4,013 research outputs found
Investigating Atomic Details of the CaF(111) Surface with a qPlus Sensor
The (111) surface of CaF has been intensively studied with
large-amplitude frequency-modulation atomic force microscopy and atomic
contrast formation is now well understood. It has been shown that the apparent
contrast patterns obtained with a polar tip strongly depend on the tip
terminating ion and three sub-lattices of anions and cations can be imaged.
Here, we study the details of atomic contrast formation on CaF(111) with
small-amplitude force microscopy utilizing the qPlus sensor that has been shown
to provide utmost resolution at high scanning stability. Step edges resulting
from cleaving crystals in-situ in the ultra-high vacuum appear as very sharp
structures and on flat terraces, the atomic corrugation is seen in high clarity
even for large area scans. The atomic structure is also not lost when scanning
across triple layer step edges. High resolution scans of small surface areas
yield contrast features of anion- and cation sub-lattices with unprecedented
resolution. These contrast patterns are related to previously reported
theoretical results.Comment: 18 pages, 9 Figures, presented at 7th Int Conf Noncontact AFM
Seattle, USA Sep 12-15 2004, accepted for publication in Nanotechnology,
http://www.iop.or
Lattice Effects in Crystal Evaporation
We study the dynamics of a stepped crystal surface during evaporation, using
the classical model of Burton, Cabrera and Frank, in which the dynamics of the
surface is represented as a motion of parallel, monoatomic steps. The validity
of the continuum approximation treated by Frank is checked against numerical
calculations and simple, qualitative arguments. The continuum approximation is
found to suffer from limitations related, in particular, to the existence of
angular points. These limitations are often related to an adatom detachment
rate of adatoms which is higher on the lower side of each step than on the
upper side ("Schwoebel effect").Comment: DRFMC/SPSMS/MDN, Centre d'Etudes Nucleaires de Grenoble, 25 pages,
LaTex, revtex style. 8 Figures, available upon request, report# UBFF30119
X-ray scattering from stepped and kinked surfaces: An approach with the paracrystal model
A general formalism of X-ray scattering from different kinds of surface
morphologies is described. Based on a description of the surface morphology at
the atomic scale through the use of the paracrystal model and discrete
distributions of distances, the scattered intensity by non-periodic surfaces is
calculated over the whole reciprocal space. In one dimension, the scattered
intensity by a vicinal surface, the two-level model, the N-level model, the
faceted surface and the rough surface are addressed. In two dimensions, the
previous results are generalized to the kinked vicinal surface, the two-level
vicinal surface and the step meandering on a vicinal surface. The concept of
crystal truncation rod is generalized considering also the truncation of a
terrace by a step (yielding a terrace truncation rod) and a step by a kink
(yielding a step truncation rod).Comment: 33 pages, 18 figure
Growth and surface alloying of Fe on Pt(997)
The growth of ultra-thin layers of Fe on the vicinal Pt(997) surface is
studied by thermal energy He atom scattering (TEAS) and Auger electron
spectroscopy (AES) in the temperature range between 175K and 800K. We find
three distinct regimes of qualitatively different growth type: Below 450K the
formation of a smooth first monolayer, at and above 600K the onset of bulk
alloy formation, and at intermediate temperature 500K - 550K the formation of a
surface alloy. Monatomic Fe rows are observed to decorate the substrate steps
between 175K and 500K. The importance of the high step density is discussed
with respect to the promotion of smooth layer growth and with respect to the
alloying process and its kinetics
Hedonic Price Indices for the Paris Housing Market
In this paper, we calculate a transaction-based price index for apartments in Paris (France). The heterogeneous character of real estate is taken into account using an hedonic model. The functional form is specified using a general Box-Cox function. The data basis covers 84 686 transactions of the housing market in 1990:01-1999:12, which is one of the largest samples ever used in comparable studies. Low correlations of the price index with stock and bond indices (first differences) indicate diversification benefits from the inclusion of real estate in a mixed asset portfolio
Polaronic state and nanometer-scale phase separation in colossal magnetoresistive manganites
High resolution topographic images obtained by scanning tunneling microscope
in the insulating state of Pr0.68Pb0.32MnO3 single crystals showed regular
stripe-like or zigzag patterns on a width scale of 0.4 - 0.5 nm confirming a
high temperature polaronic state. Spectroscopic studies revealed inhomogeneous
maps of zero-bias conductance with small patches of metallic clusters on length
scale of 2 - 3 nm only within a narrow temperature range close to the
metal-insulator transition. The results give a direct observation of polarons
in the insulating state, phase separation of nanometer-scale metallic clusters
in the paramagnetic metallic state, and a homogeneous ferromagnetic state
Breakdown of metastable step-flow growth on vicinal surfaces induced by nucleation
We consider the growth of a vicinal crystal surface in the presence of a
step-edge barrier. For any value of the barrier strength, measured by the
length l_es, nucleation of islands on terraces is always able to destroy
asymptotically step-flow growth. The breakdown of the metastable step-flow
occurs through the formation of a mound of critical width proportional to
L_c=1/sqrt(l_es), the length associated to the linear instability of a
high-symmetry surface. The time required for the destabilization grows
exponentially with L_c. Thermal detachment from steps or islands, or a steeper
slope increase the instability time but do not modify the above picture, nor
change L_c significantly. Standard continuum theories cannot be used to
evaluate the activation energy of the critical mound and the instability time.
The dynamics of a mound can be described as a one dimensional random walk for
its height k: attaining the critical height (i.e. the critical size) means that
the probability to grow (k->k+1) becomes larger than the probability for the
mound to shrink (k->k-1). Thermal detachment induces correlations in the random
walk, otherwise absent.Comment: 10 pages. Minor changes. Accepted for publication in Phys. Rev.
An Exactly Solved Model of Three Dimensional Surface Growth in the Anisotropic KPZ Regime
We generalize the surface growth model of Gates and Westcott to arbitrary
inclination. The exact steady growth velocity is of saddle type with principal
curvatures of opposite sign. According to Wolf this implies logarithmic height
correlations, which we prove by mapping the steady state of the surface to
world lines of free fermions with chiral boundary conditions.Comment: 9 pages, REVTEX, epsf, 3 postscript figures, submitted to J. Stat.
Phys, a wrong character is corrected in eqs. (31) and (32
Kinetics of step bunching during growth: A minimal model
We study a minimal stochastic model of step bunching during growth on a
one-dimensional vicinal surface. The formation of bunches is controlled by the
preferential attachment of atoms to descending steps (inverse Ehrlich-Schwoebel
effect) and the ratio of the attachment rate to the terrace diffusion
coefficient. For generic parameters () the model exhibits a very slow
crossover to a nontrivial asymptotic coarsening exponent .
In the limit of infinitely fast terrace diffusion () linear coarsening
( = 1) is observed instead. The different coarsening behaviors are
related to the fact that bunches attain a finite speed in the limit of large
size when , whereas the speed vanishes with increasing size when .
For an analytic description of the speed and profile of stationary
bunches is developed.Comment: 8 pages, 10 figure
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