Silicon negative ion implantation induced vacancy defects in thermally grown SiO2 thin films

ABSTRACT

Thermally grown SiO₂ thin films on a silicon substrate implanted with 100?keV silicon negative ions with fluences varying from 1?×?10¹⁵ to 2?×?10¹⁷ ions cm^?2 have been investigated using Electron spin resonance, Fourier transforms infrared and Photoluminescence techniques. ESR studies revealed the presence of non-bridging oxygen hole centers, E′-centers and P_b-centers at g-values 2.0087, 2.0052 and 2.0010, respectively. These vacancy defects were found to increase with respect to ion fluence. FTIR spectra showed rocking vibration mode, stretching mode, bending vibration mode, and asymmetrical stretching absorption bands at 460, 614, 800 and 1080?cm^?1, respectively. The concentrations of Si–O and Si–Si bonds estimated from the absorption spectra were found to vary between 11.95?×?10²¹ cm^?3 and 5.20?×?10²¹ cm^?3 and between 5.90?×?10²¹ cm^?3 and 3.90?×?10²¹ cm^?3, respectively with an increase in the ion fluence. PL studies revealed the presence of vacancies related to non-bridging oxygen hole centers, which caused the light emission at a wavelength of 720?nm.     

EPR study of Fe3+ and Mn2+ in CeO2 and ThO2

Attempts were made to grow CeO₂ and ThO₂ single crystals doped with transition metal ions. Only Fe³⁺ and Mn²⁺ could be detected by the EPR technique. The EPR spectrum of Fe³⁺ in CeO₂ exhibits the well-known fine structure in cubic fields. The parameters areg=2.0044(1) anda=15.6(1)·10^?4 cm^?1. The hyperfine constantA for⁵⁷Fe in hexahedral coordination was found to be 8.9(1)·10^?4 cm^?1. The EPR spectrum of Mn²⁺ in CeO₂ reveals two cubic Mn²⁺ centers. The parameters for center 1 areg=1.9999(1) andA=86.9(1)·10^?4 cm^?1 and for center 2g=1.9984(1) andA=87.0(1)·10^?4 cm^?1. Heating the Mn doped CeO₂ samples in hydrogen, the Mn²⁺ centers transform from cubic into trigonal centers with approximate values ofg=1.9988(2),A=84.5(6)·10^?4 cm^?1 andD=203(1)·10^?4 cm^?1. The two observed Mn²⁺ centers in ThO₂ exhibita priori axial symmetry with approximate values ofg=2.0006(2),A=88.9(4)·10^?4 cm^?1 andD=33(3)·10^?4 cm^?1.     

2D-Conductivity of thin Pd films condensed at low temperatures

Resistance measurements have been made on quenched condensed Pd films with thicknesses between 25 Å and 350Å. The films are prepared under different evaporation conditions by varying the system pressure between 10^?8 and 10^?5 mbar. Resistance minima with a logarithmic increase of the sheet resistance are observed for thick films (d<350Å) condensed under intentionally “bad” (10^?5 mbar) vacuum conditions, as well as for thin films (d<50Å) condensed at pressures around 10^?8 mbar. Structure investigations show that the thick films are granular. For these films the relation of granularity to 2D localization is discussed. The thin films are continuous and the logarithmic resistance increase is in agreement with predictions of 2D-theories.     

RF-sputtered LiCoO2 thick films: microstructure and electrochemical performance as cathodes in aqueous and nonaqueous microbatteries

Films of LiCoO₂ are prepared on metallized silicon substrates using RF-magnetron sputtering technique. The microstructural properties of the films are investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The films deposited at a substrate temperature of 250 °C with subsequent annealing at 650 °C exhibited hexagonal layered structure with R $ \overline 3 $ m symmetry. The kinetics of lithium ions in LiCoO₂ film cathode host matrix and its cycleability are studied in aqueous Pt//LiCoO₂ and nonaqueous Li//LiCoO₂ cell. Both the electrochemical cells at same current density of 50 μA cm^?2 delivered the same initial discharge capacity of about 60 μA h?cm^?2 μm^?1 with a chemical diffusion coefficient of ca. 10^?11 cm² s^?1 for Li⁺ ions. The capacity fade rates for the Pt//LiCoO₂ and Li//LiCoO₂ cells, in average are 3.0 and 0.15 % per cycle, respectively, for the first 20 cycles. The Pt//LiCoO₂ cell is found to be advantageous for small number of cycles and is cost effective than the Li//LiCoO₂ cell.     

Evaluation of zinc self-diffusion at the interface between homoepitaxial ZnO thin films and (0001) ZnO substrates

Isotopic ZnO thin films were deposited on the c-plane of ZnO single crystals by pulsed laser deposition. The isotopic abundance of Zn in the films was determined with a secondary ion mass spectrometry before and after the films was diffusion annealed. The diffusion profiles across the film/substrate interface behaved smooth features. The zinc diffusion coefficient (D_Zn) was obtained by analyzing the slope of the profile in the annealed sample. The temperature dependence of D_Zn was determined to be D_Zn(cm²/s)=8.0×10⁴exp(?417[kJ/mol])/RT, where R and T are gas constant and temperature. The zinc ion diffusion coefficients were of the same order as that in a ZnO single crystal. A comparison of the experimental and theoretical values indicated that the zinc ions diffused in the thin film and the single crystal through a vacancy mechanism.     

Lifetimes of charged and neutralD mesons

We have measured the lifetimes of hadronically produced charged and neutralD mesons using silicon microstrip detectors and an active silicon target in the NA32 spectrometer at the CERN SPS. We obtainτ _D± = (10.9± _1.5 ^1.9 )·10^?13s andτ _D ^(?)10 = (4.2±0.5)·10^?13s based on 59 and 90 fully reconstructed decays respectively, giving a ratioτ _D±/τ _D ^(?)10 of 2.6 ±0.5.     

Effect of annealing on the opto-electronic properties of Cu0.9In1.0Se2.0 films

The influence of annealing on the structure and opto-electronic properties of Cu_0.9In_1.0Se_2.0 films prepared by solution growth technique has been studied. The films annealed at 500–520°C in air, vacuum (10^?4 torr), In-vapour and Se-vapour show polycrystalline chalcopyrite structure with orientation perpendicular to the (220) plane. Films annealed in Se-vapour at 500°C for 30 min have maximum grain size (560 Å), minimum optical energy gap, maximum absorption coefficient, lowest resistivity, maximum photosensitivity and thus are suitable for photovoltaic applications. Annealing in In-vapour or in vacuum changesp-type CuInSe₂ inton-type which possibly arises due to the increase in Se vacancies.     

Measurement of the masses and lifetimes of the charmed mesonsD 0,D + andD s +

We present the final results on the measurement of the masses and lifetimes of the mesonsD ⁰,D ⁺ andD _s ⁺ in the NA32 experiment at the CERN SPS, using silicon microstrip detectors and charge-coupled devices for vertex reconstruction. We measure the following lifetimes: \(\tau _{D^0 } = 3.88 \pm _{0.21}^{0.23} \cdot 10^{ - 13} s\) using a sample of 479D°→K ^?π⁺π^?π⁺ and 162D°→K ^?π⁺ decays; \(\tau _{D^ + } = 10.5 \pm _{0.72}^{0.77} \cdot 10^{ - 13} s\) with a sample of 317D ⁺→K ^?π⁺π⁺ decays; \(\tau _{D_s^ + } = 4.69 \pm _{0.86}^{1.02} \cdot 10^{ - 13} s\) with a sample of 54D _s ⁺ →K ⁺ K ^?π⁺ decays. We measure the following masses:m _D ⁰=1864.6±0.3±1.0 MeV,m _D ⁺=1870.0±0.5±1.0 MeV and \(m_{D_s^ + } \) =1967.0±1.0±1.0 MeV.     

Synchrotron investigations of the electron structure of silicon nanocrystals in a SiO2 matrix

Silicon ions are implanted into silicon oxide thin films obtained by the thermal oxidation of silicon wafers in wet oxygen. The implantation dose is accumulated either once or cyclically, and the samples are annealed in dry nitrogen every time after implantation. The second series of samples is prepared in a similar way, but the technology for obtaining the oxide films includes additional annealing at 1100°C in air for three hours. X-ray absorption near-edge structure (XANES) spectra are obtained using synchrotron radiation. In all the Si L _2,3 spectra, two absorption edges are observed, the first corresponding to elemental silicon, and the second corresponding to the SiO₂ matrix. The fine structure of the first edge indicates that nanocrystalline silicon (nc-Si) can form in the SiO₂ matrix, whose atomic and electronic structure depends on the technology of its formation. In both series, the cyclic accumulation of the total dose (Φ = 10¹⁷ cm^?2) and the annealing time (2 h) gives rise to the most pronounced fine structure in the region of the absorption edge of elemental silicon. The probability of forming silicon nanocrystals decreases for the denser silicon oxide in the second series of samples.     

Anisotropy of phosphorous electron donor state in strained clusters in silicon at low temperatures

An anisotropic EPR spectrum at T = 4 K was observed in silicon samples irradiated by phosphorus ions and subsequently annealed at 1000°C. Epitaxial silicon layers with a natural isotope composition and enriched by ²⁸Si isotope grown on a natural silicon wafer were investigated. The spectrum consisted of three lines corresponding to different g-factor components: g _x ,g _y , and g _z . The central line was overlapped by the isotropic line coinciding by its g-factor with the line of the conduction electrons in silicon. The shape of the spectral lines indicated that the spectrum was due to the paramagnetic centers which belong to the randomly oriented clusters with the anisotropic g-factor. The nature of the anisotropic EPR spectrum is due to the electrons localized on donors located in the strained phosphorous clusters. The strains were caused by either incompletely annealed defects after the phosphorous implantation (E = 40 keV, D = 2 × 10¹⁴ cm⁻², T _ann = 1000°C, 1 h) or phosphorous atoms in clusters. The distance between the components strongly depended on the temperature and microwave power and decreased as they increased.     

Radiation-induced defects in annealed carbonate-containing hydroxyapatite

The effect of preliminary (before irradiation) annealing of synthetic carbonate-containing hydroxyapatite powders on the formation of paramagnetic centers under γ-ray and ultraviolet irradiation has been investigated. Annealing of the samples has been performed in the temperature range from 100 to 700°C. It has been found that electron paramagnetic resonance spectra of radiation-induced defects depend substantially on the annealing temperature. The paramagnetic centers CO ₂ ^? dominate in the samples annealed to 250°C (γ-ray irradiation) and 500°C (ultraviolet irradiation). In the samples annealed above 400°C, other defects, in particular, the O^? and CO ₃ ^3? centers, play a significant role. Annealing at some temperatures leads to an increase in the radiation sensitivity of the material. The observed effects can be associated with the escape of molecular water from the annealed hydroxyapatite samples and with the corresponding transformation of the defect subsystem of the material.     

Self-compensation of metastable centers in semiconducting chalcogenide glasses

The temperature dependences of magnetic susceptibility are employed for the first time to study the self-compensation of metastable centers with negative correlation energy in the As₂S₃ chalcogenide glass. The one-electron states of the metastable centers manifest themselves in the Curie paramagnetism at high temperatures, whereas for T≤77 K, one observes an enhancement of antiferromagnetism as a result of spontaneous dissociation of these states 2D ⁰ → D ⁺+D ^?. The observed self-compensation of the paramagnetic centers is similar to the spin-Peierls instability of magnetic lattices, which is supported by the existence of a double peak in the temperature dependence of inverse magnetic susceptibility. This peak identifies the spontaneous dissociation of two different metastable centers for T≤77 K. A comparative analysis of the data on magnetic susceptibility, optically induced absorption, and ESR shows that the one-electron paramagnetic states of these metastable centers (D ⁰) represent native hole and electronic defects formed by the chalcogen and arsenic dangling bonds, respectively. The self-compensation of the two types of metastable centers is enhanced in successive cooling runs 300 K → 3.5 K → 300 K → 3.5 K ... accompanied by optical pumping at an energy close to the Urbach absorption edge, which is reflected in a decrease in the Curie paramagnetism and an enhancement of the van Vleck paramagnetism of two-electron states with negative correlation energy (D ^?).     

Studies of some physical properties of PrFe0.7Ni0.3O3 thin films after 200 MeV Ag15+ irradiation

PrFe_0.7Ni_0.3O₃ thin films (thickness ~ 200 nm) were prepared by pulsed laser ablation technique on LaAlO₃ substrate. These films were irradiated with 200?MeV Ag¹⁵⁺ ions at various fluencies, ranging from 1 × 10¹¹ to 1 × 10¹² ions/cm². These irradiated thin films were characterized by using X-ray diffraction, dc conductivity, dc magnetization and atomic force microscopy. These films exhibit orthorhombic structure and retain it even after irradiations. The crystallite size (110–137?nm), micro strain (1.48 × 10^?2–1.75 × 10^?2 line^?2?m^?4) and dislocation density (79.7 × 10¹⁴–53.2 × 10¹⁴ line/m²) vary with ion fluencies. An enhancement in resistivity at certain fluence and then a decrease in its value (0.22175–0.21813?Ω?cm) are seen. A drastic change in observed magnetism after ion irradiation is seen. With ion irradiation, an increase in surface roughness, due to the formation of hillocks and other factors, is observed. Destruction of magnetic domains after irradiation can also be visualized with magnetic force microscopy and is in close agreement with magnetization data. The impact on various physical properties in these thin films after irradiation indicates a distortion in the lattice structure and consequently on single-particle band width caused by stress-induced defects.     

Giant optical nonlinearity of silver-doped silicon thin film at low power input: laser-triggered cluster resonance

Silver-doped silicon thin films were deposited on glass substrate in a co-sputtering procedure. Silver nanoparticles were segregatedly distributed. The nonlinear properties were extracted by z-scan measurements at low laser input power. For about 50% silver density, the nonlinear absorption and refraction coefficients peaked, respectively, at ?8.086×10^?2?m/W and 1.47×10^?9?m²/W, which, with respect to the input intensity, are several orders higher than reported data. The sudden surge of nonlinear responses was explained satisfactorily based on a self-consistent microscopic model calculation for silver clusters. Resonances exist and depend apparently on the laser-modified local cluster concentration.     

Observation of possible production and decay of short-living heavy neutral particles in the SKAT neutrino experiment

In the SKAT bubble chamber neutrino experiment production of a short-living neutral particle with mass (1.4?m?2.5) GeV/c² and lifetime τ≈6×10^?12 s has been detected. The event may be interpreted as production and decay of the heavy lepton M⁰→μ^?+e⁺+ν_e with mass (1.4?m_M⁰?2.1) GeV/c². It might also be the production of a charmed particle D⁰→e⁺+τ^?+ν_e (D⁰→e⁺+π^?+ν_e) with mass 1.4?m_D⁰?2.5) GeV/c² in a non-diagonal neutral current. The probability to interpret the event as other possible processes is very low.     

The thermal stability of atomic layer deposited HfLaOx: Material and electrical characterization

HfLaO_x based Metal–oxide–semiconductor capacitors were fabricated by atomic layer deposition in this work. The material and electrical properties of the films along with the high temperature thermal treatment were investigated. It was found that samples undergoing annealing at 900 °C exhibited the best performance. The film was found to be crystallized to a cubic structure at 900 °C, and the roughness of the films was estimated to be 0.332 nm. For electrical characterization, the C–V curve of the film is in good agreement with the corresponding simulated curve, and the capacitor does not show any hysteresis. Moreover, the D_it near the center of silicon band gap exhibits lowest value, and it was calculated to be 2.28 × 10¹¹ eV^?1 cm^?2.     

Photoluminescent studies of the condensed phase in phosphorus-doped silicon

Photoluminescent studies give evidence for the existence of the electron—hole droplet in phosphorus-doped silicon in the impurity concentration range 9.0 × 10¹⁵cm^?3 ? N_D ? 4.3 × 10¹⁹cm^?3.     

Isotope effects in the EPR spectrum of a tin-vacancy pair in silicon

The S = 1 EPR spectrum for a tin-vacancy pair in silicon reveals easily detected isotope shifts in the fine structure splitting D for the various nuclear isotopes of tin (σD/D = + 1.0 × 10^?4 per unit mass) as well as well as those for the six near neighbor silicon atoms (σD/D = ?0.67 × 10^?4 per unit mass). These are attributed to the different vibrational amplitudes vs isotopic mass.     

Spin relaxation of charged centers in silicon in the presence of photocarriers (Si: Cr+, [Cr+−B−])

Spin relaxation of deep charged centers Cr⁺ and of donor-acceptor pairs (Cr⁺?B^?)⁰ in silicon is studied by nonstationary EPR spectroscopy at liquid-helium temperatures. We observed the effect of an increase in the spin-lattice relaxation rate under band-to-band sample illumination; the magnitude of the effect is proportional to the photoelectron concentration. The spin-dependent carrier trapping is shown to play a dominant role in spin relaxation under illumination for centers of both types. Coupled rate equations describing the interaction of various subsystems with one another and with the bath are solved. A comparison of experimental data with theory yielded the electron trapping cross sections σ_r(Cr⁺)?4.9×10^?12 cm² and σ_r(Cr⁺?B^?)?1.6×10^?12 cm² at T=4.2 K. The results obtained are discussed in terms of the theory of trapping by attractive centers.     

A high-resolution study of the 14.4-μm infrared band of deuterofluoroform

The FT-IR spectrum of the ν₃ parallel band of deuterofluoroform has been recorded at a resolution of 0.0045 cm^?1. Nine independent spectral parameters were determined which reproduce some 650 observed wavenumbers with a standard error of 3 × 10^?4 cm^?1. The constants derived for the ν₃ band are (in cm^?1): ν₀ = 694.2822(3); B₀ = 0.3309321(9); B₃ = 0.3302464(11); α^B = 6.859(10) × 10^?4; α^C = 1.429 × 10^?4; D₃^J = 3.168(3) × 10^?7; D₀^J = 3.188(3) × 10^?7; D_JK³ = 4.766 × 10^?7; D_JK⁰ = 4.864 × 10^?7; and D_K⁰ ? D_K³ = 2 × 10^?10.