Ion-beam-induced bending of semiconductor nanowires.

The miniaturisation of technology increasingly requires the development of both new structures as well as novel techniques for their manufacture and modification. Semiconductor nanowires (NWs) are a prime example of this and as such have been the subject of intense scientific research for applications ranging from microelectronics to nano-electromechanical devices. Ion irradiation has long been a key processing step for semiconductors and the natural extension of this technique to the modification of semiconductor NWs has led to the discovery of ion beam-induced deformation effects. In this work, transmission electron microscopy with in situ ion bombardment has been used to directly observe the evolution of individual silicon and germanium NWs under irradiation. Silicon NWs were irradiated with either 6 keV neon ions or xenon ions at 5, 7 or 9.5 keV with a flux of 3 × 1013 ions cm-2 s-1. Germanium NWs were irradiated with 30 or 70 keV xenon ions with a flux of 1013 ions cm-2 s-1. These new results are combined with those reported in the literature in a systematic analysis using a custom implementation of the transport of ions in matter Monte Carlo computer code to facilitate a direct comparison with experimental results taking into account the wide range of experimental conditions. Across the various studies this has revealed underlying trends and forms the basis of a critical review of the various mechanisms which have been proposed to explain the deformation of semiconductor NWs under ion irradiation.

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abstract: We demonstrate very high frequency (VHF) nanomechanical resonators based upon single-crystal silicon nanowires (SiNWs), which are prepared by the bottom-up chemical synthesis. Metallized SiNW resonators operating near 200 MHz are realized with quality factor Q ≈ 2000−2500. Pristine SiNWs, with fundamental resonances as high as 215 MHz, are measured using a VHF readout technique that is optimized for these high resistance devices. The pristine resonators provide the highest Q's, as high as Q ≈ 13 100 for an 80 MHz device. SiNWs excel at mass sensing; characterization of their mass responsivity and frequency stability demonstrates sensitivities approaching 10 zeptograms. These SiNW resonators offer significant potential for applications in resonant sensing, quantum electromechanical systems, and high frequency signal processing.

title: GaAs/AlGaAs core multishell nanowire-based light-emitting diodes on Si.
abstract: We report on integration of GaAs nanowire-based light-emitting-diodes (NW-LEDs) on Si substrate by selective-area metalorganic vapor phase epitaxy. The vertically aligned GaAs/AlGaAs core-multishell nanowires with radial p-n junction and NW-LED array were directly fabricated on Si. The threshold current for electroluminescence (EL) was 0.5 mA (current density was approximately 0.4 A/cm(2)), and the EL intensity superlinearly increased with increasing current injections indicating superluminescence behavior. The technology described in this letter could help open new possibilities for monolithic- and on-chip integration of III-V NWs on Si.

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title: Sequence-Specific Label-Free DNA Sensors Based on Silicon Nanowires
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title: Piezoelectric field effect transistor and nanoforce sensor based on a single ZnO nanowire.
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title: Ion-beam processing of silicon at keV energies: A molecular-dynamics study.
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title: Focused ion beam-assisted bending of silicon nanowires for complex three dimensional structures
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title: Engineering of nanostructured carbon materials with electron or ion beams.
abstract: Irradiating solids with energetic particles is usually thought to introduce disorder, normally an undesirable phenomenon. But recent experiments on electron or ion irradiation of various nanostructures demonstrate that it can have beneficial effects and that electron or ion beams may be used to tailor the structure and properties of nanosystems with high precision. Moreover, in many cases irradiation can lead to self-organization or self-assembly in nanostructures. In this review we survey recent advances in the rapidly evolving area of irradiation effects in nanostructured materials, with particular emphasis on carbon systems because of their technological importance and the unique ability of graphitic networks to reconstruct under irradiation. We dwell not only on the physics behind irradiation of nanostructures but also on the technical applicability of irradiation for nanoengineering of carbon and other systems.

title: Ionizing radiation effects in MOS devices and circuits
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title: Advances in ion beam modification of semiconductors
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title: Optical and electrical properties of semiconducting BaSi2 thin films on Si substrates grown by molecular beam epitaxy
abstract: The electrical properties and optical absorption (OA) spectra of undoped BaSi 2 films grown by molecular beam epitaxy were investigated The electron density and mobility of BaSi 2 grown epitaxially on Si(111) were 5 × 10 15 cm − 3 and 820 cm 2 /V·s at room temperature, respectively. The conduction-band discontinuity at the BaSi 2 /Si heterojunction was estimated to be 0.7 eV from the current–voltage characteristics of n -BaSi 2 / n -Si isotype diodes. OA spectra were measured on polycrystalline BaSi 2 films grown on transparent fused silica substrates with predeposited polycrystalline Si layer. The indirect absorption edge was derived to be 1.3 eV, and the optical absorption coefficient reached 10 5 cm − 1 at 1.5 eV.

title: Ion beam induced evolution of surface morphology and optical properties of SnO2–ZnO nanocomposite thin films
abstract: Abstract SnO 2 –ZnO nanocomposite thin films, prepared by a simple carbothermal reduction based vapor deposition method, were irradiated with 8 MeV Si 3+ ions for engineering the morphological and optical properties. The surface morphology of the nanocomposites was studied by atomic force microscopy (AFM), while the optical properties were investigated by photoluminescence spectroscopy (PL) and Raman spectroscopy. AFM studies on the irradiated samples revealed growth of nanoparticles at lower fluence and a significant change in surface morphology leading to the formation of nanosheets and their aggregates at higher fluences. A tentative mechanism underlying the observed ion induced evolution of surface morphology of SnO 2 –ZnO nanocomposite is proposed. PL studies revealed strong enhancement in the UV emissions from the nanocomposite thin film at lower fluence, while a drastic decrease in the UV emissions along with a significant enhancement in the defect emissions has been observed at higher fluences.

title: Ion-beam-induced modifications in the structural and electrical properties of copper oxide selenite nanowires
abstract: Irradiation with swift heavy ions (SHIs) with energy in the MeV range is a unique tool for engineering the properties of materials. In this context, the objective of the present work is to study the conduction of charge carriers in pre- and post-ion-irradiated semiconducting nanowires. Copper oxide selenite nanowires were synthesized using a template-assisted electrodeposition technique from an aqueous solution of 0.8 M CuSO 4 ·5H 2 O and 8 mM SeO 2 . The synthesized nanowires were observed to have a monoclinic structure with linear I – V characteristics (IVC). The effect of irradiation with 160 MeV Ni +12 ions on the properties of the copper oxide selenite nanowires was investigated for fluences varying from 10 11 to 10 13  ions/cm 2 . XRD spectra confirmed no change in the phase of the swift-heavy-ion-irradiated nanowires, but a modification in the orientation of the planes was observed that depended on the ion fluence. The electrical resistivity of the semiconducting nanowires also varied with the ion fluence. Simultaneous irradiation-induced modifications to the electro-chemical potential gradient and the granular properties of the material may have been the origin of the alteration in the structural and electrical properties of the nanowires.

title: Tl4CdI6 – Wide band gap semiconductor: First principles modelling of the structural, electronic, optical and elastic properties
abstract: A novel infrared optoelectronic material Tl 4 CdI 6 was studied using the density functional theory (DFT)-based techniques. Its structural, electronic, optical and elastic properties were all calculated in the generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) and the local density approximation (LDA) with the Ceperley-Alder–Perdew-Zunger (CA–PZ) functionals. The studied material is a direct band gap semiconductor with the calculated band gaps of 2.043 eV (GGA) and 1.627 eV (LDA). The wavelength dependence of the refractive index was fitted to the Sellmeier equation in the spectral range from 400 to 2000 nm. Good agreement between the GGA-calculated values of refractive index and experimental data was achieved. To the best of our knowledge, this is the first consistent theoretical description of the title compound, which includes calculations and analysis of the structural, electronic, optical and elastic properties.

title: Modification of mechanical properties of Si crystal irradiated by Kr-beam
abstract: The application of ion-beam irradiation in fabrication of structures with micro-/nanometer scale has achieved striking improvement. However, an inevitable damage results in the change of mechanical properties in irradiated materials. To investigate the relation between mechanical properties and ion-irradiation damages, nanoindentation was performed on crystalline silicon irradiated by Kr-beam with an energy of 240 keV. Modified Young's modulus and nanohardness, provided from the indentation, indicated fluence dependence. Stopping and range of ions in matter (SRIM) calculation, transmission electron microscopy (TEM) observation, and Rutherford backscattering-channeling (RBS-C) measurement were utilized to understand the irradiation effect on mechanical properties. In addition, the longitudinal size of the phase transition region induced by indentation was firstly evaluated based on the depth profile of modified nanohardness.

title: Formation of self-organized nano-surfaces on III–V semiconductors by low energy oxygen ion bombardment
abstract: Pattern formation on surfaces of III–V compound semiconductors GaAs, GaSb, and InSb by O 2 + ion sputtering was studied. For GaAs, a ripple pattern was observed under a 2-keV primary beam energy for two ion fluences, i.e., 3.1×10 18 ions/cm 2 and 5.4×10 18 ions/cm 2 . The pattern wavelengths were 175 nm and 200.2 nm. A bubble-like structure was observed on the GaSb surface bombarded with 1-keV and 2-keV oxygen ions. In the case of InSb, several pyramidal structures with sub-micrometer dimensions were observed when the ion energy was 1 keV. When the ion energy was increased to 2 keV, the pyramidal structures acquired micrometer dimensions and a ripple pattern with a wavelength of 246 nm was observed in the surrounding area.

title: Capacitance transient measurements on point defects in silicon and silicol carbide
abstract: 4H-SiC schottky diodes have been implanted with 2.5 MeV protons to a dose of 1 x 10(12) cm(-2) and measured by deep level transient spectroscopy (DLTS). Between annealings at 150 D C and 200 D C the whole DLTS-spectra shift in temperature, most clearly revealed for the Z and M-center levels. The shift corresponds to a decrease in emission rate at a given temperature by approximately a factor of 5. It is speculated that the reason for this change in emission rate is to be found in the surrounding material rather than in the defects themselves.

title: Ion beam doping of silicon nanowires.
abstract: We demonstrate n- and p-type field-effect transistors based on Si nanowires (SiNWs) implanted with P and B at fluences as high as 10(15) cm (-2). Contrary to what would happen in bulk Si for similar fluences, in SiNWs this only induces a limited amount of amorphization and structural disorder, as shown by electrical transport and Raman measurements. We demonstrate that a fully crystalline structure can be recovered by thermal annealing at 800 degrees C. For not-annealed, as-implanted NWs, we correlate the onset of amorphization with an increase of phonon confinement in the NW core. This is ion-dependent and detectable for P-implantation only. Hysteresis is observed following both P and B implantation.

title: CONTROLLING THE ASPECT RATIO OF INORGANIC NANORODS AND NANOWIRES
abstract: Semiconductors and metals exhibit unusual optical, electronic, and magnetic properties on the nanometer scale. Chemists and materials scientists are developing methods to make non-spherical shapes of semiconductors and metals on the nanometer scale. We use a seed-mediated growth approach to make metallic nanorods and nanowires in homogeneous solution. Control of the ratio of metallic spherical seeds to metal salt in the reduction reaction contyrols the aspect ratio of the resulting rods and wires.

title: Diameter-Selective Synthesis of Semiconductor Nanowires
abstract: Nearly monodisperse samples of single crystalline GaP nanowires have been synthesized with diameters of 10, 20, and 30 nm and lengths greater than 10 μm by exploiting well-defined gold colloids as catalysts in our laser catalytic growth (LCG) synthetic methodology. 1-4 Transmission electron microscopy (TEM) studies of nanowires prepared in this way demonstrate that the distributions of nanowire diameters are defined by those of the nanocluster catalysts. High-resolution TEM shows that the wires are single-crystal zinc blende with a [111] growth direction, and energy-dispersive X-ray analysis (EDAX) confirms that the nanowire composition is stoichiometric GaP. Recent interest in low-dimensional semiconductor materials has been motivated by the push for miniaturization of electronic and optoelectronic devices and a need to understand the fundamentals of nanoscale chemistry and physics. 5,6 In particular, onedimensional (1D) systems are exciting from both fundamental and applied viewpoints. 6 Fascinating physical phenomena, such as Luttinger liquid behavior, 7,8 and numerous applications from interconnects to scanning probe microscopies, 9,10 require highquality, well-defined 1D nanostructures. Experimental progress in the field of 1D nanostructures has often been limited by the ability to create new materials in this size regime with controlled size, structure, and composition. Early approaches to 1D nanostructure synthesis employed thin film growth and lithographic techniques. In particular, “T-wires” have been fabricated by growing semiconductor quantum wells via molecular beam epitaxy, followed by cleavage and overgrowth on the cleaved surface, 11 while “V-groove” nanowires have been prepared by etching trenches on a surface and then depositing a small amount of material into the resulting grooves. 12 One of the significant limitations of these approaches is that the nanowires are embedded in a substrate, which precludes the assembly of complex 2D and 3D nanostructures. Template approaches have also been used for growing a wide-range of nanowires. 13 These methods can provide good control over the length and diameter of nanowires, although they are limited in that polycrystalline structures are often produced. Our laboratory has made significant progress toward the development of a general synthetic approach to free-standing single-crystal semiconductor nanowires via the LCG method. 1-4

title: General Synthesis of Compound Semiconductor Nanowires
abstract: The predictable synthesis of a broad range of multicomponent semiconductor nanowires has been accomplished using laser-assisted catalytic growth. Nanowires of binary group III±V materials (GaAs, GaP, InAs, and InP), ternary III±V materials (GaAs/P, InAs/P), binary II±VI compounds (ZnS, ZnSe, CdS, and CdSe), and binary SiGe alloys have been prepared in bulk quantities as high purity (>90 %) single crystals. The nanowires have diameters varying from three to tens of nanometers, and lengths extending to tens of micrometers. The synthesis of this wide range of technologically important semiconductor nanowires can be extended to many other materials and opens up significant opportunities in nanoscale science and technology. The synthesis of nanoscale materials is critical to work directed towards understanding fundamental properties of small structures, creating nanostructured materials, and developing nanotechnologies. Nanowires and nanotubes have been the focus of considerable attention because they have the potential to answer fundamental questions about one-dimensional systems and are expected to play a central role in applications ranging from molecular electronics to novel scanning microscopy probes. To explore such diverse and exciting opportunities requires nanowire materials for which the chemical composition and diameter can be varied. Over the past several years considerable effort has been placed on the bulk synthesis of nanowires, and while advances have been made using template, laser ablation, solution, and other methods, in no case has it been demonstrated that one approach could be exploited in a predictive manner to synthesize a wide range of nanowire materials. Here we describe the predictable synthesis of a broad range of binary and ternary III±V, II±VI, and IV±IV group semiconductor nanowires using the laser-assisted catalytic growth (LCG) method. Recently, we reported the growth of elemental Si and Ge nanowires using the LCG method, which exploits laser ablation to generate nanometer diameter catalytic clusters that define the size and direct the growth of the crystalline nanowires by a vapor±liquid±solid (VLS) mechanism. A key feature of the VLS growth process and our LCG method is that equilibrium phase diagrams can be used to predict catalysts and growth conditions, thereby enabling rational synthesis of new nanowire materials. Significantly, we show here that semiconductor nanowires of the III±V materials GaAs, GaP, GaAsP, InAs, InP, InAsP, the II±VI materials ZnS, ZnSe, CdS, CdSe, and IV±IV alloys of SiGe can be synthesized in high yield and purity using this approach. Compound semiconductors, such as GaAs and CdSe, are especially intriguing targets since their direct bandgaps give rise to attractive optical and electrooptical properties. The nanowires have been prepared as single crystals with diameters as small as 3 nm, which places them in a regime of strong radial quantum confinement, and lengths exceeding 10 mm. These studies demonstrate that LCG represents a very general and predictive approach for nanowire synthesis, and moreover, we believe that the broad range of III±V, II±VI, and IV±IV nanowires prepared will open up many new opportunities in nanoscale research and technology. The prediction of growth conditions for binary and more complex nanowires using the LCG method is, in principle, significantly more difficult than previous studies of elemental Si and Ge nanowires due to the complexity of ternary and higher order phase diagrams. However, this complexity can be greatly reduced by considering pseudobinary phase diagrams for the catalyst and compound semiconductor of interest. For example, the pseudobinary phase diagram of Au±GaAs shows that Au±Ga±As liquid and GaAs solid are the principle phases above 630 C in the GaAs rich region . This implies that Au can serve as a catalyst to grow GaAs nanowires by the LCG method, if

title: Growth of nanowire superlattice structures for nanoscale photonics and electronics
abstract: The assembly of semiconductor nanowires and carbon nanotubes into nanoscale devices and circuits could enable diverse applications in nanoelectronics and photonics. Individual semiconducting nanowires have already been configured as field-effect transistors, photodetectors and bio/chemical sensors. More sophisticated light-emitting diodes (LEDs) and complementary and diode logic devices have been realized using both n- and p-type semiconducting nanowires or nanotubes. The n- and p-type materials have been incorporated in these latter devices either by crossing p- and n-type nanowires or by lithographically defining distinct p- and n-type regions in nanotubes, although both strategies limit device complexity. In the planar semiconductor industry, intricate n- and p-type and more generally compositionally modulated (that is, superlattice) structures are used to enable versatile electronic and photonic functions. Here we demonstrate the synthesis of semiconductor nanowire superlattices from group III–V and group IV materials. (The superlattices are created within the nanowires by repeated modulation of the vapour-phase semiconductor reactants during growth of the wires.) Compositionally modulated superlattices consisting of 2 to 21 layers of GaAs and GaP have been prepared. Furthermore, n-Si/p-Si and n-InP/p-InP modulation doped nanowires have been synthesized. Single-nanowire photoluminescence, electrical transport and electroluminescence measurements show the unique photonic and electronic properties of these nanowire superlattices, and suggest potential applications ranging from nano-barcodes to polarized nanoscale LEDs.

title: A review of focused ion beam applications in microsystem technology
abstract: In this paper the possibilities of focused ion beam (FIB) applications in microsystem technology are reviewed. After an introduction to the technology and the operating principles of FIB, two classes of applications are described. First the subject of FIB for microsystem technology inspection, metrology and failure analysis is outlined. A procedure for cross sectioning on samples is presented, as well as some examples of how this technique can be applied to study processing results. The second part of the paper is on the use of FIB as a tool for maskless micromachining. Both subtractive (etching) and additive (deposition) techniques are discussed, as well as the combination of FIB implantation of silicon with subsequent wet etching. We will show the possibility to fabricate three-dimensional structures on a micrometre scale, and give examples of recent realizations thereof.

title: Recent Advances in ZnO Materials and Devices
abstract: Wurtzitic ZnO is a wide-bandgap (3.437 eV at 2 K) semiconductor which has many applications, such as piezoelectric transducers, varistors, phosphors, and transparent conducting films. Most of these applications require only polycrystalline material; however, recent successes in producing large-area single crystals have opened up the possibility of producing blue and UV light emitters, and high-temperature, high-power transistors. The main advantages of ZnO as a light emitter are its large exciton binding energy (60 meV), and the existence of well-developed bulk and epitaxial growth processes; for electronic applications, its attractiveness lies in having high breakdown strength and high saturation velocity. Optical UV lasing, at both low and high temperatures, has already been demonstrated, although efficient electrical lasing must await the further development of good, p-type material. ZnO is also much more resistant to radiation damage than are other common semiconductor materials, such as Si, GaAs, CdS, and even GaN; thus, it should be useful for space applications.

title: Tuning of the electronic characteristics of ZnO nanowire field effect transistors by proton irradiation.
abstract: We demonstrated a controllable tuning of the electronic characteristics of ZnO nanowire field effect transistors (FETs) using a high-energy proton beam. After a short proton irradiation time, the threshold voltage shifted to the negative gate bias direction with an increase in the electrical conductance, whereas the threshold voltage shifted to the positive gate bias direction with a decrease in the electrical conductance after a long proton irradiation time. The electrical characteristics of two different types of ZnO nanowires FET device structures in which the ZnO nanowires are placed on the substrate or suspended above the substrate and photoluminescence (PL) studies of the ZnO nanowires provide substantial evidence that the experimental observations result from the irradiation-induced charges in the bulk SiO(2) and at the SiO(2)/ZnO nanowire interface, which can be explained by a surface-band-bending model in terms of gate electric field modulation. Our study on the proton-irradiation-mediated functionalization can be potentially interesting not only for understanding the proton irradiation effects on nanoscale devices, but also for creating the property-tailored nanoscale devices.

title: Ion-beam sculpting at nanometre length scales
abstract: Manipulating matter at the nanometre scale is important for many electronic, chemical and biological advances, but present solid-state fabrication methods do not reproducibly achieve dimensional control at the nanometre scale. Here we report a means of fashioning matter at these dimensions that uses low-energy ion beams and reveals surprising atomic transport phenomena that occur in a variety of materials and geometries. The method is implemented in a feedback-controlled sputtering system that provides fine control over ion beam exposure and sample temperature. We call the method “ion-beam sculpting”, and apply it to the problem of fabricating a molecular-scale hole, or nanopore, in a thin insulating solid-state membrane. Such pores can serve to localize molecular-scale electrical junctions and switches and function as masks to create other small-scale structures. Nanopores also function as membrane channels in all living systems, where they serve as extremely sensitive electro-mechanical devices that regulate electric potential, ionic flow, and molecular transport across cellular membranes. We show that ion-beam sculpting can be used to fashion an analogous solid-state device: a robust electronic detector consisting of a single nanopore in a Si3N4 membrane, capable of registering single DNA molecules in aqueous solution.

title: A review of focused ion beam milling techniques for TEM specimen preparation
abstract: The use of focused ion beam (FIB) milling for the preparation of transmission electron microscopy (TEM) specimens is described. The operation of the FIB instrument is discussed and the conventional and lift-out techniques for TEM specimen preparation and the advantages and disadvantages of each technique are detailed. The FIB instrument may be used for rapid site-specific preparation of both cross-section and plan view TEM specimens.

title: Solid-state tellurium doping of AlInP and its application to photovoltaic devices grown by molecular beam epitaxy
abstract: Solid-state tellurium (Te) is used as an n-type dopant of AllnP grown by molecular beam epitaxy (MBE). The carrier concentration proportionally increases with increasing Te beam equivalent pressure (BEP) up to a high doping density of 1 x 10(19) cm(-3). The incorporation of Te into AllnP results in a mirror-like surface at a moderate doping density due to its surfactant effect, while the surface roughness increased with a further rising of Te doping concentration. Furthermore, for the same In and Al flux ratio, the increase of the Te flux leads to a decreased In-content, but little effect on the alloy's disorder is observed. The highly Tv-doped AllnP was used in a GaAs solar cell as a window layer. As compared with the solar cell with the Si-doped AllnP window layer, the device with the Te-doped AllnP window layer exhibits the higher efficiency and an extended increase under concentrated solar illumination, due to the benefits of the higher doping density in the Te-doped epilayer.

title: Arsenic atomic layer doping in Si using AsH3
abstract: Atomic layer doping of arsenic (As-ALD) in Si is investigated using a single wafer reduced pressure chemical vapor deposition tool. Hydrogen-free and hydrogen-terminated Si surfaces are exposed to AsH3 in the temperature range between 300 °C and 700 °C followed by Si capping using H2–SiH4 or H2–Si2H6 gas mixture at 450–700 °C. After exposing to AsH3 below 400 °C, no As spike formation is observed on both hydrogen-free and hydrogen-terminated Si surface. The incorporated As dose is increasing with increasing AsH3 exposure time and saturates. Before saturation, a higher As dose is observed at higher AsH3 partial pressure for the same AsH3 exposure time. As incorporation is not influenced by the precursor (SiH4 or Si2H6) used for Si buffer deposition. By increasing SiH4 or Si2H6 partial pressure, a higher amount of As is incorporated at AsH3 exposed surface and a higher background doping of segregated As in the Si cap is observed. The slope of the segregated As is not influenced by the growth rate at 600 °C, which means that the As segregation seems to be under thermal equilibrium. Lower segregation of As in the Si cap is observed at lower Si cap growth temperature. The results shown here may offer a precise location and dose control of As into Si.

title: Argon ion beam assisted magnetron sputtering deposition of boron-doped a-Si:H thin films with improved conductivity
abstract: Boron-doped a-Si:H thin films were deposited by ion beam assisted magnetron sputtering under different
assisted argon ion beam energies, and the changes of structural and electrical properties of the thin films
were investigated using Raman spectroscopy, spectroscopic ellipsometry and semiconductor parameter measurement
system. It was observed that the short-range order of boron-doped a-Si:H thin films decreased
slightly and the defect density of thin films increased with increasing assisted argon ion beam energy. The
dark conductivity of boron-doped a-Si:H thin films improved significantly with increasing assisted argon
ion beam energy. The conductivity of the boron-doped a-Si:H thin films with 500 eV argon ion beam bombardment
was 2.1 × 10？7 S·cm？1, which was about three orders of magnitude higher than that of the thin
films deposited without assisted ion beam. The significant change in conductivity of the boron-doped a-Si:H
thin films deposited with assisted argon ion beam was mainly ascribed to the activation of threefold coordinated
boron atoms.

title: Doping of TIPS-pentacene via Focused Ion Beam (FIB) exposure
abstract: We report on the influence of Focused Ion Beam (FIB) exposure on TIPS-pentacene layers which are often used in solution-processable organic field-effect transistors (OFETs) and in many cases yield a field-effect mobility in the order of 1 cm2/V s. We exposed TIPS-pentacene layers to a Ga+ ion beam and measured the device characteristics of OFETs. We observed a strong influence of the FIB on J–V characteristics of TIPS-pentacene-based devices and determined an increase in the OFET mobility and on–off ratio and a decrease of the threshold voltage. To further investigate the underlying process we analyzed FIB-exposed and unexposed TIPS-pentacene samples via X-ray Photoelectron Spectroscopy (XPS). Exposed samples show a clear Ga XPS signature and the C1s peak shifts about 400 meV towards smaller binding energies which is an indicator for a Fermi energy shift closer to the valence states and hence p-doping of TIPS-pentacene. With Scanning Kelvin Probe Microscopy (SKPM) we could clearly distinguish FIB exposed areas from the unexposed areas. For exposed areas the work function increases about 200 meV which is consistent with XPS measurements and again displays that the implanted Ga+ ions serve as p-dopants. Furthermore we took SKPM measurements on operating OFETs and could investigate a dramatic change in local conductance on FIB exposed areas. This demonstrates a novel way of nanopatterning conductive paths in organic semiconductors.

title: Intrinsic and extrinsic diffusion of indium in germanium
abstract: Diffusion experiments with indium (In) in germanium (Ge) were performed in the temperature range between 550 and 900 °C. Intrinsic and extrinsic doping levels were achieved by utilizing various implantation doses. Indium concentration profiles were recorded by means of secondary ion mass spectrometry and spreading resistance profiling. The observed concentration independent diffusion profiles are accurately described based on the vacancy mechanism with a singly negatively charged mobile In-vacancy complex. In accord with the experiment, the diffusion model predicts an effective In diffusion coefficient under extrinsic conditions that is a factor of 2 higher than under intrinsic conditions. The temperature dependence of intrinsic In diffusion yields an activation enthalpy of 3.51 eV and confirms earlier results of Dorner et al. . The value clearly exceeds the activation enthalpy of Ge self-diffusion and indicates that the attractive interaction between In and a vacancy does not ...

title: Intrinsic point defects in crystalline silicon: Tight-binding molecular dynamics studiesof self-diffusion, interstitial-vacancy recombination, and formation volumes
abstract: Tight-binding molecular dynamics simulations are performed to study self-diffusion, interstitial-vacancy recombination, and formation volumes of point defects in crystalline silicon. The results show that (i) self-diffusion is dominated by vacancies (V) at low temperature and by interstitials (I) at high temperature; (ii) interstitial-vacancy recombination at room temperature leads to formation of a metastable I-V complex, which has an annihilation energy barrier of 1.1 eV; (iii) interstitial and vacancy relaxation volumes in silicon are approximately equal in magnitude and opposite in sign.

title: Ion-Beam-Induced Epitaxial Recrystallization Method and Its Recent Applications
abstract: The transition from amorphous Silicon to crystalline Silicon is a process of great technological importance and has raised an enormous interest also from a purely scientific perspective. Ion irradiation through an amorphous/crystalline interface may stimulate recrystallization or layer-by-layer amorphization depending on the sample temperature and ion beam parameters. In this chapter, we address some key features of this recrystallization phenomenon. The recrystallization/amorphization process will be discussed in relation to its dependence on the energy deposited during the ion beam irradiation, the sample temperature, and the presence of impurities, such as iron atoms dissolved within an amorphous silicon layer. Also it will be discussed the specific experimental condition under which a metastable phase of the FeSi2 binary compound is trapped within a region of the recrystallized Silicon, in the form of nanoparticles. Theses nanoparticles, with different orientations and morphologies, are shown to cause interesting distortions in the surrounding Si crystal lattice. This effect reflects an important application of the ion-beam induced recrystallization process, as a method that could be used to synthesize ordered nanoparticles within a Silicon matrix.

title: Entropy of point defects calculated within periodic boundary conditions
abstract: A possibility to calculate both the entropies of formation and migration of point defects in semiconductors is presented. Knowledge of the entropic contributions is especially important for the correct description of high-temperature processes like growth or annealing. Using the self-consistent charge density-functional based tight-binding method (SCC-DFTB) we have calculated the predominant part of the entropy, resulting from lattice vibrations. Strong finite-size effects have been observed while investigating the formation entropies of isolated vacancies in diamond and silicon. We demonstrate how these problems can be overcome with the help of linear elasticity theory.

title: The role of defects during amorphization and crystallization processes in ion implanted Si
abstract: Amorphization and crystallization processes in ion implanted Si have been investigated using cross-sectional transmission electron microscopy (XTEM) measurements and molecular dynamics (MD) simulations. Amorphization mechanisms in 5 MeV Si + ion implanted Si were analyzed using XTEM measurements. High-resolution XTEM images of the amorphous/crystalline (a/c) Si interface region indicate that the a/c interface is very sharp and the amorphous Si transition occurs within a few atomic layers. Image simulations based on the divacancy and di-interstitial (D-D) pair model ( (1994) 16367) suggest that an accumulation of the D-D pairs gives rise to homogeneous amorphization in ion implanted Si and the threshold number of the D-D pairs is ∼0.3 per atom. MD calculations have been performed to simulate solid phase epitaxial growth of Si at a/c interfaces based on the ordinary Langevin equation employing the Tersoff potential for Si. It was found that crystal growth in the [001] direction occurred by attaching Si atoms in the amorphous phase at kink sites associated with {111} facets formed at the a/c interface, while in the [111] direction two-dimensional nucleation was first created on the flat (111) interface and then followed by layer-by-layer growth.

title: Ion-beam-induced amorphization and recrystallization in silicon
abstract: Ion-beam-induced amorphization in Si has attracted significant interest since the beginning of the use of ion implantation for the fabrication of Si devices. A number of theoretical calculations and experiments were designed to provide a better understanding of the mechanisms behind the crystal-to-amorphous transition in Si. Nowadays, a renewed interest in the modeling of amorphization mechanisms at atomic level has arisen due to the use of preamorphizing implants and high dopant implantation doses for the fabrication of nanometric-scale Si devices. In this paper we will describe the most significant experimental observations related to the ion-beam-induced amorphization in Si and the models that have been developed to describe the process. Amorphous Si formation by ion implantation is the result of a critical balance between the damage generation and its annihilation. Implantation cascades generate different damage configurations going from isolated point defects and point defect clusters in essentially ...

title: Amorphization of silicon by elevated temperature ion irradiation
abstract: Despite extensive study into the amorphization of silicon by ion irradiation, a detailed understanding of the mechanisms associated with the process is still not available. This is especially true in the case of elevated temperature irradiations where increased levels of dynamic annealing can balance defect production. By controlling the irradiating ion flux (defect production rate), the temperature at which an amorphous layer first appears has been determined for a specific fluence of ions, ranging in mass from 12 (C) to 132 amu (Xe), over a matrix of two orders of magnitude in ion flux and 320°C in temperature. The apparent activation energies determined from the data span from 0.7 to 1.7 eV and increase as a function of ion mass and, consequently, temperature. Previously interpreted as representing processes controlling the crystalline-to-amorphous phase transition, these values are discussed in terms of a two-stage nucleation-limited amorphization process. Results are presented which indicate, that, in the regime where dynamic defect annealing is significant, the amorphization process is initially limited by the availability of nucleation sites, supplied by stable extended defect structures produced by defect accumulation and, subsequently, by the supply of simple defects to these sites.

title: AMORPHIZATION OF ZnO NANOWIRES BY PROTON BEAM IRRADIATION
abstract: We report the effects of 70 keV proton (H(+)) irradiation on the structure of zinc oxide nanowires (ZnO NWs) for a wide range of irradiation doses at room temperature. It was found that at low dose 5 x 10(15) ions/cm(2) of protons, few defects were created in ZnO NWs and the defects' density was increased with an increasing proton irradiation dose. After the irradiation dose was increased to 2 x 10(17) ions/cm(2), the crystal structure of the ZnO NWs was almost completely damaged and the crystalline wurtzite structure of the ZnO NWs could be transformed into a disordered amorphous structure. Structural changes in the ZnO NWs upon bombardment with 70 keV protons were characterized by high resolution transmission electron microscopy (HRTEM).

title: Amorphization mechanism and defect structures in ion-beam-amorphized Si, Ge, and GaAs
abstract: We are studying ion-irradiation-induced amorphization in Si, Ge, and GaAs using molecular-dynamics simulations. Although high-energy recoils produce defects and amorphous pockets, we show that low-energy recoils (about 5--10 eV) can lead to a significant component of the athermal recrystallization of preexisting damage. For typical experimental irradiation conditions this recrystallization is, however, not sufficient to fully recrystallize larger amorphous pockets, which grow and induce full amorphization. We also examine the coordination and topological defect structures in Si, Ge, and GaAs observed in the simulations, and find that these structures can explain some experimentally observed features found in amorphous semiconductors. For irradiated amorphous GaAs, we suggest that long (about 2.8 \AA{}) and weak Ga-Ga bonds, also present in pure Ga, are produced during irradiation.

title: Ion beam doping of silicon nanowires.
abstract: We demonstrate n- and p-type field-effect transistors based on Si nanowires (SiNWs) implanted with P and B at fluences as high as 10(15) cm (-2). Contrary to what would happen in bulk Si for similar fluences, in SiNWs this only induces a limited amount of amorphization and structural disorder, as shown by electrical transport and Raman measurements. We demonstrate that a fully crystalline structure can be recovered by thermal annealing at 800 degrees C. For not-annealed, as-implanted NWs, we correlate the onset of amorphization with an increase of phonon confinement in the NW core. This is ion-dependent and detectable for P-implantation only. Hysteresis is observed following both P and B implantation.

title: Damage accumulation in neon implanted silicon
abstract: Damage accumulation in neon-implanted silicon with fluences ranging from 5×1014to5×1016Necm−2 has been studied in detail. As-implanted and annealed samples were investigated by Rutherford backscattering spectrometry under channeling conditions and by transmission electron microscopy in order to quantify and characterize the lattice damage. Wavelength dispersive spectrometry was used to obtain the relative neon content stored in the matrix. Implantation at room temperature leads to the amorphization of the silicon while a high density of nanosized bubbles is observed all along the ion distribution, forming a uniform and continuous layer for implantation temperatures higher than 250°C. Clusters of interstitial defects are also present in the deeper part of the layer corresponding to the end of range of ions. After annealing, the samples implanted at temperatures below 250°C present a polycrystalline structure with blisters at the surface while in the other samples coarsening of bubbles occurs and nanocaviti...

title: Alignment of semiconductor nanowires using ion beams.
abstract: Gallium arsenide nanowires are grown on 100 GaAs substrates, adopting the epitaxial relation and thus growing with an angle around 35 degrees off the substrate surface. These straight nanowires are irradiated with different kinds of energetic ions. Depending on the ion species and energy, downwards or upwards bending of the nanowires is observed to increase with ion fluence. In the case of upwards bending, the nanowires can be aligned towards the ion beam direction at high fluences. Defect formation (vacancies and interstitials) within the implantation cascade is identified as the key mechanism for bending. Monte Carlo simulations of the implantation are presented to substantiate the results.

title: Permanent bending and alignment of ZnO nanowires.
abstract: Ion beams can be used to permanently bend and re-align nanowires after growth. We have irradiated ZnO nanowires with energetic ions, achieving bending and alignment in different directions. Not only the bending of single nanowires is studied in detail, but also the simultaneous alignment of large ensembles of ZnO nanowires. Computer simulations reveal how the bending is initiated by ion beam induced damage. Detailed structural characterization identifies dislocations to relax stresses and make the bending and alignment permanent, even surviving annealing procedures.

title: Ion beam-induced bending of silicon nanowires
abstract: Ion implantation is the standard technique for amorphizing and doping planar films and devices in the microelectronic mainstream. On the other hand, it could be successfully applied to dope axial nanostructures such as Si nanowires (NWs). We prepared high crystalline-quality Si NWs by electron beam evaporation, a well-diffused industrial technique, and we elucidated the effects of ion irradiation on these NWs. We demonstrated that ion implantation induces bending of the NW till a full alignment in the ion beam direction occurs. We find a minimum implanted fluence threshold for the deformation and we investigated the role of beam energy and of implanted fluence. These data allow us to establish a correlation between amorphization of the structure and bending of the NW.

title: Nanoscale amorphization, bending and recrystallization in silicon nanowires
abstract: Controllable and uniform doping of nanowires (NWs) is the ultimate challenge prior to their effective application. Si NWs amorphize and bend toward the impinging ions under ion irradiation as a result of viscous flow. We demonstrate that thermal annealing induces a full recovery of the crystalline phase corresponding to the unbending of the NWs. The competition between Solid Phase Epitaxy and Random Nucleation and Growth at the nanoscale is the key parameter controlling the recovery.

title: Investigation of ion induced bending mechanism for nanostructures
abstract: Ion induced bending is a promising controlled technique for manipulating nanoscale structures. However, the underlying mechanism of the process is not well understood. In this letter, we report a detailed study of the bending mechanism of Si nanowires (NWs) under Ga+ irradiation. The microstructural changes in the NW due to ion beam irradiation are studied and molecular dynamics simulations are used to explore the ion–NW interaction processes. The simulation results are compared with the microstructural studies of the NW. The investigations inform a generic understanding of the bending process in crystalline materials, which we suggest to be feasible as a versatile manipulation and integration technique in nanotechnology.

title: Nanoscale manipulation of Ge nanowires by ion irradiation
abstract: Nanowires have generated considerable interest as nanoscale interconnects and as active components of both electronic and electromechanical devices. However, in many cases, manipulation and modification of nanowires are required to fully realize their potential. It is essential, for instance, to control the orientation and positioning of nanowires in some specific applications. This work demonstrates a simple method to reversibly control the shape and the orientation of Ge nanowires using ion beams. Crystalline nanowires were amorphized by 30 keV Ga+ implantation. Subsequently, viscous flow and plastic deformation occurred causing the nanowires to bend toward the beam direction. The bending was reversed multiple times by ion implanting the opposite side of the nanowires, resulting in straightening and subsequent bending into that opposite direction. This effect demonstrates the detailed manipulation of nanoscale structures is possible through the use of ion irradiation.

title: Ion-beam-induced bending of freestanding amorphous nanowires: The importance of the substrate material and charging
abstract: Ion-beam irradiation offers great flexibility and controllability in the construction of freestanding nanostructures with multiple advanced functionalities. Here, we present and discuss the bending of free-standing nanowires, against, towards, and ultimately parallel to a flux of directional ion irradiation. Bending components both along and perpendicular to the incident ion beam were observed, and the bending behavior was found to depend both on the ion beam scanning strategy and on the conductivity of the supporting substrate. This behavior is explained by an ion-irradiation-related electrostatic interaction. Our findings suggest the prospect of exploiting this technique to engineer 3D nanostructures for advanced applications.

title: Ion beam irradiation of nanostructures – A 3D Monte Carlo simulation code
abstract: A computer code for the simulation of ion beam irradiation of nanostructures has been developed. The code simulates the transport of energetic ions through matter by means of a Monte Carlo algorithm, similar to the often-used TRIM code (Ziegler et al. (1985) ). New effects occur compared to bulk, when irradiating nanostructures, which are of the same size as the ion range or the damage cascade. To account for these effects, the target in our code does not consist of layers like in TRIM but can be defined as an arbitrary 3-dimensional structure. This allows to obtain more accurate 3D distributions of implanted ions and implantation damage for nanostructures, which cannot be described by a stack of layers. We demonstrate the functionality of the code by comparing simulations with ion beam implantation into nanowires.

title: MIAMI: Microscope and ion accelerator for materials investigations
abstract: A transmission electron microscope (TEM) with in situ ion irradiation has been built at the University of Salford, U.K. The system consists of a Colutron G-2 ion source connected to a JEOL JEM-2000FX TEM via an in-house designed and constructed ion beam transport system. The ion source can deliver ion energies from 0.5 to 10 keV for singly charged ions and can be floated up to 100 kV to allow acceleration to higher energies. Ion species from H to Xe can be produced for the full range of energies allowing the investigation of implantation with light ions such as helium as well as the effects of displacing irradiation with heavy inert or self-ions. The ability to implant light ions at energies low enough such that they come to rest within the thickness of a TEM sample and to also irradiate with heavier species at energies sufficient to cause large numbers of atomic displacements makes this facility ideally suited to the study of materials for use in nuclear environments. TEM allows the internal microstructu...

title: SRIM – The stopping and range of ions in matter (2010)
abstract: SRIM is a software package concerning the S topping and R ange of I ons in M atter. Since its introduction in 1985, major upgrades are made about every six years. Currently, more than 700 scientific citations are made to SRIM every year. For SRIM-2010 , the following major improvements have been made: (1) About 2800 new experimental stopping powers were added to the database, increasing it to over 28,000 stopping values. (2) Improved corrections were made for the stopping of ions in compounds. (3) New heavy ion stopping calculations have led to significant improvements on SRIM stopping accuracy. (4) A self-contained SRIM module has been included to allow SRIM stopping and range values to be controlled and read by other software applications. (5) Individual interatomic potentials have been included for all ion/atom collisions, and these potentials are now included in the SRIM package. A full catalog of stopping power plots can be downloaded at www.SRIM.org . Over 500 plots show the accuracy of the stopping and ranges produced by SRIM along with 27,000 experimental data points. References to the citations which reported the experimental data are included.

title: Damage formation and annealing at low temperatures in ion implanted ZnO
abstract: N, Ar, and Er ions were implanted into ZnO at 15 K within a large fluence range. The Rutherford backscattering technique in the channeling mode was used to study in situ the damage built-up in the Zn sublattice at 15 K. Several stages in the damage formation were observed. From the linear increase of the damage for low implantation fluences, an upper limit of the Zn displacement energy of 65 eV could be estimated for [0001] oriented ZnO. Annealing measurements below room temperature show a significant recovery of the lattice starting at temperatures between 80 and 130 K for a sample implanted with low Er fluence. Samples with higher damage levels do not reveal any damage recovery up to room temperature, pointing to the formation of stable defect complexes.

title: Damage accumulation in neon implanted silicon
abstract: Damage accumulation in neon-implanted silicon with fluences ranging from 5×1014to5×1016Necm−2 has been studied in detail. As-implanted and annealed samples were investigated by Rutherford backscattering spectrometry under channeling conditions and by transmission electron microscopy in order to quantify and characterize the lattice damage. Wavelength dispersive spectrometry was used to obtain the relative neon content stored in the matrix. Implantation at room temperature leads to the amorphization of the silicon while a high density of nanosized bubbles is observed all along the ion distribution, forming a uniform and continuous layer for implantation temperatures higher than 250°C. Clusters of interstitial defects are also present in the deeper part of the layer corresponding to the end of range of ions. After annealing, the samples implanted at temperatures below 250°C present a polycrystalline structure with blisters at the surface while in the other samples coarsening of bubbles occurs and nanocaviti...

title: An in situ transmission electron microscopy study of the ion irradiation induced amorphisation of silicon by He and Xe
abstract: We used transmission electron microscopy with in situ ion irradiation to examine the ion-beam-induced amorphisation of crystalline silicon under irradiation with light (He) and heavy (Xe) ions at room temperature. Analysis of the electron diffraction data reveal the heterogeneous amorphisation mechanism to be dominant in both cases. Moreover, for the differences in the amorphisation curves are discussed in terms of intra-cascade dynamic recovery, and the role of electronic and nuclear loss mechanisms.

title: Amorphization of crystalline Si due to heavy and light ion irradiation
abstract: The formation of amorphous silicon in crystalline silicon by bombardment with light (Si) and heavy (Xe) ions has been investigated by transmission electron microscopy with in situ ion irradiation. Experiments have been carried out at room temperature and low temperature (50K) and the results are compared to a simple numerical model for amorphization. The results indicate that the amorphization mechanisms for both irradiations are heterogeneous in nature and that numerous overlaps of the collision cascade are generally required to render the crystal amorphous. Following from this, the nature of the material within the confines of collision cascades will be discussed and it will be shown that the individual cascade volume is not necessarily amorphous as previously described in the scientific literature but contains varying degrees of damage depending on the energy deposited within the cascade.

title: Ion implantation damage and crystalline-amorphous transition in Ge
abstract: Experimental studies on the damage produced in (100) Ge substrates by implantation of Ge+ ions at different energies (from 25 to 600 keV), fluences (from 2×1013 to 4×1014 cm−2) and temperature (room temperature, RT, or liquid-nitrogen temperature, LN2T) have been performed by using the Rutherford backscattering spectrometry technique. We demonstrated that the higher damage rate of Ge with respect to Si is due to both the high stopping power of germanium atoms and the low mobility of point defects within the collision cascades. The amorphization of Ge has been modeled by employing the critical damage energy density model in a large range of implantation energies and fluences both at RT and LN2T. The experimental results for implantation at LN2T were fitted using a critical damage energy density of ∼1 eV/atom. A fictitious value of ∼5 eV/atom was obtained for the samples implanted at RT, essentially because at RT the damage annihilation plays a non-negligible role against the crystalline–amorphous transition phase. The critical damage energy density model was found to stand also for other ions implanted in crystalline Ge (Ar+ and Ga+).

title: Ion beam-induced bending of silicon nanowires
abstract: Ion implantation is the standard technique for amorphizing and doping planar films and devices in the microelectronic mainstream. On the other hand, it could be successfully applied to dope axial nanostructures such as Si nanowires (NWs). We prepared high crystalline-quality Si NWs by electron beam evaporation, a well-diffused industrial technique, and we elucidated the effects of ion irradiation on these NWs. We demonstrated that ion implantation induces bending of the NW till a full alignment in the ion beam direction occurs. We find a minimum implanted fluence threshold for the deformation and we investigated the role of beam energy and of implanted fluence. These data allow us to establish a correlation between amorphization of the structure and bending of the NW.

title: First-principles calculation of intrinsic defect formation volumes in silicon
abstract: We present an extensive first-principles study of the pressure dependence of the formation enthalpies of all the know vacancy and self-interstitial configurations in silicon, in each charge state from -2 through +2. The neutral vacancy is found to have a formation volume that varies markedly with pressure, leading to a remarkably large negative value (-0.68 atomic volumes) for the zero-pressure formation volume of a Frenkel pair (V + I). The interaction of volume and charge was examined, leading to pressure--Fermi level stability diagrams of the defects. Finally, we quantify the anisotropic nature of the lattice relaxation around the neutral defects.

title: DENSITY OF AMORPHOUS SI
abstract: The density of amorphous Si has been measured. Multiple Si implants, at energies up to 8.0 MeV, were made through a contact mask to produce alternating amorphous/crystalline Si stripes with amorphous thicknesses up to ∼5.0 μm. For layers up to 3.4 μm (5 MeV), the amorphous Si is constrained laterally and deforms plastically. Above 5 MeV, plastic deformation of the surrounding crystal matrix is observed. Height differences between the amorphous and crystalline regions were measured for , thermally relaxed, and partially recrystallized samples using a surface profilometer. Combined with ion channeling measurements of the layer thickness, amorphous Si was determined to be 1.8±0.1% less dense than crystalline Si (4.90×1022 atom/cm3 at 300 K). Both relaxed and unrelaxed amorphous Si show identical densities within experimental error (<0.1% density difference).

title: Ion-beam processing of silicon at keV energies: A molecular-dynamics study.
abstract: We discuss molecular-dynamics simulations of ion damage in silicon, with emphasis on the effects of ion mass and energy. We employ the Stillinger-Weber potential for silicon, suitably modified to account for high-energy collisions between dopant-silicon and silicon-silicon pairs. The computational cells contain up to 10{sup 6} atoms and these are bombarded by B and As atoms at incident energies from 1 keV up to 15 keV. We show that the displacement cascade results in the production of amorphous pockets as well as isolated point defects and small clusters with populations which have a strong dependence on ion mass and a weaker relationship to the ion energy. We show that the total number of displaced atoms agrees with the predictions of binary collision calculations for low-mass ions, but is a factor of 2 larger for heavy-ion masses. We compare the simulations to experiments and show that our results provide a clear and consistent physical picture of damage production in silicon under ion bombardment. We studied the stability of the damage produced by heavy ions at different temperatures and the nature of the recrystallization mechanism. The inhomogeneous nature of the damage makes the characterization of the process through a single activation energymore » very difficult. An {ital effective} activation energy is found depending on the pocket size. We discuss our results considering the Spaepen-Turnbull recrystallization model for an amorphous-crystalline planar interface. « less

title: Viscoelastic model for the plastic flow of amorphous solids under energetic ion bombardment.
abstract: Under energetic ion bombardment, amorphous solids show substantial plastic flow in the form of anisotropic growth. This is attributed to the relaxation of shear stresses coupled to the thermal expansion in cylindrical thermal spikes induced by intense electronic excitations and to the subsequent freezing-in of the associated strain increment upon cooling down. An asymptotic growth rate at high electronic stopping power and low irradiation temperature is derived which correlates the growth rate with a few simple material parameters without introducing any adjustable free parameter. Good agreement with measurements justifies the basic assumptions of the model.

title: Amorphous silicon exhibits a glass transition
abstract: Amorphous silicon is a semiconductor with a lower density than the metallic silicon liquid. It is widely believed that the amorphous–liquid transition is a first-order melting transition. In contrast to this, recent computer simulations and the experimental observation of pressure-induced amorphization of nanoporous silicon have revived the idea of an underlying liquid–liquid phase transition implying the existence of a low-density liquid and its glass transition to the amorphous solid. Here we demonstrate that during irradiation with high-energy heavy ions amorphous silicon deforms plastically in the same way as conventional glasses. This behaviour provides experimental evidence for the existence of the low-density liquid. The glass transition temperature for a timescale of 10 picoseconds is estimated to be about 1,000 K. Our results support the idea of liquid polymorphism as a general phenomenon in tetrahedral networks.