A method to liberate germanium (Ge) nanocrystals from silicon dioxide (SiO2) thin films by hydrofluoric acid (HF) vapor etching is presented. Multi-energy implantation of mass separated Ge ions into 500-nm-thick wet oxide layers on silicon (Si) substrates followed by thermal annealing produces nanocrystals that are 2 to 8 nm in diameter. Raman spectra exhibit the expected asymmetric line shapes due to the phonon confinement effect, but with a higher peak frequency than predicted. To free the nanocrystals, samples are etched in HF vapor to selectively remove the SiO2 matrix and expose the nanocrystal surfaces. Raman spectra of etched samples display peak frequencies consistent with relief of compressive stress. The liberated nanocrystals show long-term stability under ambient atmospheric conditions. Ge nanocrystals can be removed from etched surfaces using an ultrasonic methanol cleaning procedure. The nanocrystal-containing solution is applied to a TEM grid and the solvent is evaporated. Subsequently obtained electron diffraction patterns confirm that the nanocrystals survive this transfer step. Thus, liberated Ge nanocrystals are expected to be accessible for a wide range of manipulation processes and direct characterization techniques.

Nanostructured magnetite/T multilayers, with T = Ni, Co, Cr, have been prepared by pulsed laser deposition. The thickness of individual magnetite and metal layers takes values in the range of 5 - 40 nm with a total multilayer thickness of 100 -120 nm. X-ray diffraction has been used to study the phase characteristics as a function of thermal treatment up to 550 °C. Small amounts of maghemite and hematite were identified together with prevailing magnetite phase after treatments at different temperatures. The mean grain size of magnetite phase increases with temperature from 12 nm at room temperature to 54 nm at 550 °C. The thermal behavior of magnetite in multilayers in comparison with powder magnetite is discussed.

Global Helium ion irradiation can tune the magnetic properties of thin films, notably their magneto-crystalline anisotropy. Helium ion irradiation through nanofabricated masks can been used to produce sub-micron planar magnetic nanostructures of various types. Among these, perpendicularly magnetized dots in a matrix of weaker magnetic anisotropy are of special interest because their quasi-static magnetization reversal is nucleation-free and proceeds by a very specific domain wall injection from the magnetically “soft” matrix, which acts as a domain wall reservoir for the “hard” dot. This guarantees a remarkably weak coercivity dispersion. This new type of irradiation-fabricated magnetic device can also be designed to achieve high magnetic switching speeds, typically below 100 ps at a moderate applied field cost. The speed is obtained through the use of a very high effective magnetic field, and high resulting precession frequencies. During magnetization reversal, the effective field incorporates a significant exchange field, storing energy in the form of a domain wall surrounding a high magnetic anisotropy nanostructure's region of interest. The exchange field accelerates the reversal and lowers the cost in reversal field. Promising applications to magnetic storage are anticipated.

The rapidly growing interest in the deposition of size-selected nanoclusters on surfaces is motivated both by technology and by basic physical questions. Due to their finite size, small particles have totally different material properties compared to their bulk crystalline counterparts. Clusters have been deposited by a monoenergetic, mass-selected ion beam with low energies (10-500 eV) on amorphous carbon substrates, which are used to minimize the influence of surface crystallography and ion-induced structural changes. Gold clusters were deposited as a model system to study the ion energy dependence, the temporal evolution, and the influence of the temperature on the cluster distribution. For impact energies below 100 eV, surface processes dominate the cluster nucleation and growth. If higher energies are used, an increasing number of ions is implanted below the surface and different processes control the cluster formation. When the energy increases above 350 eV, the cluster size drastically drops below 5 nm. The clusters are analysed with different methods such as Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), and X-Ray Photoelectron Spectroscopy (XPS) to determine their size distribution, composition and structure.

The morphology evolution of thin films was studied by molecular dynamics simulation. In this simulation four deposition and substrate elements combinations were used: Al on Al(001), Al on Co(001), Co on Co(001), Co on Al(001). The Al thin film was always grown by layer-bylayer mode regardless of substrates used. On the other hand, thin films formed by Co deposition depended on substrates used.While Co thin films on the Co substrates were grown by the island mode, a 3 monolayer (ML) thickness of CoAl surface compound was initially formed on Al substrate, before pure Co thin film growth occurred. In addition to the study on morphologies, the degrees of mixing of atoms in the interface were studied quantitatively. No surface mixing and a sharp interface were observed when Co was used as a substrate regardless of deposited atoms. On the contrary, a large amount of surface mixing or compound formation was observed when Al was used as a substrate.

A study of the synthesis of Co nanodots by ion implantation was carried out. Silica was implanted with 35 keV Co+ ion beams with doses of 8×1015, 3×1016 and 1×1017 at/cm2 and transmission electron microscopy revealed the presence of spherical nanodots in these samples. Annealing in vacuum at 900 oC was used to change the size distribution of the nanodots. The annealed samples presented an absorption band related to the plasmon collective excitation of the metallic nanodots that redshifted for higher Co contents. The magnetic character of the samples was revealed by magnetic force microscopy measurements that showed the presence of randomly distributed structures with defined magnetization in the case of annealed samples. This work shows the feasibility of synthesizing Co nanodots with controlled size distribution.

Photocrystallization is a phenomenon whereby an amorphous matrix undergoes structural changes to micro- or nano-crystals upon irradiation with photons. Topologically, a crystalline phase embedded in an amorphous matrix is expected to be advantageous over a fully crystalline phase, in applications such the as cathode material in thin film lithium-ion rechargeable batteries. As this particular microstructural feature provides a high surface area and enables smooth contacts, it may be expected to result in fast ion conduction between cathode and electrolyte, while retaining the electrochemical property associated with the specific crystal structure of the material. Amorphous films of lithium- incorporated cobalt oxide were obtained on glass and aluminium substrate using a sol gel spin-coating technique. The photocrystallization and microstructural changes in these films upon irradiation with unpolarised light were investigated using XRD, SEM, and TEM analysis.

The compositional and microstructural transformations induced by heavy ions (GeV/amu Fe and Si ions) on nanocomposite carbon (n-C) films were investigated by Raman Spectroscopy (RS), Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectrscopy (XPS). Two identical sets of n-C films were prepared in a sulfur-assisted hot filament chemical vapor deposition (HFCVD) system using methane, hydrogen and hydrogen sulfide. Films with various sp3 C and sp2 C bonding distributions were present within each set, which were obtained by varying the substrate temperature (400-600 °C). One set of films was submitted to a 20 krad dose of energetic Si and Fe ions at the NASA space radiation simulation facility hosted in Brookhaven National Laboratory's Alternating Gradient Synchrotron (AGS). All the films showed the characteristic diamond (tetragonal sp3 C) band at around 1332 cm-1 and the graphitic (trigonal sp2 C) D and G bands at around 1350 and 1590 cm-1, respectively, evidencing their composite nature. The results indicate that sp2 C ←sp3 C interconversions take place in the nanocomposite carbon material during heavy ion irradiation. A mechanism is proposed to explain this behavior. The overall results imply that there could be a range of sp3/sp2 C ratios for which carbon bonding interconversion takes place under ion radiation without significant changes to the average composition of the material. Nanocomposite carbon materials with this characteristic would be radiation insensitive. A technique could be developed based on this carbon bonding interconversion property by using focused energetic beams onto carbon films to produce a robust information storage technology that would survive catastrophic events.

Starting from two-step anodizing recipes available in the literature, we fabricated selfsupporting ordered ion-implantation masks that are several mm2 in area and 1-4 νm thick. SEM micrographs reveal self-organized structures with straight open pores, 25-150 nm in diameter, extending completely through the mask. As reported previously, the pore diameter and spacing depend critically upon the anodization parameters, e.g., type of acid and its molality, the applied voltage and the solution temperature. Ion-milling procedures were developed for opening the bottoms of the anodized pores. These masks appear quite robust during exposure to ion beams of 1-MeV He, Ne, and Kr. The steps necessary to fabricate the implantation masks, including opening the pores, are briefly described. Here we present new results obtained with a mask fabricated with pore dimensions as small as 25 nm in diameter, i.e., at the limit of what is technically feasible. Measurements are reported of the angular dependence of the transmitted ion current; these results are consistent with the physical dimensions of the opened pores. TEM images of a partial array obtained by implantation through the 25-nm pores are also shown.

A new nuclear nanoprobe facility has been developed at the Centre for Ion Beam Applications (CIBA) in the Physics Department of the National University of Singapore. This facility is the first of its type dedicated to proton beam micromachining on a micron as well as a nano scale. The design and performance of the facility, which is optimized for 3D lithography with MeV protons, is discussed here. The system has been designed to be compatible with Si wafers up to 6”.

The production of good quality high aspect ratio microstructures requires a lithographic technique capable of producing microstructures with smooth vertical sidewalls. In proton beam micromachining, a high energy (e.g. 2 MeV) proton beam is focused to a sub-100 nm spot size and scanned over a resist material (e.g. SU-8 and polymethylmethacrylate (PMMA)). When a proton beam interacts with matter it follows an almost straight path, the depth of which is dependent on the proton beam energy. These features enable the production of nanometer sized polymer structures. Experiments have shown that post-bake and curing steps are not required in this SU-8 process, reducing the effects of cracking and internal stress in the resist. Since proton beam micromachining is a fast direct write lithographic technique it has high potential for the production of high-aspect-ratio nano-structures.

Ion implantation was used to inject zinc ions into crystalline CaF2 and amorphous SiO2 substrates. Zn or ZnO nanoparticles were formed after annealing in a reducing (4% H2 + 96%Ar) or an oxidizing (10%O2 + 90% Ar ) atmosphere, respectively. When the sample was annealed in a reducing atmosphere, the absorption band at ∼ 5.3 eV for zinc implanted into SiO2 was attributed to zinc metal colloids. The absorption peak observed in the 4.3 – 4.7 eV region was due to the formation of ZnO nanocrystals, after the sample was annealed in an oxidizing environment. Both X-ray diffraction (XRD) and X-ray photospectroscopy (XPS) were used to confirm ZnO nanocrystal formation. For zinc implanted into CaF2, the as-formed ZnO nanocrystals were aligned with their [002] axes parallel to the [111] axis of the CaF2. Photoluminescence (PL) spectra showed UV and green emission from the zinc-implanted silica samples annealed under an oxygen atmosphere; however, no green emission was observed for ZnO formed in a CaF2 substrate. An additional emission was observed at ∼ 420 nm which might be due to F centers in CaF2 created by ion beam damage.

The strong visible photoluminescence (PL) of silicon nanocrystals has recently been the focus of considerable research interest. Nanocrystal composites produced by silicon implantation of a fused silica wafer followed by high-temperature thermal processing are characterized by a strong, broad photoluminescence spectrum. This light emission, centered in the near infrared and extending well into the visible range, has potential applications for the development of photonic materials based on silicon nanostructures. Here, we report on our attempts to form luminescent silica microspheres containing embedded silicon nanocrystals. Arrays of luminescent microspheres were successfully fabricated, without significant coagulation or destruction of the silica spheres during the silicon ion implantation step. However, a substantial deformation on the surface of the spheres that occurred during the high-flux implantation prevented the development of resonant cavity modes in the luminescence spectra. Resonant modes could clearly be observed for pre-implanted and annealed SiO2 wafers with a layer of pristine microspheres subsequently deposited on the implanted surface. These results suggest an alternative method for producing highly durable luminescent silica “microbeads”. At lower ion fluxes, the development of luminescent microsphere superlattices with novel optical properties due to coupling of the light emission from the silicon nanocrystals into the resonant cavity modes may be possible if the deformation effects can be reduced or eliminated.

We describe the use of ion beam induced crosslinking to harden the organic matrix material of self-assembled arrays of monodisperse (4 nm) FePt nanoparticles, providing diamondlike carbon barriers to inhibit agglomeration of the nanoparticles under heat treatment. Such stabilization is necessary for the particles to survive the >500°C annealing required for growth of the fct L10 phase of FePt, whose magnetic anisotropy is necessary for application of such arrays for high density recording. Selective area irradiation of continuous nanoparticle coatings, using ion beams patterned over a full disk by stencil mask or with ion projection optics, followed by dissolution of the unexposed coating, is proposed as a means of fabricating extended bit patterns consisting of isolated “islands” of FePt nanoparticles, with characteristic dimensions of tens of nanometers.

We have used irradiation by fast heavy ions and subsequent etching to prepare cylindrical channels in polymer/metal/polymer stacks. These channels were subsequently filled with insulator and semiconductor material, and then provided with suitable metallic contacts, to obtain a vertical field-effect transistor device. Preparation and first electronic results on this new device are reported. Typically 107 to 108 transistors per cm2 with a diameter of ∼100 nm can be obtained in this technique. The fabrication does not require lithography on the scale of a single transistor, and is suitable for large-area applications. The embedding in a soft polymer matrix results in a robust arrangement, whose electronic characteristics are largely insensitive to mechanical stress. At the present stage of development the smallest dimension of a single transistor grown by this technique is ∼50 nm. Further reduction of the device dimensions appears possible and, with it, observation of single electron effects in these devices.

We investigate the optical properties of arrays of closely spaced metal nanoparticles in view of their potential to guide electromagnetic energy with a lateral mode confinement below the diffraction limit of light. Finite-difference time-domain simulations of short arrays of noble metal nanospheres show that electromagnetic pulses at optical frequencies can propagate along the arrays due to near-field interactions between plasmon-polariton modes of adjacent nanoparticles. Near-field microscopy enables the study of energy transport in these plasmon waveguides and shows experimental evidence for energy propagation over a distance of 0.5 νm for plasmon waveguides consisting of spheroidal silver particles fabricated using electron beam lithography.

Diffractive grating structures formed by electron beam lithography have been replicated into the surface of silver commemorative coins. The detailed features of the gratings and the depth of relief were accurately transferred from the resist master plate to the surface of the fine silver coins using a Ni shim as a replication tool. This method has produced an optically variable device (OVD) in the surface of the coins which exhibited a strong intensity of first order diffraction over the area of the image (3 × 1.5 cm). A feature of the grating structures formed in the coins were fine-scale protrusions located along the length of the ridges. The presence of these protrusions has been attributed to an adhesive transfer and back-transfer of Ag during the cycle of impact loading of the Ni shim for sequential coins.

The influence of the Si+ implantation dose and postimplantation annealing temperature on the photoluminescence (PL) intensity of silicon nanoinclusions in an SiO2 matrix was experimentally investigated. The way that the PL varied with dose and annealing temperature was explained on the basis of a model which takes into account the Ostwald ripening of nanocrystals and effect of the quantum dot size on the rate of radiative recombination.

In this work we show the feasibility of producing silicon nanocrystals by means of a new method based on the oxi-reduction of silicon dioxide induced by the presence of an impurity and annealing. The choice of magnesium as the impurity relies on its chemical properties of oxireducing the SiO2 matrix while avoiding the formation of Si-based compounds. The samples were obtained by 3×1016 and 1×1017 at/cm2 ion implantation into fused silicon dioxide followed by annealing in vacuum at 900 °C for 2 or 10 h. Rutherford backscattering spectrometry (RBS) characterized the chemical content and the Mg depth distribution. In all cases, photoluminescence measurements that showed a broad band starting around 1.8 eV with increasing emission intensity for lower energies, indicating the presence of Si nanocrystals. The analysis of the photoluminescence data in the framework of the quantum confinement theory suggests the existence of relatively large Si nanocrystals. The presence of these nanocrystals was also confirmed by Raman spectroscopy.

Pt nanowires have been produced by FIB deposition of Pt thin films in a commercial Ga+ focused ion beam (FIB) system, followed by cross-sectional sputtering to form electron transparent Pt nanowires. The thermal stability of amorphous FIB manufactured Pt wires has been investigated by in-situ thermal cycling in a TEM. The Pt wires are stable up to 580-650°C where partial crystallization is observed in vacuum. Facetted nanoparticles grow on the wire surface, growing into free space by surface diffusion and minimising contact area with the underlying wire. The particles are fcc Pt with some dissolved Ga. Continued heating results in particle spheroidization, coalescence and growth, retaining the fcc structure.

In this paper we are presenting the results of silicon nano-trap memory fabricated by implanting high dose silicon into gate oxide of thickness 30 nm. The gate oxide was grown by dry oxidation. Capacitance versus voltage characteristics of MOS (metal oxide silicon) structures with silicon implanted samples annealed in nitrogen environment at a temperature of 950 °C show a memory window depending on the applied DC bias voltage. A memory window of 3V was obtained for an applied bias voltage of ± 10V. Annealing of the MOS structures in a furnace at a temperature of 800 °C for 30 minutes in oxygen resulted in complete loss or collapse of the memory window. Annealing the samples rapid thermally in oxygen environment at 800 oC for 30 seconds, resulted in a memory window of about 2 Volts for an applied voltage of ± 14V.