ATR-FTIR Study of Si(110) Surface Hydrogenated in NH4F-Based Mixtures

RCA (Radio Corporation of America) cleaning has been the important and critical step in semiconductor manufacturing for more than 30 years^[1]. As the electronics devices are shrinking and gate oxide is getting thinner, stringent requirements on metallic impurities,organic contamination and surface roughness on silicon wafer after wet chemical cleaning have attracted more attention in the mechanism of wet etching processes on Si(111) and Si(100) surfaces^[2=11]. In the past few years wet chemical and electrochemical etching of Si(110) in NH₄F solutions has been studied by using scanning tunneling microscopy (STM)^[12] and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR)^[13-14]. In the present work, we extend our study to Si(110) surface in NH₄F/HCl mixtures by using polarized attenuated total reflection FTIR (ATR-FTIR). We have compared the ex-situ ATR-FTIR results on Si(110) in various NH₄F/HCl solutions using Ge prism. Effects of potential on hydrogen-terminated structures on Si(110) surfaces have been investigated by employing in-situ electrochemical ATR-FTIR with double side polished single crystal silicon as a prism. Our ATR-FTIR spectra are correlated with the results obtained with in-situ STM.     

Self-assembled Alkylation of Atomically Flat Hydrogen-terminated Silicon (111) Surface By Using Highly Polarized Fluoroalkylsilane

Hydrogen-terminated silicon surface is of technological importance to semiconductor processes such as pre-gate^[1]. Re-contamination and re-oxidation on silicon surface become more stringent issues in order to meet the requirements in the process for producing reduced size IC chips. The modification of silicon surfaces by various strategies has attracted more attention in the past few years^[2-4]. The frequently used techniques to attach functional groups to silicon surfaces are via chemical^[2], photochemical^[3] and electrochemical reactions^[4]. Various ways to attach monlayers to silicon surfaces has been reported, including alkylation of silicon with alkenes, alkyenes, aldehydes, alcohols and Grigard reagents under photoactivated or catalytic reactions. Particularly, porous silicon prepared by chemical or electrochemical treatments has been extensively studied. Preparation of passivated layers on porous silicon surfaces has disadvantages that the silicon surfaces are damaged by reactive agents during the reaction or become porous for attachment of molecules. Recently, self-assembled monolayer of alcohols on porous silicon was reported at modest heating without the aid of catalyst or photoexcitation or potential^[5]. In the paper, we report a novel method to attach highly polarized fluoroalkylsilane on atomically flat Si(111) surface at room temperature and to form a self-assembled monolayer to prevent the silicon surface from re-contamination and re-oxidation.     

The influence of defects on the morphology of Si (111) etched in NH4F

We have implemented a kinetic Monte Carlo (KMC) simulation to study the effects of wafer miscut and wafer defects on the morphologies of Si (111) surfaces etched in NH4F. Although a conventional KMC simulation reproduced previously published results, it failed to produce the morphologies observed in our experiments. By introducing both dopant sites and lattice defect sites into the model, we are able to simulate samples having different dopant elements and densities as well as different defect concentrations. Using the modified KMC simulation, the simulated surface morphologies agree well with the morphologies observed in our experiments. The enhanced model also gives insights to the formation mechanism for multiple level stacking pits, a notable morphology on the etched surfaces of samples with very small miscut angles.     

Ion-Stimulated Chemisorption of Nitrogen on the Si(111) Surface

Russian Journal of Physical Chemistry A - Nitriding of a silicon surface with a beam of low-energy (100–700 eV) nitrogen ions from a source with electronic excitation was studied. The density...     

Synthese und Kristallstrukturen von NH4[Si(NH3)F5] und [Si(NH3)2F4]

Synthesis and Crystal Structures of NH₄[Si(NH₃)F₅] and [Si(NH₃)₂F₄] Single crystals of NH₄[Si(NH₃)F₅] and [Si(NH₃)₂F₄] are obtained by reaction of silicon powder with NH₄HF₂ in sealed Monel ampoules at 400°C. NH₄[Si(NH₃)F₅] crystallizes with the tetragonal space group P4/n (no. 85) with a = 614.91(7) pm, c = 721.01(8) pm, Z = 2. Characteristic for the structure is the anionic octahedron [Si(NH₃)F₅]^?. Si(NH₃)₂F₄ crystallizes with the monoclinic space group P2₁/c (no. 14) with a = 506.9(1) pm, b = 728.0(1) pm, c = 675.9(1), β = 93,21(2)°, Z = 2. Trans-[Si(NH₃)₂F₄] molecules are characteristic for this structure.     

Interaction of Hg Atom with Bare Si（111） Surface

1INTRODUCTION In the past decades,mercury has been a very use-ful electrode material in the fabrication and electrical measurement of molecule modified metal-metal and metal-semiconductor junctions.Majda et al.[1,2]constructed a symmetric Hg-SCn-CnS-Hg junction to study the electron tunneling properties of alkanethio-late bilayers.Whitesides et al.[3～5]fabricated Hg-SAM/SAM-Metal(Ag,Au,Cu)junctions to investi-gate the electrical breakdown voltage of self-assem-bled monolayers(SAMs…     

Theoretical Investigation on the Adsorption of Ag^＋ and Hydrated Ag^＋ Cations on Clean Si（111） Surface

In this paper, the adsorption of Ag^＋ and hydrated Ag^＋ cations on clean Si（111） surface were investigated by using cluster （Gaussian 03） and periodic （DMol^3） ab initio calculations. Si（111） surface was described with cluster models （Si14H17 and Si22H21） and a four-silicon layer slab with periodic boundary conditions. The effect of basis set superposition error （BSSE） was taken into account by applying the counterpoise correction. The calculated results indicated that the binding energies between hydrated Ag^＋ cations and clean Si（111） surface are large, suggesting a strong interaction between hydrated Ag^＋ cations and the semiconductor surface. With the increase of number, water molecules form hydrogen bond network with one another and only one water molecule binds directly to the Ag^＋ cation. The Ag^＋ cation in aqueous solution will safely attach to the clean Si（111） surface.     

醇类在Si-H表面形成单分子膜的特性

以界面电容分析法为主并结合XPS、AFM技术研究了醇类分子在Si(111)-H表面上形成的有机单分子膜的特性。并探讨了嫁接反应中影响单分子膜特性的某些因素和单分子膜的稳定性及其对硅表面氧化的钝化作用。在所选择的反应条件下，不同链长醇分子修饰的硅表面上，嫁接分子所占体积分数约为80％，平带电位约为-1．00V(vs.SSE)。研究表明，这类膜稳定性和对硅表面氧化的钝化作用非常有限。     

硅表面纳米银团簇的氧助迁移行为

 采用原位扫描隧道显微镜研究了Si（111）－7×7表面蒸镀纳米银团簇的迁移行为以及氧气氛的促进作用．在覆盖度较低的情况下，蒸镀的银原子在Si（111）－7×7表面形成具有规整三角形结构单元的有序银团簇，它们主要占据在Si（111）－7×7表面有位错的半单胞内．在氧的存在下，形成的结构单元在硅表面发生迁移，并逐渐团聚成无明显结构特征的大粒子．原位观察结果表明，在连续扫描过程中，团聚后的大粒子在氧覆盖的硅表面也会发生迁移，最后稳定在硅表面原子氧吸附位周围．进一步的观察发现，硅表面银团簇的存在对随后氧的吸附状态具有明显的影响．这些结果为解释纳米银团簇在SiO2表面具有独特的催化性能提供了依据．     

First characterization of the ammine-ammonium complex [(NH4(NH3)4)2(mu-NH3)2]2+ in the crystal structure of [NH4(NH3)4][B(C6H5)4].NH3 and the [NH4(NH3)4]+ complex in [NH4(NH3)4][Ca(NH3)7]As3S6.2NH3 and [NH4(NH3)4][Ba(NH3)8]As3S6.NH3

The compound [NH4(NH3)4][B(C6H5)4].NH3 (1) was prepared by the reaction of NaB(C(6)H(5))(4) with a proton-charged ion-exchange resin in liquid ammonia. [NH(4)(NH(3))(4)][Ca(NH(3))(7)]As(3)S(6).2NH(3) (2) and [NH4(NH3)4][Ba(NH3)8]As3S6.NH3 (3) were synthesized by reduction of As(4)S(4) with Ca and Ba in liquid ammonia. All ammoniates were characterized by low-temperature single-crystal X-ray structure analysis. They were found to contain the ammine-ammonium complex with the maximal possible number of coordinating ammonia molecules, the [NH4(NH3)4]+ ion. 1 contains a special dimer, the [(NH4(NH3)4)2(mu-NH3)2]2+ ion, which is formed by two[NH4(NH3)4]+ ions linked by two ammonia molecules. The H(3)N-H...N hydrogen bonds in all three compounds range from 1.82 to 2.20 A (DHA = Donor-H...Acceptor angles: 156-178 degrees). In 2 and 3, additional H(2)N-H...S bonds to the thioanions are observed, ranging between 2.49 and 3.00 A (DHA angles: 120-175 degrees). Two parallel phenyl rings of the [B(C(6)H(5))(4)](-) anion in 1 form a pi...pi hydrogen bond (C...C distance, 3.38 A; DHA angles, 82 degrees), leading to a dimeric [B(C6H5)4]2(2-) ion.     

Facet-dependent lithium intercalation into Si crystals: Si(100) vs. Si(111)

Fast Li transport in battery electrodes is essential to meeting the demanding requirements for a high-rate capability anode. We studied the intercalation of a Li atom into the surface and subsurface layers of Si(100) and Si(111) using density functional calculations with a slab representation of the surfaces. We suggest that the Li atom migrates on the Si surfaces and is subsequently inserted into the inside for both Si(100) and Si(111). The rate-determining steps are the surface incorporation and subsurface diffusion in Si(100) and Si(111), respectively. Our diffusion rate calculations reveal that, once the Li atom is incorporated into the Si surface, Li diffuses faster by at least two orders of magnitude along the <100> direction than along the <111> direction. The importance of careful treatment of the slab thickness for the study of impurity insertion into subsurface layers is also stressed.     

Thermal decomposition of (NH4)2MoS4 and (NH4)2WS4heat of formation of (NH4)2MoS4

The reactions (NH₄)₂MeS₄ = 2 NH₃ + H₂S + MeS₃ (Me = Mo, W) were investigated by measuring the decomposition vapour pressures. Thermochemical data were obtained from these measurements: ΔH = 52 kcal/mole and ΔS = 105 cal/deg.mole for the decomposition of the tetrathiomolybdate. Similarly, ΔH = 69 kcal/mole and ΔS = 106 cal/deg.mole were obtained for the decomposition of the tetrathiotungstate. The normal heat of formation of (NH₄)₂MoS₄ was found to be ΔH = ?140 kcal/mole. The kinetics of thermal decomposition of the above reactions were also measured.     

苯在Si(111)-7×7表面化学吸附的理论研究

采用两种大小不同的原子簇模型Si_(30)H_(28)和Si_(13)H_(16)，分别用两层 ONIOM方法（对较大原子簇）和普通量子化学方法（对较小原子族）考察了苯分子 在Si(111)-7 * 7表面的化学吸附。对三种可能的吸附物种分别用DFT或HF方法进行 了计算。通过大小原子簇吸附物种的吸附能以及几何构型优化参数的比较发现，对 于稳定的吸附物种，较小的原子簇基本上可以代替较大的原子簇进行计算，而对于 不太稳定的吸附物种，就不得不考虑周边原子的影响。计算结果表明苯在Si(111)- 7 * 7表面的主要吸附种是双σ成键的1，4加成产物，不稳定的单吸附物种可能是 1，4加成物种的前驱态。     

苯在Si(111)-7*7表面化学吸附的理论研究

采用两种大小不同的原子簇模型Si_(30)H_(28)和Si_(13)H_(16),分别用两层 ONIOM方法（对较大原子簇）和普通量子化学方法（对较小原子族）考察了苯分子 在Si(111)-7 * 7表面的化学吸附。对三种可能的吸附物种分别用DFT或HF方法进行 了计算。通过大小原子簇吸附物种的吸附能以及几何构型优化参数的比较发现,对 于稳定的吸附物种,较小的原子簇基本上可以代替较大的原子簇进行计算,而对于 不太稳定的吸附物种,就不得不考虑周边原子的影响。计算结果表明苯在Si(111)- 7 * 7表面的主要吸附种是双σ成键的1,4加成产物,不稳定的单吸附物种可能是 1,4加成物种的前驱态。     

Surface investigation of intermetallic PdGa(111)

The intermetallic PdGa is a highly selective and potent catalyst in the semihydrogenation of acetylene, which is attributed to the surface stability and isolated Pd atom ensembles. In this context PdGa single crystals of form B with (111) orientation were investigated by means of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STM), X-ray photoelectron diffraction (XPD), and low-energy electron diffraction (LEED) to study the electronic and geometric properties of this surface. UPS and thermal desorption spectroscopy (TDS) were used to probe the chemisorption behavior of CO. The PdGa(111) surface exhibits a (1 × 1) LEED and a pronounced XPD pattern indicating an unreconstructed bulk-truncated surface. Low-temperature STM reveals a smooth surface with a (1 × 1) unit cell. No segregation occurs, and no impurities are detected by XPS. The electronic structure and the CO adsorption properties reveal PdGa(111) to be a bulk-truncated intermetallic compound with Pd-Ga partial covalent bonding.     

Molecular beam investigation of hydrogen dissociation on Si(001) and Si(111) surfaces

The influence of molecular vibrations on the reaction dynamics of H2 on Si(001) as well as isotopic effects have been investigated by means of optical second-harmonic generation and molecular beam techniques. Enhanced dissociation of vibrationally excited H2 on Si(001)2 x 1 has been found corresponding to a reduction of the mean adsorption barrier to 390 meV and 180 meV for nu=1 and nu=2, respectively. The adsorption dynamics of the isotopes H2 and D2 show only small differences in the accessible range of beam energies between 50 meV and 350 meV. They are traced back to different degrees of vibrational excitation and do not point to an important influence of quantum tunneling in crossing the adsorption barrier. The sticking probability of H2 on the 7 x 7-reconstructed Si(111) surface was found to be activated both by H2 kinetic energy and surface temperature in a qualitatively similar fashion as H2/Si(001)2 x 1. Quantitatively, the overall sticking probabilities of H2 on the Si(111) surface are about one order of magnitude lower than on Si(001), the influence of surface temperature is generally stronger.     

Low-temperature STM images of methyl-terminated Si(111) surfaces

Low-temperature scanning tunneling microscopy (STM) has been used to image CH(3)-terminated Si(111) surfaces that were prepared through a chlorination/alkylation procedure. The STM data revealed a well-ordered structure commensurate with the atop sites of an unreconstructed 1 x 1 overlayer on the silicon (111) surface. Images collected at 4.7 K revealed bright spots, separated by 0.18 +/- 0.01 nm, which are assigned to adjacent H atoms on the same methyl group. The C-H bonds in each methyl group were observed to be rotated by 7 +/- 3 degrees away from the center of an adjacent methyl group and toward an underlying Si atom. Hence, the predominant interaction that determines the surface structure arises from repulsions between hydrogen atoms on neighboring methyl groups, and secondary interactions unique to the surface are also evident.     

Direct photochemical functionalization of Si(111) with undecenol

Direct UV photochemical functionalization of H-terminated Si(111) with bifunctional 10-undecen-1-ol was achieved with selective attachment via its vinyl end, resulting in the formation of a compact monolayer with free terminal alcohol groups. This is due to the faster radical propagation mechanism in hydrosilylation with alkene compared to the nucleophilic attack mechanism of alcohol, which is impeded by intermolecular hydrogen bonding present at room temperature. Evidence from X-ray photoelectron spectroscopy, infrared spectroscopy, and resistance to fluoride etching shows that Si-C is the interfacial bond, and atomic force microscopy shows the presence of a smooth, uniform monolayer conforming to the atomic terraces of the Si(111) surface. The application of such a hydroxyl-terminated monolayer was demonstrated by tethering a bromoinitiator through surface esterification and thereafter subjecting the surface to the surface-initiated atom-transfer radical polymerization of butyl methacrylate. The poly(butyl methacrylate) brushes formed were found to be smooth (R(a) < 0.3 nm) and uniform even for a thin film of 4.0 nm.