Boris Polyakov

University of Latvia | LU · Institute of Solid State Physics

Core-shell nanowires is an interesting and perspective class of radially heterostructured nanomaterials where epitaxial growth of the shell can be realized even at significant core-shell lattice mismatch. In this study epitaxial hexagonally-shaped shell consisting of WS2 nanolayers was grown on {1-100} facets of prismatic wurtzite-structured [0001]...

Hybrid nanostructures composed of layered materials have recently attracted a lot of attention due to their promising electronic and catalytic properties. In this study, we describe a novel synthesis strategy of ZnO/ZnS/MoS2 core-shell nanowire growth using a three-step route. First, ZnO nanowire array was grown on a silicon wafer. Second, the samp...

Layered 2D van der Waals (vdW) materials such as graphene and transition metal dichalcogenides have recently gained a great deal of scientific attention due to their unique properties and prospective applications in various fields such as electronics and optoelectronics, sensors and energy. Asa direct bandgap semiconductor in both bulk and monolaye...

During the synthesis of heterostructured nanomaterials, unwanted structural and morphological changes in nanostructures may occur, especially when multiple sequential growth steps are involved. In this study, we describe a synthesis strategy of heterostructured ZnS/Al2O3/MoS2 core-shell nanowires (NWs), and explore the role of the Al2O3 interlayer...

One-dimensional (1D) nanostructures – nanowires (NWs) – exhibit promising properties for integration in different types of functional devices. Their properties can be enhanced even further or tuned for a specific application by combining different promising materials, such as layered van der Waals materials and conventional semiconductors, into 1D-...

In this critical review, we call attention to a widespread problem related to the vast disagreement in elastic moduli values reported by different authors for nanostructures made of the same material. As a particular example, we focus on ZnO nanowires (NWs), which are among the most intensively studied nanomaterials due to their remarkable physical...

β-Ga2O3 thin films grown on widely available c-plane sapphire substrates typically exhibit structural defects due to significant lattice and thermal expansion mismatch, which hinder the use of such films in electronic devices. In this work, we studied the impact of a nucleation layer on MOCVD-grown β-Ga2O3 thin film structure and morphology on a c-...

Combining defect semiconductors Ga2S3 and Ga2Se3 in Ga2O3-based heterostructured nanowires (NWs) have potential in photonics and optoelectronics applications due to the materials appealing optical properties. In this work, we have developed and studied Ga2O3-Ga2S3 and, for the first time, Ga2O3-Ga2Se3 core-shell NWs. Ga2S3 and Ga2Se3 shell was obta...

Layered two-dimensional (2D) materials, such as p-type WSe2, are potential key materials in the manufacture of the next generation electronic devices. One of the remaining main challenges is the large area growth of high-quality films. A potential large-scale 2D WSe2 synthesis method is conversion (selenization) of a pre-deposited sacrificial precu...

Bulk rhenium trioxide (ReO3) has an unusually high electrical conductivity and, being nanosized, has promising catalytic properties. However, the production of pure ReO3 thin films is challenging due to the difficulty to stabilize rhenium in a 6+ oxidation state. Here we present a novel approach for the deposition of ReOx (x ≈ 1.6–2.9) thin films u...

During the synthesis of heterostructured nanomaterials, unwanted structural and morphological changes in nanostructures may occur, especially when multiple sequential growth steps are involved. In this study, we describe a synthesis strategy of heterostructured ZnS/Al2O3/MoS2 core-shell nanowires (NWs), and explore the role of the Al2O3 interlayer...

One-dimensional (1D) nanostructures - nanowires (NWs) - exhibit promising properties for integration in different types of functional devices. Their properties can be enhanced even further or tuned for a specific application by combining different promising materials, such as layered van der Waals materials and conventional semiconductors, into 1D-...

Tungsten trioxide (WO3) is a well-known electrochromic material with a wide band gap, while rhenium trioxide (ReO3) is a “covalent metal” with an electrical conductivity comparable to that of pure metals. Since both WO3 and ReO3 oxides have perovskite-type structures, the formation of their solid solutions (ReO3–WO3 or RexW1–xO3) can be expected, w...

Transition metal dichalcogenide (TMD) MoS2 and WS2 monolayers (MLs) deposited atop of crystalline zinc oxide (ZnO) and graphene-like ZnO (g-ZnO) substrates have been investigated by means of density functional theory (DFT) using PBE and GLLBSC exchange-correlation functionals. In this work, the electronic structure and optical properties of studied...

The growth direction of nanowires (NWs) can change during synthesis as a result of stochastic processes or modulation of certain growth conditions. This phenomenon is known as kinking. Although deviations from a uniform vertical growth are typically considered to be undesirable, kinking opens a route for additional tweaking of the characteristics a...

The development of nanoscale X-ray sensors is of crucial importance to achieve higher spatial resolution in many X-ray-based techniques playing a key role in materials science, healthcare, and security. Here, we demonstrate X-ray detection using individual CdS, SnO2, and ZnO nanowires (NWs). The NWs were produced via vapor–liquid–solid technique an...

Thin films of rhenium trioxide (ReO3) were produced by reactive DC magnetron sputtering from metallic rhenium target followed by annealing in the air in the range of temperatures from 200○C to 350○C. Nanocrystalline single-phase ReO3 films were obtained upon annealing at about 250○C. The thin films appear bright red in reflected light and blue-gree...

In the present paper, we investigate the effect of heat treatment on the geometry and mobility of Au nanoparticles (NPs) on a Si substrate. Chemically synthesized Au NPs of diameter ranging from 5 to 27 nm were annealed at 200, 400, 600 and 800 °C for 1 h. A change in the geometry from faceted to more rounded shapes were observed with increasing an...

In this study, pentagonal Ag and Au nanowires (NWs) were bent in cantilever beam configuration inside a scanning electron microscope. We demonstrated an unusual, abrupt elastic-to-plastic transition, observed as a sudden change of the NW profile from smooth arc-shaped to angled knee-like during the bending in the narrow range of bending angles. In...

In this study, pentagonal Ag and Au nanowires (NWs) were bent in cantilever beam configuration inside a scanning electron microscope. We demonstrated unusual abrupt elastic-to-plastic transition, observed as sudden change of the NW profile from smooth arc-shaped to angled knee-like during the bending in the narrow range of bending angles. In contra...

In the present paper we investigate the effect of heat-treatment on geometry and mobility of Au nanoparticles (NPs) on Si substrate. Chemically synthesized Au nanoparticles with median diameter of 14 nm were annealed at 200°C, 400°C, 600°C and 800°C for 1 hour. Geometry changes from faceted towards more rounded shapes were observed already for 200...

Mechanical characterisation of individual nanostructures is a challenging task and can greatly benefit from the utilisation of several alternative approaches to increase the reliability of results. In the present work, we have measured and compared the elastic modulus of five-fold twinned gold nanowires (NWs) with atomic force microscopy (AFM) inde...

Polydimethylsiloxane (PDMS) is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological properties. PDMS has found extensive usage in various fields ranging from microfluidics and flexible electronics to cosmetics and food industry. In certain applications, like e.g. dry adhesives or dry transfer of...

The surface plays an exceptionally important role in nanoscale materials, exerting a strong influence on their properties. Consequently, even a very thin coating can greatly improve optoelectronic properties of nanostructures by modifying the light absorption and spatial distribution of charge carriers. To use these advantages, 1D/1D heterostructur...

High surface energy of individual nanostructures leads to high adhesion and static friction that can completely hinder the operation of nanoscale systems with movable parts. For instance, silver or gold nanowires cannot be moved on silicon substrate without plastic deformation. In this paper we experimentally demonstrate the operational prototype o...

In recent years, nanowires have been shown to exhibit high photosensitivities, and, therefore are of interest in a variety of optoelectronic applications, for example, colour-sensitive photodetectors. In this study, we fabricated two-terminal PbS, In 2 S 3 , CdS and ZnSe single-nanowire photoresistor devices and tested applicability of these materi...

The proper choice of coating materials and methods in core-shell nanowire (NW) engineering is crucial to assuring improved characteristics or even new functionalities of the resulting composite structures. In this paper, we have reported electron beam-induced reversible elastic-to-plastic transition in Ag/Al2O3 and Au/Al2O3 NWs prepared by coating...

A comparative study of heterostructured CuO/CuWO4 core/shell nanowires and double-layer thin films was performed through X-ray diffraction, confocal micro-Raman spectroscopy and electron (SEM and TEM) microscopies. The heterostructures were produced using a two-step process, starting from a deposition of amorphous WO3 layer on top of CuO nanowires...

Metallic nanowires are known to break into shorter fragments due to the Rayleigh instability mechanism. This process is strongly accelerated at elevated temperatures and can completely hinder the functioning of nanowire-based devices like e.g. transparent conductive and flexible coatings. At the same time, the arranged gold nanodots have important...

Development of methods for direct delivery of different bioactive substances into the cell is a promising and intensively approached area of research. It has become a subject of serious research for multidisciplinary team of scientists working in such areas as physics, biology, and biotechnology. Plant calluses were grown on medium supplemented wit...

In this study, we performed finite element method simulations to investigate the effect of the structure on the elastic response of Ag and Au nanowires (NWs) with a fivefold twinned crystal structure in bending tests. Two different models of a pentagonal NW were created: a 'uniform model' having an isotropic continuous structure and a 'segmented mo...

In this work, we investigate the influence of doping on the mechanical properties of ZnO nanowires (NWs) by comparing the mechanical properties of pure and Co-doped ZnO NWs grown in similar conditions and having the same crystallographic orientation [0001]. The mechanical characterization included three-point bending tests made with atomic force mi...

In the present work, we demonstrate a novel approach to nanotribological measurements based on the bending manipulation of hexagonal ZnO nanowires (NWs) in an adjustable half-suspended configuration inside a scanning electron microscope. A pick-and-place manipulation technique was used to control the length of the adhered part of each suspended NW....

Strong enhancement of photoluminescence is demonstrated for CdS nanocrystals and rutheniumbased dye (N719) due to localized surface plasmon resonance of silver nanowires placed on silver film. Alternative reasons for photoluminescence modulation such as mirror effect and uneven coating by dye or nanocrystals due to geometrical factors are discussed...

Nanomanipulation experiments were carried out on nanodumbbells (NDs) to study their kinetic behavior and tribological properties. Ag, Au and Cu NDs were produced by laser-induced melting of corresponding nanowires (NWs). NDs were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Manipulation experiments...

In this paper we report an electron beam induced rapid (up to several tens of nm/s) growth of silver nanowhiskers from silver nanowire networks coated with TiO2 by sol-gel method. Different growth conditions are tested and it is demonstrated that growth is optimal for samples with the film thickness in the range 50-200 nm and previously annealed at...

The genotoxic effect of cadmium sulfide nanoparticles (CdS NPs) of different sizes in rucola ( Eruca sativa Mill.) plants was assessed. It was confirmed that nanoparticles < 5 nm in size were more toxic than larger particles at an identical mass concentration. Significant differences in cell ploidy, as well as in the mitotic index, were detected be...

This chapter is dedicated to manipulation of nanostructures inside a scanning electron (SEM) microscope employed for real-time tribological measurements. Different approaches to force registration and calculation of static and kinetic friction are described. Application of the considered methodology to Au and Ag nanoparticles, as well as ZnO and Cu...

The mechanical properties of thick-walled SiO2 nanotubes (NTs) prepared by a sol–gel method while using Ag nanowires (NWs) as templates were measured by using different methods. In situ scanning electron microscopy (SEM) cantilever beam bending tests were carried out by using a nanomanipulator equipped with a force sensor in order to investigate pl...

The combination of two different materials in a single composite core-shell heterostructure can lead to improved or even completely novel properties. In this work we demonstrate the enhancement of the mechanical properties of silver (Ag) nanowires (NW) achieved by coating them with a silica (SiO2) shell. In situ scanning electron microscope (SEM) n...

In this paper, metal nanodumbbells (NDs) formed by laser-induced melting of Ag nanowires (NWs) on an oxidized silicon substrate and their tribological properties are investigated. The mechanism of ND formation is proposed and illustrated with finite element method simulations. Tribological measurements consist in controllable real-time manipulation...

In this work polyhedron-like gold and sphere-like silver nanoparticles (NPs) were manipulated on an oxidized Si substrate to study the dependence of the static friction and the contact area on the particle geometry. Measurements were performed inside a scanning electron microscope (SEM) that was equipped with a high-precision XYZ-nanomanipulator. T...

In this work irradiation caused changes in individual silver nanowires and silver nanowire meshes have been investigated. Commercially available silver nanowires were deposited on glass and silicon substrates. The concentration of Ag nanowire solution and deposition stages were varied to achieve dispersed deposition of nanowires and interconnected...

h i g h l i g h t s Mechanical properties of pentagonal silver nanowires were measured. Cantilevered beam bending technique was used. Measurements were performed inside a scanning electron microscope. Young's modulus and yield point were calculated. Both plastic deformation and fracture of nanowires were observed. a b s t r a c t This paper reports...

Highly oriented pyrolytic graphite (HOPG) was scribed by pulsed laser beam to produce square patterns. Patterning of HOPG surface facilitates the detachment of graphene layers during contact printing. Direct HOPG-to-substrate and glue-assisted stamp printing of a few-layers graphene was compared. Printed graphene sheets were visualized by optical a...

Elastic and tribological properties of zinc oxide nanowires (NWs) on Si wafer and highly oriented pyrolytic graphite (HOPG) are experimentally investigated and theoretically interpreted. Measurements are performed inside a scanning electron microscope (SEM) using real-time manipulation technique that enables two possible ways of data registration:...

Young’s modulus and the bending strength of copper oxide and zinc oxide nanowires (NWs) were measured in situ using nanomanipulation techniques inside a scanning electron microscope (SEM). Young’s modulus was measured by bending half-suspended NWs and simultaneously measuring the force using a sensor based on a quartz tuning fork. Bending strength...

PbS nanodots embedded in a zirconium oxide nanofilm were explored as possible ultraviolet (UV) sensors for nanodosimetry purposes. The nanodots were excited by ultraviolet photons to get emission of weak electrons. The emitted charge correlated to UV exposure indicates that PbS nanodots have potential for use as UV sensors for nanodosimetry.

The dependence of static friction on surface roughness was measured for copper oxide nanowires on silicon wafers coated with amorphous silicon. The surface roughness of the substrate was varied to different extent by the chemical etching of the substrates. For friction measurements, the nanowires (NWs) were pushed by an atomic-force microscope (AFM...

Colloidal suspensions of CdS, PbS, Cu2S, Ag2S and ZnO nanocrystals were prepared by chemical route in presence of organic capping ligands. The formation of nanocrystals was studied by using UV-visible absorption spectroscopy. Kelvin probe measurements of work function were performed on nanocrystals thin film on ITO (indium tin oxide) coated glass.

Amorphous Si thin films deposited on thermally oxidized Si wafers have been processed by the 2nd and 3rd harmonics of Nd:YAG laser. Surface modification of amorphous silicon layers have been investigated by scanning electron microscopy before and after chemical etching of processed silicon films. The super-lateral crystal growth regime was achieved...

A novel method for in situ measurement of the static and kinetic friction is developed and demonstrated for zinc oxide nanowires (NWs) on oxidised silicon wafers. The experiments are performed inside a scanning electron microscope (SEM) equipped with a nanomanipulator with an atomic force microscope tip as a probe. NWs are pushed by the tip from on...

Friction forces for a nanowire (NW) elastically bent on flat substrate were investigated both theoretically and experimentally. Models based on elastic beam theory were proposed considering balance of external, frictional, and elastic forces along the NW. The distributed friction force was determined for two cases: (i) the NW was uniformly dragged...

A novel method for measuring the kinetic friction force in situ was developed for zinc oxide nanowires on highly oriented pyrolytic graphite and oxidised silicon wafers. The experiments were performed inside a scanning electron microscope and used a nanomanipulation device as an actuator, which also had an atomic force microscope tip attached to it...

Pure amorphous Si thin films deposited on oxidized crystalline Si surface (111) were crystallized by picosecond UV laser pulses. The Raman scattering spectra show that pulse energy of 330 mJ/cm2 is enough to fully crystallize Si film and further increase of the energy does not improve crystallinity. A large grained polycrystalline Si was obtained a...

A real-time nanomanipulation technique inside a scanning electron microscope (SEM) has been used to investigate the elastic and frictional (tribological) properties of zinc oxide nanowires (NWs). A NW was translated over a surface of an oxidised silicon wafer using a nanomanipulator with a glued atomic-force microscopic tip. The shape of the NW ela...

Amorphous Si thin films deposited on oxidized crystalline Si surface (111) were crystallized by thermal annealing and nanosecond green laser pulses. The Raman scattering spectra show that thermal annealing can provide nearly fully crystallized poly-Si film. Laser crystallization of amorphous Si is more flexible crystallization method, but it is mor...