共查询到20条相似文献,搜索用时 15 毫秒
1.
G. Kresse W. Bergermayer R. Podloucky E. Lundgren R. Koller M. Schmid P. Varga 《Applied Physics A: Materials Science & Processing》2003,76(5):701-710
Complex surface reconstructions and surface oxides, in particular, often exhibit complicated atomic arrangements, which are
difficult to resolve with traditional experimental methods, such as low energy electron diffraction (LEED), surface X-ray
diffraction (SXRD) or scanning tunnelling microscopy (STM) alone. Therefore, ab initio density functional calculations are
used as a supplement to the experimental techniques, but even then the structural determination usually relies on a simple
trial and error procedure, in which conceivable models are first constructed and then tested for their stability in ab initio
calculations. An exhaustive search of the configuration space is usually difficult and requires a significant human effort.
Solutions to this problem, such as simulated annealing, have long been known, but are usually considered to be too time-consuming
in combination with first principles methods. In this work, we show that ab initio density functional codes are now sufficiently
fast to perform extensive finite temperature molecular dynamics. The merits of this approach are exemplified for two cases,
for a complex two-dimensional surface oxide on Pd(111), and for the oxygen induced c(6×2) reconstruction of V(110).
Revised version: 15 July 2002 / Accepted: 2 October 2002 / Published online: 5 February 2003
RID="*"
ID="*"Corresponding author. Fax: +43-1/4277-9514, E-mail: Georg.Kresse@univie.ac.at 相似文献
2.
S.L. Xu Q.D. Zeng P. Wu Y.H. Qiao C. Wang C.L. Bai 《Applied Physics A: Materials Science & Processing》2003,76(2):209-212
The molecular assembly of three different trialkyloxy-substituted benzaldehydes on graphite has been studied using scanning
tunneling microscopy (STM). It is found that these benzaldehydes, which do not have intermolecular hydrogen bonding, could
form a lamella arrangement in which the headgroups are aligned side by side. The effect due to the alkyl chain length on the
lamella structure is also presented.
Received: 21 January 2002 / Accepted: 22 March 2002 / Published online: 10 September 2002
RID="*"
ID="*"Corresponding author. Fax: +86-10/6255-7908 相似文献
3.
U. Diebold 《Applied Physics A: Materials Science & Processing》2003,76(5):681-687
Titanium oxides are used in a wide variety of technological applications where surface properties play a role. TiO2 surfaces, especially the (110) face of rutile, have become prototypical model systems in the surface science of metal oxides.
Reduced TiO2 single crystals are easy to work with experimentally, and their surfaces have been characterized with virtually all surface-science
techniques. Recently, TiO2 has also been used to refine computational ab initio approaches and to calculate properties of adsorption systems. Scanning
tunneling microscopy (STM) studies have shown that the surface structure of TiO2(110) is more complex than originally anticipated. The reduction state of the sample, i.e. the number and type of bulk defects,
as well as the surface treatment (annealing in vacuum vs. annealing in oxygen), can give rise to different structures, such
as two different (1×2) reconstructions, a ‘rosette’ overlayer, and crystallographic shear planes. Single point defects can
be identified with STM and influence the surface chemistry in a variety of ways; the adsorption of water is discussed as one
example. The growth of a large number of different metal overlayers has been studied on TiO2(110). Some of these studies have been instrumental in furthering the understanding of the ‘strong metal support interaction’
between group-VIII metals and TiO2, as well as low-temperature oxidation reactions on TiO2-supported nanoscopic gold clusters. The growth morphology, interfacial oxidation/reduction reaction, thermal stability, and
geometric structure of ultra-thin metal overlayers follow general trends where the most critical parameter is the reactivity
of the overlayer metal towards oxygen. It has been shown recently that the technologically more relevant TiO2 anatase phase can also be made accessible to surface investigations.
Received: 4 March 2002 / Accepted: 20 October 2002 / Published online: 5 February 2003
RID="*"
ID="*"Corresponding author. Fax: +1-504/862-8279, E-mail: diebold@tulane.edu 相似文献
4.
We investigated the surface properties of InAs(1 1 1)A by low-temperature scanning tunneling microscopy (LT-STM) with atomic resolution and first-principles calculation. Very clear atom image was observed, showing that the surface reconstruction is an In-vacancy structure. We also observed two kinds of adsorbates on the surface. The first-principles calculations indicate that the In-vacancy structure is the most stable surface reconstruction under any experimental conditions, which is consistent with the LT-STM observation. Investigations of adsorption properties of an In atom, an As atom, and an As2 molecule by the first-principles calculations imply that the observed adsorbates are an In atom and an As2 molecule. 相似文献
5.
Si(1 1 0) surfaces covered with small amounts of In deposit and then annealed at high temperature were investigated by RHEED, and two kinds of superstructures with A = 3a and B = −a + 4b, and A = 3a − 2b and B = −2a + 4b as primitive translational vectors are reported to form on the surfaces. 相似文献
6.
M. Danckwerts E. Savinova B. Pettinger K. Doblhofer 《Applied physics. B, Lasers and optics》2002,74(7-8):635-639
We combine in situ electrochemical second-harmonic generation (SHG) with voltammetry measurements using the hanging meniscus
configuration. This setup is used to investigate the interface between a Ag (111) electrode and an alkaline electrolyte. The
study offers a new in situ insight into the electrochemical processes at the Ag (111) electrode during OH adsorption and subsequent
oxidation. The behavior of SHG isotropic and anisotropic contributions as a function of potential is discussed and related
to the interfacial electric field. Comparison of the results with previous investigations of the Ag underpotential oxidation
in alkaline solutions shows that submonolayer oxidation is followed by bulk oxidation.
Received: 16 October 2001 / Revised version: 26 March 2002 / Published online: 6 June 2002 相似文献
7.
K. Jacobi L. Geelhaar J. Márquez 《Applied Physics A: Materials Science & Processing》2002,75(1):113-127
We present a brief overview of surface structures of high-index GaAs surfaces, putting emphasis on recent progress in our
own laboratory. By adapting a commercial scanning tunneling microscope (STM) to our molecular beam epitaxy and ultra high
vacuum analysis chamber system, we have been able to atomically resolve the GaAs(
)B (8 ×1), (114)Aα2(2×1), (137), (3 7 15), and (2 5 11) surface structures. In cooperation with P. Kratzer and M. Scheffler
from the Theory Department of the Fritz-Haber Institute we determined the structure of some of these surfaces by comparing
total-energy calculations and STM image simulations with the atomically resolved STM images. We present the results for the
{112}, {113}, and {114} surfaces. Then we describe what led us to proceed into the inner parts of the stereographic triangle
and to discover the hitherto unknown stable GaAs (2 5 11) surface.
Received: 16 May 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002 相似文献
8.
M. Zorn T. Trepk J.-T. Zettler B. Junno C. Meyne K. Knorr T. Wethkamp M. Klein M. Miller W. Richter L. Samuelson 《Applied Physics A: Materials Science & Processing》1997,65(3):333-339
Received: 14 July 1997/Accepted: 14 July 1997 相似文献
9.
We report the reaction dynamics of cobalt phthalocyanine (CoPc) molecules with Bi-line structures (BLSs) on a Si(1 0 0) surface, investigated using scanning tunneling microscopy (STM). When CoPc molecules were deposited on a Si(1 0 0) surface with BLSs at room temperature, single-spot protrusions were observed in the STM image instead of four-spot images corresponding to CoPcs flat molecular structure. Moreover, domains with a c(4 × 4) periodicity appeared on the terraces of the Si(1 0 0) surface. This indicates that CoPc molecules may have decomposed on the surface by catalytic reaction with Bi atoms. 相似文献
10.
H. Rauscher J. Braun R.J. Behm 《Applied Physics A: Materials Science & Processing》2003,76(5):711-719
We report the results of a study on ultrahigh-vacuum chemical vapor deposition of SixGe1-x layers on Si(111)(7×7) with GeH4 and Si2H6 mixtures. Using combined scanning tunneling microscopy and X-ray photoelectron spectroscopy, structural properties, the growth
kinetics and the composition of the deposited alloys are analyzed as a function of the growth temperature for two different
GeH4:Si2H6 mixture ratios. The mutual influence of the precursors is shown by comparing the structures formed during deposition and
the sticking coefficients of Si2H6 and GeH4 with results obtained from exposure of Si(111) to the pure gases.
Received: 28 July 2002 / Accepted: 2 October 2002 / Published online: 5 February 2003
RID="*"
ID="*"Corresponding author. Fax: +49-731/502-5452, E-mail: hubert.rauscher@chemie.uni-ulm.de 相似文献
11.
P. Zahl P. Kury M. Horn von Hoegen 《Applied Physics A: Materials Science & Processing》1999,69(5):481-488
Lattice-mismatch-induced surface or film stress has significant influence on the morphology of heteroepitaxial films. This
is demonstrated using Sb surfactant-mediated epitaxy of Ge on Si(111). The surfactant forces a two-dimensional growth of a
continous Ge film instead of islanding. Two qualitatively different growth regimes are observed. Elastic relaxation: Prior to the generation of strain-relieving defects the Ge film grows pseudomorphically with the Si lattice constant and
is under strong compressive stress. The Ge film relieves strain by forming a rough surface on a nm scale which allows partial
elastic relaxation towards the Ge bulk lattice constant. The unfavorable increase of surface area is outbalanced by the large
decrease of strain energy. The change of film stress and surface morphology is monitored in situ during deposition at elevated
temperature with surface stress-induced optical deflection and high-resolution spot profile analysis low-energy electron diffraction.
Plastic relaxation: After a critical thickness the generation of dislocations is initiated. The rough phase acts as a nucleation center for
dislocations. On Si(111) those misfit dislocations are arranged in a threefold quasi periodic array at the interface that
accommodate exactly the different lattice constants of Ge and Si.
Received: 1 April 1999 / Accepted: 17 August 1999 / Published online: 6 October 1999 相似文献
12.
G. Çelik Ş. Ateş 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):433-437
In this contribution we present scanning tunnelling microscopy (STM) and spectroscopy (STS) investigations on isolated cobalt
clusters in contact with Ge(001). Mass-filtered nanoparticles with diameters ranging from 3 to 11 nm are generated using an
arc cluster ion source (ACIS) and deposited under soft landing conditions (Ekin/atom < 0.5 eV). Since the tip radius is of the same order as the nanoparticle diameters the recorded STM images are significantly
affected by tip folding.
By means of the “blind reconstruction method" it is possible to approximate the tip shape. After a respective deconvolution
of the image structural features of the particle facets become observable. According to the equilibrium shape of the clusters
being a truncated octahedron in the size range under investigation, hexagonal and rectangular features appear in the images.
STS is sensitive to occupied and unoccupied states near the Fermi level and reveals the existence of distinct states in the
tunnelling conductivity of the substrate as well as on the clusters. The richly structured density of states of the germanium
surface serves here as tip condition test. First measurements of the tunnelling conductivity of the CoN/Ge(001) are presented and discussed. 相似文献
13.
S. Myhra 《Applied Physics A: Materials Science & Processing》2003,76(1):63-69
Three mechanisms for spatially resolved growth and removal of oxide on silicon substrates have been investigated. Thermally
grown oxide layers with thicknesses in the range 2–6 nm were the distinctive feature of the system. The layers were characterized
and manipulated by methodologies based on atomic force microscopy (AFM) with conducting probes in a vacuum environment of
10-2–10-3 Pa. The probe is then effectively a travelling electrode that generates an electrostatic field between the tip and the substrate.
Oxide growth was induced for a positive sample bias greater than 5 V, but below the level corresponding to dielectric breakdown.
Application of a short pulse of amplitude marginally above that corresponding to dielectric breakdown, on the other hand,
had the effect of producing pits of inner diameter of about 10 nm in the pre-existing oxide layer at the point of tip-to-oxide
contact. Application of a low positive sample bias (less than that required for measurable oxide growth) in combination with
high linear scan speed had the effect of removing a pre-existing oxide layer from the scanned field of view. The most plausible
mechanisms are based on transverse ionic diffusion (for oxide growth), controlled dielectric breakdown (for formation of pits)
and lateral transport of silicaceous species (for oxide removal).
Received: 24 October 2001 / Accepted: 6 January 2002 / Published online: 3 June 2002
RID="*"
ID="*"Corresponding author. Fax: +617-3875-7656, E-mail: s.myhra@sct.gu.edu.au 相似文献
14.
Water molecule adsorption properties at the surface of InVO4 have been investigated using an ab initio molecular dynamics approach. It was found that the water molecules were adsorbed dissociatively to the three-fold oxygen coordinated V sites on the (0 0 1) surface. The dissociative adsorption energy was estimated to be 0.8-0.9 eV per molecule. The equilibrium distance between V and O of the hydroxyl -OH was almost the same as the V-O distance of tetrahedra VO4 in the InVO4 bulk crystal (1.7-1.8 Å). 相似文献
15.
T.I. Kamins K. Nauka R.S. Williams 《Applied Physics A: Materials Science & Processing》2001,73(1):1-9
Incorporating self-assembled Ge islands on Si surfaces into electronic devices has been suggested as a means of forming small
features without fine-scale litho-
graphy. For use in electronic devices, the electrical properties of the deposited Ge and their relation to the underlying
Si substrate must be known. This report presents the results of a surface photovoltage investigation of the surface energy
barrier as increasing amounts of Ge are added to a Si surface by chemical vapor deposition. The results are interpreted in
terms of band discontinuities and surface states. The surface barrier increases as a wetting layer is deposited and continues
to increase as defect-free islands form. It saturates as the islands grow. As the amount of Ge continues increasing, defects
form, and the surface barrier decreases because of the resulting allowed states at the Ge/Si interface. Qualitatively similar
behavior is found for Si(001) and Si(111). Covering the Ge with Si reduces the surface-state density and possibly modifies
the wetting layer, decreasing the barrier to one more characteristic of Si. Initial hydrogen termination of the surface decreases
the active surface-state density. As the H desorbs, the surface barrier increases until it stabilizes as the surface oxidizes.
The behavior is briefly correlated with scanning-tunneling spectroscopy data.
Received: 13 November 2000 / Accepted: 14 November 2000 / Published online: 23 May 2001 相似文献
16.
In classic carbon supports is very difficult to control pore size, pore size distribution, and surface chemical properties at the same time. In this work microporous carbons derived from furfuryl alcohol are used as support to prepare Ni-doped carbon materials. The N2 flow rate used during the carbonisation process of the precursor influences on the size of the nanospheres obtained but not in their textural properties. Microporous carbon nanospheres have been synthesised with a narrow pore size distribution centred in 5.5 Å. The surface chemistry of these materials can be easily modified by different treatments without detriment of the pore structure of the doped carbon nanospheres. 相似文献
17.
Structure, catalysis and atomic reactions on the nano-scale: a systematic approach to metal hydrides for hydrogen storage 总被引:10,自引:0,他引:10
A. Zaluska L. Zaluski J.O. Ström-Olsen 《Applied Physics A: Materials Science & Processing》2001,72(2):157-165
We show how reducing structure, catalysis and atomic reactions to the nano-scale may be used in a systematic way to substantially
enhance the hydrogenation properties of metal hydrides. We examine, with examples from a wide range of hydrides, the direct
impact of nano-scale structure, subsequent improvements in kinetics through nano-scale solid state catalysis, the special
properties of nano-composites, and the role played by nano-scale reactions.
Received: 25 August 2000 / Accepted: 14 November 2000 / Published online: 9 February 2001 相似文献
18.
J. Hayoz M. Bovet T. Pillo L. Schlapbach P. Aebi 《Applied Physics A: Materials Science & Processing》2000,71(6):615-618
We demonstrate a very simple and reliable method of manufacturing clean, single-crystalline Y2O3 films on Nb(110) substrates in situ. The method exploits the oxygen bulk contamination of Nb as a source of clean oxygen.
For substrate temperatures above 800 K oxygen segregation to the Nb surface is so efficient, that yttrium becomes oxidized
during deposition without any background oxygen pressure required in the ultrahigh vacuum system. The crystallinity and stoichiometry
of these films can be tuned by the deposition temperature. For Y deposition at 1300 K the formation of well-ordered (111)-oriented
Y2O3 films is achieved.
Received: 19 April 2000 / Accepted: 20 April 2000 / Published online: 23 August 2000 相似文献
19.
L. Palacio P. Prádanos A. Hernández M.J. Ariza J. Benavente M. Nyström 《Applied Physics A: Materials Science & Processing》2001,73(5):555-560
The surfaces of three commercial urea formaldehyde polysulfone membranes from Dow DenmarkTM (GR51, GR61 and GR81) are characterised both topographically and chemically. Their topography is studied by scanning force
microscopy to obtain the corresponding pore-size distributions, which are in fair agreement with nominal molecular weight
cut-offs.
The composition of the surfaces of the membranes is analysed by X-ray photoelectron spectroscopy. The resulting percentage
content of nitrogen, which could be attributed probably to an additive used in the manufacturing process, is shown to correlate
with the portion of the total surface with different viscoelastic properties as investigated by using phase-contrast scanning
force microscopy. Both parameters are increasing for membranes with decreasing molecular weight cut-off. Also, the additive
seems to be more sparsely distributed for the membranes with bigger pores, according to fractal analysis. Finally, all the
membranes are very similarly wettable.
Received: 22 May 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001 相似文献
20.
U. Starke J. Schardt M. Franke 《Applied Physics A: Materials Science & Processing》1997,65(6):587-596
Received: 21 March 1997 相似文献