Au/In bilayers studied with 111In deposited at the interface

Au/In bilayer samples of different stoichiometries were studied using the time-differential perturbed angular correlation technique. The ¹¹¹In probe atoms were deposited at the gold/indium interface to follow the formation of the intermetallic compounds at an early stage. Au-In phases of different composition (AuIn₂, AuIn, Au₇In₃, Au₃In) were created at the interfaces upon annealing. In addition a metastable Au₇In₃(m) phase, observed only after quenching in the bulk Au_0.7In_0.3 alloy, was found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cavities in silicon investigated with the PAC-probe 111In

The perturbed angular correlation technique (PAC) was used to study the creation and development of He-induced cavities. In order to investigate the interaction of Indium atoms with cavities in Silicon the Bonn isotope separator was used to implant overlapping profiles of He (10 keV) and radioactive ¹¹¹In (160 keV) into undoped FZ-silicon. To get insight into the cavity formation mechanism samples were prepared with various He-doses (0.6, 2 and 6× 10¹⁶ ions/cm²). The samples were measured directly after implantation and after different annealing steps (t_hold= 10 min, T = 500–1100oC). Further, different implantation and annealing sequences were used. At higher He doses (2 and 6× 10¹⁶ ions/cm²) we find a large fraction of ¹¹¹In probe atoms subjected to an electric field gradient (EFG) corresponding to a quadrupole interaction frequency (QIF) of ν_Q= 411(6) MHz with η= 0.25(4). The corresponding defect configuration is formed most effectively after He implantation into annealed, ¹¹¹In doped Si. This and the affinity of In to vacancies leads us to the assumption that, similarly to the situation in metals, the Indium atoms act as nucleation centres for vacancy clusters (cavities) and are situated on the inner walls of the cavities. This revised version was published online in August 2006 with corrections to the Cover Date.     

Initial stages in the Sm-Si(111) interface formation

The initial stages in the formation of the Sm-Si(111) interface have been studied by thermal desorption, atomic beam modulation, and low-energy-electron-diffraction spectroscopy. The structure of adsorbed films and samarium silicide films, as well as the Sm atom desorption kinetics have been investigated within a broad range of surface coverages and temperatures. The activation energy of desorption from the thermally most stable 3×2 submonolayer structure, as well as the binding energy of a single samarium atom with the substrate, have been measured. The temperature of the onset of silicide decomposition and the activation energy of this process have been determined. It is shown that the Sm-Si(111) interface forms by a mechanism close to that of Stransky-Krastanov. Fiz. Tverd. Tela (St. Petersburg) 40, 371–378 (February 1998)     

Characteristic interactions of 111Cd probes with nonradioactive In impurities doped in ZnO

Local structures produced in 0.5 at.% In-doped ZnO were investigated by means of the time-differential perturbed angular correlation method using the ¹¹¹Cd probe nuclei generated in the disintegration of different parents, ¹¹¹In and ^111mCd. From distinct perturbation patterns obtained with the probes descended from the different parents, it was ascertained that the doped In atoms locally form a unique structure dispersed in ZnO matrix without forming macroscopic agglomerates of their own.     

Potential barrier at the NaCl---Si(111) interface

The potential barrier at the NaCl---Si(111) interface has been studied using UPS. It was stated that even a very thin NaCl layer decreases the photoemission threshold of the examined system. A saturation value, equal to 3.4±0.1 eV is obtained for a 15–20 ÅA NaCl layer thickness.     

Au/Si(111) and the formation of silicides at the interface examined by spin-resolved photoemission

Au on Si(111) in the 1×1 structure for different coverages and in the , and the 5×1 reconstructions has been studied by means of spin-, angle-, and energy-resolved photoemission. The photoemission studies were performed at normal incidence of the circularly polarized light and normal electron emission. In addition to Au- and Si-derived peaks other highly spin-polarized peaks are observed for a coverage of 8 Au layers grown at room temperature. In keeping with previous work these peaks are interpreted as silicide peaks. The spin polarization of these peaks gives clues concerning the levels involved in the silicide formation. For a coverage of 16 Au layers on Si(111) in the 1×1 structure the photoemission spectra are similar to the spectra of a Au(111) crystal, but also show a contribution of the silicide peaks. For lower coverages the spectra are nearly independent of the structure (1×1, or 5×1) and already show peaks other than the pure Au- and Si-derived peaks. The Auger signal, however, does not show contributions in addition to the pure Si signal.     

Initial stages of formation of a Yb-Si(111) interface

The initial stages of formation of an Yb-Si(111) interface are investigated by several methods: thermal desorption spectroscopy, atomic beam modulation, and low-energy electron diffraction. The structure of the adsorbed films and ytterbium silicide films is analyzed over a wide range of surface coverage ratios, along with the desorption kinetics of Yb atoms. The desorption activation energies of Yb atoms are measured for 3×2, 5×1, and 2×1 submonolayer structures. The temperature interval in which ytterbium silicide decomposes and the activation energy of this process are determined. It is shown that the Yb-Si(111) phase interface evolves by a mechanism similar to the Stransky-Krastanov mechanism. Fiz. Tverd. Tela (St. Petersburg) 39, 256–263 (February 1997)     

Band alignment at the In2S3/Cu2ZnSnS4 heterojunction interface investigated by X-ray photoemission spectroscopy

The band alignment at the In₂S₃/Cu₂ZnSnS₄ heterojunction interface is investigated by X-ray photoemission spectroscopy. In₂S₃ is thermally evaporated onto the contamination-free polycrystalline Cu₂ZnSnS₄ surface prepared by magnetron sputtering. The valence band offset is measured to be 0.46 ± 0.1 eV, which matches well with the valance band offset value 0.49 eV calculated using “transitivity” method. The conduction band offset is determined to be 0.82 ± 0.1 eV, indicating a ‘type I’ band alignment at the heterojunction interface.     

Oxide circle formation at silicon-polymer interface

We demonstrate that precipitation of implanted erbium ions at silicon-polymer interface initiates oxidation reaction of Si(1 0 0) surface at room temperature. Oxidation reaction starts through spontaneous formation of circular patches of SiO_x and the diameter of these circles grows uniformly with time and touch each other to cover the entire surface by keeping the thickness of these patches almost fixed at 4 nm. The nucleation and in-plane growth rates of SiO_x circles are found to be dependent on the fluence of erbium-implantation, the condition of substrate and can be controlled by controlling oxygen partial pressure of the environment. In addition to the precipitation of erbium ions at silicon-polymer interface, enhancement of concentration of erbium ions was observed at periodic depths within polymer film confirming that in ultra-thin films polymer molecules form layers parallel to substrate surface due to confinement.     

Vacancy trapping at111In in tungsten

TDPAC measurements were carried out in tungsten foils and single crystals using implanted¹¹¹In as a probe nucleus. After damaging the bcc tungsten lattice by heavy ion implantation, electron- and proton-irradiation the trapping of three different defects in the temperature range 293–1,000 K was observed. They were characterized by quadrupole interaction frequencies of v _Q ¹ = 142(2) MHz, v _Q ² = 181(5) MHz and v _Q ³ = 263(5) MHz. The largest fraction of In nuclei experiencing electric field gradients corresponding to v _Q ¹ and v _Q ² was reached at app. 630 K whereas for v _Q ³ this maximum appeared at app. 850 K. The defect configurations producing the different electric field gradients could be identified as a monovacancy trapped in a nearest neighbour 111 position (v _Q ¹ ), a double vacancy consisting of two adjacent vacancies in the nearest neighbour shell of the probe atom (v _Q ² ) and possibly a larger cluster (v _Q ³ ).     

Magnetic hyperfine fields at 111In probes in submonolayer Cu islands on Co(1 0 0) surfaces

Cu islands in the submonolayer coverage regime deposited on Co(1 0 0) have been studied utilizing the PAC spectroscopy. The ¹¹¹In PAC probes are incorporated into the topmost monolayer, which is corroborated by the presence of a rather unique electric field gradient. In addition, weak magnetic hyperfine fields B_hf between 1.9(2) and 0.37(4) T have been observed depending on the Cu coverage. This is attributed to next neighbours of the PAC probes consisting of mixed Co/Cu configurations. A linear decrease of B_hf as a function of the number of Cu atoms replacing Co is found. This revised version was published online in August 2006 with corrections to the Cover Date.     

In situ ESR observation of interface dangling bond formation processes during ultrathin SiO2 growth on Si(111)

We report the formation processes of interface dangling bonds (Pb centers) during initial oxidation of a clean Si(111) surface using an ultrahigh-vacuum electron-spin-resonance technique. At the oxidation of one or two Si layer(s), the Pb center density reached around 2.5-3.0 x 10(12) cm(-2), which is the same density as in the case of thick SiO2. This result shows that the Pb center density does not originate from the long-range accumulation of the structural stress between two materials, but from the chemical reactions of oxidation within a few Si atomic layers.     

Electron transport via local polarons at interface atoms

Electronic transport is profoundly modified in the presence of strong electron-vibration coupling. We show that in certain situations, the electron flow takes place only when vibrations are excited. By controlling the segregation of boron in semiconducting Si(111)-square root 3 x square root 3 R 30 degrees surfaces, we create a type of adatom with a dangling-bond state that is electronically decoupled from any other electronic state. However, probing this state with scanning tunnelling microscopy at 5 K yields high currents. These findings are rationalized by ab-initio calculations that show the formation of a local polaron in the transport process.     

Bistable nonspecular reflection at a nonlinear-linear local interface

Nonspecular reflection at a nonlinear-linear dielectric interface with local Kerr nonlinearity is analyzed. The Fresnel reflectivity and the variational solution are explicitly given in a closed form. Bistable switching of the interface is demonstrated by numerical simulations based on the monotonic iteration procedure.