Self-consistent mapping of the ab initio calculations to the multi-orbital <Emphasis Type="Italic">p</Emphasis>–<Emphasis Type="Italic">d</Emphasis> model: Magnetism in α-FeSi<Subscript>2</Subscript> films as the effect of the local environment

The near infrared transmission spectra of nanoporous SiO₂/Al₂O₃ xerogel have been recorded for the first time in the process of filling of nanopores with ammonia and acetone molecules. It has been found that the physical adsorption of these gases results in a reversible increase in the translucence of xerogel samples at the frequencies of vibrational bands of surface OH groups.     

Effect of surface morphology on surface‐enhanced Raman scattering of 4‐aminobenzenethiol adsorbed on gold substrates

The substrate‐dependent surface‐enhanced Raman scattering (SERS) of 4‐aminobenzenethiol (4‐ABT) adsorbed on Au surfaces has been investigated. 4‐ABT is one of the very unique adsorbate molecules whose SERS spectral patterns are known to be noticeably dependent on the relative contribution of chemical enhancement mechanism vs electromagnetic enhancement mechanism. The SERS spectral patterns of 4‐ABT adsorbed on gold substrates with various surface morphology have thus been analyzed in terms of the symmetry types of the vibrational modes. Almost invisibly weak b₂ type vibrational bands were observed in the SERS spectra of the 4‐ABT adsorbed on Au colloidal sol nanoparticles or commercially available Au micro‐powders because of the weak contribution of the chemical enhancement. However, greatly enhanced b₂ vibrational bands were observed in the spectra of the 4‐ABT molecules adsorbed on the synthesized Au(Zn) sponge or the electrochemically roughened Au(ORC) foil caused by the strong contribution of the chemical enhancement mechanism. Copyright © 2008 John Wiley & Sons, Ltd.     

Low temperature electron energy loss spectra of acetylene chemisorbed on metal single-crystal surfaces; Cu(111), Ni(110) and Pd(110)

Vibrational spectra of acetylene chemisorbed on Cu(111), Ni(110) and Pd(110) at 110–120 K were measured using electron energy loss spectroscopy. Loss peaks were assigned to vibrational modes of the non-dissociatively adsorbed molecules with the aid of the corresponding C₂D₂ spectra. The spectra show that the molecules undergo significant rehybridisation on adsorption. Comparisons are made with the spectra of acetylene adsorbed on a range of other transition metal surfaces at low temperature. Taking into account these and earlier literature results, two distinct patterns of spectra are observed (Type A and Type B) for specular spectra. The Cu(111) spectrum is classified as Type A while the Ni(110) and Pd(110) spectra are classified as Type B. Suggestions are made for the structures of the surface species corresponding to the two spectral types.     

Adsorption of molecular SiO2 on a clean Si(1 0 0) surface

We have investigated the adsorption of molecular (gaseous) SiO₂ on a clean Si(1 0 0) p(2 × 2) reconstructed surface using density functional theory based methods. The SiO₂ molecule is found to be chemisorbed on various sites on the Si surface and the most energetically favourable structure is on top of the dimers. The minimum energy pathways for the various adsorption channels indicate that the reaction is barrierless in all cases. The corresponding vibrational spectrum is also calculated and the adsorbed molecules are, as expected, found to have red-shifted vibrational frequencies. The energetically favourable adsorption sites and adsorption energies are comparable to the results found for SiO.     

Vibrational spectroscopy characterization of magnetron sputtered silicon oxide and silicon oxynitride films

Vibrational (infrared and Raman) spectroscopy has been used to characterize SiO_xN_y and SiO_x films prepared by magnetron sputtering on steel and silicon substrates. Interference bands in the infrared reflectivity measurements provided the film thickness and the dielectric function of the films. Vibrational modes bands were obtained both from infrared and Raman spectra providing useful information on the bonding structure and the microstructure (formation of nano-voids in some coatings) for these amorphous (or nanocrystalline) coatings. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis have also been carried out to determine the composition and texture of the films, and to correlate these data with the vibrational spectroscopy studies. The angular dependence of the reflectivity spectra provides the dispersion of vibrational and interference polaritons modes, what allows to separate these two types of bands especially in the frequency regions where overlaps/resonances occurred. Finally the attenuated total reflection Fourier transform infrared measurements have been also carried out demonstrating the feasibility and high sensitivity of the technique. Comparison of the spectra of the SiO_xN_y films prepared in various conditions demonstrates how films can be prepared from pure silicon oxide to silicon oxynitride with reduced oxygen content.     

The adsorption and reaction of H2O on clean and oxygen covered Ag(110)

The adsorption and reaction of water on clean and oxygen covered Ag(110) surfaces has been studied with high resolution electron energy loss (EELS), temperature programmed desorption (TPD), and X-ray photoelectron (XPS) spectroscopy. Non-dissociative adsorption of water was observed on both surfaces at 100 K. The vibrational spectra of these adsorbates at 100 K compared favorably to infrared absorption spectra of ice Ih. Both surfaces exhibited a desorption state at 170 K representative of multilayer H₂O desorption. Desorption states due to hydrogen-bonded and non-hydrogen-bonded water molecules at 200 and 240 K, respectively, were observed from the surface predosed with oxygen. EEL spectra of the 240 K state showed features at 550 and 840 cm^?1 which were assigned to restricted rotations of the adsorbed molecule. The reaction of adsorbed H₂O with pre-adsorbed oxygen to produce adsorbed hydroxyl groups was observed by EELS in the temperature range 205 to 255 K. The adsorbed hydroxyl groups recombined at 320 K to yield both a TPD water peak at 320 K and adsorbed atomic oxygen. XPS results indicated that water reacted completely with adsorbed oxygen to form OH with no residual atomic oxygen. Solvation between hydrogen-bonded H₂O molecules and hydroxyl groups is proposed to account for the results of this work and earlier work showing complete isotopic exchange between H₂¹⁶O_(a) and ¹⁸O_(a).     

Mo(CO)6在清洁的和氧化的Si(111)表面上吸附的对比

采用高分辨电子能量损失谱对比研究Mo(CO)₆在清洁的、预吸附氧的和深度氧化的Si(111)表面上的吸附行为. 吸附Mo(CO)₆的C-O伸缩振动模式向低频方向移动,说明Mo(CO)₆与清洁Si(111)和SiO₂/Si(111)表面发生了不同的相互作用,前者较弱而后者较强. 与SiO₂/Si(111)表面的强相互作用可能引起Mo(CO)₆部分解离,形成部分分解的羰基钼物种.     

Surface‐enhanced Raman spectroscopy of 4‐tert‐butylpyridine on a silver electrode

We report the observation of large surface‐enhanced Raman scattering (SERS) (10⁶) for 4‐tert‐butylpyridine molecules adsorbed on a silver electrode surface in an electrochemical cell with electrode potential set at − 0.5 V. A decrease in electrode potential to − 0.3 V was accompanied by a decrease in relative intensities of the vibrational modes. However, there were no changes in vibrational wavenumbers. Comparison of both normal solution Raman and SERS spectra shows very large enhancement of the intensities of a₁, a₂, and b₂ modes at laser excitation of 488 nm. Enhancement of the non‐totally symmetric modes indicates the presence of charge transfer as a contributor to the enhancement. Copyright © 2011 John Wiley & Sons, Ltd.     

Low‐temperature photoluminescence of oxide‐covered single‐layer MoS2

We present a photoluminescence study of single‐layer MoS₂ flakes on SiO₂ surfaces. We demonstrate that the luminescence peak position of flakes prepared from natural MoS₂, which varies by up to 25 meV between individual flakes, can be homogenized by annealing in vacuum. We use HfO₂ and Al₂O₃ layers prepared by atomic layer deposition to cover some of our flakes. In these flakes, we observe a suppression of the low‐energy luminescence peak which appears in asprepared flakes at low temperatures. We infer that this peak originates from excitons bound to surface adsorbates. We also observe different temperature‐induced shifts of the luminescence peaks for the oxide‐covered flakes. This effect stems from the different thermal expansion coefficients of the oxide layers and the MoS₂ flakes. It indicates that the single‐layer MoS₂ flakes strongly adhere to the oxide layers and are therefore strained. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vibration spectroscopy of benzene adsorbed on Pt(111) and Ni(111)

High resolution electron energy loss spectroscopy has been applied to study the adsorption of benzene (C₆H₆ and C₆D₆) on Pt(111) and Ni(111) single crystal surfaces between 140 and 320 K. The vibrational spectra provide evidence that benzene is chemisorbed with its ring parallel to the surface, predominantly π bonded to the platinum and nickel surface respectively. A significant frequency increase of the CH-out-of-plane bending mode, largest in the case of platinum, is observed compared to the free molecule. On both metals two phases of benzene exist simultaneously, characterized by a different frequency shift. The shifts are explained by electronic interaction between the metal d-orbitals and molecules adsorbed in on top and threefold hollow sites respectively. The vibrational spectra of the multilayer condensed phase of benzene exhibit the infrared active modes of the gasphase molecule as expected.     

Potential dependent thiocyanate adsorption on gold electrodes: a comparison study between SERS and SHINERS

Potential dependent adsorption of target molecules on electrode surface has long been analyzed by several analytical techniques at the electrochemical interfaces. Here, the adsorption of thiocyanate (SCN⁻) on gold electrodes [Au (111) and Au (poly)] is investigated by electrochemical shell isolated nanoparticle‐enhanced Raman spectroscopy (EC‐SHINERS) and surface‐enhanced Raman spectroscopy. Based on the experimental observation, C − N stretching mode of N‐bound SCN⁻ can be observed around 2080 cm⁻¹ throughout the whole potential range. The band corresponding to ν_C−N of S‐bound SCN⁻ appears as a shoulder at more negative potentials, and as a well‐defined band are more positive potentials. However, the overlapped bands provoke a negative shift in the frequency of S‐bound thiocyanate. Therefore, a change in the calculated Stark slope is observed. Interestingly, SHINERS has been employed to demonstrate the thiocyanate orientation and its effect on Raman spectra. Our results widen the opportunities of SHINERS to unravel the potential‐dependent adsorption behavior of target molecules on single‐crystal electrode surfaces. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation of nanoparticulate silicon as printed layers using scanning electron microscopy,transmission electron microscopy,X‐ray absorption spectroscopy and X‐ray photoelectron spectroscopy

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High‐resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)‐ and (100)‐oriented planes which stabilizes against further oxidation of the particles. X‐ray absorption spectroscopy (XANES) and X‐ray photoelectron spectroscopy (XPS) measurements at the O 1s‐edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milled for different times. XANES results reveal the presence of the +4 (SiO₂) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2p XPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub‐oxide, +1 (Si₂O), +2 (SiO) and +3 (Si₂O₃), states are present. The analysis of the change in the sub‐oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.     

Ellipsometry studies of albumin films on tantalum oxide and SiO2

The adsorption of (1) bovine serum albumin in acetate buffer, (2) albumin followed by glutaraldehyde crosslinking, (3) albumin followed by exposure to an albumin/glutaraldehyde solution, and (4) albumin after the surface was subjected to treatment (3), has been studied using Ta oxide/Ta chips and SiO₂/Si wafers as substrates. The films were washed, air dried and measured in air using an automatic laser ellipsometer, 6328 Å. The films formed from treatment (3) and treatment (4) have a lower refractive index and are thicker than films formed from treatment (1) and treatment (2). The adsorption of albumin on SiO₂/Si wafers seems to be slower than that on the Ta oxide/Ta surfaces.     

Adsorption of azacrown ethers at solid–liquid interface. Contact angle and neutron reflectivity study

Adsorption of two alkylated N,N′-diaza-18-crown-6 ethers (decyl- and hexadecyl-derivatives, ACE-10 and ACE-16, respectively) on solid surfaces was studied by using contact angle and neutron reflectivity measurements. The solid substrates used were (a) Si covered with a native oxide layer (Si/SiO₂) and (b) Si with sputtered Pt layer (Si/Pt). The sensitivity of neutron reflectivity was drastically improved by applying the intermediate Pt layer of 150 Å, which gave rise to several Kiessig fringes in the experimentally accessible q-range. The position of the fringes is very sensitive to slight changes of the interfacial composition induced by adsorption of a thin monolayer, otherwise very difficult to detect. Unfortunately, in the studied case this sensitivity is immediately lost due to undesired adsorption of a protonated material on the Pt surface exposed to the lab air. A decrease of surface energy (increase of contact angle) of both Si/SiO₂ and Si/Pt upon exposure to toluene solutions of ACEs suggests that the latter are attached to the surface via the hydrophilic azacrown ether head with alkyl chains standing upright towards the liquid phase.     

Effect of an aliphatic spacer group on the adsorption mechanism of phosphonodipeptides containing N-terminal glycine on the colloidal silver surface

This study presents the complete solid-state vibrational assignments for a series of five zwitterionic phosphonodipeptides containing an N-terminal glycine: L -Gly-L -CH(Me)-PO₃H₂ (G1), L -Gly-C(Me,Me)-PO₃H₂ (G2), L -Gly-L -CH(Et)-PO₃H₂ (G3), L -Gly-C(Me,Et)-PO₃H₂ (G4), and L -Gly-L -CH(iBu)-PO₃H₂ (G5). The assignments are based primarily on Fourier-transform Raman spectra (FT-RS) and Fourier-transform infrared spectra (FT-IR) spectra, as well as density functional theory (DFT) calculations at the B3LYP; 6-31 + + G** level of theory. Existing literature data are also taken into consideration. The surface geometry of these molecules on a colloidal silver surface was also determined by observing the wavenumber, width, and relative intensity changes of enhanced bands in their surface-enhanced Raman scattering spectra. It is proposed that G1 mainly adsorbs onto the colloidal silver particles through the phosphonate terminus, whereas the PO bond in G3 and G5 assists in the interaction of these molecules with the silver surface. G3 interacts with Ag mainly via α-methlyalanine and the amide bond. It is also shown that the amide bond and glycine backbone are involved in the adsorption of G3 on the silver nanoparticles. In addition, the differences recorded for G4 and G5 SERS spectra are mainly due to interactions between the silver surface and the amine group and N- and P-terminus, respectively, and are manifestations of the characteristic vibrations of these groups. Copyright © 2008 John Wiley & Sons, Ltd.     

SiO adsorption on a p(2 × 2) reconstructed Si(1 0 0) surface

We have investigated the adsorption mechanism of SiO molecule incident on a clean Si(1 0 0) p(2 × 2) reconstructed surface using density functional theory based methods. Stable adsorption geometries of SiO on Si surface, as well as their corresponding activation and adsorption energies are identified. We found that the SiO molecule is adsorbed on the Si(1 0 0) surface with almost no activation energy. An adsorption configuration where the SiO binds on the channel separating the dimer rows, forming a Si-O-Si bridge on the surface, is the energetically most favourable geometry found. A substantial red-shift in the calculated vibrational frequencies of the adsorbed SiO molecule in the bridging configurations is observed. Comparison of adsorption energies shows that SiO adsorption on a Si(1 0 0) surface is energetically less favourable than the comparable O₂ adsorption. However, the role of SiO in the growth of silicon sub-oxides during reactive magnetron plasma deposition is expected to be significant due to the relatively large amount of SiO molecules incident on the deposition surface and its considerable sticking probability. The stable adsorption geometries found here exhibit structural properties similar to the Si/SiO₂ interface and may be used for studying SiO_x growth.     

Vibrational spectroscopy and DFT calculations of N,N′‐dicyclohexylcarbodiimide

Infrared (IR) and Raman spectra were obtained for N,N′‐dicyclohexylcarbodiimide (DCC) in the solid state and in CHCl₃ solution. Structures and vibrational spectra of isolated, gas‐phase DCC molecules with C₂ and C_i symmetries, computed at the B3‐LYP/cc‐pVTZ level, show that the IR and Raman spectra provide convincing evidence for a C₂ structure in both the solid state and in CHCl₃ solution. Using a scaled quantum‐chemical force field, these density functional theory calculations have provided detailed assignments of the observed IR and Raman bands in terms of potential energy distributions. Comparison of solid‐state and solution spectra, together with a Raman study of the melting behaviour of DCC, revealed that no solid‐state effects were evident in the spectra. Copyright © 2010 John Wiley & Sons, Ltd.     

Radical-Recombination Luminescence of the Uranyl Nitrate Complex in the Adsorbed State

We have investigated the luminescence of uranyl nitrate molecules on the surface of powdery SiO₂ upon excitation by UV light (PhL) and hydrogen atoms (radical-recombination luminescence (RRL)). It has been found that the PhL and RRL spectra have a clearly defined vibrational structure. The luminescence peaks of the adsorbed UO₂ ^2– ion are characterized by a systematic longwave shift from the same peaks of crystalline uranyl nitrate (by 230–430 cm^–1 at 130 K). Moreover, in the adsorption centers the vibration frequencies of UO₂ ^2– are 20–80 cm smaller than in crystalline salt and the RRL bands are 150–350 cm^–1 (130 K) wider than the corresponding PhL bands.     

Study of surface-molecule interactions using nuclear resonance photon scattering

Nuclear resonance photon scattering from the 6324-keV level in ¹⁵N was used for studying the surface-molecule interaction of nitrogen (N₂) on graphite. Other N-containing gaseous molecules (such as NO and N₂O) and other surfaces such that of activated carbon fiber (ACF) were also used. In particular, the average zero point energies of the out-of-plane vibrational and librational potentials of the molecules with respect to the adsorbing surfaces were determined. In addition, the out-of-plane orientation of the molecules versus T and as a function of the coverage were measured. In the nitrogen-graphite system, the results were used for testing the calculated in-plane and out of plane phonon spectra and for testing calculations of molecular dynamic simulations.     

Adsorption of 4,4′‐thiobisbenzenethiol on silver surfaces: surface‐enhanced Raman scattering study

Adsorption of 4,4′‐thiobisbenzenethiol (4,4′‐TBBT) on a colloidal silver surface and a roughened silver electrode surface was investigated by means of surface‐enhanced Raman scattering (SERS) for the first time, which indicates that 4,4′‐TBBT is chemisorbed on the colloidal silver surface as dithiolates by losing two H‐atoms of the S H bond, while as monothiolates on the roughened silver electrode. The different orientations of the molecules on both silver surfaces indicate the different adsorption behaviors of 4,4′‐TBBT in the two systems. It is inferred from the SERS signal that the two aromatic rings in 4,4′‐TBBT molecule are parallel to the colloidal silver surface as seen from the disappearance of ν_{C H} band (3054 cm⁻¹), which is a vibrational mode to be used to determine the orientation of a molecule on metals according to the surface selection rule, while on the roughened silver electrode surface they are tilted to the surface as seen from the enhanced signal of ν_{C H}. The orientation of the C‐S bond is tilted with respect to the silver surface in both cases as inferred from the strong enhancement of the ν_{C S}. SERS spectra of 4,4′‐TBBT on the roughened silver electrode with different applied potentials reveal that the enhancement of 4,4′‐TBBT on the roughened silver electrode surface may be related to the chemical mechanism (CM). More importantly, the adsorption of 4,4′‐TBBT on the silver electrode is expected to be useful to covalently adsorb metal nanoparticles through the free S H bond to form two‐ or three‐ dimensional nanostructures. Copyright © 2007 John Wiley & Sons, Ltd.