Surface morphology of Mn implanted Ge(1 0 0): A systematic investigation as a function of the implantation substrate temperature

Ge (1 0 0) wafers were implanted with 100 keV Mn⁺ ions with a dose of 2 × 10¹⁶ ions/cm² at different temperatures, ranging from 300 to 573 K. The surface morphology of implanted samples, analyzed with scanning electron microscopy and atomic force microscopy measurements, reveals for the 300-463 K implant temperature range the formation of a surface swelled and porous film, containing sponge-like structures. On the contrary, samples implanted in the 513-573 K temperature range present an atomically flat surface, with a roughness less than 1 nm, indicating that crystalline order has been preserved. X-ray photoemission spectroscopy depth profiling measurements indicate the presence of adsorbed oxygen in the porous layer of lower-temperature implanted samples, as well the presence of a large Mn concentration below the expected end of range for impinging ions. Mn and O concentrations at anomalously great depths are maximum in the 413 K implanted sample, indicating that the phenomenon of ion beam induced porosity is best favored at a well defined temperature.     

Synthesis of molybdenum silicide by both ion implantation and ion beam assisted deposition

Two groups of Mo/Si films were deposited on surface of Si(1 0 0) crystal. The first group of the samples was prepared by both ion beam assisted deposition (IBAD) and metal vapor vacuum arc (MEVVA) ion implantation technologies under temperatures from 200 to 400 °C. The deposited species of IBAD were Mo and Si, and different sputtering Ar ion densities were selected. The mixed Mo/Si films were implanted by Mo ion with energy of 94 keV, and fluence of Mo ion was 5 × 10¹⁶ ions/cm². The second group of the samples was prepared only by IBAD under the same test temperature range. The Mo/Si samples were analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), sheet resistance, nanohardness, and modulus of the Mo/Si films were also measured. For the Mo/Si films implanted with Mo ion, XRD results indicate that phase of the Mo/Si films prepared at 400 and 300 °C was pure MoSi₂. Sheet resistance of the Mo/Si films implanted with Mo ion was less than that of the Mo/Si films prepared without ion implantation. Nanohardness and modulus of the Mo/Si films were obviously affected by test parameters.     

Ferromagnetism in ZnO doped with Co by ion implantation

The importance of doping ZnO with magnetic ions is associated with the fact that this oxide is a good candidate for the formation of a magnetic-diluted semiconductor. Most of the studies reported in Co-doped ZnO were carried out in thin films, but the understanding of the modification of the magnetic behaviour due to doping demands the study of single-crystalline samples. In this work, ZnO single crystals were doped at room temperature with Co by ion implantation with fluences ranging between 2×10¹⁶ and 1×10¹⁷ ions cm⁻² and implantation energy of 100 keV. As implanted samples show a superparamagnetic behaviour attributed to the formation of Co clusters, room temperature ferromagnetism is attained after annealing at 800 °C, but no magnetoresistance was detected in the temperature range from 10 to 300 K.     

Magnetic and structural properties of Fe ion-implanted GaN

The magnetic and structural properties of Fe ion-implanted GaN was investigated by various measurements. XRD results did not show any peaks associated with second phase formation. The magnetization curve at 5 K showed ferromagnetic behavior for 900 °C-annealed sample. In zero-field-cooled (ZFC) and field-cooled (FC) magnetization measurements, the irreversibility and a cusp-like behavior of the ZFC curve were observed for 900 °C-annealed sample. These behaviors are typically observed in superparamagnetic or spin glass phase. While the temperature dependence magnetization of 800 °C-annealed sample showed non-Brillouin-like curve and it is not exhibited ferromagnetic hysteresis at 5 K. In XPS measurement, the coexistence of metallic Fe (Fe⁰) and Fe–N bond (Fe²⁺ and Fe³⁺) for Fe 2p core level spectra is observed in as-implanted sample. But 700–900 °C-annealed samples showed only Fe–N bond (Fe²⁺ and Fe³⁺) spectra. For Ga 3d core level spectra only Ga–N bonds showed for as implanted with 700–900 °C-annealed samples. From XPS results, it could be explained that magnetic property of our films originated from FeN structures.     

Structural and electrical transport properties of Nb-doped TiO2 films deposited on LaAlO3 by rf sputtering

We have investigated the structural and electrical transport properties of Nb-doped TiO₂ films deposited on (1 0 0) LaAlO₃ substrates by rf magnetron sputtering at temperatures ranging from 873 K to 1073 K. Films deposited below 998 K are anatase, and mixed phases between anatase and rutile exist in the film grown at higher temperatures. We find that films deposited at low temperatures exhibit semiconductor behavior, while metallic conductivity is observed in the most conducting film deposited at 998 K. For this sample, compared to electron-phonon scattering mechanism, electron-phonon-impurity interference effect plays an important role in its electron transport process. Moreover, the temperature coefficient of the resistivity for the film deposited at 1073 K is negative from 2 K to 300 K. The temperature dependence of resistivity for the film is described by ∼exp(b/T)^1/2 at temperatures from 80 K down to 30 K, and by the fluctuation induced tunneling model from 80 K to 300 K.     

Processing for optically active erbium in silicon by film co-deposition and ion-beam mixing

Techniques of film deposition by co-evaporation, ion-beam assisted mixing, oxygen ion implantation, and thermal annealing were been combined in a novel way to study processing of erbium-in-silicon thin-film materials for optoelectronics applications. Structures with erbium concentrations above atomic solubility in silicon and below that of silicide compounds were prepared by vacuum co-evaporation from two elemental sources to deposit 200-270 nm films on crystalline silicon substrates. Ar⁺ ions were implanted at 300 keV. Oxygen was incorporated by O⁺-ion implantation at 130 keV. Samples were annealed at 600 °C in vacuum. Concentration profiles of the constituent elements were obtained by Rutherford backscattering spectrometry. Results show that diffusion induced by ion-beam mixing and activated by thermal annealing depends on the deposited Si-Er profile and reaction with implanted oxygen. Room temperature photoluminescence spectra show Er³⁺ transitions in a 1480-1550 nm band and integrated intensities that increase with the oxygen-to-erbium ratio.     

Quasi-two-dimensional conductivity and magnetoconductivity of graphite-like nanosize crystallites

The temperature dependence of electrical conductivity and magnetoconductivity of new type of carbon films composed of nanosize thin graphite-like crystallites were investigated at temperature interval of 4.2-300 K and in the magnetic field range of 0-12 kG at 4.2 K, respectively. The crystallites consist of several (5-50) graphene layers which have predominant orientation perpendicularly to a film surface. At temperature ≤30 K the logarithmic conductivity decreases linearly with temperature. The positive magnetoconductivity of the films was observed in a magnetic field directed perpendicularly to the film surface in all intervals of field values. In magnetic field B≥4 kG the logarithmic asymptotic of conductivity from magnetic field was observed. That is characteristic of the systems with two-dimensional quantum corrections to magnetoconductivity. In a magnetic field directed along a film surface, the crossover from negative to positive magnetoresistivity is observed at B≥8 kG.     

Effects of the substrate temperature on the properties of CuIn5S8 thin films

Structural, optical and electrical properties of CuIn₅S₈ thin films grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The CuIn₅S₈ thin films were carried out at substrate temperatures in the temperature range 100-300 °C. The effects of heated substrate on their physico-chemical properties were investigated using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), optical transmission and hot probe method. X-ray diffraction revealed that the films are strong preferred orientation along the (3 1 1) plane upon substrate temperature 200 °C and amorphous for the substrate temperatures below 200 °C. No secondary phases are observed for all the films. The composition is greatly affected by heated substrate. From the optical transmission and reflection, an important absorption coefficient exceeds 10⁵ cm⁻¹ at 800 nm was found. As increasing the substrate temperature, the optical energy band gap decreases from 1.70 eV for the unheated films to 1.25 eV for the deposited films at 300 °C. It was found that CuIn₅S₈ thin film is an n-type semiconductor at 250° C.     

Synthesis of nanocrystalline YFeO3 and its magnetic properties

Single phase nanocrystalline YFeO₃ has been synthesized by a simple solution method. The average particle diameter is 42.2 nm. The particles exhibit ferromagnetic behaviour in the temperature range 10-300 K with a coercivity of 23 kOe. The magnetization versus temperature over the temperature range 2-300 K obeys Bloch equation with a Bloch constant value 9.98×10⁻⁶ K^−3/2. Ferromagnetic hysteresis loops have been observed up to a temperature of 300 K. At 10 K a field-cooled sample shows an exchange bias field.     

Analysis of the effect of annealing on the photoluminescence spectra of Cu ion implanted ZnS nanoparticles

In the present study, we report the photoluminescence (PL) study of nanoparticles of ZnS implanted with Cu⁺ ions at the doses of 5×10¹⁴, 1×10¹⁵ and 5×10¹⁵ ions/cm² and annealed at 200 and 300 °C. The photoluminescence spectra of the samples implanted at lower doses of 5×10¹⁴ and 1×10¹⁵ ions/cm² and annealed at 200 and 300 °C showed peaks at around 406, 418 and 485 nm. The PL emission peak at 485 nm was attributed to the transition of electrons from conduction band of ZnS to the impurity level formed by the implanted Cu⁺ ions. In the PL spectrum of the sample implanted at the highest dose of 5×10¹⁵ ions/cm², in addition to the emission peaks observed in the PL spectra of the samples implanted at lower doses, a peak at around 525 nm, the intensity of which decreased with increase in the annealing temperature, was observed. The emission peak at 525 nm was attributed to the transitions between sulfur and zinc vacancy levels. The full width at half maximum (FWHM) of the emission peak at 406 nm was observed to decrease with increase in annealing temperature, indicating lattice reconstruction. The observation of copper ion impurity related peak at 485 nm in the PL spectra of samples of the present study indicated that the doping of copper ions into the ZnS lattice is achievable by implanting Cu⁺ ions followed by annealing.     

Annealing effect on planar waveguides in LiNbO3 produced by oxygen ion implantation

We reported on planar waveguides in stoichiometric lithium niobate fabricated by 4.5 MeV oxygen ion implantation with a dose of 6 × 10¹⁴ ions/cm² at room temperature. After ion implantation, these samples were annealed at 240 °C, 260 °C, and 300 °C for 30 min. We investigated annealing effect on the guiding modes and near-field images in the waveguides by prism-coupling method and end-face coupling method respectively. We found that for the extraordinary refractive index a positive alternation occurred in the near-surface region while a negative alternation happened at the end of ion track. Moreover, we measured the transmission spectra for the pure sample and implanted samples before and after annealed at different temperatures, and we observed an absorption peak at ∼480 nm (2.6 eV) in all of these SLN samples.     

Investigations on the effect of complexation of NaF salt with polymer blend (PEO/PVP) electrolytes on ionic conductivity and optical energy band gaps

Sodium ion conducting polymer blend electrolyte films, based on polyethylene oxide (PEO) and polyvinyl pyrrolidone (PVP) complexed with NaF salt, were prepared using solution casting technique. The complexation of the salt with the polymer blend was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV-vis spectroscopy. Electrical conductivity of the films was measured with impedance analyzer in the frequency range of 1 Hz to 1 MHz and in the temperature range of 303-348 K. It was observed that the magnitude of conductivity increased with the increase in the salt concentration as well as the temperature. UV-vis absorption spectra in wavelength region of 200-800 nm were used to evaluate the optical properties like direct and indirect optical energy band gaps, optical absorption edge. The optical band gaps decreased with the increase in Na⁺ ion concentration. This suggests that NaF, as a dopant, is a good choice to improve the electrical properties of PEO/PVP polymer blend electrolytes.     

SiO2 film electret with high surface potential stability

The plasma surface treatment and ion implantation were utilized to improve the stability of charge storage in the SiO₂ film electret. It was found that the SiO₂ films treated by argon plasma with the arcing at 700 V for 15 min, or implanted by 150 keV (kilo electron volt) Ar⁺ with a dose of 2 × 10¹¹ cm⁻², after being negatively charged, showed a remnant negative potential as large as 90% of the primary value after being stored in a glass container with desiccant for 10 days. It was also found that after being negatively charged at room temperature and aged at 200-350 °C for several times, the SiO₂ films implanted by 150 keV Ar⁺ had a relatively high remnant potential and it did not decay significantly even after being heated at the aging temperature of 200-350 °C in room atmosphere for 60 min.     

Electrical properties and dielectric relaxation of thermally evaporated zinc phthalocyanine thin films

The electrical transport properties and dielectric relaxation of Au/zinc phthalocyanine, ZnPC/Au devices have been investigated. The DC thermal activation energy at temperature region 400-500 K is 0.78 eV. The dominant conduction mechanisms in the device are ohmic conduction below 1 V and space charge limited conduction dominated by exponential trap distribution in potentials >1 V. Some parameters, such as concentration of thermally generated holes in valence band, the trap concentration per unit energy range at the valence band edge, the total concentration of traps and the temperature parameter characterizing the exponential trap distribution and their relation with temperatures have been determined. The AC electrical conductivity, σ_ac, as a function of temperature and frequency has been investigated. It showed a frequency and temperature dependence of AC conductivity for films in the temperature range 300-400 K. The films conductivity in the temperature range 400-435 K increased with increasing temperature and it shows no response for frequency change. The dominant conduction mechanism is the correlated barrier hopping. The temperature and frequency dependence of real and imaginary dielectric constants and loss tangent were investigated.     

Thermal conductivity of isotopically enriched Si: revisited

The thermal conductivity of isotopically enriched ²⁸Si (enrichment better than 99.9%) was redetermined independently in three laboratories by high precision experiments on a total of four samples of different shape and degree of isotope enrichment in the range from 5 to 300 K with particular emphasis on the range near room temperature. The results obtained in the different laboratories are in good agreement with each other. They indicate that at room temperature the thermal conductivity of isotopically enriched ²⁸Si exceeds the thermal conductivity of Si with a natural, unmodified isotope mixture by 10±2%. This finding is in disagreement with an earlier report by Ruf et al. At ∼26 K the thermal conductivity of ²⁸Si reaches a maximum. The maximum value depends on sample shape and the degree of isotope enrichment and exceeds the thermal conductivity of natural Si by a factor of ∼8 for a 99.982% ²⁸Si enriched sample. The thermal conductivity of Si with natural isotope composition is consistently found to be ∼3% lower than the values recommended in the literature.     

Optical study of implantation damage recovery from Si-implanted GaN

Comprehensive and systematic optical activation studies of Si-implanted GaN grown on sapphire substrates have been made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10¹³ to 5×10¹⁵ cm⁻² at room temperature. The samples were proximity cap annealed from 1250 to 1350 °C with a 500-Å-thick AlN cap in a nitrogen environment. The results of photoluminescence measurements made at 3 K show a very sharp neutral-donor-bound exciton peak along with a sharp donor-acceptor pair peak after annealing at 1350 °C for 20 s, indicating excellent implantation damage recovery. The results also indicate the AlN cap protected the implanted GaN layer very well during high temperature annealing without creating any significant anneal-induced damage. This observation is consistent with the electrical activation results for these samples.     

The influence of substrate temperature on electrical properties of Cu/CdS/SnO2 Schottky diode

Polycrystalline CdS samples on the SnO₂ coated glass substrate were obtained by vacuum evaporation method at low substrate temperatures (T_S=200 and 300 K) instead of the commonly used vacuum evaporation at high substrate temperatures (T_S>300 K). X-ray diffraction studies showed that the textures of the films are hexagonal with a strong (0 0 2) preferred direction. Circular Cu contacts were deposited on the upper surface of the CdS thin films at 200 K by vacuum evaporation. The effects of low substrate temperature on the current-voltage (I-V) characteristics of the Cu/CdS/SnO₂ structure were investigated in the temperature range 100-300 K. The Cu/CdS (at 300 K)/SnO₂ structure shows exponential current-voltage variations. However, I-V characteristics of the Cu/CdS (at 200 K)/SnO₂ structure deviate from exponential behavior due to high series resistance. The diodes show non-ideal I-V behavior with an ideality factor greater than unity. The results indicate that the current transport mechanism in the Cu/CdS (at 300 K)/SnO₂ structure in the whole temperature range is performed by tunneling with E₀₀=143 meV. However, the current transport mechanism in the Cu/CdS (at 200 K)/SnO₂ structure is tunneling in the range 200-300 K with E₀₀=82 meV.     

Structural and optical properties of Au-implanted ZnO films

The structural and luminescence related optical behaviours of Au ion implanted ZnO films grown by magnetic sputtering and their post implantation annealing behaviours in the temperature range of 100-700 °C have been investigated. Optical absorption and transmittance spectra of the films indicate that band edge of Au-implanted ZnO has shifted to high energy range and optical band gap has increased, because the sharp difference of thermal expansion induces the lattice mismatch between ZnO and SiO₂. PL spectra reveal that UV and visible luminescence bands of ZnO films can be improved after thermal annealing due to recovery of defects and Au ions incorporation. Importantly, green luminescence band of 530 nm has been only observed in the Au-implanted and subsequently annealed ZnO films and it enhances with the increasing annealing temperature, which can be related to Au atoms or clusters in ZnO films. Furthermore, X-ray photoelectron spectroscopy measurements reveal that the Au⁰ is dominant state in Au implanted and annealed ZnO films. Possible mechanisms, such as optical transitions of Au atoms or clusters and deep level luminescence of ZnO, have been proposed for green emission.     

Surface nano-structural modifications and characteristics in nitrogen ion implanted W as a function of temperature and N energy

The surface modifications of tungsten massive samples (0.5 mm foils) made by nitrogen ion implantation are studied by SEM, XRD, AFM, and SIMS. Nitrogen ions in the energy range of 16-30 keV with a fluence of 1 × 10¹⁸ N⁺ cm⁻² were implanted in tungsten samples for 1600 s at different temperatures. XRD patterns clearly showed WN₂ (0 1 8) (rhombohedral) very close to W (2 0 0) line. Crystallite sizes (coherently diffracting domains) obtained from WN₂ (0 1 8) line, showed an increase with substrate temperature. AFM images showed the formation of grains on W samples, which grew in size with temperature. Similar morphological changes to that has been observed for thin films by increasing substrate temperature (i.e., structure zone model (SZM)), is obtained. The surface roughness variation with temperature generally showed a decrease with increasing temperature. The density of implanted nitrogen ions and the depth of nitrogen ion implantation in W studied by SIMS showed a minimum for N⁺ density as well as a minimum for penetration depth of N⁺ ions in W at certain temperatures, which are both consistent with XRD results (i.e., I_{W (2 0 0)}/I_{W (2 1 1)}) for W (bcc). Hence, showing a correlation between XRD and SIMS results.     

Temperature and N energy dependence on nano-structural modifications and characteristics of Mo surface

The surface modifications of Mo massive samples (0.5 mm foils) made by nitrogen ion implantation are studied by SEM, XRD, AFM, and SIMS. Nitrogen ions in the energy range of 16-30 keV with a fluence of 1 × 10¹⁸ N⁺ cm⁻² were implanted in molybdenum samples for 1600 s at different temperatures. XRD patterns clearly showed MoN (0 3 1) (hcp) very close to Mo (2 0 0) line. Crystallite sizes (coherently diffracting domains) obtained from MoN (0 3 1) line, showed an increase with substrate temperature. AFM images showed the formation of grains on Mo samples, which grew in size with temperature. Similar morphological changes to that has been observed for thin films by increasing substrate temperature (i.e., structure zone model (SZM)), is obtained. The density of implanted nitrogen ions and the depth of nitrogen ion implantation in Mo studied by SIMS showed a minimum for N⁺ density as well as a minimum for penetration depth of N⁺ ions in Mo at certain temperatures, which are both consistent with XRD results (i.e., I_{Mo (2 0 0)}/I_{Mo (2 1 1)}) for Mo (bcc). Hence, showing a correlation between XRD and SIMS results. This phenomenon is explained on the basis of residual gas, substrate temperature, dissociation of water in the chamber and the ion energy.