Microstructures and photoluminescence of hydrogenated amorphous carbon films produced by using organic hydrocarbon source

Thin layers of hydrogenated amorphous carbon were prepared by using organic hydrocarbon source, xylene (C₈H₁₀), in plasma-enhanced chemical vapor deposition (PECVD) system. The microstructures were characterized by using Fourier-transform infrared and Raman scattering spectra. The appearance of a sharp vibration signal in 1600 cm^-1 strongly suggests the existence of sp² carbon clusters with aromatic rings. With increasing the deposition rf power, the content of these aromatic structures is increased in the films. In contrast to a broad single PL peak in methane (CH₄)-baseda-C:H films, the PL band of xylene-based a-C:H films contains multiple peaks in blue-green light region, which is influenced by rf power. We tentatively attributed it to the radiative recombination of electron-hole pairs through some luminescent centers associated with aromatic structures. Received: 26 April 2000 / Accepted: 9 May 2000 / Published online: 13 September 2000     

Pion mass dependence of the nucleon mass in the chiral quark soliton model

The dependence of the nucleon mass on the mass of the pion is studied in the framework of the chiral quark-soliton model. A remarkable agreement is observed with lattice data from recent full dynamical simulations. The possibility and limitations to use the results from the chiral quark soliton model as a guideline for the chiral extrapolation of lattice data are discussed.     

Temperature dependence of photoluminescence in amorphous Si1-xCx:H films

We have investigated the temperature dependence of photoluminescence in hydrogenated amorphous silicon-carbon alloys a-Si_1-xC_x:H prepared by glow discharge in the low-power regime. The radiative recombination process, due to photocarriers trapped on band-edge states, is in competition with the thermal escape of the photocarriers into the mobility bands. The model gives a quantitative fit with experiment, without any adjustable parameter, provided the width of the band-edge distribution of states is taken as the width of the conduction band only (measured by “photo-induced infra-red spectroscopy”) and not as the Urbach energy, as it is usually assumed.     

Symmetries of discontinuous flows and the dual Rankine-Hugoniot conditions in fluid dynamics

It has recently been shown that the maximal kinematical invariance group of polytropic fluids, for smooth subsonic flows, is the semidirect product of SL (2, R) and the static Galilei group G. This result purports to offer a theoretical explanation for an intriguing similarity, that was recently observed, between a supernova explosion and a plasma implosion. In this paper we extend this result to discuss the symmetries of discontinuous flows, which further validates the explanation by taking into account shock waves, which are the driving force behind both the explosion and implosion. This is accomplished by constructing a new set of Rankine-Hugoniot conditions, which follow from Noether’s conservation laws. The new set is dual to the standard Rankine-Hugoniot conditions and is related to them through the SL (2, R) transformations. The entropy condition, that the shock needs to satisfy for physical reasons, is also seen to remain invariant under the transformations.     

Ion beam exposure of resists

Problems caused by the statistical variation of the number of exposing ions in ionbeam lithography are discussed. Using Poisson statistics, the minimum dose required for exposure as a function of resist sensitivity and minimum feature size is calculated. It is found that, although ion-beam resists show a very high sensitivity of 10¹¹ to 10¹³,cm^–2, it would be possible to use still more sensitive resists and obtain submicron linewidth resolution.     

On photoluminescence properties of a-Si:H-based structures

Non-Gaussian photoluminescence peaks observed in a-Si:H-based structures at 6 K are interpreted as a consequence of the presence of different phases in material. Thin films of amorphous silicon deposited on glass substrate have been analyzed.The main aims of the contribution are (i) analysis of numerical data obtained by fitting procedure and (ii) formulation of corresponding conclusions in terms of structural properties of sample. Spectrum of a-Si:H-based samples can be interpreted as superposition of photoluminescence signals arising from two domains with different degrees of structural disordering. By our knowledge this result corresponds to real situation from view of structural properties of amorphous hydrogenated silicon. Under certain circumstances, decomposition of photoluminescence spectrum can give information of geometrical structure of sample.     

Simulation of Phase-Change Random Access Memory with Ring-Type Contactor for Low Reset Current by Finite Element Modelling

A three-dimensional finite element models for phase change random access memory （PCRAM） is established to simulate thermal and electrical behaviours during RESET operation. The RESET behaviours of the conventional structure （CS） and the ring-type contact in bottom electrode （RIB） are compared with each other. The simulation results indicate that the RIB cell has advantages of high heat efficiency for melting phase change material in cell, reduction of contact area and lower RESET current with maintaining good resistance contrast. The RESET current decreases from 1.26mA to 1.2mA and the heat consumption in CST material during programming increases from 12% to 37% in RIB structure. Thus the RIB structure PCRAM cell is suitable for future device with high heat efficiency and smaller RESET current.     

Perturbative chiral violations for domain-wall QCD with improved gauge actions

We investigate, in the framework of perturbation theory at finite Ns$N_s$, the effectiveness of improved gauge actions in suppressing the chiral violations of domain-wall fermions. Our calculations show substantial reductions of the residual mass when it is compared at the same value of the gauge coupling, the largest suppression being obtained when the DBW2 action is used. Similar effects can also be observed for a power-divergent mixing coefficient which is chirally suppressed. No significant reduction instead can be seen in the case of the difference between the vector and axial-vector renormalization constants when improved gauge actions are used in place of the plaquette action. We also find that one-loop perturbation theory is not an adequate tool to carry out comparisons at the same energy scale (of about 2 GeV), and in fact in this case even an enhancement of the chiral violations is frequently obtained.     

Expression and distribution of N-acetyl and N-glycolylneuraminic acids in secreted and cell-associated glycoconjugates by two human osteosarcoma cell lines

N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc) are the dominant sialic acids (Sia) in mammals usually found in the non-reducing terminal of oligosaccharide side chains in glycoproteins and glycolipids. Their expression and distribution pattern have been correlated both with the malignant phenotype and tumor grade of human cancers. The aim of the present study was to determine by reversed-phase HPLC method the amounts of Neu5Ac and Neu5Gc as well as their distribution among the culture media and cell surface of MG-63 and Saos-2 human osteosarcoma cell lines of high and low metastatic potential. It was determined that MG-63 cells produce up to 5-fold more total sialic acid as compared with the Saos 2 cells. Neu5Ac accounts for ca 60% of the total sialic acids secreted by MG-63 cells, whereas Neu5Gc is the predominant sialic acid present on the MG-63 cell membrane. Saos 2 cells secrete considerable amounts of Neu5Ac to culture media. The obtained data indicate that the human osteosarcoma cells express both forms of Sia-containing glycoconjugates; the differences in the amounts of each of the two major Sia types and their distribution may be related to their differences in morphology and/or metastatic potentials.