Ion Channeling Measurements Research Articles

Phosphorus ion implantation in type IIA diamond

Low energy phosphorus ions (28 keV) have been implanted into type 2A natural diamond at a temperature of 800°C. Implanted diamond was characterized with 1.4 MeV He ion RBS and channeling measurements. For diamond substrate, the lowest χ min was observed along the 〈110〉 axis ( χ min=9%). For the 〈100〉 and 〈111〉 axes, the χ min was 23% and 28% respectively. For implanted phosphorus, the χ min was 45% for 〈110〉, 65% for 〈100〉 and 60% for 〈111〉. It is considered that the large size difference (43%) between phosphorus and carbon atoms is one of the major factors which prevents phosphorus atoms from obtaining high substitutionality in the diamond lattice.

On the Epitaxy of Metal Films on GaN

ABSTRACTA variety of metal films deposited at room temperature have been found to grow epitaxially under conventional vacuum conditions on GaN grown by metalorganic vapor phase epitaxy on sapphire substrates. The metal films have been characterized by X-ray diffraction using a thin-film Read camera and by MeV ion channeling measurements. Lattice mismatch between the epitaxial metals and the GaN basal planes ranges from ∼ 0.2% to ∼ 22%, and does not appear to be the determining factor in the epitaxy reported here. Surface structure of the epitaxial metal films has been studied by atomic force microscopy and found to differ considerably from that of nonepitaxial metal films grown on similar GaN substrates.

High-quality epitaxial growth of gamma -alumina films on alpha -alumina sapphire induced by ion-beam bombardment.

We report the formation of epitaxial $\ensuremath{\gamma}$-alumina thin films on $\ensuremath{\alpha}$-alumina substrates induced by ion-beam bombardment. Single-crystal (0001) $\ensuremath{\alpha}$-alumina was coated with 70-nm amorphous-alumina thin films and then bombarded with either 360-keV argon ions or 180-keV oxygen ions at 400, 500, and 600 \ifmmode^\circ\else\textdegree\fi{}C. Ion-channeling measurements showed a consistent minimum yield of 50% for the aluminum in the grown films. Crosssectional transmission-electron microscopy revealed the formation of $\ensuremath{\gamma}$-alumina epitaxially grown onto $\ensuremath{\alpha}$-alumina with an orientation relationship $[1\overline{1}0](111)\ensuremath{\gamma}\ensuremath{\parallel}[01\overline{1}0](0001)\ensuremath{\alpha}$. The epitaxy of $\ensuremath{\gamma}$-alumina was further confirmed by x-ray-diffraction $\ensuremath{\varphi}$ scans. This study indicates that ion-beam bombardment at 400-600 \ifmmode^\circ\else\textdegree\fi{}C not only induces the amorphous-to-$\ensuremath{\gamma}$ phase transformation but also effectively eliminates {111} twins of $\ensuremath{\gamma}$-alumina, which are normally observed after thermal annealing at 800-900 \ifmmode^\circ\else\textdegree\fi{}C.

Mössbauer spectroscopy investigation of body centered cubic Co in Co/Fe superlattices prepared with MBE

A new spectrum component is observed in Mossbauer spectra of thin body centered cubic Co layers prepared in Fe/Co superlattices doped with57Co. It is characterized by a large magnetic hyperfine field (31.2 T) and an isomer shift nearly equal to that of α-Fe. The decrease of the isomer shift in bcc Co with respect to hcp Co is consistent with smaller s to d charge transfer in bcc Co as compared to hcp Co. The cubic structure of the CoFe superlattices is evidenced with X-ray diffraction and ion-channeling measurements. The Fe/Co interface is investigated with conversion electron Mossbauer spectroscopy. It is shown that the interface alloy thickness is about six monolayers for growth temperatures up to 450 K and that increasing alloying occurs for higher growth temperatures.

Characterization of homoepitaxial diamond films by nuclear methods

Isotopically marked 13C diamond films were deposited by microwave-plasma-assisted chemical vapour deposition homoepitaxially on {100} and {111} natural diamond substrates. The deposition was performed at 0.5 and 1.5 vol.% 13CH4 diluted in H2. In order to study the influence of nitrogen on diamond growth, N2 was admixed with the process gas for some samples. The thickness of the homoepitaxial films was determined by Rutherford backscattering, the crystalline quality by ion channelling measurements and hydrogen concentrations by nuclear reaction analysis. The defect density and growth rate of {111} films were found to increase at the higher methane concentration. The growth rate of {100} films also increased, but the defect density decreased at the higher methane concentration. The admixture of nitrogen with the process gas yielded about 25% higher growth rates and better crystalline qualities.

Epitaxial regrowth of ruby on sapphire for an integrated thin film stress sensor

The formation of thin film ruby by the epitaxial growth of Cr-doped amorphous alumina on sapphire is described. The incorporation of Cr onto the Al cation sites has been found by ion channeling measurements. It is also confirmed by the observation of the R1 and R2 luminescence lines characteristic of ruby. The frequency of the R lines shift linearly with applied stress and the piezo-spectroscopic coefficient is the same as for bulk ruby.

Magnetic Phase Transition in the Csci Fesi Spacer in Fe/FeSi Multilayers

ABSTRACTWe report the formation of the CsCI FeSi phase in Fe/FeSi multilayers with constant Fe thickness and varying FeSi layer thickness. The crystallographic and magnetic properties of this metastable FeSi phase are determined in thick (62 nm) epitaxial silicide layers with ion channeling, X-ray diffraction and Mossbauer spectroscopy measurements which clearly show that the CsCl phase becomes increasingly magnetic upon cooling down to 4.2 K. These results indicate that the transition from antiferromagnetic to ferromagnetic coupling observed at low temperatures in such multilayers is controlled by a magnetic phase transition in the FeSi spacer layer.

Influence of Crystal Strain on Superconductivity of a-Axis Oriented YBa2Cu3Ox Films

Ion channeling measurements were executed to evaluate the crystal strain in a-axis oriented YBa2Cu3Ox (YBCO) films with different film thicknesses. The average Ba-Ba distance in the film plane as determined from the channeling angle of the Ba atomic row in the <110> (and <301>) direction was found to be close to the lattice constant of the SrTiO3 substrate regardless of the film thickness. A similar result was also obtained for oxygen atoms. These results indicate that the films grow while matching their lattice constant to that of the substrate. The simultaneous strain relief induced by the increase in film thickness was suggested from the channeling yield in the obtained dip curve. Furthermore, the relaxed grain was confirmed near the surface of the 3500 Å film from the Ba <301> axial channeling. The influence of the crystal strain on the superconductivity of the a-axis oriented YBCO films is explained on the basis of variation in the site of apical oxygen.

Thermal stability of highly Sb-doped molecular beam epitaxy silicon grown at low temperatures: Structural and electrical characterization

The structural and electrical properties of highly Sb-doped molecular beam epitaxy grown silicon have been investigated as function of rapid thermal annealing (RTA) temperature. Doping levels of 3×1020 cm−3 were obtained using low temperature epitaxy (LTE) performed at a growth temperature of 300 °C. Ion channeling and transmission electron microscopy (TEM) measurements showed that the as-grown samples were of very high quality. The combination of Hall-effect profiling and Rutherford backscattering spectroscopy revealed an electrically active Sb fraction of 0.8. Short time RTA processing improved the electron mobility and the activation: RTA at 600 °C for 10 s yielded unity activation and RTA at 800 °C gave mobilities matching phosphorus doped bulk values, thus significantly exceeding previously reported values for highly doped LTE material. A degradation of the crystalline quality was observed for higher RTA temperatures: RTA at 1000 °C for 10 s reduced both the Sb-substitutional fraction and electrical activation to 0.6 due to precipitation of Sb, and lead to the formation of a high density of dislocation loops as observed by TEM. A large fraction of the precipitates decorated these dislocation loops. Mesa isolated diodes were fabricated to evaluate the use of LTE material for device production. Current–voltage measurements on these diodes revealed high quality junctions with low reverse currents and near-ideal forward characteristic.

Low-temperature homoepitaxial growth on Si(111) mediated by thin overlayers of Au

High quality homoepitaxial growth of Si on Si(111) through an overlayer of Au is shown to occur at 450–500 °C, far below the temperature required for growth of Si of similar quality on bare Si(111). Films of unlimited thickness can be obtained with excellent crystalline quality, as revealed by Rutherford backscattering spectrometry ion channeling measurements (χmin=2.2%). A distinct range of Au coverage (0.4–1.0 monolayer) results in the best quality epitaxy, with no measurable amount of Au trapped at either the interface or within the grown films. Cross-sectional transmission electron microscopy reveals that in films grown with Au coverages below and above the optimum range, the predominant defects are twins on (111) planes and Au inclusions, respectively.

Electron microscopic and ion scattering studies of heteroepitaxial tin-doped indium oxide films

The microstructure of heteroepitaxial tin-doped indium oxide (ITO) films were studied in detail. The surface morphology of the heteroepitaxial ITO film consisted of square-shaped, in-plane oriented subgrains (∼300 Å) in contrast to that of the polycrystalline film (characteristic grain-subgrain structure). The subgrain boundaries were predominantly formed along the {110} planes in the ITO film and dislocations were observed primarily along the subgrain boundaries. Ion channeling measurements showed the dislocation density of this film to be approximately 3×1010/cm2, and the angular distribution of the ion channeling yield showed that the subgrains are aligned to within better than 0.3° (standard deviation).

Epitaxial growth of Fe-doped sapphire thin films from amorphous Al oxide layers deposited on sapphire substrates

Thin films of amorphous Al2O3, about 280 nm thick, with Fe-cation concentrations of 0–4 at. % were deposited onto alpha-alumina [0001] substrates. Epitaxial regrowth of the thin films was found to occur during a postannealing process at temperatures of 950 and 1400 °C. The regrowth quality was determined by Rutherford backscattering spectrometry and ion channeling measurements. Perfect regrowth was found in the undoped samples after annealing at 1400 °C with a minimum backscattering yield of 2% in the Al sublattice. Furthermore, ion channeling angular scans revealed that Fe dopants occupied the substitutional sites of Al sublattice upon thermal anneal. This simple method of incorporating dopants into single-crystal alumina has potential in the fabrications of thin-film planar optical waveguides.

Damage induced in LiNbO3 single crystals by GeV gadolinium ions

Single crystals of LiNbO3 with two different orientations (Y-cut and Z-cut) have been irradiated at GANIL with 5.17 MeV/amu 155Gd ions at room temperature. The fluence extended from 1.5 × 1011 to 1.2 × 1012 ions cm−2. The damage resulting from the high electronic stopping power (up to 30 keV/nm) has been characterized by both Rutherford backscattering ion channeling (RBS-C) and optical absorption measurements. By using a dégrader, the defect efficiency has also been investigated as a function of the electronic stopping power (18 keV/nm < (dE/dx)e < 30 keV/nm). The results show a defect creation by ionization process and for the highest electronic stopping powers a damage cross section of ∼ 8.5 × 10−13 cm2, corresponding to a mean track radius of about 5 nm. Surface swelling of the irradiated surfaces was measured using a surface profilometer and the height of the out-of-plane step was correlated with the damage induced by the high electronic energy losses.

Density of amorphous Si

The density of amorphous Si has been measured. Multiple Si implants, at energies up to 8.0 MeV, were made through a contact mask to produce alternating amorphous/crystalline Si stripes with amorphous thicknesses up to ∼5.0 μm. For layers up to 3.4 μm (5 MeV), the amorphous Si is constrained laterally and deforms plastically. Above 5 MeV, plastic deformation of the surrounding crystal matrix is observed. Height differences between the amorphous and crystalline regions were measured for as-implanted, thermally relaxed, and partially recrystallized samples using a surface profilometer. Combined with ion channeling measurements of the layer thickness, amorphous Si was determined to be 1.8±0.1% less dense than crystalline Si (4.90×1022 atom/cm3 at 300 K). Both relaxed and unrelaxed amorphous Si show identical densities within experimental error (&amp;lt;0.1% density difference).

Incorporation of Iron Cations Into Epitaxial Sapphire Thin Films by CO-Evaporation and Subsequent Thermal Annealing

AbstractIron-doped sapphire thin films have been successfully epitaxially grown onto sapphire single crystal substrates by electron beam deposition and subsequent thermal annealing. Amorphous A12O3 thin films, about 280–390 nm thick, cation doped with iron have been deposited on [0001] oriented sapphire substrates. Iron doping with cation concentrations (a ratio of Fe content to total cation content) up to 5 at.% can be incorporated into the octahedral sites of Al-cation sublattice during the epitaxial regrowth process at 1000–1400 C, as determined by Rutherford Backscattering Spectrometry and ion channeling measurements. Cross-sectional Transmission Electron Microscopy shows the presence of two distinct regions in the annealed films. One exhibits the epitaxial relationship with the sapphire substrate and the second region has amorphous type of contrast. External optical transmittance measurements in the ultra violet and visible light range have exhibited the absorption associated with Fe3+. This study has demonstrated a simple method of incorporating dopants into single crystal sapphire, which has potential in the fabrications of thin film planar optical waveguiles.

Backscattering spectrometry and ion channeling studies of heavily implanted As+ in silicon

Backscattering and ion channeling measurements have been carried out on 〈100〉 silicon wafers implanted with a dose of 3×1016 As+/cm2. These samples have been submitted to laser annealing and then to various thermal annealings in the 350–1000 °C temperature range. Three different crystallographic directions, 〈100〉, 〈110〉, and 〈111〉, have been explored. The deactivated As atom displacement with respect to the lattice sites has occurred already by the first stage of electrical deactivation at 350 °C. The average displacement is constant in the considered temperature range and has been found equal to 0.23±0.06 Å making an angle of 23±8° with the [100] direction. By comparing this finding with the local atomic As arrangement, deduced from previously reported extended x-ray absorption fine structure measurements performed on the same samples, new cluster models are presented. These models consist of As2V and As4V clusters during the very early stage of deactivation, and of several As4V clusters grouped together giving rise to larger AsmVn agglomerates (m up to 12 and n up to 5). In this context, the average As displacement mainly results from the combined displacements of As atoms inside the clusters. The thermal evolution of the As agglomerates at higher temperatures is also discussed.

Allotaxial growth of single-crystal Si/CoSi 2/Si(100) heterostructures

Monocrystalline buried layers of CoSi 2 in a Si(100) matrix have been grown by a new technique, named allotaxy. This is a two-step process, including the epitaxial growth of the Si host matrix with CoSi 2 precipitates and a high-temperature anneal. Si/CoSi 2/Si(100) heterostructures of different thickness were produced using various growth parameters and annealing temperatures and were characterized by RBS, ion channeling, TEM, X-ray diffraction and resistivity measurements. The quality of the produced epitaxial buried CoSi 2 layers is comparable with the best layers produced by ion-beam synthesis.

Specific behaviour of CdTe ion implantation damage

In order to study the damage produced as a function of both the chemical nature of the ion and the implantation energy, [111] CdTe single crystals were implanted with 150 keV Mn and 50, 100 and 200 keV P ions. Analysis of the damage was carried out by Rutherford backscattering spectrometry and ion channeling measurements using 4He beams at different energies. These measurements show that the disorder induced by ion implantation in CdTe exhibits specific features: (i) saturation of damage without reaching the amorphous state; (ii) existence of an almost undamaged near-surface region. In fact, whatever the implantation conditions, the normalized channeling yield (which is a measure of the integrated disorder) reaches the value of 0.6–0.7 at saturation and the low damaged layer depth is about 40 nm thick. The channeling measurements are consistent with a previous study in which the residual damage was identified as small-sized dislocation loops mainly located beyond the ion projected range R P . These results are interpreted as indicating a high mobility of defects in CdTe together with a high efficiency of the surface in their recombination process, and the role played by the dislocation-loop-induced stress.

Ion Channeling Study of SrTiO3 Substrates and As-Deposited YBa2Cu3Ox Thin Films

The crystalline quality (perfection or imperfection) of SrTiO3 substrates and subsequent as-deposited YBa2Cu3Ox superconducting films has been investigated by a high-energy ion channeling technique. Analysis was performed as a function of depth, especially at 3 typical depth regions (surface, inside, interface), to clarify junction ordering features between substrates and films. Based on ion channeling measurements, it has been found that (1) disorders of substrates affect crystalline quality of films greatly at the interface regions, (2) the film reorders over a proper amount of YBa2Cu3Ox disordered layers (as in buffer layers), (3) the film consists of an almost single domain. The crystalline quality of some SrTiO3 substrates widely used in Japan has also been investigated and the common characteristics of distortions along the c-axis have been found.

Heteroepitaxial Growth of Strontium Titanate on Lanthanum Aluminate Using the Metallo-Organic Decomposition Technique.

ABSTRACTWe demonstrate the heteroepitaxial growth of thin films of SrTiO3 prepared by the method of Metallo-organic decomposition on LaAlO3 substrates. The SrTiO3 films are prepared by spin coating and thermal decomposition of a solution of Metallo-organic precursors on single-crystal, &lt;100&gt; oriented, LaAK&gt;3 substrates. Subsequent heat treatment at 1100 – 1200 °C for 1 h results in the epitaxial alignment of the SrTiO3 films with respect to the LaAlO3 substrate.The degree of alignment of the films appears to depend on their thickness, with thinner films showing better alignment (as determined by ion-channeling measurements). This behavior is interpreted as a result of the competition between solid-phase epitaxy and random nucleation, observed during the crystallization of films prepared by Metallo-organic decomposition. However, since thinner films have been prepared by dilution of the precursor solution, there is also the possibility that the concentration of the precursor solution may influence the crystallization behavior of the films.The potential influence of the precursor formulation on the crystallization mechanism is discussed.