Medium-range order has been observed in ion-implanted amorphous silicon, suggesting a paracrystalline structure for this material. The origin of a paracrystalline structure may be due to an energy spike phenomenon. To evaluate the influence of energy spikes on a particular process, we have attempted to calculate the characteristic energy in a spike. However, the observed depth dependence of amorphous structures in as-implanted silicon is puzzling. To explain this, we simulated the depth distribution of cascade events in a particular energy range. We found a great increase of point defect concentration and cascade events as the depth increases. This result could explain the experimental depth dependence.

Cathodoluminescence (CL) Microanalysis (spectroscopy and microscopy) provides unique high sensitivity, high spatial resolution information about the defect structure and distribution of defects in wide band gap materials and therefore is an ideal technique with which to investigate the microstructural processes induced by irradiation. CL microanalytical techniques allow the in situ monitoring and post irradiation assessment of electron irradiation induced damage. Changes in the defect structure and surface topography of electron irradiated silicon dioxide polymorphs and related silicates including pure crystal quartz, pure silica glasses, pure amorphous fused quartz and alkali-borosilicate glasses, have been investigated and compared using CL microanalysis and Scanning Probe Microscopy (SPM) techniques. CL and SPM evidence shows all specimens are sensitive to electron irradiation. CL evidence is consistent with the production and micro-segregation of irradiation induced defects. The observed damage is highly correlated with the electron irradiation induced changes in the surface topography of the investigated specimens.

We report the results of comparison of radiation-induced defects (1 MeV electrons) in n+-p-p+ Si diodes doped with gallium or boron ranging in concentration from 8 × 1014 to 5 × 1016 cm−3, together with the impact of oxygen on radiation –induced defects. Present results provide evidence for new defects states in addition to those previously reported in gallium- and boron-doped Si. The combined boron and gallium data provide enough information to gain valuable insight into the role of the dopants on radiation-induced defects in Si. The interesting new future of our results is that the gallium appears to strongly suppress the radiation induced defect, especially hole level EV+0.36 eV, which is thought to act as a recombination center. Similarly the dominant electron level at EC-0.18 eV in B-doped Si (which act as a donor) has not been observed in Ga-doped CZ-grown Si.

Photon absorption (PA), Positron Beam Analysis (PBA) and Neutron Depth Profiling (NDP) is applied to study the relation between photon absorption behavior and the precipitates formed by ion implantation and thermal annealing. Monocrystals of MgO(100) were implanted with 1.0×10166Li ions cm−2 at an energy of 30 keV. The samples were thermally annealed in air in steps up to 1200 K. After each step Doppler broadening Positron Beam Analysis (PBA) was applied to monitor the depth profile of the implantation defects. The evolution of the depth profile of lithium was followed with the aid of NDP. During the annealing there is hardly any change in the location of the lithium implantation peak at 150 nm (peak concentration 2 at. %). Only after annealing to 1200 K the majority of the lithium has left the crystal and optical absorption effects have disappeared. During annealing at 750 K an absorption band develops between 400 and 600 nm; at 950 K the maximum absorption is centered at 450 nm corresponding to Mie absorption and scattering by lithium nanoclusters. Positron beam analysis shows a considerable increase of annihilations with low momentum electrons in the implanted zone. A positron method for measuring electron momentum distributions (2D-ACAR) coupled to an intense positron beam gave evidence for the presence of semi-coherent metallic lithium inclusions.

Bombardment of slightly rough, planar surfaces with an energetic gas-cluster ion beam (GCIB) is known to result in a decrease in roughness. We report comparison of measured surface evolution with simulations based on a simple phenomenological model. The model consists of a continuum rate equation for the surface height undergoing multiple cluster impacts. With suitable assumptions the main features observed in the evolution of an initially nonplanar surface can be simulated. Qualitatively, both experiment and simulation show that sharp features and asperities are rapidly eroded. Examples are given of initial surfaces that are either randomly rough and scratched, or very smooth with added nanoscale engineered features. Both types of surfaces show smoothing in microscopy evaluations of the GCIB and in the simulations, thereby identifying impact-transient surface diffusion as the primary cluster smoothing mechanism.

Self-assembled quantum dots (QDs) have attracted significant attention because of their potential applications in novel semiconductor devices. In this work, we investigated radiation effects induced by 1.0 MeV proton ion beams on InAs self-assembled quantum dots. In particular, we emphasized the effects of lattice environments of QDs on their luminescence emission after ion beam irradiation. Photoluminescence (PL) spectroscopy was used to characterize the optical properties of QDs subjected to proton irradiation and post-irradiation annealing. Compared to the single-layer QDs grown in GaAs films, the QDs embedded in an AlAs/GaAs superlattice exhibited much higher PL degradation resistance to proton beam bombardment, e.g., at the highest dose (1.0×1014 cm−2) used in this work, a difference of ~ 20-fold in PL intensity was found between the QDs configured in these two different lattice structures. After thermal annealing of irradiated QD samples, ion beam enhanced blueshift of PL was observed to be much more pronounced for the single-layer QDs. We discuss mechanisms that may result in the differences in optical response to ion beams between QDs with different lattice surroundings.

Epitaxial thin film liftoff using the ion-slicing method has been applied to SrTiO3 single crystals. Rutherford backscattering spectrometry along with channeling (RBS/C) has been used to investigate the relative disorder as a function of temperature from the samples that were irradiated by 40 KeV hydrogen ions to a fluence of 5.0×1016 H+/cm2. Hydrogen profiles were also measured as a function of annealing temperature to understand the role of hydrogen in the ion slicing process. Film cleavage occurred during or after annealing at 570 K, and cleaved film has been successfully transferred to a silicon substrate using ceramic adhesive.

The sputter-erosion of hcp Co (0001) single crystal with Ar+ ions in the 100 to 700 eV energy range was investigated using in-situ time-resolved x-ray scattering. At temperatures above 300°C the surface remains relatively smooth, erosion evolving through a layer-by-layer or step flow mechanism. In this regime the ions have a smoothening effect on the surface and the resulting roughness decreases with increasing ion energy. Below 300°C the surface develops a pattern of mounds or pits with a characteristic wavelength. The time, ion energy and temperature dependence of this wavelength were studied in detail. Epitaxial Co thin films thermally evaporated on sapphire were also sputtered through in order to synthesize self-assembled arrays of Co nanoclusters with a narrow size distribution. The degree of local order within the Co dot arrays was examined using atomic force microscopy.

In this work we report the structural and optical properties of ion implanted GaN. Potential acceptors such as Ca and Er were used as dopants. Ion implantation was carried out with the substrate at room temperature and 550 °C, respectively. The lattice site location of the dopants was studied by Rutherford backscattering/channeling combined with particle induced X-ray emission. Angular scans along both [0001] and [1011] directions show that 50% of the Er ions implanted at 550 °C occupy substitutional or near substitutional Ga sites after annealing. For Ca we found only a fraction of 30% located in displaced Ga sites along the [0001] direction. The optical properties of the ion implanted GaN films have been studied by photoluminescence measurements. Er- related luminescence near 1.54 µm is observed under below band gap excitation at liquid helium temperature. The spectra of the annealed samples consist of multiline structures with the sharpest lines found in GaN until now. The green and red emissions were also observed in the Er doped samples after annealing.

Ion bombardment during thin film growth is known to cause structural and morphological changes in the deposited films and thus affecting the film properties. These effects can be due to the variation in the bombarding ion flux or their energy. We have deposited titanium nitride films by two distinctly different methods, viz. Electron Cyclotron Resonance (ECR) plasma sputtering and bias assisted reactive magnetron sputtering. The former represents low energy (typically less than 30 eV) but high density plasma (1011cm−3), whereas, in the latter case the ion energy is controlled by varying the bias to the substrate (typically a few hundred volts) but the ion flux is low (109cm−3). The deposited titanium nitride films are characterized for their structure, grain size, surface roughness and electrical resistivity.

The formation of nanovoids in Si(100) and MgO(100) by 3He ion implantation has been studied. Contrary to Si in which the voids are generally almost spherical, in MgO nearly perfectly rectangular nanosize voids are created. Recently, the 2D-ACAR setup at the Delft Positron Research Center has been coupled to the intense reactor-based variable-energy positron beam POSH. This allows a new method of monitoring thin layers containing nanovoids or defects by depth-selective high-resolution positron beam analysis. The 2D-ACAR spectra of Si with a buried layer of nanocavities reveal the presence of two additional components, the first related to para-positronium (p-Ps) formation in the nanovoids, and a second one most likely related to unsaturated Si-bonds at the internal surface of the voids. The positronium is present in excited kinetic states with an average energy of 0.3 eV. Refilling of the cavities by means of low dose 3He implantation (1×1014 cm−2) followed by annealing reduces the formation of Ps and the width of the Ps peak in the ACAR spectrum. This width reduction is due to collisions of Ps with He atoms in the voids. In MgO, p-Ps formed with an initial energy of ~3 eV shows a final average energy of 1.6 eV at annihilation due to collisions with the cavity walls. Possibilities of this new, non-destructive method of monitoring the sizes of cavities and the evolution of nanovoid layers will be discussed.

Ion implantation, specified by parameters like ion energy, ion fluence, ion flux and sub-strate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced, which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient in understanding nanocluster evolution. Various aspects of precipitate evolution during implantation, formation of ordered arrays of nanophase domains by focused ion implantation and compound nanocluster synthesis are discussed.

The 1.5 µm luminescence from Si:Er is known to strongly depend on impurities (e.g. carbon) in silicon. In this work, we investigate the effect of carbon co-doping on the lattice location of Er atoms in Si by Rutherford backscattering(RBS)/channeling techniques. A float-zone (FZ) Si (100) wafer was first amorphized to a depth of ~ 0. 3 µm by Si ions implanted to a dose of ~ 1×1015cm2 at liquid nitrogen temperature. Carbon ions were then implanted into the amorphous silicon, which was recrystallized via solid phase epitaxial growth (SPEG) at 600°C following C implant. Finally Er ions were implanted into the C-doped and C-free Si crystals, with the substrate temperature at 25°C and 300°C respectively. The RBS/channeling results show that the Er redistribution and Si crystallinity are strongly affected by C co-doping. The incorporation of C into Si can significantly suppress Er surface segregation, and modify the lattice location of Er atoms in Si. We discuss these effects in terms of the formation of Er-C defect complexes.

Ion implantation followed by rapid thermal annealing is used to induce layer intermixing and thus selectively blue-shift the emission wavelength of InP-based quantum well hetero- structures. The intermixing is greatly enhanced over thermal intermixing due to the supersaturation of defects. The magnitude of the observed blue-shift has been studied previously as a function of ion fluence and ion mass: the dependence on ion mass is well established, with heavier ions producing a larger shift. We show here that chemical effects can also play a significant role in determining the induced blue-shift. Data are presented from the implantation of the similar mass ions; aluminum (m~27), silicon (m~28) and phosphorus (m~31). The P- induced blue shift displays a monotonic increase with fluence, consistent with previous studies; however, the fluence dependence of Al- and Si-induced blue-shifts both deviate significantly from the behaviour for P. These results have important implications for attempts to scale intermixing behaviour with ion mass.

A new method of producing a buried oxide is proposed. It involves implanting a silicon wafer with helium rather than oxygen ions and then subjecting it to high- temperature oxidation. The voids formed by helium ion implantation and subsequent annealing enhance the diffusion of oxygen atoms into the silicon. The oxygen atoms cause thermal oxide to grow at the void/silicon interface and transform the voids into buried oxide precipitates. Auger electron spectroscopy revealed that the total number of oxygen atoms in the precipitates was 9.3 × 1016 cm−2 and that the peak value of oxygen atom concentration in the wafer was approximately 25%.

Ion implantation was used to form high densities (~1019 /cm3) of small oxide precipitates in Ni in order to investigate the strength mechanism produced by such highly refined structures. Nanometer-size precipitates of Al2O3 and NiO are found to block dislocation motion in the Ni matrix, producing yield strengths up to 4.6 GPa, more than twice that of hardened bearing steel. Dispersion strengthening theory, developed for micrometer-size precipitates and spacings, was found to account quantitatively for the yield strengths produced by nanometer-size oxides as well. Nanoindentation plus finite-element modeling was used to quantify the mechanical properties of implanted metal layers, and was extended to examination of amorphous Si layers formed by self-ion implantation. The amorphous phase was found to have a yield strength of 4.45 ± 0.20 GPa, Young's modulus of 144 ± 7 GPa, and hardness of 10.3 ± 0.4 GPa. The modulus and hardness are reduced by 10% and 15%, respectively, from those of crystalline Si.

Single crystalline samples of bismuth tellurite (Bi2TeO5) were implanted with 800 keV Au+ions to a fluence of 1×1016 cm-2 at room temperature. The samples were subjected to heat treatments in two different ambients (air and high vacuum) at temperatures ranging from 400 - 700°C in a conventional furnace. Strong absorption maxima in the range from 600 - 630 nm in the optical absorption spectra and an intense blue-green color in the samples were observed for annealings performed in air at temperatures between 500 and 700°C indicating the formation of gold colloids. The average radii of the Au clusters formed were estimated to be in the range of 3-4 nm. Samples annealed under vacuum showed distinct changes in color for different annealing temperatures. Studies using the RBS/channeling technique indicate that no full recrystallization of the samples was achieved under both annealing regimes although heat treatment under vacuum provides a significantly better lattice recovery than for air ambient.

Boron is the most important p-type dopant in Si and it is essential that, especially for low energy implantation, both as-implanted B distributions and those produced by annealing should be characterized in very great detail to obtain the required process control for advanced device applications. While secondary ion mass spectrometry (SIMS) is ordinarily employed for this purpose, in the present studies implant concentration profiles have been determined by direct B imaging with approximately nanometer depth and lateral resolution using energy-filtered imaging in the transmission electron microscopy. The as-implanted B impurity profile is correlated with theoretical expectations: differences with respect to the results of SIMS measurements are discussed. Changes in the B distribution and clustering that occur after annealing of the implanted layers are also described.

Secondary Ion Mass Spectrometry (SIMS) with Gas Cluster Ion Beams (GCIB) was studied with experiments and molecular dynamics (MD) simulations to achieve a high-resolution depth profiling. For this purpose, it is important to prevent both ion-mixing and the surface roughening due to energetic ions. As the Ar cluster ion beam shows surface smoothing effects and high secondary-ion yield in the low-energy regime, the cluster ion beam would be suitable for the primary ion beam of SIMS. From MD simulations of Ar cluster ion impact on a Si substrate, the ion-mixing is heavier than for Ar monomer ions at the same energy per atom, because the energy density at the impact point by clusters is extremely high. However, the sputtering yields with Ar cluster ions are one or two orders of magnitude higher than that with Ar monomer ions at the same energy per atom. Comparing at the ion energy where the ion-mixing depths are the same by both cluster and monomer ion impacts, cluster ions show almost ten times higher sputtering yield than Ar monomer ions. Preliminary experiment was done with a conventional SIMS detector and a mass resolution of several nm was achieved with Ar cluster ions as a primary ion beam.

The evolution of the mean size and the size distribution of Au nanoclusters (NCs) under high-energy ion irradiation has been studied. Au NCs were synthesized in a 480 nm thick SiO2 layer by 330 keV Au+ implantation and subsequent annealing at T = 1000 °C for 1h in dry O2. XTEM images show a 70 nm thick layer of Au NCs, being centered at the projected ion range Rp(330keV) = 100 nm, having a mean NC size of 5 nm at Rp, and resembling the broad Lifshiz-Slyozov-Wagner (LSW) size distribution of diffusion controlled Ostwald ripening. Post-irradiation of the Au NCs by 4.5 MeV gold ions was used in order to tailor their size and size distribution. The high-energy Au+ irradiations were performed at 190...210 °C with a fluence of (0.5...1.0)×1016 cm-2. By the post-irradiation no gold was deposited into the SiO2 layer, the Au+ ions come to rest in the (001)Si substrate at Rp(4.5MeV) = 1 [.proportional]m. XTEM images of the post-irradiated Au NCs show a strong decrease of their mean size as well as the width of their size distribution. The observed NC evolution under ion irradiation agrees with recent theoretical predictions and kinetic Monte-Carlo simulations.