共查询到20条相似文献,搜索用时 673 毫秒
1.
Wenting Xu Hailing TuQinghua Xiao Qing ChangZongfeng Li Dali Liu 《Applied Surface Science》2011,257(22):9260-9263
The Si1−xGex thin layer is fabricated by two-step Ge ion implantation into (0 0 1) silicon. The embedded SiGe nanoclusters are produced in the Si1−xGex layer upon further annealing. The number and size of the nanoclusters changed due to the Ge diffusion during annealing. Micro defects around the nanoclusters are illustrated. It is revealed that the change of Si-Si phonon mode is causing by the nanoclusters and micro defects. 相似文献
2.
J. Skov Jensen T.P. Leervad Pedersen R. Pereira J. Chevallier J. Lundsgaard Hansen B. Bech Nielsen A. Nylandsted Larsen 《Applied Physics A: Materials Science & Processing》2006,83(1):41-48
Structural and optical properties of Ge nanocrystals in SiO2 films created by magnetron sputtering and heat treatment have been investigated. The formation of nanocrystals is found to be influenced by the temperature of heat treatment and the Ge concentration in the films. After heat treatment at 1000 °C nanocrystals are present throughout the film, with the exception of a region close to the surface that does not contain nanocrystals. This effect is assigned to oxidation of Ge in this part of the film. The size distribution of the nanocrystals is analyzed by transmission electron microscopy for a range of deposition and heat-treatment parameters. By analyzing the transmission electron microscopy images, it is possible to estimate the fraction of nanoclusters that are crystalline for a given set of growth parameters. This analysis shows that all the nanoclusters are created in the crystalline state. Raman spectroscopy is employed to probe the Ge–Ge bonds. In combination with transmission electron microscopy, this information can be used to distinguish between growth modes such as nucleation or Ostwald ripening. The photoluminescence spectra exhibit a strong broad line at 625 nm, the presence of which is demonstrated to correlate to the presence of Ge nanocrystals. PACS 61.46.+w; 78.55.-m; 78.67.-n 相似文献
3.
H. Ou T.P. Rørdam K. Rottwitt F. Grumsen A. Horsewell R.W. Berg 《Applied physics. B, Lasers and optics》2007,87(2):327-331
This paper reports the formation of Ge nanoclusters in silica glass thin films deposited by plasma-enhanced chemical vapor
deposition (PECVD). We studied the samples by transmission electron microscopy (TEM) and Raman spectroscopy after annealing.
TEM investigation shows that the Ge nanoclusters at two areas were formed by different mechanisms. The Ge nanoclusters formed
in a single row along the interface of a silicon substrate and the silica glass film by annealing during high-temperature
heat treatment. Ge nanoclusters did not initially form in the bulk of the film but could be subsequently formed by the electron-beam
irradiation. The interface between the silicon substrate and the silica glass film was investigated by Raman spectroscopy.
The shift of the Raman peaks around 286.8 cm-1 and 495 cm-1 suggests that the interface is a Si1-xGex alloy film and that the composition x varies along the film growth direction.
PACS 81.07.Bc; 78.66.Jg; 42.65.Wi 相似文献
4.
Wen-ting Xu Hai-ling Tu Da-li Liu Ran Teng Qing-hua Xiao Qing Chang 《Journal of nanoparticle research》2011,13(12):7095-7098
An innovative fabrication technique for the nanometer-sized SiGe/Si heterostructure was developed in this study. Ge was induced
in Si substrate by two-step ion implantation. The spherical SiGe nanoclusters are self-assembled in the Si substrate by subsequent
rapid thermal annealing at 1,100 °C. The diameter of the spherical SiGe nanoclusters is 5–7 nm. Visible photoluminescence
from this nanometer-sized SiGe/Si heterostructure at room temperature was investigated. We found three peak energies of visible
luminescence spectra at 1.97, 2.13, and 2.16 eV, respectively. The luminescence intensity depends on the number of the nanoclusters
and will be decreased because of the micro-defects around the heterostructure, which is discussed in detail. 相似文献
5.
D. Barchiesi D. Macías L. Belmar-Letellier D. van Labeke M. Lamy de la Chapelle T. Toury E. Kremer L. Moreau T. Grosges 《Applied physics. B, Lasers and optics》2008,91(1):177-181
This paper reports the formation of Ge nanoclusters in a multi-layer structure consisting of alternating thin films of Ge-doped
silica glass and SiGe, deposited by plasma-enhanced chemical vapor deposition (PECVD) and post annealed at 1100 °C in N2 atmosphere. We studied the annealed samples by transmission electron microscopy (TEM) and Raman spectroscopy. As-deposited
and annealed samples were analyzed by secondary ion mass spectroscopy (SIMS). TEM investigation shows that Ge nanoclusters
were formed in the as-deposited SiGe layer and the SiGe layer was transformed into a silicon dioxide layer embedded with Ge
nanoclusters after annealing. These nanoclusters are crystalline and varied in size. There were no clusters in the Ge-doped
glass layer. Raman spectra verified the existence of crystalline Ge clusters. The positional shift of the Ge vibrational peak
with the change of the focus depth indicates that the distribution of the stress applied to the Ge clusters varies with depth.
SIMS measurements show clearly the dramatic O increase in the as-deposited SiGe layer after annealing. The creation of Ge
nanoclusters by the combination of PECVD and annealing makes possible the application in complicated waveguide components.
PACS 81.07.Bc; 78.66.Jg; 42.65.Wi 相似文献
6.
Using the methods of scanning and spectral laser ellipsometry and Raman scattering spectroscopy, GeO2 films containing Ge nanoclusters with a Ge/GeO2 mole ratio of 1: 1 are studied. A substantial difference is found between the experimental spectral dependence of the complex permittivity of the films and the one calculated for the effective medium in the Bruggeman model. The distinction can be qualitatively explained by the influence of the quantum-size effect. With the use of theoretical models for quantitative analysis, this approach will make it possible to determine the phase composition and dimensions of the nanoclusters of germanium in a contactless way without destructing the film. 相似文献
7.
This work presents the structural characterization of nanoclusters formed from a-Si:H/Ge heterostructures processed by rapid thermal annealing (RTA) at 1000 °C for annealing times varying between 30 s and 70 s. The a-Si:H layers were grown on electron cyclotron resonance (ECR) using SiH4 and Ar precursor gases. The Ge layer was grown in an e-beam evaporation system. The structural characterizations were performed by high-resolution X-ray diffractometer (HRXRD) on grazing incidence X-ray reflection mode (GIXRR) and micro-Raman measurements. The average grain size, Ge concentration (xGe) and strain were estimated from Lorentzian GIXRR peak fit. The average grain size varied from 3 nm to 7.5 nm and decreased with annealing time. The xGe increase with annealing time and varied from 8% to 19%, approximately. The strain calculated for (1 1 1), (2 2 0) and (3 1 1) peaks at 40 s, 50 s, 60 s and 70 s annealing time suggest the geometrical changes in nanoclusters according to process time. 相似文献
8.
V. A. Volodin E. B. Gorokhov D. V. Marin H. Rinnert P. Miska M. Vergnat 《JETP Letters》2009,89(2):76-79
GeO2 films with germanium nanocrystals (NCs) were deposited from supersaturated GeO vapor with subsequent dissociation on Ge:GeO2. The films were studied using photoluminescence (PL), Raman scattering, IRspectroscopy techniques. Ge NCs in initial film
have sizes about 6–8 nm and have no visible PL signal. The broad green-red PL peak was detected in Ge:GeO2 films after thermal annealings. According to effective mass approach, maximum of PL signal from such relatively big Ge NCs
should be in IR region. The experimentally observed PL signal is presumably originated due to quasi-direct L
1-L
3’ optical transitions “folded” in germanium NCs.
The article is published in the original. 相似文献
9.
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
10.
The solidified microstructure of bulk undercooled Ag40Cu30Ge30 alloy consists of three parts: primary (Ge) phase, the complex structure of (Ag + Ge) and (Ag + ε
2) pseudobinary eutectics, and (Ag + Ge + ε
2) ternary eutectic. In comparison, the pseudobinary eutectic no longer appears in an alloy droplet solidified in a drop tube.
Once the undercooling exceeds 225 K and the cooling rate is greater than 2×103 K s−1, the microstructure of the solidified droplet is totally composed of anomalous ternary eutectic. In both cases, the primary
(Ge) phase exhibits various faceted growth morphologies at different undercoolings, such as columnar block, long dendrite,
equiaxed dendrite and rod-like crystal. Some refined side branches grow from the equiaxed (Ge) dendritic branches composed
of {111} twins, which is ascribed to the rapid epitaxial growth of (Ag + Ge) pseudobinary eutectic from the (Ge) dendritic
branches. Moreover, both the primary (Ge) phase and the (Ge) phase in the (Ag + Ge) pseudobinary eutectic are effective heterogeneous
nuclei for the (Ag+ε
2) pseudobinary eutectic. As undercooling increases, the (Ge) phase in the (Ag + Ge+ε
2) ternary eutectic transforms from faceted to non-faceted phase, while the independent nucleation and growth of the (Ag) and
ε
2 phases in the ternary eutectic displaces their previous cooperative growth. These growth kinetics transitions result in the
formation of anomalous ternary eutectic. 相似文献
11.
We present the self-assembling conditions of 1C4Sn tetrahedral nanoclusters with carbon atoms in their centers in Ge:(C, Sn) in the wide temperature range as a function of the impurity contents and temperature. These conditions are the phase diagram of Ge:(C, Sn) since nanocluster occurrence and completion of self-assembling when all carbon atoms are in nanoclusters are results of the continuous phase transitions. The significant decrease of the strain energy after formation of nanoclusters is a cause of self-assembling. It is shown that the nanocluster occurrence temperature depends only on the Sn content. The impurity content conditions when all carbon atoms are in 1C4Sn nanoclusters are obtained for the temperatures up to 855 °C. 相似文献
12.
One-pot synthesis of well dispersed, size-controlled gold nanoparticles with the average size of 10–15 nm and luminescent
gold nanoclusters with average size of 1.7–2.0 nm were successfully achieved by thermal decomposition of gold organometallic
precursor CH3AuPPh3 in the presence of thiol surfactants in o-xylene. Only difference between the preparations of two types of Au nanoparticles is the amount of thiol surfactant employed.
The mechanistic study of formation of gold nanoparticles was carried out by analyzing the samples at different reaction time
intervals and revealed that two-staged growth process was involved. The nanoclusters showed strong red emission with the maximum
intensity at about 600 nm. The maximum room temperature photoluminescence quantum yield was measured as 1.2%. The catalytic
ability of the Au nanoclusters to promote Suzuki–Miyaura coupling involving the C–C bond formation was also investigated. 相似文献
13.
Mechanical strains in a multilayer Ge/Si(001) heterostructure with vertically aligned Ge nanoclusters (quantum dots) are calculated using an interatomic potential based on the Keating valence-force-field model. It is found that the nonuniform spatial elastic strain distribution in this medium gives rise to a three-dimensional potential well for electrons in the strained Si layers near Ge nanoclusters. The depth of the potential well reaches 100 meV, and its spatial dimensions are determined by the diameter of the Ge nanoclusters. For a structure consisting of four Ge islands 23 nm in diameter arranged one above another, the electron binding energies in this well and the spatial electron density distribution are determined. The ground state has an s-like symmetry and is characterized by an electron binding energy of ~95 and ~60 meV for the elemental composition of Ge in the nanoclusters c = 1 and c = 0.7, respectively. The existence of bound electron states in the conduction band of strained Si must lead to a relaxation of the selection rules that determine the low efficiency of the radiative recombination in indirect-gap semiconductors. This explains the high value of the oscillator strength observed for the interband transitions in multilayer Ge/Si(001) structures with vertical correlation of the arrangement of Ge nanoclusters. 相似文献
14.
S. Das R. K. Singha S. Manna S. Gangopadhyay A. Dhar S. K. Ray 《Journal of nanoparticle research》2011,13(2):587-595
We have grown Ge nanocrystals (NCs) (4.0–9.0 nm in diameter) embedded in high-k HfO2 matrix for applications in floating gate memory devices. X-ray photoelectron spectroscopy has been used to probe the local
chemical bonding of Ge NCs. The analysis of Ge–Ge phonon vibration using Raman spectroscopy has shown the formation of compressively
stressed Ge NCs in HfO2 matrix. Frequency dependent electrical properties of HfO2/Ge-NCs in HfO2/HfO2 sandwich structures have been studied. An anticlockwise hysteresis in the capacitance–voltage characteristics suggests electron
injection and trapping in embedded Ge NCs. The role of interface states and deep traps in the devices has been thoroughly
examined and has been shown to be negligible on the overall device performance. 相似文献
15.
V. A. Volodin M. D. Efremov D. A. Orekhov A. I. Nikiforov O. P. Pchelyakov V. V. Ulyanov A. I. Yakimov A. V. Dvurechenskii 《Physica E: Low-dimensional Systems and Nanostructures》2004,23(3-4):320
Germanium quantum dots formed on Si (1 1 1) and (1 0 0)-oriented surfaces coated with ultra-thin oxide layers are studied using Raman spectroscopy technique. Some structural properties (height, stoichiometry and mechanical stresses) of the dots were estimated from Raman data. For analysis of the experimental data, the Raman spectra of Ge nanoclusters containing some hundreds of Ge atoms were calculated numerically. The effects of the resonance enhancement of the intensity of Raman scattering in the Ge-nanoclusters–SiO2–Si system were discussed. The influence of the lateral sizes of Ge nano-clusters on the frequencies of phonons localized in them was studied using numerical simulation. The influence of multi-layer growth on the structure of the Ge quantum dots was investigated. 相似文献
16.
Subthreshold photoemission from copper nanoclusters formed on the SiO2 surface has been observed under irradiation of the surface by photons in the 3.1–6.5-eV energy range. The average size of
copper nanoclusters on the silicon oxide surface is 250–500 nm. Besides the conventional photoemission from the filled Shockley
surface state (SS), strong photoemission has been recorded at incident photon energies of 0.5 eV below the work function of
the copper surface. This emission is assumed to be generated in direct electron transitions from the SS state to the unfilled
electron surface states formed by the Coulomb image potential, followed by escape from these states into vacuum. 相似文献
17.
C.G. Hwang N.D. Kim G. Lee S.Y. Shin S.H. Uhm H.S. Kim J.S. Kim J.W. Chung 《Applied Physics A: Materials Science & Processing》2007,89(2):431-435
We report an unusual behavior of the work function that remains unchanged while increasing the coverage (θ) of thallium (Tl)
nanoclusters regularly arranged on a Si(111)-7×7 surface. Such a constant work function with increasing θ is understood in
terms of a θ-dependent inter-cluster interaction that cancels the change induced by dipoles due to Tl nanoclusters. The spectral
changes of Si 2p and Tl 5d5/2 core-levels as a function of θ strongly indicates the presence of such an inter-clusters interaction, which is further supported
by our theoretical calculation revealing a significant charge redistribution.
PACS 73.20.-r; 73.30.+y; 68.47.Fg; 79.60.-i; 73.20.Hb 相似文献
18.
L. Patrone D. Nelson V.I. Safarov S. Giorgio M. Sentis W. Marine 《Applied Physics A: Materials Science & Processing》1999,69(7):S217-S221
We show that conventional pulsed laser ablation (PLA) of Si and Ge targets in inert buffer gases is an efficient method of nanocluster synthesis. From a photoluminescence study of Si and Ge nanoclusters produced by PLA we have demonstrated the possibility of tuning the luminescence band from the near infrared to the near ultraviolet regions. The stabilization of the properties of Si nanoclusters by reactive (H2 gas) PLA synthesis was proved by photoluminescence measurements. Finally, we report a photoluminescence study of gas-suspended Ge nanoclusters during their preparation. They exhibit a broad luminescence spectrum extended from UV to the blue-green region and modulated by a molecule-like structure. We propose an interpretation of the vibronic structure involving Ge-O-Ge vibrations at the surface of photo-excited clusters. To the best of our knowledge, we report here the first observation of vibrational effects from gas-suspended Ge nanoclusters. 相似文献
19.
O. B. Gusev J. S. Vainshtein Yu. K. Undalov O. S. Yeltsina I. N. Trapeznikova E. I. Terukov O. M. Sreseli 《JETP Letters》2011,94(5):370-373
Films of amorphous silicon suboxide α-SiO
x
containing amorphous silicon nanoclusters have been grown by direct current magnetron sputtering. It has been found that
two radiation bands are observed in the photoluminescence spectra of relatively large amorphous nanoclusters (a size of ∼2
nm) unlike one photoluminescence band of silicon nanocrystals of the same size. The form of the spectra upon the change in
the nanocluster sizes agrees with that predicted in theoretical works, in which the energy spectrum of amorphous nanoclusters
has been calculated taking into account quantum confinement of delocalized, weakly localized, and strongly localized states. 相似文献
20.
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