Hydrocarbon Plasma Research Articles

Note: Cavity enhanced self-absorption spectroscopy: A new diagnostic tool for light emitting matter

We introduce the concept of Cavity Enhanced Self-Absorption Spectroscopy (CESAS), a new sensitive diagnostic tool for analyzing light-emitting samples. The technique works without an additional light source and its implementation is straight forward. In CESAS, a sample (plasma, flame, or combustion source) is located in an optically stable cavity consisting of two high reflectivity mirrors, and here it acts both as light source and absorbing medium. A modest portion of the emitted light is trapped inside the cavity, making 10(4)-10(5) cavity round trips while crossing the sample and an artificial augmentation of the path length of the absorbing medium occurs as the light transverses the cavity. Light leaking out of the cavity simultaneously provides emission and absorption features. The performance is illustrated by CESAS results on supersonically expanding pulsed hydrocarbon plasma. We expect CESAS to become a generally applicable analytical tool for real time and in situ diagnostics.

A diagnosis of gas-phase processes in a high pressure DC CH4/H2 plasma

In this work, gas phase processes in a high pressure (～100 Torr) DC hydrocarbon plasma are investigated in situ by optical emission spectroscopy and mass spectroscopy. In the high pressure plasma, optical emission characteristics of glow layers are obviously different. C2, CH dominated band spectra and discrete spectra are distinctively observed in the positive column, whereas the emission intensity is found to decrease in the anode region. In the cathode region, a large number of complicated spectra are detected, which indicates the intensive interaction between the cathode and plasma under high pressure induces complicated atomic and molecular processes. With the the increase of pressure, electron excitation temperature decreases while gas rotational temperature goes up. High methane concentration causes increases in C2, C2H2 and C2H4 but a reduction in C2H6. Those suggest that the effect of gas temperature on gas phase process is significantly enhanced under high pressure.

Monitoring Technological Conditions for Preparing DLC Films in Supersonic Flow of Hydrocarbon Plasma

Properties of diamond-like carbon films deposited by a new method in a supersonic flow of hydrocarbon plasma generated by a disk-type magneto-hydro-dynamic accelerator were studied. Two methods are used for optical and structural characterization of diamond-like carbon films: nondestructive spectroscopic ellipsometry and Raman spectroscopy.

Cavity enhanced plasma self-absorption spectroscopy

We introduce cavity enhanced plasma self-absorption spectroscopy (CEpSAS), a sensitive spectroscopic diagnostic tool that is used here for plasma analysis, but can also be used for any light emitting sample. It works without an additional external light source. In CEpSAS, plasma is located in an optically stable cavity consisting of two high reflectivity mirrors, and here it acts both as light source and absorbing medium. We present proof of principle results to illustrate the performance of this technique that literally combines “sense and simplicity.” Quantitative absorption experiments are described on a supersonically expanding hydrocarbon plasma.

Tailor-Made Silver Release Properties of Silver-Containing Functional Plasma Polymer Coatings Adjusted Through a Macroscopic Kinetics Approach

Combining a functional plasma polymer matrix with antibacterially active silver (Ag) within a nanocomposite structure allows secure production and applications in various fields, especially in the medical sector. Therefore, nitrogen or oxygen containing hydrocarbon plasma polymers and Ag nanoparticles were simultaneously deposited. Functional groups such as amino or carboxylic groups as well as an adjusted amount of Ag can be incorporated into the growing films by controlling the plasma deposition properties. For this purpose, macroscopic kinetics were used to characterise the deposition behaviour also as a base for possible industrial up-scaling. XPS and ICP-OES were used to analyse the chemical composition of the polymer–Ag nanocomposites and the Ag content which could be incorporated depending on the plasma process conditions. Finally, the Ag release was determined in bi-distilled water for classification and comparison with the antibacterial properties. The antibacterial effect of the polymer–Ag nanocomposites was proofed with the gram− strain Pseudomonas aeruginosa PAO1 and the gram+ strain Staphylococcus aureus (ST12 Group) showing a clear efficacy dependence on the amount of released Ag and the possibility for tailor-made antibacterial active plasma films.

Inside Cover: Infrared Spectrum and Structure of the Adamantane Cation: Direct Evidence for Jahn-Teller Distortion (Angew. Chem. Int. Ed. 20/2012)

The gas-phase infrared spectrum of the adamantane radical cation, C10H16+, provides the first spectroscopic characterization of the geometric and electronic structure of this cycloalkane carbocation and direct evidence for the Jahn–Teller distortion in the 2A1 ground electronic state. In their Communication on page 4925 ff., O. Dopfer et al. show that the characteristic IR fingerprint may be used for the identification of C10H16+ in hydrocarbon plasmas, including the interstellar medium.

Ultrathin ultrananocrystalline diamond film synthesis by direct current plasma-assisted chemical vapor deposition

The synthesis of ultrathin, mirror-smooth, and void-free ultra-nanocrystalline diamond (UNCD) film was investigated using DC-PACVD. The seeding process was investigated in the previously reported “two-step” seeding scheme, where the substrate was pretreated in microwave hydrocarbon plasma prior to the ultrasonic seeding to enhance seed density; in the present study, DC plasma and hot filament process were adopted for the pretreatment, instead of the conventional microwave plasma. Two types of nano-diamond seed powders of similar grain sizes but with different zeta potentials were also compared. The pretreated substrate surface and the synthesized UNCD film were characterized by near edge x-ray absorption fine structure, FTIR, AFM, high-resolution scanning electron microscope, HR-TEM, and Raman spectroscopy. The electrophoretic light scattering spectroscopy was adopted to characterize the zeta potentials of the seeding suspensions and that of the substrates, respectively. Contrary to the previous report, the pretreatments deteriorated the seed density relative to that of the non-treated substrate. By contrast, the seed density was drastically improved by using a proper type of the nano-diamond seed powder. The seed density variation according to the substrate pretreatments and the type of the seed powders was attributed to the relative values of the zeta potentials of the substrates and that of the seed powders, which indicated the electrostatic nature of the seeding process. The variation of the substrate surface zeta potentials was attributed to the variation in the surface terminations induced by the respective pretreatments. The present DC-PACVD environment ensured that the secondary nucleation was also active enough to generate the densely packed UNCD grains in the growth stage. Consequently, the ultrathin, mirror-smooth and void-free UNCD film of 30 nm in thickness was enabled.

Optical properties and morphology of diamond-like films obtained in a supersonic flow of a hydrocarbon plasma

A possibility of using a new method of film synthesis in a supersonic flow of a hydrocarbon plasma generated by a disk-type magnetohydrodynamic accelerator is demonstrated. Two methods are used for characterization of diamond-like carbon films: nondestructive spectroscopic ellipsometry and atomic-force microscopy.

IR Spectra of C2H5+-N2 Isomers: Evidence for Dative Chemical Bonding in the Isolated Ethanediazonium Ion

The potential energy surface (PES) of C(2)H(5)(+)-N(2) is characterized in detail by infrared photodissociation (IRPD) spectroscopy of mass-selected ions in a quadrupole tandem mass spectrometer and ab initio calculations at the MP2/6-311G(2df,2pd) level. The PES features three nonequivalent minima. Two local minima, 1-N(2)(H) and 1-N(2)(C), are adduct complexes with binding energies of D(0) = 18 and 12 kJ/mol, in which the N(2) ligand is weakly bonded by electrostatic forces to either the acidic proton or the electrophilic carbon atom of the nonclassical C(2)H(5)(+) ion (1), respectively. The global minimum 3 is the ethanediazonium ion, featuring a weak dative bond of D(0) = 38 kJ/mol. This interaction strength is sufficient to switch the C(2)H(5)(+) structure from nonclassical to classical. The 1-N(2)(C) isomer corresponds to the entrance channel complex for addition of N(2) to 1 yielding the product 3. This reaction involves a small barrier of 7 kJ/mol as a result of the rearrangement of the C(2)H(5)(+) ion. The partly rotationally resolved IRPD spectrum of C(2)H(5)(+)-N(2) recorded in the C-H stretch range is dominated by four bands assigned to 3 and one weak transition attributed to 1-N(2)(H). The abundance ratio of 1-N(2)(H) and 3 estimated from the IRPD spectrum as ∼1% is consistent with the calculated free energy difference of 12 kJ/mol. As the ethanediazonium ion escaped previous mass spectrometric detection, the currently accepted value for the ethyl cation affinity of N(2) is revised from -ΔH(0) = 15.5 ± 1.5 to ∼42 kJ/mol. The first experimental identification and characterization of 3 provides a sensitive probe of the electrophilic character and fluxionality of the ethyl cation. Comparison of 3 with related alkanediazonium ions reveals the drastic effect of the size of the alkyl chain on their chemical reactivity, which is relevant in the context of hydrocarbon plasma chemistry of planetary atmospheres and the interstellar medium, as well as alkylation reactions of (bio)organic molecules (e.g., carcinogenesis and mutagenesis of DNA material).

Adhesion, Growth and Differentiation of Osteoblasts on Surface-Modified Materials Developed for Bone Implants

This review briefly outlines the history and possibilities of bone reconstruction using various types of artificial materials, which allow interaction with cells only on the surface of the implant or enable ingrowth of cells inside the material. Information is also provided on the most important properties of bone cells taking part in bone tissue development, and on diseases and regeneration. The most common cell types used for testing cell-material interaction in vitro are listed, and the most commonly used approaches to this testing are also mentioned. A considerable part of this review is dedicated to the physical and chemical properties of the material surface, which are decisive for the cell-material interaction, and also to modifications to the surface of the material aimed at integrating it better with the surrounding bone tissue. Special attention is paid to the effects of nanoscale and microscale surface roughness on cell behaviour, to material surface patterning, which allows regionally-selective adhesion and growth of cells, and also to the surface chemistry. In addition, coating the materials with bioactive layers is examined, particularly those created by deposition of fullerenes, hybrid metal-fullerene composites, carbon nanotubes, nanocrystalline diamond films, diamond-like carbon, and nanocomposite hydrocarbon plasma polymer films enriched with metals.

Formation of dust in low-pressure magnetized hydrocarbon plasmas

The rapid formation of large molecules and the subsequent production of solid-state dust particles in a low-pressure discharge is unlikely, because of the low rates of the polymerization reactions and short lifetimes of the species. Here, we suggest that C dust particles can form in atypically low (10− 3 mbar)-pressure hydrocarbon plasmas if the dust charging time is much shorter than the gas residence time in the device; we present supporting experimental evidence for this. Such a condition can be obtained by the production of high-density plasmas. The results show that dust formation from the gaseous phase can occur in a much wider parameter range than is commonly assumed.

Uniform cell colonization of porous 3-D scaffolds achieved using radial control of surface chemistry

Uniform cellular distribution is a prerequisite to forming tissue within porous scaffolds, but the seeding process often results in preferential adhesion of cells at the periphery. We develop a vapour phase coating strategy which is readily applicable to any porous solid to provide a uniform cellular distribution. Plasma polymerized allyl amine (ppAAm) is used to form a thin nitrogen-containing coating throughout porous three-dimensional (3-D) poly( d, l-lactic acid) scaffolds. Subsequent controlled deposition of a hydrocarbon plasma polymerized hexane (ppHex) allows control of the fibroblast penetration into these porous 3-D objects. In order to optimize the coating conditions, a planar pinhole model of plasma penetration into pores is developed to rapidly measure deposit penetration using picolitre water contact angle measurement. Sufficiently good control over the plasma deposition within the porous scaffold is achieved using this approach to superimpose a relatively cell-repellent ppHex coating at the scaffold periphery onto the ppAAm-coated core, with a chemical gradient between the two. This 3-D chemical gradient encourages 3T3 fibroblast cells to adhere homogeneously from the periphery to the centre, when balanced by the tortuousity of the pore structure, which cells experience when passing from the surrounding medium to the centre.

Computer modelling of the plasma chemistry and plasma-based growth mechanisms for nanostructured materials

In this review paper, an overview is given of different modelling efforts for plasmas used for the formation and growth of nanostructured materials. This includes both the plasma chemistry, providing information on the precursors for nanostructure formation, as well as the growth processes itself. We limit ourselves to carbon (and silicon) nanostructures. Examples of the plasma modelling comprise nanoparticle formation in silane and hydrocarbon plasmas, as well as the plasma chemistry giving rise to carbon nanostructure formation, such as (ultra)nanocrystalline diamond ((U)NCD) and carbon nanotubes (CNTs). The second part of the paper deals with the simulation of the (plasma-based) growth mechanisms of the same carbon nanostructures, i.e. (U)NCD and CNTs, both by mechanistic modelling and detailed atomistic simulations.

Nanocomposites and nanostructures based on plasma polymers

Nanocomposite metal/plasma polymer films have been deposited since the seventies of the last century using sputtering or thermal evaporation of a metal simultaneously with a plasma polymerization process. The main attention was paid to fluorocarbon and hydrocarbon plasma polymers as matrices for the incorporation of metals such as Au and Ag. Main deposition techniques used for the fabrication of such nanocomposites are reviewed together with an overview of their basic optical and electrical properties, composition and structure. Proposed applications are mentioned as well. In addition, RF magnetron co-sputtering of a polymer such as polytetrafluoroethylene, is also mentioned. Nanostructuring of a fluorocarbon plasma polymer by changing deposition parameters including deposition system geometry is revealed and the application in terms of superhydrophobic coating is mentioned. Cluster sources, namely the gas aggregation (condensation) cluster source (GAS) based on a planar magnetron in a compact and simple form is described and its performance for the preparation of nanocomposite and nanostructured metal/plasma polymer films is discussed.

Diagnosis of Active Species in Reactive Acetylene Plasma by Laser-Ionization Molecular-Beam Time-of-Flight Mass Spectrometry

This work reports a new laser molecular beam time-of-flight mass spectrometry (LMB-TOFMS) instrument built at Plasma Spectroscopy Lab in Dalian University of Technology (DUT). The preliminary investigation of the intermediate species distribution of acetylene plasma in an atmospheric-pressure fast-flow nanosecond-pulsed dc-discharge has been carried out. The CxH2 species (x = 4,6,8), believed to be the dominant source of negative ions in C2H2 plasma, have been detected with relatively intense peak signals and some complex radical species like C7H7, C9H5, C10H5 are also observed. The addition of Ar gas significantly influenced the detection of the intermediate species. This is might be due to the metastable Ar* with energies of 11.5 and 11.7 eV and a long lifetime. The potentialities of LMB-TOFMS for hydrocarbon plasmas diagnosis have been discussed.

A 3 µm difference frequency laser source for probing hydrocarbon plasmas

The practicality of a compact solid-state laser-based difference frequency generation system is demonstrated as a tool for probing hydrocarbon-based plasmas. The laser light of a cw Nd : YAG operating at 1064 nm and one of two distributed feedback diode lasers operating at 1560 and 1620 nm were mixed in a periodically poled lithium niobate crystal producing mid-infrared radiation at 3.35 and 3.1 µm for the detection of CH4 and C2H6 at the first wavelength and C2H2 and C2H4 at the latter. The radiation was used to probe a rf capacitively coupled CH4 plasma for a matrix of conditions, varying power (<180 W) and pressure (<1 Torr) in both direct absorption spectroscopy and wavelength modulation spectroscopy (WMS) experiments to achieve relatively high sensitivities while retaining accurate spectral information in the form of linewidths. A minimum detectable absorption coefficient αmin of 2 × 10−5 cm−1 was achieved for direct absorption spectroscopy which corresponds to a minimum detectable density for CH4 of 1.7 × 1012 cm−3 and an αmin value of 2 × 10−6 cm−1 was achieved for WMS measurements on C2H2. The depletion of CH4 was measured to increase from 23% at 40 W to 40% at 180 W at a pressure of 0.84 Torr, and the depletion increased to 56% as the pressure decreased to 0.45 Torr.

Near infrared optical materials from polymeric amorphous carbon synthesized by collisional plasma process

The synthesis of polymerlike 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 synthesized 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.

Heat resistance of the interface in the silicon-on-diamond structure at a temperature of 80 K

Heat propagation at liquid nitrogen temperature in a heterostructure consisting of a polycrystalline diamond film deposited from hydrocarbon plasma on an oriented silicon substrate is studied. A technique for measuring the cooling kinetics of a thin-film indium thermometer deposited on a diamond film after heating by nanosecond pulses of a nitrogen laser is used. The experimental data are compared with the results calculated within the theory of heat conduction for multilayer systems. The analysis performedmade it possible to simultaneously determine the thermal conductivity of the diamond film and the interfacial heat resistance of diamond/Si and In/diamond interfaces at liquid nitrogen temperature.

Determinations of Intermediate Neutral Species in Hydrocarbon Discharge Plasma

This work reports laser ionization combined with Time-Of-Flight (TOF) mass spectrometry investigation on intermediate species in the hydrocarbon plasma of atmospheric-pressure fast-flow pulsed dc-discharge. All neutral intermediate species including transient radicals from benzene/Ar discharge have been characterized by a molecular beam sampling combined with TOF mass spectrometry. This shows that with a hydrocarbon gas mixture of 0.3% C6H6 in Ar discharge the intermediate species consist of simple radicals (such as C2, C5H5, C7H7) and polycyclic organic molecules (C10H8, C13H10, C14H10). Theoretical studies on total energies and ionization potentials of the intermediate species have been carried out using the hybrid density functional theory. Effect of the ionization potential on mass spectral intensity has been discussed. Based on the observed data, the possible major neutral reaction channels of the plasma chemistry have been discussed. The developed experimental method has implications in volatile organic compounds removing and impurities diagnosis in Tokamak edge-plasma.

A coincidence between a hydrocarbon plasma absorption spectrum and theλ5450 DIB

The aim of this work is to link the broad lambda 5450 diffuse interstellar band (DIB) to a laboratory spectrum recorded through an expanding acetylene plasma. Cavity ring-down direct absorption spectra and astronomical observations of HD 183143 with the HERMES spectrograph on the Mercator Telescope in La Palma and the McKellar spectrograph on the DAO 1.2 m Telescope are compared. In the 543-547 nm region a broad band is measured with a band maximum at 545 nm and FWHM of 1.03(0.1) nm coinciding with a well-known diffuse interstellar band at lambda 5450 with FWHM of 0.953 nm. A coincidence is found between the laboratory and the two independent observational studies obtained at higher spectral resolution. This result is important, as a match between a laboratory spectrum and a - potentially lifetime broadened - DIB is found. A series of additional experiments has been performed in order to unambiguously identify the laboratory carrier of this band. This has not been possible. The laboratory results, however, restrict the carrier to a molecular transient, consisting of carbon and hydrogen.