Structural modification in swift heavy ion irradiated muscovite mica

Two-layer monoclinic(2 M) muscovite mica sheets with a thickness of 12 μm are irradiated with Sn ions at room temperature with electronic energy loss( dE/dx)_e of 14.7 keV/nm. The ion fluence is varied between 1×10~(11) and1×10~(13) ions/cm~2. Structural transition in irradiated mica is investigated by x-ray diffraction(XRD). The main diffraction peaks shift to the high angles, and the inter-planar distance decreases due to swift heavy ion(SHI) irradiation. Dehydration takes place in mica during SHI irradiation and mica with one-layer monoclinic(1 M) structure is thought to be generated in 2 M mica after SHI irradiation. In addition, micro stress and damage cross section in irradiated mica are analyzed according to XRD data. High resolution transmission electron microscopy(HRTEM) is used on the irradiated mica to obtain the detailed information about the latent tracks and structural modifications directly. The latent track in mica presents an amorphous zone surrounded by strain contrast shell, which is associated with the residual stress in irradiated mica.     

Formation of solid-state excitons in ultrathin crystalline films of PTCDA: from single molecules to molecular stacks

We directly follow the evolution of the absorption spectrum from a single molecule to a dimer and further to a one-dimensional molecular stack: We determine the optical absorption properties of ordered monolayer to multilayer films of PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) on muscovite mica(0001) surfaces by in situ differential reflectance spectroscopy. The data clearly show the transition from the single molecule to a dimer spectrum, followed by the exciton delocalization to a molecular crystal exciton. The accompanying spectral shifts compare favorably with recent model concepts.     

Static secondary ion mass spectroscopy (SSIMS) analysis of the mica surface

Static secondary ion mass spectroscopy (SSIMS) has been used to analyse the known (001) surface structure of muscovite mica, where the surface was obtained by cleavage in UHV. The spectra, which contained information from the cleavage, tetrahedral and octahedral layers of muscovite, showed no evidence of structural of compositional changes induced by primary ion impact (i.e. first-order effects). The relative yields of the major Si and Al oxide groupings in the spectra were similar to those obtained from the elemental oxidised surfaces.     

Tribological carbon-based coatings: An AFM and LFM study

In this work some carbon-based coatings were studied by atomic force microscopy (AFM) and lateral force microscopy (LFM) techniques in order to evaluate their microstructure and friction properties at the micro and nanoscale. With this aim, four samples were prepared by magnetron sputtering: an amorphous carbon film (a-C), two nanocomposites TiC/a-C with different phase ratio (∼1:1 and ∼1:3) and a nanocrystalline TiC sample. Additionally, a highly oriented pyrolytic graphite (HOPG) and an amorphous hydrogenated carbon coating (a-C:H) were included to help in the evaluation of the influence of the roughness and the hydrogen presence respectively. The topography (roughness) of the samples was studied by AFM, whereas LFM was used to measure the friction properties at the nanoscale by two different approaches. Firstly, an evaluation of possible friction contrast on the samples was done. This task was performed by subtraction of forward and reverse images and lately confirmed by the study of lateral force profiles in both directions and the histograms of the subtraction images. Secondly, an estimation of the average friction coefficient over the analysed surface of each sample was carried out. To take into account the tip evolution/damaging, mica was used as a reference before and after each sample (hereafter called sandwich method), and samples-to-mica friction ratios were calculated. The LFM was shown to be a useful tool to characterise a mixture of phases with different friction coefficients. In general, the friction ratios seemed to be dominated by the amorphous carbon phase, as it was impossible to distinguish among samples with different proportions of the amorphous phase (friction ratios between 1.5 and 1.75). Nevertheless, it could be concluded that the differences in friction behaviour arose from the chemical aspects (nature of the phase and hydrogen content) rather than surface characteristics, since the roughness (Ra values up to 5.7 nm) does not follow the observed trend. Finally, the Ogletree method was employed in order to calibrate the lateral force and estimate the friction coefficient of our samples. A good agreement was found with macroscopic and literature values going from ∼0.3 for TiC to ∼0.1 for pure carbon.     

Thermal annealing of heavy ion tracks in muscovite mica

Abstract

Thermal annealing of latent tracks caused by the passage of heavy ions, viz. Pb²⁰⁸ (13.8 MeV/n) and Ni⁵⁸ (15.37 MeV/n), in muscovite mica is investigated. The activation energy for track annealing, determined using different annealing models, is compared. The effect of thermal annealing on size and energy resolution of heavy ions in mica, based on the track etch rate and track length reduction, is discussed.     

Tribological properties of silicate materials on nano and microscale

We studied the friction properties of four model silicate materials at the nanoscale and microscale. From nanotribology, we characterized the tribological properties at single asperity contact scale and from microtribology, we characterized the tribological properties at multi asperity contact scale. First, for each material we measured chemical composition by XPS, Young's modulus by acoustical microscopy and roughness σ by atomic force microscopy (AFM). Second, we measured the nanofriction coefficients with an AFM and the microfriction coefficients with a ball probe tribometer, for three hardnesses of the ball probe. We identified one friction mechanism at the nanoscale (sliding friction) and two friction mechanisms at the microscale (sliding friction and yielding friction). Comparison of the nano and microfriction coefficients at the same sliding friction regime shown, that the tribological properties of these materials didn’t depend on roughness.     

Spherically bent mica analyzers as universal dispersing elements for X-ray spectroscopy

Spherically-bent crystal analyzers (SBCAs) see considerable use in very high-resolution hard X-ray wavelength dispersive X-ray fluorescence spectroscopy, often called X-ray emission spectroscopy (XES). While Si and Ge are the most frequently used diffractive components of SBCAs, we consider here the somewhat classical choice of muscovite mica as the dispersing element. We find that the various harmonics of a highest-quality mica-based SBCA show ~5–~40% of the integral reflectivity per unit solid angle of a typical Si or Ge SBCA in the hard X-ray range, and that the mica SBCA have comparable energy resolution to the traditional SBCAs. Interestingly, the choice of mica comes with a practical benefit: the primary (0,0,2) reflection has sufficiently strong harmonics that are fairly tightly spaced in energy so that they span the complete energy range from ~4 to ~11 keV when used at convenient Bragg angles in a Rowland circle spectrometer. Hence, a single mica SBCA can be used for every K-shell emission line of three dimensional transition metals and every L-shell emission line of the lanthanide elements simply by selecting the correct mica (0,0,2) harmonic with a final energy-dispersive solid state detector. The loss in efficiency is counteracted by an operational efficiency, i.e., the “universal” application of a single analyzer over a very large range of elements. This performance suggests future application of mica SBCAs in both laboratory-based XES and synchrotron-based photon-in, photon-out spectroscopies in the hard X-ray range.     

Dielectric effect and electrical relaxation in mica crystals

Results are given of an investigation of the dielectric state and electrical relaxation in crystals of dioctahedral muscovite mica. By comparing experimental and theoretical data for the spectra of thermostimulated depolarization (TSD) currents, the temperature dependences of the conductivity during linear heating log = f(1/T) and results of a study of the transfer of the electrical relief during contact under pressure between polarized and nonpolarized crystals, a conclusion is drawn concerning the drift mechanism of relaxation of the dielectric state in mica.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 99–101, October, 1991.     

Imaging and tracking an electrostatic charge micro-domain by Kelvin force microscopy as evidence of water adsorption on mica surface

Muscovite mica is a widely accepted substrate for scanning probe microscopy (SPM) investigations. However, mica has intrinsic properties that alter samples and obstruct their analysis due to free charges build-up, ionic exchange and water adsorption taking place at the surface. In addition to interfacial phenomena, there is a growing interest in electrostatic charges on insulators as they are crucial in diverse applications. Despite the high demand for studies of this nature, experimental set-ups capable of resolving charge build-up at the micro-scale are still scarce and technically limited. Here, we report the imaging of surface charge dissipation on freshly cleaved mica by Kelvin-probe Force Microscopy (KPFM). A local electrostatic charge micro-domain was generated by friction between an atomic force microscope (AFM) tip and mica, and its decay was tracked by two-dimensional mapping using KPFM. We found time-dependent charge dissipation, which is attributed to the adsorption of water molecules on mica surface.     

C(60) molecular bearings and the phenomenon of nanomapping

Inspired by suggestions of C(60) "nanobearings," we have measured sliding friction on fixed and rotating C(60) layers to explore whether a lubricating effect is present. We refer to this general phenomenon as "nanomapping," whereby macroscopic attributes are mapped in a one on one fashion to nanoscale entities. Our measurements are the first to directly link friction to a documented molecular rotation state. Friction is, however, observed to be higher for rotating layers, in defiance of the ball-bearing analogy. Thus, no direct mapping of macro- to nanoscale attributes can be established.     

Monolayer and aggregate formation of a modified phthalocyanine on mica determined by a delicate balance of surface interactions

An ordered layer of a phthalocyanine modified with ether tails can be formed on muscovite mica if removed from solution and dried. This ordered layer forms on potassium terminated as well as on sodium terminated mica, but not on a hydronium terminated surface. The molecules lie flat on the surface, as shown by AFM and X-ray diffraction, giving a layer thickness of approximately 1 nm. In solution, however, no in-plane ordering exists. The material is attracted to the substrate surface but instead of ordering, it aggregates in a liquid-like mobile fashion. This is likely caused by the fact that the water present in solution has a stronger interaction with the potassium ions on the mica surface than with the ether tails of the phthalocyanine.     

Atomic force microscopy evidence for K domains on freshly cleaved mica

The unit cell height in the c-direction of muscovite mica is well established at 10 Å. However, we have observed steps much lower than this whilst imaging freshly cleaved mica surfaces in an atomic force microscope. The steps, 1.0±0.05 Å high, are unstable and disappear in a period of minutes after cleavage. We propose that they are due to the presence of domains of residual K⁺ ions that form two matching patchworks on the cleaved faces. Upon cleavage, they relax inwards from the bulk equilibrium position 1.6 Å above the oxygen atoms of the tetrahedral silicate. Possible mechanisms for the disappearance of the steps are discussed.     

The angular dependence of heavy ion range (ADHIR) of energetic Bi in mica and polycarbonate

The variation of the range of 2.72 GeV ²⁰⁹Bi with crystalline anisotropy has been studied using an anisotropic detector - muscovite mica and an isotropic detector - polycarbonate (Bayer). The two detectors were irradiated at five different angles ranging between 15° and 75°. The effect of the crystal structure on the range variance has also been discussed.     

Influence of surface temperature and surface modifications on the initial layer growth of para-hexaphenyl on mica (0 0 1)

Ultra-thin films of para-hexaphenyl (6P) were prepared on muscovite mica (0 0 1) utilizing organic molecular beam deposition (OMBD) under well defined ultra high vacuum (UHV) conditions. The 6P growth characteristics were studied as a function of substrate temperature and substrate surface conditions. For the initial state of layer growth, thermal desorption spectroscopy (TDS) was used to verify the existence of a wetting layer. In this monomolecular continuous wetting layer, the molecules lie flat on the surface and are rather strongly bonded. For thicker films, in-situ X-ray photoelectron spectroscopy (XPS) in combination with (TDS) was applied to reveal the kinetics of the layer growth. Ex-situ atomic-force microscopy (AFM) was used to determine the film morphology. In particular, the influence of surface modifications (carbon contamination, sputtering) on 6P layer growth was investigated. XPS and low energy electron diffraction (LEED) were used to characterize the mica surface before the film deposition. TDS and AFM revealed a considerable change in film growth, from a needle-like island growth of flat laying molecules on top of the wetting layer (for the air cleaved mica) to terrace-like film growth of standing molecules, without a wetting layer (after surface modifications).     

Track detector study of fission of bismuth nuclei induced by He, radioactive He and Li ions

The cross-sections for fission of ²⁰⁹Bi induced by secondary beams of ⁶He by ⁴He and ⁷Li were measured. For the registration of fission fragments polyterephtalate plastic and muscovite mica detectors were used. In the case of the reaction of helium ions with bismuth the cross-section of the fission of ²⁰⁹Bi induced by ⁶He are significantly higher than the corresponding -particle-induced fission cross-section.     

Birefringence of muscovite mica

Birefringence of muscovite mica (n_e−n_o) is usually calculated from the dispersion relations of the indices n_e and n_o. As small differences between relatively large experimentally-measured values, the few available data for birefringence of mica are widely distinct and sometimes contradict basic experimental facts. A different procedure is adopted in this work to measure birefringence directly as a single quantity in terms of the thicknesses of mica plates and the wavelengths at which they act as quarterwave or halfwave phase retarders. Birefringence is found to decrease gradually from −0.0040 at 420 nm to −0.0046 at 700 nm in conformity with pertinent independent experimental results.     

Structure and Dynamics of Ethanol Adsorbed on a Mica Surface

The structural and dynamic properties of nanoscale ethanol film on a mica surface are investigated via molecular dynamics simulations.We observe a dense,almost flat ethanol bilayer formed in the vicinity of the mica surface,with the hydrophobic alkyl groups pointing outward from the surface.Remarkably,such ethanol bilayer is laterally well-ordered with patterned adsorption sites.Each ethanol molecule in the first layer donates one hydrogen bond to the surface basal oxygen atoms and accepts one hydrogen bond from that in the second layer.The ethanol molecules within the bilayer exhibit constrained lateral mobility and delayed dynamics as compared with bulk ethanol,whereas those on top of the bilayer have bulk-like characteristics.     

云母模板中Cu纳米线的制备及其光学性质研究

利用快重离子辐照的单晶白云母片产生潜径迹,蚀刻得到直径在30—180 nm纳米孔道. 孔道形状依赖于蚀刻时间,蚀刻时间短得到圆柱形孔道,蚀刻时间长得到菱柱形孔道. 从而在云母模板孔道中电化学沉积得到不同直径和形状的Cu纳米线. 通过紫外可见光谱分析,发现铜纳米线的尺寸和形状影响其光学性质. 直径小于60 nm的近似为圆柱状Cu纳米线有一个明显的表面等离子体共振峰和一个微弱的次峰. 随着直径增加,菱柱状的Cu纳米线主峰有明显的红移,次峰逐渐增强. 同时利用扫描电子显微镜、X射线衍射对Cu纳米线的形貌和晶体结构特征进行了表征. 关键词： Cu纳米线 电化学沉积 光学性质 云母模板     

Development of mica-based porous polymeric membrane and their application

To develop porous polymeric membrane, we have used poly(vinylidene-co-hexafluoropropylene) (P(VdF-HFP)) as a host matrix and the ionic liquid 1-ethyl-3-methylimidazolium tosylate as salt for the source of charge carriers in the polymer electrolyte system. Appropriate weight of mica (muscovite) has been added to the highest conducting polymer–salt electrolyte. The composite membrane has been prepared by breath figure method through controlling evaporation time and then tested this membrane for water filtration. The composite polymeric membrane has been characterized by X-ray diffraction, FTIR spectrometry, SEM, and electrochemical impedance spectroscopy. The pore volume in the mica-based film has been calculated, and it is found to be 64.3 % in the filler-dispersed membrane.     

Very low friction state of a dodecane film confined between mica surfaces

The existence of a very low friction state of a lubrication film is demonstrated in nonequilibrium molecular dynamics simulations of a six-layer dodecane film between mica walls. We argue that this low friction state is thermodynamically stable with respect to the well documented high friction film, the latter being a metastable state. These results are in striking accord with the recent report of Zhu and Granick [Phys. Rev. Lett. 93, 096101 (2004).]. The extreme low friction is the result, not of wall slip, but of layer sliding throughout the film, a mechanism similar to solid lubrication.