共查询到20条相似文献,搜索用时 15 毫秒
1.
Min YangMatthew J. Marino Vincent J. BojanOsman L. Eryilmaz Ali ErdemirSeong H. Kim 《Applied Surface Science》2011,257(17):7633-7638
This paper discusses the use of chemical derivatization methods for surface chemical composition analysis of diamond-like carbon (DLC) films synthesized through plasma-enhanced chemical vapor deposition with X-ray photoelectron spectroscopy (XPS). The main challenge in applying chemical derivatization reactions for titration of organic functional groups on the DLC surface is that sub-surface oxygenated species are not accessible to the derivatizing agent. As a simple approximation, a functional group that can be quantified unambiguously with XPS can be used as an internal reference to estimate the accessible-to-inaccessible ratio, and this information can be used to estimate the total amount of other functional groups from the chemical-derivatization-assisted XPS analysis. The use of this principle to obtain the surface composition of hydroxyl, ether, carbonyl, and carboxyl groups in the oxidized surface region of the DLC film was demonstrated. 相似文献
2.
Melanie David Wilson Agerico Diño Hiroshi Nakanishi Naoki Ando 《Surface science》2007,601(22):5241-5245
The adhesion strength of polybutylene terephthalate (PBT) on aluminum was investigated using density functional theory-based total energy calculations. Aluminum atom was connected to a PBT monomer at different orientations and total energies were calculated in order to determine the most stable orientation. The energy differences showed that the Al oriented at 180° with the ester group of the monomer bonded strongly. Using this orientation, the PBT monomer-adhesion on aluminum surface and the aluminum atom adhesion on PBT bulk were also investigated. 相似文献
3.
The effect of nitrogen and oxygen plasma on the wear properties and adhesion strength of the diamond-like carbon film coated on PTFE 总被引:1,自引:0,他引:1
Diamond-like carbon (DLC) films were deposited on polytetrafluoroethylene (PTFE) using a radiofrequency plasma chemical vapour deposition method. Prior to DLC coating, the PTFE substrates were modified with O2 and N2 plasma to enhance the adhesion strength of the DLC film to the substrate. The effect of the plasma pre-treatment on the chemical composition and the surface energy of the plasma pre-treated PTFE surface was investigated by X-ray photoelectron spectroscopy (XPS) and static water contact angle measurement, respectively. A pull-out test and a ball-on-disc test were carried out to evaluate the adhesion strength and the wear properties of the DLC-coated PTFE.In the N2 plasma pre-treatment, the XPS result indicated that defluorination and the nitrogen grafting occurred on the plasma pre-treated PTFE surface, and the water contact angle decreased with increasing the plasma pre-treatment time. In the O2 plasma pre-treatment, no grafting of the oxygen occurred, and the water contact angle slightly increased with the treatment time. In the pull-out test, the adhesion strength of the DLC film to the PTFE substrate was improved with the plasma pre-treatment to the PTFE substrate, and N2 plasma pre-treatment was more effective than the O2 plasma pre-treatment. In the ball-on-disc test, the DLC film with the N2 plasma pre-treatment showed good wear resistance, compared with that with O2 plasma pre-treatment. 相似文献
4.
We employ spin-polarized periodic density functional theory (DFT) to characterize CO adsorption and dissociation on the Fe(1 1 0) surface. We investigate the site preference for CO on Fe(1 1 0) at θCO = 0.25 and 0.5 monolayer (ML), for different functional forms of the generalized gradient approximation (GGA) to electron exchange and correlation within DFT. At 0.25 ML, we predict the existence of a new ordered structure comparable in stability to one proposed previously. At 0.5 ML, we confirm the preference of a distorted on-top adsorption configuration suggested by experiment. The calculated heats of adsorption, CO stretching frequencies, and work function changes agree well with experiment. When dissociating from the on-top site, we predict that CO first moves off the on-top site and then goes through a lying-down transition state with a barrier of 1.52 eV. Diffusion of CO on Fe(1 1 0) from the on-top site to the long-bridge site is predicted to have a very small barrier of 0.1 eV. Dissociation of CO from the long-bridge site goes through the same transition state as from the on-top site, but the former has a slightly lower barrier. After dissociation, O atoms remain on the surface while C atoms are embedded into Fe(1 1 0), indicating C atoms may readily diffuse into Fe(1 1 0). 相似文献
5.
Noboru Takeuchi 《Surface science》2007,601(16):3361-3365
The adsorption of acetylene on the Si(0 0 1)-c(2 × 4) surface at low and full coverage is studied by first principles density functional calculations using the generalized gradient approximation. For a single acetylene molecule, the most stable configuration corresponds to the di-σ site, on-top of a silicon dimer. This configuration is 0.36 eV more stable than the end-bridge site between two adjacent Si dimers. However, if there are two acetylene molecules, the paired end bridge configuration becomes the most stable. We have also studied the kinetics of the adsorption of a single acetylene molecule. Our calculations show that the reaction is barrier-free for adsorption in the di-σ configuration, while there is an energy barrier of 0.19 eV for adsorption in the end-bridge site. At monolayer coverage, the most stable configuration corresponds to acetylene molecules in the pair-end bridge configuration, in agreement with previous calculations. We have found a noticeable coverage dependence only for the end-bridge site, but not for the di-σ. Our results show that to have an accurate picture of the adsorption of acetylene on the Si(0 0 1) surface, a large unit cell is needed. 相似文献
6.
Farida SaadMourad Zemirli Mouloud BenakkiSaid Bouarab 《Physica B: Condensed Matter》2012,407(4):698-704
The coadsorption of Li and H atoms on Pt(001), Pt(110) and Pt(111) surfaces is studied using density functional theory with generalised gradient approximation. In all calculations Li, H and the two topmost layers of the metal were allowed to relax. At coverage of 0.25 mono-layer in a p(2×2) unit cell, lithium adsorption at the hollow site for the three surfaces is favoured over top and bridge sites. The most favoured adsorption sites for H atom on the Pt(001) and Pt(110) surfaces are the top and bridge sites, while on Pt(111) surface the fcc site appears to be slightly favoured over the hcp site. The coadsorption of Li and atomic hydrogen shows that the interaction between the two adsorbates is stabilising when they are far from each other. The analysis of Li, H and Pt local density of states shows that Li strongly interacts with the Pt surfaces. 相似文献
7.
NiTi alloys are potentially useful in biomedical application due to their unique superelasticity and shape memory effect. However, the materials are vulnerable to surface corrosion and the most serious issue is out-diffusion of toxic Ni ions from the substrate into body tissues and fluids. In this paper, Diamond-like carbon (DLC) film is fabricated on the NiTi alloys using plasma immersion ion implantation and deposition (PIIID) at room temperature to improve their corrosion resistance and block the out-diffusion of the Ni ions. The results show that the DLC films cannot only improve the corrosion resistance of the NiTi substrate, but also effectively suppress the Ni ions release from the substrate. The reason that the corrosion resistance of the coated samples is markedly improved due to the DLC films formation is systematically investigated. 相似文献
8.
D.E. Jiang 《Surface science》2005,583(1):60-68
We report first principles density functional theory (DFT) results of H2S and HS adsorption and dissociation on the Fe(1 1 0) surface. We investigate the site preference of H2S, HS, and S on Fe(1 1 0). H2S is found to weakly adsorb on either the short bridge (SB) or long bridge (LB) site of Fe(1 1 0), with a binding energy of no more than 0.50 eV. The diffusion barrier from the LB site to the SB site is found to be small (∼0.10 eV). By contrast to H2S, HS is predicted to be strongly chemisorbed on Fe(1 1 0), with the S atom in the LB site and the HS bond oriented perpendicular to the surface. Isolated S atoms also are predicted to bind strongly to the LB sites of Fe(1 1 0), where the SB is found to be a transition state for S surface hopping between neighboring LB sites. The minimum energy paths for H2S and HS dehydrogenation involve rotating an H atom towards a nearby surface Fe atom, with the S-H bonds breaking on the top of one Fe atom. The barrier to break the first S-H bond in H2S is low at 0.10 eV, and breaking the second S-H bond is barrierless, suggesting deposition of S on Fe(1 1 0) via H2S is kinetically and thermodynamically facile. 相似文献
9.
Ab initio calculations, based on pseudopotentials and density functional theory, have been performed to investigate the effect of hydrogenation on the atomic geometries and the energetics of substitutional boron on the generic Si(0 0 1)-(1 × 2) surface. For a single B atom substitution corresponding to 0.5 ML coverage, we have considered two different sites: (i) the mixed Si-B dimer structure and (ii) boron substituting for the second-layer Si to form Si-B back-bond structure, which is energetically more favorable than the mixed Si-B dimer by 0.1 eV/dimer. However, when both of these cases are passivated by hydrogen atoms, the situation is reversed and the Si-B back-bond case becomes 0.1 eV/dimer higher in energy than the mixed Si-B dimer case. For the B incorporation corresponding to 1 ML coverage, among the substitutional cases, 100% interdiffusion into the third layer of Si and 50% interdiffusion into the second layer of Si are energetically similar and more favorable than the other cases that are considered. However, when the surface is passivated with hydrogen, the B atoms energetically prefer to stay at the third layer of the Si substrate. 相似文献
10.
Yilin Cao 《Surface science》2006,600(19):4572-4583
To provide information about the chemistry of water on Pd surfaces, we performed density functional slab model studies on water adsorption and decomposition at Pd(1 1 1) surface. We located transition states of a series of elementary steps and calculated activation energies and rate constants with and without quantum tunneling effect included. Water was found to weakly bind to the Pd surface. Co-adsorbed species OH and O that are derivable from H2O stabilize the adsorbed water molecules via formation of hydrogen bonds. On the clean surface, the favorable sites are top and bridge for H2O and OH, respectively. Calculated kinetic parameters indicate that dehydrogenation of water is unlikely on the clean regular Pd(1 1 1) surface. The barrier for the hydrogen abstraction of H2O at the OH covered surface is approximately 0.2-0.3 eV higher than the value at the clean surface. Similar trend is computed for the hydroxyl group dissociation at H2O or O covered surfaces. In contrast, the O-H bond breaking of water on oxygen covered Pd surfaces, H2Oad + Oad → 2OHad, is predicted to be likely with a barrier of ∼0.3 eV. The reverse reaction, 2OHad → H2Oad + Oad, is also found to be very feasible with a barrier of ∼0.1 eV. These results show that on oxygen-covered surfaces production of hydroxyl species is highly likely, supporting previous experimental findings. 相似文献
11.
Xuemin WangChangle Sheng Yuyin WangLiping Peng Weidong Wu Yongjian Tang 《Physica B: Condensed Matter》2011,406(14):2777-2782
The adsorption of oxygen atoms on Mg3Nd (0 0 1) surface was studied based on density function theory (DFT), in which the exchange-correlation potential was chosen as the generalized gradient approximation (GGA) in the Perdew and Wang (PW91). The most preferred adsorption position was at the top-hollow site. Upon the optimization on top-hollow site with different coverage, it was found that the adsorption energy decreased with oxygen coverage. The density of states analysis showed that obvious charge transfer took place between O atom and the nearest Nd atom and chemical bond formed between O atom and the nearest Nd atom after O adsorption. The result of surface energy as a function of chemical potential change of oxygen indicated the clean Mg3Nd (0 0 1) surface was easy to adsorb oxygen and form 1.00 ML surface. 相似文献
12.
Surface structures and electronic properties of hypophosphite, H2PO2−, molecularly adsorbed on Ni(1 1 1) and Cu(1 1 1) surfaces are investigated in this work by density functional theory at B3LYP/6-31++g(d, p) level. We employ a four-metal-atom cluster as the simplified model for the surface and have fully optimized the geometry and orientation of H2PO2− on the metal cluster. Six stable orientations have been discovered on both Ni (1 1 1) and Cu (1 1 1) surfaces. The most stable orientation of H2PO2− was found to have its two oxygen atoms interact the surface with two PO bonds pointing downward. Results of the Mulliken population analysis showed that the back donation from 3d orbitals of the transition metal substrate to the unfilled 3d orbital of the phosphorus atom in H2PO2− and 4s orbital's acceptance of electron donation from one lone pair of the oxygen atom in H2PO2− play very important roles in the H2PO2− adsorption on the transition metals. The averaged electron configuration of Ni in Ni4 cluster is 4s0.634p0.023d9.35 and that of Cu in Cu4 cluster is 4s1.004p0.033d9.97. Because of this subtle difference of electron configuration, the adsorption energy is larger on the Ni surface than on the Cu surface. The amount of charge transfers due to above two donations is larger from H2PO2− to the Ni surface than to the Cu surface, leading to a more positively charged P atom in NinH2PO2− than in CunH2PO2−. These results indicate that the phosphorus atom in NinH2PO2− complex is easier to be attacked by a nucleophile such as OH− and subsequent oxidation of H2PO2− can take place more favorably on Ni substrate than on Cu substrate. 相似文献
13.
The adsorption properties of sodium-chloride monolayers and bilayers on the flat (1 0 0) surface and the stepped (3 1 1) surface of copper have been investigated using density functional calculations. We have identified both electrostatic and covalent contributions to the bonding between the overlayers and the substrate. The larger corrugation of the electrostatic potential on the stepped surface than on the flat surface makes the adsorption stronger on the stepped surface than on the flat surface and favours the adsorption of the chlorine atom on top of a copper atom in the steps of the stepped surface. A further stabilisation of this bonding geometry is obtained from the formation of weak covalent bond between these two atoms. A simple “image charge” model for the bonding is found to break down in this case. The large geometric buckling of the monolayer on the stepped surface is predicted to give rise to a large difference between the work functions of the monolayer and the bilayer. 相似文献
14.
Density functional theory calculations have been performed to determine the adsorption site of carbon at the Si(1 1 1):As and Si(1 1 1):H surfaces at different coverages. The As- and H-passivated surfaces were simulated by replacing the topmost Si layer by As or by saturating the Si dangling bonds with hydrogen atoms, respectively. Different high symmetry sites were considered. Carbon was placed successively in the fourfold (T4) or threefold coordinated (H3), the ontop (T1) sites or substituted for a Si atom in the S5 position located underneath the Si adatom in the T4 site. We found that the preferred carbon adsorption site depends on the coverage of the passivated surfaces. At low coverages i.e. at 1/16 ML and 1/3 ML, it prefers a distorted T4 position whereas at 1 ML, it occupies an H3 site. This contrasts with the clean surface where the most energetically favored site is the S5 at all coverages. Carbon adsorption induces a significant change in the structural geometry of the surface atoms, leading to a charge re-arrangement in the surface layers. 相似文献
15.
M.P Andersson 《Surface science》2004,549(1):87-96
In the present work we determine the adsorption site of two polyatomic molecules, methoxy and ethoxy, on Cu(1 0 0). This is accomplished by comparing experimental intramolecular vibrational modes to the corresponding modes calculated by first principle methods. We explore the three different high symmetry adsorption sites on top, bridge and hollow using several different metal clusters to represent the Cu(1 0 0) surface. The experimental results for both methoxy and ethoxy are best reproduced by the most realistic representation of the hollow position, a Cu5 cluster. 相似文献
16.
The adsorption of vinyl fluoride on the rutile TiO2(1 1 0) surface has been simulated, on the basis of a recently proposed experimental model, using hybrid-exchange density functional theory. Different surface coverages have been considered and the lateral interaction between adsorbed vinyl fluoride molecules has been quantified through a simple model of nearest and next nearest neighbouring molecules. The vibrational frequencies of the adsorbed molecule have been calculated and are found to be in excellent agreement with those observed providing support for the proposed adsorption model. The effect of the adsorption on the electronic structure of the molecule and the surface have been characterised by computing electrostatic potential maps and the local density of states. 相似文献
17.
Fabrication, handling and disposal of nuclear fuel materials require comprehensive knowledge of their surface morphology and reactivity. Due to unavoidable contact with air components (even at low partial pressures), UN samples contain considerable amount of oxygen impurities affecting fuel properties. In this study we focus on reactivity of the energetically most stable (0 0 1) substrate of uranium nitride towards the atomic oxygen as one of initial stages for further UN oxidation. The basic properties of O atoms adsorbed on the UN(0 0 1) surface are simulated here combining the two first principles calculation methods based on the plane wave basis set and that of the localized orbitals. 相似文献
18.
We present results of ab initio calculations of structural, electronic and vibrational properties of the Ge(0 0 1) surface covered with a monolayer of arsenic. The fully occupied πu bonding and πg antibonding electronic states due to the As-As dimer formation are quite close in energy and their ordering is same as that found on the Si(0 0 1) surface. Using our calculated atomic and electronic structures, surface lattice dynamics was studied by employing a linear response approach based on density functional perturbation theory. A comparison of the phonon spectrum of the Ge(0 0 1)/As(2 × 1) surface with that of the clean Ge(0 0 1)(2 × 1) surface indicates the presence of several new characteristic phonon modes due to adsorption of As atoms. 相似文献
19.
Spencer D. Miller 《Surface science》2009,603(5):794-273
Using density functional theory (DFT) we studied the adsorption of oxygen on gold and platinum fcc (1 1 1) surfaces as a function of coverage. We show how increasing coverages of oxygen atoms lead to a broadening of the surface atom d-bands and a consequent reduction in the average energy of the d-band center due to conservation of the d-band filling. The reduction in the energy of the d-band center leads to a correlated increase (weakening) in the adsorption energy. This underlying electronic structure relationship exists on both the gold and platinum surfaces, and we show that the coverage dependent adsorption energies of oxygen on these two surfaces are related by a simple near-linear correlation. 相似文献
20.
SiH4 and GeH4 dissociative adsorptions on a buckled SiGe(1 0 0)-2 × 1 surface have been analyzed using density functional theory (DFT) at the B3LYP level. The Ge alloying in the Si(1 0 0)-2 × 1 surface affects the dimer buckling and its surface reactivity. Systematic Ge influences on the reaction energetics are found in SiH4 and GeH4 reactions with four dimers of Si∗-Si, Ge∗-Si, Ge∗-Ge, and Si∗-Ge (∗ denotes the protruded atom). On a half H-covered surface, the energy barriers for silane and germane adsorption are higher than those on the pristine surface. The energy barrier for silane adsorption is higher than the corresponding barrier for germane adsorption. Rate constants are also calculated using the transition-state theory. We conclude that the SiGe surface reactivity in adsorption reaction depends on the Ge presence in dimer form. If the surface Ge is present in form of Ge∗-Ge, the surface reactivity decreases as the Ge∗-Ge content increases. If the surface Ge prefers to be in form of Ge∗-Si at low Ge contents, the surface reactivity increases first, then decreases at high Ge surface contents when Ge∗-Ge prevails. The calculated rate constant ratio of GeH4 adsorption on Si∗-Si over Ge∗-Ge at 650 °C is 2.1, which agrees with the experimental ratio of GeH4 adsorption probability on Si(1 0 0) over Si(1 0 0) covered by one monolayer Ge. The experimental ratio is 1.7 measured through supersonic molecular beam techniques. This consistency between calculation and experimental results supports that one monolayer of Ge on Si(1 0 0) exists in form of Ge∗-Ge dimer. 相似文献