N. I. Nurgazizov

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.

Investigation of micromagnetism and magnetic reversal of Ni nanoparticles using a magnetic force microscope

Isolated Ni nanoparticles were studied in situ by atomic and magnetic force microscopy in the presence of an additional external field up to 300 Oe. By comparing topographic and magnetic images, and also by computer modeling of magnetic images, it was established that particles smaller than 100 nm are single-domain and easily undergo magnetic reversal in the direction of the applied external magnetic field. For large magnetic particles, the external magnetic field enhances the magnetization uniformity and the direction of total magnetization of these particles is determined by their shape anisotropy. Characteristics of the magnetic images and magnetic reversal of particles larger than 150 nm are attributed to the formation of a vortex magnetization structure in these particles.

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.

AFM investigation of selective etching mechanism of nanostructured silica

Abstract We have developed the atomic force microscope (AFM) for in situ observation of SiO 2 etching in the HF aqueous solution. This work is devoted to the AFM investigation of etching of the SiO 2 surface layer modified by high-dose Fe + ion bombardment. Such samples have a two-phase nanostructure (SiO 2 containing buried Fe nanoparticles). Formation and dissociation of nanorelief during etching was observed in situ with AFM. The computer animation of this phenomenon was made with morphing of the experimental AFM images. The additional in situ registration of the optical absorption of Fe nanoparticles during etching, ex situ AFM and ferromagnetic resonance measurements enable us to propose that observed morphology transformation takes place because the etching rate of Fe nanoparticles is much higher than the SiO 2 etching rate. This etching mechanism was used for computer simulation of the AFM image transformation during etching of the model samples with buried nanoparticles. Good correlation of simulated and experimental AFM images and the corresponding surface roughness parameters vs. etching time confirms that this structural model and the mechanism of selective etching are correct.

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.

Scanning force microscopy of catalytic nickel particles prepared from carbon nanotubes

The method of scanning force microscopy (SFM) is used to study catalytic nickel nanoparticles deposited on a substrate of quartz glass by decomposition of carbon nanotubes. The SFM images so obtained were computer processed using an original numerical deconvolution algorithm which allowed us to determine the actual dimensions and shape of the nanoparticles. Nonoverlapping particles with diameters from 20 to 200 nm were recorded. Analysis of the SFM images revealed that the shape of the nickel particles is nearly spherical, which is in good agreement with transmission electron microscopy data.

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.

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.

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.

Formation of Co nanoparticles on a pyrolytic graphite surface in ultrahigh vacuum

Isolated cobalt nanoparticles have been obtained by annealing Co films produced by the electron-beam evaporation of a solid target onto a highly oriented pyrolytic graphite substrate in ultrahigh vacuum. Preliminary ion bombardment of the substrate reduces the average size of the particles formed during coalescence, but the shape of large particles is distorted. It is established that the Co nanoparticles retain their shape when exposed to air. Magnetic force images show that the particles of 20–40 nm in height are single-domain.