Substrate properties affect the mass loss rate in collodion at liquid helium temperature

A previous measurement showed that mass loss from collodion supported by thin carbon films was linear with electron exposure at liquid helium temperature. No other organic solid had shown a linear loss of mass at any temperature. When measurements of collodion were done using titanium supports, the loss of mass proceeded exponentially with exposure at liquid helium temperature. This result suggested that the differing electrical conductivities of these substrates might be the cause of the different mass loss effects. Carbon films, which are typically used at ambient temperatures, have much lower electrical conductivity at very low temperature than titanium films. This suggested that specimen preparation materials and techniques used routinely for room temperature studies may need to be modified when microscopy is done using superconducting objective lenses. For both substrates, the rate of mass loss is slowest at liquid helium temperature.     

Low-noise boron supports for high resolution electron microscopy

Very thin (～1.5 nm) amorphous boron films are useful as specimen supports for the study of biochemical molecules by dark-field transmission electron microscopy. The noise factor is significantly smaller than for carbon films, probably because of the tendency to bond in icosahedral B₁₂ subunits. Signal-to-noise ratio of about 2 to 3 have been obtained with bromine and strontium atoms in test molecules.     

Indirect monitoring of the dynamics at the contact interfaces of a pair of abrading titanium specimens

The novel method of using continuous tribo-electrification variations to monitor the dynamic tribological properties between metal films has been applied successfully [Y.P. Chang, A novel method of using continuous tribo-electrification variations for monitoring the tribological properties between the pure metal films, Wear, 262 (2007) 411–423]. The method was shown to produce clear and strong signals, superior to monitoring continuous friction coefficient variations. However, the above method was only shown to be suitable for the tested material pairs that were studied. In this paper, the method was improved and applied to monitoring the dynamic tribological properties between titanium oxide (TiO₂) films in the friction process. The experiment was conducted on a purposed-designed friction tester with a suitable measuring system. In order to investigate the tribological property of titanium (Ti) sliding against Ti with TiO₂ films in detail, the continuous variations of electrical contact resistance and friction coefficient were measured for monitoring the onset of film rupture between the TiO₂ films and the chemical reactions between the interfaces. Wear loss was measured by an accuracy balance and scan electron microscopy was used to observe the microstructures and material transfer. The experiments demonstrated that the novel method of using electrical contact resistance variations has great potential for monitoring the dynamic tribological properties and the chemical reactions of titanium specimens.     

Interfacial effect on thermal conductivity of diamond-like carbon films

Diamond-like carbon (DLC) has been of interest as a promising coating for protection and insulating layer in micro-electromechanical systems due to high hardness, wear resistance, transparency in IR range, chemical inertness and biocompatibility. The interfacial effect on thermal transport is studied for DLC films deposited on Al₂O₃ substrates with an ion gun method. Thermal conductivity of DLC thin films is measured with a 3ω method. DLC films show the thickness-dependent thermal conductivity, which is understood with the interfacial thermal resistance between DLC thin film and Al₂O₃ substrate. The interfacial thermal resistance and thermal conductivity of bulk DLC are determined with the measured thickness-dependent thermal conductivity of DLC films.     

Microstructural evolution of Cu-1 at% Ti alloy aged in a hydrogen atmosphere and its relation with the electrical conductivity

Copper alloys with titanium additions between 1 and 6 at% Ti emerge currently as attractive conductive materials for electrical and electronic commercial products, since they exhibit superior mechanical and electrical properties. However, their electrical conductivity is reduced owing to the residual amount of Ti solutes in the Cu solid solution (Cu_ss) phase. Since Cu shows only poor reactivity with hydrogen (H), while Ti exhibits high affinity to it, we were inspired by the idea that hydrogenation of Cu–Ti alloys would influence their microstructure, resulting in a significant change of their properties. In this contribution, the influence of aging under a deuterium (D₂) atmosphere of Cu-1 at% Ti alloys on their microstructure is investigated to explore the effects on the electrical conductivity. The specimens were investigated by means of transmission electron microscopy (TEM), field ion microscopy (FIM), computer-aided field ion image tomography (cFIIT), and atom probe tomography (APT).     

Electron cryo-microscopy of biological specimens on conductive titanium-silicon metal glass films

Thin films of the metal glass Ti88Si12 were produced by evaporation and characterized by AFM and conductivity measurements. Thin Ti88Si12 support films for electron microscopy were prepared by coating standard EM grids with evaporated films floated off mica, and characterized by electron imaging and electron diffraction. At room temperature, the specific resistance of a thin TiSi film was 10(6) times lower than that of an amorphous carbon film. At 77K, the specific resistance of TiSi films decreased, whereas that of carbon became immeasurably high. The effective scattering cross-section of TiSi and amorphous carbon for 120 kV electrons is roughly equal, but TiSi films for routine use can be approximately 10 times thinner due to their high mechanical strength, so that they would contribute less background noise to the image. Electron diffraction of purple membrane on a TiSi substrate confirmed that the support film was amorphous, and indicated that the high-resolution order of the biological sample was preserved. Electron micrographs of TiSi films tilted by 45 degrees relative to the electron beam recorded at approximately 4 K indicated that the incidence of beam-induced movements was reduced by 50% compared to amorphous carbon film under the same conditions. The success rate of recording high-resolution images of purple membranes on TiSi films was close to 100%. We conclude that TiSi support films are ideal for high-resolution electron cryo-microscopy (cryo-EM) of biological specimens, as they reduce beam-induced movement significantly, due to their high electrical conductivity at low temperature and their favorable mechanical properties.     

Interfacial energies and surface-tension forces involved in the preparation of thin,flat crystals of biological macromolecules for high-resolution electron microscopy

It is generally agreed that surface-tension forces and the direct interaction between the specimen and either the air-water interface or the water-substrate interface can influence significantly the preparation of biological materials for electron microscopy. Even so, there is relatively little systematic information available that would make it possible to control surface-tension forces and interfacial energies in a quantitative fashion. The main objective in undertaking the present work has been to understand somewhat better the factors that influence the degree of specimen flatness of large, monolayer crystals of biological macromolecules. However, the data obtained in our work should be useful in understanding the preparation of specimens of biological macromolecules in general. Data collection by electron diffraction and electron microscopy at high resolution and high tilt angles requires thin crystals of biological macromolecules that are flat to at least 1°, and perhaps less than 0·2°, over areas as large as 1 μm² or more. In addition to determining empirically by electron diffraction experiments whether sufficiently flat specimens can be prepared on various types of modified or unmodified carbon support films, we have begun to use other techniques to characterize both the surfaces involved and the interaction of our specimen with these surfaces. In the specific case of large, monolayer crystals of bacteriorhodopsin prepared as glucose-embedded specimens on hydrophobic carbon films, it was concluded that the initial interfacial interaction involves adsorption of the specimen to the air-water interface rather than adsorption of the specimen to the substrate. Surface-tension forces at the air-water interface and an apparently repulsive interaction between the specimen and the hydrophobic carbon seem to be major factors influencing the specimen flatness in this case. In the more general case it seems likely that interfacial interactions with either the substrate or the air-water interface can be variously manipulated in the search to find desirable conditions of specimen preparation.     

Friction surfacing on nonferrous substrates: a feasibility study

This work reports a feasibility study on producing friction surfaced coatings on nonferrous substrates. Commercially pure aluminum, copper, magnesium (ZM21), Inconel 800, and titanium alloy (Ti-6Al-4 V) were chosen as the substrates. Low carbon steel, aluminum alloy (AA6063), commercially pure copper and titanium were chosen as the consumable rods. Friction surfacing was attempted with all consumable rods on every substrate. In some cases metallurgically bonded coating was obtained readily over the substrate and in some other cases coating was obtained with a start-up plate. However, for certain combination of parameters, no coating could be obtained. The coatings obtained were analyzed for their microstructural features and interfacial characteristics using optical and scanning electron microscopy. The results showed that co-efficient of friction, material properties like thermal conductivity, and stability at high temperature influenced the formation of a coating. Coatings obtained exhibited fine grained microstructure with properties better than the original parent material. Dynamic recrystalization as a result of severe plastic deformation accounts for grain refinement.     

Heteroepitaxy of AIIIBV films on vicinal Si(001) substrates

GaAs films on Si substrates miscut from the (001) plane by 6° in the [110] direction are grown by molecular beam epitaxy (MBE). GaAs films are grown both on the Si surface terminated by arsenic atoms and on thin pseudomorphic GaP/Si layers. The condition of formation of the As sublayer and the first monolayer of GaP on the Si surface is defined as the GaAs film orientation (001) or \((00\bar 1)\) . The processes of Si surface preparation and formation of the As sublayer and GaAs and GaP epitaxial layers are monitored by means of high-energy electron diffraction reflection (RHEED). The grown structures are investigated by methods of X-ray diffraction, atomic force microscopy (ATM), high-resolution transmission electron microscopy (HRTEM), and low-temperature luminescences. It is shown that the epitaxial film orientation affects both the surface morphology and its crystalline properties. Intense photoluminescence is obtained from the In_0.17Ga_0.83As quantum well structure grown on the GaAs/Si buffer layer.     

Microstructure, chemical and tribological investigations of Mo x W1−x S y co-sputtered composite films

Mo _x W_1−x S _y composite films were co-sputtered by the combination of MoS₂ and WS₂ targets, which were shown to have much superior tribological performance with lower and more stable friction coefficient, longer durability and higher bearing resistance than pure MoS₂ films in room temperature air with a relative humidity of 45–50%. Especially for the Mo_0.6W_0.4S_1.6 (40 at.% WS₂) composite film, an increase in durability of more than a one order of magnitude was reached. X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used to investigate the relationship between the microstructure and the tribological performance of the films. The composite films are shown to have a densified structure and accordingly improved oxidation resistance and lubrication properties. Moreover, the composite films have a lattice expansion in the c direction, along with a reduced the friction within the films.     

Tribological properties of lubricated nanocrystalline diamond surfaces for various loads and geometries

Abstract

Diamond and diamond-like carbon films are well known for their outstanding properties such as high hardness, low coefficient of friction, good thermal conductivity, excellent biocompatibility and electrical insulation. Diamond films with nanocrystalline grains offer added advantages of higher hardness, improved surface finish (less roughness), very high sp³ content, etc. In view of the above, the present investigation is undertaken to explore the possibility of using nanocrystalline diamond films in advanced tribological applications. In this work, a nanocrystalline diamond film is deposited using a unique chemical vapour deposition (CVD) technique. The microstructural features are characterised using atomic force microscopy (AFM). Tribological behaviour of these films is evaluated by means of a reciprocating model tribometer with various lubricants. The worn surfaces are examined using three-dimensional confocal microscopy. The results show that these films have comparable friction coefficient with and without lubricants. Furthermore, they exhibited negligible wear for the tested range of loads.     

Electron microscopy of PbO2 deposited on a titanium substrate

The nucleation and growth of lead dioxide on titanium substrate has been observed using scanning electron microscopy. The size and morphology of the PbO₂ nodules have been measured in an attempt to elucidate the nucleation and growth mechanism. The effects of temperature, current density and fluorine ion addition have been qualitatively determined. The structure of a film of PbO₂ formed on the titanium has been examined using TEM and found to be heavily strained and to contain lattice defects such as dislocations and stacking faults.     

Beam heating in an asymmetrically illuminated thin circular film

The method of images is used to calculate the temperature increase produced in a circular film when the film is illuminated at any point by an electron beam of circular cross-section and constant current density over its cross-section. Formulae are given in dimensionless form for (i) the temperature increase anywhere along the line joining the centres of the beam and of the film, (ii) the temperature increase at the centre of the beam (v_c), and (iii) the position and value of the maximum temperature increase in the film v_m. The relative sizes of v_c and v_m are discussed and it is shown that (v_m – v_c)/v_m ≤ 0.079. The theory applies best to metallic films where power loss by means of thermal conductivity is dominant. A brief discussion is given of the cases where thermal radiation is important, sample calculations are given for carbon and copper films, and the effect of focusing the electron beam at constant current is considered.     

Preparation of frozen-hydrated specimens for high resolution electron microscopy

A method is presented for preserving the high resolution structure of biological membranes in a frozen-hydrated environment for electron microscopy. The technique consists of sandwiching a specimen between two carbon films and then waiting while some of the solvent evaporates. When the solvent layer is judged to be of an appropriate thickness, the specimen is then frozen in liquid nitrogen. The specimen can then be inserted into the precooled stage of an electron microscope. Electron diffraction studies of the purple membrane of Halobacterium halobium recorded at -120 degrees C have shown that the structure can be preserved to a resolution of 3.5 A. The main advantage of this method over previous techniques is that the hydrating conditions can be accurately controlled.     

Electron microscopy of unstained,freeze-dried macromolecular assemblies

A rapid cooling/cryotransfer system was designed to achieve a high reproducibility in vitrifying thin water films containing biological specimens. In order to improve the contrast these unstained specimens were deliberately freeze-dried in situ in the electron microscope. The preservation of the structure obtained by freeze-drying at 180 K and subsequent microscopy at 90 K is very encouraging as has been shown with two types of test specimen. Tubular photosynthetic membranes were used to examine the effects of a variety of freeze-drying conditions on structural preservation, as judged by flattening of the tubes. A two-dimensional protein crystal was used to evaluate problems of low-dose microscopy of unstained, freeze-dried proteins, e.g. optical density of films, motif detection by cross-correlation and transferring the accurate molecular positions from medium-dose to corresponding low-dose micrographs. The radiation sensitivity of the unstained, freeze-dried protein crystal was investigated by a dose series covering a wide range.     

Energy-filtered transmission electron microscopy of biological samples on highly transparent carbon nanomembranes

Ultrathin carbon nanomembranes (CNM) comprising crosslinked biphenyl precursors have been tested as support films for energy-filtered transmission electron microscopy (EFTEM) of biological specimens. Due to their high transparency CNM are ideal substrates for electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) of stained and unstained biological samples. Virtually background-free elemental maps of tobacco mosaic virus (TMV) and ferritin have been obtained from samples supported by ∼1 nm thin CNM. Furthermore, we have tested conductive carbon nanomembranes (cCNM) comprising nanocrystalline graphene, obtained by thermal treatment of CNM, as supports for cryoEM of ice-embedded biological samples. We imaged ice-embedded TMV on cCNM and compared the results with images of ice-embedded TMV on conventional carbon film (CC), thus analyzing the gain in contrast for TMV on cCNM in a quantitative manner. In addition we have developed a method for the preparation of vitrified specimens, suspended over the holes of a conventional holey carbon film, while backed by ultrathin cCNM.     

Morphological properties of Ag₂SeTe nano thin films prepared by thermal evaporation

Semiconducting silver selenide telluride (Ag₂SeTe) thin films were prepared with different thicknesses onto glass substrates at room temperature using thermal evaporation technique. The structural properties were determined as a function of thickness by X‐ray diffraction exhibiting no preferential orientation along any plane; however, the films are found to have peaks corresponding to mixed phase. The morphology of these films was studied using scanning electron microscope and atomic force microscopy respectively, and is reported. The morphological properties are found to be very sensitive to the thin film thickness. The composition of the films is also estimated using energy dispersive analysis using X‐rays and are also reported.     

Electron and light microscopy studies on the domain structures of Zn3B7O13Cl, Zn3B7O13Br and Zn3B7O13I ferroic boracites

The domain structures of Zn₃B₇O₁₃Cl, Zn₃B₇O₁₃Br and Zn₃B₇O₁₃I boracite single crystals were studied by means of polarized light in conjunction with electron microscopy. Single crystals of the three compositions were grown by chemical transport reactions in closed quartz ampoules, at a temperature of 900 °C and were examined by polarizing optical microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For both PLM and SEM, the same as‐grown samples were used without having to resort to metallization of the crystal faces. For TEM the single crystals were crushed and mounted on holey carbon films. Comparative electron microscope images were useful for revealing the domain structure of these ferroelectric/ferroelastic materials previously observed between the crossed polars of an optical microscope. X‐ray diffraction analysis of the pulverized crystals was performed for this triad of halogen boracites containing zinc as a common metal.     

Supported metal model catalyst surfaces examined by scanning tunnelling microscopy

Topographic and/or barrier-height images of ultrafine Pt and Au metal particles supported on a vacuum-deposited carbon film or titanium oxide thin films grown on titanium metal sheets were obtained. The topographic images of colloidal Au particles (5-nm diameter) adsorbed on a titanium oxide thin film showed a structure elongated in the direction normal to the x scan, indicating their weak interaction with the support surface. The topographic images of Pt vacuum-deposited on a carbon film showed c. 4-nm diameter particles, larger than those observed in electron microscopy. The problems inherent to the STM observation of such dispersed metal systems are identified. In the case of Pt particles vacuum-deposited on titanium oxide film, its barrier-height image gave better indication of different phases on the surface than its topographic image. The significance of obtaining barrier-height images along with topographic images for such sample systems is demonstrated.     

Humidity dependence of microwear characteristics of amorphous carbon films on silicon substrates

Influences of environmental humidity on various scanning-scratched wear characteristics, such as long-term stability of wear resistance and load dependence, scratch number dependence and scratch velocity dependence of wear depth, are evaluated by using an atomic force microscope and diamond tips. Amorphous carbon (a-C) films are deposited on silicon substrates by the electron cyclotron resonance plasma (ECR) sputtering method and the RF sputtering method combined with CVD using argon gas containing methane (CH₄) as a sputtering gas. In carbon samples with a higher hydrogen content, clear influences of the humidity on various wear characteristics are observed and their wear resistances decrease with increase of the humidity. In the ECR sputtered carbon film with low hydrogen content, wear resistance is stable during long-term exposure to an environment of high temperature and high humidity. In this film, the influences of humidity on the wear resistance and adhesion forces between the films and the substrates are not observed, since it is highly wear resistant and the wear depths are shallow in each test. Thus, amorphous carbon films with low hydrogen content are suitable as wear resistant protective overcoats from the point of view of the wear resistance, in particular the influence of the humidity on the wear resistance including its long-term stability.