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In this reflection on the origin of the nuclear disaster at Fukushima, the author shows that it was not an “unexpected catastrophe” but the result of a historical process. Moreover, it had been predicted. The danger, publicized for years, was ignored or denied by the authorities and operator. Why was it allowed to occur? The focus is on human, rather than technical, reasons.

We report on the behavior of Raman scattering for the radial and tangential vibrational modes of single-walled carbon nanotubes (CNT) with different absorption doses of high-energy electron irradiation ( E e = 1.8 MeV). We find that the atomic displacement of carbon from the CNT walls leads to the decrease of their diameter. In the case of the tangential optical vibrations the translational symmetry of CNT breaks down because of the radiation defects. Thus, new vibrational modes both for the armchair and zigzag CNT appear. Substantial changes in the intensities and broadening are observed for the high-frequency Raman bands with a 1.0 MGy absorption dose.

International audience; Ion beam synthesis has played a significant role in fabricating metallic or semiconducting nanocrystal arrays in glass for their optical or magnetic properties, but basic questions remain unanswered. What are the microscopic mechanisms that control nanocluster growth, determine their density and size distributions? To what extent can we control these processes in order to tailor the properties? We demonstrate the role of chemistry (redox properties; charge state equilibrium modified by irradiation) in Ag nanocluster nucleation and growth processes in glasses and extend the conclusions to PbS nanocluster synthesis. In the latter case, we show how charge state differences affect diffusion and growth and devise a strategy that produces PbS quantum dots emitting intense photoluminescence at 1.5 μm. In the course of this work, we also showed that the lognormal shape of cluster size distributions signals a loss of information as to the formation process and hence loss of property control.

The influence of the radiation damage to multi-walled carbon nanotubes (MWCNT) during the high-energy electron irradiation ( E e = 1.8 MeV) with different doses of absorption ( D n = 0.5; 1.0; 1.5 and 2.0 MGy) on their Raman vibrational spectra is studied in detail. The modification of both radial and tangential optical vibrations is observed depending on radiation dose. This is manifested both in the frequency shifts of the vibrational modes and in a change in the intensity of the Raman scattering, which corresponds to different optical vibrations. This behavior of Raman spectrum is explained by appearance and increase in the concentration of radiation defects and by seams of separate layers of nanotubes.

The motion of a magnetic domain wall in a He-ion-irradiated Pt/Co(0.5 nm)/Pt ultrathin film was studied in low applied magnetic fields. The field dependence of the wall velocity displays a creep behaviour, consistently with a critical slowing-down when the field tends to zero. We also show that domain wall motion is induced by large spin reversal avalanches andthat the energy barrier increase is d irectly linkedto that of the avalanche size. This observation is in excellent agreement with the theory of elastic manifolds moving in a weakly disordered medium.

The domain structure and magnetisation reversal phenomenon in ultrathin magnetic film structures with perpendicular anisotropy are reviewed. The domain wall motion is studied in virgin and He ion irradiated Pt/Co(0.5nm)/Pt films. The field (H) dependence of the mean wall velocity v does not follow a trivial Arrhenius law, where Ln (v) is proportional to H. At low field, it is perfectly interpreted within the so-called creep theory as soon as the domain wall moves in a weak pinning media. The analogy between the motion of vortices in a type-II superconductor and of walls in a magnetic ultrathin film is emphasised. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Composite oxide films (NiO–SiO2) were deposited on silicon wafers using the sol–gel dip coating technique. The average stoichiometry [NiO]/[SiO2], adjusted from the molar ratio of the two starting precursors, was typically 10%. Single and multilayer coatings were used to obtain film thicknesses from 70 to 400 nm. The samples were then irradiated at room temperature with MeV ions in the 1012–1014 cm−2 fluence range and further annealed at low temperature in argon atmosphere. Our first cross-sectional transmission electron microscopy studies show that such a treatment induces the nucleation and growth of pure Ni clusters. Some information is obtained on the specific features due to the sol–gel fabrication process.

Nanocavities of diameter

We have developed an irradiation technique that allows us to tune the magnetic properties of Co/Pt multilayers without affecting their roughness. The planarity and the ability to independently control nanostructure size and coercivity make our technique very appealing for magnetic recording. We study the irradiation-induced 1:1 replication of features drilled in a stencil mask. Both the “gap” G between the magnetic film and the mask, and the aspect ratio (AR) of the mask features are analyzed, in view of the ion straggling in the mask resulting in collateral damages. Optimal gap is such that D ⪡ G ⪡ D /tan( α ) (typically 0.1⪡ G ⪡25 μm), where the D is the feature size. The replication quality is best for AR⩾3. Since the allowed gap interval is wide, we anticipate that mask fast positioning will be possible for the applications to magnetic recording.

We show how the magnetic properties of the Pt/Co ultrathin film structure can be modified and even controlled under uniform irradiation by Ga+ ions at low fluence in the 20–100 keV range. A systematic magneto-optical study is presented for the Pt/Co(1.4 nm)/Pt(111) ultrathin-film structure. At ion fluences below D=1014 Ga+/cm2, the coercive field is steadily reduced when increasing the fluence. At large fluences, in the range D=(5–10)×1014 Ga+ ions/cm2, the magnetization of the Co layer drops rapidly and the film finally becomes paramagnetic at room temperature for D>2×1015 Ga+ ions/cm2. We demonstrate that these magnetic changes are related to the effect of ion-induced collisional intermixing of the Co/Pt interfaces, leading to the formation of stable Co–Pt alloys with varying composition across the interfaces. A simple model is derived to relate the ion beam-induced mixing to the changes in magnetic properties. The present work allows us to gain a quantitative understanding of previous experiments using a focused Ga+ ion beam to pattern magnetic properties of similar samples at a sub-100 nm scale.

Damage creation in crystalline α-quartz by irradiation is studied using gold ions of energies between 0.5 and 10 MeV. For all ions, the total stopping power (dE/dx)tot has a value of about 4.5 keV/nm, whereas the contribution of the electronic stopping power ranges from 0.93 keV/nm at 0.5 MeV to 3.6 keV/nm at 10 MeV. This variation allows us to test which role the nuclear and the electronic collisions plays for the damage processes. The kinetic of the ion induced damage was determined by channeling RBS and the volume increase by profilometry. Single ion impacts create damage when electronic stopping dominates, while several impacts are necessary to achieve damage in the nuclear stopping regime. A detailed analysis allows us to deduce the damage cross-sections of the two processes. The electronic stopping power of damage creation appears above an electronic dE/dx threshold of 1.4±0.3 keV/nm.

The aim of this work is to study the influence of displacement cascades in Fe–0.1 at.% Cu binary alloys irradiated at room temperature with Fe ion. The observation of gathered copper atoms in the solid solution, using the 3D atom-probe, tends to show that displacement cascades initiate the nucleation of copper clusters.

Damage creation in crystalline α -quartz under gold irradiation was studied at 1.0 and 5.5 MeV using the ARAMIS accelerator at CSNSM (Orsay). Although at these energies the total stopping powers are nearly equal (respectively, 4.20 and 4.46 keV nm −1 ), the electronic stopping power is only 1.23 keV nm −1 (25% of the total) at 1 MeV while it reaches 2.75 keV nm −1 (62% of the total) at 5.5 MeV. The electronic stopping power threshold for damage creation in α -quartz is about 1.8 keV/nm [1] . The experiment thus allows us to follow the damage production kinetics due to nuclear collisions (at 1 MeV) versus electronic collisions (at 5.5 MeV). The damage was determined by channeling Rutherford backscattering (RBS-C) using the 2 MV Van de Graaff at DPM (Villeurbanne). Single ion impacts create damage when electronic stopping dominates, while several impacts are necessary to achieve complete damage when nuclear stopping dominates. Differences in damage efficiencies will be discussed.

We present a method that allows magnetic patterning of a continuous magnetic film without significant modification of the surface roughness or of the film's optical indices. It involves ion irradiation of Co/Pt multilayers, using either a standard ion implantation technology combined with high resolution masking, or a focussed ion beam. We fabricated arrays of lines or dots whose magnetic properties differ on a sub-100 nm scale. We describe the ion collision physics on which the techniques are based, as well as some of the observed consequences on the micromagnetic properties of the arrays and on the ultimate resolution. Possible applications to high-density information storage are briefly discussed.

Single crystals of LiNbO3 (with y-cut orientation) were irradiated at the ARAMIS tandem using two different ions (35Cl and 79Br) accelerated in the few MeV energy range. All the irradiations were performed at room temperature, with fluences extending from 1012 to 1.2 × 1013 ion cm−2. The damage resulting from these irradiations was characterized by Rutherford Backscattering Spectrometry in Channeling geometry (RBS-C) in conjunction with Transmission Electron Microscopy (TEM) observations. Two different mechanisms concerning the disorder kinetics were discussed: (i) single overlap of a predamaged zone; (ii) nucleation and growth of amorphous phases. Depending on both the electronic stopping power (dE/dx)e and the velocity of the incident ions, the damage cross-section A e varies between 1.6 × 10−13 and 5.8 × 10−13 cm2.

The optical conductivity σ(E) in the energy range of interband transitions in the C 60 films subjected to the high-energy electron irradiation (E e = 1,8 MeV) was studied by the method of spectral ellipsometry for the different doses of absorption (Q= 1,5; 4 and 8 MGy). A change in the crystal and vibrational structure of these samples was investigated by the X-ray diffraction method and Raman spectroscopy. It was shown that the noticeable transformations of electron structure are observed depending on the dose of absorption. An increase of electronic concentration in the entire region of interband transitions with the a(E) nature retention, peculiar to the nonirradiated samples, occurs under the small doses (Q = 1,5 and 4 MGy). The a(E) changes under these doses are explained as the consequence of the transfer of charges from the displaced carbon atoms to the fullerene molecules as a result of their radiation damages. An increase in the dose of absorption to Q = 8 MGy indicates the beginning of the degradation of Can molecule structure.

Single crystals of LiNbO 3 (Y-cut orientation) were irradiated at room temperature with 3 MeV C 6 + and 2.4 MeV C 8 + clusters provided by CSNSM “ARAMIS” accelerator. The electronic stopping power was about 6.5 keV nm −1 in both cases. The fluences extended from 10 10 to 4 × 10 12 C 6 + or C 8 + cm −2 . Rutherford Backscattering Spectrometry in Channeling geometry (RBS/C) revealed the presence of extended defects, which cannot be due solely to nuclear stopping and which we ascribe to the high density of electronic energy associated with the correlated electronic stopping of the cluster components. The RBS/C analysis, providing a lattice disorder profile, confirms this interpretation: the damaged thickness closely corresponds to the cluster components correlation length (between 50 and 100 nm). The fluence evolutions of the disorder ratio, measured at the sample surface for C 6 and C 8 projectiles, correspond to damage cross sections close to 1.8 × 10 −13 cm 2 in the two cases.

The interaction of ${\mathrm{C}}_{6}^{\phantom{\rule{0ex}{0ex}}+}$ cluster ions (energy around 500 keV/atom) with SiO-Ni multilayers induces interface mixing near the surface, due to the highly nonlinear energy deposition into the electron bath when cluster breakup occurs. The mixing is strikingly anisotropic (in the direction of particle motion). A very large SiO surface layer erosion coefficient (up to 100) and roughness are found in the same experiments.

Magnetization reversal dynamics in single perpendicular Pt/Co/Pt high aspect ratio nanodisks have been studied by polar magneto-optical Kerr effect microscopy. The He${}^{+}$ ion process used to pattern these nanodisks resulted in a soft/hard nanodisk structure. The energy barrier field dependence was determined from the simple exponential variation of the nonswitching probability with time. The standard coherent reversal scenario fails to account for it whereas a two-dimensional-confined droplet model supports the experimental observations. From a ring shaped metastable domain wall in the magnetically soft outer ring, the reversal progresses via the deformation of the domain wall and the expansion of a reversed confined droplet through the nanodisk hard core. This magnetic reversal, governed by domain wall propagation alone, ensures a magnetization reversal reproducibility from nanodisk to nanodisk and the very narrow energy barrier distribution observed.

The control of buried suicide layer interfaces requires a systematic study of their formation conditions (implantation temperature, sample orientation, post-annealing conditions). At stoichiometric concentration, the layer roughness stems from the formation and overlap of B-type precipitates during implanted sample annealing. However, at such high concentrations several parameters interfere during suicide layer formation, particularly diffusion-limited precipitate growth and precipitate coalescence and Ostwald ripening. In order to analyze these factors separately, we have performed an in situ TEM study of the initial stages of CoSi2 precipitate formation and growth in Si during 50 keV Co implantation to fluences between 1015 and 1.5 × 1016 Cocm−2, at temperatures between 350 and 650°C. At 350°C, the threshold fluence for suicide precipitate observation was 2 × 1015 Cocm−2, and the size of the precipitates remained constant (about 4 nm) up to a fluence of 1.5 × 1016 Cocm−2. At higher implantation temperatures, the average growth rate at 650°C is four times higher than at 500°C until the average size of the precipitates reaches ~ 8 nm. Then the growth rate is surprisingly independent of the implantation temperature. The results are discussed in the light of a recently developed precipitation kinetic analysis.

Nanocavities were formed in Si substrates by conventional H implantation and thermal annealing, after which the samples were amorphized by Si ion irradiation. The size evolution of the nanocavities was monitored in situ during further ion irradiation with Si or As at temperatures of 300 or 600 K. The decrease in nanocavity diameter during ion irradiation depended linearly on the ion fluence. The rate of shrinkage differed according to the ion beam-induced atomic displacement rate and had little or no temperature dependence. These in situ results shed new light on possible ion-beam-induced nanocavity shrinkage mechanisms.

We have developed an irradiation technique that allows us to fabricate sets of submicron, planar magnetic nanostructures exhibiting perpendicular magnetization and very reproducible coercivity. The method is based on local 10-keV He ion irradiation of CoPt/sub 3/ alloys with initial perpendicular magnetization. Irradiation reduces the magneto-crystalline anisotropy in the matrix area around the dots. Irradiation fluence is chosen such that narrow stripes appear, creating demagnetized areas, that surround the dots. The magnetization reversal process of these dots exhibit special features since no nucleation event is ever required. Domain walls are injected from the interdot space, which acts as a domain wall reservoir. The dot coercivity in thus a propagation field, ensuring a weak spread of coercivity.

By first growing NiSi 2 precipitates in amorphous Si(a-Si) and then irradiating with a 150 keV Si beam, we have studied ion beam induced epitaxial crystallization (IBIEC) of Si initiated at the a-Si/NiSi 2 precipitate interface. We confirm our previous results regarding the existence of two, totally different mechanisms above and below 450°C. Interface roughening, leading to practically isotropic growth, was shown to prevail in the lower temperature range. We present a detailed analysis of the growth process at 500°C, via in situ transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) which demonstrates that Si crystallization is then Ni silicide-mediated, leading to planar growth.

Nanocavities in Si substrates, formed by conventional H implantation and thermal annealing, are shown to evolve in size during subsequent Si irradiation. Both ex situ and in situ analytical techniques were used to demonstrate that the mean nanocavity diameter decreases as a function of Si irradiation dose in both the crystalline and amorphous phases. Potential mechanisms for this irradiation-induced nanocavity evolution are discussed. In the crystalline phase, the observed decrease in diameter is attributed to the gettering of interstitials. When the matrix surrounding the cavities is amorphized, cavity shrinkage may be mediated by one of two processes: nanocavities can supply vacancies into the amorphous phase and/or the amorphous phase may flow plastically into the nanocavities. Both processes yield the necessary decrease in density of the amorphous phase relative to crystalline material.

Previous work on ion irradiation control of FePt thin film magnetic anisotropy is extended to ultrathin films (2–10 nm). The effects of 30 keV He ion irradiation on the magnetic properties are explored as a function of ion fluence and film thickness. Depending on their growth conditions, the thinnest films exhibit different magnetic properties. Although this affects their final magnetic behaviour, we show that after irradiation at 300 °C the easy magnetization axis may rotate entirely from in-plane to out-of-plane at very low fluences, e.g. 2 × 1013 He+ cm−2 on 5 nm thick film. This demonstrates the extreme sensitivity of the magnetic anisotropy to ion-induced local L10 ordering. Under these conditions, ultrathin films may exhibit perfectly square hysteresis loops with 100% remanent magnetization and low coercivity.

Ion-induced collisions produce athermal atomic movements at and around the surface or interface, inducing step formation and modifying growth conditions. The latter may be controlled by varying the temperature and ion-beam characteristics, guiding the system between nonequilibrium and quasiequilibrium states. Silicon is an ideal material to observe and understand such processes. For ion irradiation at or below room temperature, damage due to collision cascades leads to Si amorphization. At temperatures where defects are mobile and interact, irradiation can lead to layer-by-layer amorphization, whereas at higher temperatures irradiation can lead to the recrystallization of previously amorphized layers. This chapter focuses on the role of ion beams in the interface evolution. We first give an overview of ion beam-induced epitaxial crystallization (IBIEC) and ion-beam-induced amorphization as observed in silicon and identify unresolved issues. Similarities and differences with more familiar surface thermal growth processes are emphasized. Theories and computer simulations developed for surface relaxation help us to quantify several important aspects of IBIEC. Recent experiments provide insight into the influence of ion-induced defect interactions on IBIEC, and are also partly interpreted via computer simulations. The case of phase transformations and precipitation at interfaces is also considered.

This chapter is focused on the use of ion-beam processing for controlling the linear and nonlinear optical properties of different nanostructures based on metallic clusters embedded in silica. Three case studies will be presented: the first is the modification of the surface-plasmon resonance of metallic nanoclusters by direct implantation or irradiation. The second is the far-field and local-field modification by means of controlled ion irradiation of bimetallic nanoclusters. The last example deals with the synthesis of ordered plasmonic nanostructures using ion implantation and/or irradiation. These three examples are a sort of hierarchical approach to the control of the optical properties of nanostructures based on nanoparticles, starting from the synthesis of the functional building block of our approach, i.e., randomly positioned metal nanoparticles in silica, to end at the last level with the formation by ion-implantation-ordered arrays (chains or planar 2D assembly). In all these examples, ion implantation demonstrates to be not only a simple synthesis technique, but a very powerful processing tool for obtaining new functional properties. A brief description of the theoretical approach to the comprehension of the light-particle interaction from a semiclassical point of view will be given to aid the interpretation of the experimental results.

This book introduces materials scientists and designers, physicists and chemists to the properties of materials that can be modified by ion irradiation or implantation. These techniques can help design new materials or to test modified properties; novel applications already show that ion-beam techniques are complementary to others, yielding previously unattainable properties. Also, ion-beam interactions modify materials at the nanoscale, avoiding the often detrimental results of lithographic or chemical techniques. Here, the effects are related to better-known quasi-equilibrium thermodynamics, and the consequences to materials are discussed with concepts that are familiar to materials science. Examples addressed concern semiconductor physics, crystal and nanocluster growth, optics, magnetism, and applications to geology and biology.

Aramis is a home built multipurpose 2 MV electrostatic tandem accelerator. A large variety of ions are available for high energy implantation. Characterization possibilities are also quite large in the Van de Graaff mode owing to the Penning positive ion source in the terminal. A second beam line is now available that sends the beam into the target chamber of the 200 kV medium current implanter. We will provide a progress report on the machine and present some results regarding in situ studies of multilayer mixing and implanted silicide layers

Si containing a band of nanocavities has been irradiated with Si+ ions at elevated temperatures to study interactions of irradiation-induced defects with open volume defects. For irradiation at 100 °C, nanocavities are shown to be preferential nucleation sites for amorphization. It is proposed that this behavior occurs to minimize the local free energy, whereby less dense amorphous Si is free to expand into the cavity open volume. Furthermore, for irradiation at 300 °C, cavities are very efficient sinks for Si interstitials during irradiation, leaving a region denuded of interstitial-based clusters surrounding each nanocavity.

We show that partial chemical ordering can be obtained at moderate processing temperatures by using postgrowth ion bombardment. This was demonstrated both on disordered (S∼0) and partially ordered (S∼0.4) sputtered FePt(001) films in which the order parameter S was increased up to 0.3 and 0.6, respectively. X-ray diffraction measurements indicate that the high crystalline quality of the films is not modified as irradiation proceeds. The changes on the magnetic hysteresis loops are compatible with the expected perpendicular magnetic anisotropy increase. This novel method could have a great impact on the current race toward high anisotropy materials to increase magnetic recording density.

International audience; Some of the mechanisms by which ion beams affect the synthesis and behavior of nanostructures involving insulators are summarized, with a view toward studies and applications in novel areas of nanooptics, plasmonics and ferroics.

The dynamics of the magnetization reversal in single Pt/Co(0.5 nm)/Pt nano-discs with diameter 130 nm, fabricated by an He+ ion irradiation is investigated. They exhibit a very narrow distribution of small switching fields and a perpendicular magnetic anisotropy. In spite of the small involved magnetic volume, their dynamics cannot be interpreted within the usual Néel-Braun prediction developed and verified for uniform spin reversal in spherical nano-particles. Non-coherent magnetization reversal proceeds here by fast nucleation at nanodot borders and rather slow wall motion towards their center. Dynamics are perfectly accounted from a refined confined droplet model, involving the wall energy rather than the anisotropy energy. In counterpart, the blocking temperature for these nanodiscs is well described by the Néel-Braun model.

Magnetization reversal in a periodic magnetic field is studied on an ultrathin, ultrasoft ferromagnetic Pt/Co(0.5 nm)/Pt trilayer exhibiting weak random domain wall (DW) pinning. The DW motion is imaged by polar magneto-optic Kerr effect microscopy and monitored by superconducting quantum interference device susceptometry. In close agreement with model predictions, the complex linear ac susceptibility corroborates the dynamic DW modes segmental relaxation, creep, slide, and switching.

The synthesis of Ag nanoclusters in sodalime silicate glasses and silica was studied by optical absorption (OA) and electron spin resonance (ESR) experiments under both low (gamma-ray) and high (MeV ion) deposited energy density irradiation conditions. Both types of irradiation create electrons and holes whose density and thermal evolution - notably via their interaction with defects - are shown to determine the clustering and growth rates of Ag nanocrystals. We thus establish the influence of redox interactions of defects and silver (poly)ions. The mechanisms are similar to the latent image formation in photography: irradiation-induced photoelectrons are trapped within the glass matrix, notably on dissolved noble metal ions and defects, which are thus neutralized (reverse oxidation reactions are also shown to exist). Annealing promotes metal atom diffusion, which in turn leads to cluster nuclei formation. The cluster density depends not only on the irradiation fluence, but also - and primarily - on the density of deposited energy and the redox properties of the glass. Ion irradiation (i.e., large deposited energy density) is far more effective in cluster formation, despite its lower neutralization efficiency (from Ag+ to Ag0) as compared to gamma photon irradiation., Comment: 48 pages, 18 figures, revised version publ. in Phys. Rev. B, pdf file

Lead chalcogenide (PbS, PbSe, and PbTe) nanocrystals were synthesized by sequential implantation of Pb and one of the chalcogen species into pure silica. The implantation energy and fluence were chosen so that the implantation profiles practically overlap at a depth approximately 150 nm with a maximum concentration of about 0.3 atom %. Annealing for 1-8 h at 850-900 degrees C triggers nanocrystal growth, which is monitored by high-resolution (HRTEM) and conventional transmission electron microscopy (TEM), secondary-ion mass spectrometry (SIMS), and Rutherford backscattering spectrometry (RBS). Striking differences are found in the depth distributions and microstructures of the resulting nanocrystals. We show that the differing chemical interactions of Pb and chalcogens (between each other and with silica) play a crucial role in chalcogenide nucleation and growth. Using available information on chalcogen redox states in silicate glass, we propose a nonclassical nucleation and growth mechanism consistent with our experimental results. The complex chemistry involved at the microscopic level is shown to impair control over the nanocrystal size distribution. Finally, PbS nanocrystal-doped silica is shown to emit intense photoluminescence (PL) in the 1.5-2 microm wavelength range, an effect that we relate to the above nucleation and growth scheme.

Metallic or semiconductor nanocrystals produced by very different techniques often display size distributions whose limiting shape (e.g., after long annealing times) is self-preserving and close to lognormal. We briefly survey the diverse microscopic mechanisms leading to this behavior, and present an experimental study of its inception in the case of semiconducting nanocrystals synthesized by ion implantation in silica. This example shows how the ultimate lognormal distribution is related to the system's memory loss of initial nucleation and growth processes.

PbS nanocrystals (diameter of 5-7 nm) were synthesized via sulfur ion implantation in Pb-based glasses and postannealing. They display strong emission at around 1.5 mu m due to quantum confinement, and a very large photoluminescence (PL) excitation cross section. The PL intensity and decay rate temperature dependences provide evidence for a large energy splitting (ca. 30 meV) of the emitting exciton ground state fine structure, presumably due to the complex PbS electronic band structure. (c) 2006 American Institute of Physics.

We describe a synthesis of PbS nanocrystals in glasses, involving 150 keV sulfur implantation into Pb-containing silicate glasses at peak concentrations up to 3.6 at. % and postannealing around the glass transition temperature (500–600 °C). The PbS nanocrystals, whose growth is evidenced by transmission electron microscopy, display intense photoluminescence (PL) in the 1–1.5 µm wavelength range. Besides bypassing the sulfur retention problem occurring in traditional glass fusion techniques, our method improves control over nucleation and growth. The latter is demonstrated by the impact on the PbS nanocrystal PL properties of progressively replacing CaO by ZnO in a S-implanted Pb glass.

The diffusion properties of chalcogens (S, Se, Te) implanted into SiO 2 were studied via secondary ion mass spectroscopy (SIMS) profiling between room temperature and the glass transition temperature (800–950 °C). Annealing of Te-containing samples leads directly to precipitation of metallic tellurium nanocrystals within the implantation profile. The S and Se concentration profiles were fitted by using a simple diffusion model in order to provide estimates of the diffusion constant and approximate solubility of these fast moving chemical species. A comparison of their differing diffusion behavior with complementary data on these systems suggests that (i) their oxidation states play a crucial role and (ii) the chalcogen propagation mechanism actually involves complex chemical interactions.

As a magnetic domain wall propagates under small fields through a random potential, it roughens as a result of weak collective pinning, known as creep. Using Kerr microscopy, we report experimental evidence of a surprising deroughening of wall pairs in the creep regime, in a 0.5 nm thick Co layer with perpendicular anisotropy. A bound state is found in cases where two rough domains nucleated far away from one another and first growing under the action of a magnetic field eventually do not merge. The two domains remain separated by a strip of unreversed magnetization, characterized by flat edges and stabilized by dipolar fields. A creep theory that includes dipolar interactions between domains successfully accounts for (i) the domain wall deroughening as the width of the strip decreases and (ii) the quasistatic and dynamic field dependence of the strip width s.