Vida Mizariene

Synthesis and characterisation of porphyrin nanotubes obtained by ionic self-assembly

In this work, the porphyrin nanotubes were built by ionic self-assembly in acidic aqueous solution of two oppositely charged non-metal porphyrins, namely, the anionic meso-tetra (4-sulfonatophenyl) porphine dihydrochloride (TPPS4) and cationic meso-tetra (4-pyridyl) porphine (T4MPyP). The electrostatic forces between these porphyrin blocks contribute to the formation of porphyrin aggregates in the form of nanosheets and nanotubes, enhance the structural stability of these nanostructures. The nanosheets thickness approximately varies in the range of 3-15 nm and the sheets diameter up to 1 micron. Using the TEM and SEM, it was revealed that the mechanism of nanotubes formation is based on the wrapping of nanosheets in multiwall cigar-like structures. The porphyrin nanotubes obtained are hollow structures with a length from 200 nm up to 1,000 nm and have a diameter in the range of 50-140 nm with 20-40 nm thick walls. TEM images confirm a hollow tubular structure of the aggregates.

The status of ultrasonic motors in the former Soviet Union

Abstract From Western scientific publications it seems that many interesting results of the former Soviet Unions research are not known to the Western researchers because of the language barrier. The first experimental prototypes of ultrasonic motors in the former Soviet Union were designed in 1963–64 by M.E. Archangelskij, V.V. Lavrinenko and colleagues. The Research Center ‘Vibrotechnika’ started research and design of ultrasonic motors in 1969 for special applications and mode-coupled motors were designed in 1973. Nanometric resolution computer-controlled positioning systems were developed before 1990. This paper discusses 25 years of ultrasonic motor research and engineering in the former Soviet Union from 1970 to today.

Porphyrin controlled anisotropic and dendritic growth of thallium chloride crystals

In this work, the morphology of TlCl crystals grown at the liquid-liquid interface between Tl2SO4 and HCl solutions was investigated in the presence of various porphyrin molecules. The addition of the tetrakis(4-sulfonatophenyl)porphyrin (TPPS2) molecules changed the TlCl morphology from spherical shape to single-crystalline strips with a diameter of 100-3,000 nm. The addition of meso-tetra(4-pyridyl)porphine (TPPyP) changed morphology of TlCl crystals into branching dendrites. The presence of the different porphyrins molecules in the crystallisation medium significantly influenced the morphology of the crystals. Crystals of TlCl with elongated rod-type or branching superstructures were nucleated with high aspect ratios depending on porphyrin type that was used. The composition and microstructure of dendrites was investigated by X-ray technique, SEM and atomic force microscopy (AFM). The wires were produced by elongation and stacking of planar TlCl crystals exhibiting (100) faces. The anisotropic growth behaviour causing the wire formation is tentatively ascribed to stepwise capping of the specific surfaces of TlCl crystals by porphyrin molecules.

Ultrasonic surface vibration investigation by atomic force microscopy

Abstract This study presents a novel method to study ultrasonic surface vibrations and ultrasound influence on the surface topography image obtained by atomic force microscope (AFM). The vibrations of piezoelectric plate in the frequency range of 10–200 kHz were investigated. The experiments show the possibility of using the AFM for the detection of acoustic waves and the measurement of the amplitude of vibrations and the distribution of electric field in a piezoplate. Influence of the ultrasonic surface vibrations on AFM tip-surface interaction was noticed. Lateral surface vibrations reduced the tip-surface adhesion down to zero. Experimental results show that the AFM cantilever in the presence of vibrations has a lateral vibration mode coupled with a normal vibration mode. It increased the contrast of an image obtained in the lateral force mode.

State-of-the-art ultrasonic micromotors and their future applications

Piezoelectric actuators and ultrasonic motors have advanced enormously since their beginnings over 25 years ago. They offer advantages of low speed, low inertia and high torque operation without the need for gearboxes. They are now successfully competing with conventional electromagnetic motors in applications requiring small positioning motors. Ultrasonic stepper motors and piezoactuators have not competitors in the field of ultraprecision positioning drives. Ultrasonic motors convert high frequency vibrations of a structure excited by piezoelectric elements into rotor or slider motion by a frictional drive. This principle has been configured into many embodiments, giving rapid response times, holding torque without power applied and potentially silent motion. Their miniaturization for use in MEMS (microelectromechanical systems), microrobotics and the watch industry is particularly exciting, since they have a simple construction and excellent performance for their size. Ultrasonic motors have the potential to meet space research needs as actuators for telerobotics applications. The current difficulties in designing high performance ultrasonic motors are associated with the lack of complete models and general design rules, especially in the analysis of the frictional drive between the rotor and stator. The technical problems associated with required tolerances in construction, bonding piezoelectric materials to a stator structure and the performance of different friction layer materials are not completely solved. This work discusses the state-of -the-art ultrasonic miniature motors research, commercial application and future trends.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Atomic force microscopy investigation of supramolecular self-assembly of the porphyrin nanotubules

Structure and morphology of porphyrin aggregates and influence of temperature, microwave and ultraviolet radiation, and acoustic cavitation on aggregation process were investigated using absorption spectroscopy and atomic force microscopy. In ambient conditions TPPS4 forms stick-like J-aggregates with length of 0.05-3 μm, width 22-50 nm and height 4-5 nm. Increased temperature or MW and UV radiation does not influence the aggregates. Acoustic cavitation leads to destruction of stick-shaped aggregates and activates the formation of larger molecular complexes.

Materials surface topography and composition imaging using dynamic atomic force microscopy

A new technique has been developed to probe the surface microtopography an the viscoelastic properties with the nanometric resolution using the vibrating modes of Scanning Probe Microscopy. Weak cantilevers, although having good force sensitivity, have found limited use for investigating of materials nanomechanical properties by conventional force modulation and intermittent contact atomic force microscopy. This is due to low forces and indentations that these cantilevers are able to exert on the surface and high amplitudes needed to overcome adhesion to the surface. Here it is shown that by employing electrostatic forcing of cantilever the imaging of local elastic properties of surface and subsurface layers can be carried out. Also, by mechanically exciting the higher vibration modes in contact or intermittent contact with the surface and monitoring the phase of vibrations, the contrast due to local surface elasticity together with surface microtopography is obtained.

Vibration measurement by atomic force microscopy with laser readout

Micromachined cantilever beams are widely used for different microengineering and nanotechnology actuators and sensors applications. The micromechanical cantilever tip-based data storage devices with reading real data at the rates exceeding 1Mbit/s have been demonstrated. The vibrational noise spectrum of a cantilever limits the data storage resolution. Therefore the possibility to measure the microvibrations and acoustic fields in different micromachined devices are of great interest. We describe a method to study a micromechanical cantilever and surface vibrations based on laser beam deflection measurements. The influence of piezoelectric plate vibrations and the tip- surface contact condition on the cantilever vibrations were investigated in the frequency range of 1-200 kHz. The experiments were performed using the measurement results. The V-shaped cantilevers exited by the normal vibrations due to the non-linearity at the tip-surface contact vibrates with a complex motion and has a lateral vibration mode coupled with normal vibration mode. The possibility to use laser deflection technique for the vibration measurements in micromachined structures with nano resolution is shown.