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1.
We have investigated the adsorption of Ba on the Si(111) surface at elevated temperatures by using high-resolution electron-energy-loss
spectroscopy, low-energy-electron diffraction, and photoelectron spectroscopy with synchrotron photons. We found two new ordered
phases 2×1a and 2×1bwith increasing Ba coverage in addition to other ordered phases reported earlier. All the ordered surfaces
were found to remain semiconducting with a hybridization band gap of ∼1.1 eV almost independent of Ba coverage. We discuss
evidence for the evolution of a Ba s-s hybridization band for Ba coverage beyond 0.5 monolayers and propose structural models
for the three ordered phases, which are quite consistent with our experimental data.
Received: 16 May 2000 / Accepted: 17 May 2000 / Published online: 16 August 2000 相似文献
2.
M. Servidori F. Cembali S. Milita 《Applied Physics A: Materials Science & Processing》2001,73(1):83-90
The dimensional features of multi-crystal synchrotron X-ray topographs are explained by 3D DuMond diagrams for a flat double-crystal
monochromator and a curved sample. Symmetric Bragg-case reflections are assumed for all crystals. σ–σ and σ–π geometries are
considered, where the diffraction plane of the sample is parallel and perpendicular, respectively, to the vertical diffraction
plane of the monochromator (σ polarization). It is shown that the shape of the sample image is closely connected to the shape
of the volume shared by the diffraction domains of monochromator and sample in the 3D DuMond diagram. In particular, for the
σ–π set-up, the image shape depends on the curvature value and sign. An experiment is reported for this latter crystal geometry
to determine lattice mismatch, its lateral homogeneity and curvature value and sign in a sample made of epilayer and substrate.
Received: 31 July 2000 / Accepted: 25 January 2001 / Published online: 26 April 2001 相似文献
3.
M. Servidori F. Cembali S. Milita 《Applied Physics A: Materials Science & Processing》2001,73(1):75-82
The 3D representation of the DuMond diagram is used to explain the dimensional features of X-ray topographs obtained by multi-crystal
configuration with a synchrotron beam. Symmetric Bragg-case reflections are considered for a flat double-crystal monochromator
and a flat sample. Two ways of sample alignment are taken into account. They are referred to as σ–σ and σ–π geometries, where
the diffraction plane of the sample is parallel and perpendicular, respectively, to the vertical diffraction plane of the
monochromator (σ polarization). It is shown that the shape of the sample image is closely connected to the shape the diffraction
domain common to monochromator and sample assumes in the 3D DuMond diagram. An experiment is reported for the less commonly
used σ–π topography, showing how the lattice mismatch and its lateral homogeneity are determined in samples made by epilayer
and substrate.
Received: 31 July 2000 / Accepted: 25 January 2001 / Published online: 3 May 2001 相似文献
4.
The feasibility of liquid-phase velocity measurements in dense sprays by 2D laser-based flow tagging is demonstrated. Velocity
measurements in dense sprays are difficult with conventional techniques because of the high number densities of droplets,
the optical thickness of the medium, and multiple light-scattering effects. The present flow-tagging technique is based on
phosphorescent tracer molecules, which are excited by a grid of pulsed ‘write’ laser beams. The motion of the tagged droplet
groups can be observed by a CCD camera in this way. In addition, multiple consecutive velocity measurements are performed
by ‘droplet-group tracking’. This yields the acceleration along the trajectory of individual groups of droplets in unsteady
sprays.
Received: 5 June 2000 / Revised version: 28 July 2000 / Published online: 6 September 2000 相似文献
5.
Structural and optical properties of nanophase zinc oxide 总被引:7,自引:0,他引:7
Y. Du M.-S. Zhang J. Hong Y. Shen Q. Chen Z. Yin 《Applied Physics A: Materials Science & Processing》2003,76(2):171-176
Nanophase zinc oxide samples were synthesized by a two-step solid-state reaction method. The phase structure and microstructure
were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The vibrational Raman spectra were
compared with those from the bulk and their grain size dependence was also examined. Their photoelectric behavior was studied
by X-ray photoelectron spectroscopy (XPS). The peaks at 1044.5 and 1021.4 eV were recorded as corresponding to the respective
binding energies of Zn 2p1/2 and Zn 2p3/2, and the photoelectron spectrum of O 1s in the as-prepared powder was located at 531.2 eV. A strong visible emission centered
at 580 nm was clearly observed in the nanosized zinc oxide at room temperature. Photoluminescence (PL) spectra were investigated
as a function of grain size after different heat treatments. The origin of the luminescence is attributed to the recombination
of electrons in singly occupied oxygen vacancies with photoexcited holes in the valence band.
Received: 30 June 2001 / Accepted: 20 February 2002 / Published online: 3 June 2002
RID="*"
ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: mszhang@nju.edu.cn 相似文献
6.
Titanium-containing amorphous hydrogenated silicon–carbon films (aSi1-xCx:H/Ti) have been deposited by reactive magnetron cosputtering. Core-level photoelectron spectroscopy (XPS) and valence-band
photoelectron spectroscopy (UPS) have served as means for the characterization of these films. The spectroscopic data are
interpreted by a structural model on the basis of a nanocomposite containing clusters of a Ti-C-Si alloy being embedded in
an amorphous hydrogenated silicon–carbon matrix (aSi1-xCx:H). The Ti-C-Si compound is of metallic character and most likely a substitutional solid solution. This novel nanocomposite
material is a promising candidate for applications, especially as optical selective absorber coating for solar collectors.
Received: 10 July 2000 / Accepted: 15 September 2000 / Published online: 21 March 2001 相似文献
7.
D. P. Woodruff 《Applied Physics A: Materials Science & Processing》2008,92(3):439-445
The potential of photoelectron diffraction—exploiting the coherent interference of directly-emitted and elastically scattered
components of the photoelectron wavefield emitted from a core level of a surface atom to obtain structural information—was
first appreciated in the 1970s. The first demonstrations of the effect were published towards the end of that decade, but
the method has now entered the mainstream armoury of surface structure determination. This short review has two objectives:
First, to outline the way that the idea emerged and the way this evolved in my own collaboration with Neville Smith and his
colleagues at Bell Labs in the early years: Second, to provide some insight into the current state-of-the art in application
of (scanned-energy mode) photoelectron diffraction to address two key issue in quantitative surface structure determination,
namely, complexity and precision. In this regard a particularly powerful aspect of photoelectron diffraction is its elemental
and chemical-state specificity. 相似文献
8.
H. Hövel 《Applied Physics A: Materials Science & Processing》2001,72(3):295-302
With controlled growth in nanometer-sized pits we produced silver and gold clusters on a graphite surface. We give a summary
of the preparation method and discuss the scanning tunneling imaging and the crystalline orientation of the clusters. The
electronic structure of the clusters was studied by an in-situ combination of ultraviolet photoelectron spectroscopy (UPS)
and scanning tunneling spectroscopy (STS). For both techniques we obtained an energy resolution in the range of 10 meV employing
low sample temperatures. Dynamic final-state effects together with averaging over a cluster-size distribution result in characteristic
spectral shapes in UPS, which can be understood referring to STS data taken on individual clusters. Finally, directions for
future experiments are pointed out.
Received: 13 April 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001 相似文献
9.
D. Kreikemeyer Lorenzo M.K. Bradley W. Unterberger D.A. Duncan T.J. Lerotholi J. Robinson D.P. Woodruff 《Surface science》2011,605(1-2):193-205
The local structure of the methoxy species on Cu(110) has been investigated experimentally using chemical-state specific O 1s scanned-energy mode photoelectron diffraction (PhD), and also by density functional theory (DFT) calculations. The PhD data show a clear preference for adsorption with the O bonding atoms in short-bridge sites, though the best fit of multiple-scattering simulations to the experimental data is achieved with two slightly different short-bridge geometries. The DFT calculations also show that not only are the short-bridge sites energetically favoured in isolation, but that coordination to pairs of Cu adatoms has a similar energy. A structure consistent with both the PhD data and the DFT calculations is proposed for the previously-observed (5 × 2)pg ordered phase, based on methoxy species in short-bridge sites on pairs of Cu adatoms and on the underlying surface. Simulated scanning tunnelling microscopy images agree well with those observed experimentally, while the model is also shown to be consistent with the qualitative behaviour seen in early X-ray photoelectron diffraction (XPD) forward-scattering experiments. 相似文献
10.
We report on metal (Cr, Ni, or Pd)-induced solid-phase crystallization (MISPC) of plasma-enhanced chemical-vapor-deposited
hydrogenated amorphous silicon at annealing temperatures ≤600 °C. MISPC is found to significantly reduce the thermal budget
of crystallization at annealing temperatures as low as ∼400 °C. The lowest achievable annealing temperature is found to depend
on the metal type. The metal type is also found to influence grain size and the conductivity of the polycrystalline silicon.
Received: 21 June 1999 / Accepted: 20 October 1999 / Published online: 23 February 2000 相似文献
11.
Latha Kumari S. V. Subramanyam 《Applied Physics A: Materials Science & Processing》2009,95(2):343-349
Amorphous carbon–sulfur (a-C:S) composite films were prepared by vapor phase pyrolysis technique. The structural changes in
the a-C:S films were investigated by electron microscopy. A powder X-ray diffraction (XRD) study depicts the two-phase nature
of a sulfur-incorporated a-C system. The optical bandgap energy shows a decreasing trend with an increase in the sulfur content
and preparation temperature. This infers a sulfur incorporation and pyrolysis temperature induced reduction in structural
disorder or increase in sp
2 or π-sites. The presence of sulfur (S 2p) in the a-C:S sample is analyzed by the X-ray photoelectron spectroscopy (XPS). The sp
3/sp
2 hybridization ratio is determined by using the XPS C 1s peak fitting, and the results confirm an increase in sp
2 hybrids with sulfur addition to a-C. The electrical resistivity variation in the films depends on both the sulfur concentration
and the pyrolysis temperature. 相似文献
12.
C. Westphal 《Applied Physics A: Materials Science & Processing》2003,76(5):721-730
Angle- and energy-scanned photoelectron diffraction data can be used to investigate structures below surfaces. The modulations
in photoelectron intensity result from diffraction of the emitted electron wave at neighbor atoms. In the past, scanned-energy
photoelectron diffraction had been mainly used to determine the adsorption site of molecules at surfaces. Recent data show,
however, that the technique can also be employed to obtain information about the upper substrate layer(s). At low kinetic
energies, backward scattering is strong and in scanned-angle photoelectron diffraction the recorded patterns result from backward-
and multiple-scattering effects. For a structural analysis, the intensity modulations have to be compared with the results
for simulations performed for model clusters. As an example, recent angle-scanned photoelectron diffraction patterns recorded
for the technologically important silicon oxide/silicon interface were compared with simulations. At the Si(001) surface orientation,
the interface is extended over a few layers, whereas at the Si(111) surface orientation the transition is rather abrupt and
occurs within one or two layers.
Received: 9 September 2002 / Accepted: 2 October 2002 / Published online: 5 February 2003
RID="*"
ID="*"Corresponding author. Fax: +49-231/755-3657, E-mail: carsten.westphal@physik.uni-dortmund.de 相似文献
13.
Molar volumes, V, and compactness values, α, of 34 glassy compositions of the GeSeFe system have been obtained using their
measured densities. The property–composition dependences are examined in light of the models proposed for the structure of
these network glasses.
Received: 28 August 2000 / Accepted: 9 January 2001 / Published online: 23 March 2001 相似文献
14.
K. Wong V. Kasperovich G. Tikhonov V.V. Kresin 《Applied physics. B, Lasers and optics》2001,73(4):407-410
We produced free beams of cold nanometer-sized particles of lithium, sodium and potassium and measured the three corresponding
photo-ionization yield curves. Quadratic (Fowler) plots, originally developed for bulk surfaces, were found to provide a good
fit to the threshold shape and were used to obtain the particle ionization potentials. The latter match precisely the bulk
work functions cited in the literature, suggesting that photo-ionization of free nanoclusters may form a useful complement
to traditional photoelectron studies of surfaces. Within 0.25–1 eV above the threshold, the ionization efficiency begins to
drop. This effect, which has parallels in bulk-surface and small-cluster photoemission, is presently not well understood but
may be related to an interplay between electron emission and collective surface plasma excitations.
Received: 21 June 2001 / Revised version: 7 July 2001 / Published online: 10 October 2001 相似文献
15.
D. Di Castro G. Bianconi M. Colapietro A. Pifferi N.L. Saini S. Agrestini A. Bianconi 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):617-624
We report experimental evidence for the phase diagram of doped cuprate superconductors as a function of the micro-strain of the planar Cu-O bond length, measured by Cu K-edge EXAFS, and hole doping . The local lattice distortions are measured by EXAFS and the charge ordering is measured by synchrotron radiation diffuse
X-ray diffraction. This phase diagram shows a QCP at P() where for charge-orbital-spin stripes and free carriers co-exist. The superconducting phase occurs in the region of critical fluctuations
around this QCP. The function of two variables shows its maximum at the strain QCP. The critical fluctuations near this strain QCP give the self-organization
of a metallic superlattice of quantum wires “superstripes" that favors the amplification of the critical temperature.
Received 25 September 2000 相似文献
16.
J. Rams N.V. Sochinskii V. Munõz J.M. Cabrera 《Applied Physics A: Materials Science & Processing》2000,71(3):277-279
CdTe epilayers have been grown by vapor phase epitaxy (VPE) on glass, MgO, sapphire, LiNbO3 and mica substrates. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies show the good structural quality
of the epilayers. In these epilayers, a few optical modes were excited with a 1.33-μm laser. The measured propagation losses
were in the range between 5 dB/cm and less than 0.5 dB/cm. From dark-mode m-lines, the epilayer thickness was found to be
in the 1–3 μm range, in good accord with that obtained by SEM measurements. The refractive index obtained from the fitting
is also in good accord with that of bulk CdTe.
Received: 7 October 1999 / Accepted: 13 March 2000 / Published online: 5 July 2000 相似文献
17.
The interplay of diffraction dissociation and nuclear shakeoff is considered in a schematic but still realistic model for
the case of the break-up of halo nuclei on light targets. We demonstrate that the shakeoff effect, arising from the momentum
imparted by the core diffraction, is small but still identifiable in the experimental data for the dissociation of the one-
and two-neutron halo nuclei 11Be and 11Li.
Received: 29 October 1999 / Revised version: 15 January 2000 相似文献
18.
P. Pawłowski B. Borderie G. Auger Ch.O. Bacri N. Bellaize F. Bocage R. Bougault R. Brou P. Buchet J.L. Charvet A. Chbihi J. Colin D. Cussol R. Dayras A. Demeyer D. Doré D. Durand J.D. Frankland E. Galichet E. Genouin-Duhamel E. Gerlic D. Guinet P. Lautesse J.L. Laville J.F. Lecolley R. Legrain N. Le Neindre O. Lopez M. Louvel A.M. Maskay L. Nalpas A.D. Nguyen M. Pârlog J. Péter E. Plagnol M.F. Rivet E. Rosato F. Saint-Laurent S. Salou J.C. Steckmeyer M. Stern G. Tăbăcaru B. Tamain L. Tassan-Got O. Tirel E. Vient C. Volant J.P. Wieleczko 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):371-383
The prompt component at intermediate velocity of light charged particles is investigated. An improved coalescence model coupled
to the intra-nuclear cascade code ISABEL is used to obtain light complex particle energy spectra and multiplicities as a function
of impact parameter. The results are compared with experimental data from the 36Ar + 58Ni experiment at 95 MeV/nucleon, performed with the INDRA 4π detection system. The calculated prompt component is found to
rather well reproduce proton spectra. For complex light charged particles the calculated components well populate the high
energy part of spectra. Prompt emission can therefore explain the large transverse energies experimentally observed at mid-rapidity.
Received: 27 July 2000 / Accepted: 20 November 2000 相似文献
19.
M.J. Weida S. Ogawa H. Nagano H. Petek 《Applied Physics A: Materials Science & Processing》2000,71(5):553-559
Hot electron (E-EFermi=0.75 to 1.55 eV) lifetimes for cesiated Cu(100) and Cu(111) surfaces are measured via interferometric time-resolved two-photon
photoemission with a 19-fs intensity FWHM mode locked Ti:sapphire laser at 1.55 eV. The data are analyzed using the optical
Bloch equations and a laser pulse characterized in situ via surface second-harmonic generation interferometric autocorrelation.
It is found that the retrieved hot-electron lifetimes are unphysically fast, and have a strong dependence on the temperature
of the sample and the polarization of the laser. A simple explanation for the data is that the measured signal consists of
contributions from transitions through both virtual and real intermediate states.
Received: 26 July 2000 / Accepted: 8 September 2000 / Published online: 12 October 2000 相似文献
20.
In2(Se1-xTex)3 polycrystalline films were prepared by a dual-source thermal evaporation technique. The depositions onto glass and SnO2-coated glass substrates were carried out in a vacuum chamber and followed by an annealing in neutral ambient (Ar or N2). The structural, morphological and compositional studies of the films were made by X-ray diffraction, energy-dispersive
X-ray analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, Raman scattering and optical transmission.
Optimum conditions are investigated for the formation of the ternary compound In2(Se1-xTex)3 in order to tune the band gap by changing the Te concentration. The film properties as a function of Te amount are discussed.
It is shown that single-phase, textured and homogeneous layers of In2(Se1-xTex)3 can be grown with x≤0.2 at optimal deposition and heat treatment conditions. For x≅0.17 these films showed an energy band
gap of about 1.45 eV and an electrical conductivity at room temperature six orders of magnitude higher than that of the binary
γ-In2Se3 thin films.
Received: 9 July 1999 / Accepted: 25 November 1999 / Published online: 13 July 2000 相似文献