The etching of sapphire substrates using H 2 SO 4 , H 3 PO 4 , and a 3:1 H 2 SO 4 :H 3 PO 4 mixture, as a function of temperature and etching time, was systematically studied using atomic force microscopy. The sapphire preparation by liquid-based etchings was compared with H 2 etching at 1100°C and air-annealing at 1400°C. In liquid-based treatments, the smoothest, pit-free surface was obtained by etching in pure H 2 SO 4 at 300°C for 30 min. Sulfuric acid etching at higher temperatures or for longer periods generated an insoluble mixture of Al 2 (SO 4 ) 3 and Al 2 (SO 4 ) 3 •17H 2 O crystalline deposits on the surface. Phosphoric acid and the 3:1 H 2 SO 4 :H 3 PO 4 mixture, which is the routinely employed chemical treatment for sapphire preparation, etched the sapphire preferentially at defect sites and resulted in pit formation on the surface. Sapphire treatment using H 2 at 1100°C did not remove the surface damage. Air annealing the sapphire at 1400°C for 1 h produced an atomically smooth surface consisting of a terrace-and-step structure. The results of this study were described in terms of the chemistry of the sapphire etching process.

We report a nonaqueous passivation regime consisting of Na 2 S/benzene/15-crown-5/oxidant. The use of a nonpolar, aprotic organic medium required the addition of a specific chelating agent ͑15-crown-5͒ to solubilize sodium sulfide, and organic oxidizing agents ͑anthraquinone, benzophenone, etc.͒ to act as electron acceptors. The surface optical and chemical properties of GaSb surfaces after aqueous and nonaqueous sulfide treatments were compared. Nonaqueous passivation resulted in higher photoluminescence ͑PL͒ intensity, lower oxide content, and a less amount of elemental Sb than aqueous passivation. The PL intensity from passivated surfaces was correlated with the standard reduction potentials of electron acceptors. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1613994͔The surface properties of semiconductors are crucial determinants of device performance. Considerable efforts have been made to modify III-V semiconductor surfaces in order to improve electronic properties and device performance. The passivation of GaAs with aqueous solutions of sodium or ammonium sulfides has been extensively studied both theoretically and experimentally. [1][2][3][4] The reactions between chalcogenides and GaAs surface species change the surface electronic structures and remove the surface states from the band gap, thus unpinning the surface Fermi level and improving electrical and optical properties.GaSb is an important III-V compound semiconductor for high-speed and optoelectronic device applications, the performance of which is strongly dependent on the chemical and electronic properties of GaSb surfaces or interfaces. However, GaSb is highly chemically reactive, being easily oxidized by atmospheric oxygen with the formation of native surface oxides several nanometers thick.5 An additional consequence of surface oxidation is the formation of elemental antimony at the oxide-GaSb interface, which creates a conduction channel parallel to the interface that leads to high surface leakage current, thus limiting applications.6,7 Various surface passivation methods, including wet and dry chemical processes, [8][9][10][11] have been studied in efforts to improve GaSb surface characteristics. Unfortunately, most processing techniques are still water-based and lead to the growth of surface oxides and degrade the structural quality of the surface. Therefore, alternative, nonaqueous, solvents capable of sulfidization are of particular interest for GaSb surface processing.In this work, a specific benzene-based sodium sulfide passivation regime was developed to improve the passivation of GaSb surfaces. Chelating agents were employed to solubilize and activate sulfide anions, and organic oxidizing agents were added to the passivation solution to facilitate electron transfer. The optical and chemical characteristics, before and after chemical treatments, were studied by photoluminescence ͑PL͒ and x-ray photoemission spectroscopy ͑XPS͒. A comparison of the results of GaSb passivation in aqueous and nonaqueous sulfide solutions indicat...

The synthesis, characterization, and thermal decomposition of CpBe(SiMe 3 ) are presented as part of an exploratory investigation designed to obtain more effective chemical vapor deposition precursors of metallic beryllium. The title compound provides the first example of a direct bond between beryllium and a non-carbenoid group 14 element. The base-free reaction of LiSiMe 3 with CpBeCl in pentane affords the air-sensitive, volatile solid CpBe-(SiMe 3 ) (ca. 70% yield based on CpBeCl), which was characterized by single-crystal CCD X-ray diffraction, multinuclear NMR, and mass spectrometric studies, and theoretically by DFT/NBO analysis. The solid-state molecular geometry of CpBe(SiMe 3 ) ideally conforms to C 3v symmetry (under assumed cylindrical symmetry for the C 5 H 5 ring); the Be-Si bond length of 2.185(2) Å is markedly longer than the sum of covalent radii (2.01 Å). The DFT-optimized molecular geometry closely conforms to that determined crystallographically. Total fragment charges (based upon atomic charge NBO calculations) of -0.79 e for C 5 H 5 , +1.26 e for Be, +0.81 e for Si, and -1.28 e for the three Me groups constitute a polarity pattern consistent with the Be-Cp bonding interaction being mainly ionic and with the Be-Si bonding pair being polarized toward the more electronegative SiMe 3 fragment. Beryllium-9 and 29 Si NMR spectra exhibit a large J(Be-Si) coupling constant of 51 Hz; the 9 Be chemical shift of δ -27.70 ppm, the highest field value recorded to date, is in accordance with the calculated bond-polarity pattern, as well as a bond to Si. Mass spectra (EI) exhibited peaks for the molecular ion and its isotopomers. Thermal decomposition of CpBe(SiMe 3 ) gives rise to trimethylsilane, CpBeMe, and CpBe(SiMe 2 SiMe 3 ) as the major products, as determined by multinuclear NMR. The latter species is likewise formed by the reaction of CpBeCl with LiSiMe 2 SiMe 3 .

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Two borane salts ([(Me)4N][B3H8] and Cs[B3H8]) were examined by electrospray mass spectrometry in the positive ion mode. Acetonitrile solutions provided the most informative spectra; the salts exhibited a remarkable degree of clustering under electrospray conditions, and virtually all signals corresponded to cationic cluster ions of the general formula {[cation (m+)] x [anion (n-)] y }((mx - ny)+). In contrast, methanol solutions of these salts produced only B(OCH3) 4 (-) cluster ions under otherwise identical conditions. (11)B NMR analyses corroborate the identities of the methanol solution species that enter the electrospray source and the reaction product generated during the electrospray process.