Naturally irradiated fluorite as a historic violet pigment: Raman spectroscopic and X‐ray diffraction study

Naturally irradiated violet fluorite, a cubic CaF₂ mineral, is a rare historic pigment. Its documented usage in Europe stretches from ca. 1450 to ca. 1550. The intensely coloured violetish black naturally irradiated fluorite is commonly called antozonite, which is only vaguely defined based on its dark colour and specific odour emanated during grinding. In the published literature, there have been some discrepancies about its Raman spectrum. Therefore, sixteen samples of antozonite were analysed by Raman (micro‐)spectroscopy using five different excitation laser wavelengths (445, 532, 633, 780 and 1064 nm), which revealed specific bands located below 500 cm⁻¹ probably related to radiation‐caused defects. Their intensity increased with increasing violet colour saturation, thus providing a specification for antozonite's definition. Spectra excited at 445 and 780 nm contained also numerous broad bands above 500 cm⁻¹, which seem to be caused by the presence of rare earth elements. The structural damage of antozonite samples has been assessed by X‐ray diffraction and related to their lightness using analysis of image histograms. The obtained results have been applied in the analysis of micro‐samples of a Late Gothic altarpiece located in an Italian Court in UNESCO city Kutná Hora, Czech Republic, which contained exceptionally large grains of deep violet fluorite identified as antozonite. Copyright © 2015 John Wiley & Sons, Ltd.     

Defect study in ZnO related structures—A multi-spectroscopic approach

ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H₂O₂ pre-treatment induced ohmic to rectifying contact conversion on Au/n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure.     

Latent track creation in fused silica by 200 MeV silver beam

Studies of formation of latent tracks in swift heavy ion irradiated SiO₂ are presented. Fused silica (SiO₂) were irradiated with 200 MeV silver (Ag) ion beam at varying fluences. Radiation-induced effects were studied by ultraviolet(UV)/Visible optical absorption spectroscopy and transmission electron microscopy (TEM). UV/Visible absorption study indicated E′ centers and oxygen deficiency centers having characteristic absorption occurred at 5 eV. The density of these color centers calculated from the absorption peak intensity showed Poisson-type variation with irradiation fluence. The defects are thus entirely confined to the latent tracks created by swift heavy ions in SiO₂. The track radius estimated from optical absorption study was found to be 5.1 nm. Similar results were obtained from TEM studies of the irradiated samples.     

Synthesis and surface characteristics of CeTbO3+δ induced by femtosecond laser irradiation

This work describes the use of focused, high-intensity light from a Ti:sapphire laser that generates femtosecond pulses to irradiate mixture of CeO₂ and Tb₄O₇ under ambient conditions. The prepared samples were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). XRD and XPS measurement results demonstrated that solid solution CeTbO_3+δ with cubic fluorite structure has been synthesized on the irradiated target surface. SEM micrographs showed that the ultra-short laser irradiation resulted in the formation of foamy structure and spherical particles with size varying from about 30 to 200 nm. The formation mechanism has been discussed in detail.     

纳米Cu固体材料的X射线衍射与正电子湮没研究

 采用自悬浮-冷压法，在不同压力下制得纳米Cu固体材料并对其在不同温度和保温时间下进行退火，利用X射线衍射(XRD)和正电子湮没寿命谱(PAS)分析对材料的结构和微观缺陷进行了表征。XRD分析表明，压制而得的样品晶粒度为20 nm，低于300 ℃退火3 h后并未发现晶粒显著长大；PAS分析表明，压制后的样品缺陷主要为单空位和空位团，大空隙很少，随着退火温度的升高和退火时间的延长，单空位通过扩散结合成空位团，大空隙也在温度较高时分解为空位团，导致空位团的含量增加，而单空位和大空隙的含量降低。     

一氧化碳合成金刚石薄膜的形貌和结构分析

利用微波等离子体化学气相沉积(MPCVD)技术，采用偏压增加成核(BEN)、两步生长的方法在一氧化碳(CO)和氢气(H₂)的环境下制备了金刚石薄膜. 利用扫描电子显微镜(SEM)、Raman光谱仪和透射电子显微镜(TEM)对金刚石薄膜的形貌和结构进行了分析. 研究发现金刚石晶粒在第一步成核及生长的过程中产生了层错和孪晶，而在第二步的生长过程中产生的层错和孪晶很少，最终形成的金刚石晶粒外表面比较光滑，包含有近五次对称或者平行的片状的孪晶，并可以观察到少量的位错. 而在样品的边缘由于等离子体的不均匀产生了比样品中心成核密度低的区域. 在这个区域中，发现了一个新的非金刚石的碳结构.     

Combined field ion microscopy and transmission electron microscopy of heavy ion damage in tungsten

Abstract

A field ion microscopy (FIM) and transmission electron microscopy (TEM) investigation of radiation damage in tungsten after heavy ion bombardment has been carried out. Field ion specimens of tungsten were irradiated with 180–230 keV Xe⁺ ions. The irradiation doses were varied between 4 × 10¹¹ and 4 × 10¹² ions/cm². The irradiated specimens were examined in FIM. Experiments combining both TEM and FIM were performed in order to compare the results obtainable by these two methods. The distribution of defects visible by TEM was inhomogeneous. The influence of the imaging field in FIM on the defects visible in TEM is discussed.     

Monitoring of the microstructure of ion‐irradiated nuclear ceramics by in situ Raman spectroscopy

Raman spectroscopy is an efficient technique for studying the evolution of microstructure of materials under irradiation. For that purpose, a Raman spectrometer has been recently installed at the JANNUS‐Saclay platform. In this paper, we describe the new setup for in situ experiments. These in situ experiments allowed following the microstructural evolution of different materials (SiC, ZrO₂ and B₄C) as a function of ion fluence on a single sample (either single crystal or polycrystalline ceramics) under the same irradiation conditions. Our results show that Raman spectroscopy is a versatile non‐contact technique for studying on‐line crystalline phase changes or amorphization of irradiated iono‐covalent solids. A detailed analysis of Raman spectra is provided for the three materials (SiC, ZrO₂ and B₄C) investigated in this study, revealing quite different behaviors upon irradiation. Basically, Raman spectroscopy gives insight on these evolutions at the level of bonds given by specific phonon modes, in good agreement with Rutherford backscattering channeling (RBS/C), X‐ray diffraction (XRD) or transmission electron microscopy (TEM) data, which provide information at a long‐range scale. Copyright © 2015 John Wiley & Sons, Ltd.     

UV photoemission study on fullerene molecules deposited on defect-rich carbon surfaces

Submonolayers of C₆₀ molecules have been deposited on different carbon substrates (pristine HOPG, argon-ion irradiated HOPG and amorphous carbon) and investigated by means of Ultraviolet Photoelectron Spectroscopy. The desorption behavior and spectral changes in the valence band were examined as a function of the sample temperature. Strong fullerene-substrate interaction (chemisorption) was observed on defect-rich surfaces (irradiated HOPG, a-C), indicated by binding energy shifts and broadening of C₆₀ VB features. These chemisorbed species proved to be more resistant against temperature-induced desorption than usually observed for physisorbed molecules on pristine HOPG. The results presented here suggest that deposition of fullerenes on heated substrates might be a feasible method of surface nanostructuring by preferential chemisorption on defects.     

Role of Cr ions on superexchange coupling in α-Fe2O3 nanoparticles

Synthesis of nanocomposites of iron oxide & chromium oxide (α-Fe₂O₃–Cr₂O₃) with different concentrations was carried out by a wet-chemical method and the structural, optical and hyperfine properties have been investigated. The prepared nanocomposites were characterized by powder X-ray diffractometry (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV–VIS spectroscopy, Fourier transformed infrared (FTIR) spectroscopy and Mössbauer spectroscopy. XRD measurements confirmed the formation of pure phase composites having particle sizes in nanometer regime. The same has been corroborated by TEM micrographs, which revealed that the formation of monodispersed nanocomposites have the average particle size 44 nm. Mössbauer study of the samples showed the transition of iron oxide from anti-ferromagnetic state to paramagnetic state having a typical relaxation in the spectrum with increasing concentration of Cr₂O₃.     

Structural, optical and electrical characterization of antimony-substituted tin oxide nanoparticles

Antimony-doped tin oxide (ATO) nanostructures were prepared using chemical precipitation technique starting from SnCl₂, SbCl₃ as precursor compounds. The antimony composition was varied from 5 to 20 wt%. The lower resistance was observed at composition of Sn:95 and Sb:05, when compared with undoped and higher doping concentration of antimony. The average crystalline size of undoped and doped tin oxide was calculated from the X-ray diffraction (XRD) pattern and found to be in the range of 30-11 nm and it was further confirmed from the transmission electron microscopy (TEM) studies. The scanning electron microscopy (SEM) analysis showed that the nanoparticles agglomerates forming spherical-shaped particles of few hundreds nanometers. The samples were further analyzed by energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and electrical resistance measurements.     

Effect of Thermal Treatment on the Structure of Multi-walled Carbon Nanotubes

The effects of vacuum annealing and oxidation in air on the structure of multi-walled carbon nanotubes (MWCNTs) produced by a large-scale catalytic chemical vapor deposition (CCVD) process are studied using Raman spectroscopy and transmission electron microscopy (TEM). A detailed Raman spectroscopic study of as-produced nanotubes has also been conducted. While oxidation in air up to 400°C removes disordered carbon, defects in tube walls are produced at higher temperatures. TEM reveals that MWCNTs annealed at 1,800°C and above become more ordered than as-received tubes, while the tubes annealed at 2,000°C exhibit polygonalization, mass transfer and over growth. The change in structure is observable by the separation of the Raman G and D′ peaks, a lower R-value (I _D/I _G ratio), and an increase in the intensity of the second order peaks. Using wavelengths from the deep ultraviolet (UV) range (5.08 eV) extending into the visible near infrared (IR) (1.59 eV), the Raman spectra of MWCNTs reveal a dependence of the D-band position proportional to the excitation energy of the incident laser energies.     

XPS study on the evaporation of gold submonolayers on carbon surfaces

We investigated the early nucleation stages of evaporated gold submonolayers on different carbon surfaces (pristine HOPG, argon-ion irradiated HOPG and amorphous carbon). Gold core-level and valence band spectra were measured by monochromatised X-ray photoelectron spectroscopy (MXPS). The Au 4f spectra for the lowest coverages (0.1 Å equivalent thickness) on irradiated HOPG and amorphous carbon surprisingly exhibited two well-separated doublets. We attribute this phenomenon to a bimodal particle size distribution caused by gold atom pinning at carbon defect sites. Deposition at elevated temperatures (on irradiated HOPG) opens a possibility to grow particles preferentially on defect sites. The influence of carbon surface defects on the cluster morphology was checked by SEM imaging. These results are interesting for future applications as they help to improve control over metal nanodots growth.     

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

100 MeV Si⁺⁷ irradiation induced modifications in the structural and magnetic properties of Mg_0.95Mn_0.05Fe₂O₄ nanoparticles have been studied by using X-ray diffraction, Mössbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mössbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mössbauer spectra after ion irradiation. Mössbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.     

Dissociative adsorption of NO on TiO2(1 1 0) argon ion bombarded surfaces

The interaction of NO with TiO₂(1 1 0) Ar⁺-ion-bombarded surfaces has been studied by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Auger electron spectroscopy. Surfaces with different degrees of defects have been characterized by monitoring the evolution of the electronic structure of the surface, with the aim of studying the influence of the surface defects on the interaction with NO. The interaction was studied for exposures up to 500 L. However, the main effects occur already in the first 10 L. The exposure of the surfaces to NO resulted in the removal of defect sites without adsorption of N.     

The effect of controlled ion bombardment on the electronic structure of the Si(0 0 1) surface

We have studied the effects of controlled ion bombardment on the electronic structure of the Si(0 0 1) surface. The surface was exposed to various doses of Ar⁺ ions accelerated towards the surface at 500 eV. X-ray photoelectron spectroscopy (XPS) spectra of the irradiated H-terminated Si(0 0 1) surface reveal the appearance of peaks that are associated with the presence of cleaved Si bonds. Ultraviolet photoelectron spectroscopy (UPS) spectra of the irradiated Si(0 0 1)2 × 1 surface show that the dimer dangling-bond surface state decays monotonically with increasing dose. These results, coupled with previous scanning tunneling microscopy (STM) studies, indicate that the breaking of dimers, and possibly the creation of adatom-like defects, during ion irradiation are responsible for the changes in the electronic structure of the valence band for this surface.     

结合小波分析法与导数光声光谱技术测量弱光谱信号的实验研究

结合导数光声光谱技术与小波分析方法,精确测量了光声光谱中的弱光谱信号.首先利用自己设计的仪器装置实现光声光谱的一阶导数,在此基础上,根据导数光声光谱的数据选择合理的分析小波,将光声光谱信号分解为不同频率信号的叠加,被分解的信号满足线性性质且原信号的峰值信息保持不变,由频率的差异可区分出光声信号和噪声信号,从而提取出光声光谱中的弱光谱信号.结合物理方法与软件方法的分析结果,准确地测量了氙灯的输出光声光谱中3个不明显的弱峰值,位置分别为699.7nm、753.4nm和776.5nm.该方法可以更准确地提取出光声光谱的峰值信息,有效地提高了光声光谱的测量精度,为光声光谱分析法在生物医学及化学分析中的应用提供了一种更精确的分析方法.     

Effects of UV photon irradiation on SiOx (0 < x < 2) structural properties

Thin films of a-SiO_x (0 < x < 2) were prepared by reactive r.f. magnetron sputtering from a polycrystalline-silicon target in an Ar/O₂ gas mixture. The oxygen partial pressure in the deposition chamber was varied so as to obtain films with different values of x. The plasma was monitored, during depositions, by optical emission spectroscopy (OES) system. Energy dispersive X-ray (EDX) measurements and infra-red (IR) spectroscopy were used to study the compositional and structural properties of the deposited layers.Structural modifications of SiO_x thin films have been induced by UV photons’ bombardment (wavelength of 248 nm) using a pulsed laser. IR spectroscopy and X-ray photoemission spectroscopy (XPS) were used to investigate the structural changes as a function of x value and incident energy. SiO_x phase separation by spinodal decomposition was revealed. The IR peak position shifted towards high wavenumber values when the laser energy is increased. Values corresponding to the SiO₂ material (only Si⁴⁺) have been found for laser irradiated samples, independently on the original x value. The phase separation process has a threshold energy that is in agreement with theoretical values calculated for the dissociation energy of the investigated material.For high values of the laser energy, crystalline silicon embedded in oxygen-rich silicon oxide was revealed by Raman spectroscopy.     

Study of nanodispersed aluminum and iron alcosols by photoacoustic spectroscopy

Nanodispersed aluminum and iron alcosols were prepared by ultrasonic dispersion of nanodispersed aluminum and iron powders in absolute ethanol. The photoacoustic signal (PAS) produced in modulated CO₂ laser irradiation (1.026 and 1.096 kHz) of alcosols depends on the nature and method of nanoparticle fabrication and does not depend on their concentration in ethanol (within 1-5 g/l). Chemical interaction between metal nanoparticles and ethanol activated by laser irradiation or/and ultrasound is considered as the cause of the PAS.     

Controlling surface states and photoluminescence of porous silicon by low-energy-ion irradiation

Porous silicon (PS) was irradiated by three kinds of low-energy ions with different chemical activity, namely argon ions, nitrogen ions and oxygen ions. The chemical activity of ions has significant effect on the surface states and photoluminescence (PL) properties of PS, The photoluminescence quenching after argon ions and nitrogen ions irradiation is ascribed to the broken Si-Si bonds, while the PL recovery is attributed to the oxidation of Si-H back bonds. Oxygen ions irradiation leads to the formation of a SiO_x layer with oxygen defects and PS shows different PL evolution than PS irradiated by argon ions and nitrogen ions.