J.C. Soares

TRANSPORT AND PHOTOLUMINESCENCE OF HYDROGENATED AMORPHOUS SILICON-CARBON ALLOYS

The optoelectronic properties of hydrogenated amorphous silicon–carbon alloys (a‐SiC:H) are studied over the entire compositional range of carbon content. The films are prepared using radio‐frequency glow discharge and optimization was made with respect to deposition power and pressure, hydrogen dilution, and methane (or ethylene) ‐to‐silane gas phase ratio. Regardless of the deposition conditions and source gases used, the optical, structural, and transport properties of the a‐SiC:H alloys followed simple universal dependencies related to changes in the density of states associated with their structural disorder. The Urbach tail energy Eu and the B factor of the Tauc plot correlate with E04 (defined as the energy at which the absorption coefficient is equal to 104 cm−1) taken from photothermal deflection spectroscopy measurements. Up to E04pds≊2.6 eV, Eu increases monotonically from 50 up to ≊200 meV, while the B factor decreases from ≊800 down to ≊200 cm−1/2u2009eV−1/2. Above E04pds≊2.6 eV, both Eu and B re...

Incorporation and stability of erbium in sapphire by ion implantation

Abstract Precise results on the lattice site location and stability of Er implanted sapphire using the RBS/channeling technique are reported. The Er ions were implanted into 〈0001〉 and 〈01 1 0〉 cut samples of α-Al2O3 single crystals, at room and liquid nitrogen temperatures, with 200 keV energy at fluences between 8 × 1013 and 4 × 1015 Er+/cm2. The implantation of 8 × 1013 Er+/cm2 (0.01 at%) at room temperature leads to the incorporation of 70% of the Er ions near the free octahedral site (0.8 A displaced) along the c-axis. From the remaining fraction of Er ions, at least 20% can be in a tetrahedral site. At liquid nitrogen temperature the fluence of 6 × 1014 Er+/cm2 amorphizes sapphire, while at room temperature a fluence an order of magnitude higher produces only a damaged buried layer. The annealing at temperatures higher than 1200°C leads to the recrystallization of the amorphous layer, but the Er ions segregate to the surface or precipitate. For the samples implanted at room temperature, the annealing leads to a higher incorporation of Er in the sapphire lattice and only a small fraction segregates to the surface at 1500°C.

Lattice location of Tl and diffusion studies of Tl and Hf implanted in magnesium

Abstract The diffusion behavior of thallium and hafnium implanted in magnesium single crystals and the lattice location of thallium in magnesium were studied using the Rutherford backscattering/channeling technique. Annealing treatments in a helium atmosphere were carried out up to 875 K. The results obtained show that, in spite of both impurities being fully substitutional in the magnesium lattice, their diffusion coefficients are completely different, D Tl ⩾ (9 ± 7) × 10 −13 cm 2 s at 563 K, and D Hl = (12 ± 7) × 10 −15 cm 2 s at 875 K. A tentative explanation for these results is presented.

Characterization of alpha sources by Rutherford backscattering spectrometry

Radioactive sources for alpha spectrometry are usually prepared by electrodeposition onto stainless steel backings (and sometimes heated). In earlier work, using the conventional method with passivated implanted planar silicon detectors for the measurements, several sources had been characterized in terms of various parameters by fitting the data of each spectrum to a certain mathematical function. In the present work, the Rutherford Backscattering Spectrometry (RBS) technique with a 1.6 MeV He+ beam was used to study the influence of those factors on the surface distribution and depth profiles of the thin radionuclide layers. Simulations of the measurements using the RUMP computer code were made to interpret the data obtained in the different experiments. The correlations between the parameters measured using RBS and the results of the alpha spectrometry are presented and discussed.

Lattice location of Er in GaAs and Al0.5Ga0.5As layers grown by MBE on (100) GaAs substrates

Abstract The lattice site location of Er in semiconducting materials received considerable interest because its 4 I 13 2 −4 I 15 2 intra-4f shell luminescence, occuring at a wavelength of 1.54 μm, falls in the minimum absorption window for silica-based fibers. In the present work, results of a study of the lattice location of Er in GaAs:Er and Al 0.5 Ga 0.5 As:Er using the Rutherford backscattering/channeling method are presented. The GaAs:Er and Al 0.5 Ga 0.5 As:Er layers were approximately 1.6 μm thick and were grown by conventional elemental source molecular beam epitaxy on (100) GaAs substrates. These samples, with Er concentrations of the order of 10 19 to 10 20 cm −3 , presented intense photoluminescence. The RBS/channeling results show that Er atoms are located in the tetrahedral interstitial site in GaAs:Er, and about 70% of the Er atoms are slightly displaced from that site in Al 0.5 Ga 0.5 As:Er, the rest being in substitutional sites. For comparison an epitaxial Al 0.5 Ga 0.5 As:Er layer with Er concentration of the order of 10 18 cm −3 which does not show photoluminescence has been analysed. In this case there is clear evidence that Er is substitutionally located.

Diffusion and corrosion behaviour of tungsten-implanted Aluminium and the Al12W phase

Abstract Depth profiles of tungsten implanted into aluminium were studied as a function of the annealing temperatures using the Rutherford backscattering technique. The formation of the Al12W metastable alloy starts at a temperature of 450° C. Electrochemical corrosion studies show a shift in the corrosion potential of + 600 mV for the as-implanted samples relative to the nonimplanted ones. This shift is 50 mV lower for samples where the Al12W metastable alloy has been formed. However, the implanted samples show higher corrosion rates than the nonimplanted ones.

Ion beam mixing of chromium or zirconium films with sapphire

Abstract Ion beam mixing of thin metallic films deposited on sapphire substrates was studied for Cr or Zr films deposited on singlecrystal α-Al2O3 substrates. Evidence for the influence of equilibrium thermodynamic factors was sought by comparing the effects of bombarding with O ions (300 and 1073 K) with those of bombarding with Ne ions (300 K). Thermodynamic calculations indicate that mixing might occur for Zr/sapphire at 1073 K but not at 300 K. On this basis, Cr/sapphire should not mix at either temperature. The implantation energy placed the peak O concentration at the metal-sapphire interface in an attempt to maintain an equilibrium ratio of cations to anions to promote a radiation-induced chemical reaction across the interface. No evidence for long-range mixing was found from Rutherford backscattering-ion channeling measurements. Other experiments employed a heavier ion (Kr) as the mixing ion (300 K) in order to increase the mixing efficiency. Rutherford backscattering-ion channeling and X-ray photoelectron spectroscopy (XPS) were used to determine the extent and nature of any interface modification. The XPS results indicated that only metallic Cr was present near the interface in the as-deposited specimens and in those irradiated with Kr at 300 K. Zirconium exhibited only the metallic state (Zr0) in the as-deposited film but was present as both Zr0 and Zr4+ after irradiation. Some metallic Al (Al0) was detected near the Zr-sapphire interface after irradiation, suggesting that a local chemical reaction between Zr and the sapphire may have occurred during bombardment. No long-range material transport was detected for any experimental condition examined; the width of the “mixed” region in each case was below the limits of detection for RBS or consistent with that expected for ballistic effects.

A comparative study of CoRe superlattices sputtered on glass and Si substrates by grazing angle of incidence RBS, HRTEM, PAC, magnetic and transport properties studies

Abstract The thickness, interface sharpness and microscopic structure of Co/Re superlattices are measured by Rutherford backscattering spectrometry using grazing angle of incidence, high resolution transmission electron microscopy and perturbed angular correlations. A comparative study of structural, magnetic and transport properties as a function of the glass or silicon substrate is reported.

Hyperfine interactions and Rutherford backscattering studies of Cd and Hg in CdTe single crystals and thin films

Abstract First results obtained with the e−-γ PAC technique recently installed at CERN/ISOLDE and Rutherford backscattering measurements for as grown and 111mCd and 197mHg implanted CdTe single crystals and thin films are presented. Both probes, Cd and Hg, have a completely different behavior. While most of the Hg atoms have a cubic surrounding in the CdTe lattice, after ion implantation only a small fraction of the Cd atoms occupy regular lattice sites without defects even after high temperature implantation or furnace annealing.

Vacancy-acceptor complexes in germanium produced by ion implantation

Abstract Combining results obtained by the γ-γ perturbed angular correlation method, Rutherford backscattering and elastic recoil detection of hydrogen, a defect complex formed in germanium by indium implantation is identified as a vacancy trapped by the indium probe.