Sequential Ion Implantation Research Articles

Sequential ion implantation of copper and cobalt in silica glass: A study by synchrotron radiation techniques

Copper–cobalt nanostructures are expected to exhibit peculiar magnetic and optical properties that make them interesting for several application fields. In particular, nanoclusters of these metals can be formed upon ion implantation in dielectric matrices. In this work, Co + and Cu + ions were sequentially implanted into fused silica. Samples were analyzed by different synchrotron radiation-based techniques, namely, extended X-ray absorption fine structure spectroscopy and grazing incidence X-ray diffraction. The obtained cluster structure, and so its magnetic features, are observed to depend on the sequential implantation order.

Fretting wear study of surface modified Ni-Ti shape memory alloy.

A combination of shape memory characteristics, pseudoelasticity, and good damping properties make near-equiatomic nickel-titanium (Ni-Ti) alloy a desirable candidate material for certain biomedical device applications. The alloy has moderately good wear resistance, however, further improvements in this regard would be beneficial from the perspective of reducing wear debris generation, improving biocompatibility, and preventing failure during service. Fretting wear tests of Ni-Ti in both austenitic and martensitic microstructural conditions were performed with the goal of simulating wear which medical devices such as stents may experience during surgical implantation or service. The tests were performed using a stainless steel stylus counter-wearing surface under dry conditions and also with artificial plasma containing 80 g/L albumen protein as lubricant. Additionally, the research explores the feasibility of surface modification by sequential ion implantation with argon and oxygen to enhance the wear characteristics of the Ni-Ti alloy. Each of these implantations was performed to a dose of 3 x 10(17) atom/cm(2) and an energy of 50 kV, using the plasma source ion implantation process. Improvements in wear resistance were observed for the austenitic samples implanted with argon and oxygen. Ion implantation with argon also reduced the surface Ni content with respect to Ti due to differential sputtering rates of the two elements, an effect that points toward improved biocompatibility.

Ion beam synthesis of buried CdSe nanocrystallites in SiO 2 on (100)-silicon

Nanocrystalline precipitates of the direct band gap II–VI compound semiconductor CdSe were synthesized by sequential high dose ion implantation into thermally grown SiO 2 on (100)-silicon. The implantation doses were chosen to be 4×10 16 and 8×10 16 cm −2, respectively. Rapid thermal annealing of the as-implanted samples at temperatures of 800 and 1100 °C led to the formation of nanocrystalline randomly oriented precipitates of CdSe buried in an amorphous matrix of SiO 2. The concentration profile of the implanted elements and the size distribution of the finally formed crystallites were analysed by thin film X-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS). High-resolution transmission electron microscopy (HTEM) cross-section images show that the nanocrystallites are defect-free. Moreover, transmission electron microscopy (TEM) images provide direct information on the spatial size distribution of the nanocrystals.

Photoluminescence from CdS nanocrystals fabricated by sequential ion implantation

We have studied photoluminescence (PL) spectrum and dynamics of CdS nanocrystals fabricated by sequential Cd + and S + ion implantation into Al 2O 3 matrices. Two peaks related to free excitons of hexagonal CdS are observed in the absorption spectrum at low temperatures. The broad and efficient PL band appears near the absorption edge. The spectral shape of the PL band depends on the excitation laser intensity. Our results show that the observed PL band consists of free-exciton emission and shallow-impurity emission.

Sharp photoluminescence of CdS nanocrystals in Al2O3 matrices formed by sequential ion implantation

We report on photoluminescence (PL) experiments in CdS nanocrystals fabricated by sequential ion implantation in Al2O3 matrices. The PL spectrum and the spatial image of the PL intensity have been studied at 8 K using a scanning near-field optical microscope. The PL spectrum at each bright spot has been found to consist of narrow lines of various energies, although the spectrum measured by conventional optics shows a single and broad band locating below the free-exciton absorption energy. The origin of the sharp PL lines in CdS nanocrystals will be discussed.

Synthesis, structure and optical properties of GaN nanocrystals prepared by sequential ion implantation in dielectrics

GaN nanocrystals (in the wurtzite phase) were synthesized by sequential implantation of Ga and N ions, either crystalline or amorphous dielectrics, followed by annealing of the samples in flowing NH 3 gas at 900°C. A blue shift of the near band-edge photoluminescence (quantum confinement effect) is observed for GaN nanocrystals with a size of ∼2–3 nm, formed in the α-Al 2O 3 substrate.

Buried ZnTe nanocrystallites in thermal SiO 2 on silicon synthesized by high dose ion implantation

Nanocrystalline precipitates of the direct bandgap II–VI compound semiconductor ZnTe were synthesized by sequential high dose ion implantation of the elements. Thermal SiO 2 on (1 0 0)-silicon was chosen as target material in order to provide compatibility to silicon technology. The implantation dose was 2×10 16 and 4×10 16 cm −2 . Subsequent rapid thermal annealing of the as-implanted samples controls the formation of the nanocrystalline precipitates of ZnTe. The size distribution of the crystallites, their orientation and crystal structure were analyzed by thin film X-ray diffraction (XRD), secondary ion mass spectrometry depth profiling (SIMS) and Rutherford backscattering spectroscopy (RBS) as a function of implantation dose and annealing conditions. For selected samples transmission electron microscopy (TEM) cross-sections complete the structural investigations and provide direct information on the spatial size distribution of the nanocrystals.

Properties of InAs nanocrystals in silicon formed by sequential ion implantation

Optical and structural properties of InAs nanocrystals fabricated by co-implantation of In and As ions in Si-c(1 0 0), followed by thermal annealing are investigated. In the first sample named Si/AsIn the implantation of As ions was followed by In ion implantation, whereas in the second sample named Si/InAs the order of implantation was inverted. RBS spectra of these samples taken before and after annealing show that the depth profiles of implanted ions depend strongly on the order of implantation. XRD measurements confirm the presence of InAs crystallites oriented along the crystallographic axes of the silicon matrix irrespective of the order of implantation. Low-temperature photoluminescence measurements show a large PL band in the region 0.83–1.03 eV for the sample Si/AsIn. No PL was observed in the sample Si/InAs. The optical absorption spectrum of Si/AsIn sample shows a large absorption band in the region 0.4–0.9 eV, whereas the spectrum of sample Si/InAs contains two distinct absorption bands at 0.45 eV and 0.8 eV. This may indicate a bimodal distribution of sizes of InAs nanocrystals in the Si/InAs sample. The absorption and photoluminescence bands arise from the blueshifted bandgap absorption/emission of InAs nanocrystals, this blueshift being dependent on the size of the nanocrystals. These results indicate that in the case of As ions implanted first, the InAs nanocrystals are smaller than for the case of In ions implanted first. This effect may be explained by the low solubility of In ions in the silicon matrix, which results in agglomeration of In ions during the implantation. When As ions are implanted afterwards, the In clusters are partially transformed into InAs nanocrystals which grow in size during the annealing. Hence, the order of ion implantation is found to influence the size and distribution of the resultant nanocrystals, as well as the optical properties of the samples obtained.

Photoluminescence Dynamics of CdS Nanocrystals Fabricated by Sequential Ion Implantation

We have studied photoluminescence (PL) dynamics of CdS nanocrystals fabricated by sequential Cd+ and S+ ion implantation into Al2O3 matrices. The PL spectrum and PL decay dynamics of CdS nanocrystals are sensitive to the measurement temperature. This is because excitons trapped at shallow localized states are thermally excited to the high-energy state at high temperatures. Two PL bands appear near the absorption edge at elevated temperatures near 100 K. From time-resolved PL spectra and the PL decay dynamics, it is concluded that the observed PL bands near the absorption edge are due to free excitons and excitons trapped at shallow localized states. The PL mechanism in CdS nanocrystals is discussed.

Fabrication of Cu-coated Ag nanocrystals in silica by sequential ion implantation

Metal nanocrystal glass composites were fabricated by single and sequential element implantations of Ag + and Cu + ions into high purity silica. Implantation doses (×10 16 ions/cm 2) were 3Ag, 9Cu and 3Ag/9Cu. Composites were analyzed using Rutherford backscattering techniques (RBS), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and optical spectroscopy. An optical density spectrum based on the size distribution observed in the sequentially implanted sample for Cu shell and Ag core nanocrystals has been calculated using the dipole and quadrupole terms in a Mie series summation and is compared with the observed absorption spectrum. Results from TEM and EDS as well as the optical simulations demonstrate that Cu shell and Ag core nanocrystals are formed by the sequential implantation of Ag and Cu.

Visible light emission from GaAs nanocrystals inSiO2films fabricated by sequential ion implantation

We have studied the mechanism of visible photoluminescence (PL) in GaAs nanocrystals in ${\mathrm{SiO}}_{2}$ matrices formed by sequential ion implantation and thermal annealing. GaAs nanocrystal samples with the average diameter of \ensuremath{\sim}6 nm show a broad PL in the red spectral region. The PL peak energy of GaAs nanocrystals is blueshifted from that of the bulk GaAs crystal. Under resonant excitation at energies within the red PL band, the fine structures related to the LO phonon of the GaAs crystal are clearly observed in the PL spectrum at low temperatures. The excitation energy dependence of resonantly excited PL spectra shows that there are two different components of GaAs-related luminescence. In addition, in persistent luminescence hole-burning spectra, a pronounced hole is observed at the energy of the burning laser. The hole burnt in the luminescence spectrum has two structures related to the zero-phonon-line emission and the one-LO-phonon-assisted emission of delocalized excitons in GaAs nanocrystals. From resonantly excited PL spectra and luminescence hole-burning spectra, it is concluded that visible luminescence comes from both delocalized excitons and excitons bound to impurities in quantum-confined GaAs nanocrystals.

GISAXS study of Cu–Ni alloy clusters obtained by double ion implantation in silicate glasses

Sequential double ion implantation in silicate glasses has been used to realize copper-nickel alloy nanoclusters embedded in the host dielectric matrix. A grazing incidence small-angle X-ray scattering experiment has been performed on copper+nickel implanted silicate glasses, to obtain information on the cluster size and size distribution, as well as on the volume fraction. The potential of the technique in the study of these composite glasses is discussed.

GaAs nanocrystals fabricated by sequential ion implantation: structural and luminescence properties

We have fabricated GaAs nanocrystals in SiO2 matrices by sequential ion implantation and thermal annealing and studied their photoluminescence (PL) properties. After thermal annealing, GaAs nanocrystals are formed in SiO2 films and some PL bands appear in the red and infrared spectral region. After low-energy deuterium implantation, defect- and impurity-related PL bands disappear and the band-edge emission of GaAs nanocrystals is clearly observed. The luminescence mechanism of GaAs/SiO2 nanocomposites will be discussed.

Luminescence properties of GaAs nanocrystals fabricated by sequential ion implantation

We have studied photoluminescence (PL) properties of GaAs nanocrystals in SiO 2 matrices formed by sequential ion implantation and thermal annealing. After thermal annealing at 900–1000°C, broad PL due to GaAs nanocrystals appears in the red spectral region. The spectral shape of the red PL band depends on the hydrogen concentration in the sample. The hydrogen effect on GaAs nanocrystal luminescence will be discussed.

Cu-Ni alloy nanocluster formation by ion implantation in silicate glasses: Structure and optical properties

Sequential ion implantation (copper and nickel) in silica and soda-lime glasses has been performed. The formation of copper-nickel alloy nanocluster in the glass host has been evidenced by synchrotron radiation-based techniques, namely X-ray diffraction and absorption spectroscopy. The nanocrystals' lattice parameter value was estimated, indicating the formation of Cu55Ni45 alloy particles. Optical absorption spectra are also discussed.

Metal-Alloy Nanocluster Formation in Silica Glass by Sequential Ion Implantation

AbstractSequential ion implantation of two metal species in silica glass may give rise to the formation of alloy metal nanoclusters. Composite materials with peculiar optical properties can be therefore fabricated, with application in integrated-optical devices. In the presented experiments, different couples of transition elements were sequentially implanted in a silica glass. The resulting systems, in some cases after annealing in either reducing or oxidizing atmosphere, were studied by several analytical techniques, such as transmission electron microscopy and X-ray absorption spectroscopy. The formation of different alloy nanoclusters was evidenced, together with the cluster crystalline structure and the chemical environment of the dopant species.

A near-infrared photoluminescence study of GaAs nanocrystals in SiO2 films formed by sequential ion implantation

We have studied photoluminescence (PL) properties of Ga+ and As+ implanted SiO2 films on Si substrate. After thermal annealing, zinc blende GaAs nanocrystals are formed in SiO2 films and several PL bands appear in the red and near-infrared spectral region. Defects and impurities in GaAs nanocrystals and SiO2 cause weak luminescence in the near-infrared spectral region at low temperatures. After low-energy deuterium implantation, the defect PL intensity decreases and the red PL from GaAs nanocrystals is clearly observed. It is demonstrated that GaAs/SiO2 nanocompostites with low defect density are fabricated by sequential ion implantation followed by thermal annealing and hydrogen passivation.

Can core/shell nanocrystals be formed by sequential ion implantation? Predictions from kinetic lattice Monte Carlo simulations

High-dose ion implantation has proven to be a powerful technique to form a large variety of nanocrystals in the near surface layer of substrates. However, core/shell nanocrystals, which possess some unique physical properties, have been synthesized up to now only by colloid chemistry. A kinetic 3D lattice Monte Carlo (KLMC) model is used for the study of the diffusion, precipitation and interaction kinetics of the sequentially implanted atom types X and Y in a chemically neutral matrix. Applying a simplified model of collisional mixing, the coating behavior of previously nucleated precipitates of atom type X by atoms of type Y has been simulated.

Formation of CdS and CdSe nanocrystals by sequential implantation

Nanocrystals of CdS and CdSe have been formed in SiO 2, Al 2O 3, and Si by sequential ion implantation and annealing. In SiO 2, the nanocrystals have the hexagonal wurtzite structure and are randomly oriented. In Al 2O 3 and Si, nanocrystals are three dimensionally oriented. They have the cubic zincblende structure in Si and can be produced with either structure in Al 2O 3 by controlling the implantation conditions. In SiO 2 and Al 2O 3, nanocrystals exhibit strong optical absorption and photoluminescence (PL). Evidence for quantum confinement is observed, and the PL results for CdSe are strongly temperature dependent.

Ion beam synthesis of compound nanoparticles in SiO 2

The ion beam synthesis of group IV (SiC) and II–VI (ZnS) compound nanoparticles in SiO2 layers is studied. These systems are potentially interesting for optoelectronic applications such as electroluminescent devices emitting in the visible and UV range. The combination of structural (transmission electron microscopy, electron and X-ray diffraction), optical (infrared and raman spectroscopies, optical absorption and photoluminescence) and physico-chemical (X-ray photoelectron spectroscopy, secondary ion mass spectroscopy) techniques have been used to identify the phases formed and to correlate the optical behaviour of the layers with their microstructure. The first part is dedicated to the synthesis of luminescent SiO2 layers co-implanted with Si and C. The presence of regions with different composition in terms of C content gives rise to the formation of 3 types of nanoparticles (Si, C and SiC) leading to three intense, simultaneous and independent emission bands covering the whole visible range. A second part is dedicated to the synthesis of Mn doped ZnS nanocrystals. We have succeeded in synthesizing ZnS nanocrystals by sequential ion implantation in SiO2. The structural characterization of the annealed layers shows ZnS precipitates having a wurtzite-2H structure and with a quite narrow distribution of sizes. This population of nanocrystals is organized in two layers parallel to the free surface, as a consequence of a pure Ostwald ripening process or as a result of the implantation damage distribution. The optical analysis of samples co-implanted with Mn shows the presence of a yellow-green and intense photoluminescence corresponding to an intra- Mn2+ transition, which demonstrates the effective doping with Mn of the ZnS precipitates.