Formation Mechanisms for Multiply Twinned Particles During Nucleation in the Au/MICA System

1975 ◽  
Vol 33 ◽  
pp. 84-85
Author(s):  
Eal H. Lee ◽  
Helmut Poppa
Keyword(s):  
Deposition Time ◽  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Formation Mechanisms ◽  
Heat Treated ◽  
Cluster Density ◽  
Diffraction Patterns ◽  
Crystal Particle ◽  
Multiply Twinned Particles

The formation of thin films of gold on mica has been studied in ultra-high vacuum (5xl0-10 torr) . The mica substrates were heat-treated for 24 hours at 375°C, cleaved, and annealed for 15 minutes at the deposition temperature of 300°C prior to deposition. An impingement flux of 3x1013 atoms cm-2 sec-1 was used. These conditions were found to give high number densities of multiple twin particles and are based on a systematic series of nucleation experiments described elsewhere. Individual deposits of varying deposition time were made and examined by bright and dark field TEM after "cleavage preparation" of highly transparent specimens. In the early stages of growth, the films generally consist of small particles which are either single crystals or multiply twinned; a strong preference for multiply twinned particles was found whenever the particle number densities were high. Fig. 1 shows the stable cluster density ns and the variation with deposition time of multiple twin particle and single crystal particle densities, respectively. Corresponding micrographs and diffraction patterns are shown in Fig. 2.

UHV Microscopy of the Reconstructed Au (001) Surface

1990 ◽  
Vol 208 ◽  
Author(s):  
D. N. Dunn ◽  
L. D. Marks ◽  
J. P. Zhang
Keyword(s):  
Single Crystal ◽  
Crystal Surface ◽  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Bulk Single Crystal ◽  
Transmission Electron ◽  
Dark Field Microscopy ◽  
Reconstructed Surface ◽  
Diffraction Patterns

ABSTRACTWe investigate the evolution of the microstructure of a reconstructed Au (001) single crystal surface using ultra high vacuum transmission electron microscopy (UHV-TEM). Bulk single crystal Au (001) surfaces were prepared via standard metallographic techniques and sputter anneal cycles. After a clean surface was obtained, the (001) surface was found to reconstruct into two nearly orthogonal domains of dimensions (5 × ∼ 20 ) along the <110> directions of the unreconstructed F.C.C. (001) surface. Transmission electron diffraction patterns (TED) and dark field microscopy are the two primary techniques used to determine the symmetry and dimensions of the reconstructed surface.

Thin Pyrolytic Graphite Films for Electron Microscope Substrates

1971 ◽  
Vol 29 ◽  
pp. 226-227 ◽  
Author(s):  
George H. N. Riddle ◽  
Benjamin M. Siegel
Keyword(s):  
Vacuum Chamber ◽  
Pyrolytic Graphite ◽  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Graphite Substrate ◽  
Nickel Substrate ◽  
Routine Procedure ◽  
Field Electron Microscopy ◽  
Dark Field Electron

A routine procedure for growing very thin graphite substrate films has been developed. The films are grown pyrolytically in an ultra-high vacuum chamber by exposing (111) epitaxial nickel films to carbon monoxide gas. The nickel serves as a catalyst for the disproportionation of CO through the reaction 2C0 → C + CO2. The nickel catalyst is prepared by evaporation onto artificial mica at 400°C and annealing for 1/2 hour at 600°C in vacuum. Exposure of the annealed nickel to 1 torr CO for 3 hours at 500°C results in the growth of very thin continuous graphite films. The graphite is stripped from its nickel substrate in acid and mounted on holey formvar support films for use as specimen substrates.The graphite films, self-supporting over formvar holes up to five microns in diameter, have been studied by bright and dark field electron microscopy, by electron diffraction, and have been shadowed to reveal their topography and thickness. The films consist of individual crystallites typically a micron across with their basal planes parallel to the surface but oriented in different, apparently random directions about the normal to the basal plane.

Nucleation and initial growth of Pd2Si crystals on Si(111)

1993 ◽  
Vol 51 ◽  
pp. 844-845
Author(s):  
Xianghong Tong ◽  
Oliver Pohland ◽  
J. Murray Gibson
Keyword(s):  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Initial Growth ◽  
Surface And Interface ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Initial Stage ◽  
Effect Of Surface

The nucleation and initial stage of Pd2Si crystals on Si(111) surface is studied in situ using an Ultra-High Vacuum (UHV) Transmission Electron Microscope (TEM). A modified JEOL 200CX TEM is used for the study. The Si(111) sample is prepared by chemical thinning and is cleaned inside the UHV chamber with base pressure of 1x10−9 τ. A Pd film of 20 Å thick is deposited on to the Si(111) sample in situ using a built-in mini evaporator. This room temperature deposited Pd film is thermally annealed subsequently to form Pd2Si crystals. Surface sensitive dark field imaging is used for the study to reveal the effect of surface and interface steps.The initial growth of the Pd2Si has three stages: nucleation, growth of the nuclei and coalescence of the nuclei. Our experiments shows that the nucleation of the Pd2Si crystal occurs randomly and almost instantaneously on the terraces upon thermal annealing or electron irradiation.

Direct STEM ADF imaging of gold on silicon (111)

1989 ◽  
Vol 47 ◽  
pp. 472-473
Author(s):  
P. Xu ◽  
E. J. Kirkland ◽  
J. Silcox
Keyword(s):  
Film Growth ◽  
Heavy Atom ◽  
High Vacuum ◽  
Dark Field ◽  
Thin Metal Film ◽  
Base Pressure ◽  
Ultra High Vacuum ◽  
Specimen Preparation ◽  
Dark Field Imaging ◽  
Wide Range

Many studies of thin metal film growth and the formation of metal-semiconductor contacts have been performed using a wide range of experimental methods. STEM annular dark field imaging could be an important complement since it may allow direct imaging of a single heavy atom on a thin silicon substrate. This would enable studies of the local atomic arrangements and defects in the initial stage of metal silicide formation.Preliminary experiments were performed in an ultra-high vacuum VG HB501A STEM with a base pressure of 1 × 10-10 mbar. An antechamber directly attached to the microscope for specimen preparation has a base pressure of 2×l0-10 mbar. A thin single crystal membrane was fabricated by anodic etching and subsequent reactive etching. The specimen was cleaned by the Shiraki method and had a very thin oxide layer left on the surface. 5 Å of gold was deposited on the specimen at room temperature from a tungsten filament coil monitored by a quartz crystal monitor.

Design for a New Low Energy and Photo-Emission Electron Microscope for Surface Science Studies

1990 ◽  
Vol 48 (1) ◽  
pp. 570-570
Author(s):  
Ruud M. Tromp
Keyword(s):  
Science Studies ◽  
High Vacuum ◽  
Dark Field ◽  
Surface Cleaning ◽  
Geometric Constraints ◽  
Ultra High Vacuum ◽  
Field Mode ◽  
Projection System ◽  
Cathode Lens

A new LEEM/PEEM apparatus has been designed for the study of surfaces and surface processes in Ultra High Vacuum (UHV). The design follows the general layout of the microscope operated succesfully by Prof. Bauer and coworkers, but differs significantly in a number of details. We designed a magnetic/electrostatic cathode lens with a resolution limit close to that of the uniform electrostatic accelerating field between sample and lens. The projection system consists of transfer lens, intermediate lens and projector lens. Total magnification is between 1,000x and 10,000x, with a field of view between 4 and 40 micrometer. The illuminating system features a continuously adjustable range of illumination, such that the loss of image intensity at high magnification can be balanced by a reduction of the illumiated area, without significant loss of electron beam intensity. Both bright field and dark field imaging are possible. The location of the diffraction aperture in the projection column allows for more flexible operation of the microscope in dark field mode. Care has been taken in the design of the microscope to integrate the stringent vacuum requirements with the geometric constraints of the electron optical components. A sample stage, featuring two orthogonal translations and two (eucentric) tilts, sample heating, as well as in situ sample exchange capability has been constructed. All motions are driven by remote control, UHV compatible piezoelectric actuators, eliminating the need for mechanical feedthroughs, and ensuring a short mechanical path between sample and cathode lens. In situ deposition, using e-beam evaporators and/or Knudsen cells will be possible. A sample preparation chamber contains standard surface cleaning and analytical equipment. We will report on the progress in the construction of this machine.

Medium Energy Electron Study of Surface Structures Formed upon Oxidation of Copper

1975 ◽  
Vol 33 ◽  
pp. 66-67
Author(s):  
J. D. Landry ◽  
P. E. Højlund Nielsen ◽  
G. Hembree ◽  
J. M. Cowley
Keyword(s):  
Ion Beam ◽  
High Vacuum ◽  
Three Dimensional ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Dimensional Structure ◽  
Medium Energy ◽  
Low Oxygen ◽  
Dark Field Imaging ◽  
Electron Imaging

The oxidation of single crystal surfaces of copper with low oxygen pressure and high temperature have previously been examined by optical microscopy, microgravimetry, transmission electron microscopy and RHEED. These studies have revealed the formation of a hexagonal two-dimensional structure, followed by three dimensional nuclei of various regular shapes. In this study we have performed in situ oxidation in our REMEDIE system. The instrument was described at previous EMSA meetings. The instrument utilizes medium energy (1 to 15kV) electron diffraction, secondary electron imaging, and diffracted electron imaging (dark field imaging) in scanning mode. There is provision for specimen heating to 1000°C and ion beam cleaning in ultra high vacuum environment (2x10-9 Torr). The aim of this study was to examine the relationship between the 2-D and 3-D structures with the possibility of revealing transport of material on the surface.

SAM/EDX analysis of Cu(Nb) alloys

1992 ◽  
Vol 50 (2) ◽  
pp. 1780-1781
Author(s):  
Albert J. Bevolo
Keyword(s):  
Pure Copper ◽  
High Vacuum ◽  
Copper Matrix ◽  
Ultra High Vacuum ◽  
Ex Situ ◽  
Static Vacuum ◽  
Heat Treated ◽  
Cast Alloys ◽  
Edx Analyses

For several years our laboratory has investigated the properties of copper based alloys with transition metals such as Cu80Nb20. When heavily drawn these alloys retain the thermal conductivity of pure copper but acquire strengths usually associated with steels. Niobium dendrites, that are immiscible in the copper matrix in the as-cast form, become very fine, thermally stable filaments when heavily drawn. When heat treated in a diffusion pumped static vacuum chamber the surface unexpectedly acquires a silvery coloration rather than the reddish color expected from the dominant copper constituent. If a flow of inert gas is maintained then the surface becomes reddish. Experiments involving SAM and EDX analyses of cast alloys ex situ and in situ treated in ultra high vacuum (UHV) were performed to investigate this behavior.Auger depth profiles of the ex situ silver colored alloys showed from the Nb (167) Auger transition lineshape that the dominant phase was metallic NbO.

Defects in ErSi2/Si(111) epitaxial films

1990 ◽  
Vol 48 (4) ◽  
pp. 572-573
Author(s):  
C. Meneau D'Anterroches
Keyword(s):  
Lattice Mismatch ◽  
High Vacuum ◽  
Epitaxial Films ◽  
Zone Axis ◽  
Ultra High Vacuum ◽  
Epitaxial Relationship ◽  
Electronic Engineering ◽  
Transmission Electron ◽  
Diffraction Patterns

Silicides are studied in electronic engineering for their good metallic properties. Among them the group of rare earth silicides shows particular properties. Indeed, some of them, including ErSi2, crystallize in the AIB2 structure although they do not have the exact stoechiometry, their composition being about 1.7. Thus the physical properties and the influence of vacancies on the structure are studied.The film studied in this work was obtained by in-situ annealing, in ultra high vacuum, of a Si-Er film codeposited on a clean Si (111) substrate. Details are given by F. Arnaud d'Avitaya et al. The epitaxial relationship is (111 )Si//(001 )ErSi2 and (112)Si//(100)ErSi2. According to this orientation the lattice mismatch at the interface is - 1.3 %. The films were analysed using high resolution transmission electron microscopy : they are continuous when annealed at 900°C, and show some extra-spots in their diffraction patterns depending on the zone axis. Extra spots were observed along the {111} (3) and {112} zone axes, but not along {110} (4), We will focus in this paper on the {112}Si or {120}ErSi2 zone axis, the corresponding electron diffraction pattern being in Fig. 1.

Interface Morphology, Nucleation and Island Formation of Tisi2 on Si(111).

1990 ◽  
Vol 181 ◽  
Author(s):  
Hyeongtag Jeon ◽  
C. A. Sukow ◽  
J. W. Honeycutt ◽  
T. P. Humphreys ◽  
R. J. Nemanich ◽  
...  
Keyword(s):  
High Vacuum ◽  
Ultra High Vacuum ◽  
Nucleation Theory ◽  
Formation Mechanisms ◽  
Silicon Substrates ◽  
Interface Morphology ◽  
Free Energies ◽  
Island Formation ◽  
Flat Interface ◽  
Interface Structures

ABSTRACTIn this study we investigate the formation mechanisms and morphology of TiSi2 formed by deposition of Ti on atomically clean silicon substrates. Ti films of 50–400 Å thickness were deposited in ultra-high vacuum on Si (111) wafers and annealed to temperatures between 500–900°C. Films were monitored in situ with AES and LEED, and post preparation characterization was accomplished with SEM, TEM and Raman scattering. The results show that for films of thickness ≤, 100 Å the C49 TiSi2 phase is stable over the entire 600-800°C temperature range. However, for films of 200-400 Å thickness, the C49 to C54 phase transition occurs at temperatures varying from 700 to 800°C dependent upon film thickness. The high temperature annealing results in flat interface structures, and island formation is observed for all films with the C54 structure. The interface morphology and the mechanisms of TiSi2 island and phase formation are discussed in terms of surface and bulk free energies considerations based on nucleation theory.

Structure and morphology of Clean and Magnesium - Dosed Sapphire Surfaces

1993 ◽  
Vol 317 ◽  
Author(s):  
Yan Yu ◽  
R.J. Lad
Keyword(s):  
Photoelectron Spectroscopy ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Initial Growth ◽  
Force Microscopy ◽  
Structure And Morphology ◽  
Diffraction Patterns ◽  
Abrupt Interface ◽  
Initial Deposition

ABSTRACTThe structure and morphology of r-axis (1012) and c-axis (0001) sapphire (a-Al2O3) surfaces were studied with Low Energy and Reflection High Energy Electron Diffraction (LEED and RHEED) and Atomic Force Microscopy (AFM). Following heat treatments at 1000°C in 5×10-7 torr O2, both surfaces exhibited (1×1) diffraction patterns. Regular step-terrace structure was observed on the (1012) surface with the AFM, but no step structure was visible on the (0001) surface. The initial growth of magnesium overlayers dosed onto the (1012) surface at 25°C in ultra-high vacuum was monitored with RHEED and the chemical interactions at the Mg / Al2O3 interface were characterized with X-ray Photoelectron Spectroscopy (XPS). During the initial deposition, very little interaction between mg and the Al2O3 substrate occurs and a very abrupt interface is formed. At larger mg doses, a textured polycrystalline mg overlayer is produced. Annealing the mg film above 300°C causes some oxidation of mg at the Mg / Al2O3 interface, but most of the mg desorbs from the surface.

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