Carbon Support Film Research Articles

Trace analysis of transition elements and rare earths by parallel EELS

It has been realized for some years that electron energy loss spectroscopy (EELS) offers the potential for a highly sensitive microanalytical technique. Here, we present measurements from some NIST glass standard reference materials showing that EELS provides both high spatial resolution and trace sensitivity for a wide range of elements including the 3-d transition metals and the lanthanides.Specimens were prepared by grinding the glass and depositing the powder on to thin carbon support films. The energy loss spectra were collected by means of a Gatan 666 parallel-detection spectrometer attached to a VG Microscopes HB501 scanning transmission electron microscope (STEM) operating at 100 keV beam energy. This arrangement gave an energy resolution of approximately 0.4 eV limited by the spread of the field-emission source. Large spectral intensities were obtained by setting the probe current to about 8 nA and the collection semi-angle to 20 mrad. In order to eliminate possible hydrocarbon contamination the specimens were cooled to -160 C.

Defects in [1, 6-DI(N-Carbazolyl)-2, 4-Hexadiyne] Diacetylene Crystals

ABSTRACTThe effect of solution concentration on the morphology of [l, 6-di(N-carbazolyl)-2, 4-hexadiyne] (DCHD) diacetylene crystals has been studied by conventional TEM, SAED, and HREM. Crystals obtained by evaporating 0.1 wt% DCHD-chloroform solution on amorphous carbon films are fibrous (about 3 μm wide and 100 μm long) and have defects such as kinks, pores, cracks, and dislocations. Two characteristic single crystal textured morphologies are found in these crystals: (1) a microfibrillar structure consisting of highly-oriented crystallites, with greater axial sizes than lateral sizes, slightly misorienting with a standard deviation of 3°; and (2) a“cross-hatched”structure consisting of highly-oriented crystalline domains separated by two groups of obliquely oriented boundary planes which make (45+/-3)∘ and (37+/-3)∘ angles respectively with the [001] chain direction. Crystals obtained by evaporating more dilute (0.01 wt%) DCHD-chloroform solutions onto amorphous carbon films are about 0.1–0.2 μm long and 0.05–0.1 μm wide and have the chain axis oriented perpendicular to the carbon support film. For these crystals, lateral-chain-invariant (LCI) small angle grain boundaries have been found in HREM images of the [001] zone axis.

The Electron-Beam Sensitivity of Binary Metal Azides

AbstractThe metal azides (or azido complexes) of La, Ce, Ti, Fe(III), Co, Ni, Pd, Ag, Tl, Cd, Sn, Sb and Bi have been synthesised and subjected in situ within a high resolution transmission electron microscope, to electron-beam fluxes (ca 0.1–1.0 A/cm2) to induce rapid decomposition. The materials, which are highly energetic and some are reportedly explosively sensitive, were carefully handled during synthesis to avoid mechanical shock, and only microgram quantities were decomposed whilst on holey carbon support films. In all cases beam-induced decomposition was very rapid. The exothermicity of the reaction induced in the beam promotes vigorous melting which either precedes or is accompanied by radiolysis. The net result is a rapid evolution of nitrogen (product) gas, which causes atomisation and spallation of the metal products. These molten metal particles are hard landed on a 300–500 μm 2 area of the support film with diameters in the nanometre size range. Data is presented on the synthesis of the azides, the nature of the beam-induced process as well as representative electron micrographs of some of the pristine starting materials and the nanoparticulate products.

Electron irradiation damage and sputtering from oxidized silicon particles supported on amorphous carbon

Abstract It is found that electron irradiation, in an electron microscope, of oxidized silicon small particles (nanometers to microns in size) supported on amorphous carbon films, produce extensive surface damage of the oxide layer. During irradiation, the sputtering of the entire thickness (many nanometers) of the silica layer was observed except for a thin (∽ 1 nm) uniform layer which remained stable to further irradiation. The sputtered silica came off and deposited on the nearby carbon film, and was identified using electron energy loss spectroscopy. The carbon film surrounding the particles was seen to damage drastically during irradiation. The damage of the oxide layer seems to be catalyzed by the carbon film at the SiO2/C interface since the rate of removal of the oxide layer decreases as the supporting carbon film disintegrates and is much slower for particles that are not supported.

Effect of surface roughness of carbon support films on high-resolution electron diffraction of two-dimensional protein crystals

The surface roughness of carbon films, which are used as a specimen support in high-resolution electron microscopy, has been investigated by atomic force microscopy. Carbon films were prepared by evaporating carbon onto mica. We found that the carbon surface that had been in contact with the mica was between 3 and 9 times smoother than the surface which had faced the carbon source. Surfaces of carbon films prepared by multiple evaporation were smoother than films evaporated in a single step. The surface roughness on the mica side of these films was close to that of mica. Two-dimensional crystals of plant light-harvesting complex yielded isotropically sharp high-resolution electron diffraction patterns at high tilt angles only when supported on the smoothest carbon films, produced by multiple evaporation.

Observations of surface structures and reaction products for materials exposed in space in low-earth orbit

A preliminary study of materials exposed in space in low-earth orbit for nearly six years (in the NASA Long-Duration Exposure Facility (LDEF)) has revealed a range of micrometeorite and microparticle impact craters and blisters of unknown origin on aluminum alloy 6061-T6 samples on the leading edge of the satellite. In addition these samples were covered with an enormous range of reaction products which included crystals and polycrystalline aggregates which originated in part from other reactions and atomic oxygen degradation taking place in systems proximate to the alloy samples.A replication-type lift-off techniques was developed to remove reaction products (crystals and polycrystals, etc.) and debris from the specimen surfaces in order to isolate them from the background substrate without creating microchemical or microstructural artifacts. This technique culminates in extracted surface features resting on a carbon support film which is virtually “invisible” to observation by electron microscopy and non-dispersive x-ray analysis.

Improved transfer of two-dimensional crystals from the air/water interface to specimen support grids for high-resolution analysis by electron microscopy

Electron crystallographic analysis of two-dimensional crystals grown on lipid layers at the air/water interface has been limited by loss or damage during transfer of the crystals to an electron microscope support grid. Two methods of transfer are described which are applicable on a small scale (10 μ1 of protein solution) and which give greatly improved results for streptavidin crystals on biotinylated lipid layers. In the first method, a hydrophobic grid surface was produced by coating a carbon support film with a thin layer of SiO 2, followed by alkylation with dimethyloctadecylchlorosilane. The transfer efficiency of protein crystals approached 50% coverage of the alkylated grid surface. The degree of order of crystals transferred to the alkylated grid surface and preserved in negative stain was significantly improved over that of crystals transferred directly to a carbon support film. In the second method, crystals at the air/water interface were transferred to a holey carbon support film. The efficiency of transfer across the holes was virtually 100%, as nearly every hole was completely covered with crystals. After preservation of the crystals in 1% glucose and cooling to liquid nitrogen temperature, electron diffraction was obtained that extended to 1/2.8 Å -1 resolution. This result demonstrates that two-dimensional crystals grown on lipid layers at the air/water interface can be sufficiently well-ordered, even after transfer to a support grid, to yield high-resolution structural information.

A high-resolution electron microscopy study of silver particles and surfaces

Abstract The use of metal particles in heterogenous catalysis demands a continuous development of particle preparation methods and of methods for studying these particles. Two ways of preparing silver particles for high-resolution electron microscopy (HREM) studies have been used in this investigation; in situ reduction of silver iodide (AgI) in the electron beam and reduction of silver acetate suspended in acetic acid. The reduction of AgI in the electron beam is a straightforward method. Using an intense electron beam the method produces finite silver particles spread uniformly over the amorphous carbon support film. The preparation of silver particles by reduction of silver acetate is similar to particle preparation methods which have previously been used for other metals. The particle sample is air stable and water soluble which makes the specimen preparation for HREM easy. The two preparation methods give particle specimens well suited to HREM. Small silver particles are shown to undergo the same str...

Effects of space environment on structural materials: A preliminary study and development of materials characterization protocols

A preliminary study of materials exposed in space in a low-earth orbit for nearly 6 years (in the NASA Long-Duration Exposure Facility) has revealed a wide range of micrometeorite or microparticle impact craters ranging in size from 1–100 μm diameter, debris particles from adjacent and distant materials systems, reaction products and other growth features on the specimen surfaces, and related phenomena. The exposed-surface features included finegrained and nearly amorphous materials as well as single-crystal particles. A replication-type, lift-off technique was developed to remove reaction products and debris from the specimen surfaces in order to isolate them from the background substrate without creating microchemical or microstructural artefacts or alterations. This resulted in surface features resting on a carbon support film which was virtually invisible to observation by electron microscopy and non-dispersive X-ray analysis. Characterization of these surface features involved observations by optical metallography, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray analysis; including an analytical transmission electron microscope with a STEM attachment. The results illustrate a wide variety of materials phenomena which must be addressed in the evaluation of materials exposure in space, and the formidable materials characterization effort which will be necessary to understand these features.

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 degree, and perhaps less than 0.2 degrees, over areas as large as 1 micron2 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.

Modification of the Polaron sputter‐coater unit for glow‐discharge activation of carbon support films

We describe a modification of the Polaron sputter-coater unit series 11 HD enabling activation of carbon support films for electron microscopy of macromolecules and macromolecular assemblies. The modification is simple and the device can be used in two modes, for sputter-coating of SEM samples and for glow-discharge activation of carbon support films. Examples of protein-free spreading of DNA and negative staining of bacteriophage particles on activated carbon support films are presented.

Staphylococcus aureus α-Toxin Crystals on Lipid Layers: Effects of Trypsin Treatment

α-toxin is a lethal, dermonecrotic, cytotoxic, and hemolytic protein which is secreted by most strains of Staphylococcus aureus . The biological effects are brought about by pertubation of membrane structures making them permeable to ions and small molecules. The structural basis for the mode of action is not known in detail. One hypothesis is that an oligomeric form of the toxin, observed both biochemically and by electron microscopy, circumscribe a hydrophilic pore through which transport can occur. Recent functional studies have demonstrated that oligomerization is a necessary but not a sufficient criterion for permeabilization. For example, trypsin treated α-toxin was, despite its lack of membrane damaging activity, able to form 200 kDa aggregates on mouse adrenocortical (Yl) tumor cells. In this work we have compared the structure of trypsin treated α-toxin with that of the intact toxin.α-toxin was purified from S. aureus strain wood 46 by isoelectric focussing and gel filtration. Tryptic toxin fragments (18 and 17 kD as determined by SDS-PAGE) were generated by digestion of native α-toxin (1 mg in 1.5 ml Tris buffered saline) with 30μg trypsin for 4 h at 37°C, pH 8.0. The reaction was terminated by the addition of 30μg lima beam trypsin inhibitor. Toxin specimens were applied to lipid layers pre-formed on carbon support films. Electron microscopy was performed after negative staining either with 1% Na-PTA (pH 7.0) or with a mixture of Na-PTA and glucose. Subsequent image processing of large coherent crystalline arrays produced correlation averaged projection maps. A three-dimensional model was obtained by collecting and combining data from tilted views.

Profile Imaging of Surfaces

Profile imaging is a method whereby the atomic resolution capabilities of the modern electron microscope can be harnessed to provide direct information about the topography of particular types of surfaces. However, several prerequisites must be satisfied before the surface features visible in the profile image can be considered as genuinely representative of the specific material. The microscope must be properly adjusted (i.e. focus, alignment and astigmatism), the surface in profile must be thin (typically 100Å or less), and it should be free of contaminants or surface reaction products. In the absence of contamination or other amorphous specimen regions, however, correct operating conditions are difficult to establish. Moreover, it is not obvious that any surface reactions or reconstructions that occur along the thin profile edge of the sample are related to bulk surface morphology. Finally, facilities forin situsurface treatment must be considered as essential for materials with reactive surfaces. In this paper, recent progress in surface profile imaging is briefly reviewed, keeping in mind these diverse requirements. The possibility for dynamic image viewing and recording without loss of performance levels should also be appreciated.OxidesClean fracture surfaces of many maximally valent oxides can be obtained by the simple expedient of crushing under a clean solvent with a mortar and pestle, and the ubiquitous holey carbon support film solves the problem of a means for microscope adjustment. Alternative techniques of specimen preparation such as ion-milling or chemical thinning may be required in order to obtain extended areas of a specific surface and orientation, but care is then required to avoid surface, or near-surface, modifications. Typical projected cation spacings in the major low-index zones are such that it is possible to resolve individual cation columns, and profile images such as the [001] SnO2 crystal shown in Fig. 1 clearly reveal the atomic (re-)arrangements at the surface. Several electron-beam-induced processes during extended observations of oxide surfaces have been documented. These include surface diffusion, as well as surface, and near-surface, reduction due to electron-stimulated desorption (ESD) of oxygen. In some maximally-valent transition metal oxides, the epitaxial development of a lower (metallic) oxide takes place, but a variety of end-products can in general be anticipated depending on such factors as the initial surface cleanliness, the residual microscope vacuum and the degree of covalency/ionicity of the original oxide.

Optimum collection angle for detection of small catalyst particles in high-angle dark-field Scanning Transmission Electron Microscopy

Since Crewe et al demonstrated the detection of single heavy atoms on thin carbon support films, there has been considerable interest in the use of high angle annular dark field detectors(HADD) to study particles in the subnanometer size range. A recent contribution to this subject is the work of Treacy and Rice.Increased interest in this technique can be attributed to the minimization of diffraction and phase contrast effects in the imaging of small atom catalyst particles .In this study we calculate the expected signal using realistic electron scattering cross sections. For the high angle dark field considered, it is reasonable to assume single scattering and to consider dynamical effects averaged out by the averaging over annular aperture.The electron scattering amplitude used is given by the Mott formula;

Histone hyperacetylation can induce unfolding of the nucleosome core particle

A direct correlation exists between the level of histone H4 hyperacetylation induced by sodium butyrate and the extent to which nucleosomes lose their compact shape and become elongated (62.0% of the particles have a length/width ratio over 1.6; overall mean in the length/width ratio = 1.83 +/- 0.48) when bound to electron microscope specimen grids at low ionic strength (1mM EDTA, 10mM Tris, pH 8.0). A marked proportion of elongated core particles is also observed in the naturally occurring hyperacetylated chicken testis chromatin undergoing spermatogenesis when analyzed at low ionic strength (36.8% of the particles have a length/width ratio over 1.6). Core particles of elongated shape (length/width ratio over 1.6) generated under low ionic strength conditions are absent in the hypoacetylated chicken erythrocyte chromatin and represent only 2.3% of the untreated Hela S3 cell core particles containing a low proportion of hyperacetylated histones. The marked differences between control and hyperacetylated core particles are absent if the particles are bound to the carbon support film in the presence of 0.2 M NaCl, 6mM MgCl2 and 10mM Tris pH 8.0, conditions known to stabilize nucleosomes. A survey of the published work on histone hyperacetylation together with the present results indicate that histone hyperacetylation does not produce any marked disruption of the core particle 'per se', but that it decreases intranucleosomal stabilizing forces as judged by the lowered stability of the hyperacetylated core particle under conditions of shearing stress such as cationic competition by the carbon support film of the EM grid for DNA binding.

Structural rearrangements in small gold particles

A knowledge of the structure of small metal particles is fundamental to understanding their role in heterogeneous catalysis. It is therefore of much topical interest that structural rearrangements have been found to take place as a result of intense electron irradiation within the electron microscope. Initial observations were of gold particles on supports of carbon and silica-covered silicon, but further studies confirmed that qualitatively similar behaviour also took place for particles of Pt, Ru and Rh. Some of the factors which influence the motion have been noted, including the particle size, the nature of the substrate and, obviously, the current density of the electron beam. Considerable debate has been generated by these observations. It has been suggested, for example, that the structural fluctuations should be dampened by an electrically conducting substrate which would prevent the particles from becoming charged. It was also proposed that the “quasimelting” of gold particles was triggered by Auger decay, in effect heating the particles electronically rather than thermally. The energetics of these fluctuations have also been considered.In this paper, we report our initial efforts to quantify some of the experimental factors involved in this quasimelting process. Three sets of samples were prepared: one was a normal holey carbon support film, the second was a holey silicon support film, and the third was a carbon film upon which graphitised carbon had been deposited.

Transmission Electron Microscopical studies of chemical rearrangements in bismuth uranium oxide

Electron beam induced transformations in metal oxides have been the subject of a number of TEM studies, including, recently, transition metals (eg 1), lanthanides and actinides (eg 2). In this paper we present preliminary results of a high resolution TEM study of bismuth uranium oxide (Bi2UO6), in which several unusual electron beam induced phenomena have been observed. Samples exhibit one of four different types of behaviour in the electron beam. Although in each case the onset of the phenomena is dose-rate dependent, differences in dose-rate do not seem to be solely responsible for the observed differences in behaviour. Although all the samples are nominally of the same chemical stoichiometry, microscopic inhomogeneities in composition may result in differing decomposition behaviour. In this respect, the known ability of Bi2UO6 to give up large proportions of its lattice oxygens (3) without apparently changing crystal structure may be directly relevant.The observed types of behaviour are as follows: a) The sample remains unchanged, apparently indefinitely, under periods of continous electron irradiation. b) The sample remains unchanged for a period, after which it suddenly “explodes”, depositing crystalline material on the surrounding carbon support film.

On the catalytic oxidation of amorphous carbon by Pd and PdAg particles

The catalytic oxidation of amorphous carbon by small Pd and PdAg particles (15–20 nm in diameter) was investigated using a transmission electron microscope. The catalytic activities of the particles were measured by observation of the growth of holes oxidized into the carbon support films. The results show an increase of activity with growing size of the particles and increasing temperature and oxygen pressure. The highest activities were observed for pure Pd particles whereas pure Ag particles were completely inactive. Small concentrations of Ag reduced the activity drastically, compared with the expected value corresponding to the bulk composition. This is interpreted in terms of surface segregation and of the size of the site required for oxygen adsorption.

ChemInform Abstract: Formation of NaCl‐ and Cu2O‐Type Oxides of Platinum and Palladium on Carbon and Alumina Support Films.

AbstractIt is found that vacuum deposition of thin films of Pt and Pd on carbon and alumina supports (350‐400 °C, 10‐5 torr) yields not only metallic particles but also new cubic oxides, namely PtO, PdO (NaCl‐type, Fm3m, Z=4), Pt2O, and Pd2O (Cu2O‐type, Pn3m, Z=2).

Formation of NaCl- and Cu 2O-type oxides of platinum and palladium on carbon and alumina support films

Vacuum deposition of ultrathin films of platinum and palladium on carbon and alumina supports at a substrate temperature of 350–400 °C and a working pressure of 10 −5 Torr is shown to give rise not only to metallic particles but also to the formation of two new cubic oxides, namely, an NaCl-type (space group Fm3m, Z = 4) and a Cu 2O-type oxide (space group Pn3m, Z = 2) with lattice parameters: PtO a = 0.515 ± 0.005 nm PdO a = 0.565 ± 0.005 nm Pt 2O a = 0.395 ± 0.005 nm Pd 2O a = 0.428 ± 0.005 nm Electron microscopic observations reveal that the NaCl-type oxide is in the form of thin, well-spread single crystals, whereas the fine dispersed particles correspond to metal and/or Cu 2O-type oxides. It seems that the partial pressure of oxygen at 10 −5 Torr is enough for finely divided platinum or palladium to form oxides at 350–450 °C. The existence of these new oxides in the bulk state has yet to be established, however. The formation of Pt 2O and Pd 2O suggests a valency of one for platinum and palladium in certain situations. Alternatively, these oxides may exhibit non-stoichiometry.