10,530 research outputs found
Ion beam induced enhanced diffusion from gold thin films in silicon
Enhanced diffusion of gold atoms into silicon substrate has been studied in
Au thin films of various thicknesses (2.0, 5.3, 10.9 and 27.5 nm) deposited on
Si(111) and followed by irradiation with 1.5 MeV Au2+ at a flux of 6.3x10^12
ions cm-2 s-1 and fluence up to 1x10^15 ions cm-2. The high resolution
transmission electron microscopy measurements showed the presence of gold
silicide formation for the above-mentioned systems at fluence greater than
equal to 1x1014 ions cm-2. The maximum depth to which the gold atoms have been
diffused at a fluence of 1x10^14 ions cm-2 for the cases of 2.0, 5.3, 10.9 and
27.5 nm thick films has been found to be 60, 95, 160 and 13 nm respectively.
Interestingly, at higher fluence of 1x1015 ions cm-2 in case of 27.5 nm thick
film, gold atoms from the film transported to a maximum depth of 265 nm in the
substrate. The substrate silicon is found to be amorphous at the above fluence
values where unusually large mass transport occurred. Enhanced diffusion has
been explained on the basis of ion beam induced, flux dependent amorphous
nature of the substrate, and transient beam induced temperature effects. This
work confirms the absence of confinement effects that arise from spatially
confined structures and existence of thermal and chemical reactions during ion
irradiation.Comment: 15 pages, 3 figure
Flux dependent 1.5 MeV self-ion beam induced sputtering from Gold nanostructured thin films
We discuss four important aspects of 1.5 MeV Au2+ ion-induced flux dependent
sputtering from gold nanostrcutures (of an average size 7.6 nm and height 6.9
nm) that are deposited on silicon substrates: (a) Au sputtering yield at the
ion flux of 6.3x10^12 ions cm-2 s-1 is found to be 312 atoms/ion which is about
five times the sputtering yield reported earlier under identical irradiation
conditions at a lower beam flux of 10^9 ions cm-2 s-1, (b) the sputtered yield
increases with increasing flux at lower fluence and reduces at higher fluence
(1.0x10^15 ions cm-2) for nanostructured thin films while the sputtering yield
increases with increasing flux and fluence for thick films (27.5 nm Au
deposited on Si) (c) Size distribution of sputtered particles has been found to
vary with the incident beam flux showing a bimodal distribution at higher flux
and (d) the decay exponent obtained from the size distributions of sputtered
particles showed an inverse power law dependence ranging from 1.5 to 2.5 as a
function of incident beam flux. The exponent values have been compared with
existing theoretical models to understand the underlying mechanism. The role of
wafer temperature associated with the beam flux has been invoked for a
qualitative understanding of the sputtering results in both the nanostructured
thin films and thick films.Comment: 25 pages, 5 figures, 1 table To be Appeared in J. Phys. D: Appl. Phy
Edges and Diffractive Effects in Casimir Energies
The prototypical Casimir effect arises when a scalar field is confined
between parallel Dirichlet boundaries. We study corrections to this when the
boundaries themselves have apertures and edges. We consider several geometries:
a single plate with a slit in it, perpendicular plates separated by a gap, and
two parallel plates, one of which has a long slit of large width, related to
the case of one plate being semi-infinite. We develop a general formalism for
studying such problems, based on the wavefunctional for the field in the gap
between the plates. This formalism leads to a lower dimensional theory defined
on the open regions of the plates or boundaries. The Casimir energy is then
given in terms of the determinant of the nonlocal differential operator which
defines the lower dimensional theory. We develop perturbative methods for
computing these determinants. Our results are in good agreement with known
results based on Monte Carlo simulations. The method is well suited to
isolating the diffractive contributions to the Casimir energy.Comment: 32 pages, LaTeX, 9 figures. v2: additional discussion of
renormalization procedure, version to appear in PRD. v3: corrected a sign
error in (70
Sesquiterpene Lactones Isolated from Elephantopus scaber L. Inhibits Human Lymphocyte Proliferation and the Growth of Tumour Cell Lines and Induces Apoptosis In Vitro
This study was designed to isolate the compounds responsible for the cytotoxic properties of South Indian Elephantopus scaber L. and further investigate their effects on quiescent and proliferating cells. Bioassay-guided isolation of the whole plant of chloroform extract of South Indian Elephantopus scaber afforded the known sesquiterpene lactone, deoxyelephantopin, and isodeoxyelephantopin whose structures were determined by spectroscopic methods. These compounds caused a dose dependent reduction in the viability of L-929 tumour cells in 72 h culture (IC50 value of 2.7 μg/mL and 3.3 μg/mL) by the cell viability assay. Both the compounds act selectively on quiescent and PHA-stimulated proliferating human lymphocytes and inhibited tritiated thymidine incorporation into cellular DNA of DLA tumour cells. The compound deoxyelephantopin at a concentration of 3 μg/mL caused maximum apoptotic cells. It also exhibited significant in vivo antitumour efficacy against DLA tumour cells. The results, therefore, indicate that the antiproliferative property of deoxyelephantopin and isodeoxyelephantopin could be used in regimens for treating tumors with extensive proliferative potencies
Asymptotic behavior of the least common multiple of consecutive arithmetic progression terms
Let and be two integers with , and let and be
integers with and . In this paper, we prove that , where is a constant depending on and .Comment: 8 pages. To appear in Archiv der Mathemati
Damping in Torsional Vibrations of Embedded Footings
The existing theoretical models to explain the dynamic behavior of embedded footings, overestimate the real response by neglecting damping forces which are inevitable as a result of slip at the interface of the embedded footing and soil. Many researchers in the field of Soil Dynamics have suggested that the inclusion of friction damping and internal damping in the mathematical model is necessary to improve the reliability of theoretical predictions. In this paper, results of the experimental investigations on full scale model embedded footings subjected to torsional mode of vibration have been presented. The results have been analyzed making use of three theoretical models, as developed by, Novak and Sachs (1973); Sankaran et al (1978) and Sankaran et al (1980). The importance of d-ping in predicting the dynamic response is brought out by a comparison of field vibratory test data with the corresponding values predicted by each of the above mentioned theoretical models
Phosphate mediated regulation of carbohydrate metabolism in Neurospora crassa
Phosphate mediated regulation of carbohydrate metabolism in Neurospora crass
Constant magnetic field and 2d non-commutative inverted oscillator
We consider a two-dimensional non-commutative inverted oscillator in the
presence of a constant magnetic field, coupled to the system in a
``symplectic'' and ``Poisson'' way. We show that it has a discrete energy
spectrum for some value of the magnetic field.Comment: 7 pages, LaTeX file, no figures, PACS number: 03.65.-
Noncommutative gravity: fuzzy sphere and others
Gravity on noncommutative analogues of compact spaces can give a finite mode
truncation of ordinary commutative gravity. We obtain the actions for gravity
on the noncommutative two-sphere and on the noncommutative in
terms of finite dimensional -matrices. The commutative large
limit is also discussed.Comment: LaTeX, 13 pages, section on CP^2 added + minor change
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