Effect of PbO on precipitation of laser-induced gold nanoparticles inside silicate glasses

We report on three-dimensional precipitation of Au nanoparticles in gold ions-doped silicate glasses by a femtosecond laser irradiation and further annealing. Experimental results show that PbO addition plays the double roles of inhibiting hole-trapped centers generation and promoting formation and growth of gold nanoparticles. Additionally, glass containing PbO shows an increased non-linear absorption after femtosecond laser irradiation and annealing. The observed phenomena are significant for applications such as fabrications of three-dimensional multi-colored images inside transparent materials and three-dimensional optical memory, and integrated micro-optical switches.     

Silver nanoclusters formation in ion-exchanged glasses by thermal annealing,UV-laser and X-ray irradiation

The Ag-exchanged commercial soda-lime silicate glasses were treated by three methods: thermal annealing, UV-laser irradiation, and X-ray irradiation, in order to promote the silver nanoclusters formation. Absorption spectrometry and electron spin resonance measurement results indicated that the silver ions transferred to silver atoms after the above three treatments. The silver atoms diffused and then aggregated to become nanoclusters after thermal annealing in air, or after UV-laser irradiation. However, X-ray irradiation, which induced defects and reduction of Ag⁰ atoms, would not promote the silver nanocluster formation. After annealing at 600 °C for 45 h, the spherical nanoclusters with a diameter of 3–8 nm were formed. The nanoclusters with a diameter of about 2 nm were formed after 30 min UV-laser irradiation without subsequent heating. The surface plasmon resonance peak position of silver nanoclusters changed from 411 nm after thermal annealing to 425 nm after UV-laser irradiation. The peak position shift was due to the nanoclusters size difference.     

Preparation and optical properties of silicate glasses containing Pd nanoparticles

We report the space selective precipitation of Pd nanoparticles in Pd²⁺-doped silicate glass by ultrashort laser pulses irradiation and further annealing. Absorption spectra, transmission electron microscopy, refractive index measurement and Z-scan technique demonstrated that metallic Pd nanoparticles were precipitated in the glass sample after irradiation by an 800-nm femtosecond laser and subsequent annealing at 600 °C. We discuss a refractive index change and nonlinear absorption that combines the precipitation of Pd nanoparticles.     

The structure and melting of a lead nanocrystalline layer in reduced lead-germanate glass

A surface layer of lead nanoclusters has been obtained by thermal treatment of Pb_0.3Ge_0.7O_1.7 glass in hydrogen atmosphere. The thickness and structure of such layers depend heavily on the temperature and time of reduction. Structural studies of the lead layer have been performed with atomic force microscopy and X-ray diffraction. It has been shown that melting and solidification of lead nanoclusters induce a radical change in the surface conductivity of the reduced glass. Characteristic changes of melting and solidification temperature with Pb granules’ diameter have been found.     

Growth and melting of metallic nanoclusters in glass: A review of recent investigations

The mechanisms of nucleation and growth and the solid-to-liquid transition of metallic nanoclusters embedded in sodium borate glass were recently studied in situ via small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). SAXS results indicate that, under isothermal annealing conditions, the formation and growth of Bi or Ag nanoclusters embedded in sodium borate glass occurs through two successive stages after a short incubation period. The first stage is characterized by the nucleation and growth of spherical metal clusters promoted by the diffusion of Bi or Ag atoms through the initially supersaturated glass phase. The second stage is named the coarsening stage and occurs when the (Bi-or Ag-) doping level of the vitreous matrix is close to the equilibrium value. The experimental results demonstrated that, at advanced stages of the growth process, the time dependence of the average radius and density number of the clusters is in agreement with the classical Lifshitz-Slyozov-Wagner (LSW) theory. However, the radius distribution function is better described by a lognormal function than by the function derived from the theoretical LSW model. From the results of SAXS measurements at different temperatures, the activation energies for the diffusion of Ag and Bi through sodium borate glass were determined. In addition, via combination of the results of simultaneous WAXS and SAXS measurements at different temperatures, the crystallographic structure and the dependence of melting temperature T _m on crystal radius R of Bi nanocrystals were established. The experimental results indicate that T _m is a linear and decreasing function of nanocrystal reciprocal radius 1/R, in agreement with the Couchman and Jesser theoretical model. Finally, a weak contraction in the lattice parameters of Bi nanocrystals with respect to bulk crystals was established. The text was submitted by the authors in English.     

Microwave assisted diffusion of Au-nanoclusters in vitreous silica

Gold nanocluster composite glasses were prepared via the evaporation of a thin gold layer, followed by microwave-assisted diffusion. Increased diffusion using a microwave (MW) oven as compared to the traditional diffusion in a muffle furnace is observed and measured. The influence of diffusion temperature and time on diffusion depth and surface plasmon resonance (SPR) absorption bands of the so-obtained gold nanocluster have been studied. The diffusion parameters have been shown to influence the size of the metal nanoclusters and hence, the position of the SPR absorption bands.     

退火工艺对可控硅辐照效应的影响

应用1.4 MeV电子束对单向可控硅晶圆芯片进行固定注量率辐照,通过触发电流和少子寿命表征辐照效应,研究了退火工艺对辐照效应的影响。结果表明：电子辐照缩短单向可控硅少子寿命,增大触发电流。经350℃退火后触发电流恢复到辐照前水平,少子寿命虽有一定恢复,但远比辐照前短。在试验的注量范围内k系数为常数,退火后k系数与注量相关,小注量时较小。常温存放对辐照效应有较大影响,长时间存放不利于200℃退火而有利于300℃退火。     

Comparative molecular dynamics study of melting and crystallization of Ni and Au nanoclusters

The melting and crystallization hysteresis for nanoclusters of two transition metals (nickel and gold) have been comparatively studied using the molecular dynamics method and the tight-binding potential. It is established that the onset and end temperatures of the corresponding first kind of phase transition (i.e., melting and crystallization temperatures) should be considered for Ni nanoclusters, whereas Au nanoclusters are melted and crystallized at certain temperatures. The size dependence of the melting temperature of Au nanoclusters determined using the computation results is compared with the molecular dynamics data from other researchers and the results of two independent laboratory experiments. It is shown that our molecular dynamics results are in much better agreement with the experimental data than those obtained by other researchers.     

Relations between the optical properties of Cu–Ag:Si3N4 nanocermets and the microstructure of the metallic nanoclusters

Ion beam sputtering has been used to prepare Ag/Cu, Ag and Cu nanoclusters embedded in a Si₃N₄ dielectric matrix with the goal to correlate structural information and optical properties. The optical transmittance spectra of the bimetallic nanoclusters are compared with those obtained in the case of the single metallic nanocermets in the as-deposited state. The influence of a post annealing treatment, at different temperatures, on the optical properties of the bimetallic nanocermets is also discussed. The nanocluster structure has been investigated by X-ray absorption spectroscopy and X-ray diffraction. The chemical composition has been analysed by Rutherford backscattering spectroscopy. The surface plasmon resonance occurring after annealing in a definite temperature range is interpreted as due to the specific atomic arrangement resulting from this treatment.     

Micro-Raman studies on 50 keV electron irradiated silicate glass

A potassium–lime-silicate glass was irradiated with a 50 keV electron beam. The impact of irradiation conditions on the glass structure (beam diameter, current, and irradiation time) was studied by Micro-Raman spectroscopy. For irradiation time less than the incubation time (around 360 s), structural evolutions are attributed to a glass densification. Irradiations longer than the incubation period led to a precipitation of supposed calcium enriched phase and formation of a more depolymerized silicate phase. A non-homogeneous irradiated glass structure was observed with the existence of an area (along the electron beam border) composed by a mixture of a concentrated Ca phase diluted into the amorphous silicate phase.     

UV assisted local crystallization in Er3+ doped oxy-fluoride glass

We report on fabrication of Er³⁺-activated LaF₃ nanocrystals in transparent glasses using an original technique, which combines both heat treatment, below glass crystallization temperature, and ultraviolet laser irradiation at 244 nm. The main advantage of this method is to control the spatial localization of the nanoparticles in the glass sample, whereas annealing solely at the crystallization temperature leads to a fully crystallized glass sample. Thermal differential analysis was used to determine the crystallization temperature of the sample. The photoluminescence spectra behaviour of Er³⁺ ions, collected from the UV-irradiated and unirradiated regions, allowed us to follow and to distinguish the structural changes in the glass network under heat treatment and ultraviolet exposure.     

Photostructural relaxation in As–Se–S glasses: Effect of network fragility

The effect of photoinduced structural relaxation in As–S–Se glass is investigated during sub-bandgap irradiation. It is shown that the glass undergoes rapid optically induced structural relaxation upon photoexcitation of bonding electrons. Fragile systems exhibit larger relaxation as expected from their enthalpy profile. This suggests that the process is thermodynamically driven and that the kinetic impediment to relaxation at low temperature is lifted through photoinduced softening of the glass matrix. Activation energy for enthalpy relaxation measurement and an annealing study near T_g show that the photorelaxation effect is not a thermally activated process. The 〈r〉 dependence of photostructural changes is addressed and explained using the energy landscape formalism.     

Nonlinear optical studies of lead lanthanum borate glass doped with Au nanoparticles

Synthesis, characterization and optical nonlinearity of lead lanthanum borate glass embedded with gold nanoparticles have been investigated. DSC thermogram shows characteristics glass transition temperature at T_g = 775 K. Glasses doped with Au were subjected to heat treatment at 823 K with different annealing time and then, slowly cooled to room temperature show striking ruby color. SAED and TEM analyses have confirmed that f.c.c. Au nanoparticles of ~ 40 nm size are present in these glasses. An absorption peak centered on 563 nm has been observed in heat treated samples, which is attributed to surface plasmon resonance of gold nanoparticles. Nonlinear optical studies with open aperture Z-Scan technique show saturable absorption for heat treated samples at low intensity and reverse saturable absorption in samples without heat treatment at high intensity.     

Surface modification and crystallization of the BaO–B2O3–SiO2 glassy system using CO2 laser irradiation

The surface modification and crystallization process of BaO–B₂O₃–SiO₂ glass compositions when exposed to CO₂ laser irradiation was evaluated as a function of the laser power, irradiation time and surface condition. The glass surface was modified by the application of laser power exceeding 0.40 W and an irradiation time of more than 300 s. Micro-Raman and X-ray diffraction measurements revealed at high laser power the formation of β-BaB₂O₄ (β-BBO) crystalline phase. The crystallization of the irradiated region was enhanced when β-BBO micrometer sized particles were dispersed on the surface of the glass sample. The intensity of the second harmonic generation observed in the crystallized region was found to depend mainly on the condition of the glassy surface prior to glass irradiation.     

Infrared transmitting chalcogenide glass ceramics

Infrared glass ceramics transmitting light from 2 to 15 μm have been produced from a Ga-Ge-Sb-Se glass. The glass composition is selected in the middle of the glass forming region and the annealing temperature must be close to T_g to avoid excessive crystal growth. A heating time of the order of two weeks is necessary to see evolution of the thermal expansion coefficient of the composite while keeping the optical transmission properties of the glass.     

Composition of Ge+ and Si+ implanted SiO2/Si layers: Role of oxides in nanocluster formation

X-ray photoelectron spectroscopy (XPS) has been used to examine the atomic content of implanted SiO₂/Si layers. In particular, an XPS analysis permits to identify elemental Ge and Si, as well as GeO₂ precipitations in SiO₂ matrices. The XPS results reveal valuable information not only about the formation mechanism of Ge and Si nanoclusters but also on the annealing kinetics of SiO₂ whose properties are known to be significantly altered during the process of ion implantation and subsequent annealing. The composition of ion beam-modified SiO₂ layers strongly depends on the annealing temperature. With respect to germanium implanted samples a possibility of Ge nanocrystals formation appears at high (above 1000 °C) annealing temperatures. It has been shown that an intermediate step in the Ge oxide formation is necessary for the creation of Ge nanoclusters. Additionally, the presence of a subsurface zone GeO_x (about 100 nm thick) predicted in kinetic three-dimensional lattice simulations has been confirmed. In the case of Si⁺ implanted samples substoichiometric silicon oxide lines in the XPS spectra of a SiO₂ layer for all samples have been observed. No evidence of a line connected to the Si–Si bonding has been observed even at the highest annealing temperatures, at which only stoichiometric SiO₂ has been detected.     

Structural and physical properties of cobalt nanocluster composite glasses

Composite systems with metallic nanoparticles embedded in dielectrics present peculiar physical properties which are attractive in several application fields. In the case of transition elements, the magnetic properties of the metal clusters embedded in a dielectric matrix mainly depend on the particle size and structure. In this work, silica films containing cobalt atoms were synthesized by RF magnetron co-sputtering deposition technique, with cobalt concentration of a few atomic percent. X-ray diffraction and transmission electron microscopy showed the presence of hcp cobalt nanoclusters in the as-deposited sample with the highest cobalt concentration. After deposition, thermal treatments were performed to promote cobalt compounds or nanoparticle formation. The thermal treatments were able to change the oxidation state of cobalt atoms, as well as the structure of metallic cobalt nanoclusters (from hcp to fcc), their final size depending on both the preparation parameters and the subsequent annealing atmospheres.     

Structural relaxation in sputter-deposited silica glass

We investigated structural relaxation below the glass transition temperature in sputter-deposited silica glass. Structural relaxation was obtained from annealing behavior of the IR reflection structural band position. Results were compared with that of bulk silica glass. Results showed the following. (1) The structural relaxation time is 10⁶ times shorter than that of bulk silica glass. (2) The activation energy is close to that of bulk silica glass. (3) Once the structural relaxation reaches a steady state, the structure of silica glass film resembles that of bulk silica glass.     

Structural evolution of metallic glasses during annealing through in situ synchrotron X-ray diffraction

In this work we study the structural evolution of Al and Fe based metallic glass compositions. The samples were obtained as ribbons by melt-spinning, their glass stability and crystallization were analyzed by differential scanning calorimetry and dilatometry, structural changes were followed by in situ synchrotron X-ray diffraction during annealing throughout glass transition and crystallization. The synchrotron results are compared with the calorimetric and dilatometric measurements and the structural changes occurred during annealing are determined and described for each alloy.     

Kinetic approach to the decomposition of radiation-induced absorption spectra

We propose a kinetic approach to the decomposition of the radiation-induced absorption spectra into individual Gaussian absorption bands. It is based on the correlated analysis of a series of induced absorption spectra obtained in the course of multi-step irradiation and during room temperature long-term post-radiation annealing. The methodology is demonstrated using data on Co⁶⁰ gamma irradiated samples of commercial boro-silicate glass N-BK7 from SCHOTT. We show that physically meaningful spectroscopic parameters of absorption bands can be obtained without a priori knowledge of the band peak position and bandwidth.