Comparative surface and bulk analysis of oxygen in Si3N4 powders

Summary Five commercially available -Si₃N₄ powders and one in the modification were subjected to Auger electron spectroscopy (AES) and carrier-gas-heat extraction (CGHE) analysis.AES depth profiles of the oxygen/nitrogen ratio could be obtained, from which total oxygen contents were calculated and compared to CGHE data. It is demonstrated that by the latter method also dissolved oxygen in -Si₃N₄ is detected, whereas by AES only chemically bound oxygen can semiquantitatively be analyzed. Evidence is found for the existence of water, adsorbed or present as hydroxyl groups, near the surface.

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Vergleichende Oberflächen- und Bulkanalyse von Sauerstoff in Si₃N₄-Pulvern

List of Symbols A Surface area of an idealized Si₃N₄ grain - c _o ^AES Bulk concn. (by wt.) of oxygen in Si₃N₄ as estimated from AES depth profiles - C _O ^GHE Bulk concn. (by wt.) of oxygen in Si₃N₄ as obtained using CGHE in the fixed temperature mode - C _pr Bulk concn. (by wt.) of oxygen in Si₃N₄ as obtained using CGHE in the temperature programme mode - C_surf Bulk concn. (by wt.) of oxygen in Si₃N₄, tentatively assigned to superficial oxygen on Si₃N₄ particles, as obtained using CGHE in the temperature programme mode - C _U c _o ^AES as recalculated from X_U - d Diameter of an idealized Si₃N₄ grain (1 m) - M_index Formula mass of the species named in the index (O, 2 SiO₂, Si₃N₄) - m _o Mass of oxygen in the Si₃N₄ material - M_x Estimated formula mass of a (SiO₂)_2XSi₃N₄ compound as detected by AES via X - r Radius of an idealized Si₃N₄ grain (0.5 m) - V Volume of an idealized Si₃N₄ grain - X atomic oxygen-to-nitrogen ratio (AES) - X_a X values obtained in the scanning beam (area) mode - X_dec X values obtained in the fixed beam (point) mode after about 30 min measuring time (i.e., in some cases, severe decomposition) - X_p X values obtained in the fixed beam (point) mode within about 2 min measuring time (before severe decomposition) - X_U Background value for X in the AES depth profiles - xxps Atomic oxygen-to-nitrogen ratio as obtained from XPS data - Z Sputter depth - Z _E End value for the integration below the depth profile curves - _O Oxygen mass per unit area - _O Oxygen mass per unit volume (recalculated bulk concentration) - _U Oxygen mass per unit volume as recalculated from X_U.     

Factor analysis of AES depth profiles on Si3N4 ceramic powders

Summary Factor analysis of AES depth profiles is performed on combined spectral regions, thus employing a maximum amount of information. Applied to untreated and oxidized, sub-gm ceramic Si₃N₄ powders as well as to Si₂N₂O, this method reveals significant differences with regard to number and stoichiometry of main components. In case of hydrolyzed Si₃N₄, no significant difference compared with the untreated powder was observed, probably because of irradiation effects.

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Faktorenanalyse von AES-Tiefenprofilen an keramischen Si₃N₄-Pulvern

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Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

Stress analysis in tungsten and Si3N4 coated silicon wafers

A paper by G. Gerald Stoney [Gerald Stoney, The Tension of Metallic Films Deposited by Electrolysis, Proc. R. Soc. Lond. A 82 (1909) 172–175], entitled “The Tension of Metallic Films deposited by Electrolysis,” was presented to the Royal Society of London by the Hon. C. A. Parsons. It was well known at that time that films deposited electrolytically were liable to peel off when exceeding a certain thickness. After examining many thin Steel rules of thickness d which have a thin, t, deposit of Nickel, which curved the Rule to a radius r. Taking the moments about the point b for the steel, Stoney then arrived at the following equation where the integral must be equal to zero;

(1)

From the solution of Eq. (1), we obtain the important fact that the neutral plane is at 2/3 the thickness of the rule from film surface. This also implies that the absolute value of the stress on the film side is twice that on the opposite side of the steel rule. The important point is that if the absolute stress in the silicon on the film side is twice that on the opposite side then the position of the neutral plane must be at 2/3 d. The purpose of this paper is to show that the neutral plane in silicon wafers, which have a thin film (~ 3 μm) of tungsten or Si₃N₄ is indeed at 2/3 the thickness of the wafer.     

Transient SIMS depth-profiles at the interface Si3N4/GaAs

Summary A transient secondary ion signal enhancement during sputtering through the interface of a two-layer target of Si₃N₄/GaAs could be demonstrated to be an artefact caused by the bombardment with oxygen ions, which were used as a primary beam. A simple model is established which describes ion-induced composition changes during sputtering (sputter-emission and recoil implantation from the surface, cascade mixing, and implantation of projectiles). The application of this model permits the simulation of internal profiles of a trace element, the matrix atoms and of implanted primary ions, and consequently the simulation of the emitted particle flux during sputtering. These calculations indicate an accumulation of implanted primary ions at the GaAs-side of the interface which considerably enhances the yield of positive secondary ions in this zone. The calculated response fits experimental data within a factor of less than 2.

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Quantitative SIMS-Analyse an der Grenzfläche Si₃N₄/GaAs

Zusammenfassung Bei der Analyse von Verunreinigungen (Chrom) in Si₃N₄-Schichten auf GaAs mit der Sekundärionen-Massenspektrometrie (SIMS) tritt am Schichtübergang ein transienter Anstieg der Intensität positiver Sekundärionen von Chrom und Arsen auf. Es wird experimentell gezeigt, daß dieser Anstieg nicht auf das Vorhandensein einer parasitären Zwischenschicht aus Chrom oder eines Oxides, sondern auf den Beschuß mit einem Sauerstoff-Primärstrahl zurückzuführen ist. Es wurde ein einfaches Modell erstellt, das die ioneninduzierten Veränderungen der gesputterten Probe beschreibt (Sputter-Emission und Recoil-Implantation aus der Oberfläche, Vermischung der Matrixatome durch Kaskadenmischung, Implantation der Primärionen). Die numerische Simulation der SIMS-Messung durch Anwendung dieses Modelles auf die untersuchten Proben zeigt eine Anhäufung implantierter Primärionen knapp hinter dem Schichtübergang. Im Fall von Sauerstoff erhöht dieser lokal die Ausbeute an positiven Sekundärionen. Der erechnete Verlauf dieser Signalüberhöhung stimmt innerhalb eines Faktors < 2 mit den Experimenten überein.

     

Random-Walk Aggregation Phenomena in Solid Bimodal Liquid Dispersions: Transition to Nondeterminism from Si3N4to Si3N4+ Al2O3Aqueous Systems

This paper, which is based on another recent work, (Mezzasalma, S. A.,Phys. Rev. E55(4), (1997)) deals with experiments and theory concerning an aqueous dispersed system formed from silicon nitride (Si₃N₄), alumina (Al₂O₃), and mixed silicon nitride + alumina (Si₃N₄+ Al₂O₃) solid agglomerates. From titration data applied to a thermodynamic equilibrium condition, the minimum number of each agglomerate species and their maximal average dimensions have been derived as functions of the aqueous solution pH. These parameters are of the order of, respectively, (1–2) μm for Si₃N₄and Al₂O₃agglomerates and (20–50) μm for the mixed agglomerates. The numbers of solid particles of all species are poorly correlated with changes in pH of the liquid phase. This behavior has been interpreted as intrinsically related to the complexity of the system which, due to the many interactions among the different species, probably becomes nondeterministic. In order to describe such behavior a probabilistic approach has been developed. The probability of finding a given solid agglomerate number within a scatter band varies with the suspension pH. Furthermore, the scatter band amplitude becomes negligible near the isoelectric point. Accordingly, only the numbers of aggregates derived in the neighborhood of the isoelectric point are predictable.     

Vibrational Spectra of the Cyclic SN-Compounds S4N4, S4N4H4 and S3N3Cl3

The IR and Raman spectra of solid and dissolved S₄N₄, S₄N₄H₄, S₄N₄D₄ and S₃N₃Cl₃ have been recorded and are assigned according to D_2d, C_4v and C_3v symmetry respectively. In the solid state, many forbidden bands and splittings of degenerate vibrations are observed because of the symmetry lowering in the crystals. Due to the different size and shape of the rings and to strong coupling of the normal modes there is no clear correlation between the SN ring stretching vibrations and the strength of the SN bonds, except for the one of the E modes. However, the stretching force constant show the trend expected from changes in interatomic distances.     

用透射电子显微技术研究Si3N4/纳米SiC复相陶瓷的微观结构与力学性能

利用透射电子显微镜,观察了Si3N4/纳米SiC复相陶瓷材料的显微结构特点、分析比较了纳米复相陶瓷与单相Si3N4陶瓷的显微结构差异、讨论了复相陶瓷材料的力学性能与其微观结构的关系,并提出在材料中引入纳米SiC粒子后,可以起到抑制Si3N4晶体长大,使材料的力学性能得到显著提高.     

One-step growth of Si3N4 stem-branch featured nanostructures: Morphology control by VS and VLS mode

We report here one-step synthesis of Si₃N₄ nanodendrites by selectively applying a vapor-solid (VS) and vapor-liquid-solid (VLS) strategy via direct current arc discharge method. The resultant nanodendrites were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy and X-ray powder diffraction. The spine-shaped nanodendrites were generated by a noncatalytic growth following a VS mode. The uniform secondary nanowire branches were epitaxial grown from two side surfaces of the nanowire stems. The pine-shaped nanodendrites were obtained through a catalytic growth in a VLS process. These branch nanowires were unsystematically grown from the nanocone-like stems. The photoluminescence spectra of the nanodendrites show a strong white light emission around 400-750 nm, suggesting their potential applications in light and electron emission devices.     

Preparation and characterization of a supported Si3N4 membrane via a non-aqueous sol–gel process

We report a novel fabrication process of a mesoporous Si₃N₄ membrane on an Al₂O₃ support via a non-aqueous sol–gel technique. The membrane was prepared by dipping an -Al₂O₃ support disk into a silicon diimide sol that was synthesized by catalytic ammonolysis of tris(dimethylamino)silylamine, H₂NSi(NMe₂)₃. The SEM image and nitrogen adsorption analysis indicate that amorphous Si₃N₄ layers with nano-sized pores have formed on the surface and also inside the pores of the Al₂O₃ support disk. The new membrane demonstrates high selective absorption of NO₂, suggesting a potential application as a selective filter for gas sensors.     

Synthesis, stoichiometry and thermal stability of Zn3N2 powders prepared by ammonolysis reactions

Zn₃N₂ powders were prepared by ammonolysis reactions at 600 °C and examined by thermogravimetric analysis, powder X-ray and neutron diffraction. The powders obtained in this way are unstable in an oxygen atmosphere above 450 °C. In an argon atmosphere, the powders are stable up to their decomposition point at around 700 °C. Structural models obtained from Rietveld refinements against the powder neutron diffraction data indicate that the Zn₃N₂ powders so-prepared have the anti-bixbyite structure and are almost certainly stoichiometric with no compelling evidence of nitrogen vacancies. Further, no evidence was found for aliovalent oxygen substitution at the nitrogen sites. The calculated bond valence sums imply that Zn₃N₂ cannot be described as a 100% ionic compound. The structural findings are supported by photoluminescence measurements that reveal a band gap of approximately 0.9 eV.     

Gas phase electron diffraction study of SiH3N3 and (SiH3)2 NCN

The molecular structures of SiH₃N₃ and (SiH₃)₂ NCN have been determined by electron diffraction : SiH₃N₃ has a non-linear SiN₃ skeleton, and (SiH₃)₂ NCN is a carbodiimide with SiNCN Si probably linear. A new model is proposed which rationalises the observed geometry of a number of molecular pseudohalides.     

π-facial interactions between Cl and [S4N3]. X-ray crystal structure of [S4N3]Cl

The X-ray structure of [S₄N₃]Cl reveals three independent molecules, which all display π-facial interactions between the Cl⁻ and the pseudo-aromatic [S₄N₃]⁺ rings to produce a structure containing “inverse sandwich” systems.     

g-C3N4纳米管的制备及其光催化降解性能

以三聚氰胺和碳酸氢铵混合物为原料,采用简便热解法制备g-C_3N_4纳米管。热解过程中碳酸氢铵分解释放出大量的NH3,能够诱导纳米管的形成。利用X射线衍射(XRD)、扫描电子显微镜(SEM)、红外光谱(IR)、N_2吸附-脱附、紫外-可见漫反射光谱以及紫外可见光谱(UV)等分析测试方法对该光催化剂的微观形貌结构和催化性能进行了表征。以罗丹明光催化降解为模型反应研究了g-C_3N_4纳米管的光催化活性。g-C_3N_4纳米管的表面积明显增大,且能够有效地促进光生电子转移,在可见光下具有较强的光催化性能,降解率在60和120 min时分别能达到95%和99.4%,且循环重复利用5次后降解率不低于92%。     

Au@g-C3N4支架的制备及其光催化性能

以三聚氰胺、甲醛、尿素等原料合成具有可塑性的三聚氰胺树脂,通过发泡法构建前驱体支架,并通过磁控溅射法在支架表面沉积金,550℃下热聚合后,成功制备得到负载Au的石墨相氮化碳(Au@g-C₃N₄)支架,其比表面积可达1 480 m²·g^-1。负载6%Au后,Au@g-C₃N₄支架的紫外吸收光谱在550 nm处出现了新的吸收峰,吸收带边红移至507 nm,禁带宽度缩小至2.45e V,Au@g-C₃N₄支架荧光强度和阻抗显著降低,光电流从0.28μA·cm^-2提升至0.62μA·cm^-2。负载Au既拓宽了Au@g-C₃N₄支架可见光吸收性能,又抑制了电子-空穴对的复合,光催化性能稳定,光催化降解罗丹明B的降解率提高近1倍。此外,Au@g-C₃N₄支架强度适中,具有一定韧性,在光催化领域应...     

第四组元对Y2O3—Al2O3—SiO2钎料连接氮化硅陶瓷的影响

在Y2O3－Al2O3-SiO2（YAS）钎料中添加TiO2（YT）和Si3N4(YN),并进行氮化硅陶瓷的连接,用四点弯曲方法测定不同连接工艺下的连接强度,并对连接界面进行SEM,EPMA和XRD分析,接头强度随着保温时间、连接温度的增加,而逐渐增加,在达到峰值后,连接强度逐渐降低。在YSA中添加TiO2,可以形成Si3N4/Y-Sialon玻璃＋TiN/Tin/Y-Sialo玻璃的榜样经度层界面;而在YAS钎料中添加Si3N4,可以降低接头界面的热应力,改善接头强度,微观分析表明：接头强度的变化主要与界而面反应有关。     

Dissociative excitation of SiH4, SiD4, Si2H6 and GeH4 by 0–100 eV electron impact

We have measured emission cross sections of various electronically excited fragments produced by electron-impact dissociation of SiH₄, SiD₄, Si₂H₆ and GeH₄. At low impact energy (10–20 eV), the measured appearance potentials are correlated to specific dissociation processes. Below 22 eV superexcited states of SiH₄ play a dominant role in the formation of neutral excited fragments. In agreement with the results obtained on alkanes, the cross sections for fragment emission from Si₂H₆ are lower than those for SiH₄. On the other hand, the comparison of cross sections at 100 eV for fragment emission, dissociation and ionization on going from CH₄ to SiH₄ and GeH₄ shows an increase of the probability for production of neutral ground-state fragments at the cost of excited or ionic fragments. Both effects can be explained by a growing probability for internal conversion among the decay channels of superexcited states with increasing number of atoms or electrons in the parent molecule. For each molecule, the H Balmer-emission cross sections at 100 eV are proportional to n^−b, where n 3 is the principal quantum number of the upper state of H and 3 < b < 5 is a parameter characteristic of the parent molecule. Finally, a detailed analysis of the isotopic effect between SiH₄ and SiD₄ on both fragment emission and ionization cross sections from 0 to 100 eV gives strong evidence of the competition between dissociation and autoionization in the decay of superexcited states.     

g-C3N4纳米管的制备及其光催化降解性能

以三聚氰胺和碳酸氢铵混合物为原料,采用简便热解法制备g-C₃N₄纳米管。热解过程中碳酸氢铵分解释放出大量的NH₃,能够诱导纳米管的形成。利用X射线衍射（XRD）、扫描电子显微镜（SEM）、红外光谱（IR）、N₂吸附-脱附、紫外-可见漫反射光谱以及紫外可见光谱（UV）等分析测试方法对该光催化剂的微观形貌结构和催化性能进行了表征。以罗丹明光催化降解为模型反应研究了g-C₃N₄纳米管的光催化活性。g-C₃N₄纳米管的表面积明显增大,且能够有效地促进光生电子转移,在可见光下具有较强的光催化性能,降解率在60和120 min时分别能达到95%和99.4%,且循环重复利用5次后降解率不低于92%。     

石墨相氮化碳/二氧化锡复合材料的制备及光催化性能

采用热聚合法和水热法相结合的方法制备了g-C_3N_4/SnO_2复合光催化剂。利用XRD、SEM、TEM、FT-IR和UV-Vis DRS等多种测试手段对所得样品的物相结构、微观形貌和吸光特性等进行了表征。结果表明,异质结构复合光催化剂的最大光吸收边位置相对纯相SnO_2发生了明显的红移,并且SnO_2颗粒均匀分布于g-C_3N_4表面,其中最优组分(50%-g-C_3N_4/SnO_2)光催化降解染料罗丹明B(RhB)的效率达到了纯相g-C_3N_4的3.78倍。