What makes a dangling bond a binding site for thermal CH3 radicals? — A combined molecular dynamics and potential energy analysis study on amorphous hydrocarbon films

Identification of dangling bonds on amorphous films is not as straight forward as in the case of crystalline materials. The task is further complicated in the case of amorphous hydrocarbon (a-C:H) films by the existence of a wide variety of atomic arrangements. We present a technique based on potential energy analysis of a-C:H films to identify dangling bonds and physisorption sites. However, molecular dynamics simulations of the sticking of thermal CH₃ on a-C:H surfaces show that not all dangling bonds are binding sites for a CH₃ radical. Furthermore, the total sticking coefficient of the surface is not solely linked to the number of dangling bonds and can even decrease for the same number of dangling bonds because the carbon atoms that possess a binding site, active carbon atoms, show drastically different reactivity towards CH₃. The reactivity of active carbon atoms is decided by (a) their type, which is decided by the bonding partners, (b) their distance from the local surface and (c) the local environment. The reactivity of the active carbon atoms can be largely increased by energetic ion bombardment due to hydrogen depletion and local rearrangement.     

Photoluminescence of Amorphous Multilayer Structures <Emphasis Type="Italic">a</Emphasis>-C:H/<Emphasis Type="Italic">a</Emphasis>-Si:H

The optical absorption edge and the photoluminescence spectra of amorphous hydrogenated diamond-like carbon (a-C:H) films are investigated in the temperature range 4.2–900 K. Low-dimensional multilayer structures a-C:H/a-Si:H, in which a-C:H with an optical band gap E _g = 4.5 eV is used as a barrier, are prepared for the first time. It is found that amorphous hydrogenated silicon (a-Si:H) films with a thickness d < 100 Å exhibit quantum-confinement effects. Analysis of the photoluminescence spectra and the optical absorption edge of the a-Si:H films shows that the structures a-C:H/a-Si:H have a sharp interface and that charge carriers in the a-Si:H film undergo quantization.Original Russian Text Copyright © 2005 by Fizika i Khimiya Stekla, Babaev, Kamilov, Sultanov, Askhabov.     

Electrochemical behaviour of thin films deposited by plasma DBD torch on copper: An O2-diffusion barrier

In the field of corrosion protection, the research of environmentally friendly coating processes is one of the research topics. The use of gaseous atmospheric plasma, especially dielectric barrier discharge (DBD) plasma is an interesting way to rapidly form a thin protective coating. The aim of this work is to characterize the electrochemical behaviour of a SiO_xC_yN_z film, formed from different organosilicon precursors, in neutral corrosive environment on copper. The film morphology and composition were determined by transmission electron microscopy (TEM) observations and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the different treated copper was studied by stationary techniques and electrochemical impedance spectroscopy (EIS). With the same plasma parameter, the kind of organosilicon precursor determines the chemical stability of the coatings in water, then their protective properties. When the SiO₂-like structure contains a low carbon level, the SiO_xC_yN_z films present a good stability in water, and acts clearly as an O₂ barrier membrane.     

An efficient method for a numerical description of virgin olive oil color with only two absorbance measurements

Four polynomial expressions are obtained that provide a good approximation and an easy, rapid calculation of the chromatic coordinates and the chroma—L ^*, a ^*, b ^*, and C—for the illuminant C and the standard observer, for a virgin or extra virgin olive oil; absorbance is measured at only 480 and 670 nm. These are as follows: L ^*=0.556458(A₄₈₀)²−2.51145A₄₈₀+0.55504(A₆₇₀)²−8.53016A₆₇₀+98.4089; a ^*=0.177372(A₄₈₀)²+2.1363A₄₈₀+1.43254(A₆₇₀)²−0.789231A₆₇₀−13.9246; b ^*=−16.0277(A₄₈₀)²+79.8932A₄₈₀−5.06558(A₆₇₀)²+3.36169A₆₇₀+31.9405; C=−15.8439(A₄₈₀)²+78.9312A₄₈₀−5.26784(A₆₇₀)²+3.56917A₆₇₀+33.3927. These give acceptable results, making the method a practical alternative to the extremely laborious Commission Internationale d’Eclairage (CIE) L ^* a ^* b ^* system, by which 391 absorbance values must be measured individually, nanometer by nanometer, before applying more complex equations. The validity of the proposed method has been confirmed by comparison, using a set of 20 sample oils different from the set of 25 oils used to generate the order of the equations. The variations between the values provided by the proposed and standard methods, respectively, had a mean of 0.00 for each of the chromatic variables—L ^* , a ^* , b ^* , and C; SD were moderate (0.71, 0.52, 1.22, and 1.22, respectively); the root mean square and the R ²-terms also confirmed the validity of the method.     

Evaluation of protein adsorption on hydrogenated amorphous carbon films by surface plasmon resonance phenomenon

To develop an anti-thrombogenic coating, hydrogenated amorphous carbon (a-C:H) and related films were studied in terms of their protein adsorption during the initial process in thrombogenesis by surface plasmon resonance (SPR) phenomenon using a multilayer device consisting of an a-C:H layer on Au. Two a-C:H films with different hydrogen contents, a nitrogenated a-C:H (a-C:N:H) and a fluorinated amorphous carbon (a-C:F) film were prepared on the Au layer in the multilayer device. Human serum albumin (HSA) in a phosphor buffer (PB) was used as a protein. Na₂HPO₄·12H₂O, NaH₂PO₄·2H₂O and deionized water were mixed to coordinate PB. From the attenuation of reflected light, the SPR angle was determined to the angle at minimum reflection intensity. The observed behavior of the SPR angle indicated that HSA was adsorbed on all films. The SPR angle was analyzed to estimate the multilayer index of the HSA-adsorbed layer on each film. The HSA adsorption ability of both a-C:H and a-C:N:H films was similar, and the absorption ability of the a-C:F film was lower than that of the other films. Hence, the surface polarization dominates the adsorption ability of HSA on a-C:H films and related film.     

Influence of the methyl group on the dielectric constant of boron carbon nitride films containing it

LSI interconnect insulators made using low dielectric constant (low-k) materials are required for high performance devices with a small RC delay. We investigated a boron carbon nitride film containing the methyl group (Me–BCN) using tris-di-methyl-amino-boron (TMAB: B[N(CH₃)₂]₃) gas as a low-k material. In addition, we studied the influence of the methyl group on the dielectric constant (k-value) and the properties of the Me–BCN films. It was found that the k-value of the Me–BCN films decreases with increasing number of C–H bonds due to the methyl group (CH₃). The number of O–H bonds due to water incorporation is suppressed by increasing the number of C–H bonds. Consequently, we suggested that a lower k-value can be realized by the suppression of water invasion by a hydrophobic surface due to methyl bonds. Thus, the control of the methyl group is important to achieve a low-k material using Me–BCN films.     

Effect of the fold surface of the lamellae on the behavior of the trapped radicals in irradiated Polyamide-1010

Two types of macromolecular free radicals —CH₂CONHĊHCH₂— (a) and —CH₂Ċ=O (b) trapped in irradiated Polyamide-1010 (PA1010) and PA1010 filled with neodymium oxide (Nd₂O₃) were characterized by an ESR approach. It was found out that a was mainly trapped in the fold surface of the lamellae and b in the amorphous phase. This result suggested that trapped radicals mainly existed in the noncrystalline phases. The effect of the fold surface area of the lamellae on the behavior of the trapped radicals are discussed in this article. Whether for the specimens with similar crystallinities but different crystallite sizes or for those with the same concentration of neodymium oxide but different crystallinities, radical a exists dominantly in a specimen with a larger fold surface area of the lamellae. Under a certain circumstance, radical a can transform into radical b for a specimen with a larger fold surface area of the lamellae. It means that the fold surface area of the lamellae plays an important role in the transformation of radical a to b. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1335–1339, 1998     

Synthesis and characterization of per-substituted spermine-bridged cyclophosphazene derivatives: the first example of syn/anti conformational polymorphism in a bridged cyclophosphazene

The synthesis and characterization of a series of per-substituted spermine-bridged cyclophosphazene derivatives are reported based on the known compound [N₃P₃X₄(NHCH₂CH₂CH₂N)CH₂CH₂]₂, (1a) (where X = Cl), to give a number of new compounds (1b–1h) in which X = OPh, [spiro-O(CH₂)₃O]_0.5, OCH₂CF₃, NHPh, NC₄H₈, Ph and NHBu^t, respectively. Two synthetic routes were utilized: (i) using the chloro-precursor 1a in nucleophilic substitution reactions with a variety of anionic and neutral nucleophiles to give compounds 1b–1f and (ii) reaction of spermine with the appropriate di-gem tetrasubstituted cyclophosphazene to give compounds 1g and 1h. Bridged compounds such as 1a–1h may exist as syn or anti conformers in the solid state and the first example of syn and anti conformational polymorphism is reported for a bridged cyclophosphazene, viz. for compound 1a.     

New insights into the mechanism of CVD diamond growth: Single crystal diamond in MW PECVD reactors

CVD Diamond can now be deposited either in the form of single crystal homoepitaxial layers, or as polycrystalline films with crystal sizes ranging from mm, μm or nm, and with a variety of growth rates up to 100s of μm h^− 1 depending upon deposition conditions. We previously developed a model which provides a coherent and unified picture that accounts for the observed growth rate, morphology, and crystal sizes, of all of these types of diamond. The model is based on competition between H atoms, CH₃ radicals and other C₁ radical species reacting with dangling bonds on the diamond surface. The approach leads to formulae for the diamond growth rate G and average crystallite size <d> that use as parameters the concentrations of H and CH_x (0 ≤ x ≤ 3) near the growing diamond surface. We now extend the model to show that the basic approach can help explain the growth conditions required for single crystal diamond films at pressures of 100–200 Torr and high power densities.     

The effect of argon on the electron field emission properties of α-C:N thin films

Amorphous carbon nitride (α-C:N) thin films were synthesized on silicon as electron emitters by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) system in which a negative dc bias was applied to the graphite substrate holder and a mixture of C₂H₂ and N₂ was used as precursors. The addition of Ar combined with the application of a negative dc bias can increase nitrogen content (N/C) measured by X-ray photoelectron spectroscopy (XPS), eliminate the dangling bonds in the film determined by Fourier transform infrared (FTIR) spectroscopy, decrease the film thickness measured by field emission scanning electron microscope (FE-SEM), increase the film roughness measured by atomic force microscope (AFM) and raise the graphitic content examined by Raman spectroscopy. The result shows that the onset emission field of α-C:N with Ar addition to the precursors can be as low as 4.5 V μm⁻¹ compared with 9.5 V μm⁻¹ of the film without the addition of Ar.     

Molecular dynamics simulations for the growth of diamond-like carbon films from low kinetic energy species

In this study, molecular dynamics simulations using the Brenner potential for hydrocarbons have been used to simulate the formation of diamond-like carbon (DLC) films grown from low-energy hydrocarbon radicals (<2 eV). With these simulations, insight is gained in the processes occurring in this type of deposition. The initial surface is a previously deposited DLC surface; impinging particles include Ar⁺ ions, with an energy of 2 eV, as well as several carbon radicals and molecules, and hydrogen atoms, with an energy of 1 eV. Two different radical flux compositions were examined: in the first condition, only C, C₂, and CH were used as growth species, as well as a large flux of H atoms. In the second condition, the same carbon radicals were considered, as well as the C₂H radical and C₂H₂, C₄H₂, and C₆H₂ molecules, but without the H atom flux. These fluxes are similar to different experimental conditions in an expanding thermal Ar/C₂H₂ plasma (expanding thermal plasma, or ETP), using different influxes of acetylene. Several properties of the resulting films will be presented, focusing mainly on the carbon coordination and the bonding network. The simulations suggest that lowering the acetylene influx results in films having a more extensive bonding network, but with more H incorporated. This leads to more polymeric films having a less diamond-like character, as is expected also from experiments. The aim of this work is twofold. The first objective is to compare the structural composition of the simulated films to the structure of the experimentally deposited films by applying similar conditions. Second, the simulations can give us valuable information about the key mechanisms in the deposition process.     

Effects of acetylene addition on mechanical and dielectric properties of amorphous carbon films

The para-xylene added with acetylene from 15% to 50% was plasma polymerized at 50 to 150 W to deposit the a-C:H films. After the films were annealed from 200 to 400 °C, the network structure, hardness and dielectric constant of films were analyzed by FT-IR, Raman, nanoindentor and capacitance–voltage plot, respectively. Those measured results suggest that hydrocarbon bonds and oxygen related bonds of the a-C:H film effectively reduce and the number of ordered aromatic rings increases with decreasing the deposition power after annealing at 400 °C. In addition, both the dielectric constant and the hardness, respectively, increase up to 2.82 and 2.37 GPa, but the adhesion strength decreases with increasing the C₂H₂ concentration and deposition power. Therefore, the a-C:H films not only have a lower dielectric constant, but also have enough mechanical strength for the IC processing.     

Potential reaction paths in NOx reduction over Cu/ZSM-5

The reaction of NO with adsorbed acetone oxime has been studied over Cu/ZSM-5 employing FTIR and MS. It is found that¹⁵NO_gas reacts with¹⁴N labelled acetone oxime and/or its hydrolysis product, hydroxylamine, to form¹⁴N¹⁵NO and¹⁴N¹⁵N at 40°C. As acetone oxime is easily formed from alkyl radicals and NO via alkylnitroso compounds, the results indicate possible reaction paths for the SCR of NO _x by hydrocarbons over zeolite based catalysts. The isotopic data suggest predominant formation of N-N bonds occurs via interaction of gaseous NO with a nitrogen containing adsorbed complex.     

ELECTROLESS PLATING OF GLASS AND SILICON SUBSTRATES THROUGH SURFACE PRETREATMENTS INVOLVING PLASMA-POLYMERIZATION AND GRAFTING PROCESSES

Electroless plating of nickel (or copper) was carried out on glass (or silicon) substrates that were previously surface modified by using plasma-polymerization and grafting processes, and then activated by immersion in a simple acidic PdCl₂ solution. Three pretreatments based on the deposition of plasma-polymerized thin films (PACVD process) on O₂ plasma-cleaned substrates were investigated. They include film deposition of (1) amorphous hydrogenated carbon (a-C:H) grown from CH₄, whose surface is subsequently plasma-functionalized in NH₃ or N₂; (2) amorphous hydrogenated carbon nitride (a-CN_x:H) grown from CH₄/NH₃ or CH₄/N₂ mixtures; and (3) amorphous hydrogenated carbon nitride grown from volatile organic precursors (allylamine, acetonitrile).

In the three cases, X-ray photoelectron spectroscopy (XPS) results show that chemisorption of the catalyst occurs on the nitrogen-containing functionalities created by plasma polymerization and grafting and thus that the electroless deposition is possible. Differences were observed depending on the nature and thickness of the plasma-polymerized thin films, as well as on the nature and concentration of the nitrogen-containing functionalities present or grafted at the surface. Practical adhesion of Ni films was investigated using a Scotch® tape test. Ni films up to 3 or 4?μm in thickness were shown to pass this test successfully, i.e., without causing any metal detachment.     

Effects of annealing on low dielectric constant carbon doped silicon oxide films

Dielectric materials with lower permittivity (low k) are required for isolation to reduce the interconnect RC delay in deep submicron integrated circuit. In this work, carbon doped silicon oxide [SiO(C–H)] films are investigated as a potential low k material. The films were prepared by the radio frequency plasma enhanced chemical vapor deposition (PECVD) technique from trimethylsilane (C₃H₁₀Si or 3MS) in an oxygen (O₂) environment. SiO(C–H) films deposited with O₂ and 3MS flow rates of 100 sccm and 600 sccm, respectively have been previously found to produce dielectric constant as low as 2.9. This is attributed to the incorporation of carbon in the form of Si–CH₃ bond, which has lower polarizability compared to the Si–O bonds that were replaced. In this work, these low k films were annealed at 400, 500, 600 and 700 °C in a N₂ atmosphere for 30 min to determine the thermal stability of their properties. The films were characterized in terms of their thickness shrinkage, refractive indices, dielectric constants, infrared absorption, surface morphology and stress upon annealing. For annealing temperatures up to 500 °C, which is beyond the current highest processing temperature for back end of the line structure of around 450 °C, a slight decrease in the refractive indices and dielectric constants of the films are observed. The SiO(C–H) films also remain smooth and exhibit tensile stress with stress level that is within practical acceptable range. The results suggest that the SiO(C–H) films are thermally stable to be applied as low dielectric constant materials for deep submicron integrated circuit.     

A cis-directing effect towards diols by an exocyclic P-NHR moiety in cyclotriphosphazenes

Cyclophosphazenes containing the P-NHR moiety in an exocyclic spiro ring, N₃P₃Cl₄[NH(CH₂)₃O], (1), and N₃P₃Cl₄[NH(CH₂)₃NMe], (2), were used to investigate a possible directing effect of the P-NHR moiety on the formation of products in the nucleophilic substitution reactions with diols such as tetraethyleneglycol, 1,3-propanediol and 2,2-dimethyl-1,3-propanediol. The ³¹P NMR spectra of the reaction mixtures showed that only one kind of ansa product is formed in each of these reactions. X-ray crystallographic studies of the ansa products [(4a), (5a), (6a) and (7a)] have provided definitive proof of the cis-directing effect of the P-NHR moiety in cyclotriphosphazenes. It is likely that hydrogen-bond interaction between the incoming nucleophile and the P-NHR moiety of the reactant accounts for the preference for products with the substituents cis to the NH group.     

Enhancing effect of S and F moieties on the performance of Fenton system in the selective oxidation of propane

The selective oxidation of propane to oxygenated products (isopropanol, n-propanol, propionic aldehyde and acetone) mediated by the Fe(II)/H₂O₂ Fenton system at 80 °C in the presence of solid acid and superacid promoters containing S and F moieties has been studied. The occurrence of a radical reaction pathway accounting for the activation of the CH bonds of the propane molecule by OH radicals has been proved by assessing the inhibiting effect of both Cl⁻ and NO₃⁻ radical scavengers and organic (CH₃COOH, CH₃CN, DMSO) reaction media on the reaction pattern. S and F functionalities of several solid agents promote the electron transfer processes controlling the H₂O₂ activation. Any effect of the Brönsted acid features of the solid promoters on the reaction kinetics and pathway has been disregarded.     

Structures and luminescence properties of polymer-like a-CNx:H films

Polymer-like hydrogenated amorphous carbon nitride (a-CNx:H) films were prepared in CH₄/N₂ r.f. plasma with different CH₄/N₂ mixing ratio and r.f. power input, and the structural and luminescence properties of these films were examined. Both optical band gap and PL peak energies of the a-CNx:H films were shifted with a variation of nitrogen content in the film. The theoretical PL efficiency described well the experimental data, and it was suggested that the PL of the a-CNx:H films arise from tail-to-tail electron-hole recombination in the localized π and π* states. From the FT-IR measurements, it was found that the films with lower nitrogen content included a large amount of sp³C–H bond, while in the film with higher nitrogen content, N–H, C=N and CN bonds were predominantly formed. From the EL devices fabricated using both a-CNx:H film and thin organic layers, EL spectra with a broad band of 350–700 nm were observed. Both EL and PL from the a-CNx:H film indicated almost the same behavior, and the components observed in the PL spectrum of each organic material were not included in the EL spectrum.     

Cathodoluminescence of the a-C:N films deposited by a filtered cathodic arc plasma system

Amorphous carbon nitride (a-C:N) films were successfully synthesized on silicon using a 90°-bend magnetic filtered cathodic arc plasma (FCAP) system. ESCA analysis demonstrated that the N/C ratios reached 1.08. Many investigations on photoluminescence (PL) spectra of diamondlike carbon films have been performed, but cathodoluminescence (CL) spectra have seldom been discussed. This work investigated a-C:N films using the CL spectra at 300 K. This work presents CL spectra of a-C:N films obtained at 1.5–3.5 eV and verifies luminescence from the a-C:N films in the visible region. The most prominent luminescence in the CL spectra from the a-C:N films has two peaks centered ∼2.67 eV (blue light) and ∼1.91 eV (red light), but the a-C film yielded only the band at ∼1.91 eV. These optical emissions are intrinsic and extrinsic to the a-C:N film and are sensitive to the content of nitrogen.     

Reactions and products revealed by NMR spectra of deuterated dimethylsulfoxide with iodomethane in neutral and basic media

Reactions occurring within each one of two mixtures, a mixture of deuterated dimethylsulfoxide, DMSO-d₆, with CH₃I (system I) and another mixture of DMSO-d₆ with CH₃I, NaOH and water (system II), were monitored by 1D and 2D nuclear magnetic resonance (¹H, ¹³C, heteronuclear multiple quantum correlation, heteronuclear multiple bond correlation and diffusion-ordered NMR spectroscopy). The analysis of the spectra as a function of reaction time revealed the formation of methoxy-bis(trideuteromethyl)sulfonium iodide, 3; the precipitation of hexadeuterated trimethyloxosulfonium, 2a; a methyl exchange between DMSO-d₆ and 2a to produce trideuterated dimethylsulfoxide, DMSO-d₃, 4, and nona-deuterated trimethyloxosulfonium iodide, 2b; and the production of small quantities of methanol, 5, trideuterated dimethylsulfide, 6, and dimethyl ether, 7, in both systems. Only system II precipitated deuterated [Na₄(DMSO-d_x)₁₅][(I₃)₃I], 1a, a green solid with metallic shine that corresponds to an isotopomer of 1, which is produced by the self-assembly of DMSO and CH₃I in the presence of NaOH and water.