Effect of Surface Segregation on the Temperature Dependence of Ion-Bombardment Induced Surface Morphology

1998 ◽  
Vol 527 ◽  
Author(s):  
B. Aufray ◽  
H. Giordano ◽  
V. Petrova ◽  
D. N. Seidman
Keyword(s):  
Surface Morphology ◽  
Heating Rate ◽  
Point Defects ◽  
Room Temperature ◽  
Surface Segregation ◽  
Elevated Temperatures ◽  
Rapid Heating ◽  
Ion Bombardment ◽  
Scanning Tunneling ◽  
Near Surface

ABSTRACTWe present a scanning tunneling microscopy (STM) study, performed at different elevated temperatures, on the influence of Sb surface segregation on the morphology of the (111) surface of a Cu-0.45 at.% Sb solid-solution single-crystal; the surface was initially cleaned at room temperature by Ar+ ion sputtering. Unexpectedly, when the temperature is increased from room temperature to 380°C, the typical (111) surface morphology, obtained after sputtering, evolves in two very different manners that depend on the heating rate. If the heating rate is rapid (approximately a few minutes), it evolves to a structure with large terraces, whereas if it is slow (about 10 hours) the morphology does not evolve -- i.e., it is frozen. These unexpected results are interpreted in terms of excess subsurface point defects (vacancies and self-interstitials) created during ion bombardment, which are mobile and can mediate Sb diffusion at low temperatures. This is mainly on step edges, but the point defects can precipitate out of solution, for a rapid heating rate, thereby forming small secondary clusters in the near-surface region, in which Sb atoms are trapped.

Microstructural Developments During Implantation of Metals

1983 ◽  
Vol 27 ◽  
Author(s):  
D. I. Potter ◽  
M. Ahmed ◽  
S. Lamond
Keyword(s):  
Chemical Composition ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Auger Spectroscopy ◽  
Phase Region ◽  
Dislocation Loops ◽  
Two Phase ◽  
Model Calculations ◽  
Near Surface ◽  
Composition Profiles

ABSTRACTThe chemical and microstructural changes caused by the direct implantation of solutes into metals are examined. The particular case involving Al+-ion implantation into nickel is treated in detail. Chemical composition profiles measured using Auger spectroscopy and Rutherford backscattering, and average near-surface chemical composition measured using an analytical electron microscope, are compared with model calculations. The microstructures that develop during implantation are investigated using transmission electron microscopy. For low fluences implanted near room temperature, these microstructures contain dislocations and dislocation loops. Dislocation loops, dislocations, and voids result from implantations at temperatures near 500°C. Higher fluences at these elevated temperatures produce precipitates when the composition of implanted solute lies in a two-phase region of the phase diagram. Implanted concentrations corresponding to intermetallic compounds produce continuous layers of these compounds. Room temperature, as compared to elevated temperature, implantation may produce the same phases at the appropriate concentrations, e.g. β'-NiAl, or different phases, depending on the relative stability of the phases involved.

Epitaxy of Germanium on SI(001) Grating Templates

1993 ◽  
Vol 317 ◽  
Author(s):  
C.C. Umbach ◽  
J.M. Blakely
Keyword(s):  
Room Temperature ◽  
Elevated Temperatures ◽  
Scanning Tunneling ◽  
Growth Morphology ◽  
Tunneling Microscopy ◽  
Step Flow ◽  
Growth Modes ◽  
Step Density ◽  
Temperature Scanning ◽  
Substrate Temperatures

ABSTRACTEpitaxial Ge films (< 3 ML) have been grown at elevated temperatures on Si (001) grating substrates (repeat spacing of 2.0 μm) and imaged using room temperature scanning tunneling Microscopy (STM). The Ge films exhibit the 2×n reconstruction associated with missing dimer rows. The value of n and the growth morphology are influenced by the deposition rate and by annealing. At substrate temperatures of 600° C and deposition rates >0.5 ML/Min., islands elongated along the the dimer row direction nucleate at steps and on terraces. With sufficient annealing at 800° C, the islands coarsen and are eventually eliminated. The roughness of the A-type step becomes greater than that of the B-type step, which is the reverse of the situation with pure Si (001). The separation between missing dimer rows and hence the value of n are increased by annealing. Differences in substrate terrace widths due to the periodically varying step density of thegratings affect the growth Modes: two-dimensional islands occur near the extrema of the gratings whereas step flow occurs when steps are separated by ∼150 Å or less.

Electron microscope studies of climb of dissociated dislocations

1978 ◽  
Vol 36 (1) ◽  
pp. 324-325
Author(s):  
C.B. Carter ◽  
D. Cherns ◽  
P.B. Hirsch ◽  
H. Saka
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Point Defects ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Al Alloys ◽  
Weak Beam ◽  
High Supersaturation ◽  
Beam Technique

The mechanism of climb of dissociated dislocations in f.c.c. metals and alloys is not well understood. Climb of dislocations by absorption or emission of vacancies at existing jogs in dissociated dislocations has been observed using the “weak-beam” technique of electron microscopy, but the mechanism of nucleation of jogs is not clear. In this paper we report some results of experiments designed to study the nucleation problem, and more generally the mechanism of absorption of point defects under conditions of high supersaturation.Thin (111) sections of deformed single crystals of Cu-Al alloys, of various compositions, have been electron irradiated in an AEI EM7 HVEM up to 1 MeV, either at room temperature, or elevated temperatures up to 200°C, using a goniometer heating stage. Observations under weak beam conditions have been made a) in situ in the HVEM b) at 100kV in an JEM100B, following irradiation in the HVEM. Interstitials produced by the irradiation are expected to be preferentially attracted to the dislocations because of the strong dislocation-interstitial interaction.

Detection of Near-Surface 52Cr Segregation in Irradiated 51V(Cr) By Rbs

1986 ◽  
Vol 82 ◽  
Author(s):  
L. E. Rehn ◽  
P. M. Baldo
Keyword(s):  
Surface Layer ◽  
Surface Segregation ◽  
Elevated Temperatures ◽  
High Sensitivity ◽  
Near Surface ◽  
Segregation Behavior

ABSTRACTIrradiation at elevated temperatures of V(Cr) alloys is known to create a near-surface layer of nonequilibrium Cr enrichment. Highly reproducible RBS spectra were accumulated from a V-15%Cr alloy irradiated at 750°C, and from unirradiated portions of the same specimen. Differences between these spectra are used to demonstrate the high sensitivity of conventional RBS techniques for determining near-surface segregation behavior. Sensitivities obtained utilizing differences in the acquired spectra are much higher than those typically assumed for RBS measurements. Using 1.8 MeV 4He, and conventional RBS equipment and scattering geometries, segregation of < two atomic layers of 52Cr in 51V- 15at.%Cr over a depth of ∼5 nm has been observed.

SEGREGATION PHENOMENA ON PtxNi1−x LOW INDEX SINGLE CRYSTAL SURFACES STUDIED BY STM

1996 ◽  
Vol 03 (05n06) ◽  
pp. 1831-1845 ◽  
Author(s):  
P. VARGA ◽  
M. SCHMID ◽  
W. HOFER
Keyword(s):  
Single Crystal ◽  
Surface Segregation ◽  
Elevated Temperatures ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Chemical Ordering ◽  
Preferential Sputtering ◽  
Altered Layer

Surface segregation changes the composition of alloy surfaces. It influences both the geometrical and the chemical structure of the surface. In this paper segregation phenomena are shown for low index single crystal surfaces of different PtNi alloys which can be seen only by scanning tunneling microscopy (STM). STM experiments performed with atomic resolution revealed the existence of subsurface dislocation networks. A closer study of the conditions of their existence allowed us to understand the effects of preferential sputtering and annealing on the segregation behavior (i.e. building up a rather stable altered layer and its disappearance only at elevated temperatures). In addition, local chemical ordering in small domains and shifted row reconstructions with a large and varying periodicity (i.e. phenomena that are hardly seen by other methods like e.g. LEED) have been observed.

Evolution of Defect and Impurity Profile During High Dose Co Implantation into Si at Elevated Temperatures

1993 ◽  
Vol 320 ◽  
Author(s):  
S. Schippel ◽  
A. Witzmann
Keyword(s):  
Point Defects ◽  
Elevated Temperatures ◽  
Rutherford Backscattering Spectrometry ◽  
High Dose ◽  
Impurity Profile ◽  
Gaussian Shape ◽  
Near Surface ◽  
Gaussian Distributions ◽  
Transmission Electron ◽  
Effective Center

ABSTRACT<111> -Si was implanted with 250 keV Co ions at a target temperature of 350°C. The ion dose was varied between 1 × 1014 cm−2 and 2 × 1017 cm−2. The evolution of the defect and impurity profile was investigated by Rutherford Backscattering Spectrometry (RBS), channeling and transmission electron microscopy (TEM).Up to a dose of 1 × 1015 Co cm−2 no defects can be detected. At higher Co doses, we find correlated defects in the center of the Co distribution and point defects in the region below. Moreover, damage accumulation at the surface is observed. The concentration of defects increases with increasing ion dose and reaches its level of saturation at a dose of 2 × 1016 cm−2.The Co profiles of samples implanted at 350°C differ considerably from the Gaussian shape. The near surface and the back flank are parts of Gaussian distributions. However, the standard deviation of the near surface flank is always smaller than that of the back flank. Moreover, the distributions show tails into the substrate at depths > 320 nm. This proves that radiation damage acts as an effective center for the nucleation of CoSi2.During annealing we find a redistribution of Co towards the defective regions for Co doses between 1 × 1016 cm−2 and 5 × 1016 cm−2.

Influence of the Temperature of Implantation on the Morphology of Defects in MeV Implanted GaAs.

1989 ◽  
Vol 147 ◽  
Author(s):  
G. Braunstein ◽  
Samuel Chen ◽  
S.-Tong Lee ◽  
G. Rajeswaran.
Keyword(s):  
Thermal Annealing ◽  
Rapid Thermal Annealing ◽  
Point Defects ◽  
Room Temperature ◽  
Surface Region ◽  
Amorphous Region ◽  
Liquid Nitrogen Temperature ◽  
Dislocation Loops ◽  
Near Surface ◽  
Epitaxial Regrowth

AbstractWe have studied the influence of the temperature of implantation on the morphology of the defects created during 1-MeV implantation of Si into GaAs, using RBS-channeling and TEM. The annealing behavior of the disorder has also been investigated.Implantation at liquid-nitrogen temperature results in the amorphization of the implanted sample for doses of 2×1014 cm−2 and larger. Subsequent rapid thermal annealing at 900°C for 10 seconds leads to partial epitaxial regrowth of the amorphous layer. Depending on the implantation dose, the regrowth can proceed from both the front and back ends of the amorphous region or only from the deep end of the implanted zone. Nucleation and growth of a polycrystalline phase occurs concurrently, limiting the extent of the epitaxial regrowth. After implantation at room temperature and above, two distinct types of residual defects are observed or inferred: point defect complexes and dislocation loops. Most of the point defects disappear after rapid thermal annealing at temperatures ≥ 700°C. The effect of annealing on the dislocation loops depends on the distance from the surface of the sample. Those in the near surface region disappear upon rapid thermal annealing at 700°C, whereas the loops located deeper in the sample grow in size and begin to anneal out only at temperatures in excess of 900°C. Implantation at temperatures of 200 - 300°C results in a large reduction in the number of residual point defects. Subsequent annealing at 900°C leads to a nearly defect-free surface region and, underneath that, a buried band of partial dislocation loops similar to those observed in the samples implanted at room temperature and subsequently annealed.

GROWTH OF PERCOLATED Ag NANOSTRUCTURES ON Si(111)-(7 × 7) SURFACES

2011 ◽  
Vol 10 (01n02) ◽  
pp. 123-127
Author(s):  
D. K. GOSWAMI ◽  
A. PAL
Keyword(s):  
Statistical Analysis ◽  
Surface Morphology ◽  
Room Temperature ◽  
Atomic Layer ◽  
Atomic Scale ◽  
Growth Exponent ◽  
Scanning Tunneling ◽  
Scaling Exponent ◽  
Scaling Exponents ◽  
Growth Scaling

Growth of Ag nanostructures on Si (111)-7 × 7 surfaces has been investigated at the atomic scale regime by studying the evolution of nanoscale surface morphology with Ag coverage. Ag growth on Si (111)-7 × 7 surfaces at room temperature showed a strongly preferential height with even atomic layer thick flat top percolated islands. Here we report that the roughness scaling exponent α and growth scaling exponents β associated with such electronic growth mode are determined by statistical analysis of rough surfaces obtained from scanning tunneling micrograph images of Ag nanostructures grown on Si (111)-7 × 7 surfaces. Observed roughness and growth exponent for this system are 0.82±0.02 and 0.45±0.04, respectively.

GaAs(100) Surface Modifications at Elevated Temperatures, Studied By In-Situ Spectroscopic Ellipsometry

1990 ◽  
Vol 202 ◽  
Author(s):  
Huade Yao ◽  
Paul G Snyder ◽  
John A Woollam
Keyword(s):  
Spectroscopic Ellipsometry ◽  
Room Temperature ◽  
Molecular Beam ◽  
Elevated Temperatures ◽  
Surface Region ◽  
Gaas Surface ◽  
Near Surface ◽  
Before And After ◽  
Surface Changes

ABSTRACTSpectroscopic ellipsometric (SE) measurements of GaAs (100) were carried out in an ultrahigh vacuum (UHV) chamber, without arsenic overpressure, at temperatures ranging from room temperature (RT) to ∼610°C. Surface changes induced at elevated temperatures were monitored by in-situ spectroscopic ellipsometry. The SE data clearly displayed in real time the process of desorption of the GaAs-surface-oxide overlayer at ∼580°C. In addition, changes in the near-surface region were observed before and after the oxide desorption. The near-subsurface region (top 50–100 Å) became less optically dense after being heated to 540°C or higher. For comparison, a pre-arsenic-capped molecular-beam-epitaxy (MBE)-grown GaAs surface was also studied. After the arsenic cap was evaporated off at ∼350°C, this surface remained smooth and clean as it was heated to higher temperatures.

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