scholarly journals High Concentration Erbium Implantation of Epitaxially Grown Caf2 /Si Structures.

1995 ◽  
Vol 392 ◽  
Author(s):  
S. Raoux ◽  
A. S. Barriere ◽  
H. J. Lozykowski ◽  
I. G. Brown
Keyword(s):  
Light Emission ◽  
High Vacuum ◽  
Charge Compensation ◽  
High Refractive Index ◽  
High Energy ◽  
Ultra High Vacuum ◽  
High Concentration ◽  
Integrated Devices ◽  
Compensation Mechanisms ◽  
Conversion Efficiencies

AbstractCalcium fluoride thin films grown on silicon substrates by sublimation under ultra high vacuum are well known to be highly efficient hosts for rare earth luminescence properties. For this reason we incorporate erbium by ion implantation in order to form optoelectronic integrated devices. Here we describe the incorporation conditions of erbium in CaF2/Si structures and their luminescence characteristics. The properties of the material have been investigated for implantation doses varying from 4×1014 to 1×1017 at.cm−2. The role of oxygen in the charge compensation mechanisms is investigated and it is shown that the maximum emission in erbium at 1.53μm occurs for an implanted dose of 2×1016 at.cm−2. This corresponds to an Er concentration three orders of magnitude greater than for the case of classical-erbium-doped semiconductors. At this high concentration (up to 15 at.%) the light emission mechanisms are of great theoretical interest. They involve strong Er-Er coupling effects: energy transfer, cross-relaxation phenomena and high conversion efficiencies.These properties make erbium-implanted CaF2/Si structures excellent candidates for the production of optically active waveguides. The guiding structure can be formed by high energy implantation to build a buried active region of high refractive index within the CaF2 thin film.

Transmission Electron Microscopy of Epitaxial silicides grown by ultra high vacuum deposition

1989 ◽  
Vol 47 ◽  
pp. 462-463
Author(s):  
D. Loretto ◽  
J. M. Gibson ◽  
S. M. Yalisove
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
High Vacuum ◽  
High Energy ◽  
Energy Electron ◽  
Ultra High Vacuum ◽  
Ex Situ ◽  
Transmission Electron

The silicides CoSi2 and NiSi2 are both metallic with the fee flourite structure and lattice constants which are close to silicon (1.2% and 0.6% smaller at room temperature respectively) Consequently epitaxial cobalt and nickel disilicide can be grown on silicon. If these layers are formed by ultra high vacuum (UHV) deposition (also known as molecular beam epitaxy or MBE) their thickness can be controlled to within a few monolayers. Such ultrathin metal/silicon systems have many potential applications: for example electronic devices based on ballistic transport. They also provide a model system to study the properties of heterointerfaces. In this work we will discuss results obtained using in situ and ex situ transmission electron microscopy (TEM).In situ TEM is suited to the study of MBE growth for several reasons. It offers high spatial resolution and the ability to penetrate many monolayers of material. This is in contrast to the techniques which are usually employed for in situ measurements in MBE, for example low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED), which are both sensitive to only a few monolayers at the surface.

Modifications of a JEOL 2000EX TEM for insSitu surface studies

1993 ◽  
Vol 51 ◽  
pp. 640-641
Author(s):  
Michael T. Marshall ◽  
Xianghong Tong ◽  
J. Murray Gibson
Keyword(s):  
Electron Diffraction ◽  
Surface Science ◽  
Film Growth ◽  
High Vacuum ◽  
High Energy ◽  
Energy Electron ◽  
Ultra High Vacuum ◽  
Transmission Electron ◽  
Fundamental Insight

We have modified a JEOL 2000EX Transmission Electron Microscope (TEM) to allow in-situ ultra-high vacuum (UHV) surface science experiments as well as transmission electron diffraction and imaging. Our goal is to support research in the areas of in-situ film growth, oxidation, and etching on semiconducter surfaces and, hence, gain fundamental insight of the structural components involved with these processes. The large volume chamber needed for such experiments limits the resolution to about 30 Å, primarily due to electron optics. Figure 1 shows the standard JEOL 2000EX TEM. The UHV chamber in figure 2 replaces the specimen area of the TEM, as shown in figure 3. The chamber is outfitted with Low Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES), Residual Gas Analyzer (RGA), gas dosing, and evaporation sources. Reflection Electron Microscopy (REM) is also possible. This instrument is referred to as SHEBA (Surface High-energy Electron Beam Apparatus).The UHV chamber measures 800 mm in diameter and 400 mm in height. JEOL provided adapter flanges for the column.

scholarly journals The Growth of Semiconductor Thin Films Studied by RHEED

1990 ◽  
Vol 43 (5) ◽  
pp. 583
Author(s):  
GL Price
Keyword(s):  
Thin Films ◽  
Surface Science ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Large Area ◽  
Growth Modes ◽  
Semiconductor Thin Films ◽  
Wide Range ◽  
Recent Developments

Recent developments in the growth of semiconductor thin films are reviewed. The emphasis is on growth by molecular beam epitaxy (MBE). Results obtained by reflection high energy electron diffraction (RHEED) are employed to describe the different kinds of growth processes and the types of materials which can be constructed. MBE is routinely capable of heterostructure growth to atomic precision with a wide range of materials including III-V, IV, II-VI semiconductors, metals, ceramics such as high Tc materials and organics. As the growth proceeds in ultra high vacuum, MBE can take advantage of surface science techniques such as Auger, RHEED and SIMS. RHEED is the essential in-situ probe since the final crystal quality is strongly dependent on the surface reconstruction during growth. RHEED can also be used to calibrate the growth rate, monitor growth kinetics, and distinguish between various growth modes. A major new area is lattice mismatched growth where attempts are being made to construct heterostructures between materials of different lattice constants such as GaAs on Si. Also described are the new techniques of migration enhanced epitaxy and tilted superlattice growth. Finally some comments are given On the means of preparing large area, thin samples for analysis by other techniques from MBE grown films using capping, etching and liftoff.

A Mechanism of Sliding on the Nanometer-Thick Ag Layers

2005 ◽  
Author(s):  
F. Honda ◽  
M. Goto
Keyword(s):  
Friction Coefficient ◽  
Normal Load ◽  
High Vacuum ◽  
High Energy ◽  
Thin Layers ◽  
Ultra High Vacuum ◽  
Wear And Friction ◽  
Thickness Measurements

Tribological performance of sub-nano to nanometer-thick Ag layers deposited on Si(111) have been examined to understand the role of surface thin layers to the wear and friction characteristics. The slider was made of diamond sphere of 3 mm in radius. Sliding tests were carried out in an ultra-high vacuum environment (lower than 4 × 10−8 Pa) and analyzed in-situ by Auger electron spectroscopy (AES) for the quantitative thickness-measurements, by reflection high-energy electron diffraction (RHEED) to clarify the substrate cleanliness and crystallography of the Ag films, and by scanning probe microscopy (SPM) for the morphology of the deposited/slid film surfaces. As the results, a minimum of the friction coefficient 0.007 was observed from the film thickness range of 1.5–10 nm, and exactly no worn particles were found after 100 cycles of reciprocal sliding. Results have directly indicated that solid Ag(111) sliding planes allowed to reduce the friction coefficient very low without any detectable wear particles, and Ag nanocrystallites in Ag polycrystalline layers increase the size to 20–40 nm order, during sliding. The friction coefficient was slightly dependent to the normal load. Results were discussed on the role of the surface atoms to the friction, and a mechanism of sliding on Ag thin layers.

In situ quantitative analysis of GeXSi1-X alloys during growth by reflection EELS

1991 ◽  
Vol 49 ◽  
pp. 878-879
Author(s):  
Shouleh Nikzad ◽  
Channing C. Ahn ◽  
Harry A. Atwater
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Film Growth ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Mbe Growth ◽  
Electron Microscopes ◽  
Electron Energy Loss

The universality of reflection high energy electron diffraction (RHEED) as a structural tool during film growth by molecular beam epitaxy (MBE) brings with it the possibility for in situ surface chemical analysis via spectroscopy of the accompanying inelastically scattered electrons. We have modified a serial electron energy loss spectrometer typically used on an electron microscope to work with a 30 keV RHEED-equipped MBE growth chamber in order to determine the composition of GexSi1-x alloys by reflection electron energy loss (REELS) experiments. Similar work done in transmission electron microscopes has emphasized the surface sensitivity of this technique even though these experiments have never been done under ultra-high vacuum conditions. In this work, we are primarily concerned with the accuracy with which core losses can be used to determine composition during MBE growth.

Modification of a TEM for ultra-high-vacuum reflection-EM (UHV-REM) applications

1995 ◽  
Vol 53 ◽  
pp. 582-583
Author(s):  
Tung Hsu ◽  
Min-Yi Shih ◽  
A. V. Latyshev
Keyword(s):  
Electron Microscope ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Objective Lens ◽  
Pole Piece ◽  
High Energy Electron ◽  
Normal Position ◽  
Crystal Surfaces ◽  
Specimen Holder

A JEOL JEM-100C electron microscope was modified by adding a cryogenic UHV specimen holder for studying clean crystal surfaces with the reflection high energy electron diffraction (RHEED) and REM techniques. The Si(111) (l×l) and (7×7) phase transitions have been successfully observed (Fig. 1). Further modification is in progress for better resolution and other functions. Fig. 2.a shows the unmodified specimen holder and the objective lens of the microscope. The cryogenic holder based on the Novosibirsk design is shown in Fig. 2.b. Liquid nitrogen is continuously pumped through the shell of the holder for achieving UHV inside. The tilt/rotation controls and the current for heating of the specimen are fed through the holder. In this modification, the specimen was not placed at the normal position of the lens and therefore is not at the best position for imaging and diffraction.A new holder is shown in Fig. 2.c. This holder is inserted into the pole piece to place the specimen at the normal position.

Effect of the Er3+ Concentration on the Luminescence of Ca1-xErxF2+x Thin Films Epitaxially Grown on Si(100)

1993 ◽  
Vol 298 ◽  
Author(s):  
A.S. Barriere ◽  
S. Raoux ◽  
P.N. Favennec ◽  
H. L'haridon ◽  
D. Moutonnet
Keyword(s):  
Thin Films ◽  
Solid Solution ◽  
Substitution Rate ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Visible Range ◽  
Doped Semiconductors ◽  
Potential Applications ◽  
Er Doped

AbstractCa1-xErxF2+x thin films, with a substitution rate, x, varying from 1 to 20%, were deposited on Si(100) substrates by sublimation of high purity solid solution powders under ultra-high-vacuum. Rutherford backscattering studies have shown that the films have the composition of the initial solid solution powders, are quite homogeneous and are epitaxially grown on the substrates.The optical properties of these films were studied by means of cathodoluminescence and photoluminescence. At room temperature, the emissions due to the de-excitations from the 4S3/2, 4F9/2, 4I11/2 and 4I13/2 excited levels to the 4I15/2 ground state of Er3+ (4f11) ions are easily detected (λ = 0.548, 0.66, 0.98 and 1.53 μm)The strong 1.53 μm infrared luminescence, which presents evident potential applications for optical communications, is maximum for an erbium substitution rate included between 15 and 17%. These Er concentrations are three or four orders of magnitude greater than the optimum ones in the case of Er-doped semiconductors, which are close to 1018 cm-3. In the visible range, the luminescences are also important.They allow us to detect high energy ion or electron beams. However their maximum efficiencies were observed for a relatively low erbium concentration, close to 1%. These different behaviours are explained by the cross relaxation phenomena, which depopulate the higher levels to the benefit of the 4I13/2 → 4I15/2 transition.The energy distribution of the Stark sublevels of the 4I15/2 state, which results from crystal field splitting, was deduced from a photoluminescence study at 2K. The obtained results show that the environment of the luminescent centres does not change with the erbium concentration.At last, it must be noted that the refractive index of the layers increases with the erbium concentration, leading to the realization of optical guides. Consequently opto-electronic components could be developed from such erbium doped heterostructures.

scholarly journals Stm at High Temperature: What you see is what you see … usually

1993 ◽  
Vol 1 (5) ◽  
pp. 4-4
Author(s):  
Michael M. Kersker
Keyword(s):  
Electron Diffraction ◽  
Surface Structure ◽  
High Vacuum ◽  
High Energy ◽  
Atomic Level ◽  
Energy Electron ◽  
Ultra High Vacuum ◽  
Scanning Probe ◽  
Sem Images ◽  
Optical Discs

There remains two basic axioms of all microscopists: the first….if you look, you're bound to see something, and the second….not everything you will see is artifact. These axioms apply particularly well to scanning probe microscopy at the molecular and atomic level. Fortunately, coarser resolution images share comforting similarities with images from other established scanning methods. Holes in optical discs look like holes when probed with AFM tips, and these holes look very much like SEM images, a subject with which we have some familiarity. At the molecular and atomic level, however, the scanning probe instruments may or may not be “seeing” the sample, though they are clearly seeing something.Comparison of surface structure observed with indirect surface structural measurements, for example by LEED (Low Energy Electron Diffraction) or RHEED (Reflection High Energy Electron Diffraction) usually under ultra-high vacuum conditions can lead, by inference, to an understanding of the real bulk or average surface structure.

Slow positron beam design notes

1982 ◽  
Vol 60 (4) ◽  
pp. 551-557 ◽  
Author(s):  
K. F. Canter ◽  
A. P. Mills Jr.
Keyword(s):  
Figure Of Merit ◽  
Transverse Energy ◽  
High Vacuum ◽  
Positron Beam ◽  
Ultra High Vacuum ◽  
High Flux ◽  
Slow Positron ◽  
Beam Design ◽  
Positron Beams ◽  
Conversion Efficiencies

Recent methods of producing high flux. (105–106) s−1 slow positron beams are briefly reviewed. Currently, slow positron beams are produced most efficiently using a single crystal Cu(111) + S backscatter geometry moderator for ultra-high vacuum (UHV) conditions and an annealed W-vane converter for non-UHV conditions. The respective fast positron to slow positron conversion efficiencies for the Cu(111) + S and W-vane converters are (9 ± 3) × 10−4 and (1.2 ± 0.2) × 10−4. A new figure of merit, the "normalized brightness-per-volt", for converters is introduced which takes into account the transverse energy spread as well as the conversion efficiency. The importance of the normalized-brightness-per-volt in beam design and future methods to improve this figure of merit are discussed.

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