Механическая сканирующая зондовая нанолитография: моделирование и применение

The paper presents a study on modeling the mechanical interaction between the tip of a scanning atomic force microscope (AFM) and surfaces of various types, which makes it possible to optimize parameters and modes for mechanical AFM nanolithography. The practical assessment of mechanical nanoprobe lithography based on the method of a direct surface patterning was carried out during fabrication of functional elements for molecular electronics. Polymethine dye nanowires of a specified configuration and the cross-section 3×20 nm have been successfully formed in a multilayer polytetrafluoroethylene/gold/silicon nanostructure.В роботі представлено моделювання механічної взаємодії вістря скануючого атомно-силового мікроскопа (АСМ) з поверхнями різних типів, що дає можливість оптимізувати параметри і режими для механічної АСМ нанолітографії. Реалізовано прототип механічної нанозондової літографії за методом прямого нанесення зображення на поверхню при виготовленні функціональних елементів молекулярної електроніки. Зокрема в багатошаровій наноструктурі политетрафторетилен/золо-то/крем¬ній сформовані нитки поліметинового барвника перерізом 3х20 нм.В работе представлено моделирование механического взаимодействия острия сканирующего атомно-силового микроскопа (АСМ) с поверхностями различных типов, что дает возможность оптимизировать параметры и режимы для механической АСМ нанолитографии. Реализовано прототип механической нанозондовой литографии методом прямого нанесения изображения на поверхность при изготовлении функциональных элементов молекулярной электроники. В частности в многослойной наноструктуре политетрафторетилен / золото / кремний сформированы нити полиметиновых красителей сечением 3х20 н

Chronobiological approaches to antiangiogenic photodynamic therapy of tumors: the first experimental evaluatIon

In research of the last decade, rhythmic (circadian) variations of vascular endothelial growth factor (VEGF) production by tumors were discovered. The present paper authors have earlier synthesized and characterized a new derivative photosensitizer — an immunoconjugate of hematoporphyrin with antiVEGF antibodies. Aim: To elaborate and to test a novel modification of the photodynamic therapy of tumors (PDT) method, founding upon a timed introduction of the immunoconjugated photosensitizer to tumor-bearing animals, so that this coincides with a maximum content of VEGF in tumor tissues. Methods: Circadian variations of VEGF contents in murine transplanted tumors, Lewis lung carcinoma and sarcoma 180, were determined by ELISA method. Immunoconjugated photosensitizer concentrations in tumors were estimated by spectrofluorometry. Photoirradiation of the tumors was carried out with a red light (wavelength of 635 nm) from a semiconductor laser. Light doses were chosen, calculating on a partial inhibition of tumor growth, in order that a dependence of PDT efficiency on a daily time-moment (circadian rhythm phase) of the treatment could be observed distinctly. Results: Circadian variations of the VEGF levels in Lewis lung carcinoma and sarcoma 180 were demonstrated with the maximum at 14:00 h and the minimum at 02:00 h. Intra-abdominal introduction into tumor-bearing mice of the immunoconjugated photosensitizer resulted in a greater accumulation of the immunoconjugate in tumors at 14:00 h than at 02:00 h. Laser irradiation of carcinomas and sarcomas at 14:00 h or 02:00 h after introduction of the immunoconjugated photosensitizer to mice the day before at the same time points, induced a significantly enhanced inhibition of tumor growth in animals treated at day-time versus those treated at night-time. Conclusion: The obtained results justify further attempts to transfer principles of tumor chronochemotherapy onto photodynamic therapy

Chlorin e6 combined with albumin nanoparticles as a potential composite photosensitizer for photodynamic therapy of tumors

Aim: To synthesize and to study for photodynamic activity a composite photosensitizer consisting of chlorin e6 and human serum albumin nanoparticles (HSA NPs). Materials and Methods: Starting from sorption-purified HSA, the albumin nanoparticles with a different degree of lysine residues cross-linking (10; 20; 40, and 100%) were obtained by the coacervation method. The HSA NPs were used for synthesis of nanocomposites with chlorin e6 and fluorescein isothiocyanate (FITC)-labled preparations. Malignant lymphocytes of the MT-4 (human T-cell leukemia) line and normal lymphocytes of healthy donors served as cell targets. For photodynamic treatment, a semiconductor laser was exploited as a light source, and cell viability was assessed by MTT or trypan blue dye exclusion tests. For cell imaging and HSA NPs visualization, the fluorescence microscopy and transmission electron microscopy were applied, respectively. C57Bl/6 mice were used in animal experiments. Results: The absorption and fluorescence spectra of chlorin e6-HSA NPs composites were characterized, and by the electron microscopy investigation the size of NPs (nanospheres) was estimated: 100–120 nm. FITC-labled albumin preparations allowed to establish that HSA NPs have much higher exposition and concentration dependent affinity to malignant cell surface than initial HSA. In experiments with MT-4 cells on PDT activity of chlorin e6-HSA NPs, the nanocomposite effectiveness elevated along with increasing percentage of cross-linked aminoacid residues, and for the nanocomposite with 100% of albumin cross-linking it exceeded the activity of free chlorin e6. In contrast to malignant cells, the complexation of chlorin e6 with HSA NPs decreased its photodynamic effect on normal human lymphocytes. Intravenous introduction of the chlorin e6-HSA NPs composite to mice showed prolonged circulation of the nanocomposite in blood in comparison with free PS. Conclusion: Promising results obtained with chlorin e6-HSA NPs composites warrant conduction of full-fledged PDT studies in vivo using the nanocomposites as photosensitizers. Key Words: human serum albumin, nanoparticles, photodynamic therapy, chlorin e6, cell line MT-4, C57Bl/6 mice

Ultrasonic assisted nanomanipulations with atomic force microscope

Demonstrated experimentally in this work was the possibility of controlled handling the nanoparticles with the size from 50 up to 250 nm on a semiconductor surface by using an atomic force microscope under conditions of acoustic excitation. It has been shown that the selective transport of particles of a certain size is possible owing to the change of an ultrasonic vibration amplitude. Also in this study, possible mechanisms in which ultrasound may influence the particle-surface interaction and the probe-particle (surface) interaction have been analyzed

Influence of absorption level on mechanisms of Braggdiffracted x-ray beam formation in real silicon crystals

The methods of numerical calculations based on the formulae of the X-ray dynamic scattering theory by real crystals and of the Takagi-Topin equations were used for investigation of the basic regularities of inherent to the Bragg diffraction in conditions of a strong and weak absorption. The mechanisms of profile formation of a spatial intensity distribution of diffracted beams depending on an energy of radiation and on structural perfection parameters of crystals are discussed. The formulae for an analytical description of spatial intensity distribution profiles which take into account the dynamical corrections (coefficients of extinction) for coherent and incoherent components of the total reflectivity were used

Nanoprobe spectroscopy of capillary forces and its application for a real surface diagnostics

The paper presents an overview and analysis of the most reliable and at the same time rather simple theoretical models describing liquid nanomeniscus geometry and forces occurring between atomic force microscope (AFM) probe and a real surface. There are experimental results in capillary bridge force rupture measured in air, and interaction force under water buffer obtained over surfaces of different nature. It is shown that the theoretical models quite adequately describe the processes observed experimentally and, in particular, bridge ruptures dynamics at the vertical probe withdraw for different speeds. Discussed here are some methodological peculiarities and nanocapillary force spectroscopy diagnostic capabilities for surface energy mapping, prospects of using of a liquid nanomeniscus in local nanochemistry, nanolithography and nano-electrochemistry of a surface

Mechanical scanning probe nanolithography: modeling and application

The paper presents a study on modeling the mechanical interaction between the tip of a scanning atomic force microscope (AFM) and surfaces of various types, which makes it possible to optimize parameters and modes for mechanical AFM nanolithography. The practical assessment of mechanical nanoprobe lithography based on the method of a direct surface patterning was carried out during fabrication of functional elements for molecular electronics. Polymethine dye nanowires of a specified configuration and the cross-section 3×20 nm have been successfully formed in a multilayer polytetrafluoroethylene/gold/silicon nanostructure

Investigation of growth conditions, crystal structure and surface morphology of SmS films fabricated by MOCVD technique

The polycrystalline SmS films were fabricated by MOCVD technique using a number of ditiocarbamates, synthesized by different techniques. The growth kinetics and temperature dependencies of the film growth rate are investigated, which allowed us to determine the activation energies and the reaction type. The investigations of the structure and surface morphology of films were carried out. The technological conditions are determined providing the fabrication of single-phase SmS films of cubic modification with the most ordered crystal structure

Screen-printed p-CdTe layers for CdS/CdTe solar cells

Correlation of the recrystallization process technological parameters with the morphology and structure of screen-printed p-CdTe layers intended for CdS/CdTe solar cell fabrication has been established. The optimal regimes to form layers with required characteristics have been found. As distinct from the used previously screen-printing techniques for CdS/CdTe solar cell fabrication, CdTe layers were doped with Ag or Au not by their diffusion from the layer surface but in the course of layer preparation. For this purpose, tellurides of those metals were added into the raw paste used for CdTe screen printing. It is shown that the developed method has some advantages and allows to prepare CdTe films, structural and electrophysical parameters of which are suitable to fabricate CdS/CdTe solar cells

Direct current transport mechanisms in n-InSe/p-CdTe heterostructure

The authors created n-InSe/p-CdTe heterojunction by deposition over optical contact, investigated temperature evolution of its current-voltage dependences under the forward bias, and determined the prevailing current transport mechanisms in the structure. It was shown that misfit dislocations at the boundary between the semiconductors form a stable periodic structure acting as slow recombination centers for the carriers. The properties of the material suggest promising application perspectives for n-InSe/p-CdTe heterojunction, especially for the devices working at high temperatures and elevated radiation