The effects of Xe irradiation on He and H co-implanted Si

A combination of X-ray diffraction, cross-sectional transmission electron microscopy (XTEM), and Raman spectroscopy was used to study the effects of irradiation with swift heavy ions on helium and hydrogen co-implanted silicon.<100>-oriented silicon wafers were co-implanted with 30 keV helium to a dose of 3×10¹⁶He⁺/cm² and 24 keV protons to a dose of 2×10¹⁶ H⁺/cm². Moreover, selected helium and hydrogen co-implanted Si wafers were irradiated with 94 MeV xenon. After He and H co-implantation and Xe-irradiation, the wafers were annealed at a temperature of 673 K for 30 min. The damage region of the wafers was examined by the XTEM analysis. The results reveal that most of the platelets are aligned parallel to the (100) plane in the He and H co-implanted Si. However, majority of the platelets lie in<texlscub>111</texlscub>planes after Xe irradiation. Blisters do not occur on the sample surface after Xe irradiation. Raman results reveal that the intensities of both SiH₂ and V₂H₆ modes increase with the increase in the dose of Xe. A possible explanation is that strong electronic excitation during Xe irradiation produces annealing effect, which reduces both lattice damage and the out-of-plane tensile strain.     

Formation of metallic nanophases in silica by ion beam mixing. Part II: cluster formation

2 matrix by ion-beam mixing of SiO₂/Ag multilayers is studied via Rutherford backscattering spectrometry, optical absorption, and transmission electron microscopy experiments. In a first step, irradiation with MeV heavy ions transforms the continuous Ag layers into a string of micrometer-sized Ag inclusions. This mechanism can be attributed to lateral segregation of metallic atoms induced by irradiation. In a second step, the Ag inclusions are broken up by incoming ions and Ag nanoclusters are formed by agglomeration of mobile Ag atoms. The latter mechanism is likely due to a combination of ballistic mixing and radiation-induced segregation or radiation-enhanced diffusion processes. The size of the metallic nanoclusters formed depends also on the irradiation temperature. Received: 27 October 1997/Accepted: 3 February 1998     

Ag-Cu离子注入玻璃后不同气氛退火的光吸收研究

采用MEVVA源（metal vapor vacuum arc ion source）引出的强束流脉冲Ag,Cu离子先后注入到SiO₂玻璃，x射线光电子能谱仪（XPS）分析显示Ag，Cu大多仍为金属态，有部分氧化态Cu存在.透射电镜观察分析和光学吸收谱都表明在衬底中形成了纳米合金颗粒.结合有效媒质理论，得到模拟的光学吸收谱，与实验结果基本符合，较好地验证了以上结论.样品退火后颗粒发生分解，分解的颗粒在氧化气氛下被氧化，且有部分向样品表面蒸发；在还原气氛下氧化态元素被还原并成核生长.故 关键词： 离子注入 纳米颗粒 退火 光学吸收率     

Influence of the ion synthesis and ion doping regimes on the effect of sensitization of erbium emission by silicon nanoclusters in silicon dioxide films

The photoluminescence spectra of erbium centers in SiO₂ films with ion-synthesized silicon nanoclusters under nonresonant excitation were investigated. Erbium was introduced into thermal SiO₂ films by ion implantation. The dependences of photoluminescence intensity on the dose, the order of ion implantation of Si and Er, the annealing temperature, and additional Ar⁺ and P⁺ ion irradiation regimes, i.e., factors determining the influence of radiation damage and doping on sensitization of erbium luminescence by silicon nanoclusters, were determined. It was found that the sensitization effect and its amplification due to doping with phosphorus are most pronounced under the conditions where nanoclusters are amorphous. The quenching of photoluminescence due to radiation damage in this case manifests itself to a lesser extent than for crystalline nanoclusters. The role of various factors in the observed regularities was discussed in the framework of the existing concepts of the mechanisms of light emission and energy exchange in the system of silicon nanoclusters and erbium centers.     

Light-emitting Si nanostructures formed in silica layers by irradiation with swift heavy ions

Thin SiO₂ layers were implanted with 140 keV Si ions to a dose of 10¹⁷ cm⁻². The samples were irradiated with 130 Mev Xe ions in the dose range of 3×10¹²–10¹⁴ cm⁻², either directly after implantation or after pre-annealing to form the embedded Si nanocrystals. In the as-implanted layers HREM revealed after Xe irradiations the 3–4 nm-size dark spots, whose number and size grew with increase in Xe dose. A photoluminescence band at 660–680 nm was observed in the layers with the intensity dependent on the Xe dose. It was found that passivation with hydrogen quenched that band and promoted emission at ∼780 nm, typical of Si nanocrystals. In spectra of pre-annealed layers strong ∼780 nm peak was observed initially. Under Xe bombardment its intensity fell, with subsequent appearance and growth of 660–680 nm band. The obtained results are interpreted as the emission at ∼660–680 nm belonging to the imperfect Si nanocrystals. It is concluded that electronic losses of Xe ions are mainly responsible for formation of new Si nanostructures in ion tracks, whereas elastic losses mainly introduce radiation defects, which quench the luminescence. Changes in the spectra with growth of Xe ion dose are accounted for by the difference in the diameters of Xe ion tracks and their displacement cascades.     

Tailoring of the optical properties of Ag:Si3N4 nanocermets by changes of the cluster morphology

The variation of the optical properties of embedded metallic nanoclusters induced by changes of their morphology is investigated by an approach combining electron microscopy, grazing incidence small angle X-ray scattering and transmission measurements. For this purpose, silver nanoclusters with various shapes (from prolate to oblate) and embedded in an amorphous Si₃N₄ matrix are elaborated by ion beam sputtering using either a co-deposition process or an alternate sputtering. Moreover, a post-irradiation with Ar⁺ ions (at different fluences and low incident energy of 75–100 keV) is used to complement the fabrication process in order to tailor the nanoclusters shape. Prolate and oblate nanoclusters become then more spherical leading to a spectral shift of their surface plasmon resonance. PACS 61.46.+w; 78.67.Bf; 81.07.b; 81.15.cd     

Phase formation and redistribution of Xe implanted in the Ni-Si system after fast melting and solidification

The behaviour of Xe implanted at the Ni-Si interface and irradiated with Nd-laser pulses is studied in details and compared with Xe implantation into NiSi₂ and into pure Si. Ion beam mixing followed by laser irradiation is able to form good quality epitaxial NiSi₂ layer on Si.An inward segregation of Xe is observed with retention of Xe at a depth of 30 nm inside pure silicon. Implantation of Xe into NiSi₂ or pure Si causes broadening and loss of Xe, as generally observed for implantation into pure materials. The different behaviour of Xe at the Si/NiSi₂ interface must thus be ascribed to peculiar characteristics of the interface itself.     

Effect of gas mixing on Xe ion currents from an ECR ion source

Gas mixing technique has been used in order to increase the current of highly charged ions of Xe at the TIFR-ECRIA. The He, N₂, O₂, Ne, and Ar are used as support gases, and their effect on output currents of Xe ions is studied. The effective ion charge and the total loss rate of ions are calculated from the measured currents. It is found that molecular gases, such as N₂ and O₂, exhibit better mixing effect in the enhancement of output of highly charged Xe ions. Furthermore, we describe this 14.5-GHz ECR ion source mounted on a high voltage (400 kV) deck, with its four beamlines, as well as the control system for the remote operation.     

Ion implantation inducing nanovoids characterized by TEM and STEM

The evolution of nanoparticles in sequentially ion-implanted Ag and Ag/Cu into silica glasses has been studied. The doses for implantation (×10¹⁶ ions/cm²) were 5Ag, 5Ag/5Cu and 5Ag/15Cu. Ag nanoclusters have been formed in the implanted 5Ag specimen. In the implanted 5Ag/5Cu specimen, some formed nanoclusters have brighter center features. With an increase of Cu ions dose, the nanoclusters with brighter center features become prevalent. The microstructural properties of the nanoparticles are characterized by transmission electron microscopy. Scanning transmission electron microscope high-angle annular dark field and high-resolution transmission electron microscopy are also utilized to study the formed nanoparticles. The results show that nanovoids have been induced into metal nanoparticles during the ion implanting process, not the core-shell nanoparticles as other workers believed. The nanovoids can be the aggregation of vacancies induced by irradiation.     

Temperature dependent preferential sputtering in CoSi2 and NbSi2

Sputtering of CoSi₂ and NbSi₂ has been carried out by Xe ion bombardment at room temperature, as well as at elevated temperatures putting these systems in their radiation-enhanced diffusion regimes. The range of the Xe ions (at 200–260 keV) was appreciably less than the thickness of the silicides. The samples were analyzed by 2 MeV He⁺ backscattering spectrometry, x-ray diffraction and optical microscopy. The ratio of the sputtering yield of Si to that of the metal (i.e., Co or Nb) always exceeds the stoichiometric ratio 21, leading to Si depleted surface layers. The amount of the sputtered species increases almost linearly with dose until intermixing of the silicide with the underlying Si becomes appreciable. This happens at lower doses in the radiation-enhanced diffusion regime than at room temperature. Irradiation of CoSi₂ samples at high temperature leads to a broadening of the implanted Xe profile compared to the room temperature profile. No such phenomenon has been found in NbSi₂. The effect of Xe broadening on the sputtering yields is discussed.     

Lattice strain in garnet single crystals caused by high-energy heavy ion irradiation

The effect of high-energy heavy ion bombardment on the lattice parameter of single crystal garnets is investigated. Lattice expansion normal to the surface corresponding to lateral compressive strain is observed via x-ray reflection topography and rocking curve analysis using a double-crystal diffractometer. Studied are (111) garnet wafers of differing composition and epitaxial ferrimagnetic iron garnet films on pure and MgZr-substituted (111) Gd₃Ga₅O₁₂ substrates. Using¹³²Xe and²⁰⁸Pb ions of 1.4MeV/nucleon specific energy, the lattice expansion increases approximately linearly with dose over several orders of magnitude. The specific lattice parameter change is approximately 10⁻¹⁴ per ion per cm² for¹³²Xe ions. A triple epitaxial film is used to obtain strain depth profiles     

Ion mixing in Al,Si, and their oxides

The redistribution of thin metallic markers due to ion irradiation was studied by backscattering spectrometry in Al, Al₂O₃, Si, and SiO₂. Marker species were selected for their similar masses and different chemical reactivities with the host media and included Ti, Fe, W, Pt, and Au. It was found that the marker signals are Gaussian and that the variance ² of the marker atom distributions increases linearly with the dose of the irradiation, is insensitive to the temperature of irradiation in the range of 80–300 K, and depends linearly on the nuclear stopping power of the incident ions. The absolute values of ² for Ti, Fe, W, Pt, and Au markers in Al and Al₂O₃, W, and Pt in SiO₂ and W in Si is, within±50 %, of 6.5×10³Å² for 300 keV, 8×10¹⁵ Xe ions/cm². These observations suggest that collisional cascade mixing is a dominant mechanism in this type of impurity-matrix combinations. Only Au and Pt in Si mix at a larger rate: ² for Pt is about 3 and for Au about 5 times larger than ² for all other markers. Lower threshold displacement energies and/or the contribution of processes other than cascade mixing are possible considered reasons. In polycrystalline Al, a rapid migration of Au and Pt atoms throughout the Al layer, similar to grain boundary diffusion, is observed.     

Influence of ion irradiation on the morphology, structure, and optical properties of gold nanoparticles synthesized in SiO2 and Al2O3 dielectric matrices

Irradiation of fused quartz (SiO₂) and sapphire (Al₂O₃) by Ne⁺ and F⁺ ions with medium energies and their subsequent annealing enables us to control the intensity and frequency of surface plasmon resonance in Au nanoparticles (NPs) synthesized in oxide matrices. The control process can be implemented because NPs dissolve during irradiation and undergo partial reconstruction at annealing. The degree of reconstruction depends on the matrix material and the type and dose of ions. It has been found that the difference in the results obtained by means of irradiation with ions with similar masses is substantially affected by the chemical nature of the ions. The composition, morphology, and structure of the unirradiated and irradiated layers are investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry.     

Deposition and fabrication of alkanethiolate gold nanocluster films on TiO2(1 1 0) and the effects of plasma etching

Deposition and fabrication of films of Au nanoclusters protected by alkanethiolate ligands are attempted on a TiO₂(1 1 0) surface and the structures of films are observed by a scanning tunneling microscope (STM). Effects of oxygen and hydrogen-plasma etching in addition to UV irradiation on the structure and chemical composition of the films are also investigated by using STM and X-ray photoelectron spectroscopy. Alkanethiolate Au nanoclusters are produced using a modified Brust synthesis method and their LB films are dip-coated on TiO₂(1 1 0). Alkanethiolate Au nanoclusters are weakly bound to the substrate and can be manipulated with an STM tip. Net-like structures of alkanethiolate Au nanoclusters are formed by a strong blast of air. Oxygen-plasma etching removes alkanethiolate ligands and simultaneously oxidizes Au clusters. At room temperature, prolonged oxygen-plasma etching causes agglomeration of Au nanoclusters. UV irradiation removes ligands partly, which makes Au nanoclusters less mobile. The net-like structure of alkanethiolate Au clusters produced by a blast of air is retained after oxygen and hydrogen-plasma etching.     

Thermoluminescence and opitical absorption of BaF2 crystals

Abstract

Nominally pure and Dy-doped BaF₂ crystals were investigated concerning their optical absorption (OA) and thermoluminescence (TL) properties. Peaks at 120—150 and 200°C were observed for a heating rate of 1.7°C/s. The TL response for γ-rays and the TL emission spectra were obtained for these peaks. Except for the purest crystal, all BaF₂ crystals produced OA bands before irradiation typical of Ce³⁺ ions. After irradiation, Dy doped crystals showed bands due to Dy²⁺ ions. A nominally pure sample gave bands related to Ce²⁺ ions and photochromic centers of Ce³⁺ ions. and photochromic centres of Ce³⁺ ions. The correlation between some OA bands and TL peaks is discussed.     

Photoreduction processes and nanocluster formation induced by a CO2 laser on silicate surfaces

The photoreduction processes stimulated either the cw (power density 10⁵–10⁶ W/cm²) or pulsed (pulse energy 3–4 J, pulse duration 200 ns, effective laser spot diameter 1 mm) radiation of a CO₂ laser on the surfaces of fused and crystalline quartz, as well as of natural silicates (nepheline KNa₃[AlSiO₄]₄, rhodonite CaMn₄[Si₅O₁₅], and zircon ZrSiO₄), are studied. The X-ray emission analysis of irradiated surfaces showed that the laser irradiation of these materials leads to the sublimation of silicon oxides and the enrichment of surfaces with constituent metal elements. Laser radiation also stimulates the formation of silicon and metal nanoclusters on irradiated surfaces. The appearance of these nanoclusters is confirmed by both photoluminescence and X-ray emission studies of irradiated surfaces.     

Kinetics of luminescence of interface defects and resonant Er ions in nanostructured SnO2:SiO2

Silica glass with SnO₂ nanocrystals and Er³⁺ ions are prepared by the sol-gel route and treatment above 1000 °C. Transmission electron microscopy evidences a homogeneous dispersion of nanoclusters 4-6 nm in size in the amorphous silica matrix. Photoluminescence spectra excited at 3.5 eV, outside erbium transitions, show an inhomogeneous spectral distribution of light emission from interface defects, in the range 1.9-2.4 eV, resonant with transitions of erbium ions. The analysis of kinetics and temperature dependence of luminescence allows to quantify the efficiency of the energy transfer channel between nanoclusters and erbium ions.     

IR,UV and visible absorption of X irradiated single crystals of sodium nitrite

X irradiation of NaNO₂ single crystals, induces a motion of some NO₂^? ions, mainly around the axis perpendicular to their planes (a axis). The change in the orientation of NO₂^? is observed on the v₂ vibration of NO₂^? (by IR absorption) and on the vibronic structures associated with the NO₂^? electronic transitions (by UV and visible absorption). Other centers, like no₃^?, are also produced by irradiation. Their evolution with temperature is studied.     

Metallophilic Bond‐Induced Quenching of Delayed Fluorescence in Au25@BSA Nanoclusters

The metallophilic bond is a weak interaction between closed‐shell ions and has been widely used a probe for various sensing of toxic chemicals for environmental safety concerns. Here, the interaction between Au nanoclusters (NCs) and metallic ions (mercury (Hg²⁺) and copper (Cu²⁺) ions) is explored using steady‐state and time‐resolved luminescence and transient absorption measurements. For Hg²⁺ ions, the delayed fluorescence (DF) of bovine serum albumin (BSA) protected Au₂₅ (Au₂₅@BSA) NCs is quenched via an effective triplet state electron transfer through the metallophilic bond. However, the Cu²⁺ ions do not alter the DF in Au₂₅@BSA NCs because of the absence of the metallophilic interaction. Furthermore, for Au₈@BSA and Au₁₀@histidine, in which there are no Au⁺ ions on the surface, the fluorescence is not quenched by Hg²⁺ ions. Such a novel triplet electron transfer process through metallophilic bonds are observed and reported for the first time. The reduction of the reverse intersystem crossing is the crucial for Hg²⁺ ion sensing in the fluorescent Au₂₅@BSA NCs.