Surface Of Flakes Research Articles

Controlled CVD growth of ultrathin Mo2C (MXene) flakes

MXenes combine distinctive properties, including high electrical conductivity, high thermal conductivity, and efficient absorption of electromagnetic waves, which allow them to be utilized in various applications such as electrical energy storage, sensors, and functional composites. This study aims to grow thin and large area Mo2C flakes in a controlled manner by using chemical vapor deposition, avoiding surface functionalization, and limited lateral dimensions. Herein, we investigate the effects of CH4 flow, the precursor/catalyst (Mo/Cu) ratio, and flow rates of carrier gas on the growth of two-dimensional Mo2C structures. This study examines the effects of the precursor/catalyst (Mo/Cu) ratio and flow rates of carrier gas on the growth of Mo2C structures. Our results show that when the flow rates of CH4, catalyst/precursor (Cu/Mo) ratio, and carrier gas (N2/H2) ratio are varied, we can control both thickness (from 7 to 145 nm) and coverage of the substrate surface (from 11% to 68%) of the Mo2C flakes. Therefore, this study reveals that it is possible to realize centimeter-scale surface coverage and controllable thicknesses by adjusting the process parameters. The deposited films and flakes are analyzed by optical microscopy, atomic force microscopy, and Raman scattering spectroscopy techniques. The Raman spectra are also compared with the theoretical calculations using density functional theory. Overall, the present work is expected to provide a significant impact for utilization of MXenes in various applications.

Direct graphene synthesis on Si(1 0 0) by inductively coupled plasma beam source

The graphene was synthesized directly on the Si(100) substrate by an Inductively Coupled Plasma Beam Source without any catalyst. Plasma power, methane gas flow, hydrogen gas flow, temperature and time effects on graphene layers number and flake size, defects density, and surface morphology were studied. Prevailing defects type was considered. Boundary defects dominated in most samples due to the polycrystalline nature of the directly synthesized graphene. However, high methane gas flows, low synthesis times, and low synthesis temperatures were beneficial for the hydrogenation of the growing graphene. On-site defects prevailed in these samples. It was found that synthesis power, temperature, and time should be optimized to avoid out-of-plane graphene growth. An additional hydrogen gas flow effectively controlled graphene layers number. D + D‘ and D + D“ peaks were explored. It was supposed that the D + D‘ peak is mainly related to the on-site defects associated with a hydrogen atom bonded to the carbon atom in the graphene sheet. The line-of-sight graphene deposition was demonstrated. The main graphene growth-related physical and chemical processes were considered. The observed results were explained by a competition between graphene growth, hydrogen etching, hydrogenation, and thermal stress release.

Elastic interface in few‐layer graphene/poly(vinylidenefluoride‐trifluoroethylene‐chlorofluoroethylene) nanocomposite with improved polarization

AbstractPolymer film capacitor exhibits extensive applications in advanced electronics because of its flexibility and huge power density. The current research interests of polymer capacitor are addressed on large energy density and high charge–discharge efficiency of composite film. Here we developed the compatible elastic interface composed of hyperbranched poly(methyl acrylate) copolymer in graphene/poly(vinylidenefluoride‐trifluoroethylene‐chlorofluoroethylene) (P(VDF‐TrFE‐CFE)) nanocomposite with high energy capability. This hyperbranched copolymer comprising polyethylene core that was grafted with poly(methyl acrylate) (PMA) segments and pyrene units was synthesized by atom transfer radical polymerization. The few‐layer graphene was exfoliated with assistance of hyperbranched copolymer that was attached on surface of flakes via π‐π non‐covalent interactions between pyrene groups and delocalized π electrons of nanosheets. Graphene/P(VDF‐TrFE‐CFE) nanocomposite film was prepared by solution casting method. The compatibility between graphene and fluoropolymer is greatly improved due to the elastic interphase of PMA segments in hyperbranched copolymer, which enhances the interfacial polarization and decreases the accumulation of charge carriers under high electric field. The energy density of 7.0 J/cm3 with charge–discharge efficiency of 60% at 300 MV/m is achieved for 0.1 wt% nanocomposite. This work reveals an effective architecture of polymer composite with elastic interface to increase the energy capability of polymer dielectric film.

Polycaprolactone Adsorption and Nucleation onto Graphite Nanoplates for Highly Flexible, Thermally Conductive, and Thermomechanically Stiff Nanopapers.

Free-standing nanopapers based on graphene and its related materials have been widely studied and proposed for flexible heat spreader applications. Given that these materials are typically brittle, this work reports the exploitation of polycaprolactone (PCL) as a polymer binder to enhance resistance and flexibility of nanopapers based on graphite nanoplates (GNP), while maintaining a high thermal conductivity. Properties of nanopapers appear to correlate with the excellent PCL adhesion and strong nucleation of the surface of GNP flakes. Furthermore, different crystalline populations were observed for PCL within the nanopaper and were investigated in detail via differential scanning calorimetry advanced techniques and X-ray diffraction. These demonstrated the coexistence of conventional unoriented PCL crystals, oriented PCL crystals obtained as a consequence of the strong nucleation effect, and highly stable PCL fractions explained by the formation of crystalline pre-freezing layers, the latter having melting temperatures well above the equilibrium melting temperature for pristine PCL. This peculiar crystallization behavior of PCL, reported in this paper for the first time for a tridimensional structure, has a direct impact on material properties. Indeed, the presence of high thermal stability crystals, strongly bound to GNP flakes, coexisting with the highly flexible amorphous fraction, delivers an ideal solution for the strengthening and toughening of GNP nanopapers. Thermomechanical properties of PCL/GNP nanopapers, investigated both on a heating ramp and by creep tests at high temperatures, demonstrated superior stiffness well above the conventional melting temperature of PCL. At the same time, a thermal conductivity > 150 W/m·K was obtained for PCL/GNP nanopapers, representing a viable alternative to traditional metals in terms of heat dissipation, while affording flexibility and light weight, unmatched by conventional thermally conductive metals or ceramics. Besides the obtained performance, the formation of polymer crystals that are stable above the equilibrium melting temperature constitutes a novel approach in the self-assembly of highly ordered nanostructures based on graphene and related materials.

Mineral foraging and etching by the fungus Talaromyces flavus to obtain structurally bound iron

Fungi possess remarkable abilities to acquire mineral nutrients through foraging for and weathering minerals, and these fungal behaviors are influenced by the physiochemical properties of the minerals. Here, we investigated the dynamic processes underlying these behaviors in the interactions between the common fungus Talaromyces flavus and two serpentine minerals (antigorite and lizardite) and quartz as a control. In the culture of T. flavus on solid Czapek medium with these minerals, we found that the elongation rates of T. flavus hyphae toward antigorite and lizardite particles were similar, and both were much higher than those toward quartz particles. After reaching the minerals, the growth of T. flavus was promoted significantly by antigorite and lizardite. Atomic force microscopy measurements uncovered the production of distinct dissolution channels with a depth of 29.34 ± 6.18 nm on the lizardite surface, but no local dissolution was found on the antigorite surface. Laser ablation multicollector inductively coupled plasma mass spectrometric analysis indicated that the total Fe in T. flavus hyphae grown on the surfaces of lizardite and antigorite flakes was ~8.3 and 2.3 times, respectively of those grown on the surface of medium. Whewellite was ubiquitously found at the hyphal tips and their vicinity during T. flavus interactions with lizardite. These results demonstrate that fungal hyphae have a remarkable capacity to sense and respond to minerals and to extract structurally bound inorganic nutrients, and highlight that the instant weathering of minerals by fungi represents an important but unassessed contributor to the short-term release of mineral nutrients and should be incorporated into biogeochemical models.

Direct Z-scheme construction of g-C3N4 quantum dots / TiO2 nanoflakes for efficient photocatalysis

The rapid recombination rate of photogenerated carriers in TiO2 has been limiting the photocatalytic performance. Herein, TiO2 thin flakes modified by g-C3N4 quantum dots (g-C3N4 QDs) were fabricated successfully through a facile thermal treatment of restacked single-layer nanosheets of Ti1.73O41.07- in the presence of urea as a source of g-C3N4 QDs. Characterizations showed that g-C3N4 QDs with a size of ~10 nm were homogeneously deposited on the surface of TiO2 thin flakes. Quenching experiments of •OH radicals and the detection of radicals by EPR certified the direct Z-scheme heterojunctions between g-C3N4 QDs and TiO2 flakes. The TiO2 nanoflakes/g-C3N4 QDs hybrid exhibited excellent activity for the photocatalytic hydrogen evolution from a methanol solution and the degradation of RhB due to the enhanced charge separation efficiency and improved light absorption in the direct Z-scheme heterojunctions. This study demonstrates that the rational design of heterojunction is effective for attaining the superior photocatalytic performance.

Plasmon-assisted MXene grafting: tuning of surface termination and stability enhancement

The properties of MXenes, new generation of 2D materials, are determined by the surface terminations, which depends on flake preparation method. Changing the surface termination chemical groups can significantly modify the MXene flake properties and functionality. However, the common methods of MXene flake surface chemistry tuning require high-energy treatments and often lead to flake damage. In this work, we propose a plasmon-assisted chemical transformation for tuning the surface chemistry and termination of MXene flakes. The plasmon resonance was directly excited on MXene flakes and induced the generation of highly reactive radicals from electrostatically absorbed iodonium salt cations, leading to immediate grafting of the created radicals to the flake edges and basal planes. We used bis-CF3-substituted iodonium salts, and subsequent analysis of the Ti3C2T x MXene flake surface composition indicated decreases in the total oxygen concentration and oxidized titanium with a simultaneous increase in the fluorine surface concentration, which was related to –C6H3(CF3)2 moiety attachment. The ability to substitute the hydrophilic oxygen-containing groups with hydrophobic and oleophilic –CF3 groups containing functional groups allows us to create a stable suspension of a MXene in nonpolar organic solvents and prepare a superhydrophobic, water-repellent and oxidation-stable conductive MXene coating.

Gold and silver nanocomposite-based biostable and biocompatible electronic textile for wearable electromyographic biosensors

Wearable biosensors have received significant attention due to the possibility of measuring physiological signals on demand. Particularly, the monitoring of electromyographic (EMG) signals on demand by wearable platforms has significant potential to revolutionize the diagnostics and treatment of neuromuscular diseases and for advancing human–computer interfaces. Electronic textile-based biosensors have several advantages, including the simple scale-up process and the ease of fabricating multiple large area electrodes over the whole body to obtain precise measurements. Hence, the electronic textile production requires an affordable approach to fabricate biocompatible and biostable electronic circuits on textile materials. This work explores the possibility of combining screen printing and electrodeposition techniques to produce a biostable nanocomposite-based EMG biosensor on textile. Screen printing was selected to fabricate conductive fabrics that would ultimately be a highly durable textile-based sensor. Silver paste, including microscale silver flakes, was printed on PET/cotton blended fabrics. However, the microscale silver surface was limited for EMG sensors due to low surface area and toxicity, causing low signal detection performance and skin irritation. Gold nanoparticles (Au NPs) were deposited on silver flakes to address the requirements of high-performance and biocompatible biosensors. We confirmed that the gold functionalization improved electrical and electrochemical performance. In addition, various tests were performed to determine electrochemical and biological stability under physiological conditions. The test results proved that Au NPs have successfully encapsulated the surface of silver flakes, preventing the exposure of the silver to the physiological environment. EMG signal recording was performed to confirm the functionalization effect that improved the signal to noise ratio (SNR) of 12.5 with 120 nm Au NPs. Moreover, EMG sensing from bicep workouts and finger movements showed the high sensitivity of the electronic fabrics. Although the SNR of EMG signals dropped to 7.2 after a 15-time washing test, the stabilized SNR after 5 washing cycles indicated that the Au/Ag biosensors showed washing durability. The study demonstrates that this affordable approach can be considered for large-scale production of wearable EMG biosensors.

Effect of Flake Surface Treatment on Mechanical Properties of Aluminum Flake Filled Epoxy Resin Composites

Effect of Flake Surface Treatment on Mechanical Properties of Aluminum Flake Filled Epoxy Resin Composites

Correlation Between Corrugation-Induced Flexoelectric Polarization and Conductivity of Low-Dimensional Transition Metal Dichalcogenides

Tunability of polar and semiconducting properties of low-dimensional transition metal dichalcogenides (TMDs) have propelled them to the forefront of fundamental and applied physical research. These materials can vary from non-polar to ferroelectric, and from direct-band semiconductor to metallic. However, in addition to classical controls such as composition, doping, and field effect in TMDs the additional degrees of freedom emerge due to the curvature-induced electron redistribution and associated changes in electronic properties. Here we numerically explore the elastic and electric fields, flexoelectric polarization and free charge density for a TMD nanoflake placed on a rough substrate with a sinusoidal profile of the corrugation using finite element modelling. Numerical results for different flake thickness and corrugation depth yield insight into the flexoelectric nature of the out-of-plane electric polarization and establish the unambiguous correlation between the polarization and static conductivity modulation caused by inhomogeneous elastic strains coupled with deformation potential and strain gradients, which evolve in TMD nanoflake due to the adhesion between the flake surface and corrugated substrate. We revealed a pronounced maximum at the thickness dependences of the electron and hole conductivity of MoS2 and MoTe2 nanoflakes placed on a metallic substrate, which opens the way for their geometry optimization towards significant improvement their polar and electronic properties, necessary for their advanced applications in nanoelectronics and memory devices.Specifically, obtained results can be useful for elaboration of nanoscale straintronic devices based on the bended MoS2, MoTe2 and MoSTe nanoflakes, such as diodes and bipolar transistors with a bending-controllable sharpness of p-n junctions.

In situ construction of multi-dimensional Co3O4/NiCo2O4 hierarchical flakes on self-supporting carbon substrate with ultra-high capacitance for hybrid supercapacitors

Research on environmentally friendly energy storage devices is an important strategy to solve the energy crisis and environmental pollution. Herein, a novel self-supporting electrode based on multi-dimensional Co3O4/NiCo2O4 hierarchical flakes coating on graphene/carbon sphere (rGO/CS) conductive substrate is reasonably designed. Firstly, a simple hydrothermal method is used to synthesize NiCo2O4 with both flake and nanoneedle morphology on the rGO/CS substrate. Subsequently, Co3O4/NiCo2O4@rGO/CS is obtained by in-situ growth of metal organic frameworks polyhedrons on the surface of NiCo2O4 flakes followed by calcination. In the unique structure, benefitting from the synergy between the substrate and multi-element transition metal oxides, the integrated film shows good conductivity, high specific surface area and abundant active sites. Thus, the binder-free electrode exhibits an ultra-high specific capacitance of 3876.6 F g−1 (538.4 mA h g−1) at 1 A g−1. A hybrid supercapacitor is assembled with activated carbon as the negative electrode and Co3O4/NiCo2O4@rGO/CS as the positive electrode, the device shows a highest energy density of 56.5 Wh kg−1 at a power density of 800 W kg−1. After 6000 charge–discharge cycles, 92.5% of the initial capacitance can be still maintained, indicating its good application prospects in energy storage materials.

Effect of hydrogen and oxygen plasma on the photoelectronic current and photo-response time of SnS2 flakes

The photoelectronic properties of SnS2 flakes have been widely studied due to the abundance and environmentally friendly qualities of this material. However, the defects and residual molecules adsorbed on the SnS2 surface can have a negative influence on the photoelectronic current and photo-response time. In this paper we examine the effects of these two factors on the photoelectronic currents of SnS2 flakes. Defects on a single crystal SnS2 surface are fabricated using hydrogen and oxygen plasma and are characterized by atomic force microscopy, confocal micro-Raman spectroscopy and photoluminescence spectroscopy. Doping by oxygen plasma can be demonstrated by x-ray photoelectron spectroscopy. Both the photoelectronic current and the switching speed (on and off times) are reduced after hydrogen plasma treatment. However, oxygen plasma has two effects on SnS2 thin film transistors. First, oxygen plasma can remove the residual molecules within a short irradiation time. In this case, the photoelectronic current of SnS2 treated with oxygen plasma is enhanced several times. Second, with a longer treatment time oxygen plasma induces many defects and doping on the SnS2 flake surface, as reflected in the reduced photoelectronic current and switching speed. Results of this work have significant practical applications for photoelectronic detection with SnS2 flakes.

Effectiveness of fresh cement kiln dust as a soil stabilizer and stabilization mechanism of high swelling clays

The expansive clay soils, which cover most of the new urbanized areas in Egypt, create major damages in most of the engineering structures and infrastructures such as buildings, roads, bridges, pipelines and others due to bad human activities, e.g. lack of maintenance for sewage and drinking lines, and flood irrigation of golf areas which causes fluctuation of water content through the foundation clay layers associated with shrink-swell behavior. These geotechnical challenges and their treatment solutions consume most of the urbanized project budget and delay the development plan. Therefore, in this study the high plasticity and soft to firm clay soils were stabilized using various dosages of fresh cement kiln dust (CKD) as an economical alternative to the other expensive stabilizing agents (stabilizers or binders) such as lime, cement and other chemical stabilizers. The effectiveness of this type of CKD as a stabilizing agent, soil stabilization mechanism, and changes in mineralogical and microstructural characteristics of stabilized soils due to this stabilization process were evaluated through Atterberg limits, unconfined compressive strength (UCS), stiffness (stress–strain behavior, Es), pH, electrical conductivity (EC), total dissolved solids (TDS), X-Ray diffraction (XRD) and scanning electron microscope (SEM) investigations. The present study revealed that by adding CKD, the workability of the treated clays was increased by decreasing the liquid limit and plasticity index as well as increasing the bearing capacity and decreasing the settlement by increasing UCS and Es. This study also showed that by adding CKD, the initial pH, EC, and TDS of CKD-clay system increased, creating favorable conditions for dissolution of edges and surfaces of clay flakes. The active montmorillonite clay flakes adsorbed the soluble calcium cation and sulfate anion on their surfaces that are rich in soluble silica and alumina and then the cation exchange and flocculation–agglomeration processes began. With curing, the pozzolanic products grew on the surfaces and edges of clay flakes and extended into the voids of the agglomerated inter-clay particles resulting in the filling of these micro-voids. The present investigation also found that, the progressive decreasing in pH, EC, and TDS values of CKD-clay systems through different curing periods is a good indicator for pozzolanic activity.

Vertically-interlaced NiFeP/MXene electrocatalyst with tunable electronic structure for high-efficiency oxygen evolution reaction

Layered double hydroxides (LDHs) with decent oxygen evolution reaction (OER) activity have been extensively studied in the fields of energy storage and conversion. However, their poor conductivity, ease of agglomeration, and low intrinsic activity limit their practical application. To date, improvement of the intrinsic activity and stability of NiFe-LDHs through the introduction of heteroatoms or its combination with other conductive substrates to enhance their water-splitting performance has drawn increasing attention. In this study, vertically interlaced ternary phosphatised nickel/iron hybrids grown on the surface of titanium carbide flakes (NiFeP/MXene) were successfully synthesised through a hydrothermal reaction and phosphating calcination process. The optimised NiFeP/MXene exhibited a low overpotential of 286 mV at 10 mA cm−2 and a Tafel slope of 35 mV dec−1 for the OER, which exceeded the performance of several existing NiFe-based catalysts. NiFeP/MXene was further used as a water-splitting anode in an alkaline electrolyte, exhibiting a cell voltage of only 1.61 V to achieve a current density of 10 mA cm−2. Density functional theory (DFT) calculations revealed that the combination of MXene acting as a conductive substrate and the phosphating process can effectively tune the electronic structure and density of the electrocatalyst surface to promote the energy level of the d-band centre, resulting in an enhanced OER performance. This study provides a valuable guideline for designing high-performance MXene-supported NiFe-based OER catalysts.

Flaky FeSi particles with tunable size, morphology and microstructure developing for high-efficiency and broadband absorbing materials

Compared with spherical ferromagnetic particles, flaky particles due to the higher permeability present great potentials as high-efficiency electromagnetic absorbing materials, especially in S band (2–4 GHz). FeSi flakes with different diameters were synthesized by ball-milling and subsequent screened processes, and hydrogen annealing and SiO2 coating were then utilized to further optimize the electromagnetic parameters for high-efficiency absorption. FeSi flakes with high diameter possess higher permittivity for the larger specific areas and higher permeability for the increased shape anisotropy. The decreased defects after annealing induce the reducing permittivity. The eddy current effect can be effectively suppressed after the SiO2 is coated on the surface of FeSi flakes. As for the coating containing 70 wt% FeSi@SiO2 flakes, the maximum reflection loss (RLmax) of –73 dB can be observed at 2.5 GHz with the coating thickness of 3 mm. Effective absorption band (ERL5, RL < –5 dB) can reach 13 GHz at a very thin thickness of 1 mm, and ERL5 covers the whole S-C band when the thickness of 2.5 mm is utilized. The coatings containing FeSi and FeSi@SiO2 flakes as fillers present adjustable electromagnetic absorbing (EMA) performances and can be promising candidates for EMA application, especially in S band.

Effects of In Situ Graphitic Nanocarbon Coatings on Cycling Performance of Silicon-Flake-Based Anode of Lithium Ion Battery

We coated graphitic nanocarbons by thermal chemical vapor deposition (CVD) on silicon flakes recycled from the waste of silicon wafer manufacturing processes as an active material for the anode of lithium ion battery (LIB). Ferrocene contains both iron catalyst and carbon, while camphor serves as an additional carbon source. Water vapor promotes catalytic growth of nanocarbons, including carbon nanotubes (CNTs), carbon fibers (CFs), and carbon films made of graphitic carbon nanoparticles, at temperatures ranging from 650 to 850 °C. The container of silicon flakes rotates for uniform coatings on silicon flakes of about 100 nm thick and 800–1000 nm in lateral dimensions. Due to short CVD time, besides CNTs and CFs, surfaces of silicon flakes deposit with high-density graphitic nanoparticles, especially at a low temperature of 650 °C. Nanocarbon coatings were characterized by SEM, EDX, ESCA, and Raman spectroscopy. Half-cells were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and retention of capacity in discharge/charge cycling. Silicon-flake-based anode with nanocarbon coatings at both 650 and 850 °C exhibited capacity retention of 2000 mAh/g after 100 cycles at 0.1 C, without needing any conductivity enhancement material such as Super P.

Theranostic two-dimensional superparamagnetic maghemite quantum structures for ROS-mediated cancer therapy.

In this work, size- and shape-controlled two-dimensional (2D) superparamagnetic maghemite (γ-Fe2O3) quantum flakes (MQFs) with high surface area and mesoporosity were prepared by facile hydrothermal synthesis for biological applications. These quantum flakes exhibited superparamagnetic behaviours over a wide temperature range of 75-950 K with high saturation magnetization of Ms - 23 emu g-1 and a lower coercivity of Hc - 6.1 Oe. MQFs also demonstrated a good colloidal stability and a positively charged flake surface. Selective toxicity dependent upon selective ROS scavenging/generation and cellular MQF uptake towards non-malignant human keratinocyte (HaCaT) and malignant melanoma (A357) and human breast cancer (MDA-MB 231) cell lines were witnessed. An increased ROS concentration resulted due to the peroxidase-like activity of MQFs in malignant cells. In contrast, ROS scavenging was observed in non-malignant cells due to dominant catalase-like activity. In vitro fluorescence properties added the diagnostic ability to the ambit of MQFs. Furthermore, the therapeutic efficiency could be significantly enhanced by the hyperthermic (25-47 °C) ability of MQF in cancerous cells. Our findings reveal the novel theranostic MQF structure with immense cancer therapeutic potential via augmentation of ROS generation by hyperthermia in a selective microenvironment.

Лахути IV – новая стоянка раннего палеолита в долине реки Оби-Мазар (Южный Таджикистан)

The article presents the results of a joint Russian-Tajik geoarchaeological expedition in the middle reaches of the Obi-Mazar River (Republic of Tajikistan). During 2021 fieldwork two Tajikistan Loess Palaeolithic sites were studied: Kuldara (14 pedocomplexes) and Obi-Mazar (7 pedocomplexes). A significant amount of palaeogeographic work was carried out at both sites including sampling for a wide range of geological analyses. At Kuldara, five excavation trenches were established and a small amount of artifacts from pedocomplexes 4 and 5 as well as a few items from PC’s 10 and 11 were collected. Lakhuti IV corresponding to PC 5 was found between the known sites of Obi-Mazar-6 and Lakhuti I. The excavation area was 6 m2 and 2.2 m deep. Archaeological material (662 specimens) was deposited at 8 levels, but can be regarded a single industry. The primary reduction is based on several simple flaking techniques — radial flaking from a single surface, citron and parallel flaking. Some cores were prepared on large and thick spalls; the ventral surface was used as a prepared flaking surface. “Citron flakes” were also found (~ 8 % of the total number of flakes). Not a single blade was discovered. The complex contains roughly equal proportions of scrapers on large spalls, notched-denticulate tools and unifaces. According to the available set of geological data for the Obi-Mazar Valley, PC 5 is dated to ca. 0.5 Ma. The Lahuti IV materials have parallels in the synchronous Early Palaeolithic industries of Tajikistan. A distinctive feature of this site is a very high concentration of artifacts and their occurrence in well-defined cultural horizons, which is recorded for the first time at Loessic Palaeolithic sites.

МЕЛКОПЛАСТИНЧАТОЕ РАСЩЕПЛЕНИЕ В ИНДУСТРИЯХ РАННЕГО ВЕРХНЕГО ПАЛЕОЛИТА ДЕНИСОВОЙ ПЕЩЕРЫ: ДАННЫЕ АНАЛИЗА ПОСЛЕДОВАТЕЛЬНОСТИ СКОЛОВ

The paper discusses the results from an analysis of five cores associated with Layer 11 in the Southern Chamber of Denisova Cave, intended to obtain small elongated blanks such as bladelets and small blades. Analysis of a lithic reduction sequence employed in the research has made it possible to clearly recognize the phases in producing flake scars on lithic artifacts through the preparation of core blanks, and in core reduction, as well as to determine stages at which some of these pieces were used as tools. The analysis provided insights into a general flaking pattern for the cores under study. Such artifacts were predominantly made on large massive flake blanks, had a plain striking platform, and the working edge showing traces of reduction associated with detaching the target flakes. These technological characteristics are fully consistent with the technological repertoire of a hominin group, based on cores from the same assemblage, intended to obtain larger target removals such as flakes and blades. A cross section of the flaking surface shows no evidence for a deliberately created and maintained convex relief, while typologically four of the five artifacts were defined as sub-prismatic. The analysis of a lithic reduction sequence shows that artifacts from the examined collection related to the production of blanks in the form of small flake-blades, without using new techniques and the controlled reduction of a flaking surface.

BARMAKY SITE IN THE CONTEXT OF EPIGRAVETTIAN OF THE MIDDLE DNIEPER BASIN

The Upper Paleolithic site Barmaky, 2nd cultural layer from Volyhnia-Lublin upland is the most western manifestation of Epigravettian of the Mid Dnieper basin. During several field campaigns the 147 m2 of cultural deposits with three pits and one chalk / marl concentration were studied (fig. 1). The silty-loess deposits of Barmaky, 2 accumulated about 19 kyr cal BP (table 1) under the permafrost conditions. The fauna assemblage is represented by: mammoths, bison, reindeer, red deer, horse, bear, wolf, wolverine, polar fox, fox and hare. More than 100 thousand artifacts were recovered during the last two field campaigns. In essential account (without chips, chunks, unidentifiable debitage), the artifacts assemblage is represented by: cores and pre-cores — 0.87 %; flakes — 45.23; blades — 17.34; bladelets — 14.27; micro-blades — 7.34; burin spalls — 8.08; tools — 6.79 % (table 2). The reduction sequences are based on the flaking of uni-, bidirectional sub-cylindrical and narrow flaking surface unidirectional cores for blades and bladelets (table 3; fig. 2). There is no evidence of micro-blade technology implication. The structure of tool-kit is characterized by the dominance of burins — about 50 %; microliths — 25 %; and truncated pieces — about 18 % (table 4). The rest of tool classes are represented by a few percentages each. Among them are the end-scrapers on blades with truncated base (fig. 3). The most part of burins are represented by pieces made on obliquely truncated blades (table 5; fig. 4). Also, the obliquely truncated blades dominate the truncated pieces assemblage (table 6; fig. 5). The most representative type of microliths is the micro-points with abruptly retouched straight back and obliquely retouched base (table 7; fig. 6). The points, pendants, bracelet fragment made on tusk and perforated fossil marine shells from local chalk deposits are available. The composition of microliths, burins and end-scrapers in Barmaky, 2 tool-kit is characteristic to the cultural layers beyond the dwelling structures on such base-camps as Mezhyrich (fig. 7). Also, the presences of pits and fauna composition are close to what expected from Epigravettian base-camps. The artifacts assemblage of Barmaky, 2 belongs to the Mizyn industry. Also, Barmaky, 2 is the earliest manifestation of Epigravettian in the Mid Dnieper basin.