共查询到20条相似文献,搜索用时 421 毫秒
1.
S. M. Soloviev N. D. Potekhina C. Pettenkofer I. I. Pronin 《Physics of the Solid State》2013,55(7):1510-1518
Subthreshold photoelectron emission was observed to emerge from palladium nanoclusters formed on pyrographite surface under irradiation by photons in the energy range 3.1–6.5 eV. The average size of the palladium nanoclusters on the pyrographite surface was 50–80 nm, and the average height, 2–4 nm. Besides conventional photoemission from states below the Fermi level, photoelectron emission was observed at the energies of photons irradiating the surface 0.9 eV below the work function of the Pd surface. It is assumed that this emission is stimulated by direct electron transitions from Pd states below the Fermi level to the unfilled electron surface states formed in the Coulomb potential of image forces (image states) and, subsequently, into vacuum. This phenomenon is assumed to originate from the contact spot field generated above the surface which is nonuniform in work function. This assumption is supported by the calculations presented in the paper. 相似文献
2.
The distortions of the optically stimulated electron emission (OSEE) spectra resulting from the exponential decay in the recording
time have been analyzed. It has been shown that taking account of the emission current nonstationary in analyzing the emission
spectra permits obtaining isochronal temperature dependences of intensity for selective OSEE bands. The procedure for calculating
the quantum yield of the OSEE and the activation barriers of thermal ionization of the excited states of defects is described.
Analysis of the photoemission kinetics permits estimating the concentration of active OSEE centers with unknown parameters
(optical transition oscillator strength, quantum yield). For diamagnetic oxygen-deficient centers in glassy SiO2, the photoemission kinetics has been calculated and the thermal ionization barrier of the photoexcited singlet state and
the quantum yield of the OSEE have been determined.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 615–621, September–October, 2005. 相似文献
3.
A. Rizzi M. Kocan J. Malindretos A. Schildknecht N. Teofilov K. Thonke R. Sauer 《Applied Physics A: Materials Science & Processing》2007,87(3):505-509
AlGaN layers with Al content varying over the whole range of compositions were grown by molecular beam epitaxy (MBE) on n-6H-SiC
substrates. The band gap energy is obtained from the vanishing of Fabry–Pérot oscillations in a fit to optical reflection
spectra near the band gap absorption edge. The surface potential was determined by in-situ X-ray photoemission spectroscopy
(XPS) and is found to increase as a function of the Al content from (0.5±0.1) eV to (1.3±0.1) eV, from GaN to AlN. A Si3N4 thin passivation layer was formed in-situ onto a 2DEG AlGaN/GaN structure. The mechanism underlying the passivation of high
electron mobility transistor (HEMT) structures is suggested to be based on the formation of interface states, which keep the
Fermi level fixed at a position close to that of the free AlGaN surface.
PACS 73.20.-r; 73.40.-c; 73.40.Kp 相似文献
4.
Hot electron dynamics was investigated, with a focus on scattering between bulk states and the C1 surface state that is formed on the (2×4)-reconstructed In-rich surface of InP(100). The latter surface was prepared via metal organic chemical vapor deposition (MOCVD) and monitored by reflectance anisotropy spectroscopy (RAS/RDS). Two-color twophoton photoemission (2PPE) was employed with laser pulses of about 50 fs duration. Hot electrons were generated in bulk states about 0.5 eV above the C1 surface state, thereby avoiding any significant direct optical population of the surface state. A time constant of 35 fs was determined from the experimental data for electron scattering from isoenergetic bulk states to the C1 surface state by analyzing the rise of a C1-specific peak in the 2PPE spectrum. The decay of this C1 peak was ascribed to energy relaxation of the photo-generated electrons to bulk states below the surface state. Analogous measurements were carried out with a (2×1/2×2)-reconstructed P-rich surface of InP(100) that was also grown via MOCVD. No sign of a surface statewas detected in the 2PPE spectra for the latter surface in the corresponding energy range of the conduction band. PACS 73.20.-r; 78.47.+p; 79.60.-i; 79.60.Bm 相似文献
5.
Ali Safaei 《Journal of nanoparticle research》2010,12(3):759-776
The size dependency of the cohesive energy of nanocrystals is obtained in terms of their averaged structural and energetic
properties, which are in direct proportion with their cohesive energies. The significance of the effect of the geometrical
shape of nanoparticles on their thermal stability has been discussed. The model has been found to have good prediction for
the case of Cu and Al nanoparticles, with sizes in the ranges of 1–22 nm and 2–22 nm, respectively. Defining a new parameter,
named as the surface-to-volume energy-contribution ratio, the relative thermal stabilities of different nanoclusters and their
different surface-crystalline faces are discussed and compared to the molecular dynamic (MD) simulation results of copper
nanoclusters. Finally, based on the size dependency of the cohesive energy, a formula for the size-dependent diffusion coefficient
has been presented which includes the structural and energetic effects. Using this formula, the faster-than-expected interdiffusion/alloying
of Au(core)–Ag(shell) nanoparticles with the core–shell structure, the Au-core diameter of 20 nm and the Ag-shell thickness of 2.91 nm, has been
discussed and the calculated diffusion coefficient has been found to be consistent with its corresponding experimental value. 相似文献
6.
We have studied the effect of channel formation in an Ni/n-Si/V2O5−B2O3−CaO surface barrier structure on the capacitance-voltage characteristics, the dependence of the small-signal photovoltage
on the state of the surface and the modulation frequency of the test signal, and the planar distribution of the photovoltage
and the noise properties for the high-resistance and low-resistance states of the formed channel. It has been established
that forming of the dielectric causes the appearance of regions of thermal-field recombination of the charge carriers, burst
noise, strengthened heterogeneity of the photoelectric properties, and the appearance of two peaks in the density of surface
states from silicon divacancies at the interphase boundary. It is proposed that an important role in the creation of the properties
of the electrically formed structures is played by shock waves which propagate from the forming channel, the additional lattice
defects formed during dissipation, and the phase state of the crystallites in the channel.
Tomsk State University. Systems for Control and Radio Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii,
Fizika, No. 5, pp. 85–91, May, 1997. 相似文献
7.
Investigation of the state of the electrochemically generated adsorbed O species on Au films interfaced with Y2O3-doped-ZrO2 总被引:1,自引:0,他引:1
Adsorbed O species on Au interfaced with Y2O3-doped-ZrO2 are generated by electrochemical O2− supply. It was found that two oxygen chemisorbed states are formed, which desorb at 420 °C (state α) and 550 °C (state β)
with activation energies of desorption ranging between 115–145 kJ/mol and 235–270 kJ/mol, respectively. The strong interaction
of the β-state O species with the Au surface causes an over 600 mV increase in Au surface potential and work function while
the α-state O species is formed at even more positive catalyst-electrode potential. State α is attributed to normally adsorbed
atomic O while the more ionic state β is only created electro-chemically and is mainly responsible for the work function increase
of the Au catalyst-electrode surface. Their desorption activation energies of both states decrease linearly with increasing
catalyst-electrode potential with slopes of the order of four.
Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000. 相似文献
8.
Ceria supported copper catalysts were synthesized by laser vaporization and controlled condensation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX) and temperature programmed reduction (TPR). The catalytic activity of the nanopowders for CO oxidation reaction was tested in a fixed bed flow tube reactor in Ar–20%O2–4%CO mixture. Irrespective of the copper content, the catalytic activity of the nanopowders is similar in the initial CO test, and the catalytic activity improves (i.e. the light-off temperature decreases) during a subsequent run. The lowest light-off temperature during the second run is recorded in the material with 20% copper. TEM studies on 20%Cu–CeO2 sample in the as-prepared condition and after CO test exhibit two types of ceria particles namely, polygonal particles 3–5 nm in size and spherical particles of 15–20 nm in size. Rapid cooling of the nanoparticles formed during the laser ablation results in incorporation of a large amount of copper within the ceria as solid solution. Presence of solid solution of copper is confirmed by EDAX and electron diffraction analyses. In addition, copper-rich surface layer of Cu2O is found over the spherical particles. The cerium oxide components are essentially identical before and after CO test, except that the polygonal CeO2 particles contain newly formed fine crystals of CuO. TPR results reveal two reduction peaks, which further supports, the presence of two different copper species in the material. The shift in light-off temperature during the second run is attributed to the synergistic interaction between newly formed CuO crystals with the CeO2 matrix. 相似文献
9.
We describe an interferometric time-resolved photoemission technique that makes it possible to simultaneously observe the decay of optical induced polarizations and populations at surfaces in a two-color excitation scheme. In this scheme initially unoccupied electronic surface states are coherently excited by the interaction of laser pulses with frequency ωa and the two-photon polarization which is induced by laser pulses with frequency ωa/2. Interference is observed by changing the delay between both laser pulses using an actively stabilized two-color Mach–Zehnder interferometer. We demonstrate this technique for excitation of the n=1 image-potential state on a Cu(100) surface. PACS 78.47.+p; 79.60.Bm; 73.20.-r; 82.53.Kp; 42.50.Md 相似文献
10.
11.
The dependence of the intrinsic line width Γ of electron and hole states due to inelastic scattering on the wave vector k
∥ in the occupied surface state and the first image potential state on the Cu(111) and Ag(111) surfaces has been calculated
using the GW approximation, which simulates the self-energy of the quasiparticles by the product of the Greens’s function
and the dynamically screened Coulomb potential. Different contributions to the relaxation of electron and hole excitations
have been analyzed. It has been demonstrated that, for both surfaces, the main channel of relaxation of holes in the occupied
surface states is intraband scattering and that, for electrons in the image potential states, the interband transitions play
a decisive role. A sharp decrease in the intrinsic line width of the hole state with an increase in k
∥ is caused by a decrease in the number of final states, whereas an increase in Γ of the image potential state is predominantly
determined by an increase of its overlap with bulk states. 相似文献
12.
The results of the theoretical investigation of the surface electronic structure of A2VB3VI compounds containing topologically protected surface states are reported. The ideal Bi2Te3, Bi2Se3, and Sb2Te3 surfaces and surfaces with an absent external layer of chalcogen atoms, which were observed experimentally as monolayer terraces,
have been considered. It has been shown that the discrepancy between the calculated Fermi level and the value measured in
the photoemission experiments can be attributed to the presence of the “dangling bond” states on the surface of the terraces
formed by semimetal atoms. The fraction of such terraces on the surface has been estimated. 相似文献
13.
A study of the geometric characteristics of copper nanoclusters incorporated in an amorphous hydrogenated carbon matrix is
reported. It makes use of small-angle x-ray scattering and transmission electron microscopy (100 keV). The fractal dimension
and nanocluster diameter have been determined from the x-ray scattering indicatrix for different copper concentrations. TEM
images of copper nanoclusters have been analyzed, and a cluster distribution function in size constructed. The shape of the
distribution function is discussed in terms of the theory of nucleation of a new phase.
Fiz. Tverd. Tela (St. Petersburg) 40, 568–572 (March 1998) 相似文献
14.
We demonstrate n-type doping of pentacene with the powerful reducing molecule decamethylcobaltocene (CoCp2*). Characterization of pentacene films deposited in a background pressure of CoCp2* by X-ray photoemission spectroscopy and Rutherford backscattering confirm that the concentration of incorporated donor molecules
can be controlled to a level as high as 1%. Ultraviolet photoemission spectroscopy show Fermi level (E
F) shifts toward unoccupied pentacene states, indicative of an increase in the electron concentration. A 1% donor incorporation
level brings E
F to 0.6 eV below the pentacene lowest unoccupied molecular orbital. The corresponding electron density of ∼1018 cm−3 is confirmed by capacitance–voltage measurements on a metal–pentacene–oxide–silicon structure. The demonstration of n-doping
suggests applications of CoCp2* to pentacene contacts or channel regions of pentacene OTFTs. 相似文献
15.
Martin Månsson Oscar Tjernberg Tomas Claesson Henrik S. Karlsson Ulf O. Karlsson 《Applied Surface Science》2006,252(15):5308-5311
Transiently excited electron states at the GaSb(0 0 1) surface have been studied by means of time- and angle-resolved photoemission spectroscopy based on a femtosecond laser system. A normally unpopulated surface electron state has been found at ∼250 meV above the valence band maximum with a strong confinement at the center of the surface Brillouin zone. The lifetime of transiently excited carriers at the intergap surface states has been found to be ∼11 ps, associated with rapid carrier diffusion. 相似文献
16.
S. A. Teys E. M. Trukhanov A. S. Ilin A. K. Gutakovskii A. V. Kolesnikov 《JETP Letters》2010,92(6):388-395
The results of the structural and morphological studies of Ge growth on a Si(111) surface at the initial stages of epitaxy
by means of scanning tunneling microscopy and high-resolution transmission electron microscopy are presented. Epitaxy of Ge
has been performed in the temperature range of 300 to 550°C under the quasi-equilibrium growth conditions and low deposition
rates of 0.001–0.01 bilayers per minute. The stages of the formation and decay of the nanoclusters as a result of the redistribution
of the Ge atoms into two-dimensional pseudomorphic Ge islands before the formation of the continuous wetting layer have been
experimentally detected. The positions of the preferable nucleation of three-dimensional Ge islands on the wetting layer formed
after the coalescence of the two-dimensional islands have been analyzed. The c2 × 8 → 7 × 7 → c2 × 8 phase transitions due
to the lateral growth of the islands and the plastic relaxation of the misfit strains occur on the surface of the three-dimensional
Ge islands when their strain state changes. The misfit dislocations gather at the interface and two types of steps lower than
one bilayer are formed on the surface of the three-dimensional islands during the relaxation process. 相似文献
17.
S. Padovani F. D'Acapito E. Cattaruzza A. De Lorenzi F. Gonella G. Mattei C. Maurizio P. Mazzoldi M. Montagna S. Ronchin C. Tosello M. Ferrari 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):11-17
Composite silica films containing metal nanoclusters were prepared by the rf- sputtering technique, in which SiO2 was co-deposited with gold+copper, gold+silver, or copper+silver. The formation of either pure or alloy clusters was studied
by extended X-ray absorption fine structure spectroscopy and transmission electron microscopy. For all systems, the presence
of alloy aggregates was evidenced. Moreover, small amounts of pure metal aggregates as well as dispersed or oxidized dopants
were observed.
61.46.+w Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals – 61.10.Ht X-ray absorption spectroscopy:
EXAFS, NEXAFS, XANES, etc. – 81.05.Pj Glass-based composites, vitroceramics
Received 29 June 2001 相似文献
18.
D. A. Romanov E. A. Budovskikh V. E. Gromov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(6):1112-1117
The surface topography and structure of copper layers exposed to multiphase plasma jets of products of electrical explosion
of molybdenum and copper foils are studied using profilometry and scanning electron and light microscopy. Such treatment allows
deposition of either layered coatings or alloyed composite layers. It is found that the surface layer roughness parameter
is R
a
= 3.2−4.0 μm. The thickness of some copper and molybdenum layers of coatings is 15–20 μm. Electroexplosive alloying produces
layers 25 μm thick. Sizes of copper inclusions in the molybdenum matrix near the surface of such layers vary from 30 nm to
1–2 μm. 相似文献
19.
V. D. Borman M. A. Pushkin V. N. Tronin V. I. Troyan 《Journal of Experimental and Theoretical Physics》2010,110(6):1005-1025
The electronic properties of nanoclusters of transition (Ni, Co, Cr) and noble (Au, Cu) metals deposited on the surface of
highly oriented pyrolytic graphite (HOPG) are studied using the method of X-ray photoelectron spectroscopy. The laws of variation
of a change ΔE
b in the binding energies of core-level electrons in the initial (ΔE
i) and final (ΔE
f) states of atoms in nanoclusters, the intrinsic widths γ of photoelectron lines, and their singularity indices α as functions
of the metal cluster size d are determined. A qualitative difference in behavior of the ΔE
i(d) and α(d) values in metals of the two groups (Ni, Cr versus Co, Cu) is found. The values of the final-state energy (ΔE
f < 0) and the line width (Δγ > 0) in the clusters of all metals studied vary in a similar manner. It is shown that a significant
contribution to E
i is due to a transfer of the valence-shell electrons at the cluster-substrate interface, which is caused by the contact potential
difference. The value of an uncompensated charge per nanocluster is determined as a function of the cluster size and the number
of atoms in the cluster. The behavior of ΔE
f(d) is controlled by the Coulomb energy of a charged cluster and by a decrease in the efficiency of electron screening, which
is different in the metals studied. The broadening of photoelectron lines is determined by a spread of the cluster sizes and
by lower electron screening in the final Fermi system. An asymmetry of the core-level electron spectra of nanoclusters can
be explained using notions about the electron-hole pair excitation near the Fermi level. The effect of the structure of the
density of electron states in the d band of transition metals on the asymmetry of photoelectron lines is considered and it is concluded that this structure near
the Fermi level qualitatively changes with a decrease in the nanocluster size. The obtained results indicate that the behavior
of the electron subsystem of clusters of the d-metals in a size range of 2–10 nm under consideration is close to the behavior of a normal Fermi system. 相似文献
20.
S. Carturan A. Quaranta M. Bonafini A. Vomiero G. Maggioni G. Mattei C. de Julián Fernández M. Bersani P. Mazzoldi G. Della Mea 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):243-251
Silver nanoclusters embedded in two transparent
fluorinated polyimides, 4,4'-hexafluoroisopropylidene diphthalic anhydride –
2,3,5,6-tetramethyl paraphenylene diamine (6FDA-DAD) and 3,3',4,4' –
biphenyltetracarboxylic acid dianhydride – 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (BPDA-3F), have been
produced by surface modification with KOH aqueous solution followed by
K-assisted Ag doping and thermal reduction in hydrogen atmosphere. The
reaction rate of the nucleophilic hydrolysis in KOH, studied by Fourier
transform infrared spectroscopy (FT-IR) and Rutherford backscattering
spectrometry (RBS), depends on the polyimide chemical structure. After
ion-exchange in AgNO3 solution and subsequent annealing, the polyimide
structure recovery was monitored by FT-IR whereas the characteristic surface
plasmon absorption band of silver nanoparticles was evidenced by optical
absorption measurements. The structure of silver nanoclusters as related to
size and size distribution in the different polyimide matrices was
thoroughly investigated by Transmission electron microscopy (TEM) and X-ray
diffraction (XRD). The collected data evidenced a uniform distribution of Ag
clusters of nanometric size after thermal treatment at 300 ○C in both
polyimides. For the same ion-exchange treatment parameters and annealing
temperature, XRD analyses evidenced the presence of crystallites with
similar sizes. 相似文献