Glow Discharge as a Tool for Surface and Interface Analysis

Abstract

This review article focuses on the analytical capabilities of glow discharge optical emission spectrometry (GD‐OES) and mass spectrometry (GD‐MS) to perform compositional depth profiling (GD‐CDP). The properties of the Grimm‐type glow discharge as well as basic processes of sputtering are described and their influence on the GD as a surface and interface analytical tool are discussed. A series of examples from recent literature ranging from computer hard disks to molecular monolayers on copper substrates are presented to illustrate the excellent depth resolution that can be achieved with GD surface analytical techniques. The conditions for obtaining nanometer or even atomic‐layer depth resolution are discussed. Following this introduction is the possibilities of the technique a selection of applications principally chosen from our laboratories, demonstrating that GD‐OES and GD‐MS can be successfully employed as an analytical tool assisting the development of new materials and coatings. The applications cover common industrial tasks such as heat treatments, studies of diffusion processes at interfaces, and electrochemical depositions for biocompatible material. However, limitations and known artifacts are also discussed.     

The Rhodes-Wohlfarth parameter as assessment of the displacive degree in ferroelectrics: The case of the Ф4> model

The Rhodes-Wohlfarth parameter extended to ferroelectrics by Tokunaga [J. Phys. Soc. Jap. 57, 4275 (1988)] is here analyzed within the model. It is shown that it can be directly related with the displacive degree of the transition as described by the ratio C / E ₀ , between the non-local coupling, C, driving the transition and the depth of the energy well, E₀, associated with the distorted structure. However, the Rhodes-Wohlfarth parameter becomes asymptotically constant as C / E ₀ decreases, i.e. for systems closer to the order disorder limit. Under this viewpoint, the very limited range of values observed for this experimental parameter is explained and is shown that, in general, it can only assess quantitatively the character of the transition in rather displacive cases. The argument can be generalized to more complex systems, and when applied to well known materials, a rough estimation of the displacive degree and the relevant microscopic energetic parameters in rather displacive ferroelectrics is possible. Received 23 December 1998 and Received in final form 4 May 1999     

X-ray diffraction scattering and determination of the structural parameters of a film with a variable strain gradient

Characteristics of the x-ray diffraction field in structures with a variable strain gradient are analyzed using a model with an exponential profile. It is shown that the problem of reconstructing the structural parameters of the strained layer from the angular positions of the principal maximum and the oscillations is generally multivalued even when the strain varies monotonically over depth. Conditions are determined for which this problem can be solved. An analogy is identified with the results of an approach to determine the parameters of the strained layer based on using the integral characteristics of the diffraction reflection curve. Zh. Tekh. Fiz. 69, 67–70 (June 1999)     

Self-referential order

Abstract

We introduce the concept of self-referential order which provides a way to quantify structural organization in non-crystalline materials. The key idea consists in the observation that, in a disordered system, where there is no ideal, reference, template structure, each sub-portion of the whole structure can be taken as reference for the rest and the system can be described in terms of its parts in a self-referential way. Some parts carry larger information about the rest of the structure and they are identified as motifs. We discuss how this method can efficiently reduce the amount of information required to describe a complex disordered structure by encoding it in a set of motifs and matching rules. We propose an information-theoretic approach to define a self-referential-order-parameter and we show that, by means of entropic measures, such a parameter can be quantified explicitly. A proof of concept application to equal disk packing is presented and discussed.     

Nonlinearity in Intensity versus Concentration Dependence for the Deep UV Resonance Raman Spectra of Toluene and Heptane

Abstract: The relation between Raman scattering, resonance Raman scattering, and absorption is reviewed to determine to what extent quantitative analysis can be applied in resonance Raman spectroscopy. In addition, it is demonstrated experimentally that normal Raman spectra can be dramatically inhibited by absorption and resonance Raman effects. Raman spectra of toluene and heptane mixtures—with progressively increasing concentrations of heptane—were measured using 229-nm laser excitation. The results show that the characteristic band intensities are not directly proportional to the relative concentrations of the compounds and deviate due to absorption resonance effects. An approximated mathematical model is developed to demonstrate that the intensities of the normal Raman scattering bands are suppressed. An inhibition coefficient K_i is introduced to describe the situation and determine the penetration depth. Most remarkably, it is shown that the intensity of the resonance Raman scattering bands can be constant even when the concentration ratios differ substantially in the sampled mixtures.     

Higher-order <Emphasis Type="Bold">?</Emphasis> corrections in the semiclassical quantization of chaotic billiards

In the periodic orbit quantization of physical systems, usually only the leading-order ? contribution to the density of states is considered. Therefore, by construction, the eigenvalues following from semiclassical trace formulae generally agree with the exact quantum ones only to lowest order of ?. In different theoretical work the trace formulae have been extended to higher orders of ?. The problem remains, however, how to actually calculate eigenvalues from the extended trace formulae since, even with ? corrections included, the periodic orbit sums still do not converge in the physical domain. For lowest-order semiclassical trace formulae the convergence problem can be elegantly, and universally, circumvented by application of the technique of harmonic inversion. In this paper we show how, for general scaling chaotic systems, also higher-order ? corrections to the Gutzwiller formula can be included in the harmonic inversion scheme, and demonstrate that corrected semiclassical eigenvalues can be calculated despite the convergence problem. The method is applied to the open three-disk scattering system, as a prototype of a chaotic system. Received 10 September 2001 and Received in final form 3 January 2002     

A New Approach to Analysis of Molecular Structure in Thin Films: Infrared Multiple‐Angle Incidence Resolution Spectrometry

Abstract

Multiple‐angle incidence resolution spectrometry (MAIRS) is a potentially useful spectroscopic technique for quantitative analysis of molecular orientation in thin films deposited on a solid substrate. Although the technique is based on a unique measurement concept and theory, it can easily be equipped on a commercial FT‐IR and the operation is user friendly. In this review, representative application studies of MAIRS are summarized as well as a recent new theoretical approach to get over a conventional experimental limitation that a high‐refractive‐index substrate is necessary for quantitatively reliable MAIRS analysis.     

Energy,fluence and temperature dependence of MeV nitrogen implantation profiles in steel

Abstract

1 to 2 MeV nitrogen (N⁺ and N₂ ⁺) ions were implanted at high fluences in stainless steel, and their depth distributions were measured subsequently by Rutherford backscattering and thermal neutron depth profiling. The range profiles were broader than theoretically expected. With increasing fluence, deviations from ballistic computer codes increase. These deviations can well be described by the assumption of radiation enhanced diffusion for which a simple analytical model is presented. The thermal mobility shows a different behavior for low, and for high implanted fluences.     

Vortex structure in the presence of tilted columnar defects

It is argued that vortices in layered superconductors will be trapped by tilted columnar defects even when the external magnetic field is oriented along the c axis. For such tilted, trapped vortices the interaction at long distances becomes attractive in some directions. This must result in the formation of vortex chains with an intervortex distance of the order of the London penetration depth. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 507–511 (25 September 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Correlation functions in the theory of atomic collision cascades: Ion location and the distribution in depth and size of damage clusters

Abstract

Simple depth distribution functions of ion bombardment damage predict the spatial extension of the cumulative damage caused by a beam of ions. Correlation functions need to be considered when more detailed information is desirable, such as the average size or depth of individual damage clusters, the average location of an ion within its damage cluster, and the fluctuations of these quantities. In this paper we establish an integral equation for the pair correlation function, coupling the individual ion range with the deposited energy. This pair correlation function determines the damage caused by all those ions that come to rest at a specific penetration depth. Solutions of the integral equation are found by standard methods. Explicit results are presented for elastic scattering governed by power cross sections. The depth distribution of damage clusters turns out to be significantly narrower than the gross damage distribution at all mass ratios except for M ₁ ? M ₂, and the size distribution appears insensitive to depth when measured perpendicular to the ion beam, but varying with depth when measured parallel. Predictions on ion location suffer from a surprizingly sensitive dependence on the scattering cross section. A note on the fluctuation of the sputtering yield by individual ions concludes the paper.     

Depth Profiling of Polymer Surfaces with FT-IR Spectroscopy

INTRODUCTION

The composition and structure at the surface of polymeric materials can vary with depth as a result of surface treatments, surface-specific processing variables, or thermodynamic forces active at the surface. For example, low molecular weight oils are applied to the surface of polymers for lubrication purposes. The distribution or depth gradient of the oil in the polymer depends on a variety of interacting factors, such as diffusion, solubility, temperature, chemical or physical interaction, porosity, etc. In the coatings and lamination industries, gradients can occur as a result of the direct deposition of Material A on the surface of Material B. When A does not mix with B, as is often desirable, the integrity of the surface is of importance. The thickness of the layer(s) and the sharpness of the interface(s) can be critical to the intended application of the material. Polymer surfaces are often treated to obtain specific surface properties. An example of this is in the corona poling of such surfaces to improve the printability in commercial applications. Material properties are based on the depth to which the surface treatment propagates, the chemistry of the reactions, and the resulting products.     

Theoretical antineutrino detection,direction and ranging at long distances

In this paper we introduce the concept of what we call “NUDAR” (NeUtrino Direction and Ranging), making the point that measurements of the observed energy and direction vectors can be employed to passively deduce the exact three-dimensional location and thermal power of geophysical and anthropogenic neutrino sources from even a single detector. Earlier studies have presented the challenges of long-range detection, dominated by the unavoidable inverse-square falloff in neutrinos, which force the use of kiloton scale detectors beyond a few kilometers. Earlier work has also presented the case for multiple detectors, and has reviewed the background challenges. We present the most precise background estimates to date, all handled in full three dimensions, as functions of depth and geographical location. For the present calculations, we consider a hypothetical 138 kiloton detector which can be transported to an ocean site and deployed to an operational depth. We present a Bayesian estimation framework to incorporate any a priori knowledge of the reactor that we are trying to detect, as well as the estimated uncertainty in the background and the oscillation parameters. Most importantly, we fully employ the knowledge of the reactor spectrum and the distance-dependent effects of neutrino oscillations on such spectra. The latter, in particular, makes possible determination of range from one location, given adequate signal statistics. Further, we explore the rich potential of improving detection with even modest improvements in individual neutrino direction determination. We conclude that a 300 MW_th reactor can indeed be geolocated, and its operating power estimated with one or two detectors in the hundred kiloton class at ranges out to a few hundred kilometers. We note that such detectors would have natural and non-interfering utility for scientific studies of geo-neutrinos, neutrino oscillations, and astrophysical neutrinos. This motivates the development of cost effective methods of constructing and deploying such next generation detectors.     

Long-range spin-pairing order and spin defects in quantum spin- $${1 \over 2}$$ ladders

For w-legged antiferromagnetic spin-1/2 Heisenberg ladders, a long-range spin pairing order can be identified which enables the separation of the space spanned by finite-range (covalent) valence-bond configurations into w +1 subspaces. Since every subspace has an equivalent counter subspace connected by translational symmetry, twofold degeneracy, breaking translational symmetry is found except for the subspace where the ground state of w = even belongs to. In terms of energy ordering, (non)degeneracy and the discontinuities introduced in the long-range spin pairing order by topological spin defects, the differences between even and odd ladders are explained in a general and systematic way. Received 19 July 1999 and Received in final form 8 October 1999     

More about neutron–mirror neutron oscillation

It was pointed out recently that oscillation of the neutron n into a mirror neutron n′, a sterile twin of the neutron with exactly the same mass, could be a very fast process with baryon number violation, even faster than the neutron decay itself. This process is sensitive to magnetic fields and it could be observed by comparing the neutron loss rates in the UCN storage chambers for different magnetic backgrounds. We calculate the probability of the n−n′ oscillation in the case when a mirror magnetic field B′ is non-zero and show that in this case it can be suppressed or resonantly enhanced by applying the ordinary magnetic field B, depending on its strength and on its orientation with respect to B′. The recent experimental data, under this hypothesis, still allow for an n−n′ oscillation time of order 1 s or even smaller. Moreover, they indicate that the neutron losses are sensitive to the orientation of the magnetic field. If these hints will be confirmed in future experiments, this would point to the presence of a mirror magnetic field on the Earth of the order of 0.1 G, or some equivalent spin-dependent force of other origin that makes a difference between the neutron and mirror neutron states.     

Effects of pressure on protein structure

Abstract

The main targets for the pressure induced changes in proteins are those regions primarily stabilised by hydrophobic and electrostatic interactions, since hydrogen bonds are almost pressure insensitive. Thus pressure treated proteins may well have very different structures to their native or heat treated counterparts and as a consequence different functionalities. This concept is used to discuss how pressure can modify the foaming, emulsifying and gelling properties of some food proteins and can also be used to modify the activity of some enzymes of importance in dictating food quality.     

Empirical sets

The pillar concept of Foulis and Randall's school is surely that of a manual of operations. They chose to regard an operation as the set of possible outcomes, thereby taking a manual of operations to be a family of partially overlapping operations. Our previous work is a development of their ideas in two points. First, each operation is represented not by the set of possible outcomes, but by the complete Boolean algebra of observable events. Second, since each complete Boolean algebraB possesses the Scott-Solovay modelV ^(B) of classical set theory as its higher-order companion, the Scott-Solovay universes of all the operations in the manual lump together into a family of Boolean set theories interconnected by geometric morphisms, which we suggestively designated an empirical set theory. The principal concern of this paper is to show how to get a cross-operational set concept by choosing an internal set withinV ^(B) for each operationB in the manual and bundling them up. The resulting structure is denominated an empirical set. We show that the category of empirical sets is complete, is cocomplete, has a subobject classifier for well-rounded subobjects, and has exponentials only for degraded objects.     

Designing of Optical Fiber Sensing Probe

Evanescent wave configuration has been extensively used in the development of fiber-optic sensor for different biomedical applications. In the present investigation we have theoretically proposed the designing of single-mode and multimode optical fiber sensing probes, which can be prepared by removing a few centimeters of cladding near the distal end of the step index optical fiber. In this theoretical study, we found that the removal of cladding causes V-number mismatching and this has led to the loss of signal acquisition from the sensing region. Therefore, to minimize these losses we have proposed to reduce the radius by step etch and tapering technique. It was found that step etching and tapering enhances the strength and penetration depth of the evanescent wave significantly.     

Imaging of random surfaces and inverse scattering in the Kirchoff approximation

Abstract

Imaging of random surfaces can be modelled by integration over angular spectra of scattered plane waves. This approach suggests the representation of surface scattering in the Kirchhoff approximation using the concept of three-dimensional spatial frequencies. Optical methods of surface profiling can thus be modelled, leading to an insight into reconstruction of surface profiles from scattering data. The methods can also be extended to cover thin-film multilayer structures.     

The treatment and the solution of the mixing equations with composition dependent atomic volumes

Abstract

The computer program IMPETUS calculates sputter depth profiles by solving Fokker-Plank type equations for mixing. In the standard model, the effective volume of the mixing constituents is taken to be constant throughout the mixing regardless of the composition of their atomic environment. Experimentally measured values for atomic densities of materials and compounds indicate that this assumption is not correct and that non-constant atomic volumes need to be considered. Although the way in which the variation of the volumes take place is not known, the present work is aimed at developing the treatment of Fokker-Plank type equations such that composition dependent effective atomic volumes can be included. The complexity of the equations and a method for solution together with its application for a simple case are explained in this paper