CN Species Research Articles

Structure and bonding mechanism of cyanide adsorbed on Pt(111)

The low coverage adsorption modes of CN on Pt(1 1 1) have been studied by means of density functional theory and both cluster and slab models; geometry, adsorption energy and vibrational frequencies have been computed. The most favourable adsorption mode is C-down on top, with the CN axis perpendicular to the surface. Hollow sites are also stable minima, but the bridge site is a second order saddle point on the potential energy surface. Energetic differences between different sites are very small, suggesting a high mobility of the CN species on the surface. N-down structures are always less stable than C-down, being the difference of ∼1 eV for each site. The metal CN bond is described as a mixing of covalent and ionic contributions with a charge on chemisorbed CN of ∼−0.5e. The analysis of the bond permits to understand the changes in both adsorption energies and vibrational frequencies.

Si2CN: a stable nitrogen-containing radical with cyclic ground state.

The structures and isomerization of Si(2)CN species are explored at density functional theory and ab initio levels. Fourteen minimum isomers are located connected by 23 interconversion transition states. At the coupled-cluster single double (CCSD)(T)/6-311+G(2df)//QCISD/6-311G(d) +zero-point vibrational energies level, the thermodynamically most stable isomer is a four-membered ring form cSiSiCN 1 with Si-C cross bonding. Isomer 1 has very strong C-N multiple bonding characters, formally suggestive of a radical adduct between Si(2) and CN. Such a highly pi-electron localization can effectively stabilize isomer 1 to be the ground state. The second low-lying isomer is a linear form SiCNSi 5 (9.8 kcal/mol above 1) with resonating structure among [Si=C-*N=Si], *[Si=C=N=Si], and [Si=C=N-Si*]* with the former two bearing more weight. The species 1 and 5 have very high kinetic stability stabilized by the barriers of at least 25 kcal/mol. Both isomers should be experimentally or astrophysically observable. In light of the fact that no cyclic nitrogen-containing species have been detected in space, the cyclic species 1 could be a very promising candidate. The calculated results are compared to those of the analogous molecules C(3)N, C(3)P, SiC(2)N, and SiC(2)P. Implications of Si(2)CN in interstellar and N-doped SiC vaporization processes are also discussed.

Structure and bonding mechanism of cyanide adsorbed on Pt(1 1 1)

The low coverage adsorption modes of CN on Pt(1 1 1) have been studied by means of density functional theory and both cluster and slab models; geometry, adsorption energy and vibrational frequencies have been computed. The most favourable adsorption mode is C-down on top, with the CN axis perpendicular to the surface. Hollow sites are also stable minima, but the bridge site is a second order saddle point on the potential energy surface. Energetic differences between different sites are very small, suggesting a high mobility of the CN species on the surface. N-down structures are always less stable than C-down, being the difference of ∼1 eV for each site. The metal CN bond is described as a mixing of covalent and ionic contributions with a charge on chemisorbed CN of ∼−0.5 e. The analysis of the bond permits to understand the changes in both adsorption energies and vibrational frequencies.

Infrared absorption spectroscopy of the CnXe (n = 2, 3, 5, 7, 9) species

CnXe (n = 2, 3, 5, 7, 9) compounds, generated by pulsed laser evaporation of a carbon pellet or by the electrical discharge of acetylene, have been deposited in an argon matrix at 12 K and studied by Fourier transform infrared absorption spectroscopy. Five new vibrational bands at 1774.2, 2033.3, 2161.4, 2126.6 and 1997.2 cm−1 have been observed. Using ab initio MP2 theoretical methods, the first two bands have been assigned to the fundamental stretching modes of C2Xe and C3Xe, respectively. These assignments are supported by 13C isotopic shift data. The C–Xe bond in C2Xe is predicted to be stronger than in C3Xe. Although bent C3Xe is a little more stable than linear C3Xe, both species have very flat potential surfaces and both may exist in Ar matrices. The latter three bands are tentatively assigned to C–C asymmetric stretches in C5Xe, C7Xe, and C9Xe, respectively. Despite the lack of isotopic data for these species, this assignment is reasonable based on the smooth frequency shift for the CnXe species compared to the Cn species.

PH Dependence of the Au–CN Species Adsorbed onto Activated Carbon – Comments

In a recent paper by McGrath et al. [Hyp. Interact. 139/140 (2002), 471] the authors appear to have overlooked a body of prior work on the aurocyanide activated carbon system based on X-ray photoelectron spectroscopy. Unlike Mossbauer spectroscopy, limited to chemical state interpretations for a single absorber, XPS is usually capable or both quantitative chemical state assignment and stoichiometry for most atoms within the system. This earlier work shows that rather than producing a mixture of Au(CN) 2 − and AuCN the effect of acid on the aurocyanide adsorbed on activated carbon is to actually produce limited chain length oligomers such as the tetramer Au4(CN) 5 − . It clearly demonstrates the evolution of bridging (Nb) and terminal (Nt) nitrogen atoms with the relative concentration (for both N : Au and Nb : Nt) terminating at a stoichiometric ratio indicative of the oligomer. Other shortcomings of the paper in question are discussed.

PH Dependence of the Au–CN Species Adsorbed onto Activated Carbon – Reply to Comments

Several aspects of a recent paper [McGrath, A. C. et al., Hyp. Interact. 139/40 (2002), 471] have been criticised by Klauber [Klauber, C., Hyp. Interact. 155 (2004), 65]. Although some of the points in Klauber [Klauber, C., Hyp. Interact. 155 (2004), 65] are shown to be incorrect, we show that a further analysis of the data in McGrath et al. [McGrath, A. C. et al., Hyp. Interact. 139/40 (2002), 471] does lend support to Klauber's tetramer model for the AuCN species on activated carbon, but not necessarily for its method of bonding.

Computations of the catalytic effects in the stone–wales fullerene isomerizations: N and CN agents

AbstractThe Stone–Wales rearrangement has long been considered as a plausible, albeit hypothetical, mechanism for fullerene annealing and isomerizations. In the view of a recently applied new catalyst, KCN, for incorporation of noble gases in fullerenes, the CN radical is studied here computationally as a possible catalytic species acting in kinetics of the Stone–Wales fullerene transformation, and a possible role of K+ is also investigated. The computations are performed on the PM3‐optimized bowl‐shaped model C34H12 to which the CN radical is attached by its C or N atom. The activation energies are evaluated at the UPM3, UHF/6‐31G*, UB3LYP/6‐31G*, ROB3LYP/6‐31G*, ROHF/6‐31G**, and ROB3LYP/6‐31G** levels. However, the reduction of the kinetic barrier owing to the catalyst action is modest so that a free N atom, neutral or charged, still remains a more efficient option. Effects of negatively charged CN species and of K+ are also found insufficient. Small amounts of nitrogen are indeed always present during fullerene synthesis, especially from He gas. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Experimental and theoretical studies of Si–CN bonds to eliminate interface states at Si/SiO 2 interface

Cyanide treatment, which includes the immersion of Si in KCN solutions followed by a rinse, effectively passivates interface states at Si/SiO 2 interfaces by the reaction of CN − ions with interface states to form Si–CN bonds. X-ray photoelectron spectroscopy (XPS) measurements show that the concentration of the CN species in the surface region after the cyanide treatment is ∼0.25 at.%. Take-off angle-dependent measurements of the XPS spectra indicate that the concentration of the CN species increases with the depth from the Si/SiO 2 interface at least up to ∼2 nm when ultrathin SiO 2 layers are formed at 450 °C after the cyanide treatment. When the cyanide treatment is applied to metal–oxide–semiconductor (MOS) solar cells with 〈ITO/SiO 2/n-Si〉 structure, the photovoltage greatly increases, leading to a high conversion efficiency of 16.2% in spite of the simple cell structure with no pn-junction. Si–CN bonds are not ruptured by air mass 1.5 100 mW cm −2 irradiation for 1000 h, and consequently the solar cells show no degradation. Neither are Si–CN bonds broken by heat treatment at 800 °C performed after the cyanide treatment. The thermal and irradiation stability of the cyanide treatment is attributable to strong Si–CN bonds, whose bond energy is calculated to be 1 eV higher than that of the Si–H bond energy using a density functional method.

Adsorption Chemistry of Cyanogen Bromine and Cyanogen Chlorine on Silicon(100)

The adsorption and decomposition of cyanogen halides, XCN (X = Br, Cl), on Si(100) is investigated utilizing X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). For submonolayer exposures, XPS indicates that the CN triple bond of XCN remains intact upon adsorption at 100 K. The UPS spectrum contains two peaks assigned to the π-electrons in the CN triple bond. The splitting indicates that some fraction of the XCN molecules adsorbs molecularly at low temperature. XPS analyses of the C 1s photoelectron peak following submonolayer exposure at low temperature suggest a greater fraction of BrCN (60%) adsorbs molecularly than ClCN (40%). XPS and UPS measurements at room temperature show that the X−CN bond breaks, while the CN bond remains intact during room-temperature adsorption on Si(100). Thus, the UPS spectrum of XCN adsorbed at room temperature on Si(100) contains a peak at 6.0 eV due to the unperturbed π electrons of the CN species. Upon annealing a CN-saturated Si(100) surface to higher temperatures, the UPS spectra indicate that the CN bond remains intact until approximately 700 K. Simultaneous changes in the C 1s and N 1s photoelectron peaks are consistent with the idea that CN bond cleavage is correlated with silicon carbide and nitride formation. These results are compared with a previous study of ICN adsorption on Si(100).

Hyperthermal rare-gas ion-stimulatedCN−desorption from a nitrogenated graphite surface

The mechanism of hyperthermal (2--30 eV) rare-gas (RG) ions induced ${\mathrm{CN}}^{\ensuremath{-}}$ desorption from a nitrogenated graphite surface is investigated. ${\mathrm{CN}}^{\ensuremath{-}}$ desorption occurs at an incident energy as low as 2 eV and gains a relatively high energy from the desorption process in comparison with the incident kinetic energy. A strong correlation is observed between the ${\mathrm{CN}}^{\ensuremath{-}}$ maximum translational energy (MTE) and the incident RG ion energy, suggesting a localized interaction between the incident ion and surface CN species. A MTE of \ensuremath{\sim}5 eV is obtained at 0-eV incident energy, and is found independently of the incident ion species. It is proposed that ${\mathrm{CN}}^{\ensuremath{-}}$ emission occurs as a result of the potential desorption of chemisorbed surface CN species mediated by the formation of a localized hole at its bonding or nonbonding orbital via (quasi)resonant neutralization of an incident RG ion.

Structural characterisation of CN x thin films deposited by pulsed laser ablation

Carbon nitride (CN x ) film growth by 193 nm pulsed laser ablation of graphite in a low pressure of N 2 has been investigated both by studying optical emission from the plume and by analyses of the composition, structure and bonding of material deposited at a range of substrate temperatures. Spectral analysis of the emission reveals the presence of C + ions, C atoms, C 2 and CN radicals and N 2 + molecular ions within the ablation plume travelling towards the substrate. Films deposited at low substrate temperature ( T sub) are amorphous, with an N/C ratio of ∼20 at.%. Raman analysis shows CN x films grown at higher T sub to be increasingly nanocrystalline, but thinner, and suggests that N inclusion encourages nanocrystallite formation. X-ray photoelectron spectroscopy reveals that CN x films grown at higher T sub also have a reduced overall N content. The observations have been rationalised by assuming an increased propensity for sputtering or desorption of more labile CN species from the growing film surface at higher T sub, resulting in a higher fraction of CC bonding—most probably in the form of graphitic nanocrystallites embedded in an amorphous matrix.

Adsorption chemistry of cyanogen iodide on silicon ( [formula omitted

The adsorption of cyanogen iodide (ICN) on a silicon (1 0 0) surface is studied by X-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS) and temperature programmed desorption (TPD) spectroscopy. After submonolayer exposures, XPS indicates that the CN triple bond of ICN remains intact upon adsorption at 100 K. The UPS spectrum for submonolayer exposures at 100 K contains two peaks assigned principally to the π electrons in the CN triple bond. The splitting is due to the interaction between the π electrons of the cyanogen and the p electrons of the iodine. These results show that a portion of ICN molecules adsorbed molecularly. Higher exposures result in multilayer molecular ICN film. TPD spectra from both the submonolayer and multilayer films formed at 100 K show a peak at 170 K due to the desorption of adsorbed molecular ICN. In contrast to the low-temperature results, the UPS spectrum of ICN adsorbed at room temperature (RT) on Si(1 0 0) contains only one peak which originates principally from the π electrons in the CN triple bond. The lack of splitting in the RT UPS spectrum is a result of IC bond dissociation upon adsorption on Si(1 0 0). At RT the IC bond breaks while the CN bond remains intact. Upon annealing the Si(1 0 0) surface to higher temperatures, the UPS and XPS spectra indicate that the CN triple bond starts to disappear at ≈470 K. Simultaneous changes in the C 1s and N 1s photoelectron peaks between 470 and 800 K are consistent with the idea that CN bond cleavage in ICN is correlated with silicon carbide and nitride formation. By 800 K, all adsorbed CN species decompose completely into silicon carbide and nitride.

Interaction of ambient nitrogen gas and laser ablated carbon plume: Formation of CN

Pulsed laser ablated carbon plasma in a nitrogen background gas in the pressure range from 10 mTorr to 100 Torr is investigated by optical emission spectroscopy using 1.064 and 0.355 μm laser wavelengths. C 2 and CN emission bands dominated the emitted spectrum at all ambient gas pressures at low incident laser intensity commonly used for pulsed laser deposition of thin films. The light intensity of C 2 and CN band heads is highly dependent on laser wavelength, laser energy, and ambient gas pressures. Emission from N 2 + was detected at all nitrogen pressures. N I and N II are also observed in the emitted spectrum at the background gas pressure greater than 1 Torr. The vibrational temperature of CN species is found to be greater than that of C 2 species. The mechanism of formation of C 2 and CN molecules is discussed.

Influence of chemical sputtering on the composition and bonding structure of carbon nitride films

The achievement of high N concentration is one necessary condition for the synthesis of crystalline C 3N 4 compounds. Other demands are the formation of the correct bonding configuration of carbon (sp 3) and nitrogen (sp 2) and the ability to produce adequate amounts of compact continuous crystalline material to allow definitive mechanical testing. However, for a number of deposition methods like ion beam assisted deposition (IBAD), reactive sputtering etc., the chemical sputtering effect, involving the formation of volatile CN species during film growth, is responsible for the limitation of the N content below 40 at.%. For low energy nitrogen irradiation (<100 V) using IBAD a critical arrival rate N 2 +/C≈1.8 was established above which no deposit is formed. Below this limit, the analysis of X-ray photoelectron spectra reveals a mixed CN x phase consisting of an aromatic and a non-aromatic structure, each of them containing a variety of local bonding environments. The fraction and the particular microstructure of the aromatic phase, which has a strong influence on film properties like hardness, can be adjusted as a function of N content and nitrogen ion current density. Experiments performed by evaporation of 8-aza-6-aminopurine (C 4N 6H 4) and simultaneous irradiation by low energy nitrogen ions show that CN:H films can be grown with a C/N ratio up to 1.3. Although a polymer-like phase is formed, an important aspect of this method is that chemical sputtering can be avoided by thermal condensation of a molecular precursor resulting in a significantly larger N content in the deposit. The proposed model for the evolution of the microstructure with N concentration, based on a critical discussion of our results together with a number of recent studies, can be helpful for the structural characterization of CN x films produced by other methods.

NO reburning study based on species quantification obtained by coupling LIF and cavity ring-down spectroscopy.

NO reburning is studied in a low pressure (15 hPa) premixed flame of CH4-O2 seeded with 1.8% of NO. Measurements were carried out by using cavity ring-down spectroscopy (CRDS) and laser induced fluorescence (LIF) techniques. The temperature profile was obtained by OH-LIF thermometry in the A-X (0-0) band. The OH profile was determined by LIF and calibrated by single pass absorption. The NO concentration profile was obtained by LIF in the A-X (0-0) band and corrected for Boltzmann fraction and quantum yield variations. The absolute concentration profile was determined in the burned gases by CRDS allowing a direct experimental determination of the NO reburning amount. Finally CH and CN mole fraction profiles were obtained by CRDS by exciting rotational transitions in the B-X (0-0) bands of CH and CN around 387 nm. We found a peak mole fraction of 29 ppm for CH and 3.3 ppm for CN. This last result is in contrast with a previous study of W. Juchmann, H. Latzel, D. L. Shin, G. Peiter, T. Dreier, H. R. Volpp, J. Wolfrum, R. P. Lindstedt and K. M. Leung, XXVIIth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, 1998, p. 469, performed in a similar flame, which reported much lower levels of CN. In that study the absolute concentration of CN was indirectly obtained by LIF calibrated by Rayleigh scattering. In a second part, experimental species profiles are compared with predictions of the GRI 3.0 mechanism. Comparison between experimental and predicted profiles shows a good agreement particularly for CN and NO species. A qualitative analysis of NO reburning is then performed.

A SIMS study on positive and negative ions sputtered from graphite by mass-separated low energy Ne +, N 2+ and N + ions

Temperature effect on positive and negative ion yields sputtered from graphite by low energy Ne +, N 2 + and N + ions was studied using a special mass-separated low energy ion beam system and secondary ion mass spectrometry (SIMS) measurements. The origin of dominant positive and negative ions was discussed according to the obtained temperature effect. It was found that C + ion emission was enhanced by nitrogen ion bombardment compared with Ne + bombardment and decreased to the same level as Ne + bombardment at elevated temperature. The enhancement effect was attributed to adsorption or deposition of nitrogen to form weakly bound C δ+–CN δ− species on the surface. No chemical enhancement effect was observed on C 2 − emission during nitrogen ion bombardment. The C 2 − yield increased with temperature during Ne + and nitrogen ion bombardment and was assigned to originate from carbon network of graphite as a consequence of physical sputtering. During nitrogen ion bombardment, CN − ions dominated both the positive and negative ion emission. CN − ion yield during 800 eV N 2 + and N + bombardment decreased at elevated temperature, whereas during 100 eV N 2 + bombardment, it increased with temperature. CN − yield as a function of kinetic energy of primary ions also exhibited difference from that of C + and C 2 −. Three possible channels for CN − emission have been proposed. At higher primary energy (several hundred eV and above), physical sputtering can partly account for CN − emission. At lower primary energy (below 100 eV), it is attributed to chemical etching of surface carbon atoms by energetic nitrogen atoms and ion-induced desorption of CN species.

Quantitative measurement of CN radical in a low-pressure methane/air flame by cavity ring-down spectroscopy

The ultrasensitivity of the cavity ring down spectroscopy technique has been used to detect the minor CN species in a premixed rich ( φ=1.2) methane/air flame stabilized at 53 hPa. The CN radical has been probed around 387 nm on the B–X (0–0) band. A peak concentration of 4.7·10 9 cm −3 has been measured which corresponds to a mole fraction of 0.022 ppm. A detection limit of a few ppb has been reached despite the presence of an important off-resonance background due to the flame.

High-precision measurement of magnesium isotopes by multiple-collector inductively coupled plasma mass spectrometry

Multiple-collector inductively coupled plasma mass spectrometry has been used for the precise measurement of variations in the isotopic composition of Mg in a range of materials. The contributions of CC, CN, and MgH molecular species to the mass spectrum in the Mg mass region are minimised. Variations in sample 26Mg/24Mg and 25Mg/24Mg ratios are expressed as δ26Mg and δ25Mg units, which are deviations in parts per 103 from the same ratio in the SRM 980 Mg standard. The long-term repeatability of the 26Mg/24Mg and 25Mg/24Mg ratios of a sample Mg solution relative to the SRM 980 Mg isotope standard are 0.12‰ and 0.06‰, respectively, at 95% confidence. The addition of Na, Al, and Ca in a solution of Mg having a known isotopic composition induces 0.2‰–1‰ increase of δ26Mg. This chemical bias is a result of a mass-dependent process and is observed to be greater with Ca than Na. Isobaric interference from doubly charged 48Ca ions on mass 24 is observed to be significant when [Ca]/[Mg] ≥ 0.5. The results obtained on nine terrestrial material show a variation of Mg-isotopes of 4‰ in δ26Mg. When plotted in a three-isotope diagram, all the data fall on a single mass fractionation line. The excess of 26Mg has been determined by the deviation from that mass-dependent relationship, and its long-term repeatability is 0.06‰ at 95% confidence.

The effect of d.c. substrate bias on the properties of nitrogen-rich CN x films

The influence of d.c. substrate bias on the properties of nitrogen-rich CN x films deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) utilizing transport reactions has been investigated. The film forming species are CN and/or (CN) 2 generated by the interaction of the atomic nitrogen from the ICP with a solid pure carbon mesh; they are deposited on the substrate in the presence of nitrogen species from the plasma. A study of the surface topography of the coatings by atomic force microscopy (AFM) shows that the average roughness slightly increases from below 1 nm without bias to 1.6 nm at −300 V. The deposition rate decreases by a factor of 1.3–1.5 (depending on the working pressure) with increasing the bias up to −300 V, mainly as a result of desorption of CN species from the substrate enhanced by the ion bombardment. The CN x films deposited with bias exhibit nitrogen atomic fraction N/(C+N) in the range of 50–60%, as revealed by surface and bulk techniques. The chemical bonding structure of the layers investigated by Fourier transform infrared (FTIR) spectroscopy showed only a marginal influence of the d.c. substrate bias. The increase of the refractive index n from 1.6 to 1.8 is probably due to slight densification of the films deposited with substrate biasing as a result of reduction of voids.

Density Functional Based Tight Binding Study of C2 and CN Deposition On (100) Diamond Surface

ABSTRACTA density-functional based tight binding method was used to study elementary steps in the growth of ultrananocrystalline (UNCD) diamond. It was shown previously that C2 dimers are the dominant growth species in hydrogen-poor argon plasmas. Recent experimental evidence shows that nitrogen addition to the plasma profoundly changes the morphology of the UNCD film. CN species are believed to play a major role. Reactions of C2 and CN molecules with reconstructed diamond (100) surfaces were studied. A single CN prefers an end-on attachment to a surface atom on the unhydrided (100) surface with its C end down. It is shown how further C2 addition to the surface leads to CN-mediated diamond growth and how the CN species remain on top of the growing diamond layer.