2 MeV Si ion implantation damage in relaxed Si1−xGex

The damage produced by implanting, at room temperature, 3 μm thick relaxed Si_1−xGe_x layers with 2 MeV Si⁺ ions has been measured as a function of Ge content (x = 0.04, 0.13, 0.24 or 0.36) and Si dose in the dose range 10¹⁰–10¹⁵ cm⁻². The accumulation of damage with increasing dose has been studied as a function of Ge content by Rutherford Backscattering Spectrometry, Optical Reflectivity Depth Profiling and Transmission Electron Microscopy and an increased damage efficiency in Si_1−xGe_x with increasing x is observed. The characteristics of implantation-induced defects have been investigated by Electron Paramagnetic Resonance. The results are discussed in the context of a model of the damage process in SiGe.     

Stopping powers of Al and Cu for protons from 3 TO 9 MeV

The stopping powers of Al and Cu for protons having energies from 3 to 9 MeV have been measured with an accuracy of ± 0.4%. The results have been compared with the Risø and the Aarhus data of Andersen et al. and with Tschalär's data for Al. The mean excitation energies have been extracted from the present results using the Bonderup shell correction, the Barkas correction and the Bloch correction as 167.4 ± 0.5 eV for Al and 326.3 ± 0.6 eV for Cu. A set of parameters χ = 1.340 and b = 1.26 was used in these determinations. By using the mean excitation energies thus determined, the Bonderup shell corrections, the Barkas corrections and the Bloch corrections, stopping powers have been calculated up to 30 MeV for Al and up to 20 MeV for Cu. The calculated stopping powers agree very well with the Aarhus data. For A1, the agreement between the calculated stopping powers and Tschalär's data is surprisingly good up to 30 MeV.     

Carbon clustering in Si1−xCx formed by ion implantation

Silicon-carbon alloys were formed by multiple energy implantation of C⁺ ions in silicon and in Silicon on Sapphire (SOS). The ion fluence ranged between 5 × 10¹⁶ − 3 × 10¹⁷ ions/cm² and the energy between 10–30 keV in order to obtain constant carbon concentration into a depth of 100 nm. The carbon atomic fraction (x) was in the range 0.22–0.59 as tested by Rutherford backscattering spectrometry (RBS). Thermal annealing of the implanted films induced a transition from amorphous to a polycrystalline structure at temperatures above 850°C as detected by Infrared spectrometry (IR) in the wavenumber range 600–900 cm⁻¹. The optical energy gap and the intensity of the infrared signal after annealing at 1000°C depended on the film composition: they both increased linearly with carbon concentration reaching a maximum at the stoichiometric composition (x = 0.5). At higher carbon concentration the IR intensity saturated and the optical energy gap decreased from the maximum value of 2.2 to 1.8 eV. The behaviour at the high carbon content has been related to the formation of graphitic clusters as detected by Raman spectroscopy.     

Density measurement of amorphous SixGe1 − x alloys

The atomic density of amorphous Si_xGe_{1 − x} alloys (x = 1, 0.85, 0.67, 0.50, 0.20 and 0) has been measured. Mono-crystalline Si_xGe_1−x layers Were implanted with 1.50–2.75 MeV Si²⁺ and Ge²⁺ ions to produce the amorphous material. Using surface profilometry and RBS/channeling, it was found that amorphous alloys are less dense than the crystalline alloys, and that Vegard's law underestimates the a-Si_xGe_1−x density.     

Chemical thermodynamic representation of AmO2−x

The AmO_2−x solid solution data set for the dependence of the oxygen potential on the composition, x, and temperature was retrieved from the literature and represented by a thermodynamic model. The data set was analysed by least-squares using equations derived from the classical thermodynamic theory for the solid solution of a solute in a solvent. Two representations of the AmO_2−x data were used, namely the Am_5/4O₂–AmO₂ and AmO_3/2–AmO₂ solid solution. No significant difference was found between the two, and the Am_5/4O₂–AmO₂ solution was preferred on the basis of the phase diagram. From the results the Gibbs energy of formation of Am_5/4O₂ has been derived.     

Rapid thermal annealing of arsenic implanted relaxed Si1−xGex

The electrical activity and redistribution during rapid thermal annealing (RTA) of high concentrations of As implanted into epitaxially grown, relaxed Si_1−xGe_x for x≤0.5 have been studied as a function of composition x and RTA parameters. At a given RTA temperature the maximum carrier concentration decreases and the redistribution increases with increasing x. Maximum carrier concentrations and junction depths as a function of composition and RTA parameters are given.     

Characterization of Si/GexSi1 − x heterojunction bipolar transistors formed by Ge ion implantation in Si

Epitaxial Si/Ge_xSi_{1 − x} heterojunctions were formed by high dose Ge ion implantation in Si followed by rapid thermal annealing at 1000°C for 10 s. This technique was adopted to fabricate Si/Ge_xSi_{1 − x} heterojunction n-p-n bipolar transistors (HBT) using a self-aligned, double polycrystalline silicon process commonly used for fast Si bipolar transistors. The devices are characterized by a 60 nm wide neutral base with a Ge concentration peak of ≈ 7 at.% at the base-collector junction. Good static and dynamic electrical characteristics are demonstrated and discussed.     

Interferences in electron emission from O2 by 30 MeV O impact

Interference structures in the ejected electron spectra for 30 MeV O^5,8+ + O₂ are investigated. The measured electron yields were studied for electron energies from 5 to 400 eV and observation angles of 30°, 60°, 90°, 120° and 150° with respect to the incident beam direction. Experimental molecular cross-sections were normalized to theoretical molecular one-center cross-sections revealing oscillatory structures suggestive of secondary interferences as evidenced by the independence on the observation angle. An oscillation interval for 30 MeV O^5,8+ + O₂ of Δk ∼ 4 a.u. is found, a value two times larger than that previously observed for 3 MeV H⁺ + N₂. No obvious evidence for primary Young-type interferences was seen.     

RBS investigations of buffer layers between YBa2Cu3O7−x and silicon

The deposition of high-quality high-T_c superconducting films on silicon wafers for future hybrid electronic devices is strongly hampered by the interdiffusion between films and substrate. This effect degrades the superconducting properties seriously and is a strong function of temperature. Since high processing temperatures are inevitable for good films, suitable buffer layers are needed to reduce the interdiffusion. We have investigated the combinations ZrO₂/Si(100), BaF₂/Si(100), and noble-metal/TiN/Si(100) at temperatures up to 780°C in oxidizing ambient. YBa₂Cu₃O_7−x films have been deposited onto the buffer layers by laser ablation. Thereafter the interfaces have been analyzed by Rutherford backscattering. So far only ZrO₂ has demonstrated sufficient stability to serve as a buffer layer for the laser-ablated YBa₂Cu₃O_7−x films. All other combinations suffer from interdiffusion or oxidation.     

Electrical and optical properties of Co ion implanted a-Si1 − xCx:H alloys

Low resistivity a-Si_1 − xC_x:H alloy films have been formed by high dose Co⁺ ion implantation. The influence of the carbon content of the films on the resistivity has been studied and the lowest values, of the order of 10 Ω/Sq, have been observed for the carbon free films. Even lower resistivities, a further reduction of up to 50%, have resulted from annealing at temperatures up to 500°C. Changes in the optical and structural properties of the implanted a-Si_1 − xC_x:H films have been studied by means of IR and Raman spectroscopy. Results show that the implantation produces considerable structural and chemical modifications. The formation of, and the transition to, a possible CoSi₂ phase has been observed by examining the IR and Raman spectra as a function of implant dose.     

Diffusion and strain relaxation in Si/Si1−xGex/Si structures studied with Rutherford backscattering spectrometry

The thermal stability of strained Si/Si_1−xGe_x/Si structures grown by molecular beam epitaxy was investigated by resistive heating and in situ Rutherford backscattering spectrometry. Ge profiles obtained from a 50 nm Si_1−xGe_x layer on a Si(100) substrate capped with 50 nm Si were evaluated for different Ge concentrations after sequential heating periods at a particular temperature between 850 and 1010° C. The diffusion coefficients, calculated from the increase in signal in the tail of the Ge profile, proved to be comparable to the value for Ge in bulk Si. A more pronounced decrease of the signal at the center of the Ge profile indicated a faster diffusion within the SiGe layer which was confirmed by analysis of the FWHM of the Ge profile. Ion channeling measurements were used to characterize tetragonal strain in the buried SiGe layers. Angular scans through the 111 direction were interpreted with Monte Carlo channeling calculations and used to study strain relaxation in dislocation-free and partially relaxed layers.     

A comparative EPR study of ion implantation induced damage in Si, Si1−xGex (x ≠ 0) and SiC

Electron Paramagnetic Resonance (EPR) measurements have been made to investigate the build up of damage in silicon in relaxed crystalline Si_1−xGe_x (x = 0.04, 0.13, 0.24, 0.36) and in 6H-SiC as a result of increasing the ion dose from low levels (10¹² cm⁻²) up to values (10¹⁵ cm⁻²) sufficient to produce an amorphous layer. Si, Si_1−xGe_x (x ≠ 0) and SiC were implanted at room temperature with 1.5 MeV Si, 2 MeV Si and 0.2 MeV Ge ions respectively. A comparison is made between the ways in which the type and population of paramagnetic defects depend on ion dose for each material.     

Sensitivity of trace-element analysis by X-ray emission induced by 0.1–10 MeV electrons

Bremsstrahlung production cross sections have been calculated as a function of target and angle for electrons in the energy range 0.1–10 MeV. Used in conjunction with the corresponding K and L X-ray production cross sections and nonfundamental experimental quantities (detector resolution and ambient background), they allow determination of the theoretical detection limit using K or L X-ray emission induced by direct electron beam excitation.     

Stopping of 0.3-1.2 MeV/u protons and alpha particles in Si

The stopping cross sections ε(E) of silicon for protons and alpha particles have been measured over the velocity range 0.3-1.2 MeV/u from a Si//SiO₂//Si (SIMOX) target using the Rutherford backscattering spectrometry (RBS) with special emphasis put on experimental aspects. A detection geometry coupling simultaneously two solid-state Si detectors placed at 165° and 150° relative to each side of the incident beam direction was used to measure the energies of the scattered ions and determine their energy losses within the stopping medium. In this way, the basic energy parameter, E_x, at the Si/SiO₂ interface for a given incident energy E₀ is the same for ions backscattered in the two directions off both the Si and O target elements, and systematic uncertainties in the ε(E) data mainly originating from the target thickness are significantly minimized. A powerful computer code has been elaborated for extracting the relevant ε(E) experimental data and the associated overall uncertainty that amounts to less than 3%. The measured ε(E) data sets were found to be in fair agreement with Paul’s compilation and with values calculated by the SRIM 06 computer code. In the case of ⁴He⁺ ions, experimental data for the γ effective charge parameter have been deduced by scaling the measured stopping cross sections to those of protons crossing the same target with the same velocity, and compared to the predictions of the SRIM 06 computer code. It is found that the γ-parameter values generated by the latter code slightly deviate from experiment over the velocity region around the stopping cross section maximum where strong charge exchanges usually occur.     

Analysis of structural modifications in γ-irradiated PbO–B2O3–SiO2 glasses by FTIR spectroscopy

The effect of γ-irradiation on the structure of lead borosilicate glasses of varying composition has been probed by FTIR spectroscopy, before and immediately after γ-irradiation. The glasses were irradiated at Calliope ⁶⁰Co plant (RC ENEA Casaccia, Rome), and the spectra were recorded after absorbed doses of 50 Gy, 500 Gy, and 4 kGy. The structural analysis have been made considering both the effect of composition and of irradiation. The experimental results clearly indicate that after irradiation a significant change in structure of borosilicate glass network is observed.     

Micro-RBS characterisation of the chemical composition and particulate deposition on pulsed laser deposited Si1−xGex thin films

The formation and deposition of particulates by pulsed laser deposition of Si_1−xGe_x semiconductor alloy thin films are discussed. Using Rutherford backscattering spectrometry with micrometer lateral resolution (micro-RBS) the film composition was measured with high accuracy, even in the presence of particulates with a high areal density of 20,000–30,000 particulates per mm². We show that on impact of a particulate, the part of the thin film which is already deposited probably melts and its Ge content segregates to the surface.     

Magnetic ordering in superconducting YBa2(Cu1−xFex)3Oy oxide

Magnetic susceptibility measurement and the zero-field muon-spin-relaxation experiment have been made for the YBa₂(Cu_1−xFe_x)₃O_y system. The susceptibility has been measured in the field strong enough for the magnetic flux to penetrate the superconductor and the resultant temperature dependence has demonstrated the field cooled effect and a cusp at low temperatures below T_c. The cusp has been observed when the high field has been applied. The dynamical depolarization rate of the muon obtained by the muon-spin-relaxation experiment has shown the maximum at the same temperature as the cusp. The results suggest that the spin glass freezing of localized magnetic moment takes place at the temperature of the cusp, which is consistent with the previous Mössbauer effect experiments. The magnetic phase diagram for the system has been obtained.     

Silicon detector response to heavy ions at energies of 1–2 MeV/amu

The response of silicon detectors has been measured for He, O, S, Cl, Br, Ag and Pb ions in the energy range 1–2 MeV/amu. Following deliberate, long exposures of the detector, a transient effect was observed for 140 MeV Br ions, in which the pulse height decreased with increasing ion dose and then partially recovered within an hour of the final exposure. Using brief, consecutive exposures, the effective energy for creating a detectable electron–hole pair was determined using the pulse height difference method. The energy deposited by ions in the ‘dead-layer' at the detector surface and energy loss via non-ionizing events was taken into account. For ions with atomic numbers 2Z17 and energies above the Bragg peak, the effective energy was found to decrease linearly with increasing electronic stopping power at first, and then to level off at 3.52 eV/electron–hole pair. For intermediate mass ions (17<Z40), at energies close to the Bragg peak, increases slightly (2%) with increasing stopping power. For the heaviest ions studied (Z40), whose energies are below the Bragg peak of the stopping power curve, increases strongly (10–20%), even though the electronic stopping power is approximately constant.     

Neutron cross-sections of Pu in the energy range 5–20 MeV

The evaluation of neutron cross sections and angular distributions of ²⁴²Pu in the energy range 5–20 MeV was performed using the direct interaction treatment by coupled channel method and the compound nucleus mechanism (statistical model) taking account of pre-equilibrium effects. The calculated cross-sections are in very good agreement with the existing experimental data (total and fission cross-sections). More accurate theoretical data have been obtained by the extension of procedures and parameterizations (previously used only for the main compound nucleus) in the incident neutron energy range where more compound nuclei are involved.     

Determination of the Li/Ni ratio in LixNi1 − xO thin films by PIXE-PIGE analysis

Li/Ni ratios in Li_xNi₁ − xO films were determined by simultaneous use of the PIXE (particle-induced X-ray emission) and PIGE (proton-induced gamma-ray emission) techniques using the 3.5 MeV proton beam provided by the CISE tandem Van de Graaff accelerator. The general features of the experimental setup are presented and discussed along with the results on the dependence of Li/Ni ratios on the e-beam evaporation and thermal treatments. Preliminary results obtained by XRD (X-ray diffraction) are also discussed. The combined use of PIXE and PIGE proves to be a unique opportunity for nondestructive measurement in thin films and, through the correlation with structural data, it allows a careful optimization of the deposition process and thermal treatment parameters to be obtained.