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

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.

The monography "Low-Energy Electron Diffraction" (LEED), written by three wellknown specialists in this field and published within the Springer series in Surface Sciences, is a unique representation of this powerful method. According t o the given subtitle "EXperiment, Theory and Surface Structure Determination" the whole discipline of lowenergy electron diffraction is covered.The authors state that similar t o solid state physics, where the detection of the correlatiou between the microstructure and the properties of bulk materials is of the utmost importance, in surface science there is an exigence of elucidating the connection between surface structure and surface properties. With respect t o crystalline surfaces LEED is the key method to allow a reliable characterization of the relative position of atoms, thus being the basis for attaining exprimental results in surface crystallography.Starting with the description of the historical development of LEED the authors describe practical aspects for carrying out LEED experiments (instrumentation, data acquisition) and for gaining structure information by carefully interpreting diffraction patterns.It follows a very clear treatment of the kinematical theory of LEED and of the dynamical LEED theory.The field of application of the method is dealt with in detail. The authors point t o the results of structural analyses with respect to clean unreconstructed and reconstructed surfaces, resp., and to adsorbed atomic and molecular layers, resp. Special emphasis is placed on the detection and explanation of two-dimensional orderdisorder phase transitions, e.g. given by the interaction of hydrogen with well-defined metal surfaces (Ni, Pd, Fe). As further fields of the application of LEED, chemical reactions at surfaces are mentioned as well as the island formation of a species. Finally, the authors point to the future trend with respect to the LEED experimentation and theory and to the progress in structure determination.Besides the complete description of the possibilities and limitations of the LEED technique the book shows the importance of this method within other surface-sensitive techniques (for comparison, a valuable table is added). With respect t o the results of LEED investigations, a detailed reference list is given as well as a table of surface structures.The clearly written and well-illustrated book should be of great interest for researchers working in surface science and surface techniques, e.g. in the field of catalysis, corrosion, coatings, adhesion, lubrication, and last not least in microelectronics. On the one hand, for a scientist working in the general field of surface problems the book is an excellent introduction showing the power of the LEED technique; on the other hand, for the specialist being already familiar with low-energy electron diffraction, in a concise manner the book offers and updated representation of the field and of experimental and theoretical details, supplemented by a valuable list of about 700 references.There is no doubt that VAN...

97where the matrix elements Mij are very complicated functions of & y, v , sin 28, and cos 28. The light intensity at the detector is Y2e-"'c[(P,Z + P,2)[Moo + MO2 sin (6 + a) -Mo3 cos (6 + a ) ] + (Px2 -P,2)[sin 2a[Mlo + M I 2 sin (6 + a) -M I 3 cos (6 + a)] + cos 2a[M,O + M32 sin (6 + a) -M33 cos (6 + a)]]] (68) = The W, and dc components of the electric signal are v a c (0' 9 W m ) = (4K/*)[[(Px2 + P,2)M02 + (P,2 -P,Z)[M12 sin 2a + M32 cos 2a]. [J16,' sin Wmt cos a + J26,'R(2W,) sin a] -[(P2 + Py2)Mo3 + (P,Z -P,Z)(Ml3 sin 2a + M33 cos 2a)] [J2Smo R(2Wm) cos a -J l b m o sin Wmt sin a]] (69) v d c ( 0 ) = (Px2 + P;)[Mo0 + M02J06m0 sin a -MozJo6,0 cos a] + (Px2 -P y 2 ) [ [ M l o + MI2J06,' sin a -M13Jo6,' cos a] X sin 2a + [M30 + M32JO6,' sin a -M33J06m0 cos a] cos 2a]The output to the recorder, CD, = Vac (W,)/vdc, is not equal to zero. Thus, there is the apparent CD spectra having no relation to the CD in any aspects. The rotation of the helical pile around the light beam induces no "CD" sign change in the apparent CD spectra because of its helical structure. Thus, we can never conclude from the apparent CD spectra that the optically inactive molecules become chiral when dissolved in cholesteric liquid crystals. ConclusionThe above considered cases show clearly that there may be several obscure points in LCICD data reported so far in the literature. We cannot deny completely the possibility that achiral molecules becomes optically active in cholesteric liquid crystals. But the apparent CD spectra observed in cholesteric liquid crystals with commercially available CD spectrophotometers can generally not provide us with the proof that the optical activity is induced in achiral molecules. Other methods besides CD spectroscopy are therefore necessary to confirm experimentally the presence of the induced optical activity in optically inactive molecules.Finally, let us give a bit of advice to persons who intend to study induced CD in possibly anisotropic systems. Read the book on polarized light,8 a paper on the Mueller matrix approach to the polarization-modulation spectro~copy$~'~ and a number of papers on problems of CD s p e c t r o p~l a r i m e t e r s~~~~~~~~~~~~ before starting work. We believe it is essential to fully understand the real meanings of the signal which will be observed.We are going to comment on fluorescence detected circular dichroism in the next paper.Acknowledgment. This work was supported, in part, by research grants (56540254) to Fukui University from the Ministry of Education and Culture. We are grateful to K. Mizuno for her helpful advice and assistance.(17) Schonhofer, A.; Kuball, H. G.; Puebla, C.Abstract The adsorption of gaseous dimethyl methylphosphonate (DMMP) on aluminum oxide film surfaces has been investigated with inelastic electron tunneling spectroscopy. Surface temperatures ranged between 200 and 673 K, and exposures ranged between 3 X lo4 and 10 torres. Tunneling spectra of deuterium-labeled DMMP, methyl alcohol-d,, methyl methylphosphonate, methylphosphonic acid, and trim...