D. A. Bizyaev

Nickel nanoparticles and nanowires obtained by scanning probe lithography using point indentation technique

A lithographic method of obtaining metal nanowires and nanoparticles on solid substrates is proposed, which employs a polymer mask with windows for the metal deposition formed by indentation in an atomic force microscope. Using this method, Ni nanowires with a minimum width of 60 nm, thicknesses within 6–20 nm, and lengths up to 20 μm and Ni nanoparticles with a preset ordered arrangement have been obtained on a SiO2 surface. The domain structure in obtained nanoobjects has been studied by the magnetic force microscopy technique.

Fabrication of magnetic micro- and nanostructures by scanning probe lithography

Planar magnetic structures based on cobalt nanofilms have been obtained by scanning probe lithography. It has been shown that ferromagnetic nanoparticles with different domain structures can be formed by local oxidation of a cobalt film on a graphite substrate with the use of a conductive probe of an atomic force microscope (AFM). Using AFM nanoengraving of polymethylmethacrylate, masks were formed to obtain microcontact pads connected by cobalt nanowires with a width of 250–1400 nm and a thickness of 10–30 nm on the silicon dioxide surface. The topography and magnetization structure of the obtained samples were controlled by atomic and magnetic force microscopy.

Atomic force microscopy of cobalt nanoparticles with electro-catalytic properties

A method of controlled potential electrodeposition of the cobalt nanoparticles with sizes from 30 to 400 nm on the surface of highly oriented pyrolytic graphite has been developed. The images of nanoparticles were obtained with an atomic force microscope. A computer program was applied to obtain the size distribution of electrodeposited particles depending on the electrodeposition potential, electrolytic concentration, and deposition time. Using voltammetry it has been established that the cobalt nanoparticles with the diameter of about 50 nm show the maximal catalytic activity during electro-oxidation of ethanol.

Creation of lithographic masks using a scanning probe microscope

The experimental results on scanning probe lithography (SPL)—the formation of lithographic masks using scanning probe microscope—are presented. Polymethylmethacrylate (PMMA)-based masks prepared by the SPL method are used to form metal nanoparticles of the specified sizes and shape, as well as the metallic nanowires connecting the contact areas. The analysis of various SPL modes showed that the procedure of point indentation with the switched-on microscope feedback is optimal for the formation of round nanoparticles. When forming the rectangular particles, the procedure of multiple scanning of one region in the contact mode is optimal. The quality of lithographic masks can be substantially increased by the additional use of chemical etching to remove excess PMMA after the mask is formed. The topography and magnetization structure of the formed structures were monitored by atomic force microscopy and magnetic force microscopy.

Magnetic force microscopy investigation of the magnetization reversal of permalloy particles at high temperatures

The magnetization reversal of an array of permalloy particles formed by scanning probe lithography on the silicon dioxide surface has been investigated in the temperature range from room temperature to 800 K. Using scanning magnetic force microscopy and numerical calculations of the magnetic anisotropy field of a particle at different temperatures, it has been shown that an increase in the temperature leads to a decrease in the external magnetic field required to reverse the magnetization direction of the particle. From the obtained results, it has been concluded that the magnetization reversal of the studied particles is accompanied by the formation of an intermediate state with an inhomogeneous magnetization structure.

Atomic-force microscopy of nickel nanoparticles possessing electrocatalytic properties

Surface morphology of highly oriented pyrolytic graphite with electrodeposited nickel nanoparticles was studied by atomic-force microscopy in the presence and absence of ethanol. Voltammetric and atomic-force microscopic data and histograms of particle size distribution were used to evaluate the unit-area catalytic activity of the nanocatalyst in relation to conditions of its preparation.

Magnetic structure of nickel nanowires after the high-density current pulse

Changes in the magnetic structure of nickel nanowires formed on a nonconductive surface after the high-density current pulse have been investigated using magnetic force microscopy and voltammetry. Based on the obtained experimental data and results of the computer simulation, it has been concluded that the main reason for the change in the magnetic structure is the heating of the nanowire by a current pulse. It has been shown that, during the subsequent cooling, the newly formed magnetic structure is pinned by surface roughnesses of the relief of the nanowire under investigation.

AFM study of thin films of oligopeptide L-valyl-L-valine before and after interaction with vapors

The effect of the substrate type, ambient relative humidity, water vapor and vapors of organic compounds on the surface morphology of films based on dipeptide L-valyl-L-valine are studied using atomicforce microscopy. It is found that at a low relative humidity the dipeptide is crystallized on a hydrophobic substrate with the formation of pyramidal structures, while at a high relative humidity hollow truncated cones are observed. A dipeptide film coated with irregularly shaped objects is observed on hydrophilic substrates. After saturation of the L-valyl-L-valine film with the vapors of proton-donor solvents the formation of new objects on its surface or the destruction of initial objects can occur, while water vapor does not affect the surface morphology. For proton acceptors the major factor affecting the surface morphology of dipeptide film is their energy of the hydrogen bond with proton donors. It is shown that the effect of organic vapors on the film morphology depends on the substrate type.

Determination of the curie temperature of a single Ni nanowire from the analysis of current-voltage characteristics

A new method of measuring the Curie temperature of a single nanowire located on the surface of an insulating substrate has been proposed. The method is based on the analysis of the current-voltage characteristics of the nanowire obtained at different initial temperatures of the sample. A maximum is observed on the dependence of the first derivative of the resistance on the applied power, the position of which is shifted to lower powers with increasing initial temperature. The Curie temperature is determined graphically as the temperature at zero power. The Curie temperature of a nickel nanowire formed on a SiO2/Si surface by the scanning probe lithography method has been measured. The critical current density at which the transition from the ferromagnetic to the paramagnetic state occurs has been determined.

A study of the formation of magnetically active solid dispersions of phenacetin using atomic and magnetic force microscopy

A lot of pharmaceutical substances have a poor solubility that limits their absorption and distribution to the targeted sites to elicit the desired action without causing untoward effects on healthy cells or tissues. For such drugs, new modes of delivery have to be developed for efficient and effective delivery of the drug to the target site. Formation of magnetically active solid dispersion of such drugs could be a useful approach to addressing this problem because they combine targeted delivery and good solubility. In this work, the distribution of superparamagnetic nanoparticles in the solid dispersion of polyethylene glycol with average molecular weight 950-1050 g/mol and phenacetin was studied using atomic force and magnetic force microscopy. The distribution of nanoparticles was found to be uniform in studied composites. Magnetically active solid dispersions may find application in the production of the capsulated drug delivery systems with enhanced solubility parameters.