Pavel Tománek

Morphological features in aluminum nitride epilayers prepared by magnetron sputtering

Abstract The aim of this study is to characterize the surface topography of aluminum nitride (AlN) epilayers prepared by magnetron sputtering using the surface statistical parameters, according to ISO 25178-2:2012. To understand the effect of temperature on the epilayer structure, the surface topography was investigated through atomic force microscopy (AFM). AFM data and analysis of surface statistical parameters indicated the dependence of morphology of the epilayers on their growth conditions. The surface statistical parameters provide important information about surface texture and are useful for manufacturers in developing AlN thin films with improved surface characteristics. These results are also important for understanding the nanoscale phenomena at the contacts between rough surfaces, such as the area of contact, the interfacial separation, and the adhesive and frictional properties.

Detection and Localization of Defects in Monocrystalline Silicon Solar Cell

Near-surface defects in solar cell wafer have undesirable influence upon device properties, as its efficiency and lifetime. When reverse-bias voltage is applied to the wafer, a magnitude of electric signals from defects can be measured electronically, but the localization of defects is difficult using classical optical far-field methods. Therefore, the paper introduces a novel combination of electric and optical methods showing promise of being useful in detection and localization of defects with resolution of 250 nm using near-field nondestructive characterization techniques. The results of mapped topography, local surface reflection, and local light to electric energy conversion measurement in areas with small defects strongly support the development and further evaluation of the technique.

Near-field measurement of ZnS:Mn nanocrystal and bulk thin-film electroluminescent devices.

A near‐field study of the electro‐optical phenomena and aging characteristics of nanostructured and bulk ZnS:Mn alternating‐current thin‐film electro‐optical devices is presented. ZnS:Mn nanocrystals embedded in the glass matrices as well as ZnS:Mn thin‐film phosphors contain four different concentrations of Mn (from 0.05 to 1.0 mol%). The activator impurity in the phosphor influences the spectral properties and, to a large extent, the temporal properties of optical emission and an aging process of the devices. Therefore, a local photoluminescence and electroluminescence investigation using a scanning near‐field optical microscope technique is provided and the aging characteristics of ZnS:Mn nanocrystal structure also presented.

Hybrid STM/R-SNOM with novel probe

Abstract A reflection-mode scanning near-field optical microscope joined with scanning tunneling microscope having a common revolving detection head and mounted on a classical optical microscope stage is proposed. This arrangement combines advantages of both near-field and far-field imageries and is able to display the images of surfaces with superresolution beyond the diffraction limit. Its function is characterized by the wide range of resolution and/or by the possibility to study different kinds of surfaces with nanometer-scale accuracy. A novel probe is used in the optical stage of the microscope. During its fabrication the light power of an Ar–Kr laser coupled to the single-mode fiber allows a local heating of a buffered HF solution in the vicinity of the extremity of fiber. By tuning the output power of the laser, the flux of energy at the very tip of the fiber varies, and different cone angles of the probe could be obtained. This process is faster than the classical chemical etching. The etching speed, and shapes of the fiber versus temperature are therefore discussed. A comparison of the two different images obtained with a STM and R-SNOM parts of the microscope is also presented.

Measurement of dynamic variations of polarized light in processed meat due to aging

The propagation of laser light in biological tissues is of growing importance in many medical and food applications. This problem is seriously studied in live science. The biological tissues consist of cells which dimensions are bigger than wavelength of visible light and display large compositional variations, inhomogeneities, and anisotropic structures. Therefore a Mie scattering of transmitted or backscattered light occurs and different polarization states arise. The changes of polarization state due to the multiple scattering of light in the biological cellular tissues also allow measure the freshness of processed victuals. The transmitted and backscattered laser light exhibits multiple scattering on the thin slice of sample. The phenomenon is different if the cellular tissues are living or dead. In the case of meat, there are temporal and dynamic changes not only as a result of chemical process, but also geometric deformations due to the water evaporation from intracellular and extracellular sites. The polarization measurement shows the changes in polarization orientation due to the muscle orientation and meat aging. Two types of measurements were provided: a) Measurement of polarized light reflected and twice transmitted forward and backward through the biological tissue samples - meat slice attached on sample holder mirror. b) Measurement of polarized light transmitted through the biological tissue sample. The relationship between polarization changes and meat freshness, and a dynamic temporal behavior of polarization states in the aged meat is reported.

Thickness measurement of thin dielectric films by evanescent total reflection fluorescence

The electric field of an evanescent wave generates fluorescence in the interface between a dielectric surface and an adjacent, fluorescing, medium of lower refractive index. The difference between the fluorescing signals from covered and noncovered surfaces enables nondestructive measurement of the film thickness to be made in the range 1–15 nm.

Characterizing SiC-AlN semiconductor solid solutions with indirect and direct bandgaps

The objective of the study is to characterize the dependence of the optical properties of solid solutions of silicon carbide and aluminum nitride on composition. Even small differences in composition provide manipulation of band gap features over a wide range. Data for this paper were collected by X-ray diffraction, photoluminescence and absorption spectroscopy. The evolution of the observed optical properties as a result of compositional changes were studied. X-ray studies confirm the presence of a(SiC)1-x(AlN)x solid solution. Investigation of absorption spectra shows the optical band gap of the sample with composition (SiC)0,88(AlN)0,12 is 3.5eV, and 4.24 eV for the (SiC)0,36(AlN)0,64 solid solution. The photoluminescence spectra demonstrate the strong dependence of the spectra on composition x. The experimental results are in agreement with theory. These data demonstrate the optimization of optical properties for particular optoelectronic applications by varying the (SiC)1-х(AlN)х composition.

AFM imaging of natural optical structures

The colors of some living organisms assosiated with the surface structure. Irridesence butterfly wings is an example of such coloration. Optical effects such as interference, diffraction, polarization are responsible for physical colors appearance. Alongside with amazing beauty this structure represent interest for design of optical devices. Here we report the results of morphology investigation by atomic force microscopy. The difference in surface structure of black and blue wings areas is clearly observed. It explains the angle dependence of the wing blue color, since these micrometer and sub-micrometer quasiperiodical structures could control the light propagation, absorption and reflection.

Polarization of scattered light in biological tissue

The real-time nondestructive inspection of biological tissues begins to be one of important tools which could contribute to better human life not only in medical diagnosis but also in everyday mankind activities. A biological tissue is considered as a turbid medium in which light is scattered. Although single or multiple scattering in tissue multiple randomizes polarization states of incident light, linear, circular and elliptical polarization states in the medium are considered, and there are circumstances when appreciable degree of polarization can be observed in diffusive scattering. Our work shows that with a sufficient degree of sensitivity is possible to detect structural changes due to the aging of processed meat by using Mueller matrix polarimeter. Moreover, it demonstrated that the degree of polarization of the backscattered light is sensitive to the optical properties of specimen material and to its thickness.

Near-Field Study of Hot Spot Photoluminescence Decay in ZnS:Mn Nanoparticles

The local spatial distribution of photoluminescence due to the creation of hot luminescence centers was measured in the optical near-field by Scanning near-field optical microscope at emission peaks of materials (λ =595nm), which is due to the luminescence of Mn2+ in ZnS. The excitation bandgap of ZnS forms exitons, and these excitons get the center of Mn2+ through nonradiation dominates, by means of transition of 4T1 – 6A1 luminescence. This spectrum is evidence that Mn2+ has been incorporated into the ZnS nanoparticles. In comparison with the bulk ZnS:Mn phosphors these nanoparticles have clearly higher luminescent efficiency with its luminescent decay time at least 4 orders of magnitude slower. It means that the oscillator intensity of luminescent centers in ZnS:Mn nanocrystal enhances at least 4 orders of magnitude than that in corresponding bulk ZnS:Mn.