148 research outputs found
Investigation of laser ablated ZnO thin films grown with Zn metal target: a structural study
High quality ZnO thin films were gown using the pulsed laser deposition
technique on (0001) AlO substrates in an oxidizing atmosphere, using a
Zn metallic target. We varied the growth conditions such as the deposition
temperature and the oxygen pressure. First, using a battery of techniques such
as x-rays diffraction, Rutherford Backscattering spectroscopy and atomic force
microscopy, we evaluated the structural quality, the stress and the degree of
epitaxy of the films. Second, the relations between the deposition conditions
and the structural properties, that are directly related to the nature of the
thin films, are discussed qualitatively. Finally, a number of issues on how to
get good-quality ZnO films are addressed.Comment: To be published in Jour. Appl. Phys. (15 August 2004
Generalized Smoluchowski equation with correlation between clusters
In this paper we compute new reaction rates of the Smoluchowski equation
which takes into account correlations. The new rate K = KMF + KC is the sum of
two terms. The first term is the known Smoluchowski rate with the mean-field
approximation. The second takes into account a correlation between clusters.
For this purpose we introduce the average path of a cluster. We relate the
length of this path to the reaction rate of the Smoluchowski equation. We solve
the implicit dependence between the average path and the density of clusters.
We show that this correlation length is the same for all clusters. Our result
depends strongly on the spatial dimension d. The mean-field term KMFi,j = (Di +
Dj)(rj + ri)d-2, which vanishes for d = 1 and is valid up to logarithmic
correction for d = 2, is the usual rate found with the Smoluchowski model
without correlation (where ri is the radius and Di is the diffusion constant of
the cluster). We compute a new rate: the correlation rate K_{i,j}^{C}
(D_i+D_j)(r_j+r_i)^{d-1}M{\big(\frac{d-1}{d_f}}\big) is valid for d \leq
1(where M(\alpha) = \sum+\infty i=1i\alphaNi is the moment of the density of
clusters and df is the fractal dimension of the cluster). The result is valid
for a large class of diffusion processes and mass radius relations. This
approach confirms some analytical solutions in d 1 found with other methods. We
also show Monte Carlo simulations which illustrate some exact new solvable
models
Rate Equations and Scaling in Pulsed Laser Deposition
We study a simplified model for pulsed laser deposition [Phys. Rev. Lett.
{\bf 87}, 135701 (2001)] by rate equations. We consider a set of equations,
where islands are assumed to be point-like, as well as an improved one that
takes the size of the islands into account. The first set of equations is
solved exactly but its predictive power is restricted to a few pulses. The
improved set of equations is integrated numerically, is in excellent agreement
with simulations, and fully accounts for the crossover from continuous to
pulsed deposition. Moreover, we analyze the scaling of the nucleation density
and show numerical results indicating that a previously observed logarithmic
scaling does not apply.Comment: 8 pages, 9 figure
The influence of Ga-irradiation on the transport properties of mesoscopic conducting thin films
We studied the influence of 30keV Ga-ions -- commonly used in focused ion
beam (FIB) devices -- on the transport properties of thin crystalline graphite
flake, LaCaMnO and Co thin films. The changes of the
electrical resistance were measured in-situ during irradiation and also the
temperature and magnetic field dependence before and after irradiation. Our
results show that the transport properties of these materials strongly change
at Ga fluences much below those used for patterning and ion beam induced
deposition (IBID), limiting seriously the use of FIB when the intrinsic
properties of the materials of interest are of importance. We present a method
that can be used to protect the sample as well as to produce selectively
irradiation-induced changes.Comment: 14 pages, 11 figures, will be published in Nanotechnology 201
Recent advances in pulsed-laser deposition of complex-oxides
Pulsed-laser deposition (PLD) is one of the most promising techniques for the
formation of complex-oxide heterostructures, superlattices, and well-controlled
interfaces. The first part of this paper presents a review of several useful
modifications of the process, including methods inspired by combinatorial
approaches. We then discuss detailed growth kinetics results, which illustrate
that 'true' layer-by-layer (LBL) growth can only be approached, but not fully
met, even though many characterization techniques reveal interfaces with
unexpected sharpness. Time-resolved surface x-ray diffraction measurements show
that crystallization and the majority of interlayer mass transport occur on
time scales that are comparable to those of the plume/substrate interaction,
providing direct experimental evidence that a growth regime exists in which
non-thermal processes dominate PLD. This understanding shows how kinetic growth
manipulation can bring PLD closer to ideal LBL than any other growth method
available today.Comment: 37 pages, 9 figures. Revie
Optical Thomson scatter from a laser-ablated magnesium plume
International audienc
Fabrication of patterned DNA surfaces.
Two photolithographic methods are described for the formation of patterned single or multiple DNA species on SiO2 substrates. In the first approach, substrates are treated with a photochemically labile organosilane monolayer film. Irradiation of these surfaces with patterned deep UV (193 nm) light results in patterned chemically reactive groups which are then reacted with heterobifunctional crosslinking molecules. Covalent attachment of modified synthetic DNA oligomers to the crosslinker results in stable DNA patterns. Alternatively, a photoresist is spin-coated over a silane film which had been previously modified with the heterobifunctional crosslinker. Upon patterned irradiation and subsequent development, the underlying crosslinker-modified layer is revealed, and is then reacted with a chemically modified DNA. Feature dimensions to 1 micron are observed when a single fluorescent DNA is attached to the surface. By performing sequential exposures, we have successfully immobilized two distinguishable DNA oligomers on a single surface. Synthetic DNA immobilized in this manner retains the ability to hybridize to its complementary strand, suggesting that these approaches may find utility in the development of miniaturized DNA-based biosensors
- …