V. D. Frolov

Scanning probe microscopy of laser-graphitized diamond-like carbon films

A complex technique of scanning probe microscopy/spectroscopy (SPM/SPS) based on the microscopy of lateral forces and registration of a local electrical conductivity in combination with measurements of the microrelief has been developed for studies of laser-graphitized carbon microstructures. The method includes multiple direct and reverse probe scanning with the subsequent correction of the map position, their pixel-by-pixel subtraction and averaging, and a statistical processing of resulting data arrays concerning the distribution of lateral forces (friction forces). In addition, based on the measurements of currentvoltage (I–V) characteristics, a distribution of the electrical conductivity is built in the probe-sample circuit. Carbon structures based on hydrogenated diamond-like films of a-C:H type, which were deposited onto Si substrates, are used as the objects for studies. A local graphitization of the surface has been carried out by the irradiation of the films with an excimer KrF laser according to a preset microscopic pattern. Based on the resulting data, it is found that the reaction of the lateral forces (friction forces) in the laser-graphitized region is reversed to the temperature variations: when the temperature increases (from room to ∼120°C), the distribution of the friction forces shifts towards higher values and returns practically to the initial values when the temperature decreases to the initial level, which proves the influence of a water adsorbate on the friction properties of laser-graphitized regions on the film surface. It is also found that the laser-graphitized region is structurally inhomogeneous, which is proven by a decrease in the electrical conductivity from the center to the periphery.

Fabrication of graphene nanostructures by probe nanoablation

We present the results of the study of graphene nanoablation under mechanical stress of an ultrasharp (the rounding radius is ∼2 nm) tip of a scanning probe microscope (SPM)). It was found that the SPM probe contact with graphene results in average removal of 7 · 10−3−5 · 10−2 nm of film per scan, i.e., only a few carbon atoms or clusters, in the impact area. The capability of this precision nanoablation process was shown in developing graphene nanoislands and nanoribbons ∼1 µm long and ∼10 nm wide.

The determination of key factors for low-field electron emission from carbon nanostructures

A new statistical method for determining the key factors of the process of field electron emission (FEE) from nanostructures based on a comparison of the microscopic measurements of the work function of electrons with the results of a macroscopic characterization of the FEE is presented. Using the example of nanocrystalline carbon films, the possibilities of this statistical method for a quantitative estimation of the influence of the local field enhancement and the work function reduction on the FEE threshold decrease are demonstrated.

Scanning Probe Lithography of Dendrite-Like Nanostructures in Ultrathin Diamond-Like Nanocomposite Films

Dendrite-like structure growth in ultrathin diamond-like nanocomposite a-C:H,Si:O films have been studied in the course of electrically induced scanning probe lithography in the presence of a water adsorbate. The threshold magnitude of the electrical action is about 2 V, which is close to the potential of water electrolysis—1.23 V. The environment humidity crucially influences the growth of dendrite-like structures. Therefore, at a relative humidity of ~20%, hill-like protrusions occur, whereas, at a relative humidity of ~40%, some radially directed protrusions (ridges) appear and, at a relative humidity of ~60%, some branches arise from the ridges. It is established that the surface of the dendrite-like nanostructures is characterized by a higher friction force in the nanoscale when compared with the initial material under AFM testing. The growth mechanism and friction properties of the dendrite-like nanostructures are discussed.

SPM probe-assisted surface nanostructuring of boron-doped diamond

Surface modification of conductive boron-doped diamond has been conducted using the electrical field of the probe of a scanning probe microscope (SPM) at varying relative humidity (RH) of the ambient environment. It has been found that, under the action of positive polarity pulses applied to the sample via a grounded SPM probe, the sample material undergoes modification. The modification pattern depends on atmospheric RH: low (up to 32%) and high humidity values (above 35%) lead to the formation of cavities and protrusions, respectively. It has been found that the resulting protrusions exhibit temporary instability; that is, a protrusion is partially transformed into an array of nanoobjects. The mechanism of modification of boron-doped diamond–local anodic oxidation–has been discussed.

Manipulations with diamond nanoparticles in SPM: the effect of electric field of the conductive probe tip

The role of the electric field during manipulations with diamond nanoparticles on a silicon substrate by a scanning probe microscope (SPM) tip is studied. It is found that the attractive force appearing in the contact between nanodiamond and an electrically charged tip is sufficient to detach and displace a chosen nanoparticle from initial to goal position under moderate mechanical stresses of the probe to nanoparticle. The problem of the control of the tip motion trajectory during manipulations is solved by visualizing the tip trace of the sample surface. The results obtained will be used for precision positioning of single-photon emitters based on luminescent nanodiamonds in microcavities.

Laser nanoablation of graphite in argon atmosphere

The results of comparative studies of laser ablation of highly oriented pyrolytic graphite in air and in an inert medium upon exposure to nanosecond pulsed laser irradiation with an energy density in the range E = 0.4 − 3 J/cm2 are presented. It is found that the nanoablation mode is established below the evaporative ablation threshold (E < Ea ≈ 1 J/cm2) in both cases (the average ablation rate is lower than 10−3 nm/pulse); in this case, the nanoablation rate in argon is lower than in air by a factor to 6. The experimental data count in favor of the oxidation mechanism of graphite nanoablation.

Optical properties of a-C:H:Si films and their structural modifications

The measurement data on visible and UV light reflection spectra of diamondlike a-C:H:Si films and their structural modifications caused by electrical influences in a scanning probe microscope (SPM)-lithograph are presented. Numerical evaluations of the experimental data, taking into account interference effects, show that modification is of the bulk character and causes a change in the material refractive index from n ∼ 2.2 to ∼ 1.5. A decrease in the optical density of the modified material is attributed to an increase in the film porosity in the region of SPM influences.