Auger Valence Electron Spectroscopy Research Articles

Structural evolution and valence electron-state change during ultra thin silicon-oxide growth

We have studied valence electron-state changes of Si during initial oxidation of Si(111) clean surface, HF-treated Si(001) and Si(111) surfaces by Auger valence electron spectroscopy (AVES). The results showed that the valence electron-state changes during initial oxidation were sensitively reflected in Si[2s,2p,V] (V=3s,3p) AVES spectra and that they depended on both initial surface treatment and surface orientation. The local valence electron-states, local density of states in other words, showed the characteristic-structure evolution depending on the initial surface treatment and surface orientation.

Auger electron spectroscopy of super-doped Si:Mn thin films

Thin films of Si heavily doped with Mn impurities at nonequilibrium doping levels have been successfully prepared by Laser-Ablation MBE. The electronic structure of Mn-doped Si thin films have been investigated by Auger Valence Electron Spectroscopy (AVES). The peak positions of Mn[3p,V,V] (V=3d) Auger spectra of Si:Mn thin films were located at the higher energy region than those of pure Mn and Mn 5Si 3 compound. For the Si:Mn thin film grown on SiO 2/Si(001) substrate, the new Auger peak was observed around 50 eV. The changes of the line shape were observed in Mn[L,M,M] (L=2s,2p; M=3s,3p,3d) Auger spectra of Si:Mn thin films compared with those of pure Mn and Mn 5Si 3 compounds. In the Mn[2s,M,V] (M=3s,3p,V=3d) spectra for Si:Mn thin films, the new peaks were appeared around 700 eV. These new peaks were considered to arise from the new split of the 3d electron states due to the formation of the Mn–Si bonds in Si:Mn thin films.

Valence states analysis of Ca and Si in CaSi2 during CaSi2–H2O reaction

The changes in the valence electron states of CaSi2 during the chemical reaction with H2O have been investigated by Auger Valence Electron Spectroscopy (AVES). In order to study the reaction process, the reaction was precisely controlled by applying dc voltage between Pt electrode and CaSi2 specimen. The Si[2s, 2p,V] Auger spectra of CaSi2 specimen remain unchanged under the applied voltage lower than −15 V relative to the Pt electrode in H2O. At higher applied voltage, 3p components of Si[2s, 2p, V] (V = 3s, 3p) Auger spectra get weak while the 3s components increase drastically. The peak position due to Ca[2p, 3p, 3p] transitions gradually shifted toward the lower energy side by raising the applied voltage. The peak shift is due to the formation of Ca–O bonds in CaSi2. A new peak, which arises from the split of the valence electron states in Ca atoms due to the Ca–O bonds, appeared in Ca[2p, 3p,V] Auger spectra for CaSi2 after the reaction with H2O.

Valence-electron spectral change and charge transfer mechanism of CaSi 2 during CaSi 2H 2O reaction

The changes in the valence electron states of CaSi 2 during the chemical reaction with H 2O have been investigated by Auger valence electron spectroscopy (AVES). The drastic changes in the valence electron spectra of 3s and 3p states, which are caused by the oxidization of the Si atoms in CaSi 2, were observed in Si[2s, 2p, V] spectra for CaSi 2 after the reaction. In particular, the Si[2s, 2p, V] spectra of CaSi 2 samples reacted with H 2O at 60 or 80°C for 3 h were almost similar to that of SiO 2. The peak shift of Ca[2p, 3p, 3p] Auger transition toward the lower energy side has been observed, suggesting the formation of bonds between Ca 3p and O orbitals. New peaks due to CaO or CaOH bonds also appeared in the valence electron region of Ca[2p, 3p, V] Auger transition. The charge transfer and the chemical-bond formation can be well demonstrated by AVES during the CaSi 2H 2O reaction.

Auger valence electron spectra in Ca-silicides

CaSi2 and CaSi have been investigated by Auger Valence Electron Spectroscopy (AVES). Some drastic differences of the Auger peak due to 3s states in the Si atoms were observed in the Si[2s, 2p, V] Auger spectra. The peak that arised from valence electron states in the Ca atoms was observed in the Ca[2p, 3p, V] Auger spectra for both Ca-silicides. This result suggests that the Ca–Si bonds are partially ionic. However, the number of the valence electrons in Ca atoms for CaSi was larger than that for CaSi2. This result implies that the part of homopolar bonds between the Si and Ca atoms in CaSi is stronger than that in CaSi2. Based on these results, it has been concluded that the change of the Si [2s, 2p,V] Auger spectra is associated with the difference of the part of homopolar bonds between the Si and Ca atoms.

Analysis of bonding state in pure and gold‐implanted amorphous SiC by a combination of UHVEM and AES

SUMMARYSingle crystalline α‐SiC films and Au(target metal)/α‐SiC(substrate) bilayer films were irradiated with 2‐MeV electrons in an ultrahigh‐voltage electron microscope (UHVEM) to form, in situ, pure amorphous SiC (a‐SiC) and gold‐implanted a‐SiC. respectively. In the latter case, sample films were set so that the electron beam was incident on the gold layer. Differences in the bonding state between pure a‐SiC and gold‐implanted a‐SiC were studied by Auger valence electron spectroscopy (AES). In pure a‐SiC. the carbon valence state was markedly different from that of α‐SiC but the silicon valence state was similar to that of α‐SiC. In gold‐implanted α‐SiC. both the carbon and the silicon valence states were different from those of α‐SiC. It is suggested that a high density of molecularized carbon clusters are formed in the amorphous matrix in gold‐enriched a‐SiC.

Site-Selective Analysis of Local Electronic Structures in GaAs1-xPx Alloy Semiconductors by Auger Valence Electron Spectroscopy.

A systematic study of local electronic structures in alloy semiconductor GaAs1-xPx, has been made by using Auger valence electron spectroscopy (AYES). Particular emphasis has been paid to the local valence electronic states of constituent atoms having different local atomic configurations in the alloy lattice. Dependencies of Auger valence electron spectra of Ga [3s, 3d, V], As [3d, V, V] and P [2p, V, V] transitions on the alloy composition were measured and correlated with the local atomic bonding structure of these constituent atoms. Simple tight-binding calculation of Auger valence electron spectra of the constituent elements of GaAs1-xPx, alloys has been also performed to analyze the valence electron states of constituent elements on the basis of the local density of states of the constituent elements.

Bond formation in hafnium atom implantation into SiC induced by high-energy electron irradiation

Abstract Bilayer films of Hf (target atoms)/α-SiC (substrate) were irradiated with 2 MeV electrons in an ultra-high voltage electron microscope (UH VEM), with the electron beam incident on the hafnium layer. As a result of the irradiation, hafnium atoms were implanted into the SiC substrate. Changes in the microsctructure and valence electronic states associated with the implantation were studied by a combination of UHVEM and Auger valence electron spectroscopy. The implantation process is summarized as follows. (1) Irradiation with 2MeV electrons first induces a crystalline-to-amorphous transition in α-SiC. (2) Hafnium atoms which have been knocked-off from the hafnium layer by collision with the 2 MeV electrons are implanted into the resultant amorphous SiC. (3) The implanted hafnium atoms make preferential bonding to carbon atoms. (4) With continued irradiation, the hafnium atoms repeat the displacement along the beam direction and the subsequent bonding with the dangling hybrids of carbon and silicon....

The magic size determined by valence fluctuation in germanium atom clusters

When the size of solids becomes smaller than the critical size of the nanometre scale, their bonding states and atom periodicity are influenced. As a result, the properties of materials are changed remarkably [1]. Such functional ultrafine particles are here named "atom clusters". The interatomic bondings, particularly in atom clusters, differ from those in bulk crystals because the size of the region affected by the long-range interaction force among the constitutive atoms is close to or larger than the cluster size. We call such a cluster size the "magic size". The behaviour of semiconducting materials in the size below the magic size, particularly relating to structural fluctuations, has been observed as follows. The relationship between the crystalline size and lattice constant of silicon measured by X-ray diffraction suggested that amorphization occurs with decreasing crystalline size [2]. In addition, the Raman spectra of silicon and germanium ultrafine particles changed to amorphous-like spectra with decreasing particle sizes [3-5]. These results show that the magic size is 2-10 nm in covalent materials, such as silicon and germanium. The purpose of this work was to determine the magic size of germanium on the basis of a fluctuation of the valence electronic states in germanium atom clusters by Auger valence-electron spectroscopy (AES). Germanium atom clusters were prepared by the vacuum vapour deposition method. Germanium was first evaporated on a film-substrate of amorphous carbon from a tungsten filament under a base pressure below 4.0 x 10 -8 Pa at room temperature. The germanium deposition here became an amorphous film. Therefore, in order to form atom clusters, these films were heated by electron bombardment at 573 K for 1.8 ks (the formation of atom clusters under this condition was ascertained by in situ observation under heating in a transmission electron microscope (TEM)). The cluster sizes were controlled by the germanium coverages. After the preparations, the Ge Auger valence spectra were measured in the first-derivative mode with the resolution of A E / E = 0.3% by summing up more than 30 scans and processing by numerical integrations. The electron gun was operated at the primary acceleration voltage of 3 kV and the primary specimen current of 0.2 ~tA. The size distributions of clusters in the same specimen as that measured by AES were estimated by TEM observation. The average diameters were calculated from histograms. In addition, the germanium atom dusters were formed on MgO single crystals under the same conditions to observe the profile images of the clusters. The microstructures were observed by the many-beam lattice image method. The TEM used was operated at 200 and 300 kV. It was confirmed that the specimen was not damaged by the primary electron beam from 200 to 300 kV. Fig. 1 shows the Ge (M2,3Mn5V) Auger valence spectra as a function of the cluster size, where V indicates the Ge 4s(N1) and 4p(N23) valence states. As the Auger lineshape fluctuates variously in clusters below about 7 nm in size, a typical one (i.e.

Structural and valence electronic analysis of electron-irradiation-induced foreign-atom implantation by a combination of UHVEM and AES

Bilayer films of Pt or Au (target atoms) / α-SiC (substrate) were irradiated with 2 MeV electrons in an ultrahigh-voltage electron microscope, with the electron beam incident on the metal layer. By irradiation, noble-metal atoms were implanted into the SiC substrate. Changes in the microstructures and valence electronic state associated with the implantation were studied by a combination of ultrahigh-voltage electron microscopy and Auger valence electron spectroscopy. The results obtained can be summarized as follows. (1) Irradiation with 2 MeV electrons first induces a crystalline-to-amorphous transition in α-SiC. (2) The noble-metal atoms which have been knocked-off from the metal layer by the elastic collision with the 2 MeV electrons are implanted into the resultant a-SiC (3) The implanted metal atoms make preferential bonding with silicon atoms having dangling bonds. Interaction with carbon atoms may also be present in the Pt/SiC system. (4) During continued irradiation, the metal atoms repeat knocking-off along the beam direction and subsequent bonding with the dangling bonds. The repetition of knocking-off and subsequent bonding is essential to the deep implantation of noble-metal atoms into the SiC substrate.

Local atomic configuration and Auger valence electron spectra in BiSrCaCuO single crystals

Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ (2212) and Ca-doped Bi/sub 2/Sr/sub 2/CuO/sub y/ (2201) single crystals were systematically investigated by Auger valence electron spectroscopy (AVES). In AVES measurements on two kinds of crystals, a drastic difference was observed in the spectral shape of Ca(2p,3p,3p) reflecting a difference in spin-orbit splitting induced by local atomic configuration in the vicinity of Ca atoms. Furthermore, a Ca(2p,3p,4s) spectrum appeared in both crystals, indicating that the real valence of Ca atoms deviates from +2 in the crystals. The results suggest that AVES is a promising probe for characterizing local atomic configuration and valence electron states of the constituent elements.

Auger valence electron spectroscopy of a structural phase transformation in metastable alpha-Sn grown on InSb (001)

A type of surface structural transformation of metastable alpha-Sn epitaxially grown on InSb (001) has been investigated in situ with RHEED and Auger valence electron spectroscopy. Concerned with structural transformation of bulk Sn from the alpha (diamond cubic structure) to beta (tetragonal structure) phase, a type of surface structural transformation has been observed in RHEED. The eoitaxial layer of alpha-Sn showed a 2 × 1 two-domain superstructure. Upon heating, the superstructure disappeared at the critical temperature. Three-dimensional islands were found by transformation in the thick specimens. The transformation temperature depended on the layer thickness of metastable alpha-Sn. Related to the structural transformation, the spectral change in Sn[4 p, V, V] Auger transition has been found also at the critical temperature. The Auger and RHEED data suggest the crucial role of the lattice matching condition between the epitaxial layer and the substrate on the critical temperature.

Gold Atom Implantation into α-SiC by High-Energy Electron Irradiation and State Analysis of the Resultant Phase

Bilayer films of Au (target atom)/α-SiC (substrate) were irradiated with 2MeV electrons in an ultra-high voltage electron microscope. By irradiation, gold atoms in the upper layer were implanted into the SiC substrate. Changes in the microstructures and bonding state associated with the implantation were studied by ultra-high voltage electron microscopy and scanning Auger valence electron spectroscopy, respectively. The results obtained are as follows; (1) Irradiation with 2MeV electrons first induces a crystalline-to-amorphous transition in α-SiC. (2) Gold atoms which have been knocked-off from the gold layer by the collision with 2MeV electrons are recoil-implanted into the resultant amorphous SiC. (3) The implanted gold makes preferential bonding with silicon having dangling bonds, and new bonding states are formed between them. (4) During continued irradiation, the gold atoms repeat displacement towards the beam direction, which is induced by the collision with electrons and subsequent bonding with silicon atoms having dangling bonds. The repetition results in the deep implantation of gold into the SiC substrate.

Electronic Structures Localized at the Boron Atom in Amorphous Fe-B and Fe-B-P Alloys

The electronic structures localized at the B in amorphous Fe-B and Fe-B-P alloys and their crystallized alloys were studied by Auger valence electron spectroscopy and the states of solute B are discussed based on the change in the degree of covalent bonding and the charge transfer between the Fe and B atoms. In amorphous phases, the charge transfers from Fe to B above 15at%B where B atoms occupy the substitutionallike situations, and from B to Fe below 15at%B where B atoms occupy the interstitiallike situations. Magnetic properties depend on such states of solute B. In crystalline phases, covalent bonding becomes dominant because the electron excitation occurs to the B2p state. Consequently, amorphous phases are more metallic in character than crystalline phases and amorphous structures are stabilized by a mixture of more than two different bonding states.

Behaviour of valence electrons in the ageing process of Al-2·2at.% Cu crystals

Abstract The formation processes of Guinier-Preston (GP) zones, θ- and θ-phase structures in an Al-2.2 at.% Cu alloy have been investigated by a combined method of Auger valence electron spectroscopy and high-resolution transmission electron microscopy. An Auger valence electron spectrum of pure aluminium was subtracted from those of the aged specimens to analyse a small change in the L2,3 VV spectrum of aluminium atoms in the alloy. The spectrum consists of three peaks as follows. One peak is a positive peak and always appears in all ageing stages including the asquenched state. The intensity of this peak shows a good correspondence to the coherent strain around microstructures formed by ageing. The other two peaks are negative and appear in GP-1 formation. Subsequently, their intensities show the maximum values in θ-phase formation and decrease again in θ-phase formation. We conclude that these two peaks are closely related to the local chemical bonding between aluminium and copper atoms. On the basis o...

Evaluation of on-site 3d electron correlation of copper in La2CuO4, La2-xSrxCuO4 and Y1Ba2Cu3O7−y by L 3M 4,5M 4,5 auger valence electron spectra

On site Coulomb interaction energy U of 3d electron of copper was evaluated by Auger valence electron spectroscopy in La2CuO4, La2-xSrxCuO4, tetragonal YlBa2Cu3O7−x and orthorhombic YlBa2Cu3O7−x and was compared with those of Cu and CuO. Values of U in La2CuO4 and La2-xSrxCuO4 were 6.9 and 7.6, respectively. The values were larger than those of YBaCuO, which showed U ≅W.