Lattice Location Of Impurities Research Articles

Raman and Rutherford Backscattering Characterization of Ti-implanted Si above the Mott Limit

AbstractWe have analyzed the degree of crystalline lattice recovery in samples implanted with Ti concentrations well above the Mott limit and subsequently Pulsed-Laser Melting (PLM) annealed by means of Raman spectroscopy and Rutherford Backscattering Spectroscopy (RBS). Since very recently, theoretical studies predicted Ti interstitial sites for the Intermediate Band (IB) formation, the knowledge of the Ti impurity lattice location after PLM annealing is an essential point that can be elucidated by means of RBS measurements. After PLM annealings, Raman and RBS measurements have shown a decrease in the lattice crystalline quality as implanted dose is increased, yielding a significantly improvement of the lattice quality at the highest energy density studied. The RBS channeling spectra show that after PLM annealings Ti impurities are mostly occupying interstitial lattice sites.

Annealing reactions in lead implanted copper

The terminal solubility of Pb in Cu is extremely low and does not exceed 0.09 at.% at 875 K. Ion implantation of lead ions at 100 keV into Cu single crystals produces metastable solutions. Annealing of the samples causes redistribution of the implanted atoms to equilibrium or near-equilibrium aggregate states which may be reflected in a change in the type of impurity lattice location in the host matrix. We have studied the effect of annealing on single crystalline Cu implanted at temperatures around 375 K with Pb to a concentration of a 1–2 at.%. Rutherford backscattering/channeling analysis and transmission electron microscopy of the as-implanted samples have shown that the implanted Pb forms a supersaturated solid solution with a major fraction of the Pb atoms located on substitutional sites in the host lattice or in very small clusters. At higher annealing temperatures up to 870 K more than half of the lead is lost by outdiffusion and the remaining fraction forms nanometer-sized crystalline inclusions by cooling to room temperature. Melting and solidification temperatures of the inclusions have been followed by in situ channeling measurements.

Incorporation of hexavalent impurities into LiNbO3

The influence of the valence state on the lattice location of impurities in lithium niobate LiNbO3 crystals was investigated using hexavalent dopants (W6+ and U6+) introduced by doping of congruent melt. The distribution coefficients were determined by Rutherford Backscattering Spectrometry to be k = 0.2 for W and k = 0.07 for U. Channeling studies showed that the hexavalent impurities are located on the Nb site in both cases. The preferential occupation of Nb sites suggests that the formation of Li-vacancies is favored. This result is a strong evidence for the Li-vacancy defect model for congruent LiNbO3.

Nuclear reaction channeling

Nuclear reaction channeling (NRC) provides a tool for the investigation of concentration and lattice location of impurities in a crystal. In this work NRC is applied to the analysis of light element impurities (B, C, N, O) in semiconductor materials (GaAs, Si). Depending on the nuclear reaction used for the investigation, concentrations below 100 ppma are analysed. The channeling angular scans in different crystalline directions allow to specify the site of the impurities up to a range of the thermal vibration amplitude of the host crystal. These results are deduced from the MABIC simulation code.

Impurity lattice location and recovery of structural defects in semiconductors studied by emission channeling

Doping of semiconductors by ion implantation usually requires implantation doses below 1013 cm−2 to obtain typical impurity concentrations of <1018 cm−3. The lattice location of impurities as well as the defect recovery after such low dose implantations can be studied using the emission channeling technique. In this technique, single crystals are doped with radioactive probe atoms and the channeling effects of electrons, positrons or α-particles emitted from these atoms are measured. We present a quantitative analysis of electron emission channeling measurements after heavy-ion implantation into Si and III–V compound semiconductors by comparison with calculated channeling profiles based on the dynamical theory of electron diffraction. For In atoms implanted into Si, complete substitutionality was found after rapid thermal annealing to 1200 K. For lower annealing temperatures, the observed channeling effects indicate small mean displacements (of about 0.2 A) of the In atoms from substitutional sites, caused by residual implantation defects. For GaAs, GaP and InP implanted at low temperatures with In or Cd isotopes, pronounced recovery stages around 300, 400 and 350 K, respectively, were observed and substitutional fractions close to 100% were derived after annealing above the stage.

Angle-resolved imaging of single-crystal materials with MeV helium ions

Abstract The simplest form of angle-resolved mapping for single-crystal materials is the creation of a channeling angular scan. Several laboratories have expanded this simple procedure to include mapping as a function of two independent tilts. These angle-resolved images are particularly suited to the assessment of crystal parameters including disorder, lattice location of impurities, and lattice stress. This paper will describe the use of the Charles Evans & Associates RBS-400 scattering chamber for acquisition, display, and analysis of angle-resolved images obtained from backscattered helium ions. Typical data acquisition times are 20 min for a ±2° X-Y tilt scan with 2500 pixels (8/100° resolution), and 10 nC per pixel. In addition, we will present a method for automatically aligning crystals for channeling measurements based on this imaging technology.

Lattice disorder and behavior of implanted atoms in In-implanted TiO 2 (rutile)

The lattice disorder and lattice location of impurities in In-implanted TiO 2 have been investigated by the RBS-channeling method. In + ions were implanted at room temperature at 100 keV with various doses from 10 14 to 10 14/cm 2. Lattice disorder was observed as a peak consisting of two subpeaks in the aligned spectra. These peaks were interpreted as due to radiation damage and the presence of In atoms. The maximum in the lattice disorder saturated at a dose of around 2 × 10 15/cm 2. Recovery of the disorder proceeded through two annealing stages; around 650 K and above 1000 K. For a dose below the saturation dose, most of the In atoms were located at Ti substitutional sites and the remaining atoms at 0 0 1 4 sites. With increasing dose, the fraction of 0 0 1 4 site occupancy increased. For a dose higher than 2 × 10 15/cm 2, almost all In atoms were at random sites. Observation after annealing at 973 K revealed the disappearance of 0 0 1 4 site occupancy. This occupancy is discussed in terms of the interaction of In with the defects introduced during implantation.

Characterization of Defects and Interfaces by the Ion Channeling Technique

AbstractChanneling of fast, light ions in crystals has been widely used as a tool for studying crystal defects. This subject has been reviewed earlier at MRS-1980. During MRS-1980, principles of ion channeling, and examples of channeling analysis on bulk defects and surface structures, lattice location of impurities, and clustering phenomena were given. In this review, we give a brief overview of defect studies by the channeling technique and then elaborate on recent developments in channeling analysis of interfacial structure. The ion beam channeling technique permits characterization of heteroepitaxial growth starting at monolayer coverages and allows quantitative measurement of the lattice strain in heteroepitaxial layers. The strain analysis has been developed for multilayer structures and, for example, the tetragonal distortions of strained-layer superlattices can be determined for lattice mismatches as low as 0.2% corresponding to lattice distortions of 0.01Å.

Impurity lattice location in ion-implanted beryllium: Measurements and systematics

As part of a program to examine the ion implantation process in metals, the lattice location of 24 elements implanted into beryllium has been studied using the ion-beam channeling technique. A qualitative inspection of the data showed that the major fraction of all implants, except H and He, occupy a highly unique site in the vicinity of either the substitutional, the tetrahedral interstitial, or the octahedral interstitial position in the Be lattice. Quantitative comparisons of the data were made with the results of analytical calculations in the continuum model of the channeling process as well as with the results of a Monte Carlo computer simulation using the binary collision model. Classical metallurgical parameterizations, such as Darken-Gurry plots fail to adequately account for observed impurity site preference. Elemental parameters devised by Miedema have however been successful in relating choice of lattice site to the properties of the impurity relative to those of Be.

Impurity Lattice Location Using Channeling Effect

Impurity Lattice Location Using Channeling Effect

Study of the rare-earth-oxygen interaction in iron by lattice location and perturbed-angular- correlation experiments

In a study of the rare-earth-oxygen interaction in iron, lattice location and integral perturbed-angular-correlation experiments were performed after implantation of Yb and $^{16}\mathrm{O}$ in iron single crystals and foils. The ion-implantation energies were chosen so that the depth profiles overlapped almost completely. A strong Yb-O interaction is evidenced in both types of experiments. However, its effects on channeling results and on hyperfine-interaction measurements are found to be entirely different: In the present case, the usually assumed simple corespondence between impurity lattice location and hyperfine-field values certainly does not hold. The results are discussed in the light of a simple statistical model for the interaction probability between rare-earth and oxygen atoms.

Distribution across the channel of defects induced by nitrogen bombardment in silicon

Silicon crystals have been implanted at room temperature with 3.2×1015 ions/cm2 of 300-keV N+. The spatial distribution of displaced atoms has been determined by the backscattering energy spectra as a function of the crystal tilting angle with respect to the 〈111〉 axis. The changes in the extracted depth profiles have been correlated to the nonuniform distribution of defects across the channel. The radial distribution of displaced atoms has been determined on the basis of the flux-peaking treatment for impurity lattice location.

Positive−ion−induced Kossel lines in copper

Proton beams have been used to generate Kossel lines in single crystals of copper by the excitation of characteristic radiation at atomic sites inside the crystals. The observed lines exhibit a fine structure similar to lines previously generated using incident electrons and x rays. A key advantage of the positive−ion technique is that the bremsstrahlung background associated with the electron generation of Kossel lines is eliminated. The possible application of the positive−ion technique to impurity lattice location is discussed.

Observation of internal x-ray wave fields during Bragg diffraction with an application to impurity lattice location

By a simple extension of a previous experimental technique we demonstrate how the detailed standing-wave features of the internal x-ray wave field during the diffraction process may be observed even when a strong reflection occurs. The preliminary results reported here indicate that dynamical diffraction may be developed as a useful lattice-location technique in nearly perfect crystals.