Features of Wavelet Analysis in X-Ray Reflectometry of Thin Films

Specific features of the use of wavelet transform for estimating the thickness of layers and their order in a film density profile based on X-ray and synchrotron reflectometry data are considered. Some ways are proposed to reveal the characteristic features of Langmuir film packing by constructing a wavelet transform for the corresponding reflectograms. Dependences of the X-ray attenuation length on the grazing incidence angle are plotted by an example of multilayered box model of film profile; these dependences demonstrate possibilities of mapping the spatial signal delay (which occurs when rays are reflected from layers of different density) in a waveletgram.     

Study of the process of PbS nanocrystal formation in lead stearate and behenate Langmuir-Blodgett films by electron diffraction and x-ray reflectometry

Special features of the formation of PbS nanocrystals in Langmuir-Blodgett (LB) films of lead stearate and behenate under the action of H₂S are studied. It is shown that structural transformations in a multilayered LB film can be controlled using electron diffraction patterns of the oblique-texture type and x-ray reflectometry data.     

Difference method for solution of the inverse problem of reflectometry of multilayer films

A schematic of a reflectometric experiment whose results make it possible to reconstruct the structure of multilayer films on substrates is proposed. A mathematical apparatus is developed that allows for determining the numerical values of the main parameters (electron density, thickness, and roughness) for each layer of the model film. Until now, there have been no methods for determining the structure of multilayer films from experimental data, and the problem has been solved by the trial-and-error method. Some model examples of reconstruction of the film structure are reported.     

Formation of Langmuir-Blodgett films in solutions of comblike polymers

The structures have been analyzed of the monolayers of comblike precursor polymers of polyimides and mixed cellulose esters formed at the water/air interface and of the Langmuir-Blodgett films obtained by transfer of these condensed monolayers onto solid substrates. The important factors that ensure the structure control and supramolecular organization of these monolayers and films are established.     

Invariants of reflectometry curves and the structural features of thin films

It is shown that the integral of the autocorrelation function of freestanding layered films determines the square of the mean electron density in the film cross section. Data-processing techniques are proposed to deal with the results of reflectometry measurements for films on substrates. Comparison of the autocorrelation functions calculated on the basis of the experimental curve and the model provides an opportunity to evaluate the sample quality.     

Restoration of structure of thin multilayer films from reflectivity data by stepwise model refinement

The computational experiment on the restoration of the model parameters of the cross-section profile of the scattering density of thin multilayer films is described. It is shown that the use of the stepwise model of the structure, which is described by the thickness, density, absorption, and roughness parameters makes the problem of profile restoration multimodal and ill-conditioned. The analysis of the numerical experiments performed allowed us to propose a procedure of consecutive refinement of the initial-model parameters using the results of the local minimization of the discrepancy functional applied for the characteristic segments of the reflectivity curve. The methods proposed were used to restore the structure of a multilayer film deposited on a silicon substrate by the Langmuir-Blodgett method.     

Application of time–frequency wavelet analysis in the reflectometry of thin films

Crystallography Reports - The application of time–frequency wavelet analysis for solving the reflectometry inverse problem is considered. It is shown that a simultaneous transform of specular...     

The influence of structure change on electrical properties of conducting LB films produced from hexadecyl-TCNQ and heptadecyldimethyl-TTF mixture

Conducting Langmuir-Blodgett films of hexadecyl-TCNQ and heptadecyl dimethyl-TTF mixture in the ratios from 1:1 to 1:2.5 are studied. Temperature dependence of film conductivity possesses some specific features. Strong increase of conductivity and decrease of activation energy take place after annealing at 307–315 K. On the other hand, the film loses conductance after heating above 315 K. To explain this behaviour the investigations of conducting multilayers by means of electron diffraction, electron microscopy, and X-ray small-angle scattering were carried out. Some relations between changes of electrical properties and structural transformations are ascertained.