Surface-near analyses of ultra thin silicon nitride layers by NRA, channeling RBS, FT IR ellipsometry and AFM

Homogeneous ultra thin silicon nitride layers (SiN_x layers) close to the surface have been produced by 10 keV ¹⁵N ₂ ⁺ molecular ion implantation and an ion current density of 10 A/cm², into single crystal silicon at room temperature. Stoichiometric SiN_x layers with thicknesses of about 28 nm (analyzed by NRA) were obtained at fluences of 1.5×10¹⁷ at/cm². NRA analyses of samples annealed by EB-RTA at T=1150° C for 15 s indicated that the N/Si ratio and the layer thickness did not change drastically. FT IR ellipsometry analyses indicated the existence of Si₃N₄ bonds in as-implanted specimens. A disordered Si layer (d-Si, typically 15 nm thick) underneath the implantation region caused by the ion implantation was found by channeling RBS analyses. The d-Si layer partly recrystallized during EB-RTA showing a thickness of 6 nm afterwards. The SiN_x layers showed no decomposition and detachment after EB-RTA. Due to EB-RTA, however, the smooth surface of the as-implanted specimens changed into a surface with remaining whisker-like structures surrounded by circular recesses as shown by AFM analyses. A model for the growth of these whisker-liker structures caused by low energy ion implantation and EB-RTA is presented on the basis of the thickness of the SiN_x layer, the existence of the d-Si layer and the special annealing process.     

Molecular ion implantation in silicon

¹⁵N₂ ⁺ molecular ions were implanted with 10keV (j=10 A/cm²) under high vacuum conditions close to room temperature in 100 silicon (c-Si) to study the¹³N depth distributions, particularly the dependence of peak concentration and dose on the ion fluence. The analysis were performed by the resonant nuclear reaction¹⁵N(p, )¹²C(NRA). A maximum peak concentration of 65 at.% was measured. Thin stoichiometric silicon nitride layers with a thickness of approx. 20 nm (15 at.% nitrogen at the specimen surface) were produced by this low-energy implantation of¹⁵N₂ ⁺ ions with an ion fluence of 1.5·10¹⁷ ions/cm². NRA analysis of 38 keV¹⁵N₂ ⁺ and 19keV¹⁵N⁺ ion implantations were performed to compare the¹⁵N depth distributions. No significant changes in the depth distributions are measured, that means, the molecular¹⁵N₂ ⁺ ions are already disintegrated passing the very first atomic layers of the sample during implantation. Non-Rutherford RBS with⁴He⁺ ions and 3.45 MeV was performed in order to confirm the results obtained by NRA.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Characterisation of thin sputtered silicon nitride films by NRA, ERDA, RBS and SEM

Summary Thin, amorphous silicon nitride (a-SIN_x) films were deposited on n-type (100) silicon substrates using an argon ion beam for sputtering a HPSN block under high vacuum conditions. The substrates were kept at room temperature. Nitrogen depth distributions were determined by NRA using the resonance reaction ¹⁵N(p,)¹²C at 429 keV. Hydrogen profiles were analysed by NRA (¹H(¹⁵N,)¹²C at E_o=6.385 MeV) and by ERDA (²⁰Ne²⁺, E_o=10 MeV). The NRA was used to determine the depth distributions (concentration vs. areal density) of nitrogen and hydrogen taking calibration standards into consideration. The silicon depth distributions and the N/Si ratios of the deposited a-SiN_x films were determined by RBS (⁴He⁺, E_o=2.0 MeV). Film thicknesses were obtained by SEM. The density of the deposited a-SiN_x films was found to be =2.7 (±0.1) g/cm³ by correlating RBS data and real film thicknesses as obtained by SEM.     

Investigation of implanted gallium depth distributions in ZnSxSe-x by EPMA

In the present work EPMA combined with Monte Carlo simulation was applied to investigate implanted gallium depth distributions in ZnS_xSe_1–x layers. The layers of about 1 to 4 m thickness were grown by MOVPE on (100)-GaAs substrate. The overlap of the Ga and zinc L X-ray spectra and the low gallium net count rates were overcome by stripping the spectra of non implanted layers and by applying appropriate beam currents and counting times. Capabilities and limitations of the EPMA technique as applied to depth profile analysis are demonstrated.Despite the mentioned L interference, the detectability limit of EPMA for 340 keV Ga in ZnS_xSe_1–x is as low as 10¹⁴ cm^–2. The measured Ga L intensity versus beam energy curves reveal variations of the Ga depth profiles during annealing. Evaluation of the intensity curves by means of Monte Carlo simulations yields the implanted dose densities and the first two moments of the depth distributions, i.e. the projected range and its standard deviation. The nonannealed profiles agree well with expectations, but after thermal annealing the profiles were significantly shifted towards the surface. Comparison of EPMA and SIMS results with the example of a non annealed profile in ZnSe has shown good agreement.     

Crystalline Inclusions Formed in C+N+BF2 Coimplanted on Silicon (111)

In the present work, high-doses (10¹⁷–10¹⁸cm^–2) of carbon, nitrogen, and boron (BF₂⁺) ions were coimplanted on silicon (111) substrates at 21, 25 and 77keV, respectively. Two series of samples have been implanted (series A and B) and subsequently annealed. Series A samples have been implanted at room temperature and treated one minute by rapid thermal annealing (RTA) and 3 hours at 1200°C. Series B samples have been implanted at 600°C and subsequently annealed at 1200°C during 3 hours. The annealing in both series has been carried out in N₂ at atmospheric pressures.The structure of the buried layers has been determined by conventional and high resolution transmission electron microscopy (CTEM and HRTEM). Polycrystalline silicon and new crystalline phases are observed by electron diffraction patterns. The polycrystalline silicon inclusions have been confirmed from analysis of HRTEM images.     

Effects of post-deposition annealing on chemical composition of SiNx film in SiO2/SiNx/SiO2/Si stacked structure

To systematically evaluate the quality of SiN_x films in multi-stacked structures, we investigated the effects of post-deposition annealing (PDA) on the film properties of SiN_x within the SiO₂/SiN_x/SiO₂/Si stacked structure by performing X-ray photoelectron spectroscopy (XPS), X-ray reflectivity (XRR), Fourier transform infrared (FT-IR) spectroscopy, and scanning transmission electron microscope–electron energy loss spectroscopy (STEM-EELS) analyses. The XPS results showed that PDA induces the oxidation of the SiN_x layer. In particular, new finding is that Si-rich SiN_x in the SiN_x layer is preferentially oxidized by PDA even in multi-stacked structure. The XRR results showed that the SiN_x layer becomes thinner, whereas the interface layer between the SiN_x layer and Si becomes thicker. It is concluded by STEM-EELS and XPS that this interface layer is SiON layer. The density of N–H and Si–H bonding within the stacked structure strongly depends on the PDA temperature. Our study helps elucidate the properties of SiN_x films in stacked structures from various perspectives.     

Trigonale kristallfelder in oxidischen spinellverbindungen

Zusammenfassung Die Spektren der Spinellmischkristalle Ni_2-x Mg_xGeO₄ (0,0 x 1,2₅) und Co_2-x Mg_xGeO₄ (0,0 x 1,0) im Kristallfeldgebiet zeigen starke Unregelmäßigkeiten, die durch die kristallographisch begründete Annahme gedeutet werden können, daß Ni²⁺ und Co²⁺ sich in entlang der trigonalen Achse gestauchten Koordinationsoktaedem befinden. Es wird ein Kristallfeldformalismus entwickelt, der eine quantitative Behandlung dieser Spektren gestattet. Weiter zeigt sich, daß nicht immer, wenn eine trigonale Kristallfeldkomponente zugegen ist, Aufspaltungen der Oktaederbanden zu beobachten sind.

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The spectra of the spinel type phases Ni_2-x Mg_xGeO₄ (0,0 x 1,2₅) and Co_2-x Mg_xGeO₄ (0,0 x 1,0) in the crystal field region show remarkable band splitting effects. They can be explained by the crystallographically plausible assumption, that the coordination octahedra of Ni²⁺ and Co²⁺ are compressed along their trigonal axes. A crystal field formalism is developed which allows a quantitative treatment of the spectra. Finally examples are given showing that band splittings are not always observed in the presence of a trigonal component.

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Résumé Le spectre des phases de type spinelle Ni_2-x Mg_xGeO₄ (0,0 x 1,2₅) et Co_2-x Mg_xGeO₄ (0,0 x 1,0) dans la région du champ cristallin montre des effets remarquables de séparation de bandes. Ils peuvent être expliqués par l'hypothèse cristallographiquement plausible selon laquelle l'octaèdre de coordination de N²⁺ et de Co²⁺ est comprimé selon l'axe trigonal. Un formalisme de champ cristallin développé ici permet un traitement quantitatif des spectres. Enfin on donne des exemples qui montrent que les séparations de bandes ne sont pas toujours observées en présence d'une composante trigonale.

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Aus der Habilitationsschrift D. Reinen, Bonn 1965.

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Herrn Dr. H. H. Schmidtke habe ich für die kritische Durchsicht des Manuskripts und der Deutschen Forschungsgemeinschaft für die Bereitstellung von Sachbeihilfen zu danken.     

Infrared investigation of the silicon oxide phase in [perfluoro-carboxylate/sulfonate (bilayer)]/[silicon oxide] nanocomposite membranes

[Perfluoro-organic]/[silicon oxide] hybrids were formed by conducting sol-gel reactions of tetraethylorthosilicate within a perfluoro(carboxylate/sulfonate) bilayer membrane in the Co⁺² form. FTIR and ²⁹Si solid-state NMR spectroscopies were used to probe general aspects of molecular structure within the silicon oxide phase as a function of its relative content. The internal gel structure is considerably unconnected in terms of the population of Si O Si groups in cyclic vs. linear substructures and degree of Si atom coordination about bonded SiO₄ units. In situ (HO)_xSiO_2[1-1/4x] intrastructure become increasingly less connected and more strained with regard to bonding geometry with increasing percent silicon oxide. Structural differences are seen between the silicon oxide component incorporated in carboxylate and sulfonate layers. These inorganically modified perfluorinated ionomers have potential as fast-proton conducting membranes for fuel cells and as permselective membranes in liquid pervaporation cells. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 595–606, 1998     

Kinetics and mechanism of dissociation of some tri- and tetra-dentate complexes of copper(II) in acid media

Summary Kinetics of the dissociation ofm-phenylene-dibiguanidecopper(II) ion,N-salicylideneglycyl-glycinatocuprate(II) ion andN-salicylideneglycinato-aquocopper(II) in acid media, forming aquo-copper(II) ion, have been studied by the stopped-flow spectrophotometric technique. Dissociation of the complexes occurs in two consecutive steps, the first being faster than the second. For them-phenylenedibiguanide complex each step exhibits second order acid dependance,k _x=k _x [H⁺]² wherek _x is the observed pseudo-first order rate constant. However, the Schiff base complexes show first order acid dependance,k _x=k _x [H⁺], for both steps. The results, with relatively low H and highly negative S values, are consistent with a solvent-assisted dissociative process.     

Ab Initio Modeling of Interatomic Interactions in 3C–SiC:M, M = Cr, Mn, Fe, Co

The electronic structure and chemical binding parameters of impurity atoms M = Cr, Mn, Fe, Co in cubic silicon carbide are considered in DFT (density functional theory) and X-DV (discrete variation) approximations. A scheme for calculating the binding energies in the cluster approach is suggested. Stoichiometric and superstoichiometric models of impurity incorporation are investigated. The binding energy is higher for the stoichiometric model. In the superstoichiometric model, the titanium and iron atoms preferably occupy the Si₄ interstice. For all other atoms, the MSi, Sii model is preferable. The incorporated impurity weakens the basic Si–C bonds.     

Electrochemical Intercalation of Lithium Ions into Electrolytic Vanadium Pentoxide

The discharge of thin films of Li _x V₂O₅ is described by a mathematical diffusion model. The chemical diffusion coefficient for lithium ions, estimated with the model, is equal to (1.01–2.5) × 10^–11 cm²/s. As the film thickness increases, the discharge capacity at a current of 20 A/cm² tends to the calculated limiting of 3.12 C/cm². The optimum thickness of the film electrode calculated for a discharge current of 20 A/cm² is 33.4 m and agrees satisfactorily with the experimental value.     

The Sialons MLn[Si4−xAlxOxN7−x] with M = Eu,Sr, Ba and Ln = Ho‐Yb – Twelve Substitution Variants with the MYb[Si4N7] Structure Type

The oxonitridoalumosilicates (so‐called sialons) MLn[Si_4?xAl_xO_xN_7?x] with M = Eu, Sr, Ba and Ln =Ho, Er, Tm, Yb were obtained by the reaction of the respective lanthanoid metal, the alkaline earth carbonates or europium carbonate, resp., AlN, “Si(NH)₂” and MCl₂ as a flux in a radiofrequency furnace at temperatures around 2100 °C. The compounds MLn[Si_4?xAl_xO_xN_7?x] are relevant for the investigation of substitutional effects on the materials properties due to their ability of tolerating a comparatively large phase width up to x ≈ 2.0(5). The crystal structures of the twelve compounds were refined from X‐ray single crystal data and X‐ray powder data and are found to be isotypic to the MYb[Si₄N₇] structure type. The compounds crystallize in space group P6₃mc (no. 186, hexagonal) and are made up of chains of so‐called starlike units [N^[4](SiN₃)₄] or [N^[4]((Si,Al)(O,N)₃)₄], respectively. These units are formed by four (Si,Al)(N/O)₄ tetrahedra sharing a common central nitrogen atom. The structure refinement was performed utilizing an O/N‐distribution model according to Paulings rules, i.e. nitrogen was positioned on the four‐fold bridging site and nitrogen and oxygen were distributed equally on both of the two‐fold bridging sites, resulting in charge neutrality of the compound. The Si and Al atoms were distributed equally on their two crystallographic sites, referring to their elemental proportion in the compound, due to being poorly distinguishable by X‐ray methods. The chemical compositions of the compounds were derived from electron probe micro analyses (EPMA).     

The energy levels for a symmetric and nonsymmetric double-well potential in a two-dimensional system using the Hill determinant approach

Energy levels of the Schrödinger equation for a double-well potentialV(x, y; Z _x ², Z_y ²,) = –Z _x ² x ² -Z _y ² y ² +[a _xx x ⁴ + 2a _xy ^x 2y2 +a _yy y ⁴] in a two-dimensional system are calculated using the Hill determinant approach for several eigenstates and over a wide range of values of the perturbation parameters (, Z _x ²,Z _y ²). Some of the results calculated by the Hill determinant approach are compared with those results produced by the inner product technique.     

1A1⇔5T2 Spin Transition in Heterometallic Solid Phases FexNi1-x(Htrz)3(NO3)2 · H2O (Htrz = 1,2,4‐Triazole)

Solid phases Fe_xNi_1-x(Htrz)₃(NO₃)₂ · H₂O (0.4 x 0.8$) and Ni(Htrz)₃(NO₃)₂ · H₂O were synthesized and studied. The phases were studied by means of magnetochemistry, powder Xray difraction analysis, and electronic and IR spectroscopy. The heterometallic phases are described by the stoichiographic method of differentiating dissolution (DD). The values of x were determined by two methods — atomic absorption and DD. Magnetochemical data showed that the solid phases exhibit a hightemperature ¹A₁ ⁵T₂ 0.5 x 0.8 and disappears at x = 0.4. The spin transition is accompanied by thermochromism (color changed from pink to white at 0.6 x 1 and from pink to light lilac at x = 0.5). A decrease in x leads to a decrease in the temperature of the forward (under heating T_c ) and reverse (under cooling T_c ) transitions, a decrease in hysteresis value ( T_c), and a smearing of the spin transition.     

Crystal Structures of Two New Holmium Polysulfides in the Series of Rare-Earth Polychalcogenides

The crystal structures of two polysulfide phases HoS_1.885(5) (I) and HoS_1.863(8) (II) were determined; the integer stoichiometric ratio was found to be Ho₈S₁₅. The data were collected on an Enraf-Nonius CAD-4 automatic diffractometer using the standard procedure (MoK, graphite monochromator, an absorption correction applied based on -scan data). Crystal I: space group P4/nmm, a = 3.820(1), c = 7.840(3) , V = 114.40(6) ³, Z = 2 for the composition HoS_1.885(5), d _calc = 6.542 g/cm³, R = 0.0520 for 184 unique reflections with I_hkl > 2 _I; crystal II: space group P2₁/m, a = 10.961(2), b = 11.465(2), c = 10.984(2) , = 91.27(3)°, V = 1380.0(4) ³, Z = 24 for the composition HoS_1.863(8), d _calc = 6.486 g/cm³, R = 0.0596 for 5354 unique reflections with I_hkl > 2 _I. In both compounds, the Ho atoms are surrounded by 9 (8+1 for three atoms in II) S atoms forming monocapped square antiprisms. The Ho–S distances vary from 2.717 to 3.067 irrespective of the type of ion [S^2– or (S₂)^2–]; the maximal distance to the atoms completing the coordination is 3.684 . The compounds have PbFCl type structures composed of ...(S₂)^2–...Ho³⁺...S^2–...S^2–...Ho³⁺...(S₂)^2–... layer packets differently oriented in space relative to the unit cell axes. The S^2–...S^2– and S^2–...(S₂)^2– interlayer distances are mostly shorter than the sum of the ionic radii and vary within the limits of 3.331-3.558 and 3.029-3.784 for the first and second types, respectively. For I, the calculated site occupancies and densities are given depending on the composition Ho-S_2-x (x = 0.25-0); for II, the most probable formulas of rational compositions in the same range of x are presented.     

Inclusion complexes of the natural product gossypol. Crystal structure of the 2:1 complex of gossypol withm-Xylene

The crystal structure of a 2: 1 inclusion complex of gossypol withm-xylene has been determined by X-ray structure analysis. The crystals of C₃₀H₃₀O₈·0.5C₈ H₁₀ are triclinic, space groupPl^–,a = 8.478(1),b = 14.087(2),c = 14.411(2) Å, = 115,39(1), = 75.11(1), = 86.80(1)°,V = 1475.2(4) ų,Z = 2,D _x = 1.29 g cm^–3,T = 295 K, (CuK ) = 7.01 cm^–1. The structure has been solved by direct methods and refined to the finalR value of 0.079 for 3910 observed reflections. The gossypol molecules are linked by intermolecular hydrogen bonds and form bimolecular layers parallel to the ab plane. Disorderedm-xylene molecules occupy cavities between these layers. All polar groups of the gossypol molecule are packed in the interior of the bilayer while non-polar groups are directed outwards. An analysis of the crystal packing of other inclusion complexes of gossypol shows that such bilayers are formed in four complexes and three of those structures are generically related to each other.Deceased.     

Optical Spectroscopy of Hybrid Sol-Gel Coatings Doped with Noble Metals

Sol-gel coatings in the xM (100-x) SiO₂ system, (M = Cu, Ag and Au) x =0.1–10 mol%), are deposited on soda lime glass slides by using silicon tetramethoxide Si(OCH₃)₄) and methyltriethoxysilane (SiCH₃[OCH₂CH₃]₃) as silica precursors. Anhydrous CuCl, CuCl₂ 2H₂O, Cu(NO₃)₂ 3H₂O, CuSO₄ 5H₂O, AgNO₃ and HAuCl₄ 3H₂O are used as copper, silver and gold sources. Coatings with thicknesses ranging from 100 to 900 nm are deposited on the subs trates by dip-coating and subsequently densified at 500°C for 1 h in air. Spectroscopic studies of the coatings as a function of the thicknesses and the metal concentration are carried out by photoluminescence (PL) and optical absorption (OA). In addition, direct observations of some gold coatings were performed by transmission electron microscopy (TEM). Results indicate that for silver and copper containing coatings the excitation and emission spectra arise from electronic transitions in Ag⁺ and Cu⁺ ions and no significant absorption bands due to colloidal precipitation are observed. Gold containing coatings show purple coloration due to an absorption peaking in the 520–560 nm range, which is characteristic of gold colloids. The presence of these colloids is confirmed by TEM observations.     

Structure of intercalated compounds of graphite fluoride C2FX

Conclusion The results obtained in the present work show that the use of the method proposed in [3] to study the structure of intercalated compounds of graphite fluoride has made it possible to resolve in principle the question of the distribution of the C₂F_X layers along the z axis in these compounds and to determine the nature of the arrangement of the inserted molecules between the layers.In intercalated compounds of stage I with an expanded structure of the filled layer, the molecules of the inserted solvent are distributed chiefly in two layers between the C₂F_x layers, whereas in the compounds with the simple structure they are distributed in one layer.In the intercalated compounds of stage II, the thickness of the unfilled layer is 6 Å, and the thickness of the filled layer coincides with the thickness of the layer in the corresponding inercalated compounds of stage I with the simple structure of the filled layer.The fluorine atoms in C₂F_x are arranged symmetrically on each side of the carbon layer.In the intercalated compounds heated to a temperature of 200°C, the graphite fluoride layers form stacks with a distance of 6.0 Å between the layers.On the basis of the results obtained, it has been suggested that the most probable reason for the strong retention of the inserted component in the intercalated compounds of stage II is the paired linking of the edge sections of the C₂F_x layers.Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 29, No. 3, pp. 78–83, May–June, 1988.