Enhanced luminescence from encapsulated silicon nanocrystals in SiO2 with rapid thermal anneal

It is well known that Si ion implantation into SiO₂ and subsequent high-temperature anneals induce the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of rapid thermal annealing to enhance the photoluminescence intensity have been investigated. Ion implantation was used to synthesize specimens of SiO₂ containing excess Si with different concentrations. Si precipitation to form nanocrystals in implanted samples takes place with a conventional furnace anneal. The photoluminescence intensity and the peak energy of emission from Si nanocrystals depend on implanted ion dose. Moreover, the luminescence intensity is strongly enhanced with a rapid thermal annealing prior to a conventional furnace anneal. The luminescence intensity, however, decreases when rapid thermal annealing follows conventional furnace annealing. It is found that the order of heat treatment is an important factor in intensities of the luminescence and that the luminescence peak energy is found to be dependent, but only by a small factor, on the thermal history of specimens. Enhancement is found to be typical for low dose samples. Furthermore, the observation that the prolonged anneal induces saturation and a blue shift of the luminescence strongly indicates the emission is not simply due to electron-hole recombination inside the Si nanocrystals. Based on our experimental results, we discuss the mechanism for the enhancement of the photoluminescence, together with the mechanism of photoemission.     

CuCl+注入α-Al2O3晶体退火后表面亚微米颗粒的形成情况研究

CuC l+离子注入不同晶向的α-A l2O3晶体中,对在还原气氛下退火后的试样进行SEM表面观察。结果发现,不同注入条件和不同温度退火的不同晶向α-A l2O3晶体表面均形成弥散的亚微米颗粒。说明CuC l+离子注入α-A l2O3晶体产生的缺陷损伤在退火过程中,单个分散的带电色心缺陷与CuC l+离子形成的缺陷缔合体在恢复过程中发生了CuC l原子的偏聚,随着退火时间的增加,偏聚程度提高而形成颗粒,并逐渐长大形成亚微米颗粒。颗粒的大小和分布随注入条件以及退火温度不同而不同。     

Controlling the growth of ZnO quantum dots embedded in silica by Zn/F sequential ion implantation and subsequent annealing

We report the formation of embedded ZnO quantum dots (QDs) by Zn and F ion sequential implantation and subsequent annealing. Optical absorption and photoluminescence spectrum measurements, transmission electron microscopy bright field images and selected area electron diffraction patterns indicate that ZnO QDs were formed after annealing in air or vacuum at temperatures higher than 500?°C. Atomic force microscopy images show a comparatively flat surface of the annealed samples, which indicates that only very few Zn atoms are evaporated to the surfaces. The formation of ZnO QDs during the thermal annealing can be attributed to the direct oxidization of Zn nanoparticles by the oxygen molecules in the substrate produced during the implantation of F ions. The quality of ZnO QDs increases with the increase of annealing temperature.     

Photoelectric Properties of Single-Crystal InSb Implanted with Mg Ions

The nonuniform distributions of defects and impurities, as well as polishing damage, have a profound effect on the secondary-defect formation in InSb single crystals during ion implantation. The spectral dependences of photoconductance of ion-implanted InSb samples show that surface preparation and subsequent ion bombardment may result in the formation of electrically active defects at large depths below the irradiated surface. The annealing behavior of the irradiation damage is determined by the wafer-preparation procedure rather than by the irradiation and heat-treatment conditions.     

Through Thickness Variation of Cross Shear Rolling Texture in Grain Oriented Silicon Steel

The texture inhomogeneity in cross shear rolled grain oriented Si steel was investigated by means of the through thickness texture analysis. For the chosen rolling reductions (55%, 66.5%) and mismatch speed ratios (1.0, 1.1, 1.3), the deformation textures in various thickness layers consist of three major components, i.e. strong γ-fiber, medium α-fiber and weak η-fiber, and they show an asymmetrical distribution throughout the thickness. The effect of reduction on the texture gradient is found to be more significant at and near the center layer; however, the effect of mismatch speed ratio is less important. In most cases, a strong {111}<112> texture component appears in the subsurface layers, that may favour the formation of a sharp Goss texture during the subsequent annealing.     

Combined impurity gettering effects of helium-induced cavities and oxygen precipitates created by plasma immersion ion implantation

Helium bubbles are formed in silicon by high dose implantation using the plasma immersion ion implantation technique. Thermal annealing of the implanted samples at a temperature above 700 °C causes the helium to diffuse out of silicon and form cavities which can be observed by cross-sectional transmission electron microscopy. The well-defined band of helium-induced cavities both with and without oxygen precipitates (formed by subsequent oxygen implantation and annealing) have been studied as gettering layers for copper and gold. Our secondary ion mass spectrometry and Rutherford backscattering spectrometry results demonstrate that the presence of oxygen does not increase significantly the gettering efficiency of these cavities. The combined cavity/oxygen gettering sites also remain stable up to 1200 °C     

Effect of Co Ion Implantation on GMR of [NiFeCo(10 nm)/Ag(10 nm)] ×20Multilayer Film

The composition, phase structure and microstructure of the discontinuous multilayer film [NiFeCo(10 nm)/Ag(10 nm)]×20 were investigated after Co ion implantation and annealing at 280, 320, 360 and 400℃, respectively.GMR (giant magnetoresistance) ratio of the film with/without Co ion implantation was measured. The results showed that Co ion implantation decreased the granule size of the annealed multilayer film, and increased Hc value and GM R ratio of the multilayer film. After annealing at 360℃, the multilayer film [NiFeCo(10 nm)/Ag(10 nm)] ×20with/without Co ion implantation both exhibited the highest GMR ratio of 12.4%/11% under 79.6 kA/m of applied saturation magnetic field.     

Effect of Co Ion Implantation on GMR of [NiFeCo(10 nm)/Ag(10 nm)]×20 Multilayer Film

The composition, phase structure and microstructure of the discontinuous multilayer film [NiFeCo(10 nm)/ Ag(10 nm)]×20 were investigated after Co ion implantation and annealing at 280, 320, 360 and 400℃, respectively. GMR (giant magnetoresistance) ratio of the film with/without Co ion implantation was measured. The results showed that Co ion implantation decreased the granule size of the annealed multilayer film, and increased Hc value and GMR ratio of the multilayer film. After annealing at 360℃, the multilayer film [NiFeCo(10 nm)/Ag(10 nm)]×20 with/without Co ion implantation both exhibited the highest GMR ratio of 12.4%/11% under 79.6 kA/m of applied saturation magnetic field.     

Accelerator based synthesis of hydroxyapatite by MeV ion implantation

Accelerator based MeV ion implantation of Ca²⁺ and P²⁺ into the titanium substrate to form hydroxyapatite (HA) has been carried out. Calcium hydroxide was formed after heating the calcium implanted titanium in air at 80 °C for 3 h. Upon subsequent annealing for 5 min at 600 °C HA was formed on the surface. Penetration depth of the HA layer in this method is much higher as compared to keV ion implantation. By elemental analysis, Ca/P ratio of the HA was found to be 1.76 which is higher than the ideal 1.67. This higher Ca/P ratio is attributed to the higher penetration depth of the MeV technique used.     

Ion irradiation effects in nonmetals: formation of nanocrystals and novel microstructures

Ion implantation is a versatile and powerful technique for producing nanocrystal precipitates embedded in the near-surface region of materials. Radiation effects that occur during the implantation process can lead to complex microstructures and particle size distributions, and in the present work, we focus on the application of these effects to produce novel microstructural properties for insulating or semiconducting nanocrystals formed in optical host materials. Nanocrystal precipitates can be produced in two ways: by irradiation of pure (i.e., non-implanted) crystalline or amorphous materials, or by ion implantation followed by either thermal annealing or subsequent additional irradiation. Different methods for the formation of novel structural relationships between embedded nanocrystals and their hosts have been developed, and the results presented here demonstrate the general flexibility of ion implantation and irradiation techniques for producing unique near-surface nanocomposite microstructures in irradiated host materials. Received: 28 October 1999 / Reviewed and accepted: 12 November 1999     

A new route toward semiconductor nanospintronics: highly Mn-doped GaAs nanowires realized by ion-implantation under dynamic annealing conditions

We report on highly Mn-doped GaAs nanowires (NWs) of high crystalline quality fabricated by ion beam implantation, a technique that allows doping concentrations beyond the equilibrium solubility limit. We studied two approaches for the preparation of Mn-doped GaAs NWs: First, ion implantation at room temperature with subsequent annealing resulted in polycrystalline NWs and phase segregation of MnAs and GaAs. The second approach was ion implantation at elevated temperatures. In this case, the single-crystallinity of the GaAs NWs was maintained, and crystalline, highly Mn-doped GaAs NWs were obtained. The electrical resistance of such NWs dropped with increasing temperature (activation energy about 70 meV). Corresponding magnetoresistance measurements showed a decrease at low temperatures, indicating paramagnetism. Our findings suggest possibilities for future applications where dense arrays of GaMnAs nanowires may be used as a new kind of magnetic material system.     

Monte-Carlo program MODEX: Simulation of point defect clustering during irradiation and subsequent annealing

A Monte Carlo program MODEX is presented, capable of simulating the defect clustering process during ion implantation and subsequent annealing. The program considers four different types of point defects, e.g. implanted ions, vacancies, self-interstitials and impurities, as mobile. Depending on the mobility of the point defect the diffusion equations are solved in the stationary or non-stationary form. The clustering process of point defects is described by a set of rate equations and is simulated through a number of elementary trapping and dissociation events. The use of the program is demonstrated in examples of helium implantation in molybdenum, vanadium and silicon and the simulation results are discussed in relation to the results of helium desorption experiments.     

Thermal effects on the microstructure and mechanical properties of ion implanted ceramics

The effects of varying the substrate temperature on the implantation-induced structures and surface mechanical properties of single crystal sapphire and MgO have been investigated for a range of 300 keV implanted ions. As the implantation temperature is lowered, the dose at which amorphization occurs is reduced and thus, for the same doses, more amorphous material is produced at lower temperatures. Quantitative modelling shows that the activation energy for annealing of the amorphous material during implantation is very much lower than might be expected for post-implantation thermal annealing of the same material. Also, as the implantation temperature increases there is a small amount of damage annealing in the damaged-but-crystalline material.Both the microhardness and implantation-induced stresses depend critically on the presence of amorphous material since this is relatively soft and can support only small stresses. However, while the hardness behaviour in the damaged-but-crystalline material is dominated by radiation hardening, the substitutionality, ionic misfit and charge state of the implanted ions have also been found to contribute to the further solid solution component of the hardening produced by ion implantation. These effects are also observed to be temperature dependent. Crazing of the implanted layers has also been reappraised. It has been established that the formation and configuration of crazes is a sensitive function of implantation temperature, and it is now proposed that crazes form in response to the stresses generated as a result of the thermal expansion mismatch between the amorphous layer and the substrate.     

Si nanocrystals formation in SiO2 by ion implantation: The effects of RTA and UV irradiation on photoluminescence

Si ion implantation was widely used to synthesize specimens of SiO₂ containing supersaturated Si and subsequent high temperature annealing induces the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of excimer UV-light (172 nm, 7.2 eV) irradiation and rapid thermal annealing (RTA) to enhance the photoluminescence and to achieve low temperature formation of Si nanocrystals have been investigated. The Si ions were introduced at acceleration energy of 180 keV to fluence of 7.5 × 10¹⁶ ions/cm². The implanted samples were subsequently irradiated with an excimer-UV lamp. After the process, the samples were rapidly thermal annealed before furnace annealing (FA). Photoluminescence spectra were measured at various stages at the process. We found that the luminescence intensity is strongly enhanced with excimer-UV irradiation and RTA. Moreover, effective visible photoluminescence is found to be observed even after FA at 900 °C, only for specimens treated with excimer-UV lamp and RTA. Based on our experimental results, we discuss the effects of excimer-UV lamp irradiation and RTA process on Si nanocrystals related photoluminescence.     

Structures and properties of Ti alloys after double implantation

The paper presents new results on investigation of structure and physical-mechanical properties of near surface layers of titanium alloys after (W⁺, Mo⁺) ion implantation and subsequent thermal annealing under 550 °C for 2 h. Using back scattering (RBS) of helium ions and protons, scanning electron microscopy (SEM) with microanalysis (EDS), (WDS), proton (ion) induced X-ray emission (PIXE), X-ray phase analysis (XRD) with a grazing incidence geometry (0.5° angle), measurements of nanohardness and elastic modulus, friction wear (cylinder-plate), measurements of corrosion resistance in a salt solution, we investigated the VT-6 samples, and determined their fatigue resistance under cyclic loads. Double increase of hardness, decrease of wear and increased fatigue resistance were found, which was related to the formation of small dispersion (nanodimension) nitride, carbonitride, and intermetalloid phases.     

Secondary ion mass spectrometry of dopant and impurity elements in wide bandgap semiconductors

Based on secondary ion mass spectrometry (SIMS) measurements, we have compiled state-of-the-art data concerning dopant elements and natural impurities in the wide bandgap semiconductor materials diamond, SiC, ZnSe, GaN and AlN. Samples were prepared by ion implantation of different elements into these materials and post-implantation thermal annealing. SIMS depth profiling techniques were used to determine atomic depth profiles of implanted elements and subsequent changes produced by annealing. Range statistics and SIMS relative sensitivity factors were established for major dopant and impurity elements in these wide bandgap materials. Results of these studies are presented in tabular form along with representative depth profile figures.     

Gas-sensor properties of SnO2 films implanted with gold and iron ions

SnO₂ gas-sensor films were modified by implantation of gold and iron ions. The change in electrical resistivity of the films caused by inflammable gases, H₂, CO, CH₄ and C₂H₅OH, was measured in the temperature range 100–500°C, and compared to non-implanted films. The morphological changes caused by gold and iron ion implantation were also investigated by atomic force microscopy. After ion implantation and annealing at 600°C, the sensitivity to H₂ and CO gas was found to increase, and the dynamic range of the sensitivity to ethanol was improved. The sensitivity to CH₄ was low before and after ion implantation. Fe₂O₃ (3%SnO₂) film was also modified by gold ion implantation for comparison. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optical properties of a single mode planar waveguide in Nd:YVO4 fabricated by multienergy He ion implantation

We fabricated a single-mode planar waveguide in z-cut Nd:YVO(4) by multienergy He ion implantation in total fluence of 4.5×10(16) ions/cm(2) at room temperature and investigated optical properties of Nd:YVO(4) before and after He ion implantation by measuring transmission, confocal microluminescence, and confocal Raman spectra. Absorption bands and the photoluminescence features of the bulk Nd:YVO(4) crystal have been preserved after He ion implantation. In Raman spectra, most of the peak positions and peak widths had no obvious change before and after He ion implantation. The guiding mode and near-field image in the waveguide were measured by the prism coupling method and end-face coupling method, respectively. We investigated the damage behavior of a Nd:YVO(4) waveguide after implantation, annealing treatment by the Rutherford backscattering/channeling technique. The minimum yield of the virgin z-cut Nd:YVO(4) was 1.98%, which increased to 4.73% after He ion implantation and decreased to 3.20% after annealing at 600 K for 30 minutes.     

Nanocluster evolution in Ge ion implanted Ta2O5 layers

Ion implantation-induced nanoclusters were synthesized in reactive sputtered Ta₂O₅ films by Ge⁺ implantation and subsequent annealing. The effects of ion fluence and post-implantation thermal treatment on the kinetics of the nanoclustering were investigated. Ge⁺ ions with energy of 40 keV and fluences of 5 × 10¹⁵, 1 × 10¹⁶ and 5 × 10¹⁶ cm^− 2 were implanted in the Ta₂O₅ layers at room temperature. The samples were thermally treated by rapid thermal annealing in vacuum at 700 °C and 1000 °C for 30, 60 and 180 s. Structural studies of all samples were done by Cross-sectional Transmission Electron Microscopy in diffraction and phase contrast mode. Under optimized conditions (high implantation fluence, subsequent annealing) nanoclusters are formed around the projected ion range of the implanted Ge⁺ ions. The structure of the implanted Ta₂O₅ matrix changes from amorphous to orthorhombic when the annealing was performed at 1000 °C. Although the Ta₂O₅ matrix crystallizes, no evidence is obtained for crystallization of the embedded nanoclusters even after annealing at 1000 °C.     

The investigation of lateral damage effects of ion-implanted layers by back-scattering techniques

Using a particle beam of small diameter the back-scattering technique can be applied to the microanalysis of small geometries. By moving a sample in steps of 5 μm with respect to the beam, lateral properties of the surface layers can be investigated. Particle beams of He⁺ ions with diameters of 5–100 μm have been used.We found that the width of a damaged area which was defined by SiO₂ masking during ion implantation was smaller than the width of the window in the mask itself.A wire for masking was placed at a distance of 1 mm from the surface of the sample. In this case lateral annealing of the implanted area was observed, which might be due to an effect of the scanning ion beam.