L. Margulis

Vacuum-deposited gold films: I. Factors affecting the film morphology

Abstract Thin (300–1000 A) gold films were deposited on glass, mica and silicon substrates (preheated or held at room temperature) by sputtering or evaporation. The films were characterized by transmission electron microscopy (TEM), electron diffraction (ED) and voltammetric measurements. Gold sputtering produces pebble-type structures with very small grains and no crystallographic texture. Evaporation of gold onto glass or mica produces large, flat crystallites, with a pronounced {111} texture, while on smooth silicon (100) it results in non-textured films. Annealing of the films at 250°C always has the effect of grain enlargement, and, in the case of gold on glass or mica, enhancement of the {111} texture.

Preparation and microstructure WS2 thin films

Abstract Thin tungsten films were ion beam sputter deposited onto quartz slides and then reacted at temperatures from 500 to 1000°C in an open system under a gas flow consisting of a mixture of H 2 S and forming gas. The reaction products were examined by X-ray diffraction, transmission electron microscopy, electron probe microanalysis, Auger electron spectroscopy, optical transmission spectra and sheet resistivity measurement. The onset of the reaction between tungsten and H 2 S to give WS 2 thin films was found to be 650°C. Orientation of the WS 2 crystallites could be controlled by choice of reaction temperature and sulphur concentration in the gas flow: low reaction temperatures (up to 900°C) and high sulphur concentrations lead to films where competition between the reaction rate and the rate of crystallization. The importance of these results lies in the fact that the latter orientation is needed for solar cells and optimum lubrication uses, but the former has been found in the majority of reported cases.

Effect of substrate on growth of WS2 thin films

Abstract Thin sputtered tungsten films on various substrates (molybdenum or tungsten foils, quartz and glass slides) were reacted with H 2 S at temperatures from 400 to 1000 °C. In general, it was found that the WS 2 crystallites nucleate from an amorphous WS 3 phase. It was established that the substrate has a critical role in determining both the reaction onset temperature and the texture. For glass substrates, the reaction to give WS 2 begins at T ⩾ 400 °C, and the WS 2 grains grow predominantly with the van der Waals (vdW) planes parallel to the substrates (in this orientation, the c axis is perpendicular to the substrate, and is designated ⊥c) at 500 °C. On quartz substrates, reaction begins only at 650 °C and the texture is predominantly vdW planes perpendicular to the substrate )this orientation is designated ‖c) below 950 °C, and exclusively ∋ texture at higher temperatures. These differences between glass and quartz are believed to be due to sites on the quartz, absent (or present to a smaller extent) on glass, which strongly bind the tungsten and WS 2 . Molybdenum substrates give only the ‖c orientation even at 1000 °C, while bulk tungsten (or tungsten sputtered on tungsten) gives randomly oriented WS 2 . For oxidized tungsten on quartz, reaction onset is lowered to 500 °C (compared with 650 °C for W/quartz), and predominantly ⊥c orientation is obtained at 800 °C. Exclusively ⊥c orientation was never achieved with this system, even at 1000 °C. It was found that the ‖c orientation changes to the ⊥c orientation when diffusion conditions (temperature and time) were sufficient, indicating that the latter orientation is energetically favourable.

Electron Diffraction and Imaging of Uncompressed Monolayers of Amphiphilic Molecules on Vitreous and Hexagonal Ice

A new approach is described for probing domains of ordered self-assemblies of amphiphilic monolayers at the aqueous solution interface. The method has potential importance for the study of membrane structure, Langmuir-Blodgett films, and nucleation processes of two-and three-dimensional crystals. Electron diffraction (ED) patterns indicative of two-dimensional crystalline self-assembly were obtained from samples, which were examined by cryo-electron microscopy, of monolayers of water-insoluble amphiphiles on vitrified aqueour substrates. The apparent hexagonal symmetry of an ED pattern from a C16H33OH monolayer was interpreted in terms of multiple twinning. Monolayers of the CL31H63OH and cadmium salt of C19H39CO2H that were studied by dark-field techniques displayed faceted two-dimensional crystallites with a maximal size of 1 to 2 micrometers. Epitaxial nucleation of hexagonal ice by the C31H63OH monolayer has also been demonstrated by ED.

TEM study of chirality in MoS2 nanotubes

The dark‐field diffraction contrast of helical nanotubes (NTs) is shown to be asymmetric when an NT is tilted at appropriate angle with respect to the incident electron beam. This phenomenon was used for the chirality determination of multi‐shell NTs observed in MoS2 layered compound. Both kinds of NT — helical and non‐helical — were found. In the case of helical NTs only right‐hand chirality was observed.

Electrodeposited quantum dots: II. High resolution electron microscopy of epitaxial CdSe nanocrystals on {111} gold

CdSe quantum dots, electrodeposited epitaxially on {111} gold substrates, were studied by high resolution transmission electron microscopy (HREM). Images corresponding to wurtzite {10.0}CdSe and {11.0}CdSe as well as {220}Au and 13{422}Au, directly confirmed the epitaxial relationships previously shown by electron diffraction, namely {111}Au‖{00.1}CdSe and 〈110〉Au‖〈11.0〉CdSe. Further analysis of the HREM images by optical diffraction (selected-area nanodiffraction) provided structural information on the orientation of single nanocrystals with respect to the substrate and allowed detection of slight misalignments of individual quantum dots.

Aggregate structure in CuBSe2/Mo films (B=In,Ga): Its relation to their electrical activity

CuBSe2/Mo films of about 3 μm in thickness prepared on different substrates (Si single crystal, glass, alumina) by three‐source evaporation have been investigated by electron and optical microscopic techniques: Scanning electron microscopy [including (EBIC) electron‐beam‐induced current mode], conventional transmission electron microscopy (TEM), and optical Nomarski microscopy. They show, on top of their well‐known dense polycrystalline structure (≊1 μm average grain size), a more coarse ‘‘aggregate’’ structure with aggregate dimensions of 20–100 μm, depending on the substrate used. The aggregate boundaries are characterized by very poor EBIC collection efficiency. For samples on glass substrates, this structure, as detected in EBIC, correlates with deformation patterns of the Mo layer seen by Nomarski contrast when viewed through the glass side of the samples. Local electrical measurements made on small Schottky contacts reveal a correlation between the aggregate structure and the I‐V characteristics. TE...

Vacuum‐Deposited Gold Films II . Role of the Crystallographic Orientation of Oxide‐Covered Silicon Substrates

The influence of the orientation of oxide-covered Si substrates on the morphology, overall surface roughness, and crystallographic texture of 35 nm thick evaporated gold films was investigated using scanning tunneling microscopy (STM), transmission electron microscopy (TEM), and cyclic voltammetry (CV). It is shown that gold films on Si (100) are substantially different from gold films on Si (111). The films deposited on Si (111) contain larger grains than those on Si (100). Annealed Au on Si (111) contains large atomically flat terraces which enable STM imaging at atomic resolution. The overall surface roughness measured by CV is smaller for annealed gold on Si (111), whereas for nonannealed samples, the gold on Si (100) is smoother. While very strong {111} texture is obtained for gold on Si (111), the Au on Si (100) is nontextured. Annealing of the gold films deposited on Si promotes grain enlargement, surface smoothness, and (for Si (111)) strong enhancement of the gold {111} texture. The different gold morphologies obtained on oxide-covered Si (111) and Si (100) are discussed in terms of the structural properties of the Si/Si oxide interface

Electrodeposited quantum dots IV. Epitaxial short-range order in amorphous semiconductor nanostructures

The structure of diffraction-amorphous CdSe (a-CdSe) quantum dots (QDs) electrodeposited on evaporated Pd substrate was studied by high resolution transmission electron microscopy (HRTEM), and compared with epitaxial (crystalline) QDs obtained by the same procedure on Au, as well as with a simulated image of random a-CdSe. Digital analysis of HRTEM images established the existence of repeating ordered motifs in a-CdSe QDs on Pd substrates, in the form of epitaxial sub-nanometre to nanometre size clusters. The QDs are shown to be intermediate between crystalline and random amorphous material. Digital Fourier analysis indicated epitaxial relationship with the 111inPd substrate, rotated 30° relative to the orientational relationship on 111Au.

Effects of chemical and electrochemical etching on polycrystalline thin films of CuGaSe 2

Electrochemical and, especially, chemical oxidative etching drastically improves the photoresponse of liquid electrolyte/CuGaSe2-on-Mo junctions. This is expressed in decreased effective doping levels and increased effective minority carrier diffusion lengths. It is accounted for by removal of highly defective surface layers, which also leads to an increase in the barrier height, as judged from a positive shift of the flat band potential (on the electrochemical scale). The etching effects are seen clearly in Zn/CuGaSe2 devices, by electron beam-induced current. This last method also reveals a supra-grain structure, which is tentatively explained by thermal stress-induced strain at the Mo-CuGaSe2 interface.