Despite the fact that H-terminated, HF-etched Si crystals are the starting point for construction of most contemporary electronic devices, 1 little is known about the chemical reactions of H-terminated Si surfaces under ambient temperature and pressure. 2,3 Functionalization of Si without partial oxidation and/or formation of electrical defects is potentially important in fabricating improved electronic devices 4,5 as well as in measurement of charge transfer rate constants at semiconductor/ liquid contacts. 6 One recently described approach involves the reaction of HF-etched Si(111) with olefins and organic diacyl peroxides, in which formation of a self-assembled (near)monolayer of Si-alkyls was hypothesized. 2 We report here an alternative strategy to functionalize HF-etched Si surfaces involving halogenation and subsequent reaction with alkyl Grignard or alkyl lithium reagents. We report vibrational spectroscopic and temperature programmed desorption data which confirm that the alkyl groups are bonded covalently to the Si surface, and we demonstrate that such overlayer formation can impede the undesirable oxidation of Si in a variety of environments while providing surfaces of high electrical quality.The H-terminated Si surface 7 was first exposed to PCl 5 for 20-60 min at 80-100 °C, in chlorobenzene with benzoyl peroxide as the radical initiator. 8,9 Upon chlorination, the XP survey spectra (Figure 1) showed peaks at 270.2 ( 0.4 binding electron volts, BeV, (Cl 2s) and 199.3 ( 0.4 BeV (Cl 2p), indicating that this procedure yielded Cl on the surface. The high-resolution XP spectrum of the Si 2p peak of this surface displayed, in addition to the substrate Si signal, an additional peak located at 0.98 ( 0.12 BeV higher in binding energy (Figure 2) whose position and intensity was consistent with the formation of a surface Si-Cl bond. 10 Auger electron spectra (AES) also confirmed the presence of Cl on the silicon surface. High resolution electron energy loss spectra (HREELS) of this surface exhibited a characteristic peak at 560 cm -1 that was not present on the H-terminated Si surface, confirming the formation of covalent Si-Cl bonds at the surface. 11 Temperature programmed desorption spectra of the chlorinated surface showed dominant signals at 64 (SiCl), 71 (Cl 2 ), and 135 (SiCl 3 ) amu, peaking at 670 and 850 K, which is characteristic of chlorinated silicon surfaces. 10,12 The 560 cm -1 peak in the HREELS and the Cl peak in the AES disappeared following thermal desorption.Exposure of the chlorinated Si surface to alkyl-Li (RLi: R

Oxidative stress (OS) has been considered a major contributory factor to the infertility. Oxidative stress is the result of imbalance between the reactive oxygen species (ROS) and antioxidants in the body which can lead to sperm damage, deformity, and eventually male infertility. Although high concentrations of the ROS cause sperm pathology (ATP depletion) leading to insufficient axonemal phosphorylation, lipid peroxidation, and loss of motility and viability but, many evidences demonstrate that low and controlled concentrations of these ROS play an important role in sperm physiological processes such as capacitation, acrosome reaction, and signaling processes to ensure fertilization. The supplementation of a cryopreservation extender with antioxidant has been shown to provide a cryoprotective effect on mammalian sperm quality. This paper reviews the impacts of oxidative stress and reactive oxygen species on spermatozoa functions, causes of ROS generation, and antioxidative strategies to reduce OS. In addition, we also highlight the emerging concept of utilizing OS as a tool of contraception.

A two-step procedure, involving radical-initiated chlorination of the Si surface with PCl 5 followed by reaction of the chlorinated surface with alkyl-Grignard or alkyl-lithium reagents, has been developed to functionalize crystalline (111)-oriented H-terminated Si surfaces. The surface chemistry that accompanies these reaction steps has been investigated using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), temperature programmed desorption spectroscopy (TPDS), high-resolution electron energy loss spectroscopy (HREELS), infrared (IR) spectroscopy in both glancing transmission (TIR) and attenuated total multiple internal reflection (ATR) modes, ellipsometry, and contact angle goniometry. The XPS data show the appearance of the Cl signal after exposure to PCl 5 and show its removal, and concomitant appearance of a C 1s signal, after the alkylation step. Auger electron spectra, in combination with TPD spectroscopy, demonstrate the presence of Cl after the chlorination process and its subsequent loss after thermal desorption of Si-Cl fragments due to heating the Si surface to 1200 K. High-resolution XP spectra of the Si 2p region show a peak corresponding to Si-Cl bond formation after the chlorination step, and show the subsequent disappearance of this peak after the alkylation step. IR spectra show the loss of the perpendicularly polarized silicon monohydride (Si-H) vibration at 2083 cm -1 after the chlorination step, whereas HREELS data show the appearance of vibrations due to Si-Cl stretches upon chlorination of the Si surface. The HREELS data furthermore show the disappearance of the Si-Cl stretch and the appearance of a Si-C vibration at 650 cm -1 after alkylation of the Si surface. Ellipsometric measurements indicate that the thickness of the alkyl overlayer varies monotonically with the length of the alkyl group used in the reactant. Contact angle and IR measurements indicate that the packing of alkyl groups in the monolayers produced by this method is less dense than that found in alkylthiol monolayers on Au. As determined by XPS, the alkylated surfaces show enhanced resistance to oxidation by various wet chemical treatments, compared to the H-terminated Si surface. The two-step reaction sequence thus provides a simple approach to functionalization of (111)-oriented, H-terminated silicon surfaces using wet chemical methods.

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A two-step chlorination/alkylation method was used to introduce −C n H2 n +1 (n = 1−6) functionality onto single-crystal, (111)-oriented, n-type Si surfaces. H-terminated Si photoanodes were unstable under illumination in contact with an aqueous 0.35 M K4Fe(CN)6−0.05 M K3Fe(CN)6 electrolyte. Such electrodes displayed low open-circuit voltages and exhibited a pronounced time-dependent deterioration in their current density vs potential characteristics due to anodic oxidation. In contrast, Si surfaces functionalized with −CH3 and −C2H5 groups displayed significant improvements in stability while displaying excellent electrochemical properties when used as photoelectrodes in the aqueous Fe(CN)6 3-/4- electrolyte.

The electrochemical properties of alkyl-terminated, (111)-oriented, n-type Si surfaces, prepared via a twostep halogenation/alkylation procedure, were analyzed in contact with CH 3 OH-1,1′-dimethylferrocene +/0 (Me 2 Fc +/0 ) solutions. Current density-potential and differential capacitance-potential measurements of these surfaces in contact with CH 3 OH-Me 2 Fc +/0 indicated that the electrochemical properties of the alkyl-terminated surfaces were very similar to those of the H-terminated Si surface. The alkyl overlayers did not shift the Si band edges or induce significant surface recombination, but they did provide an additional electrical series resistance to charge transfer across the Si/liquid interface. The efficacy of alkyl overlayers in preventing photooxidation and photocorrosion of n-silicon surfaces was measured in contact with CH 3 OH-Me 2 Fc +/0 solutions to which a known amount of water had been added. Under these conditions, the alkyl-terminated surfaces consistently showed excellent current density-potential characteristics and displayed lower oxidation rates than the H-terminated surface, indicating that stability toward oxidation had been achieved without any significant compromise in the electrochemical qualities of the silicon surface.

High levels of selenium can cause adverse effects in plants as well as animals. In a greenhouse experiment, rapeseed (Brassica napus) was grown in an alkaline sandy loam soil treated with different levels of selenate-Se and selenite-Se ranging from 0 to 4 mg kg −1 . Total dry matter yield of selenium-treated rapeseed plants decreased significantly as compared to control plants. Plants were stressed at a very early stage of vegetative growth and produced fewer rosettes and flowers. Plant height and leaf production were negatively affected by selenate-Se. Dry matter of leaves was significantly higher in selenite-than in selenate-treated plants. Selenate-treated plants accumulated 75-160 times more Se in shoots and 2-18 times more in roots as compared to selenite-treated plants at the rosette formation stage, with this difference narrowing at peak flowering stage. Rapeseed leaves were subjected to biochemical analysis at rosette and peak flowering stages. Accumulation of selenium in leaves resulted in a significant increase in lipid peroxidation, chlorophyll, vitamin C and free amino acids, and a decrease in phenols, total soluble sugars and starch concentration.

The surface chemistry of n-type Si electrodes that had been etched, exposed to electrolyte, and electrochemically cycled has been probed using high-resolution X-ray photoelectron spectroscopy (XPS). n-Si surfaces etched in hydrofluoric acid-ethanol solutions (in air or N, ambients) displayed spectra in the Si 2p region that were free of detectable substrate oxide signals (15 X lo-" mol cm-, SO,; equivalent to 14% of a monolayer). Exposure of HF-C2H50H etched or of 49% HF(aq) etched n-Si surfaces to an electrolyte solution containing CH30H, dimethylferrocene (Me2Fc), and dimethylferricenium (Me2Fc+) generated very low levels, 1 ( 2 f 1) X mol cm-2 of silicon suboxides. Only sub-monolayer levels of SiO,, (4 f 2) X mol cm-2, were detected after electrochemical cycling of illuminated n-Si anodes in contact with CH30H-Me2Fc+/0 electrolytes. Even n-Si photoanodes maintained at short circuit with the CH30H-Me2Fc+/0 electrolyte for substantial periods (> 1000 C cm-, anodic charge passed) formed less than a single monolayer of strained Si02 at the silicon surface. Deliberate anodization of the Si surface in these electrolyte solutions yielded controlled amounts of thicker (8-10 A) Si02 overlayers; these overlayers provided a useful oxide for the formation of high-performance metal-insulatorsemiconductor device structures. These studies demonstrate that HF-C2H50H-or HF(aq)-etched n-Si surfaces are remarkably resistant to oxide formation during photoelectrochemical cycling in CH30H-based electrolytes, and that the outstanding photoelectrochemical Z-Vproperties of the n-Si/CH30H-Me2Fc+/0 junction are not a result of formation of passivating oxide overlayers on the Si surface.