The mechanism of plasma-induced deposition of amorphous silicon from silane

Time-resolved mass spectrometric data show that the concentration of di- and trisilane, which are formed from monosilane under discharge conditions typical for the deposition of high electronic quality amorphous silicon, correlate with the measured deposition rate of a-Si. The data can be quantitatively and self-consistently described by a simple set of consecutive reactions:

1. SiH₄ →-SiH₂ + H₂
2. SiH₂ + SiH₄ → Si₂H₆
3. SiH₂ + Si₂H₆ → Si₃H₈
4. Si _n H_{2(n + 1)} →n ·a-Si:H+(n+1)H₂,n=2,3

The only fitting parameter necessary for an excellent fit of the measured data over a wide range of experimental parameters is the value of the reactive sticking coefficient .for the decomposition of di- and trisilane (reaction 3). The resultant value agrees well with the published data of other authors and with those calculated from the measured deposition rate and Si₂H₆, concentration. We did not find and physically meaningful way to lit the measured data with the various “SiH₃ models” proposed by other authors who assumed that the dominant species responsiblefor the deposition of a-Si: H is the SiH₃, radical. For this and some additional reasons mentioned in the present paper. the SiH₃ model is in disagreement with available experimental data.     

Ab Initio Chemical Kinetics for SiHx Reactions with Si2Hy (x = 1,2,3,4; y = 6,5,4,3; x + y = 7) under a‐Si:H CVD Condition

Gas‐phase reactions of SiH_x with Si₂H_y (x = 1,2,3,4; y = 6,5,4,3) species, respectively, which may coexist under chemical vapor deposition (CVD) conditions, have been investigated by means of ab initio molecular orbital and statistical theory calculations. Potential energy surface (PES) predicted at the CCSD(T)/CBS//B3LYP/6–311++G(3df,2p) level shows that these reactions take place primarily via trisilany radicals, n‐Si₃H₇ and i‐Si₃H₇. For example, SiH₂ can associate with Si₂H₅ producing n‐H₂SiSiH₂SiH₃ exothermically by 55.8 kcal/mol; SiH₃ can undergo addition to H₂SiSiH₂ to produce n‐Si₃H₇ or associate with H₃SiSiH barrierlessly forming i‐Si₃H₇; whereas SiH can insert into one of the Si─H bonds of Si₂H₆ to give excited n‐Si₃H₇. Similarly, H₂SiSiH and SiSiH₃ can undergo insertion reactions with SiH₄ producing n /i‐Si₃H₇ intermediates, respectively, to be followed by fragmentation to various smaller species. These processes are fully depicted in the complete PES. The predicted heats of formation of various species agree well with available thermochemical data. The rate constants and product branching ratios for the low‐energy channel products have been calculated for the temperature range 300–1000 K by variational RRKM (Rice–Ramsperger–Kassel–Macus) theory with Eckart tunneling corrections. The results may be employed for realistic kinetic modeling of the plasma‐enhanced chemical vapor deposition growth of a‐Si:H thin films under practical conditions.     

Ion—molecule reactions in GeH4/SiH4 systems studied by ion trap mass spectrometry

Gas phase ion—molecule reactions occurring in GeH₄/SiH₄ systems under different partial pressures and their mechanisms have been investigated by ion trap mass spectrometry (ITMS). SiH⁺_n (n=0–3) and GeH⁺_n (n = 0–3) are the main ionic species at zero reaction time when the GeH₄: SiH₄ ratio is in the range 1:1 to 1:12. Self-condensation sequences are observed at increasing reaction times. Moreover, formation of ions containing GeSi bonds, such as GeSiH⁺_n (in = 2–5) and GeSi₂H⁺_n (n = 4, 5), occurs by reactions of Si₂H⁺_n (n = 2–5) and Si₃H⁺_n (n = 4, 5) with GeH₄. At longer reaction times, further substitution of silicon with germanium in GeSiH⁺_n (n = 2–5) ions has been observed, to give Ge₂H⁺_n (n = 2–5).     

Molecular beam multiphoton-ionization studies on ammonia—water binary clusters

Two-photon ionization mass spectra are obtained for NH₃H₂O binary clusters both with a nozzle beam and an ArF excimer laser. The detected major ions are H⁺(NH₃)_n(H₂O)_m(1 <m + n < 9). The results suggest that ammonia molecules constitute an inner shell which is surrounted by water molecules.     

Präparative Darstellung von Disilanyl- und Trisilanyljodiden

Zusammenfassung Die Darstellung von Si₂H₅J sowie von Si₂H₄J₂ (SiH₃–SiHJ₂+SiH₂J–SiH₂J), Si₃H₇J (SiH₃–SiH₂–SiH₂J+SiH₃–SiHJ–SiH₃) und Si₃H₆J₂ (Isomerengemisch) durch Umsetzung der entsprechenden Silane mit elementarem Jod (ohne Verwendung eines Lösungsmittels) wird mitgeteilt. Durch katalytische Mengen Alkohol wird die Reaktion von Jod mit Silanen beschleunigt, gleichzeitig jedoch die Spaltung der Si–Si-Bindung gefördert.

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Preparation of disilanyl iodide and trisilanyl iodide

The preparation of Si₂H₅J as well as Si₂H₄J₂ (SiH₃–SiHJ₂+SiH₂J–SiH₂J), Si₃H₇J (SiH₃–SiH₂–SiH₂J+SiH₃–SiHJ–SiH₃) and Si₃H₆J₂ (isomeric mixture) by reaction of the corresponding silanes with elementary iodine without using a solvent is communicated. The reaction of iodine with silanes is accelerated by catalysings amounts of alcohol. At the same time, however, the cleavage of the Si–Si-bond is stimulated.

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Mit 3 Abbildungen

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19. Mitt.:F. Fehér, D. Schinkitz undH. Strack, Z. anorg. allgem. Chem.385, 202 (1971).

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B. Mostert, Dissertation Univ. Köln 1961.

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A. G. Wronka, Dissertation Univ. Köln 1961.

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G. Betzen, Dissertation Univ. Köln 1967,G. Betzen, Diplomarbeit Univ. Köln 1963.     

Ditopic complexes of silene H2SiCH2 with bidentate ligands Me2NCH2SiHnF3-n. Structures, formation energies, AIM and ELF analyses.

Ditopic complex formation of silene H₂SiCH₂ with bidentate ligands Me₂NCH₂SiH_nF_3-n (n = 0-3) was studied at the MP4(SDQ(T)6-311G(d,p))//MP2/6-31G(d,p) levels of theory. The AIM and ELF analyses have shown that π-bonding in the silenic Si¹C moiety in the relatively weak (H₂Si¹CH₂)·(Me₂NCH₂Si²H_nF_3-n) (n = 2, 3) ditopic complexes is partially preserved.     

Electronic structure of silanes in the semi-empirical equivalent orbital method

The problem of the prediction of the valence IPs for silanes is considered. It is shown that the data on the silicon band structure combined with the photoelectron spectra of SiH₄, and Si₂H₆ permit to obtain the parameter scale, which includes all the nearest neighbour, second neighbour and the main third neighbour interaction parameters. Using the derived parameter scale the vertical ionization potentials of Si₃H₈, SiH(SiH₃)₃, Si(SiH₃)₄, the infinite polysilane valence band structure and the inner a _1g level for disilane are calculated. All the calculated levels are located above ? 20 eV and are expected to be measurable by the He (I) photoelectron spectroscopy.     

A study of the electronic structure of phenylsilanes by X-ray emission spectroscopy and quantum chemical calculation methods

The electronic structure of a series of phenylsilanes Ph_4?n SiH _n (n = 0?C3) is studied by X-ray emission spectroscopy and quantum chemical calculations by the density functional theory method. Based on the calculations theoretical X-ray emission SiK??₁ spectra of phenylsilanes Ph_4?n SiH _n (n = 0?C4) are constructed and their energy structure and shape turn out to be well consistent with experiment. The distribution of the electron density of states with different symmetry of Si, C, H atoms are also constructed. An analysis of the obtained X-ray fluorescent SiK??₁ spectra and the distribution of the electron density of states in Ph₄Si and Ph₃SiH compounds shows that their energy structure is mainly determined by a system of the energy levels of phenyl ligands weakly perturbed by interactions with valence AOs of silicon. In the energy structure of MOs of the PhSiH₃ compound, energy orbitals related to t ₂ and a ₁ levels of tetrahedral SiH₄ are mainly presented.     

Spektroskopische und physikalische Daten von Jodsilanen

Zusammenfassung Von den Jodderivaten der Silane SiH₄, Si₂H₆ und Si₃H₈ werden Dichte, Dampfdruck und Molrefraktion sowie die entsprechenden Atom- und Bindungsinkremente mitgeteilt. Die Ramanspektren von SiH₃J, Si₂H₅J und Si₃H₇J werden aufgenommen und zugeordnet.

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Spectroscopic and other physical investigations of silanyl iodides

Density, vapour pressure and molecular refraction as well as the corresponding atom increments and bond increments of the iodine derivatives of the silanes SiH₄, Si₂H₆ and Si₃H₈ are communicated. The Raman spectra of SiH₃J, Si₂H₅J and Si₃H₇J are recorded and assigned.

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XX. Mitt.:F. Fehér, B. Mostert, A. G. Wronka undG. Betzen, Mh. Chem.103, 959 (1972).

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A. G. Wronka, Dissertation Univ. Köln 1961.

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B. Mostert, Dissertation Univ. Köln 1961.     

Theoretical Study of Interaction Between S2 and SiHx (x=1, 2, 3) in Porous Silicon

The interaction between S₂ molecule and SiH_x (x=1, 2, 3) in porous silicon is investigated using the B3LYP method of density functional theory with the lanl2dz basis set. The model of porous silicon doped with CH₃,Si-O-Si and OH species is built. By analyzing the binding energy and electronic transfer, we conclude that the interaction of S₂ molecule with SiH_x (x=1, 2, 3) is much stronger than the interaction of S₂ molecule with CH₃ and OH, as S₂ molecule is located in different sites of the model. Using the transition state theory, we study the Si₂H₆+S2→H₃SiH₂SiS+HS reaction, and the reaction energy barrier is 50.2 kJ/mol, which indicates that the reaction is easy to occur.     

Plasma Composition by Mass Spectrometry in a Ar-SiH<Subscript>4</Subscript>-H<Subscript>2</Subscript> LEPECVD Process During nc-Si Deposition

Mass spectrometry has been used to assess plasma composition during a low-energy plasma-enhanced chemical vapor deposition (LEPECVD) process using argon-silane-hydrogen (Ar-SiH₄-H₂) gas mixtures with input flows of 50 sccm Ar, 2–20 sccm SiH₄ and 0–50 sccm H₂ at total pressures of 1–4 Pa. Energy-integrated ion densities, residual gas analysis and threshold ionization mass spectrometry have been used to characterize the transition from amorphous (a-Si) to nano-crystalline silicon (nc-Si) deposition at constant LEPECVD operating parameters. While relative ion densities have a marked decrease with H₂ input, the densities of SiH_x (x < 4) radicals show evolution trends depending on the SiH₄ and H₂ input. For conditions leading to nc-Si growth a turning point is reached above which SiH is the main radical. Observed SiH_x density trends with H₂ input are explained based on kinetic reaction rates calculated from previously obtained Langmuir probe data.     

An iets study of alumina and magnesia supported —sihx and their use as substrates for inorganic vibrational spectroscopy

Tunneling spectra of Al₂O₃/—SiH_x, MgO/—SiH_x, Al₂O₃/—SiD_x, and Al₂O₃/—SiH_x + NCS^? are reported. Analysis of the vibrational spectra observed from isotopic substitution of the barriers obtained by deposition of a thin film of SiO onto alumina and magnesia indicate that the supported species is —SiH. The Al₂O₃/—SiH barrier can be used as a support for studying inorganic ions by IETS.     

Ab initio chemical kinetics for the unimolecular decomposition of Si2H5 radical and related reverse bimolecular reactions

For plasma enhanced and catalytic chemical vapor deposition (PECVD and Cat‐CVD) processes using small silanes as precursors, disilanyl radical (Si₂H₅) is a potential reactive intermediate involved in various chemical reactions. For modeling and optimization of homogeneous a‐Si:H film growth on large‐area substrates, we have investigated the kinetics and mechanisms for the thermal decomposition of Si₂H₅ producing smaller silicon hydrides including SiH, SiH₂, SiH_3, and Si₂H₄, and the related reverse reactions involving these species by using ab initio molecular‐orbital calculations. The results show that the lowest energy path is the production of SiH + SiH₄ that proceeds via a transition state with a barrier of 33.4 kcal/mol relative to Si₂H₅. Additionally, the dissociation energies for breaking the Si? Si and H? SiH₂ bonds were predicted to be 53.4 and 61.4 kcal/mol, respectively. To validate the predicted enthalpies of reaction, we have evaluated the enthalpies of formation for SiH, SiH₂, HSiSiH₂, and Si₂H₄(C_2h) at 0 K by using the isodesmic reactions, such as ²HSiSiH₂ + ¹C₂H₆→¹Si₂H₆ + ²HCCH₂ and ¹Si₂H₄(C_2h) + ¹C₂H₆ → ¹Si₂H₆ + ¹C₂H₄. The results of SiH (87.2 kcal/mol), SiH₂ (64.9 kcal/mol), HSiSiH₂ (98.0 kcal/mol), and Si₂H₄ (68.9 kcal/mol) agree reasonably well previous published data. Furthermore, the rate constants for the decomposition of Si₂H₅ and the related bimolecular reverse reactions have been predicted and tabulated for different T, P‐conditions with variational Rice–Ramsperger–Kassel–Marcus (RRKM) theory by solving the master equation. The result indicates that the formation of SiH + SiH₄ product pair is most favored in the decomposition as well as in the bimolecular reactions of SiH₂ + SiH₃, HSiSiH₂ + H₂, and Si₂H₄(C_2h) + H under T, P‐conditions typically used in PECVD and Cat‐CVD. © 2013 Wiley Periodicals, Inc.     

Elastic and inelastic neutron studies of hydrogen molybdenum bronzes

Hydrogen molybdenum bronzes H_xMoO₃ (～0.3 < x < 2.0) have been investigated with elastic and inelastic neutron scattering. Neutron diffraction studies of orthorhombic D_0.36MoO₃ show that deuterium is incorporated as -OD without any major structural change to the MoO₃ layer lattice. The inelastic neutron scattering spectra of H_xMoO₃ phases confirm that, for H_0.34MoO₃, H is present as -OH, but, for the monoclinic phases H_0.93MoO₃, H_1.68MoO₃ and H_2.0MoO₃, only peaks associated with -OH₂ groups are found.     

Neutral and ion chemistry in a C2H4-SiH4 discharge

This paper reports on a mass spectrometric study of the neutral and ionic species in a low-pressure rf discharge sustained in a C₂H₄-SiH₄ mixture diluted in helium. It is shown that C₂H₄ is readily decomposed into C₂H ₂ ^* and C₂H₃. The formation of secondary products such as C₄H₂, C₄H₄, and C₄H₆ is observed and confirms the presence of C₂H₂ in the discharge. Methylsilane (CH₃SiH₃) and ethylsilane (C₂H₅SiH₃) are also synthesized in this discharge. It is also observed that the major ions C₂H ₄ ⁺ , C₃H ₅ ⁺ , SiH ₃ ⁺ , Si₂H ₄ ⁺ , SiCH ₃ ⁺ , SiC₂H ₃ ⁺ , and SiC₂H ₇ ⁺ are not representative of the direct ionization of neutral species. Their formation is thus interpreted on the basis of ion-molecule reactions.     

Structural study of gels of V2O5: Vibrational spectra of xerogels

A complete vibrational study of xerogels of vanadium oxide corresponding to the formula V₂O₅ · nH₂O with n = 1.6, 1.2, 0.6, 0.4, and 0.3, was performed. Raman and infrared spectra of powder and oriented films of the samples have been recorded at 100 and 300 K. It has been possible to verify the existence of two different structures. For n = 0.3, V₂O₅ layers are connected as in the crystal through VOV bonds, each water molecule trapped into cavities being linked by its two hydrogen atoms to the oxygen lattice, the interlayer distance (b parameter) should be close to that of the crystal. For n = 0.6, the V₂O₅ layers are not connected as in the crystal through the long VO bonds, but the vanadium atoms are coordinated to H₂O molecule by VOH₂ bonds. For 0.6 < n < 1.4 three kinds of water molecules are likely present. Finally, it is shown that the conclusions are consistent with the literature structural models proposed from diffraction methods.     

AB Initio molecular orbital calculations on the si2h4molecule

Ab initio molecular orbital calculations using an extended Gaussian basis set have been performed on C₂H₄, CH₂SiH₂ and Si₂H₄. The species CH₂ and SiH₂ have also been examined. Geometries were partially optimized and the energy difference between the planar singlet and orthogonal or twist triplet geometries of Si₂H₄ was studied in order to provide a measure of the strength of the Si-Si bond in this molecule. Mulliken population analyses were carried out on CH₂CH₂ and SiH₂SiH₂, to further study the nature of the Si-Si double bond in comparison with the C—C double bond.     

Theoretical study on the substitution reactions of fluorosilylenoid H2SiLiF with SiH3XH n−1 (X = F,Cl, Br,O, N; n = 1, 1, 1, 2, 3)

The substitution reactions of H₂SiLiF (A) with SiH₃XH _n?1 (X = F, Cl, Br, O, N; n = 1, 1, 1, 2, 3) have been studied using DFT and ab initio methods. The results indicate that the substitution reactions of A with SiH₃XH _n?1 proceed via two reaction paths, I and II. The following conclusions emerge from this work. (i) The substitutions of A with SiH₃XH _n?1 are nucleophilic reactions and occur in a concerted manner. Path I is more favorable than path II. The substitution barriers of A with SiH₃XH _n?1 for path I decrease with the increase of the atomic number of X for the same period systems, whereas the barriers increase with the increase of the atomic number of X for the same family systems. (ii) The substitution products are H₂SiFSiH₃ and LiXH _n?1. If the H atoms in SiH₃ of SiH₃XH _n–1 are substituted by different atoms or groups, silanes H₂SiFSiH₃ obtained via paths I and II would be enantiomers. (iii) All the substitution reactions of A with SiH₃XH _n?1 are exothermic.     

The structure and energy of SiH+5. comparisons with CH+5 and BH5

Differences between SiH⁺₅ and CH⁺₅ are more significant than the similarities. The proton affinity of SiH₄ exceeds than of CH₄ by ≈25 kcal/mol. but the heat of hydrogenation of SiH⁺₃ is smaller than that of CH⁺₃ by nearly the same amount. Like CH⁺₅ the C₅ structures of SiH⁺₅ are preferred, but SiH⁺₅ is best regarded as a weaker SiH⁺₃—H₂ complex. D_3h, C_2v, and C_4v forms are much higher in energy and SiH⁺₅ should not undergo hydrogen scrambling (pseudorotation) readily, as does CH⁺₅ The neutral BH₅ is only weakly bound toward loss H₂, and the D_3h. C_2v, and C_4v forms are also high in energy. The contral-atom electronegativities, C⁺ > B > Si⁺, control this behavior. The electronegativities also determine the ability to bear positive charges. Thermodynamically. SiH⁺₅ and SiH⁺₃ are more stable than CH⁺₅ and CH⁺₃, respectively; hydride transfer occurs from SiH₄ to CH⁺₃ and proton transfer from CH⁺₅ to SiH₄.     

Bildung siliciumorganischer Verbindungen. 111. Die Hydrierung Si-chlorierter,C-spiroverbrückter 2,4-Disilacyclobutane mit LiAlH4 und iBu2AlH. Der Zugang zum Si8C3H20

Formation of Organosilicon Compounds. 111. The Hydrogenation of Si-chlorinated, C-spiro-linked 2,4-Disilacyclobutanes with LiAlH₄ or iBu₂AlH. The Access to Si₈C₃H₂₀ The hydrogenation of Si-chlorinated, C-spiro-linked 2,4-disilacyclobutanes containing C(SiCl₃)₂ terminal groups with LiAlH₄ in Et₂O proceeds under complete cleavage of the fourmembered rings and under elimination of one SiH₃ group. Such, Si₈C₃Cl₂₀ 4 forms (H₃Si)₂CH? SiH₂? CH(SiH₃)? SiH₂? CH(SiH₃)₂ 4 α, and even Si₈C₃H₂₀ 4a with LiAlH₄ forms 4 α. The hydrogenation of related compounds containing however CH(SiCl₃) terminal groups similarly proceeds under ring cleavage but no SiH₃ groups are eliminated. Such, (Cl₃Si)CH(SiCl₂)₂CH(SiCl₃) 41 forms (H₃Si)₂CH? SiH₂? CH₂(SiH₃) 41 α. However, in reactions with iBu₂AlH in pentane neither the disilacyclobutane rings are cleaved nor are SiH₃ groups eliminated. Only by this method Si₈C₃H₂₀ is accessible from 4 , Si₆C₂H₁₆ 3a from Si₆C₂Cl₁₆ 3 and Si₄C₂H₁₂ 41a from 41 . C(SiCl₃)₄ cleanly produces C(SiH₃)₄. Based on the knowledge about the different properties of LiAlH₄ and iBu₂AlH in hydrogenation reactions of disilacyclo-butanes it was possible to elucidate the composition and the structures of the hydrogenated derivatives of the product mixture from the reaction of MeCl₂Si? CCl₂? SiCl₃ with Si(Cu) [1] and to trace them back to the initially formed Si chlorinated disilacyclobutanes Si₆C₂Cl₁₅Me 34 , Si₆C₂Cl₁₄Me₂ 35 , Si₈C₃Cl₁₉Me 36 and Si₈C₃Cl₁₈Me₂ 37 . Compound 4a forms colourless crystals of space group P1 with a = 799.7(6), b = 1263.6(12), c = 1758.7(14) pm, α = 103.33(7)°, β = 95.28(6)°, γ = 105.57(7)° and Z = 4.