded samples. This reduces the disorder in the a-SiGe network as well as the defect density. The preferential attachment coefficient for these films is near unity. The optical and electrical properties of the a-SiGe:H alloy have been studied as a function of the ion beam energy and the ion-to-atom ratio at the substrate. The best films had a photosensitivity of sigma(ph)/sigma(d) = 1.7 x 10(4) and E(g)= 1.65 eV. The ion beam increases the optical gap, lowers the dark conductivity and increases the electrical activation energy.
An electron cyclotron resonance plasma-assisted deposition method has been used to prepare polycrystalline GaN films. These GaN films can have dark conductivities as low as 10(-10) S cm(-1) and they exhibit well-defin...
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An electron cyclotron resonance plasma-assisted deposition method has been used to prepare polycrystalline GaN films. These GaN films can have dark conductivities as low as 10(-10) S cm(-1) and they exhibit well-defined conductivity activation energies. The sample conductivity is decreased by surface adsorption of gases and it increases again when the adsorbed species is photodesorbed from the surface using UV light. As a result, the photoresponse is very slow, especially the decay process, which may require several days for a sample to recover when it is mounted in a vacuum. This recovery time can be reduced significantly if the sample temperature is increased or the sample is exposed to air. In this respect, these GaN films have a number of features in common with ZnO.
The Raman and infrared wavenumbers of solid HCONH2 and DCOND2 were measured at 20 K and high temperatures. More peaks were observed in both the lattice and internal mode regions than were expected from the known struc...
The Raman and infrared wavenumbers of solid HCONH2 and DCOND2 were measured at 20 K and high temperatures. More peaks were observed in both the lattice and internal mode regions than were expected from the known structure, so the structure was redetermined. The resulting structure is in agreement with earlier determinations, so the extra peaks are attributed to second-order effects produced by a large anharmonicity associated with the hydrogen bonds. Attempts to model the structural details and the lattice dynamics had only a limited success, which may again be attributed to anharmonic effects and to the basic inadequacies of the models.
The effect of polydispersity on the isotropic-nematic phase transition of rigid rods is analyzed in terms of a second-order perturbation theory, in which the width σ of an arbitrary number fraction is used as a pertu...
The effect of polydispersity on the isotropic-nematic phase transition of rigid rods is analyzed in terms of a second-order perturbation theory, in which the width σ of an arbitrary number fraction is used as a perturbation parameter. These results show that the isotropic-nematic phase transition takes place at the isotropic density nI, where nIL¯N2D=4.189(1+2.128σ2), and the nematic density nN, where nNL¯N2D=5.336(1+1.655σ2), with D and L¯N being the diameter and the number-averaged length of rods in the nematic phase. At the transition density, the weight- and number-averaged orientation order parameters have the values SW=0.7922+1.1333σ2 and SL=0.7922+0.816σ2; the ratio between the number-averaged length of rods in the isotropic phase, L¯I, and that in the nematic phase, L¯N, is L¯I/L¯N=1-1.844σ2. These perturbation results are compared with the numerical solution of the equilibrium conditions for the isotropic-nematic transition of rods obeying two modeled number fraction distributions.
We examine possible nematic to smectic and nematic to columnar phase transitions for binary mixtures of perfectly parallel aligned hard cylinders with equal diameters but different lengths by using the free-energy fun...
We examine possible nematic to smectic and nematic to columnar phase transitions for binary mixtures of perfectly parallel aligned hard cylinders with equal diameters but different lengths by using the free-energy functional within the third virial coefficient approximation. The regions of stability are located and the phase diagram of the system is calculated for different values of the ratio of the two cylindrical lengths. The nematic phase can directly transform into the columnar phase for values with a length ratio smaller than 0.635, showing that dispersity in molecular length can stabilize columnar versus smectic ordering of these mixtures.
The self-consistent-field model for K shakeoff in β± decay and electron-capture decay is extended to deal with the processes of L shakeoff accompanying K capture and K shakeoff accompanying L capture. The result...
The self-consistent-field model for K shakeoff in β± decay and electron-capture decay is extended to deal with the processes of L shakeoff accompanying K capture and K shakeoff accompanying L capture. The results indicate that many-body effects play an important role and reduce the shakeoff probability.
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