The determination of local structural units in amorphous SiBN 3C by means of X-ray photoelectron and X-ray absorption spectroscopy

X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy at the K-edge of Si, N, and B are presented as techniques suited to determine structural units in amorphous SiBN₃C. The measurements reported give evidence for the presence of tetrahedral (SiN₄)- and planar (BN₃)-groups. It is concluded that these structural elements dominate the atomic surroundings of B and Si, respectively. From the spectroscopic results we conclude that C is mainly bonded to N and is not present as a pure carbide.     

Shining light on dinitrogen cleavage: structural features, redox chemistry, and photochemistry of the key intermediate bridging dinitrogen complex

The key intermediate in dinitrogen cleavage by Mo(N[t-Bu]Ar)3, 1 (Ar = 3,5-C6H3Me2), has been characterized by a pair of single crystal X-ray structures. For the first time, the X-ray crystal structure of (mu-N2)[Mo(N[t-Bu]Ar)3]2, 2, and the product of homolytic fragmentation of the NN bond, NMo(N[t-Bu]Ar)3, are reported. The structural features of 2 are compared with previously reported EXAFS data. Moreover, contrasts are drawn between theoretical predictions concerning the structural and magnetic properties of 2 and those reported herein. In particular, it is shown that 2 exists as a triplet (S = 1) at 20 degrees C. Further insight into the bonding across the MoNNMo core of the molecule is obtained by the synthesis and structural characterization of the one- and two-electron oxidized congeners, (mu-N2)[Mo(N[t-Bu]Ar)3]2[B(Ar(F))4], 2[B(Ar(F))4] (Ar(F) = 3,5-C6H3(CF3)2) and (mu-N2)[Mo(N[t-Bu]Ar)3]2[B(Ar(F))4]2, 2[B(Ar(F))4]2, respectively. Bonding in these three molecules is discussed in view of X-ray crystallography, Raman spectroscopy, electronic absorption spectroscopy, and density functional theory. Combining X-ray crystallography data with Raman spectroscopy studies allows the NN bond polarization energy and NN internuclear distance to be correlated in three states of charge across the MoNNMo core. For 2[B(Ar(F))4], bonding is symmetric about the mu-N2 ligand and the NN polarization is Raman active; therefore, 2[B(Ar(F))4] meets the criteria of a Robin-Day class III mixed-valent compound. The redox couples that interrelate 2, 2(+), and 2(2+) are studied by cyclic voltammetry and spectroelectrochemistry. Insights into the electronic structure of 2 led to the discovery of a photochemical reaction that forms NMo(N[t-Bu]Ar)3 and Mo(N[t-Bu]Ar)3 through competing NN bond cleavage and N2 extrusion reaction pathways. The primary quantum yield was determined to be Phi(p) = 0.05, and transient absorption experiments show that the photochemical reaction is complete in less than 10 ns.     

Functionalization of aminophosphanes: synthesis and X-ray crystal structure of novel dilithium and trilithium complexes containing silicon-fused heteronuclear SiN2PLi five-membered rings

A first structurally characterized primary aminophosphane (Ar 2PNH 2 ( 2); Ar = 2,4,6- iPr 3C 6H 2) that is a stable solid at room temperature without decomposition by self-condensation is reported. Reactions of N-phosphanyllithium amide ( tBu 2PNHLi ( 3)) with Me 2SiCl 2 and MeSiCl 3 in Et 2O result in the formation of Me 2Si(NHP tBu 2) 2 ( 4) and MeSi(NHP tBu 2) 3 ( 5), respectively. Subsequent treatment of 4 and 5 with 2 and 3 equiv of nBuLi gave the dilithium ( 6) and trilithium ( 7) complexes, respectively. Further treatment of 5 with 3 equiv of AlMe 3 yielded the trialuminum complex MeSi[N(AlMe 2)P tBu 2] 3 ( 8). These three complexes were investigated by microanalysis and multinuclear NMR spectroscopy. The dilithium complex [Me 2Si(NLiP tBu 2) 2.3THF] ( 6) and the trilithium complex [MeSi(NLiP tBu 2) 3.3Et 2O] ( 7) were further characterized by single-crystal X-ray structural analysis.     

An X-ray photoelectron spectroscopic study of novel SiON glasses

Novel SiON glasses obtained by melting mixtures of crystalline α-SiO₂ and α-Si₃N₄ were investigated by means of X-ray photoelectron spectroscopy (XPS). The incorporation of nitrogen into the SiO₂ network was recently proved by ²⁹Si-MAS-NMR (magic-angle spinning nuclear magnetic resonance) and Si K-XANES (X-ray absorption near edge structure). The Si 2p XPS and the Si KLL XAES (X-ray excited Auger electron spectroscopy) studies of the SiON glasses confirm the formation of mixed structural units (SiO_xN_4-x) by the presence of an additional spectral component energetically located between SiO₂- and Si₃N₄-like signals. The N 1s and O 1s XPS spectra support the conclusion about the incorporation of nitrogen into the SiO₂ network.     

Reactivity of bis(2,2,5,5-tetramethyl-2,5-disila-1-azacyclopent-1-yl)tin with CO(2), OCS, and CS(2) and comparison to that of bis[bis(trimethylsilyl)amido]tin

The heterocumulenes carbon dioxide (CO(2)), carbonyl sulfide (OCS), and carbon disulfide (CS(2)) were treated with bis(2,2,5,5-tetramethyl-2,5-disila-1-azacyclopent-1-yl)tin {[(CH(2))Me(2)Si](2)N}(2)Sn, an analogue of the well-studied bis[bis(trimethylsilyl)amido]tin species [(Me(3)Si)(2)N](2)Sn, to yield an unexpectedly diverse product slate. Reaction of {[(CH(2))Me(2)Si](2)N}(2)Sn with CO(2) resulted in the formation of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane, along with Sn(4)(μ(4)-O){μ(2)-O(2)CN[SiMe(2)(CH(2))(2)]}(4)(μ(2)-N═C═O)(2) as the primary organometallic Sn-containing product. The reaction of {[(CH(2))Me(2)Si](2)N}(2)Sn with CS(2) led to formal reduction of CS(2) to [CS(2)](2-), yielding [{[(CH(2))Me(2)Si](2)N}(2)Sn](2)CS(2){[(CH(2))Me(2)Si](2)N}(2)Sn, in which the [CS(2)](2-) is coordinated through C and S to two tin centers. The product [{[(CH(2))Me(2)Si](2)N}(2)Sn](2)CS(2){[(CH(2))Me(2)Si](2)N}(2)Sn also contains a novel 4-membered Sn-Sn-C-S ring, and exhibits a further bonding interaction through sulfur to a third Sn atom. Reaction of OCS with {[(CH(2))Me(2)Si](2)N}(2)Sn resulted in an insoluble polymeric material. In a comparison reaction, [(Me(3)Si)(2)N](2)Sn was treated with OCS to yield Sn(4)(μ(4)-O)(μ(2)-OSiMe(3))(5)(η(1)-N═C═S). A combination of NMR and IR spectroscopy, mass spectrometry, and single crystal X-ray diffraction were used to characterize the products of each reaction. The oxygen atoms in the final products come from the facile cleavage of either CO(2) or OCS, depending on the reacting carbon dichalogenide.     

Strong intramolecular secondary si.N bonds in trifluorosilylhydrazines

The simple silylhydrazines F(3)SiN(Me)NMe(2) (1), F(2)Si(N(Me)NMe(2))(2) (2), and F(3)SiN(SiMe(3))NMe(2) (3) have been prepared by reaction of SiF(4) with LiN(Me)NMe(2) and LiN(SiMe(3))NMe(2), while F(3)SiN(SnMe(3))NMe(2) (4) was prepared from SiF(4) and (Me(3)Sn)(2)NNMe(2) (5). The compounds were characterized by gas-phase IR and multinuclear NMR spectroscopy ((1)H, (13)C, (14/15)N, (19)F, (29)Si, (119)Sn), as well as by mass spectrometry. The crystal structures of compounds 1-5 were determined by X-ray crystallography. The structures of free molecules 1 and 3 were determined by gas-phase electron diffraction. The structures of 1, 2, and 4 were also determined by ab initio calculations at the MP2/6-311+G** level of theory. These structural studies constitute the first experimental proof for the presence of strong Si.N beta-donor-acceptor bonds between the SiF(3) and geminal NMe(2) groups in silylhydrazines. The strength of these non-classical Si.N interactions is strongly dependent on the nature of the substituent at the alpha-nitrogen atom of the SiNN unit, and has the order 3>4>1. The valence angles at these extremely deformed alpha-nitrogen atoms, and the Si.N distances are (crystal/gas): 1 104.2(1)/106.5(4) degrees, 2.438(1)/2.510(6) A; 3 83.6(1)/84.9(4) degrees, 2.102(1)/2.135(9) A; 4 89.6(1) degrees, 2.204(2) A.     

Synthesis and Characterization of a New Alkenyldecaborane and Alkenyl Monocarbon Carboranes

Decaborane(14) reacts with 1-(CH(3))(3)SiC&tbd1;CC(4)H(9) in the presence of dimethyl sulfide to give the new alkenyldecaborane 5-(S(CH(3))(2))-6-[(CH(3))(3)Si(C(4)H(9))C=CH]B(10)H(11) (I). Crystal data for 5-(S(CH(3))(2))-6-[(CH(3))(3)Si(C(4)H(9))C=CH]B(10)H(11): space group P2(1)/n, monoclinic, a = 9.471(1) ?, b = 13.947(3) ?, c = 17.678(3) ?, beta = 100.32(1) degrees. A total of 3366 unique reflections were collected over the range 2.0 degrees /= 3sigma(F(o)(2)) and were used in the final refinement. R(F)() = 0.083; R(w)(F)() = 0.094. The single-crystal X-ray structure of 5-(S(CH(3))(2))-6-[((CH(3))(3)Si)(2)C=CH]B(10)H(11) (A) is also reported. Crystal data for 5-(S(CH(3))(2))-6-[((CH(3))(3)Si)(2)C=CH]B(10)H(11): space group, P2(1)2(1)2(1), orthorhombic, a = 9.059 (3) ?, b = 12.193(4) ?, c = 21.431(3) ?. A total of 4836 unique reflections were collected over the range 6 degrees /= 3sigma(F(o)(2)) and were used in the final refinement. R(F)() = 0.052; R(w)(F)() = 0.059. The reactions of 5-(S(CH(3))(2))6-[(CH(3))(3)Si(C(4)H(9))C=CH]B(10)H(11) and 5-(S(CH(3))(2))6-[((CH(3))(3)Si)(2)C=CH]B(10)H(11) with a variety of alkyl isocyanides were investigated. All of the alkenyl monocarbon carboranes reported are the result of incorporation of the carbon atom from the isocyanide into the alkenyldecaborane framework and reduction of N&tbd1;C bond to a N-C single bond. The characterization of these compounds is based on (1)H and (11)B NMR data, IR spectroscopy, and mass spectrometry.     

Structure of Co-Doped Alq3 thin films investigated by grazing incidence X-ray absorption fine structure and Fourier transform infrared spectroscopy

The structural properties of Co-doped tris(8-hydroxyquinoline)aluminum (Alq(3)) have been studied by grazing incidence X-ray absorption fine structure (GIXAFS) and Fourier transform infrared spectroscopy (FTIR). GIXAFS analysis suggests that there are multivalent Co-Alq(3) complexes and the doped Co atoms tend to locate at the attraction center with respect to N and O atoms and bond with them. The FTIR spectra indicate that the Co atoms interact with the meridional (mer) isomer of Alq(3) rather than forming inorganic compounds.     

Formation of phosphino-substituted isocyanate by reaction of CO2 with group 2 complexes based on the (Me3Si)(i-Pr2P)NH ligand

The group 2 complexes [(Me(3)Si)(i-Pr(2)P)N](2)M(THF)(x) (M = Mg, x = 1; M = Ca/Sr, x = 2) as well as an unusual dimagnesium complex {[(Me(3)Si)(i-Pr(2)P)N](3)Mg}Mg(n-C(4)H(9)) have been prepared and characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction. Each complex was shown to react with CO(2) under extremely mild conditions (15 min, 1 atm, room temperature) to give the isocyanate (i-Pr)(2)P-N═C═O. The independent syntheses of (i-Pr)(2)P-N═C═O and the carbodiimide dimer [(i-Pr)(2)PNCNP(i-Pr)(2)](2) are also reported.     

Alkali metal complexes of sterically demanding amino-functionalized secondary phosphanide ligands

The reaction between {(Me(3)Si)(2)CH}PCl(2) (4) and one equivalent of either [C(6)H(4)-2-NMe(2)]Li or [2-C(5)H(4)N]ZnCl, followed by in situ reduction with LiAlH(4) gives the secondary phosphanes {(Me(3)Si)(2)CH}(C(6)H(4)-2-NMe(2))PH (5) and {(Me(3)Si)(2)CH}(2-C(5)H(4)N)PH (6) in good yields as colourless oils. Metalation of 5 with Bu(n)Li in THF gives the lithium phosphanide [[{(Me(3)Si)(2)CH}(C(6)H(4)-2-NMe(2))P]Li(THF)(2)] (7), which undergoes metathesis with either NaOBu(t) or KOBu(t) to give the heavier alkali metal derivatives [[{(Me(3)Si)(2)CH}(C(6)H(4)-2-NMe(2))P]Na(tmeda)] (8) and [[{(Me(3)Si)(2)CH}(C(6)H(4)-2-NMe(2))P]K(pmdeta)] (9) after recrystallization in the presence of the corresponding amine co-ligand [tmeda = N,N,N',N'-tetramethylethylenediamine, pmdeta = N,N,N',N',N'-pentamethyldiethylenetriamine]. The pyridyl-functionalized phosphane 6 undergoes deprotonation on treatment with Bu(n)Li to give a red oil corresponding to the lithium compound [{(Me(3)Si)(2)CH}(2-C(5)H(4)N)P]Li (10) which could not be crystallized. Treatment of this oil with NaOBu(t) gives the sodium derivative [{[{(Me(3)Si)(2)CH}(2-C(5)H(4)N)P]Na}(2) x (Et(2)O)](2) (11), whilst treatment of with KOBu(t), followed by recrystallization in the presence of pmdeta gives the complex [[{(Me(3)Si)(2)CH}(2-C(5)H(4)N)P]K(pmdeta)](2) (12). Compounds 5-12 have been characterised by (1)H, (13)C{(1)H} and (31)P{(1)H} NMR spectroscopy and elemental analyses; compounds 7-9, and 12 have additionally been characterised by X-ray crystallography. Compounds 7-9 crystallize as discrete monomers, whereas 11 crystallizes as an unusual dimer of dimers and 12 crystallizes as a dimer with bridging pyridyl-phosphanide ligands.     

A biomimetic approach to the chemical inactivation of chrysotile fibres by lichen metabolites

Some lichens were recently reported to modify the surface state of asbestos. Here we report some new insight on the physico-chemical modifications induced by natural chelators (lichen metabolites) on two asbestos samples collected in two different locations. A biomimetic approach was followed by reproducing in the laboratory the weathering effect of lichen metabolites. Norstictic, pulvinic and oxalic acid (0.005, 0.5 and 50 mM) were put in contact with chrysotile fibres, either in pure form (A) or intergrown with balangeroite, an iron-rich asbestiform phase (B). Mg and Si removal, measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), reveals an incongruent dissolution for pure chrysotile (A), with Mg removal always exceeding that of Si, while chrysotile-balangeroite (B) follows a congruent dissolution pattern in all cases except in the presence of 50 mM oxalic acid. A much larger removal of Mg than Si in the solutions of 0.5 and 50 mM oxalic acid with chrysotile (A) suggests a structural collapse, which in the case of chrysotile-balangeroite (B) only occurs with 50 mM oxalic acid; in these cases both samples are converted into amorphous silica (as detected by X-ray diffraction (XRD)). Subsequent to incubation, some new phases (Fe(2)O(3), CaMg(CO(3))(2), Ca(C(2)O(4)) x H(2)O and Mg(C(2)O(4))2 x H(2)O), similar to those observed in the field, were detected by XRD and micro-Raman spectroscopy. The leaching effect of lichen metabolites also modifies the Fenton activity, a process widely correlated with asbestos pathogenicity: pure chrysotile (A) activity is reduced by 50 mM oxalic acid, while all lichen metabolites reduce the activity of chrysotile-balangeroite (B). The selective removal of poorly coordinated, highly reactive iron ions, evidenced by NO adsorption, accounts for the loss in Fenton activity. Such fibres were chemically close to the ones observed in the field. Chrysotile-rich rocks, colonised by lichens, could be exposed to a natural bioattenuation and considered as a transient environmental hazard.     

A novel crown ether generation containing different heteroaromatic cations: synthesis, characterization, solid-phase (13)C NMR, X-ray crystal structure, and selective amino acid recognition

The synthesis and structural characterization of a novel generation of crown ethers, 3, 5 and 6 containing pyrilium, thiopyrilium, and pyridinium subunits, respectively, are reported. The crown ether unit is potentially capable of forming host-guest complexes with inorganic and organic cations, while the heteroaromatic cationic unit is suitable to bind with anions. A variety of physicochemical methods including electrospray mass spectrometry, UV-vis spectroscopy, solution and solid-phase NMR, and X-ray crystallography were applied for structural characterization of the new crown ether derivatives. The (1)H and (13)C NMR studies indicate rapid rotation of the B9C3 unit about the C-C bond that connects the two units to each other. Single crystals for 3, 4, and 5 were successfully obtained, and their X-ray crystal structures were resolved. The perchlorate anion in 3 (orthorhombic, space group P2(1)2(1)2(1)) and 5 (orthorhombic, space group P2(1)) is far from O(+) and close to S(+). The solid-phase structure of 3 and 5 show small deviation from planarity for the four aromatic rings, whereas two of the aromatic rings in 4 are out of heteroaromatic ring. Spectrophotometric studies in methanol solution revealed that the ligand 3 can be successfully applied to selective amino acid recognition.     

TAS+(Z)-Me3CNSN- and TAS+(E)-Me3SiNSN-: does the anion-cation interaction influence the configuration?

TAS+ salts (TAS = (Me2N)3S) of the sulfur diimide anions Me3XNSN- (X = C (1a), Si (1b)) were prepared by Si-N bond cleavage from the corresponding sulfur diimides Me3XNSNSiMe3 and TAS-fluoride ((Me2N)3S+Me3SiF2-) and characterized by X-ray crystallography and multinuclear NMR spectroscopy. According to the experimentally determined bond lengths and theoretical calculations, the Me3XNSN- anions are best described as thiazylamides Me3X-N-S identical to N rather than sulfur diimides Me3X-N=S=N. In agreement with the calculated and experimentally determined structures of the isoelectronic thionylimides RNSO, 1a adopts the Z-configuration, which is electronically favored due to anomeric effects. The electronically disfavored E-configuration of 1b in the solid state can be explained by weak anion-cation interaction.     

液相放电法合成氮化碳晶体

自从 Cohen等 [1,2 ] 预言了一种碳氮化合物 ( β- C3N4 )可能具有比金刚石还高的硬度和其它优异的力学、电学和光学性能以来 ,人们竟相采用各种技术手段 (如化学气相沉积、磁控溅射、离子束沉积和激光刻蚀等 )尝试合成这种新材料 [3,4 ] .但是 ,大多数合成的氮化碳材料为非晶或者是少量的晶体包埋在非晶的碳和 CNx 材料中 ,尚未制得可以精确地研究其晶体结构的足够大的单晶 .1 999年 ,Fu等 [5] 将液相电沉积技术应用于氮化碳材料的合成 ,从乙腈中沉积了氮含量为 2 5 %的氮化碳薄膜 .目前电化学沉积法制备的氮化碳薄膜多为非晶膜 [6～ 9]…     

X-ray absorption near edge structure study of BN nanotubes and nanothorns

Two boron nitride (BN) nanostructures, the bamboo-like nanotubes and nanothorns where the nanosize h-BN layers are randomly stacked looking like thorns, were synthesized selectively via thermal chemical vapor deposition of B/B(2)O(3) under the NH(3) flow at 1200 degrees C. Electron energy-loss spectroscopy reveals the N-rich h-BN layers with a ratio of B/N = 0.75-0.85. Angle-resolved X-ray absorption near edge structure of these two N-rich nanostructures has been compared with that of h-BN microcrystals. The pi transition in the N K-edge shifts to the lower energy by 0.8-1.0 eV from that of h-BN microcrystals, and the second-order signals of N 1s electrons become significant. We suggest that the N enrichment would decrease the band gap of nanostructures from that of h-BN microcrystals. The Raman spectrum shows the peak broadening due to the defects of N-rich h-BN layers.     

1H,89Y HMQC and further NMR spectroscopic and X-ray diffraction investigations on yttrium-containing complexes exhibiting various nuclearities

2D (1)H,(89)Y heteronuclear shift correlation through scalar coupling has been applied to the chemical-shift determination of a set of yttrium complexes with various nuclearities. This method allowed the determination of (89)Y NMR data in a short period of time. Multinuclear NMR spectroscopy as function of temperature, PGSE NMR-diffusion experiments, heteronuclear NOE measurements, and X-ray crystallography were applied to determine the structures of [Y(5)(OH)(5)(L-Val)(4)(Ph(2)acac)(6)] (1) (Ph(2)acac=dibenzoylmethanide, L-Val=L-valine), [Y(2)(OTf)(3)] (3), and [Y(2)(4)(OTf)(5)] (5) (2: [(S)P{N(Me)N=C(H)Py}(3)], 4: [B{N(Me)N=C(H)Py}(4)](-)) in solution and in the solid state. The structures found in the solid state are retained in solution, where averaged structures were observed. NMR diffusion measurements helped us to understand the nuclearity of compounds 3 and 5 in solution. (1)H,(19)F HOESY and (19)F,(19)F EXSY data revealed that the anions are specifically located in particular regions of space, which nicely correlated with the geometries found in the X-ray structures.     

Syntheses and X-ray crystal structures of organoantimony diazides

Antimony(III) complexes of the general type LSbF(2) (3: L(1) =[tBuC(NiPr)(2)]; 4: L(2) =[tBuC(NDipp)(2) , Dipp=2,6-iPr(2)C(6)H(3)) and LSb(N(3))(2) (6: L(1); 7: L(2)) were prepared in high yields and characterized by elemental analyses, NMR and IR spectroscopy and single-crystal X-ray diffraction. Moreover, the solid-state structures of [L(2)SbF(2)][L(2)Li] (5), [L(2) AlH(2)] (1), and [L'H][L'K(thf)(3)] (2; L'=HC(NDipp)(2)) are described, in which the Li (5) and K atoms (2) adopt rather unusual coordination modes.     

Ruthenium agostic (phosphinoaryl)borane complexes: multinuclear solid-state and solution NMR, X-ray, and DFT studies

The reactivity of the (o-phosphinophenyl)(amino)borane compound HB(N(i)Pr(2))C(6)H(4)(o-PPh(2)) prepared from Li(C(6)H(4))PPh(2) and HBCl(N(i)Pr(2)) toward the bis(dihydrogen) complex RuH(2)(H(2))(2)(PCy(3))(2) (1) was studied by a combination of DFT, X-ray, and multinuclear NMR techniques including solid-state NMR, a technique rarely employed in organometallic chemistry. The study showed that the complex RuH(2){HB(N(i)Pr(2))C(6)H(4)(o-PPh(2))}(PCy(3))(2) (3), isolated in excellent yield as yellow crystals and characterized by X-ray diffraction, led in solution to PCy(3) dissociation and formation of an unsaturated 16-electron complex RuH(2){HB(N(i)Pr(2))C(6)H(4)(o-PPh(2))}(PCy(3)) (4), with a hydride trans to a vacant site. In both cases, the (phosphinoaryl)(amino)borane acts as a bifunctional ligand through the phosphine moiety and a Ru-H-B interaction, thus featuring an agostic interaction.     

Formation mechanism of Si3N4 nanowires via carbothermal reduction of carbonaceous silica xerogels

Si3N4 nanowires prepared from the carbothermal reduction of carbonaceous silica xerogels with metal salt additives usually contain a small amount of nanotubes. This paper is devoted to the investigation of the formation mechanism of the Si3N4 nanowires. As-prepared samples heated at 1300 degrees C for different reaction times (1, 5, 10, and 30 h) were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results showed that all the samples mainly consisted of nanowires, while their crystalline phases changed with the heating time. Nitrogen-doped silicon oxide nanowires were first produced via the vapor-liquid-solid process and then underwent a stepwise surface nitrogenization to silicon nitride. The suggested mechanism can easily explain the existence of nanotubes in the Si3N4 nanowires.     

Chemical interactions in the layered system BC x N y /Ni(Cu)/Si, produced by CVD at high temperature

Layered samples Si(100)/C/Ni/BC(x)N(y) and Si(100)/C/Cu/BC(x)N(y) were produced by physical vapor deposition of a metal (Ni, Cu, resp.) and low-pressure chemical vapor deposition of the boron carbonitride on a Si(100) substrate. Between the Si and the Ni (Cu) and on the surface of the Ni (Cu) layer, thin carbon layers were deposited, as a diffusion barrier or as a protection against oxidation, respectively. Afterwards, the surface carbon layer was removed. As precursor, trimethylamine borane and, as an auxiliary gas, H(2) and NH(3) were used, respectively. The chemical compositions of the layers and of the interfaces in between were characterized by total-reflection X-ray fluorescence spectrometry combined with near-edge X-ray absorption fine-structure spectroscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry. The application of H(2) yielded the BC(x)N(y) compound whereas the use of NH(3) led to a mixture of h-BN and graphitic carbon. At the BC(x)N(y)/metal interface, metal borides could be identified. At the relatively high synthesis temperature of 700 °C, broad regions of Cu or Ni and Si were observed between the metal layer and the substrate Si.