Disturbed Surface Layer Research Articles

A three-dimensional study of the microstructure of an aluminium alloy as revealed within its thick anodically formed oxide

Most of the microscopically visible constituents in the aluminium alloy Hiduminium 48 have been observed to persist, with unchanged morphology, in the relatively transparent coatings formed by anodic oxidation in a sulphuric acid electrolyte. This has made it possible to study the features of the original microstructure, in three dimensions, using the optical microscope to view detail directly through the top surface of the coating. This internal examination of the distribution of the micro-constituents has been found to be particularly helpful in the assessment of residual “ingotism”. It can also aid the study of machining-induced disturbance of “near surface” microstructure by avoiding the problems presented by section preparation, with the special requirement to preserve the specimen edge. The influence of the disturbed surface layer, as induced by machining or other forms of surface deformation, on both the fatigue and the stress corrosion behaviour of aluminium alloys, is well known. The approach described in this paper should provide a better understanding of the way this disturbance affects these properties.

Investigation of surface-layer structure of single crystals with triple-crystal X-ray diffractometry

The possibilities of the X-ray triple-crystal diffractometry (TCD) method in studying the tails of rocking curves of both a perfect crystal and a crystal with a disturbed surface layer are shown. It was found that at large deviation angles (α) from the Bragg condition the pseudopeak of the TCD curves significantly exceeds the main peak. The thermal diffuse scattering in the monochromator crystal is discussed as one of the reasons for this effect. This phenomenon is also responsible for the violation of the I(α) ∝ l/α2 dependence in double-crystal diffractometry (DCD). By measuring the intensities of the main peaks of TCD curves, it is possible to separate the diffuse and the coherent scattering components in the rocking curves obtained by DCD.

Characteristics of the distribution of electromagnetic radiation in a surface layer of cadmium sulfide subjected to combined electron and optical annealing

An investigation is reported of the propagation of electromagnetic radiation in a layer-periodic structure formed in a disturbed surface layer of cadmium sulfide subjected to electron and optical annealing. This structure has a period of d0?=???/?2n1 and is due to annealing of the disturbed material (during the first pulse) in the vicinity of the intensity maxima in an interference pattern and also due to the difference between the refractive indices of the disordered phase n1 and the perfect material n0. The intensity maxima in a layer-periodic structure are located outside the regions annealed during the first pulse. This increases the volume of the annealed regions from one pulse to the next. Annealing of the whole disturbed layer can be achieved simply by displacement of the recrystallization front by ~?d0, since the displacement should occur in each of the periods. The structure period d0 is close to that at which the nontransmission effect is observed. This leads to anomalies of the distribution of the intensity I(x) in the structure. A quasiperiodicity is exhibited by I(x) and the quasiperiod is considerably greater than d0, whereas the intensity at the maximum may be considerably greater than the intensity of the incident wave, which enhances the effectiveness of annealing of the internal regions.

Topography of etched rhombohedral faces of quartz crystals: evidence for orientation effects

A study has been made of the rate at which the rhombohedral faces of a natural quartz crystal are etched in a concentrated ammonium bifluoride solution. The thickness of the disturbed surface layer created by an initial mechanical lapping is estimated from rate data. The etching rate as well as this thickness are found to be sensitive to natural face orientation. The changes in the surface texture of the rhombohedral faces with repeated chemical etchings are investigated. The variation in the roughness parameters with the average depth of etch shows both directional and orientation effects. The chemical attack results in the formation of stable etch figures characteristic to the orientation of the surface on which they lie and which enlarge with repeated etchings. finally, schematic etch figures are proposed for the differently oriented rhombohedral faces.

Photoemission curves obtained in conditions of X-ray grazing-incidence Laue diffraction from crystals with a disturbed surface layer

It has been shown that photoemission curves obtained using the X-ray standing wave technique in grazing-incidence Laue diffraction scheme are essentially more sensitive to structure distortions in surface layers of a crystal as compared to the conventional diffraction scheme in the Bragg geometry. A gas-flow proportional counter with a resolution as small as 16% used as photoelectron energy analyzer allows to establish the presence of disturbed layers with thicknesses ≈ 10 nm and less. Es wird gezeigt, daß die mittels stehender Röntgenwellentechnik im Laue-Beugungsfall bei streifender Inzidenz erhaltenen Photoemissionskurven gegenüber Strukturverzerrungen in den Oberflächenschichten eines Kristalls im Vergleich zum konventionellen Beugungsfall in Bragg-Geometrie wesentlich empfindlicher sind. Ein Gasfluß-Proportionalzähler mit einer Auflösung von 16%, der als Photoelektronenenergieanalysator benutzt wird, erlaubt die Feststellung von gestörten Schichten mit Dicken von ≈ 10 nm und darunter.

Laser annealing of cadmium sulfide crystals

Cadmium sulfide crystals with a disturbed surface layer about 5 μ thick were annealed by KrF* laser pulses of 10 nsec duration. This improved the crystal structure when the cadmium side was irradiated. The effect was not detectable on the sulfur side. The threshold energy density of the effect was ~0.25 J/cm2.

The investigation of disturbed surface layer structure by the external photoeffect under X-ray diffraction conditions

Results of experimental studies of the disturbed surface layer structure in Si crystals after an ion implantation and subsequent annealing as well as epitaxial layers of GaAs and Ge are presented. The method of measuring and calculating theoretically an angular dependence of the external X-ray photoeffect under the diffraction conditions is used for finding the deformation distribution profile in dependence on the distance from the surface. The conclusion is made that the method of comparing the theoretical and experimental curves using the two channels (X-ray reflection and photoemission) simultaneously proved to be a very comfortable and reliable way for the determination of the surface layer structure. Es werden die Ergebnisse von experimentellen Untersuchungen der gestorten Oberflachenschicht-Struktur sowohl in Si-Kristallen nach Ionenimplantation und nachfolgender Temperung als auch von GaAs- und Ge-Epitaxieschichten mitgeteilt. Eine Methode zur Messung und theoretischen Berechnung der Winkelabhangigkeit des auseren Rontgen-Photoeffekts unter Beugungsbedingungen wird zur Bestimmung der Deformationsverteilungsprofile in Abhangigkeit von der Entfernung von der Oberflache benutzt. Es wird festgestellt, das die Methode des Vergleichs der theoretischen und experimentellen Kurven bei gleichzeitiger Benutzung der beiden Kanale (Ront-genref lexion und Photoemission) einen sehr bequemer und zuverlassiger Weg zur Bestimmung der Oberflachenschichtstruktur darstelit.

On the theory of external photoeffect accompanying X-ray diffraction in an ideal crystal with disturbed surface layer

en

Electrokinetic properties of calcium aluminate hydrates

The surface charge of Ca3Al2(OH)12 in water and NaOH solutions is negative when the solution is saturated towards this compound. When Ca3A12(OH)12 is formed during the reaction of Ca3A12O6 with water and NaOH solutions a positive surface charge is present. This positive charge is also found for other hydrates existing during this reaction; it indicates a disturbed surface layer with excess Ca2+ ions on the solid. Further it was shown that the absolute value of the surface charge calculated with the change of the activity coefficient in the diffuse double-layer taken into account is smaller than calculated with the equation without this correction.

Vapour growth of SbSI on a seed

Large isometric (up to 5 x 7 x 10 mm 3) single crystals of SbSI were grown from the vapour phase on seeds. The seeds were cut from a thick needle and were treated to remove the disturbed surface layers. Two growing techniques were compared: the method of a constant temperature gradient in conventional ampoule and the method of the reversal gradient in Scholz' ampoule geometry. It was found that in the former method growth in the c-direction (i.e., along the needle axis) proceeds only in whisker form, probably due to a poison impurity effect, whereas in the latter a bulk crystal was grown. This result is attributed to prevention of the poison effect during the reverse (i.e., etching) stage. Prismatic faces ( hk0) grow principally by a chain-type mechanism.

X-ray diffraction in a perfect crystal with disturbed surface layer

en

Investigations on the defect depth of electroerosive‐cut Te single crystals by reflection electron diffraction (RHEED)

AbstractResults of the experimentally determined defect depth due to electroerosive working of Te single crystals as a function of crystal orientation and electric cutting energy by RHEED are given. The abrasion of the disturbed surface layer was made by chemical etch polishing as well as by bombardment with Ar+ ions. The defect depths determined from the RHEED patterns depend on the crystal orientation and the applied cutting energy. In case of the lowest cutting energy, it has a value of about 3 μm for the (0001)‐orientation and 6 μm for the (1010)‐orientation, the corresponding values for the highest cutting energy are about 8 μm and 20 μm, respectively. It is discussed in how far defect depths determined from the interpretation of RHEED patterns correspond to the “real defect depths” which can be determined by other measuring techniques.

Epitaxy of Molybdenum on Sapphire

Thin films of molybdenum were deposited by the electron beam evaporation method on single crystal sapphire substrates to establish the effects of substrate orientation, deposition temperature, and evaporation rate on the structure, orientation and morphology of the deposited films. The films were characterized by replication and high resolution reflection electron diffraction methods.The epitaxy of molybdenum on sapphire substrates of orientations (0001), (1012), and (1012) were studied over a substrate temperature range of 25 through 1000°C with deposition rates of 500 and 1000 Å/min. Strain-free substrate surfaces were prepared by removing the disturbed surface layer by means of thermal etching in-situ at 1450°C for 2 hours in a pressure of 10−9 Torr.

Structure and chemistry of silicon surfaces after pre- and backsputtering, studied with Auger spectroscopy, ellipsometry, and RHEED

Presputtering and backsputtering are cleaning processes usually performed prior to the sputter deposition of thin films. The effectiveness of these cleaning procedures was investigated with ellipsometry, RHEED, and Auger spectroscopy, using silicon substrates. Presputtering produced no deposits or disturbed surface layer, and the major surface contaminants were C and O totalling ∼ 3 monolayers which adsorbed during air exposure, prior to presputtering. Backsputtering produced an amorphous Si substrate surface, contaminated with Ar, C, and W, totalling ≳ 3 monolayers. Ar (2–20 at% in the first 5 atom layers of the surface) was incorporated from the sputtering gas, and C (5–50%) and W (15–70%), were sputtered from the substrate support plate and redeposited on the substrate. W films deposited on Si substrates after backsputtering contained ≲ 1 Å of silicon oxide layer at the W-Si interface; this result was obtained by following the chemical depth profile of various elements by using simultaneous Ar ion-milling and Auger spectroscopy. The detection limit of this technique for an SiO 2 interface layer was < 1 Å.

Quartz Dissolution as Influenced by pH and the Presence of a Disturbed Surface Layer

AbstractQuartz particles (10 to 2 microns in diameter, produced by grinding) released 45 ppm of SiO2 to a buffer solution of pH 7 during a 48 hr period. The grinding of quartz particles produced a disturbed surface layer with solubility properties intermediate between crystalline quartz (6 ppm SiO2) and amorphous silica (120 ppm SiO2). Removal of the disturbed layer by treatment with 1N HF lowered the SiO2 dissolution from 45 to 3 ppm. Use of 12N HF decreased the amount of SiO2 dissolved to 2 ppm, a result found to coincide with a preferential dissolution of the finer quartz particles in addition to the removal of the disturbed surface layer. The rate of dissolution of SiO2 from quartz particles, subsequent to treatment with 1N HF, increased with decrease in particle size, from 1 to 3 ppm for quartz particles 50 to 20 microns in diameter to 30 to 44 ppm for particles 2 to 0.2 microns in diameter, during each of three consecutive 14‐day extractions with pH 7 buffer solution. The amount of SiO2 dissolved from quartz in buffer solutions increased in the pH range of 4 to 10, from 0.6 ppm of SiO2 at pH 4 to 19 ppm at pH 10 during a 14‐day period of extraction from quartz particles, 10 to 2 microns in diameter. Quartz particles, subsequent to the removal of the disturbed surface layer, removed SiO2 from pH 4 and pH 8 buffer solutions prepared with more SiO2 in solution than would be released from quartz in the respective solution.

Effects of surface condition on the mechanical properties of ice crystals

A comparative study of the deformation behaviour of mechanically and chemically polished ice crystals is described. For single crystals, mechanical disturbance of the surface layer greatly reduces the maximum stress for basal glide in constant strain rate tests in compression. Single crystals with sub-boundaries do not show any prominent surface effect, but exhibit quite a low maximum stress. The results indicate that mechanically disturbed surface layers and sub-boundaries do not appear to act as strong barriers to dislocation movement in ice crystals, but rather as sources of dislocations. Surface condition does not appear to affect the maximum stress for polycrystals. The influence of strain rate (range 2·1 × 10−5 to 1·7 × 10−4 s−1) and temperature (range −10 to −30°C) upon the maximum stress was also investigated for both single crystals and polycrystals of ice.

Photoconductivity of Silver Chloride Crystals Under Pulsed X-Ray Irradiation

The photoconductivity produced by irradiation with 0.2-\ensuremath{\mu}sec x-ray pulses was studied in AgCl as a function of temperature (80-280\ifmmode^\circ\else\textdegree\fi{}K), x-ray intensity and penetration, field strength, and crystal preparation, in order to obtain information about lifetimes and mobilities of electrons and holes. The measurements of electron lifetimes (\ensuremath{\sim}1 \ensuremath{\mu}sec) and mobilities in air-grown crystals are in agreement with those reported in the literature. The photoconductive response can be described by assuming deep electron traps throughout the volume of the crystal and possibly a disturbed surface layer. No hole motion is observed below 250\ifmmode^\circ\else\textdegree\fi{}K; above that temperature the schubweg per unit field is estimated at 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ ${\mathrm{cm}}^{2}$/v. The electron lifetime in crystals grown and annealed in He is much smaller than in the air-grown samples. Assuming the same mobility in both samples the life-time at 80\ifmmode^\circ\else\textdegree\fi{}K is 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}9}$ sec. At higher temperatures the pulses show long tails, and between 200\ifmmode^\circ\else\textdegree\fi{} and 280\ifmmode^\circ\else\textdegree\fi{}K the saturation time varies exponentially with $\frac{1}{T}$. It is assumed that shallow traps exist (\ensuremath{\sim}0.08 ev) in a thin surface region which otherwise has a long electron lifetime as compared with the bulk of the crystal. Measurements on crystals doped with 20 ppm ${\mathrm{Cu}}^{+}$ indicate that the ${\mathrm{Cu}}^{+}$ ions do not act as effective electron traps. On the other hand, the presence of 1 ppm Ni ions reduces the lifetime at 80\ifmmode^\circ\else\textdegree\fi{}K to less than 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}11}$ sec, indicating a capture cross section of the Ni ion larger than 300 ${(\mathrm{A})}^{2}$.

Physico‐chemical studies on dusts. X. A comparative study of the solubility and adsorptive properties of finely divided silica and titania

AbstractTitania (crystalline or amorphous) has a negligibly small water‐solubility over the pH range approx. 3–12; silica (crystalline or amorphous) has a low but quite measurable solubility, with a minimum at pH about 2.5–3.Rutile, lightly etched with hydrofluoric acid, shows an enhanced solubility, but quartz, similarly treated, shows a reduced solubility.The rate of solution in aqueous media provides no evidence for the existence on rutile of a highlysoluble disturbed surface layer such as exists on quartz.Adsorption of basic dyestuffs by titania broadly resembles that shown by silica, although the extent of adsorption is greater.

A Study of the Etching Rate of Single‐Crystal Germanium

A study has been made of the rate at which single‐crystal germanium is etched under various conditions. For simplicity, the principal etchants used were composed of only , , and water. Data are given for the rate as a function of temperature and composition of the etchant, and as a function of the orientation and impurity content of the crystal. An equation which assumes two reactions taking place in sequence on the surface fits the rate vs. temperature data within the limits of experimental error. In the range studied, the rate‐controlling processes are sensitive to sample orientation. From etching data, a value was obtained for the thickness of the disturbed surface layer due to abrasive grinding. This was found to be in the range of 2–10 μ and to depend on sample orientation and abrasive particle size. Comparative data are given for two common etchants of a more complicated composition.