Region Of Total Reflection Research Articles

Roughness correlation and interdiffusion in thin films of polymer chains

The surface morphology of thin bilayer polymer films on top of glass substrates was investigated. The bilayer consists of a blend film of protonated and deuterated polystyrene and an underlying deuterated polystyrene film. Choosing the thickness of the top film larger than 8 times and smaller than 2 times the radius of gyration of the chains enables the determination of film thickness and confinement effects. With diffuse neutron scattering at grazing incidence in the region of total external reflection, a depth sensitivity and a contrast even at the internal polymer–polymer interface was achieved. The underlying film is conformal to the substrate, and depending on the thickness of the top film two different types of roughness correlations are observed. Thin confined films nestle to the underlying polymer films, while the stiffness of thicker bulky films provides an independent morphology. In both cases, annealing above the glass-transition temperature yields an interdiffusion at the internal polymer–polymer interface, and the polymer–air surface remains essentially unchanged with respect to roughness correlations. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2862–2874, 1999

Combination of specular and off-specular low-angle X-ray diffraction in the study of metallic multilayers

The use of resonant low-angle X-ray diffraction, combining specular and off-specular scans, has been used to characterize accurately and self-consistently the mesoscopic structure and the quality of interfaces for a set of magnetron sputtered Co/Cu multilayers. In addition, the use of a simulation program to fit experimental patterns, which is based on the Distorted Wave Born Approximation has permitted to confirm its validity in the region of total external reflection in a system having a high degree of complexity.

Phase Separation and Dewetting of Weakly Incompatible Polymer Blend Films.

The phase separation and dewetting of thin films of blends of deuterated polystyrene (dPS) and poly(p-methylstyrene) (PpMS) were investigated during annealing. The surface morphology, obtained from atomic force microscopy and phase measurement interference microscopy, the density profile, determined by X-ray reflectivity in the region of total external reflection, and the surface composition obtained from static secondary ion mass spectroscopy, are reported. This system is only weakly incompatible. The interaction of the components with substrate and air during phase separation leads to a bilayer formation with a broad polymer-polymer interface. PpMS segregates to the air interface. The bilayer structure is unstable and defines the starting point for the dewetting of PpMS on top of the dPS layer. In the final dewetting state a homogeneous layer of dPS on top of the substrate is covered with an ultrathin layer of PpMS as well as with quite thick mesoscopic drops of PpMS.

Dewetting of thin polymer films: an X-ray scattering study

The surface morphology of different dewetting states of thin polymer films (polystyrene) on top of silicon substrates was investigated. With diffuse X-ray scattering in the region of total external reflection a high in-plane resolution was achieved. We observe a new nano-dewetting structure which coexists with the well known mesoscopic dewetting structures of holes, cellular pattern and drops. This nano-dewetting structure consists of small dimples with a diameter in the nanometer range. It results from the dewetting of a remaining ultra-thin polymer layer and can be explained with theoretical predictions of spinodal decomposition. The experimental results of the scattering study are confirmed with scanning-force microscopy measurements.

Neutron double multilayer monochromator-polarizer Co/Ti

The proposed neutron multilayer monochromator-polarizer, consisting of the alternating layers of Co and Ti, prepared by the method of thermal vacuum evaporation on glass and silicon substrates is considered. In this monochromator the distance between first Bragg order peak and edge of total reflection plateau are considerably increased for glass substrate compare with Fe/Ag monochromator and for silicon substrate the total reflection region is absent for reflection of the beam from silicon. The curves of intensities of direct beam and for both spin components of the beam of cold neutrons reflected four times from this double monochromator-polarizer together with data from thermal neutron reflectometer are presented.

Correlated Roughness, Long-Range Correlations, and Dewetting of Thin Polymer Films

The surface morphology of thin polymer films (polystyrene) on top of silicon substrates as prepared by spin-coating and after the dewetting of an initially homogeneous polymer film was examined. We investigated the influence of film thickness, molecular weight, annealing temperature, and used solvent. With diffuse X-ray scattering in the region of total external reflection a depth sensitivity was achieved. The in-plane structure of the untreated samples shows significant differences: Starting from a molecular weight of 28k the samples show conformal roughness over a range of film thickness between 50 and 1160 Å, whereas in an equivalent film thickness range for a low molecular weight sample no correlation between the substrate and the polymer surface was detected. Above the glass transition temperature the roughness correlation was lost and therefore has no influence on the dewetting behavior of the polymer films. A variation of the solvent used for the spin-coating gives rise to different dewetting structures that originate from different in-plane film structures right after the preparation. Thus, diffuse scattering is well suited for probing long-range correlations and mobility.

Kardar-Parisi-Zhang growth of amorphous silicon onSi/SiO2

Amorphous silicon films with thicknesses ranging from about 20 \AA{} to 2000 \AA{} were evaporated onto silicon substrates. The surface and interfaces were then investigated by specular and diffuse x-ray scattering experiments in the region of total external reflection. A model of self-affine interfaces was used for the refinement. The rms roughness \ensuremath{\sigma} and the in-plane correlation length \ensuremath{\xi} vs film thickness follow power laws with exponents of $\ensuremath{\beta}=0.1\ifmmode\pm\else\textpm\fi{}0.05$ and $1/z=0.6\ifmmode\pm\else\textpm\fi{}0.2,$ and the average Hurst parameter is $h=0.23\ifmmode\pm\else\textpm\fi{}0.05.$ The resulting parameters are compatible with growth models based on the Kardar-Parisi-Zhang equation.

Submicrometer x-ray beam production by a thin film waveguide

A hard x-ray waveguide capable of reducing a 13 keV monochromatic beam in one direction from 30 to only 0.1 μm has been characterized with synchrotron radiation. The guiding structure consisted of a carbon layer sandwiched between two Ni layers sputter-deposited onto float glass. A beam exiting at the end of the guide in guiding direction was observed when a resonance effect due to the formation of x-ray standing waves in the total reflection region takes place. The measured beam divergence (1.3 mrad) agrees with expectations. The total efficiency (exiting photon flux/incident photon flux) can ideally exceed 10−2 but is only 10−4 for this first prototype.

Characterization of Si/Ge interfaces by diffuse X-ray scattering in the region of total external reflection

Four samples with different numbers of Si/Ge-bilayers were grown at the same time by high vacuum vapor deposition onto Si(111)-substrates at room temperature. Diffuse scattering experiments within the region of total external reflection were carried out to investigate the mesoscopic roughness of the interfaces. The data are explained quantitatively using the distorted wave Born approximation (DWBA) for correlated layer systems with self-affine interfaces. Because all samples were grown under identical conditions the interface parameters of the simpler systems were used for the more complex samples in order to reduce the number of free parameters in the refinement. The resulting trends for the roughness amplitude and the in-plane correlation lengths are compared to predictions from different growth models.

Interface structure of MBE-grown CoSi2/Si/CoSi2 layers on Si(111): Partially correlated roughness and diffuse x-ray scattering.

The detailed interface structure of a ${\mathrm{CoSi}}_{2}$/Si/${\mathrm{CoSi}}_{2}$/Si(111) layer system grown by molecular-beam epitaxy is investigated in this paper. Measurements of the diffuse scattering in the region of total external reflection were performed and analyzed within the distorted-wave Born approximation. The analysis of the specularly reflected and the diffusely scattered intensity leads to a consistent set of interface and layer parameters, which are compared with results of Rutherford backscattering/channeling, transmission electron microscopy, and scanning tunneling microscopy. Although the diffuse intensity is dominated by a very rough surface layer, the roughness distribution of the buried interfaces of the epitaxial layers was determined rather exactly. It was found that the roughnesses of the interfaces of all epitaxial layers are of the order of monolayer steps. Very good agreement between the measurements and the calculations is achieved, if conformal roughness of the adjacent interfaces of each ${\mathrm{CoSi}}_{2}$ layer is included. Furthermore, the interfaces of the sandwiched Si layer are partially correlated, which means that the step structure is partially transferred through all interfaces up to the surface of the upper ${\mathrm{CoSi}}_{2}$ layer. \textcopyright{} 1996 The American Physical Society.

Transient scattering responses from a plane interface between dielectric half‐spaces

AbstractThe transient scattered electromagnetic field due to an impulsive line source placed near the boundary between two dielectric media is formulated by the Cagniard‐de Hoop method. The scattered field is divided into the direct wave and the reflected wave. Then the reflected wave is divided further into the conventional reflected wave, and the head wave contribution appearing in the total reflection region. The rigorous solutions for each contribution are obtained. The wavefront approximation that can be used immediately after the wave arrival also is derived. The relationship between the wavefront approximation and the high‐frequency asymptotic geometrical optics field derived in the frequency domain is discussed.

X-ray study of growing wetting films

X-ray scattering experiments of liquid films on top of solid substrates were performed. With a short pulse disturbance, caused by a temperature difference between the substrate and the vapour in the X-ray cell, the wetting film thickness is reduced. Afterwards the time dependence of the growing film is monitored by X-ray reflectivity measurements in the region of total external reflection. We have examined CCl4- and CCl3Br-films on top of silicon wafers and CCl3Br on glass/gold and glass/silver substrates. The film thickness as function of time is explained by the Kolmogorov growth model. From the data we obtain rather long time constants and the dimensiond=2 of the growing process

X-ray diffraction from Si/Ge layers: Diffuse scattering in the region of total external reflection.

In this paper it is shown that diffuse-scattering experiments within the region of total external reflection can be explained quantitatively using the distorted-wave Born approximation for layer systems. Three Si/Ge samples with different degrees of complexity were investigated. The simultaneous analysis of the specular reflected intensity and the diffuse scattering leads to one consistent set of interface and layer parameters, which is able to fit both the shapes and the locations of all dynamic peaks in the off-specular scans and the characteristics of the reflected intensity. Therefore the distorted-wave Born approximation seems to give a correct and complete description of the diffuse scattering in the region of total external reflection.

X-ray diffraction from laterally structured surfaces: Total external reflection.

In this work x-ray-diffraction measurements from GaAs surface gratings are presented. The experiments were performed using a three-crystal diffractometer. Measurements in the region of total external reflection (small incidence angles) for five samples were done and compared with model calculations based on a dynamical scattering theory. The theory is able to explain all experiments quantitatively. Mesoscopic grating parameters as well as microscopic surface roughnesses of the samples were obtained from fits of the data. For three samples scanning-electron-microscope pictures were taken. The analysis of these pictures leads to the same mesoscopic parameters as obtained from x-ray diffraction.

Novel design and method of fabrication of inhomogeneous mirrors

On the basis of numerical calculations of a laser resonator, a novel design of a laser mirror with a step amplitude transmittance inhomogeneity has been developed. The output coupler was structured in such a way that it contained a partial transmission region surrounded by a total reflection region. The optimal combination of a dielectric multilayer and a profiled metal film with negligible thickness provides, practically constant reflection phase over the whole surface. Such mirrors have been used, as highly efficient couplers, in a HeNe laser bearing an output transverse mode with a rectangular function profile.

X-ray diffraction from mesoscopic systems

Two activities of our group concerning structures on mesoscopic length scales are presented: (1) CoSi 2 layers buried in Si-wafers have been studied with many scattering geometries; the emphasis is on diffuse scattering from rough interfaces and diffuse scattering from atomic scale defects. (2) The other example is an investigation of laterally structured surfaces in the region of total external reflection and around Bragg peaks. In both cases extensions of the presently available models the necessary.

Wetting of laterally structured surfaces

An x-ray scattering study of a laterally structured solid surface wetted by a liquid is reported. GaAs (001) samples with etched trapezoidal surface gratings are used as substrates. Due to the lattice spacing of d = 5900 A and the height h of about 450 A such gratings can be regarded as a row of free edges and wedges. The special wetting behaviour of these wedges with a liquid film of CCl4 was studied using x-ray reflectivity in the region of total external reflection. The reflectivity of the film on top of the laterally structured GaAs substrate is explained by model calculations which contain the electron density depth profile perpendicular to the surface. The thickness of the liquid wetting film on top of the stepped surface was obtained from the fit of the data.

Radiative transfer in nonuniformly refracting layered media: atmosphere–ocean system

We have applied the discrete-ordinate method to solve the radiative-transfer problem pertaining to a system consisting of two strata with different indices of refraction. The refraction and reflection at the interface are taken into account. The relevant changes (as compared with the standard problem with a constant index of refraction throughout the medium) in formulation and solution of the radiative-transfer equation, including the proper application of interface and boundary conditions, are described. Appropriate quadrature points (streams) and weights are chosen for the interface-continuity relations. Examples of radiative transfer in the coupled atmosphere-ocean system are provided. To take into account the region of total reflection in the ocean, additional angular quadrature points are required, compared with those used in the atmosphere and in the refractive region of the ocean that communicates directly with the atmosphere. To verify the model we have tested for energy conservation. We also discuss the effect of the number of streams assigned to the refractive region and the total reflecting region on the convergence. Our results show that the change in the index of refraction between the two strata significantly affects the radiation field. The radiative-transfer model we present is designed for application to the atmosphere-ocean system, but it can be applied to other systems that need to consider the change in the index of refraction between two strata.

Neutron ellipsometry

We discuss the similarities which exist between the reflection of neutrons from ferromagnetic media and the reflection of light from media rendered gyrotropic by the application of a magnetic field, and show that the vector character of the neutron polarisation can be fully exploited in spin-analysed neutron reflection measurements (termed ‘neutron ellipsometry’ because of the similarity to optical ellipsometry) to give valuable magnetometric information for ultrathin films and multilayers, and with certain advantages over conventional polarised neutron reflection measurements. We show that for the case of a single ultrathin magnetic layer with uniform magnetisation, the component of the in-plane magnetisation perpendicular to the incident neutron polarisation determines both the spin conserving and spin flipping reflectivities in the region of total reflection, while a more complex regime obtains in the partially reflecting region. Making neutron ellipsometric measurements in both reflection regions thus allows the magnitude and orientation of the in-plane magnetisation vector to be directly determined. This is illustrated by numerical calculations for a single ultrathin iron layer supported by a silver substrate and with a silver cap.

The role of total-reflection X-ray fluorescence in atomic spectroscopy

Total-reflection X-ray fluorescence (TXRF) is a universal and economic method for the simultaneous determination of elements with atomic numbers > 11 down to the lower pg-level. It is a microanalytical tool for the analysis of small sample amounts placed on flat carriers and for contaminations on flat sample surfaces. Analyses of stratified near-surface layers are made possible by varying the incident angle of the primary beam in the region of total-reflection. This non-destructive method is especially suitable for thin layers of a few nanometres, deposited on wafer material although not usable as a microprobe method with a high lateral resolution. Furthermore, depth profiles of biological samples can be recorded by means of microtome sectioning of only a few micrometres, as, for example in the gradient analysis of human organs. In addition to micro- and surface-layer analysis, TXRF is effectively applied to element trace analysis. Homogeneous solutions, for example aqueous solutions, high-purity adds or body fluids, are pipetted onto carriers and, after evaporation, the dry residues are analysed directly down to the pg ml region. Particularly advantageous is the absence of matrix effects, so that an easy calibration can be carried out by adding a single internal standard element. A digestion or separation step preceding the actual determination becomes necessary if a more complex matrix is to be analysed or especially low detection limits have to be reached. A critical evaluation of the recent developments in atomic spectroscopy places TXRF in a leading position. Its outstanding features compete with those of e.g. electrothermal atomic absorption spectrometry (ETAAS), microwave induced plasma optical emission spectroscopy (MIP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) in the field of micro- and trace analysis and with Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS) in the surface-layer analysis.