Sequential Ion Implantation Research Articles

Fabrication of TiO2-based composite films by sequential ion implantation and subsequent annealing

A special method for fabricating a series of TiO2-based composite catalyst film is presented. There are two steps in this method. Firstly, two kinds of elements are sequentially implanted into the substrate. Then, the implanted samples are annealed in oxygen atmosphere. This method involves a solid phase growth process, which can be successfully used to prepare noble metal nanoparticles modified TiO2 film (Au NP-TiO2), metallic (Fe, V) and non-metallic (N) doped TiO2, and narrow-width band gap heterojunctions (Fe2O3-TiO2). These TiO2-based composite catalyst films show good crystallinity and stability, easy catalyst immobilization and recycling in photocatalytic experiments. In addition, the detailed growth processes and mechanisms of these TiO2-based composite films were systematically studied.

Conductivity type and crystal orientation of GaAs nanocrystals fabricated in silicon by ion implantation and flash lamp annealing

The integration of III–V semiconductor material within silicon technology is crucial for performance of advanced electronic devices. This paper presents the investigations of microstructural and opto-electronic properties of GaAs quantum dots (QDs) formed in silicon by means of sequential ion implantation and flash lamp annealing (FLA). Formation of crystalline GaAs QDs with well-defined crystal orientation and conductivity type was confirmed by high resolution transmission electron microscopy and μ-Raman spectroscopy. The influence of the post implantation millisecond-range annealing on the evolution of the nanoparticles size, shape, crystallographic orientation and doping type of GaAs QDs is discussed.

Raman Scattering and Backscattering Studies of Silicon Nanocrystals Formed Using Sequential Ion Implantation

Silicon nanocrystals were produced using a two-stage gold ion implantation technique. The first stage implantation using low energy ions led to the formation of an amorphous Si (a-Si) layer. A subsequent high energy Au irradiation in the second stage was found to produce strained Si NCs. An annealing step at a temperature as low as 500 °C was seen to result in strain free NCs. Higher temperature annealing of the samples was found to result in a growth in size from recrystallization of the a-Si matrix. Raman Scattering, X-Ray diffraction and Rutherford Backscattering Spectrometry have been used to study the effect of annealing on the samples and the size of the Si NCs formed. The data can be well explained using a phonon confinement model with an extremely narrow size distribution. The XRD results are in line with the Raman analysis.

III-V Quantum Dots in Dielectrics Made by Ion Implantation and Flash Lamp Annealing

Di erent semiconductor nanocrystals synthesized in dielectrics on silicon are very interesting for applications in non-volatile memories and photovoltaics. In this paper we present an overview of microstructural and opto-electronic properties of di erent III V quantum dots embedded in SiO2 and Si3N4 made by sequential ion implantation and millisecond range ash lamp annealing. It is shown that within 20 ms post-implantation annealing high quality crystalline III V quantum dots can be formed in di erent matrices. Formation of crystalline III V quantum dots was con rmed by cross-section transmission electron microscopy, photoluminescence and μ-Raman spectroscopy. Flash lamp annealing is essentially a singleash-single-wafer technique whose main attributes are the ease and control of processing over large wafer batches.

Atomic retention and near infrared photoluminescence from PbSe nanocrystals fabricated by sequential ion implantation and electron beam annealing

Nanocrystals of PbSe have been fabricated in a silicon dioxide matrix by sequential low energy ion implantation followed by an electron beam annealing step. Transmission electron microscopy reveals PbSe nanocrystals with typical sizes between 3 and 10nm in the sub-surface region. Rutherford Backscattering Spectrometry has been used to study the total atomic retention, as a function of implanted atoms, following annealing. Photoluminescence was observed in various samples, at 4K, as a broad peak between 1.4 and 2.0μm, with observation of a dependence of the peak wavelength on annealing temperature. Room temperature photoluminescence was observed for samples with a high retention of implanted atoms, demonstrating the importance of nanocrystal density for achieving ambient temperature emission in these systems.

Optical Limiting Properties of Ag-Cu Metal Alloy Nanoparticles Analysis by using MATLAB

Ag-Cu alloy nanoparticles were formed by sequential ion implantation (Ag and Cu) in silica using a metal vapor vacuum arc (MEVVA) ion source. Third-order nonlinear optical properties of the nanoparticles were measured at 1064 nm excitations using the Z-scan technique. Curve fitting analysis, based on the MATLAB features for Ag-Cu alloy nanoparticle optical limiting experiments, is used. The results show that Ag-Cu alloy nanoparticles display a refractive optical limiting effect at 1064nm.

Formation of nanoclusters with varying Pb/Se concentration and distribution after sequential Pb + and Se + ion implantation into SiO 2

First results obtained from electron beam annealed sequentially implanted Pb + (29 keV) and Se + (25 keV) ions into a SiO 2 matrix are presented. Key results from Rutherford backscattering spectrometry and transmission electron microscopy investigations are: (1) Pb and Se atoms are found to bond in the SiO 2 matrix during implantation, forming into nanoclusters even prior to the annealing step, (2) Pb and Se atoms are both present in the sample after annealing at high temperature ( T = 760 °C, t = 45 min) and form into PbSe nanoclusters of varying sizes within the implanted region, and (3) the broader concentration profile of implanted Se creates a number of secondary features throughout the SiO 2 film, including voids and hollow shell Se nanoclusters. A sequential ion implantation approach has several advantages: selected areas of nanocrystals can be formed for integrated circuits, the technique is compatible with present silicon processing technology, and the nanocrystals are embedded in an inert matrix – making them highly durable. In addition, a higher concentration of nanocrystals is possible than with conventional glass melt techniques.

Optical and microstructural properties of self-assembled InAs quantum structures in silicon

Abstract The InAs quantum structures were formed in silicon by sequential ion implantation and subsequent thermal annealing. Two kinds of crystalline InAs nanostructures were successfully synthesized: nanodots (NDs) and nanopyramids (NPs). The peaks at 215 and 235 cm−1, corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs single-phonon modes, respectively, are clearly visible in the Raman spectra. Moreover, the PL band at around 1.3 µm, due to light emission from InAs NDs with an average diameter 7±2 nm, was observed. The InAs NPs were found only in samples annealed for 20 ms at temperatures ranging from 1000 up to 1200°C. The crystallinity and pyramidal shape of InAs quantum structures were confirmed by HRTEM and XRD techniques. The average size of the NPs is 50 nm base and 50 nm height, and they are oriented parallel to the Si (001) planes. The lattice parameter of the NPs increases from 6.051 to 6.055 Å with the annealing temperature increasing from 1100 to 1200°C, due to lattice relaxation. Energy dispersive spectroscopy (EDS) shows almost stoichiometric composition of the InAs NPs.

Formation of InAs quantum dots in silicon by sequential ion implantation and flash lamp annealing

InAs quantum dots (QDs) were successfully formed in single-crystalline Si by sequential ion implantation and subsequent milliseconds range flash lamp annealing (FLA). Samples were characterized by μ-Raman spectroscopy, Rutherford Backscattering Spectrometry (RBS) high-resolution transmission electron microscopy (HRTEM) and low temperature photoluminescence (PL). The Raman spectrum shows two peaks at 215 and 235 cm−1 corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs phonon modes, respectively. The PL band at around 1.3 μm originates from the InAs QDs with an average diameter 7.5±0.5 nm and corresponds to the increased band gap energy due to the strong quantum confinement size effect. The FLA of 20 ms is sufficient for InAs QDs formation. It also prevents the out-diffusion of implanted elements. Moreover, the silicon layer amorphized during ion implantation is recrystallized by solid-phase epitaxial regrowth during FLA.

Effects of He-irradiation on the Metal-to-insulator Transition of Vanadium Dioxide Nanoclusters

AbstractIn this work nanoclusters of vanadium dioxide (VO2) buried in 200 nm thick SiO2 on silicon have been irradiated with increasing fluences of He ions. The projected range of He was chosen to be 650 nm in order to avoid residual He in the VO2 nanoclusters and the surrounding SiO2. The VO2 nanoclusters have been synthesized by sequential ion implantation of the elements vanadium and oxygen followed by a rapid thermal annealing step. Irradiation with He ions leads to the generation of reversible lattice point defects in the nanocrystalline VO2 precipitates. Simultaneously there is no electronic doping by He incorporation. The effect of the local- and long-range structural disorder on the metal-to-insulator phase transition has been investigated as a function of He fluence by μ-Raman spectroscopy and temperature dependent spectral ellipsometry. The disappearance of a low-frequency Raman mode indicates increasing disorder in the long-range crystal structure due to He irradiation. At the same time the thermal hysteresis of the metal-to-insulator transition narrows.

Formation of Au−Ag Core−Shell Nanostructures in Silica Matrix by Sequential Ion Implantation

Formation of Au core-Ag shell bimetallic nanoparticles in silica matrix is demonstrated through sequential implantation of Ag and Au ions and subsequent thermal annealing. Formation of core-shell structures is verified through optical absorption spectroscopy, high-resolution transmission electron microscopy, electron energy loss spectroscopy, and simulated optical extinction spectra. A mechanism for the formation of such unusual structures in ion-implanted silica is proposed. By controlling the implantation energy of the two ions properly and keeping the implantation sequence Ag first and then Au, it is possible to create Au core-Ag shell nanoparticles in the silica matrix with homogeneous distribution.

Semiconductor-metal Phase Transition in Doped Ion Beam Synthesized VO2 Nanoclusters

AbstractWe have synthesized W and Mo doped VO2 nanoclusters embedded in 200 nm thick thermally grown SiO2 on 4-inch silicon wafers by sequential ion implantation of the elements V, W, Mo and O. The implantation energies have been chosen to locate the mean projected range in the centre of the SiO2 thin film. A post implantation rapid thermal annealing step in flowing Ar at 1000°C for 10 min leads to the growth of doped VO2 nanoclusters. The optical properties of the nanoclusters were analyzed by temperature dependent spectral ellipsometry in the spectral range of 320 to 1700 nm. It will be shown, that the semiconductor-metal phase transition hysteresis width starting at 50K in the undoped case can be systematically closed by increasing dopand concentration.

Ion beam synthesis of Mn/Sb clusters in silicon

In order to investigate the formation of Mn/Sb clusters embedded in crystalline silicon, sequential ion implantation with fluences of 1 × 1016 at cm−2 and 2 × 1016 at cm−2, respectively, was used to incorporate Mn and Sb ions at high concentrations into Si(0 0 1). Based on investigations with Rutherford backscattering spectroscopy (RBS) and corresponding channelling measurements (RBS/c), we report on a temperature dependent redistribution of the implanted species during the rapid thermal annealing process governed by the radiation-induced defects. Additionally performed cross-sectional TEM analyses, including EDX measurements, clearly show the presence of hexagonal shaped elementary Sb precipitates as well as compound clusters consisting of Mn and Sb, which are aligned to the crystal structure of the host silicon. In electron magnetic resonance measurements many samples exhibit broad resonance bands persisting up to approximately 60 K. For out-of-plane rotations, the bands show a weak angular dependence of the resonance field but a strong angular dependence of the intensity. Zero-field-cooled and field-cooled magnetization curves were measured on selected samples with a SQUID magnetometer between 10 and 400 K at different applied fields. The curves show a weak magnetic signal generated by different magnetic phases while at least one can be ascribed to superparamagnetic nanoparticles of MnSb.

Splitting kinetics of Si0.8Ge0.2 layers implanted with H or sequentially with He and H

We have performed systematic measurements of the splitting kinetics induced by H-only and He+H sequential ion implantation into relaxed Si0.8Ge0.2 layers and compared them with the data obtained in Si. For H-only implants, Si splits faster than Si0.8Ge0.2. Sequential ion implantation leads to faster splitting kinetics than H-only in both materials and is faster in Si0.8Ge0.2 than in Si. We have performed secondary ion mass spectrometry, Rutherford backscattering spectroscopy in channeling mode, and transmission electron microscopy analyses to elucidate the physical mechanisms involved in these splitting phenomena. The data are discussed in the framework of a simple phenomenological model in which vacancies play an important role.

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

We report the formation of embedded ZnO quantum dots (QDs) by Zn and Fion sequential implantation and subsequent annealing. Optical absorption andphotoluminescence spectrum measurements, transmission electron microscopy brightfield images and selected area electron diffraction patterns indicate that ZnOQDs were formed after annealing in air or vacuum at temperatures higher than500 °C. Atomic force microscopy images show a comparatively flat surface of the annealedsamples, which indicates that only very few Zn atoms are evaporated to the surfaces. Theformation of ZnO QDs during the thermal annealing can be attributed to the directoxidization of Zn nanoparticles by the oxygen molecules in the substrate produced duringthe implantation of F ions. The quality of ZnO QDs increases with the increase ofannealing temperature.

Investigations of SiC semiconductor nanoinclusions formed by sequential ion implantation and annealing in thermally oxidized Si

AbstractThe methods of X‐ray photoelectron and extended electron energy loss fine structure (EELFS) spectroscopy were used for the investigation of phase composition and structure of SiO2 layer implanted sequentially by Si+ (energy of 100 keV, dose of 7 × 1016 cm−2) and C+ (energy of 50 keV, dose of 7 × 1016 cm−2) ions and postannealed at 1000 or 1100 °C (2 h). The SiSi and SiC bonds in carbide (SiC) nanoinclusions and CC bonds of sp3 type in carbon inclusions are identified. The concentration of dangling bonds significantly decreases with elevation of annealing temperature. The distribution of SiC nanoinclusions at 1100 °C annealing corresponds to the distribution of implanted atoms, whereas sp3‐C phase is distributed nearly homogeneously over the implanted layer. The ratio of SiC to sp3‐C quantities is lower when intermediate annealing at 1100 °C is provided after Si+ implantation. The local atomic structure near the surface is determined from the EELFS. The experimental results demonstrate the physical basis of white photoluminescence, originating from the SiC nanocrystals, diamond‐like carbon particles, matrix, and interfacial defects. Copyright © 2008 John Wiley & Sons, Ltd.

Carrier-mediated ferromagnetism in p-Si(100) by sequential ion-implantation of B andMn

Ferromagnetic Si1−xMnx wasprepared by implanting B+ and Mn+ ions in sequence into p-type Si(100) at room temperature and post-annealing at700–900 °C. Superparamagnetic nano-sized silicide precipitates, 10–27 at.% Mn, were found near the surface of allSi1−xMnx samples.Annealing at 800 °C or below leads to the formation of a thin Si(Mn) layer, with 1.1 at.% Mn,∼180 nm beneath the surface, giving rise to ferromagnetism with a Curie temperatureabove 250 K. The high-temperature ferromagnetism is attributed to the indirectexchange mediated by localized carriers in the impurity states. The Mn content of1–1.5 at.%, having been separately reported to show room-temperature ferromagnetismseveral times by different groups, seems meaningful for Si-based diluted magneticsemiconductors (DMS). Possible extensions of our work presented here are elucidated.

Memory effects in optically active CdSe nanocrystal doped MOS structures

We present a first study of the synthesis of CdSe nanocrystals embedded in 50 nm thick thermally grown SiO 2 on p-type silicon by sequential ion implantation of Cd (30 keV) and Se (26 keV) followed by a rapid thermal annealing step. A metal-oxide-semiconductor (MOS) capacitor structure was fabricated by evaporation of an optically transparent thin Au gate electrode on top of the nanocluster doped SiO 2 layer. The observed band edge emission of CdSe is fully intensity tuneable by applying a high electric field over the MOS structure. Strong hysteretic electric field enhancement and quenching of the photoluminescence (PL) was observed when sweeping the electric field strength between ±1 MV/cm. Further an electro optical memory effect was observed in this device and investigated upon its long time stability. Possible mechanisms for this behavior are discussed.

The effect of Ti and O on the optical properties and microstructure of Ag nanocrystals formed in silica by sequential ion implantation

The implantation of Ti and O results in the modification of the silica with polarizable Ti ions. After annealing the Ti ions are incorporated with the O in the network to form a Ti–O–silicate layer. Subsequent implantation of Ag into this layer results in the formation of Ag metal nanocrystals with significantly modified optical properties compared to samples without the Ti ions. The incorporation of the Ti results in a shift in the wavelength of the surface plasmon resonance of the Ag nanocrystals and a change in the magnitude of the surface plasmon resonance absorption. The results are interpreted using effective medium theory.

Formation of metal nanoparticles in silica by the sequential implantation of Ag and Cu

Spherical-like nanoparticles have been formed by sequentially ion-implanting Ag/Cu into silica glasses. During sequential Ag/Cu ion implantation, the diameter of Cu nanoparticles is increased and the average Ag nanoparticle diameter is decreased with increasing Cu ion dose. The evolution of nanoparticles is characterized by grazing incidence X-ray diffraction, extended X-ray absorption fine structure spectroscopy and transmission electron microscopy. Nanovoids in the nanoparticles are formed by sequential ion implantation.