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The use of carbon nanotubes as anticancer drug delivery cargo systems is a promising modality as they are able to perforate cellular membranes and transport the carried therapeutic molecules into the cellular components. Our work describes the encapsulation process of a common anticancer drug, Isatin (1H-indole-2,3-dione) as a guest molecule, in a capped single-walled carbon nanotube (SWCNT) host with chirality of (10,10). The encapsulation process was modelled, considering an aqueous solution, by a molecular dynamics (MD) simulation under a canonical NVT ensemble. The interactions between the atoms of Isatin were obtained from the DREIDING force filed. The storage capacity of the capped SWCNT host was evaluated to quantify its capacity to host multiple Isatin molecules. Our results show that the Isatin can be readily trapped inside the volume cavity of the capped SWCNT and it remained stable, as featured by a reduction in the van der Waals forces between Isatin guest and the SWCNT host (at approximately − 30 kcal mol−1) at the end of the MD simulation (15 ns). Moreover, the free energy of encapsulation was found to be − 34 kcal mol−1 suggesting that the Isatin insertion procedure into the SWCNT occurred spontaneously. As calculated, a capped SWCNT (10,10) with a length of 30 Å, was able to host eleven (11) molecules of Isatin, that all remained steadily encapsulated inside the SWCNT volume cavity, showing a potential for the use of carbon nanotubes as drug delivery cargo systems.

A highly versatile, low-cost, and robust tactile sensor capable of acquiring load measurements under static and dynamic modes employing a poly(vinylidene fluoride

BACKGROUND: Glaucoma, a characteristic type of optic nerve degeneration in the posterior pole of the eye, is a common cause of irreversible vision loss and the second leading cause of blindness worldwide. As an optic neuropathy, glaucoma is identified by increasing degeneration of retinal ganglion cells (RGCs), with consequential vision loss. Current treatments only postpone the development of retinal degeneration, and there are as yet no treatments available for this disability. Recent studies have shown that replacing lost or damaged RGCs with healthy RGCs or RGC precursors, supported by appropriately designed bio-material scaffolds, could facilitate the development and enhancement of connections to ganglion cells and optic nerve axons. The consequence may be an improved retinal regeneration. This technique could also offer the possibility for retinal regeneration in treating other forms of optic nerve ailments through RGC replacement. METHODS: In this brief review, we describe the innovations and recent developments in retinal regenerative medicine such as retinal organoids and gene therapy which are specific to glaucoma treatment and focus on the selection of appropriate bio-engineering principles, biomaterials and cell therapies that are presently employed in this growing research area. RESULTS: Identification of optimal sources of cells, improving cell survival, functional integration upon transplantation, and developing techniques to deliver cells into the retinal space without provoking immune responses are the main challenges in retinal cell replacement therapies. CONCLUSION: The restoration of visual function in glaucoma patients by the RGC replacement therapies requires appropriate protocols and biotechnology methods. Tissue-engineered scaffolds, the generation of retinal organoids, and gene therapy may help to overcome some of the challenges in the generation of clinically safe RGCs.

The degree of laser-induced graphitisation from a sp3-bonded to a sp2-bonded carbon fraction in a single crystal chemical vapour deposited (CVD) diamond under a varying fluence of an ultrashort pulsed laser (30 fs, 800 nm, 1 kHz) irradiation has been studied. The tetrahedral CVD sp3-phase was found to transition to primarily an sp2-aromatic crystalline graphitic fraction below the critical fluence of 3.9 J/cm2, above which predominantly an amorphous carbon was formed. A fractional increase of fluence from 3.3 J/cm2 to 3.9 J/cm2 (~ 20 %) resulted in a substantial (~ three-fold) increased depth of the sp2-graphitised areas owing to the non-linear interactions associated with an fs-laser irradiation. Additionally, formation of C=O carbonyl group was observed below the critical threshold fluence; the C=O cleavage occurred gradually with the increase of irradiation fluence of 30 fs laser light. The implications for these findings on enhancement of fs-driven processing of diamond are discussed., Comment: 21 pages, 4 figures

To mitigate the negative environmental effects of the overuse of conventional materials—such as cement—in soil improvement, sustainable engineering techniques need to be applied. The use of biopolymers as an alternative, environmentally friendly solution has received a great deal of attention recently. The application of lignin, a sustainable and ecofriendly biobased adhesive, to enhance soil mechanical properties has been investigated. The changes to engineering properties of lignin-infused soil relative to a lignin addition to soil at 0.5, 1, and 3.0 wt.% (including Atterberg limits, unconfined compression strength, consolidated undrained triaxial characteristics, and mechanical properties under wetting and drying cycles that mimic atmospheric conditions) have been studied. Our findings reveal that the soil’s physical and strength characteristics, including unconfined compressive strength and soil cohesion, were improved by adding lignin through the aggregated soil particle process. While the internal friction angle of the soil was slightly decreased, the lignin additive significantly increased soil cohesion; the addition of 3% lignin to the soil doubled the soil’s compressive strength and cohesion. Lignin-treated samples experienced less strength loss during wetting and drying cycles. After six repeated wetting and drying cycles, the strength of the 3% lignin-treated sample was twice that of the untreated sample. Soil treated with 3% lignin displayed the highest erosion resistance and minimal soil mass loss of ca. 10% under emulated atmospheric conditions. This study offers useful insights into the utilization of lignin biopolymer in practical engineering applications, such as road stabilization, slope reinforcement, and erosion prevention.

The stem cell-based retinal ganglion cells (RGCs) replacement therapy offers a potential to restore vision in progressive optic neuropathies including glaucoma by replacing degenerated RGCs and by simulating axonal regeneration. Injured optic nerve axons do not regenerate owing to the limited intrinsic capacity of the neurons and the inhibitory environment at the injury site. Polymeric tissue scaffolds are able to modulate the physical environment while providing structural support for transplanted cells, however, their application specific to the RGC generation has been far from conclusive. The successful generation of clinically safe and functional RGCs that can appropriately integrate into the hosts' retinas still remain largely unresolved. Our study reports on a process that enables generation of RGCs from human embryonic stem cells (hESCs) that is simple, straightforward and repeatable and, investigates the influence of the aligned poly(glycerol sebacate) (PGS)/poly(e-caprolactone) (PCL) scaffold on this differentiation process. Our findings demonstrate that PGS/PCL scaffold promotes differentiation of hESCs into RGC-like cells possibly by the simulation of cell active environmental signalling and, facilitates the growth of RGCs neurites along their lengths. STATEMENT OF SIGNIFICANCE: Glaucoma can lead to the degeneration of retinal ganglion cells (RGCs), with consequential vision loss. RGCs are incapable of self-renewal, replacement of diseased RGCs with healthy cells has been a goal to restore vision in glaucoma patients. In this regard, stem cell RGC replacement therapy has been shown to improve vision in animal models of glaucoma, which could be facilitated by using tissue-engineered polymeric scaffolds. In this study, we generated homogenous stem cell-derived RGCs via a straightforward differentiation protocol and evaluated the effects of PGS/PCL scaffold on RGCs differentiation and growth of RGCs neurites. Our study contributes to the knowledge on how biomaterial scaffolds are able to support the regeneration of RGC neurites (i.e., axons or dendrites) as a part of a possible future clinical therapy for the treatment of glaucoma.

Stem cell-based therapeutic approaches have opened promising avenues to restoring vision in progressive optic neuropathies, including glaucomatous, and as such, the stem cell-based retinal ganglion cells (RGCs) replacement therapy offers a potential to replace degenerated RGCs and promote RGC axon regeneration. However, challenges associated with the successful generation of clinically safe and functional RGCs, which can appropriately integrate into the hosts’ retinas still remain unresolved. The use of polymeric tissue-supporting scaffolds is a known and tested solution to enhance the efficiency of cell delivery and differentiation process due to providing an appropriate physical environment and structural support, however, for RGC generation their application has been far from conclusive. Our study aims, firstly, to reveal a process that enables generation of RGCs from human embryonic stem cells (hESCs) that is simple, straightforward and repeatable and, secondly, to show the influence of the aligned poly(glycerol sebacate) (PGS)/poly(e-caprolactone) (PCL) scaffold on this differentiation process. Our findings demonstrate that PGS/PCL scaffold promotes differentiation of hESCs into RGCs, possibly, by simulating cells active environmental signalling, as well as, by supporting the growth of RGCs neurites along their lengths.

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.

The retinal ganglion cells (RGCs) are not able to regenerate following optic nerve injury resulting in an irreversible vision loss in patients with optic neuropathies including glaucoma. Recent findings in ocular regeneration have opened promising avenues to apply stem cell-based modalities to restore vision in progressive optic neuropathies. Stem cell-based therapies can help to improve retinal regeneration by solving two major problems: (1) by preventing secondary degeneration of RGCs and preserving the remaining vision, and (2) by replacing degenerated RGCs and promoting RGC axon regeneration in the damaged area. The first approach, known as neuroprotective therapy, uses stem cells incorporated into the degenerating retina with an aim to offer a nourishing environment for damaged RGCs resulting in anatomic and functional improvement. The second approach, known as RGC replacement therapy, ultimately aims at replacing the damaged RGCs with healthy RGCs or RGC precursors (Gao et al., 2012; Fu et al., 2019) in order to restore the visual function. Both approaches are graphically represented in [Figure 1]. The implementation of cell replacement therapeutic approaches requires successful generation of clinically safe and functional RGCs in an environment where the transplants survive, appropriately integrate and engraft, as well as establish neurites within the hosts’ retina and direct consequent axons towards the relevant regions in the brain (Behtaj et al., 2020). In this work, we discuss the challenges that are required to be addressed prior to the implementation of stem cell-based therapies in clinical practice and, suggest potential solutions to overcome the current limitations.

The design, development and application of an automated electrical cable harness testing system (ECHTS) with the capability of testing diverse cable harness configurations is presented. The ECHTS is able to test up to 32 conductors via an interchangeable connector, expandable to an additional 32 conductors through the use of an expansion board, detecting open- and short- circuit and incorrect pinning in a harness under test. The use of an LCD screen to display the status of a harness ensures faults are easily understood and displayed in the ECHTS, while providing a more comprehensive communication of detected faults compared to conventional testing and/or measurement systems. Compared to conventional systems, the ECHTS showed an improvement of testing times for a 1:1 and a one-to-multiple connector configuration, to 73% and a 15%, respectively, and a short operator's learning time.

Recent advances in cell transplantation technologies have shown that polymeric fibrous tissue-engineered scaffolds provide a suitable physical environment, including the structural support, for cell delivery and effectively mimic the transplanted cells’ extracellular matrix. Our study investigates the structure, composition and properties of three most commonly used polyester-based biopolymer materials blended with poly(e-caprolactone) (PCL) at 2:1 (wt.%) ratio, namely, poly(glycerol sebacate) (PGS)/PCL, polylactic-co-glycolic acid (PLGA)/PCL, poly-l-lactide (PLLA)/PCL and pure PCL as carrier vehicles for retinal progenitor cell (RPC) attachment and RPC proliferation. The physicochemical properties of PGS/PCL, PLLA/PCL, PLGA/PCL and pure PCL fibrous scaffolds, fabricated under the identical electrospinning conditions, were analysed employing scanning electron microscopy, contact angle analysis, Raman spectroscopy, electrical and ionic conductivity measurements, and supplemented by an in-vitro RPC adhesion and proliferation studies. Our findings have shown that PGS/PCL scaffolds promote RPC attachment and RPC proliferation more favourably compared to other polymeric blends and pure PCL, owing to a combination of advantageous surface and bulk properties, overall demonstrating a potential for PGS/PCL blend to become a suitable vehicle for RPC delivery in a possible future clinical therapy for the treatment of retinal degenerative disorders.

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.

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.

We report the synthesis of extended two-dimensional organic networks on Cu(111), Ag(111), Cu(110), and Ag(110) from thiophene-based molecules. A combination of scanning tunnelling microscopy and X-ray photoemission spectroscopy yields insight into the reaction pathways from single molecules towards the formation of two-dimensional organometallic and polymeric structures via Ullmann reaction dehalogenation and C-C coupling. The thermal stability of the molecular networks is probed by annealing at elevated temperatures of up to 500 °C. On Cu(111) only organometallic structures are formed, while on Ag(111) both organometallic and covalent polymeric networks were found to coexist. The ratio between organometallic and covalent bonds could be controlled by means of the annealing temperature. The thiophene moieties start degrading at 200 °C on the copper surface, whereas on silver the degradation process becomes significant only at 400 °C. Our work reveals how the interplay of a specific surface type and temperature steers the formation of organometallic and polymeric networks and describes how these factors influence the structural integrity of two-dimensional organic networks.

We report on the structural stability of ideal (defect-free) and structurally and morphologically degenerate carbon nanotubes and nanotube junction systems under axial loading based on the finite element method. We estimated the values for critical buckling load for uncapped and capped single-walled carbon nanotubes (SWCNTs) and linear and angle-adjoined SWCNT heterojunctions in ideal and structurally degenerate systems containing single-, double-, triple-, pinhole- and pentagon–heptagon (i.e., 5–7) structural defects and also containing a substitutional nitrogen (N) atom inclusion under compressive loading. Absolute atomic vacancy (defect) concentration in studied SWCNTs models was assumed to be nil for ideal systems, and was up to 3.0 at.% for structurally and morphologically degenerate systems. It was found that all types of structural defects and the morphological N-defect had reduced the load carrying capacity and mechanical strength in all SWCNT systems studied. The SWCNT models containing physically large vacant sites, such as triple- and pinhole-defects, displayed significantly lower critical load values compared to the systems that contained only a single-, double- or triple-vacancies. In addition, we found that capped SWCNTs performed marginally better in critical load carrying capacity compared to uncapped SWCNT systems. Furthermore, majority of the investigated structures displayed reduced load in SWCNTs with narrower tube widths, proportional to the size and the type of the defect investigated. The effects of chirality, such as zigzag- versus armchair-type, on the structural stability of the investigated SWCNT models were also investigated.

Inclusions of sp-hybridised, trans-polyacetylene [trans-(CH)x] and poly(p-phenylene vinylene) (PPV) chains are revealed using resonant Raman scattering (RRS) investigation of amorphous hydrogenated carbon (a-C:H) films in the near IR - UV range. The RRS spectra of trans-(CH)x core Ag modes and the PPV CC-H phenylene mode are found to transform and disperse as the laser excitation energy \hbar{\omega}L is increased from near IR through visible to UV, whereas sp-bonded inclusions only become evident in UV. This is attributed to \hbar{\omega}L probing of trans-(CH)x chain inhomogeneity and the distribution of chains with varying conjugation length; for PPV to the resonant probing of phelynene ring disorder; and for sp segments, to \hbar{\omega}L probing of a local band gap of end-terminated polyynes. The IR spectra analysis confirmed the presence of sp, trans-(CH)x and PPV inclusions. The obtained RRS results for a-C:H denote differentiation between the core Ag trans-(CH)x modes and the PPV phenylene mode. Furthermore, it was found that at various laser excitation energies the changes in Raman spectra features for trans-(CH)x segments included in an amorphous carbon matrix are the same as in bulk trans-polyacetylene. The latter finding can be used to facilitate identification of trans-(CH)x in the spectra of complex carbonaceous materials., Comment: 31 page, 9 figures

Diamondlike amorphous carbon films have been deposited on silicon and quartz substrates by laser ablation of graphite using 120 fs pulses from an amplified Ti:sapphire laser operating at 800 nm. Ultraviolet/visible (UV/VIS) and micro-Raman spectra of these materials have shown that the sp3-bonded carbon fraction in these films is ≈27%, 55%, and 20% when deposition occurs at substrate temperatures of 77, 300, and 573 K, respectively. The presence of sp1 chains in these films is indicated by the appearance of an excitation band at 2000–2100 cm−1 in UV-Raman spectra. We also find a remarkable increase in the Tauc energy gap calculated from in situ UV/VIS optical spectra immediately after exposure to air together with a 1 eV redshift of the C 1s core-level energy in x-ray photoelectron spectra of these samples. The properties of sp1-, sp2- and sp3-bonded components of these materials have also been studied using UV/VIS Raman spectroscopy. The enhanced stability of sp1 chains in tetrahedral carbon matrix is di...

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.

There is a notion that in carbonaceous materials the sp3 hybridised fraction determines the mechanical properties, while the sp2 fraction controls the electro-optical properties. We investigated a narrow range of a-C:H films synthesised in an open hydrocarbon plasma source. The a-C:H films displayed unambiguous variation in mechanical properties as measured by nanoindentation measurements. However the proportion of sp3 constituent, determined using X-ray C1s core-level photoelectron spectroscopy and Fourier transform infrared spectroscopy, was found to be essentially the same for all studied samples. The Tauc gap was found to be controlled by the perturbation of the π tail states of sp2 phase and its magnitude varied inversely with a surface conduction gap determined by scanning tunnelling microscopy measurements. These results indicate that mechanical properties of a-C:H films are also influenced by the degree of disorder of the sp2 fraction, as characterised by bond saturation and symmetry.

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.

Amorphous hydrogenated carbon (a-C:H) films were synthesised using an inductively coupled plasma reactor under varying DC substrate bias voltage. Films were characterised using nanoindentation measurements, UV (325 nm) and visible (633 nm) Raman spectroscopy. Film microhardness was found to vary from 15.2 to 18.6 GPa with harder films deposited at higher bias. While visible Raman spectroscopy is a routinely accepted technique used to study the sp 2 fraction in a-Cs, we found that it was ineffective in our instance to identify differences between the samples fabricated, as indicated by largely unchanged G peak position and D peak intensity for the selected films. UV Raman analysis revealed that the sp 3 fraction is essentially the same for all the films studied, while the sp 2 fraction was found to have higher degree of bond disorder in both aromatic rings and olefinic chains in films deposited at higher substrate bias. Furthermore, an additional peak at 1200 cm − 1 appeared in both visible and UV spectra of all films examined. We believe that the peak originates from the small, hydrogenated sp 2 sites with a narrow band gap and arranged in minute clusters. We hypothesize that the observed variation of the mechanical properties of a-C:H films are not controlled by the amount of the sp 3 fraction but are also determined by the nature of the disorder within the sp 2 -bonded fraction. a-C:H films displaying higher hardness and Young's modulus have sp 2 -bonded aromatic sites arranged in smaller domains with a higher degree of ring distortion and have sp 2 -bonded olefinic sites with higher degree of clustering. This phenomenon was observed as a result of a low temperature plasma deposition.

Surface modification of poly( l lactide) ( l -PLA) and polycaprolactone (PCL) bioresorbable polymers by radio-frequency thermal glow discharge plasma is reported. Improved biocompatibility of l -PLA and PCL materials was obtained by employing hydroxyapatite target sputtering in Ar + plasma as evidenced by the change of l -PLA and PCL properties from highly hydrophobic to hydrophilic, with absolute wettability obtained for both materials, and enhanced cell line EA-hy 926 attachment to modified surfaces. Surface roughness and surface free energy were found to increase significantly for both polymers under prolonged plasma exposure and, a longer chain aliphatic PCL were found to display a marginally better post plasma-treated biocompatibility compared to l -PLA.

Metallic nanowires constitute a distinctive class of nanostructures that are able to guide surface plasmons in subwavelength dimensions. The effective use of light in- and out-coupling in low dimensional systems, such as excitation of surface plasmon polaritons along metallic nanowires, has been proposed to reduce physical dimensions of opto-electronic and nano-optical components and for high-resolution microscopy applications. Our investigation of light in- and out-coupling on silver nanowire systems by scanning optical coupling microscopy (SOCM) performed in combination with atomic force microscopy (AFM) revealed that the maximum coupling was obtained when the exciting laser light is projected at the end of the nanowire with a positioning accuracy of approximately 100 nm. Furthermore, it was found that a nanoparticle positioned at the end of a nanowire imparts an enhanced (by almost the factor of 4) plasmon in- and out-coupling light efficiency as compared to a free nanowire under the same excitation co...

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.

Diamond-like carbon is a promising material for MEMS and opto-electronic systems applications. There is a notion that the hybridised sp 3 (diamond-like) fraction controls the mechanical properties and the sp 2 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 C 1s 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 sp 3 constituent, whereas the configuration of the sp 2 fraction was different. The sp 2 fraction of both aromatic rings and olefinic chains in examined films. We found that Tauc gap E t , was controlled by the perturbation of the n tail states of the sp 2 fraction. The Tauc gap E t , was determined by N-IR and surface conduction band E oi , measured by SPM changed inversely with an increase of bias. Results obtained using nanoindentation measurements show that mechanical properties such as hardness and Young's modulus increased with an increase of bias for all films studied. These results indicate that mechanical properties of a-C:H films (hardness and Young's modulus) not only controlled by the amount of the sp 3 bonding but also are determined by the degree of the sp 2 bonding arrangement.

The synthesis of polymer-like amorphous carbon (a-C:H) thin-films by microwave excited collisional hydrocarbon plasma process is reported. Stable and highly aromatic a-C:H were obtained containing significant inclusions of poly(p-phenylene vinylene) (PPV). PPV confers universal optoelectronic properties to the synthesised material. That is a-C:H with tailor-made refractive index are capable of becoming absorption-free in visible (red) - near infrared wavelength range. Production of large aromatic hydrocarbon including phenyl clusters and/or particles is attributed to enhanced coagulation of elemental plasma species under collisional plasma conditions. Detailed structural and morphological changes that occur in a-C:H during the plasma synthesis are also described., Comment: 12 pages, 4 figures

The resonant Raman scattering in N-IR - UV range from amorphous hydrogenated carbon (a-C:H) reveal 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 ca. 1175 cm-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 of free-standing chains thus facilitating identification of trans-(CH)x in complex carbonaceous materials spectra., 11 pages, 3 figures

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.

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...

Microscopic phase transformation from graphite to sp-bonded carbon chains (carbyne) and nanodiamond has been induced by femtosecond laser pulses on graphite surface. UV/surface enhanced Raman scattering spectra and x-ray photoelectron spectra displayed the local synthesis of carbyne in the melt zone while nanocrystalline diamond and trans-polyacetylene chains form in the edge area of gentle ablation. These results evidence possible direct "writing" of variable chemical bonded carbons by femtosecond laser pulses for carbon-based applications.