Raman scattering from amorphous ice films

The Raman spectrum from thin films of amorphous ice has been obtained by using a new laser beam trapping technique. Both the OH-stretching region of the spectrum and the always present intense scattering background have been interpreted.     

Raman characterization of thermal conduction in transparent carbon nanotube films

Using materials with high thermal conductivity is a matter of great concern in the field of thermal management. In this study, we present our experimental results on two-dimensional thermal conductivity of carbon nanotube (CNT) films obtained by using an optical method based on Raman spectroscopy. We use four kinds of CNTs in film preparation to investigate the effect of CNT type on heat spreading performance of CNT films. This first comparative study using the optical method shows that the arc-discharge single-walled carbon nanotubes yield the best heat spreading film. We also show that the Raman method renders reasonable thermal conductivity value as long as the sample is a transparent film by testing CNT films with various transmittance. This study provides useful information on characterization of thermal conduction in transparent CNT films and could be an important step toward high-performance carbon-based heat spreading films.     

Electrodeposition and characterization of Pd nanoparticles doped amorphous hydrogenated carbon films

Palladium (0) nanoparticles incorporated hydrogenated amorphous carbon (Pd/a-C:H) films were synthesized on single crystal silicon (100) substrates by electrochemical deposition route using methanol and camphor as carbon source, and Pd nanoparticles as dopant. The characterization results indicate that Pd nanocrystalline particles with diameter in the range of 1–5 nm dispersed in the amorphous carbon matrix. Compared with pure a-C:H films, the introduction of Pd nanoparticles didn't change the structure of carbon films. At the end, the growth mechanism of the Pd/a-C:H composite films was discussed.     

Surface enhanced Raman spectroscopic characterization of molecular structures in diamond-like carbon films

Vibrational bands associated with the out of plane bending modes of CH groups attached to various aromatic ring structures have been identified in surface enhanced Raman spectra of diamond-like amorphous carbon films deposited by femtosecond laser ablation of graphite. The appearance of enhanced modes associated with specific ring structures is assigned to solo-, duo-, trio- and quartet-CH groups and to pendant rings. Analysis of these bands provides insight into the nature of the molecular ring components of fs-DLC films. The resulting composition consists of polycyclic aromatic carbon (PAH)-like ring molecules and polyyne chains stabilized in a sp³-bonded network.     

Quantitative XPS-analysis of tantalum-containing amorphous carbon films

Summary Amorphous carbon films with different amounts of tantalum, normally used as hard coatings with low friction coefficients (<0.2), were analysed with XPS. Besides the indentification of different chemical states, a quantitative analysis was performed. In this paper we focus on the influence of surface contaminations and on the cleaning process (Ar sputtering) on quantitative XPS data. Depth profiles are presented. To verify the analytical results, the atomic concentrations are determined using own and published reference data. The quantitative XPS data were compared to EPMA measurements (a not surface-sensitive analysing technique), which reflect directly the bulk concentrations.

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Quantitative XPS-Analyse von Ta-haltigen amorphen Kohlenstoff-Filmen

     

PECVD of amorphous hydrogenated oxygenated nitrogenated carbon films

An actinometric optical emission spectroscopy (AOES) study of the trends in the concentrations of the plasma species H, CH, CO, OH, and CN in film-producing glow discharges of mixtures of isopropanol and nitrogen was undertaken. Conventional AOES was used to obtain the trends in the plasma concentrations of these species as a function of the proportion of nitrogen in the feed, R_n. A dynamic variant of actinometry in which trends in the concentrations of plasma species are measured as a function of time following the cutting of one of the principal gas flows was also employed to investigate the relative importance of gas phase and plasma/polymer–surface interactions in the production of the species of interest. Each of the above-mentioned species is produced, to some degree, by plasma/polymer–surface reactions. As revealed by transmission infrared spectroscopy, the films deposited contain C H, CO, and O H groups. For R_n > 0, the films become nitrogenated, with both N H and CN groups being present. As revealed by transmission ultraviolet-visible spectroscopy, both the optical gap and the refractive index of the deposited films decrease as R_n is increased. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1881–1888, 1998     

The Raman spectrum of amorphous and crystalline solid carbon disulphide

Raman spectra of solid CS₂ were investigated between 13 and 90 K. Upon deposition, the spectra show the coexistence of crystalline and amorphous solids. The latter is eliminated through annealing. For the crystal, temperature effects on the lattice modes, ν₁, ν₂ and 2ν₂ bands, are reported. The secondary structure of the overtone is attributed to crystal-field effects.     

Elemental distribution in fluorinated amorphous carbon thin films

Focused ion beam-secondary ion mass spectrometry (FIB-SIMS) with 20 nm spatial resolution has been used to analyze amorphous fluorinated carbon thin films, deposited by plasma assisted chemical vapor deposition (PACVD), at micro- to nano-scale. Mass spectra and ion imaging of film surface were acquired and the presence and distribution of contaminants were investigated. Surface images show the secondary ion distribution for F(-), CH(-), CF(-). A change in size and topology of fluorine-rich areas is correlated with film hardness and with microstructure transition from diamond-like to polymer-like, as indicated by infrared and Raman spectroscopies. Based on the surface distributions of CF(-) and CH(-) and on the vibrational spectroscopy results, a mechanism of fluorine substitution for hydrogen and an attempt to explain the film structure and microstructure is proposed.     

Analytical characterization of thin carbon films

CH(x) films on silicon substrates deposited by a Mesh Hollow Cathode Process (MHC) were analyzed by various techniques. The films were produced with varying deposition times, resulting in thicknesses ranging from ~2-20 nm. X-Ray Reflectivity (XRR) was used to determine the film thicknesses and the deposition rate. A good correlation of measured XRR thicknesses with SIMS sputter depths down to the film-substrate transition was found.An AFM-based nanoscratching technique was applied to test the wear resistance of the thin overcoats. The MHC films reveal slightly decreasing scratch resistance for reduced film thicknesses, which can be explained by a higher fraction of soft interface zones for thinner films.This is in accordance with Raman spectroscopic measurements in the visible spectral range which were carried out to examine the carbon bonding properties. Combined analysis of G peak position and D/G peak intensity ratio indicates a more graphitic structure for film thicknesses less than 10 nm.     

Ultrafast electrodeposition of amorphous carbon nitride films from fullerene derivative

Amorphous carbon nitride films with good photoluminescence could be ultrafastly fabricated by liquid-phase electrochemical decomposition of fullerene derivative, C₆₀[(NH₂)₂CNCN]₅. The structure of the as-prepared films, characterized by transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, was consisted of sp² hybrid C, sp³ hybrid C, C–N, CN and CN bands. Further study showed that the thickness of the films increased with the increase of the deposition time and the concentration of C₆₀[(NH₂)₂CNCN]₅. The optical tests indicated that the as-obtained films have distinct photoluminescence, no obvious decrease was observed more than one month later.     

Raman study of structural relaxation and boson peak in amorphous films of adamantane

Low-frequency Raman scattering was used to study amorphous solid films of adamantane, a globular non-polar hydrocarbon molecule. As evidenced by its spectral characteristics this type of disorder is different from the orientational disorder found in the room temperature plastic phase by the absence of the translational order as well. This gives rise to the boson peak related to acoustic phonons which gradually disappears upon heating with simultaneous emerging of the phonon line at 50 cm-1 which characterizes the low-temperature ordered phase of adamantane. Adamantane dynamics resembles that of C60 fullerene although not in the same temperature range. All this makes adamantane an attractive system that could serve as a practical reference in molecular simulation studies of the glassy phase of model fluids.     

Structure evolution of hydrogenated carbon films from amorphous carbon to fullerene‐like nanostructure

A–C:H (hydrogenated amorphous carbon) films were deposited by pulsed direct‐current (d.c.) plasma enhanced chemical vapor deposition on silicon substrates. This study investigated the structural and mechanical evolution of the as‐deposited films with fullerene‐like nanostructure. The results showed that pulsed d.c. negative bias (?500 ~ ?1000 V) signally influenced the growth rate, hardness, surface roughness, sp³ content, and friction behavior of the films. As the pulsed d.c. negative bias voltage increased, the sp³ content, surface roughness, hydrogen content and the friction coefficient of the films decreased; however, the growth rate and the hardness increased. The films deposited at ?1000 V with fullerene‐like microstructure display a nanohardness of about 19.7 GPa and the smallest friction coefficient (~0.06). The evolution on mechanical and structural properties of the films are explained by the a–C:H growth mechanism based on the interaction on plasma‐surface interface and the subsurface reactions in the film. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of temperature on the surface free energy of amorphous carbon films

Diamond-like carbon (DLC) and tetrahedral amorphous carbon (ta-C) have attracted much attention recently for biomedical and antifouling applications due to their excellent biocompatibility and inherent nonstick properties. It has been demonstrated that the solid surface free energy is a dominant factor in cellular or fouling adhesion. However, few data for the surface free energy of DLC and ta-C coatings at temperatures in the range 37-95 degrees C are available. In this study DLC and ta-C coatings on stainless steel 304 sheets were prepared using an unbalanced magnetron sputtering system and a filtered cathodic vacuum arc system, respectively. The contact angles of water, diiodomethane and ethylene glycol on the coated surfaces at temperatures in the range 20-95 degrees C were measured using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the coatings and their components (e.g., dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the total surface free energy and dispersive surface free energy of the ta-C coatings, DLC coatings, stainless steel 304 and titanium decreased with increasing surface temperature, while the acid-base SFE component increased with increasing temperature.     

Fabrication of hydrophobic fluorinated amorphous carbon thin films by an electrochemical route

A novel electrochemical route for the preparation of hydrophobic fluorinated amorphous carbon (a-C:F) films with nanostructured surfaces on single crystal silicon substrate was reported. The films were investigated in terms of the surface morphology, chemical composition, microstructure and hydrophobic behavior. The results showed that a highly uniform and densely packed bamboo shoot-like nanostructure was obtained without any use of template. The incorporation of fluorine presented mainly in the forms of CF₂ chains and CCF_x (x = 1, 2) in the films. Sessile drop water contact angle measurements showed that the contact angle of a-C:F films deposited by electrochemical route was about 145°, which can be attributed to the lower surface energy of CF_x groups and higher diffusion resistance of the special nanostructured surface to water. Moreover, the related growth mechanism of the resulting films in liquid-phase electrodeposition is discussed as well.     

Covalent photochemical functionalization of amorphous carbon thin films for integrated real-time biosensing

Recent studies have demonstrated that carbon, in the form of diamond, can be functionalized with molecular and/or biomolecular species to yield interfaces exhibiting extremely high stability and selectivity in binding to target biomolecules in solution. However, diamond and most other crystalline forms of carbon involve high-temperature deposition or processing steps that restrict their ability to be integrated with other materials. Here, we demonstrate that photochemical functionalization of amorphous carbon films followed by covalent immobilization of DNA yields highly stable surfaces with excellent biomolecular recognition properties that can be used for real-time biological detection. Carbon films deposited onto substrates at 300 K were functionalized with organic alkenes bearing protected amine groups and characterized using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The functionalized carbon surfaces were covalently linked to DNA oligonucleotides. Measurements show very high selectivity for binding to the complementary sequence, and a high density of hybridizing DNA molecules. Samples repeatedly hybridized and denatured 25 times showed no significant degradation. The ability to use amorphous carbon films as a basis for real-time biosensing is demonstrated by coating quartz crystal microbalance (QCM) crystals with a thin carbon film and using this for covalent modification with DNA. Measurements of the resonance frequency show the ability to detect DNA hybridization in real time with a detection limit of <3% of a monolayer, with a high degree of reversibility. These results demonstrate that functionalized films of amorphous carbon can be used as a chemically stable platform for integrated biosensing using only room-temperature processing steps.     

Characterization of amorphous carbon films by 13C CP MAS NMR spectroscopy

¹³C CP MAS NMR spectroscopy was used to characterize α-C:H materials generated from methane and hydrogen mixtures using a microwave plasma. Dipolar dephasing experiments indicate a range of T_dd making quantification of quaternary “diamond”-like carbons difficult. Unconstrained lineshape analysis is not suitable for the deconvolution of the NMR spectra, but linewidth constrained analyses gave reasonable results. © 1993 John Wiley & Sons, Inc.     

Raman characterization of orientation in poly(lactic acid) films

Poly(lactic acid) is a new biopolymer material which is marketed by Cargill Dow Polymers under the tradename Nature Works*. One major application for this material is biaxially oriented films for food packaging because it possesses excellent barrier for flavor constituents, deadfold and heat sealability. Shrinkage must be minimized when the film is heat sealed for these applications and, therefore, characterization of the orientation of the amorphous phase of PLA films is necessary. Raman spectroscopy methodology has been developed to quantify orientation in PLA films. Bands were assigned to crystalline and amorphous phases of PLA such that orientation in both phases could be monitored. Raman depolarization ratios were used to characterize uniaxial systems but were insufficient for most biaxial draws. A new phenomenon for oriented films involving Raman band shifts was observed in these systems, and was shown to be capable of determining orientation, even for symmetrical biaxially drawn films. The origin of these shifts, as well as their use for the quantification of orientation will be discussed. Further, since the line widths of the bands could be used to quantify crystallinity, both crystallinity and orientation could be determined with one measurement.     

Multilayer graphene/amorphous carbon hybrid films prepared by microwave surface‐wave plasma CVD: synthesis and characterization

Hybrid films of multilayer graphene (MG) containing amorphous carbon (a‐C) were synthesized on Al substrates by microwave surface‐wave plasma chemical vapor deposition. Raman scattering and surface transmission electron microscopy showed that the carbon films contained a large quantity of MG when a radio frequency (RF) substrate bias was not applied. Amorphization of graphene in the carbon film was promoted by applying an RF bias, which generated Ar⁺ in the plasma. The bandgaps of the films were found to increase as the Raman intensity ratios between the 2D‐band (at 2700 cm^?1) and D‐band (at 1350 cm^?1) decreased, indicating the formation of a‐C. The MG/a‐C all‐sp² phase of carbon hybrid films exhibited an increase in current density under 5 mW/cm² of AM1.5G solar simulated irradiation as the RF bias increased because of Ar⁺‐induced amorphization of the graphene. Copyright © 2016 John Wiley & Sons, Ltd.     

Autophobic dewetting of Z-tetraol perfluoropolyether lubricant films on the amorphous nitrogenated carbon surface

The thermodynamic stability of thin films of the perfluoropolyether (PFPE) Z-Tetraol, as a function of molecular weight, on amorphous nitrogenated carbon, CNx, is investigated. An optical surface analyzer is used to image the autophobic dewetting of the Z-Tetraol films. Film dewetting results when the PFPE film thickness applied to the CNx surface exceeds a critical value. This critical dewetting thickness is identified as the monolayer thickness of the adsorbed PFPE film via measurements of the changes in the surface energy as a function of lubricant film thickness. The observed dewetting coincides with the film thickness at which the disjoining pressure goes to zero. The critical dewetting thickness is dependent on the PFPE molecular weight.