离子注入制备纳米晶研究进展

离子注入技术是一种在材料近表面形成埋层纳米晶的一种非常有效的方法，纳米晶的出现使得基体材料具有特殊的物理性质，综述了近几年来利用离子注入技术的金属，半导体、磁性材料纳米晶的发展情况及其潜在的应用，并提出了现存的问题。     

A microstructural and mechanical study on the effects of carbon ion implantation on zirconia-toughened-alumina

Biomedical grade (>99.97% purity) alumina, zirconia and zirconia-toughened-alumina (ZTA) have been implanted with carbon ions at a dose of 5 × 10¹⁷ C ions/cm² using an ion energy of 75 keV. The near-surface hardness of these bioceramics was examined using a load partial-unload indentation technique, both before and after implantation. The surfaces of the bioceramics have also been examined in cross-section using transmission electron microscopy (TEM) both before and after implantation and the implantation data correlated with a computer based simulation, TRIM (Transport and Range of Ions in Matter). The grinding and polishing treatment used prior to the implantation treatment has been found to have a strong influence on the surface microstructures for all three ceramics, although more significant modifications are brought about by carbon ion implantation. A comparison was made between the near-surface hardness of the unimplanted and carbon ion implanted surfaces of these bioceramics with relation to the modified microstructure. TEM examination of the implanted surfaces has demonstrated the formation of a sub-surface amorphous layer in all three materials as well as other microstructural modifications, such as microcracking and an increase in the near-surface dislocation density, that are characteristic of ion damage. The hardness data reveals that carbon ion implantation tends to decrease the surface hardness of alumina and zirconia with increasing ion dose, with a significant decrease occurring at the immediate near surface for both materials.     

Nanocomposites based on highly luminescent nanocrystals and semiconducting conjugated polymer for inkjet printing

In this work nanocomposites based on organic-capped semiconductor nanocrystals formed of a core of CdSe coated with a shell of ZnS (CdSe@ZnS), with different sizes, and a semiconducting conjugated polymer, namely poly[(9,9-dihexylfluoren-2,7-diyl)-alt- (2,5-dimethyl-1,4-phenylene)] (PF-DMB) have been investigated. The nanocomposites are prepared by mixing the pre-synthesized components in organic solvents, thereby assisting the dispersion of the organic-coated nano-objects in the polymer host. UV-vis steady state and time-resolved spectroscopy along with (photo)electrochemical techniques have been performed to characterize the obtained materials. The study shows that the embedded nanocrystals increase the PF-DMB stability against oxidation and, at the same time, extend the light harvesting capability to the visible spectral region, thus resulting in detectable photocurrent signals. The nanocomposites have been dispensed by means of a piezo-actuated inkjet system. Such inks present viscosity and surface tension properties well suited for stable and reliable drop-on-demand printing using an inkjet printer. The fabrication of arrays of single-color pixels made of the nanocomposites and micrometers in size has been performed. Confocal and atomic force microscopy have confirmed that inkjet-printed microstructures present the intrinsic emission properties of both the embedded nanocrystals and PF-DMB, resulting in a combined luminescence. Finally, the morphology of the printed pixels is influenced by the embedded nanofillers.     

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.     

Direct observation of defect-mediated cluster nucleation

Ion implantation is widely used to introduce electrically or optically active dopant atoms into semiconductor devices. At high concentrations, the dopants can cluster and ultimately form deactivating precipitates, but deliberate nanocrystal formation offers an approach to self-assembled device fabrication. However, there is very little understanding of the early stages of how these precipitates nucleate and grow, in no small part because it requires imaging an inhomogenous distribution of defects and dopant atoms buried inside the host material. Here we demonstrate this, and address the long-standing question of whether the cluster nucleation is defect-mediated or spontaneous. Atomic-resolution illustrations are given for the chemically dissimilar cases of erbium and germanium implanted into silicon carbide. Whereas interstitial loops act as nucleation sites in both cases, the evolution of nanocrystals is strikingly different: Erbium is found to gather in lines, planes and finally three-dimensional precipitates, whereas germanium favours compact, three-dimensional structures.     

Ion beam synthesis of compound nanoparticles in SiO2

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.     

The role of electronic energy loss in ion beam modification of materials

The interaction of energetic ions with solids results in energy loss to both atomic nuclei and electrons in the solid. In this article, recent advances in understanding and modeling the additive and competitive effects of nuclear and electronic energy loss on the response of materials to ion irradiation are reviewed. Experimental methods and large-scale atomistic simulations are used to study the separate and combined effects of nuclear and electronic energy loss on ion beam modification of materials. The results demonstrate that nuclear and electronic energy loss can lead to additive effects on irradiation damage production in some materials; while in other materials, the competitive effects of electronic energy loss leads to recovery of damage induced by elastic collision cascades. These results have significant implications for ion beam modification of materials, non-thermal recovery of ion implantation damage, and the response of materials to extreme radiation environments.     

High concentration erbium doping of silicon-rich SiO2 thin films on silicon

In this work, high concentration erbium doping in silicon-rich SiO₂ thin films is demonstrated. Si plus Er dual-implanted thermal SiO₂ thin films on Si substrates have been fabricated by using a new method, the metal vapor vacuum arc ion source implantation with relatively low ion energy, strong flux and very high dose. X-Ray photoelectron spectroscopy measurement shows that very high Er concentrations on the surfaces of the samples, corresponding to 10 at.% or the doping level of 10²¹ atoms cm⁻³, are achieved. This value is much higher than that obtained by using other fabrication methods such as the high-energy ion implantation and molecular beam epitaxy. Reflective high-energy electron diffraction, atomic force microscopy and cross-section high-resolution transmission electron microscopy observations show that the excess Si atoms in SiO₂ matrix accumulate to form Si clusters and then crystallize gradually into Si nanoparticles embedded in SiO₂ films during dual-ion implantation followed by rapid thermal annealing. Er segregation and precipitates are not formed. Photoluminescence at the wavelength of 1.54 μm exhibits very weak temperature dependence due to the introduction of Si nanocrystals into the SiO₂ matrix. The 1.54-μm light emission signals from annealed samples decrease by less than a factor of 2 when the measuring temperature increases from 77 K to room temperature.     

Improvement of metal properties by ion implantation

Ion implantation is being investigated as a technique for the beneficial modification of surface-sensitive and life-limiting properties of metals including resistance to wear and fatigue. Ion implantation is a process of accelerating ions to high velocities and directing them into the near-surface regions of materials (e.g. alloys) to produce in essence a different material (alloy) in the near-surface region. Ion implantation can produce a graded alloy from the surface to the unchanged underlying bulk alloys so that both the surface and the bulk alloys can be independently optimized. The implanted layer is typically hundreds to thousands of ångströms deep with implanted atom concentrations of up to fifty atomic per cent or more. The sliding-wear rate between various steel alloys was significantly reduced by implanting one of the surfaces with selected elemental species such as nitrogen, carbon and titanium. Experiments were conducted on a number of materials including stainless steel, too steel, bearing alloys and silicon nitride. The implantation technique has also been reported to increase fatigue lifetimes in low-carbon steel by a factor of 50–100. Experimentation is now being directed towards other materials of major technological interest such as titanium alloys. The effect of ion implantation on (1) the wear and fatigue properties and (2) the microstructural characteristics of implanted materials with selected examples is discussed.     

Effect of ion doping with donor and acceptor impurities on intensity and lifetime of photoluminescence from SiO2 films with silicon quantum dots

Doping with donor and acceptor impurities is an effective way to control light emission originated from quantum-size effect in Si nanocrystals. Combined measurements of photoluminescence intensity and kinetics give valuable information on mechanisms of the doping influence. Phosphorus, boron, and nitrogen were introduced by ion implantation into Si+ -implanted thermal SiO2 films either before or after synthesis of Si nanocrystals performed at Si excess of about 10 at.% and annealing temperatures of 1000 and 1100 degrees C. After the implantation of the impurity ions the samples were finally annealed at 1000 degrees C. It is found that, independently of ion kind, the ion irradiation (the first stage of the doping process) completely quenches the photoluminescence related to Si nanocrystals (peak at around 750 nm) and modifies visible luminescence of oxygen-deficient centers in the oxide matrix. The doping with phosphorus increases significantly intensity of the 750 nm photoluminescence excited by a pulse 337 nm laser for the annealing temperature of 1000 degrees C, while introduction of boron and nitrogen atoms reduces this emission for all the regimes used. In general, the effective lifetimes (ranging from 4 to 40 micros) of the 750 nm photoluminescence correlate with the photoluminescence intensity. Several factors such as radiation damage, influence of impurities on the nanocrystals formation, carrier-impurity interaction are discussed. The photoluminescence decay is dominated by the non-radiative processes due to formation or passivation of dangling bonds, whereas the intensity of photoluminescence (for excitation pulses much shorter than the photoluminescence decay) is mainly determined by the radiative lifetime. The influence of phosphorus doping on radiative recombination in Si quantum dots is analyzed theoretically.     

Structures and light emission properties of nanocrystalline FeSi2/Si formed by ion beam synthesis with a metal vapor vacuum arc ion source

Thin layers of nanocrystalline FeSi₂ embedded in Si structures have been formed by Fe implantation using a metal vapor vacuum arc (MEVVA) ion source under various implantation and thermal annealing conditions. The microstructures were studied in details and correlated with the photoluminescence (PL) properties. It is found that higher lattice coherence between the FeSi₂ nanocrystals and the Si matrix is associated with better light emission efficiency. Multiple-cycle implantation schemes were introduced and it is shown that with appropriate process design the dose quenching effect can be suppressed to achieve light emission enhancement in higher dose samples. De-convolution of the PL spectra into two or three peaks was performed and their temperature and excitation power dependence were analyzed. The analysis results indicate that the 1.55-μm emission really originated from FeSi₂ and that the emission peaks are likely donor- or accepted-level-related. MOS structures with the incorporation of implanted nanocrystalline FeSi₂ were fabricated. Electroluminescence (EL) spectra from these devices showed two peak features of which one peak corresponds to FeSi₂ emission and the other corresponds to enhanced Si band-edge emission. Clear room-temperature EL signals from these device structures were observed. A model is proposed to qualitatively understand the temperature dependence of the EL spectra.     

Charge storage behaviors of Ge nanocrystals embedded in SiO2 for the application in non-volatile memory devices

Ge nanocrystals distributed in the SiO2 of metal-oxide-semiconductor structure are synthesized by low-energy Ge ion implantation with various energies and doses. Their charge storage behaviors are influenced by both the ion implantation dose and energy. The larger flatband voltage shift achieved by increasing either the implantation dose or energy is explained by the locations and concentration of the charge trapping sites. The smaller charge loss achieved by decreasing the implantation dose or increasing the implantation energy is explained by the co-existence of the charge leakage to the gate electrode and the lateral charge loss to the adjacent Ge nanocrystals.     

Microstructural evolution of a silicon carbide-carbon coated nanostructured ferritic alloy composite during in-situ Kr ion irradiation at 300℃ 450℃

This work focuses on irradiation behaviors of a novel silicon carbide and carbon coated nanostructured ferritic alloy (SiC-C@NFA) composite for potential applications as a cladding and structural material for next generation nuclear reactors.The SiC-C@NFA samples were irradiated with 1 MeV Kr ions up to 10 dpa at 300 and 450 ℃.Microstructures and defect evolution were studied in-situ at the IVEM-Tandem facility at Argonne National Laboratory.The effects of ion irradiation on various phases such as α-ferrite matrix,(Fe,Cr)7C3,and (Ti,W)C precipitates were evaluated.The α-ferrite matrix showed a continuous increase in dislocation density along with spatial ordering of dislocation loops (or loop strings) at ＞5 dpa.The size of the dislocation loops at 450 ℃ was larger than that at 300 ℃.The nucleation and growth of new (Ti,W)C precipitates in α-ferrite grains were enhanced with the ion dose at 450 ℃.This study provides new insight into the irradiation resistance of the SiC-C@NFA system.     

Hydrogen in semiconductors

Hydrogen in crystalline semiconductors has become a recent curiosity because of its high diffusivity and strong chemical activity in such materials. In contrast to the proton motion in ionic materials which gives rise to an enhanced conductivity, hydrogen in electronic materials interact with structural disorders and chemical impurities to control the electronic flow. Deep gap states in crystalline semiconductors due to various disorders such as surface/interface, grain boundaries, dislocations, irradiation and implantation damage etc. have been removed due to hydrogen bondings. Hydrogen incorporation is done by plasma and direct ion beam hydrogenation methods, implantation technique and by a novel technique of damage free introduction. The most studied materials are silicon and gallium arsenide.I - V,C - V, DLTS and IR studies have been carried out on hydrogenated semiconductors to characterize the electronic flow, gap states and the nature of chemical bonds. Improvement in ideality factors of diodes, reduction in free carrier concentration, removal or reduction of deep states and appearance of new bondings such as Si-H, P-H, B-H etc. have been observed from various techniques. The present paper reviews the various features of hydrogenation studies in crystalline silicon and gallium arsenide and highlights our results of hydrogenation studies on Pd/semiconductor devices.     

Magneto-optical stokes polarimetry and nanostructured magnetic materials

Stokes parameters fully characterize the polarization state of light in an experimentally accessible manner. Photoelastic modulator (PEM) based Stokes polarimetry offers a very high sensitivity which is particularly suitable for the investigation of the magneto-optical properties of nanostructured magnetic materials. In this paper, we shall describe a robust methodology recently developed by us that utilizes a dual PEM setup. As an example of its application, we report on the magneto-optical characteristics of focused Ga ion beam patterned Fe films. We have investigated Ga ion irradiation of single-layer polycrystalline Fe films deposited on Si3N4 substrates, which allows us to study the effects of ion implantation with minimum added complications. Complemented by structural and other characterization techniques, the absolute measurement of magneto-optical effects through the determination of Stokes parameters has enabled us to effectively separate the various contributions from film thinning due to sputtering, structural modifications and compositional changes caused by Ga incorporation. A comparison is also made between the magneto-optical behavior of patterned thin films and that of anodic aluminum oxide embedded magnetic nanowire arrays.     

PbS nanocrystals embedded in microstructures produced by micromoulding in capillaries

The study presents a new method to prepare PbS nanocrystals embedded in poly(acrylic acid) (PAA) microstructures by micromoulding in capillaries (MIMIC). The micropatterns were fabricated first from aqueous solution of acrylic acid lead monomer, and subsequently solidified by γ-ray polymerization. The resulting samples were treated with aqueous Na₂S solution to convert Pb precursor to PbS in the matrix. The final micropatterns of PAA embedded with PbS nanocrystals were of high resolution. The products were characterized by IR, XRD, TEM and SPM, respectively, and the results demonstrated that PbS embedded in PAA was nanocrystals.     

Luminescence properties of ZnS:Mn nanocrystals embedded in SiO2 by ion implantation

Sequential multi-energy implantations of zinc and sulphur ions have been performed in a 250-nm thick SiO₂ layer thermally grown on 1 1 1 silicon. Energies and doses have been chosen to produce 10 at.% constant concentration profiles overlapping over about 100 nm. Manganese is subsequently introduced at various levels by the same way. Thermal treatments (from 700 to 1100 °C) lead to the formation of nanometric precipitates of the luminescent compound ZnS:Mn. A bimodal size distribution is observed, with a quasi-single layer of large particles (40 nm) in the end-of-range region and much smaller precipitates between this layer and the surface. The orange emission is maximal when the Mn concentration is close to 3%. Several hours at 900 °C is the best thermal budget for maximal luminescence intensity at room temperature. A shift of the excitation spectrum related to size variations, shows that the particles of smaller size are mainly responsible for the observed luminescence. In agreement with other authors, the luminescence lifetime is found in the ms range and increases with the nanocrystal diameter, tending to the lifetime of bulk ZnS. The luminescence of ZnS:Mn nanoparticles embedded in SiO₂ by ion implantation is also shown to be very stable during long UV light irradiation.     

Optical properties of ZnTe and ZnS nanocrystals by critical-points and Tauc-Lorentz models

The optical properties of ZnTe and ZnS nanocrystals (ZnTe-NC and ZnS-NC) were determined by Spectroscopic Ellipsometry. The nanocrystals were embedded in a SiO₂ matrix by ion implantation technique. Their sizes were characterized by transmission electron microscopy. The ZnTe-NC and ZnS-NC were modelled using Critical Points (CPs) dispersion formulas developed by Adachi. Besides the CPs model, the Tauc-Lorentz model was found to be another choice to get a good spectral fitting. Here we demonstrated that these models yield reasonable values of optical constants of II-VI nanocrystals. The best agreement was found with the experimental data over the entire range of 0.6 to 6.5 eV.     

Preparation and characterization of rare-earth bulks with controllable nanostructures

The preparation and characterization of pure rare-earth-metal bulks with controllable nanostructures are reported in this paper. A novel 'oxygen-free' in?situ synthesis technique that combines inert-gas condensation with spark plasma sintering (SPS) technology is proposed. Taking into account the special mechanisms of SPS consolidation and the scale effects of nanoparticles, we introduced practical procedures for preparing rare-earth bulks of amorphous, mixed amorphous and nanocrystals, and nanocrystalline microstructures, respectively. Compared with the conventional polycrystalline bulk, these nanostructured bulks exhibit substantially improved physical and mechanical properties. This technique enables comprehensive studies on the microstructures and properties of a large variety of nanostructured metallic materials that are highly reactive in the air.     

Ionen- und plasmagestützte Verfahren der Oberflächentechnik für die Randschichtbehandlung von Leichtmetallwerkstoffen

Surface engineering of light weight materials with ion- and plasma-assisted methods Increasing applications of light weight materials are expected in the future. Pursuing this trend surface engineering of these materials – especially ion- and plasma-assisted methods – swill be of increasing interest to enhance their wear and corrosion resistance. In a research co-operation some promising methods were examined on different aluminium and titanium alloys to assess their potential to increase the surface properties. Among these were magnetron sputtering of chromium nitride, ion beam assisted deposition of Cr/CrN and Al/A₂O₃ layers, ion implantation and ion beam assisted nitriding. Compared to the steel substrates the assessment of the mechanical properties such as the critical load of the scratch test of the coated light weight materials is different. Furthermore, it could be shown that both spherical section and glow discharge optical spectroscopy are useful methods to characterize the near-surface zone influenced by ion implantation.