102 research outputs found
Acceleration of Diffusional Jumps of Interstitial Fe with Increasing Ge Concentration in Si1 − x Ge x Alloys Observed by Mössbauer Spectroscopy
Radioactive 57Mn isotopes have been implanted into Si1 − x Ge x crystals (x ≤ 0.1) at elevated temperatures for Mössbauer studies of the diffusion of interstitial 57Fe daughter atoms. The atomic jump frequency is found to increase upon Ge alloying. This is attributed to a lowering of the activation energy, i.e. the saddle point energy at hexagonal interstitial sites with Ge neighbour atom
Amorphization of ZnSe by ion implantation at low temperatures
Radioactive Cd and Se ions were implanted into high-resistivity ZnSe single crystals around 60 K and 300 K. Their lattice sites were determined by measuring the channelling and blocking effects of the emitted conversion electrons or positrons directly after implantation and after annealing at different temperatures up to 600 K. Implantation doses were in the range of 3 - 3/cm. The experimental results of this emission channelling technique yield a high substitutional fraction of the implanted ions directly after implantation at room temperature. At 60 K the substitutional fraction of implanted ions is highly sensitive to the ion dose. Above a critical dose of around 1.4 Cd/cm or 2.1 Se/cm the substitutional fraction completely disappears indicating an amorphous surrounding of the probe atom. Damage recovery was observed below room temperature and at an annealing temperature around 500 K. A quantitative analysis of measured channelling yields will be given by comparison with calculated electron channelling profiles based on the dynamical theory of electron diffraction
-emission channeling investigations of the lattice location of Li in Ge
The -emission channeling and blocking technique is a direct method for lattice site determination of radioactive atoms in single crystals. Position-sensitive detection of emitted -particles provides an efficient means of carrying out such experiments at very low doses (10-10 implanted probe atoms per spectrum). Comparison of the experimental data to Monte Carlo simulations of complete two-dimensional channeling patterns (e.g. ±2°C around , and axes, which also includes all relevant planar directions) allows for straight-forward identification and rather accurate quantitative determination of occupied lattice sites, while at the same time the energy spectrum of emitted a particles gives information on the probe atom depth distribution. We illustrate this for the case of ion implanted Li (t_=0.8 s) in Ge, where we identify mainly tetrahedral Li at room temperature, and bond-centered Li at slightly elevated temperature
Lattice sites of ion-implanted Li in diamond
Published in: Appl. Phys. Lett. 66 (1995) 2733-2735
citations recorded in [Science Citation Index]
Abstract: Radioactive Li ions were implanted into natural IIa diamonds at temperatures between 100 K and 900 K. Emission channelling patterns of a-particles emitted in the nuclear decay of 8Li (t1/2 = 838 ms) were measured and, from a comparison with calculated emission channelling and blocking effects from Monte Carlo simulations, the lattice sites taken up by the Li ions were quantitatively determined. A fraction of 40(5)% of the implanted Li ions were found to be located on tetrahedral interstitial lattice sites, and 17(5)% on substitutional sites. The fractions of implanted Li on the two lattice sites showed no change with temperature, indicating that Li diffusion does not take place within the time window of our measurements.
Experimental and theoretical study of electronic and hyperfine properties of hydrogenated anatase (TiO): defects interplay and thermal stability
In this study we report on the results from emission Fe
Mssbauer Spectroscopy experiments, using dilute Mn implantation
into pristine (TiO) and hydrogenated anatase held at temperatures between
300-700 K. Results of the electronic structure and local environment are
complemented with ab-initio calculations. Upon implantation both Fe and
Fe are observed in pristine anatase, where the latter demonstrates the
spin-lattice relaxation. The spectra obtained for hydrogenated anatase show no
Fe contribution, suggesting that hydrogen acts as a donor. Due to the
low threshold, hydrogen diffuses out of the lattice. Thus showing a dynamic
behavior on the time scale of the Fe 14.4 keV state. The surrounding
oxygen vacancies favor the high-spin Fe state. The sample treated at
room temperature shows two distinct processes of hydrogen motion. The motion
commences with the interstitial hydrogen, followed by switching to the
covalently bound state. Hydrogen out-diffusion is hindered by bulk defects,
which could cause both processes to overlap. Supplementary UV-Vis and
electrical conductivity measurements show an improved electrical conductivity
and higher optical absorption after the hydrogenation. X-ray photoelectron
spectroscopy at room temperature reveals that the sample hydrogenated at 573 K
shows presence of both Ti and Ti states. This could imply that a
significant amount of oxygen vacancies and -OH bonds are present in the
samples. Theory suggests that in the anatase sample implanted with Mn(Fe),
probes were located near equatorial vacancies as next-nearest-neighbours,
whilst a metastable hydrogen configuration is responsible for the annealing
behavior
Novel method for the production of spin-aligned RI beams in projectile fragmentation reaction with the dispersion matching technique
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