V. A. Skryshevsky

Evaluation of quantum efficiency of porous silicon photoluminescence

The influence of photoluminescence of top porous silicon layer on deep p-n junction photocurrent is studied. The measurement of additional photocurrent caused by adsorption of porous silicon emission is shown to allow evaluation of the external quantum efficiency of photoluminescence. This can reach approximately 4% on n-Si upon illumination by the short wavelength tail of air mass (AM) 1.5 spectra.

Charge-driven selective localization of fluorescent nanoparticles in live cells

Covalent grafting of amino groups onto the carboxylic acid functionalities, naturally covering the surface of fluorescent nanoparticles produced from silicon carbide (SiC NPs), allowed tuning of their surface charge from negative to highly positive. Incubating 3T3-L1 fibroblast cells with differently charged SiC NPs demonstrates the crucial role of the charge in cell fluorescent targeting. Negatively charged SiC NPs concentrate inside the cell nuclei. Close to neutrally charged SiC NPs are present in both cytoplasm and nuclei while positively charged SiC NPs are present only in the cytoplasm and are not able to move inside the nuclei. This effect opens the door for the use of SiC NPs for easy and fast visualization of long-lasting biological processes taking place in the cell cytosol or nucleus as well as providing a new long-term cell imaging tool. Moreover, here we have shown that the interaction between charged NPs and nuclear pore complex plays an essential role in their penetration into the nuclei.

Impact of cell division on intracellular uptake and nuclear targeting with fluorescent SiC-based nanoparticles

Semiconductor nanoparticles (NPs) became important and wide-used tool for cell imaging because of their unique remarkable properties. Nevertheless, all previous investigations in this area were done on proliferating cells. For the first time, this work demonstrates strong influence of cell active proliferation/contact inhibition of proliferation on uptake of NPs. In addition, we show that cell division plays key-role in penetration of silicon carbide based NPs (SiC NPs) inside the cell nucleus. This may very likely concern other types of NPs able to reach the cell nuclei. In particular, observed effect of cell division gives perspectives for future selective cancer treatment with NPs.

Investigation of the solar cell emitter quality by LBIC-like image techniques

Abstract The distributed properties of solar cell emitters and p–n junctions such as sheet resistance, local potential and shunt resistance were studied by original methods based on the laser scanning technique. To study the shunt resistance defects the dynamical optical reflectance thermography technique has been developed thanks to new possibilities of signal treatment and 2D scanning. The experimental factors that influence on PV LBIC-like signal are analyzed. It is shown that the information about the local potential and sheet resistance distribution is contained in the LBIC-like signal measured in the galvanostatic circuit and extracted by comparison of the signal distributions obtained under different applied voltage and laser beam parameters. The samples of the mapping of the resistive properties are presented for multicrystalline silicon solar cells without and with selective porous silicon antireflection coating.

Extraction of ultraviolet emitting silicon species from strongly hydrogenated nanoporous silicon

Ultraviolet emitting silicon species were extracted from strongly hydrogenated porous silicon nanostructures. Their photoluminescence spectra depend on size distribution of the species and can be tuned by centrifugation. Molecular structure of the extracted Si species is assumed to be very similar to some kinds of polysilanes which were theoretically described earlier by Allan et al. [Phys. Rev. B 48, 7951 (1993)]. Absence of photoluminescence signal coming from the polysilanes in the initial porous nanostructures is supposed to be due to the competitive absorption and to the energy transfer between the polysilanes and Si red emitting porous nanoparticles.

Vapor phase mediated cellular uptake of sub 5 nm nanoparticles

Nanoparticles became an important and wide-used tool for cell imaging because of their unique optical properties. Although the potential of nanoparticles (NPs) in biology is promising, a number of questions concerning the safety of nanomaterials and the risk/benefit ratio of their usage are open. Here, we have shown that nanoparticles produced from silicon carbide (NPs) dispersed in colloidal suspensions are able to penetrate into surrounding air environment during the natural evaporation of the colloids and label biological cells via vapor phase. Natural gradual size-tuning of NPs in dependence to the distance from the NP liquid source allows progressive shift of the fluorescence color of labeled cells in the blue region according to the increase of the distance from the NP suspension. This effect may be used for the soft vapor labeling of biological cells with the possibility of controlling the color of fluorescence. However, scientists dealing with the colloidal NPs have to seriously consider such a NPs natural transfer in order to protect their own health as well as to avoid any contamination of the control samples.

AN AFM INVESTIGATION OF SURFACE ENERGY OF PENTACENE FILMS ON PARYLENE-C AND BENZOCYCLOBUTENE

In view to put in light morphology peculiarities of pentacene, the widely used material for organic transistors, a detailed atomic force microscopy (AFM) investigation of the pentacene growth mode in relationship with the film thickness (in the range 6–60 nm) is reported. Local surface energy measurements based on contact AFM spectroscopy were performed to explain the thickness dependent morphology of the pentacene films onto two polymer dielectrics (parylene-C and benzocyclobutene). Our analysis provided an exhaustive description not only of the accessible film surface but also of its inner structural properties. Evidenced by these approaches, a critical thickness of 30 nm was found in relation with a transition from the orthorhombic thin film phase to triclinic bulk phase for pentacene growth on parylene-C and benzocyclobutene. This thickness was previously observed to be corresponding to organic field effect transistors (OFETs) with optimized mobility.

Effect of thermal treatment and ageing on IR transmission and visible photoluminescence of nanostructured aluminum oxyhydroxide

IR transmission and visible photoluminescence (PL) were studied in raw nanoporous aluminum oxyhydroxide (NOA) and in samples after thermal treatment at different temperatures. Structural and chemical modifications of the NOA sample were related to the water content and adsorption/desorption process at the surface. The differences observed in the FTIR spectra in vacuum and after ageing of the samples can be explained by the effects of molecular water and OH− groups on the stability of the low-temperature phases of NOA. A considerable increase in PL intensity and spectrum expansion to longer wavelengths were observed in all NOA samples after water desorption. This was accompanied by strong changes in the PL decay kinetics. Quenching of the fast luminescent decay and low-energy transitions in aged samples were observed after ageing of the samples. Partial passivation of the NOA surface and defective sites under ambient conditions is discussed.

SELF-ASSEMBLY ARCHITECTURES OF NEW DNA-BASED STRUCTURES IN AIR AND IN LIQUIDS ANALYZED BY ATOMIC FORCE MICROSCOPY

The architecture of self assembled X shaped DNA structure was studied by AFM on mica. The dimensions and extent of self assembled structures were influenced by mica surface treatment and depended on whether observations were performed in air or in Tris buffer solution. A molecular model is proposed.

Laser scanning for sensing and study the operation of semiconductor devices

Advanced scanning technique on the base of laser microscope and evaluation of the induced photovoltaic (PV) signal is discussed. It is able to obtain non-destructively the 2D distribution of the several important parameters of semiconductor PV devices such as surface potential, sheet resistance, efficiency and losses of energy conversion, nanosize deviations of their layers.