J. Vaniš

Measurement of Electrical Oscillations and Mechanical Vibrations of Yeast Cells Membrane Around 1 kHz

Fröhlich postulated coherent polar oscillations as a fundamental biophysical property of biological systems. Recently, Pelling et al. (2004, 2005) detected mechanical vibrations of yeast cell membrane with atomic force microscope (AFM) and analyzed by Fourier analysis in the frequency range 0.5–2 kHz with amplitudes of the order of 1 nm. This article describes the measurement of electric activity of yeast cells in the acoustic frequency range and of mechanical vibrations of cell membrane. Spectrum analyzer and electrically and electromagnetically screened box with point sensor and amplifiers fed by batteries were used for measurement of synchronized and non synchronized tubulin mutants of yeast cells. We show that the electric activity of synchronized cells in the M phase is greater that of non synchronized cells. That corresponds to the findings of Pohl et al. (1981). Obtained results of measurement of cell electric activity are in good agreement with AFM findings.

Ballistic electron emission spectroscopy/microscopy of self-assembled InAs quantum dots of different sizes embedded in GaAs∕AlGaAs heterostructure

Self-assembled InAs quantum dots embedded in GaAs∕GaAlAs heterostructure were visualized by ballistic electron emission microscopy. The spectroscopic characteristics on individual quantum dots were examined. Quantum dots had images of elliptical shapes. Their length was from about 10to20nm. Below one-electron p1-like state, one-electron and two-electron ground states and excited two-electron states were observed. The Coulomb interaction and exchange energies between two electrons in quantum dots were determined and compared with the previously published theoretical results.

High-power fiber laser with a polarizing diffraction grating milled on the facet of an optical fiber

We milled a sub-wavelength diffraction grating on the facet of a large mode area fiber. The diffraction grating had different reflectivities for TE and TM polarized light. It was tested in a thulium-doped fiber laser where it functioned as a low reflectivity output mirror integrated with an intracavity polarizer. Compared to the laser with a perpendicularly cleaved output fiber, the laser with diffraction grating had a slightly increased threshold power and the same slope efficiency. The beam quality factor M2 was not impaired. Polarization extinction ratios of about 20 dB that were observed at low laser powers dropped to 10 dB at high powers.

Study of InAs quantum dots in AlGaAs∕GaAs heterostructure by ballistic electron emission microscopy/spectroscopy

Self-assembled InAs quantum dots in GaAs∕GaAlAs structures were examined by ballistic electron emission microscopy/spectroscopy. The studied structures were grown by metal-organic chemical vapor deposition. Quantum dots with an image of elliptical shape were studied. Ballistic current-voltage characteristics through the quantum dot and outside the quantum dot are compared in the voltage range of 0.55–2V. In the voltage range from 0.55to0.8V examples of ballistic characteristics and their derivatives are given. In a detailed study, measurements with 1mV step in the energy range from 0.55to0.63V are presented.

Probing of InAs/AlSb double barrier heterostructures by ballistic electron emission spectroscopy

InAs/AlSb resonant tunneling heterostructures have been studied by ballistic electron emission spectroscopy. Current thresholds attributed to quasibound states in the quantum well and emission over the AlSb barriers are observed. The observed shape of thresholds is consistent with inelastic processes in the InAs layers of the structures, where a high number of electron–hole pairs are generated. A threshold consistent with the generation of electron–hole pairs in quantum well states is observed.

Measurement of Electrical and Mechanical Oscillations of Yeast Cells Membrane in Acoustic Frequency Range

Frohlich postulated coherent polar oscillations as a fundamental biophysical property of biological systems. Pelling et al. detected recently mechanical vibrations of yeast cell membrane in the frequency range 0.5-2 kHz with atomic force microscope (AFM). This paper describes the measurement of electric activity of yeast cells at frequencies around 1 kHz and of mechanical vibrations of cell membrane. Synchronized and non- synchronized tubulin mutants of yeast cells were measured. The paper includes a description of the laboratory equipment with a platinum wire point sensor and a spectrum analyzer. Obtained results are in good agreement with AFM findings.

Scanning Thermal Microscopy of Thermoelectric Nanostructures

We present the development and results of a new simple method for thermal conductivity characterization of thin films and thermoelectric structures using a scanning thermal microscope in pulsed current mode. The presented method does not allow measurement of absolute thermal conductivity of the studied system, but only relative to the Si substrate. We present the results of the method on the Si substrate/layer step boundary. The nano-layers of different thickness and different materials were prepared for the experiments by the pulsed laser deposition from hot-pressed targets.

Characterization of laser prepared Bi2Te3 nano-layers

A method for relative thermal conductivity characterization of thin thermoelectric layers and multi-layered structures in nanometre range using a scanning thermal microscope working in an active constant current mode is suggested. The method requires a very smooth and high quality surface of the studied thermoelectric system. To fulfil these requirements a study of the influence of principal deposition conditions including substrate temperature and laser beam density on surface quality of Bi2Te3 layers prepared by pulsed laser deposition was performed and its results are presented.

Electrical Vibrations of Yeast Cell Membrane

Cytoskeleton with microtubules is the main organization structure of the eukary- otic cell. Possible sources of vibrational excitations of electrically polar cytoskeleton components are enumerated. Temperature stabilized, triple screened box (electrically and electromagnetically by mumetal) with point sensor and preampliflers was used for measurement of electrical oscilla- tions of yeast cell. Preliminary flndings of the electrical measurement and local nanomechanical AFM measurements are presented. Findings correspond to the Frolichs postulate of coherent electrically polar longitudinal vibrations in biological systems.

Anti-reflection and polarizing photonic structures for high-power fiber applications

We investigated behaviours of 1D binary diffraction gratings fabricated on optical fiber facets. Only sub-wavelength structures were considered to suppress higher diffraction orders. The aperiodic rigorous coupled wave analysis, the Fourier modal method and the finite-difference time-domain numerical methods were used to compute and optimize the modal reflectance of the investigated structures. Optimized gratings were milled on fiber facets by focused ion beam. One of the gratings was tested in a thulium-doped fiber laser where it acted as a low re ectivity polarizing output mirror. A slope efficiency of the laser and a beam quality parameter were conserved while lasing threshold slightly increased.