Maksym Rybachuk

Spectroscopic characterization of carbon chains in nanostructured tetrahedral carbon films synthesized by femtosecond pulsed laser deposition

A comparative study of carbon bonding states and Raman spectra is reported for amorphous diamondlike carbon films deposited using 120 fs and 30 ns pulsed laser ablation of graphite. The presence of sp(1) chains in femtosecond carbon films is confirmed by the appearance of a broad excitation band at 2000-2200 cm(-1) in UV-Raman spectra. Analysis of Raman spectra indicates that the concentrations of sp(1)-, sp(2)-, and sp(3)-bonded carbon are approximately 6%, approximately 43%, and approximately 51%, respectively, in carbon films prepared by femtosecond laser ablation. Using surface enhanced Raman spectroscopy, specific vibrational frequencies associated with polycumulene, polyyne, and trans-polyacetylene chains have been identified. The present study provides further insight into the composition and structure of tetrahedral carbon films containing both sp(2) clusters and sp(1) chains.

Charge transport and activation energy of amorphous silicon carbide thin film on quartz at elevated temperature

We report on the temperature dependence of the charge transport and activation energy of amorphous silicon carbide (a-SiC) thin films grown on quartz by low-pressure chemical vapor deposition. The electrical conductivity as characterized by the Arrhenius rule was found to vary distinctly under two activation energy thresholds of 150 and 205 meV, corresponding to temperature ranges of 300 to 450 K and 450 to 580 K, respectively. The a-SiC/quartz system displayed a high temperature coefficient of resistance ranging from −4,000 to −16,000 ppm/K, demonstrating a strong feasibility of using this material for highly sensitive thermal sensing applications.

Nanobuckling and x-ray photoelectron spectra of carbyne-rich tetrahedral carbon films deposited by femtosecond laser ablation at cryogenic temperatures

The growth, surface morphology, and electronic binding states of diamondlike films deposited by femtosecond laser ablation on Si wafers at 77 K have been studied in order to elucidate the mechanical properties of this material. Nanoscale buckling has been observed and is found to have a morphology that exhibits a strong dependence on film thickness. Nanobuckling takes the form of quasiperiodic discrete pointlike excursions extending over widths of 50–100 nm. This morphology converts to a regular structure of grooves/ripples with a modulation period of 30–50 nm as the film thickness increases to 300–600 nm. We find that microhardness is not changed in regions where nanobuckling is present. Analysis of Raman and x-ray photoelectron spectra (XPS) demonstrate that nanobuckling can be attributed to the relaxation of internal stress and to the formation of strong C-Si covalent bonds at the C-Si interface. XPS spectra show that the C 1s peak is broadened compared to that found in spectra of films deposited using...

Resonant Raman scattering from polyacetylene and poly(p-phenylene vinylene) chains included into hydrogenated amorphous carbon

The resonant Raman scattering in N-IR–UV range from amorphous hydrogenated carbon (a-C:H) reveals inclusions of trans-polyacetylene [trans-(CH)x] chains with approximate length of up to 120 CC units and inclusions of poly(p-phenylene vinylene) (PPV) polymer chains. The PPV is evidenced by a strong dispersive mode at ∼1175cm−1. It was found that the Raman response from core Ag trans-(CH)x modes incorporated into a−C:H to changing excitation energy is identical to that of freestanding chains, thus facilitating identification of trans-(CH)x in complex carbonaceous materials spectra.

Anisotropic mechanical properties of fused deposition modeled parts fabricated by using acrylonitrile butadiene styrene polymer

Abstract The anisotropic mechanical properties of parts that are fabricated using acrylonitrile butadiene styrene (ABS) polymer relative to part-built orientation employing the fused deposition modelling process are reported in this work. ABSplus-P430 polymer was used to investigate the effects of infill orientation on the parts’ mechanical properties under tensile and compression loading. Results revealed that infill orientation strongly affected the tensile properties of fabricated ABS samples. Specifically, the values for Young’s modulus ranged from ~1.5 to ~2.1 GPa, ultimate tensile strength from ~12.0 to ~22.0 MPa, yield strength from ~1.0 to ~21.0 MPa, and elongation-at-break from ~0.2 to ~4.8% for different infill orientations. Samples with infill orientation aligned to the vertical (i.e. Z-) axis displayed the highest values relative to all other infill orientations investigated. Mechanical properties anisotropy was lower for parts under compressive loading, such that the Young’s modulus, ultimate compressive and yield strength were weakly correlated with infill orientation apart from samples whose built orientation was aligned at 45° to the vertical Z-axis. The latter samples displayed inferior mechanical properties under all compressive tests. The effects of sample gauge thickness on tensile properties and ABS sample micro- and bulk- hardness with respect to infill orientation are also discussed.

Pathway Distribution Model for Solute Transport in Stratum Corneum

One of the main functions of the skin is to reduce the amount of water evaporating from the surface of a human body with outermost layer of the epidermis, stratum corneum (SC), forming a barrier, which protects underlying tissue from dehydration. Empirical data obtained for water penetration in SC are normally analysed using mathematical models, among which the homogeneous membrane (HM) model is commonly employed to describe transport kinetics in SC. However, the HM model failed to fit simultaneously the experimental data for water permeation and desorption (Anissimov YG, Roberts MS. 2009. J Pharm Sci 98:772-781), as the model does not account for a complex structure of SC and irregular distribution of corneocytes. Our previous work (Anissimov YG, Roberts MS. 2009. J Pharm Sci 98:772-781) introduced a slow binding (SB) model that is more aligned with the true biological structure of SC. This report provides an alternative/additional model to both the HM and SB models and takes into account the distribution of effective pathways across SC for water transport.

Growth of diamond-like carbon films using low energy ion beam sputter – bombardment deposition with Ar ions

An alternative to a widely used ion assisted deposition method has been developed where a single beam of low energy Ar ions is used to simultaneously sputter a graphite target and to bombard a growing film. By placing the substrate at low incident angles to the axis of the ion beam and therefore subjecting the growing film to the additional ion energy we aimed to promote the formation of sp3 bonding. Sp2 rich amorphous carbon (a-C) and diamond-like carbon (DLC) films with significant fractions of sp3 bonding were formed by sputtering from a Kaufmann - type ion source. Experimental results revealed that when the substrate was placed at grazing angles to the incoming ions no DLC, but only polymeric a-C films were produced as a result of a secondary resputtering process. For DLC synthesis the optimal angles of the target and the substrate to the ion flux were found to be 30° and 0° respectively and the ion energies of 0.8 – 1.0 keV.

SYNTHESIS OF DIAMOND-LIKE CARBON FILMS USING A BI-MODAL SPUTTER DEPOSITION WITH Xe IONS

An alternative approach to a sputtering process was examined where a single incident beam of Xe ions was used to simultaneously sputter a carbon target and bombard a growing film. The hypothesis that by positioning a substrate at grazing angles to the central axis of the ion beam, the additional energy provided will be beneficial to the formation of sp3 bonding. Amorphous carbon (a-C) and diamond-like carbon (DLC) films were synthesized by sputtering a graphite target from a Kaufmann-type ion source. Experimental results revealed that when a substrate was placed at grazing angles due to a secondary resputtering process, it was not possible to fabricate DLCs but only sp2-rich polymeric a-C. For DLC synthesis the optimal angles of the target and the substrate to the ion flux were found to be 30° and 0°, respectively, and the ion energies of 0.8–1 keV.

Defects in carbon nanotubes

Abstract In this chapter, different concepts from production to the characterization of carbon nanotubes (CNTs) are described. The construction of the actual chapter mainly starts with the description and comparison of the common synthesis techniques i.e. arc discharge, laser ablation, chemical vapour deposition (CVD), flame synthesis, and silane solution methods for the production of the CNTs, followed by the purification process and application potentials of these nanomaterials. Then, a fundamental demonstration and insight in the atomic structure of main CNT configurations (armchair, zigzag and chiral) is provided. In the subsequent subsection, various defect types, classified into two general groups of macroscopic disorders (curvature, twist and hetero-junction kink) and atomic scale defects (vacancies, impurities, perturbation and Stone-Wales defect), and their influence on the properties of CNTs as well as functionalization of CNTs and harvesting these defects for various applications are elucidated. Finally, the experimental and theoretical CNT characterization approaches are discussed and the pertaining results in the literature are presented. The results from literature reveals the fact that these nanostructures, not only involve different defect and disorder types from their synthesis process which reduce their individual mechanical stabilities and often necessitate purification process for their redundant impurities and by-products removal, but also from their functionalization process in which particular defects i.e. adatom doping and multi-CNT welding through hetero-junctions are intentionally employed for enhancing the properties and functionality of the CNTs for various applications from energy storing, gas detection and materials reinforcement to drug delivery and molecules transportation.

The morphology of hydrogenated diamond-like films and the effect of the sp2 fraction disorder on electronic and micro-mechanical properties

Diamond-like carbon is a promising material for MEMS and opto-electronic systems applications. There is a notion that the hybridised sp3 (diamond-like) fraction controls the mechanical properties and the sp2 fraction (graphite-like) determines the electro-optical properties. We investigated amorphous hydrogenated diamond-like carbon (a-C:H) films synthesised using an inductively coupled hydrocarbon plasma reactor under varying bias. The films were characterised using UV Raman, X-ray C1s photoelectron, N-IR spectroscopy, scanning probe microscopy (SPM) and nano-indentation measurements. We found that all examined samples displayed essentially the same amount of the sp3 constituent, whereas the configuration of the sp2 fraction was different. The sp2 fraction of both aromatic rings and olefinic chains in examined films. We found that Tauc gap Et, was controlled by the perturbation of the π tail states of the sp2 fraction. The Tauc gap Et, was determined by N-IR and surface conduction band Eoi, measured by SPM changed inversely with an increase of bias. Results obtained using nanoindentation measurements show that mechanical properties such as hardness and Youngs modulus increased with an increase of bias for all films studied. These results indicate that mechanical properties of a-C:H films (hardness and Youngs modulus) not only controlled by the amount of the sp3 bonding but also are determined by the degree of the sp2 bonding arrangement.