Initial oxidation of the Rh(110) surface: ordered adsorption and surface oxide structures

The initial oxidation of the Rh(110) surface was studied by scanning tunneling microscopy, core level spectroscopy, and density functional theory. The experiments were carried out exposing the Rh(110) surface to molecular or atomic oxygen at temperatures in the 500-700 K range. In molecular oxygen ambient, the oxidation terminates at oxygen coverage close to a monolayer with the formation of alternating islands of the (10x2) one-dimensional surface oxide and (2x1)p2mg adsorption phases. The use of atomic oxygen facilitates further oxidation until a structure with a c(2x4) periodicity develops. The experimental and theoretical results reveal that the c(2x4) structure is a "surface oxide" very similar to the hexagonal O-Rh-O trilayer structures formed on the Rh(111) and Rh(100) substrates. Some of the experimentally found adsorption phases appear unstable in the phase diagram predicted by thermodynamics, which might reflect kinetic hindrance. The structural details, core level spectra, and stability of the surface oxides formed on the three basal planes are compared with those of the bulk RhO2 and Rh2O3.     

K-stabilized high-oxygen-coverage states on Rh(110): a low-pressure pathway to formation of surface oxide

Using scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy, we studied the evolution of the structure and chemical state of a Rh(110) surface, modified by K adlayers and exposed to high O2 doses at elevated temperatures. We find that oxygen coadsorption on the K-covered Rh(110) leads to massive reconstruction of the Rh(110) surface. Stable reconstructed (10 x 2) and (8 x 2) segmented phases with a local coverage of more than two oxygen atoms per surface Rh atom were observed. Formation of surface oxide, which coexists with the (10 x 2) and (8 x 2) segmented adsorption phases, is evidenced at the highest O2 doses. The development of strongly reconstructed adsorption phases with oxide-like stoichiometry and surface oxide under UHV conditions is explained in terms of the stabilization of the (1 x 2) reconstruction and promotion of O2 dissociation by the K adatoms.     

Ultrathin Rh films on Ru(0001): oxidation in confinement

Ultrathin rhodium films with a thickness ranging from 1 to a few monolayers were deposited on a single-crystal Ru(0001) surface in order to investigate the oxidation behavior of ultrathin epitaxial films on a dissimilar substrate. It is found that rhodium grows on Ru(0001) initially layer by layer, adapting the in-plane lattice parameters of Ru(0001). When exposing Rh films to oxygen environment (approximately 4.8 x 10(6) L O2 exposure) at 660 K, 2-4 ML Rh films form a surface oxide composed of (9 x 9) O-Rh-O trilayers. Quite in contrast, oxidation of the 1 ML RhRu(0001) film leads to a poorly ordered oxide with a rutile structure reminiscent of RuO2(110) on Ru(0001). The oxidized 1 ML RhRu(0001) film contains much more oxygen than the oxidized thicker Rh films. Lower temperatures (535 K) and high doses of oxygen lead to a (1 x 1)-O overlayer on the 1 ML RhRu(0001) surface, whose atomic geometry resembles closely that of the (1 x 1)-O phase on clean Ru(0001).     

Catalytic oxidation activity of Pt3O4 surfaces and thin films

The catalytic oxidation activity of platinum particles in automobile catalysts is thought to originate from the presence of highly reactive superficial oxide phases which form under oxygen-rich reaction conditions. Here we study the thermodynamic stability of platinum oxide surfaces and thin films and their reactivities toward oxidation of carbon compounds by means of first-principles atomistic thermodynamics calculations and molecular dynamics simulations based on density functional theory. On the Pt(111) surface the most stable superficial oxide phase is found to be a thin layer of alpha-PtO2, which appears not to be reactive toward either methane dissociation or carbon monoxide oxidation. A PtO-like structure is most stable on the Pt(100) surface at oxygen coverages of one monolayer, while the formation of a coherent and stress-free Pt3O4 film is favored at higher coverages. Bulk Pt3O4 is found to be thermodynamically stable in a region around 900 K at atmospheric pressure. The computed net driving force for the dissociation of methane on the Pt3O4(100) surface is much larger than that on all other metallic and oxide surfaces investigated. Moreover, the enthalpy barrier for the adsorption of CO molecules on oxygen atoms of this surface is as low as 0.34 eV, and desorption of CO2 is observed to occur without any appreciable energy barrier in molecular dynamics simulations. These results, combined, indicate a high catalytic oxidation activity of Pt3O4 phases that can be relevant in the contexts of Pt-based automobile catalysts and gas sensors.     

GaAs(100)表面氧化的XPS研究

X-ray photoelectron spectroscopy（XPS）was used to study two different oxidation treatments on the GaAs（100）surface———the thermal oxidation in the air,and the ultraviolet-light oxidation in the UV-ozone. A series of properties including the oxide composition,chemical states,the surface Ga/As atomic ratio and the thickness of the oxide layer grown on GaAs surface were compared. The results indicate that the oxide composition,the surface Ga / As atomic ratio and the thickness of the oxide layer oxide on GaAs surface are different for different oxidation methods. The oxides on GaAs surface grown by thermal oxidation in the air are composed of Ga2O3,As2O5,As2O3 and elemental As;and the Ga/As atomic ratio is drifted off the stoichiometry far away. The Ga/As atomic ratio of oxide layer on GaAs surface is increases with the thickness of oxide. However,the oxides on GaAs surface grown by UV-ozone are made up of only Ga2O3 and As2O3,As2O5 and elemental As are not detected,the Ga/As atomic ratio is close to unity. The thickness of oxide layer on GaAs can be controlled by the UV exposing time. The mechanism of oxidation of GaAs is also discussed. The UV-light radiation not only causes the oxygen molecular excited forming atomic oxygen,but also induces the valence electrons of the GaAs excited from the valence band,and then the reactivity of Ga and As atom increase,and they can easily react with the excited atomic oxygen at the same reactive velocity.     

Ru(0001) model catalyst under oxidizing and reducing reaction conditions: in-situ high-pressure surface X-ray diffraction study

With surface X-ray diffraction (SXRD) using a high-pressure reaction chamber we investigated in-situ the oxidation of the Ru(0001) model catalyst under various reaction conditions, starting from a strongly oxidizing environment to reaction conditions typical for CO oxidation. With a mixture of O(2) and CO (stoichiometry, 2:1) the partial pressure of oxygen has to be increased to 20 mbar to form the catalytically active RuO(2)(110) oxide film, while in pure oxygen environment a pressure of 10(-5) mbar is already sufficient to oxidize the Ru(0001) surface. For preparation temperatures in the range of 550-630 K a self-limiting RuO(2)(110) film is produced with a thickness of 1.6 nm. The RuO(2)(110) film grows self-acceleratedly after an induction period. The RuO(2) films on Ru(0001) can readily be reduced by H(2) and CO exposures at 415 K, without an induction period.     

Rh-promoted methanol decomposition on cerium oxide thin films

Methanol adsorption and reaction have been studied on Rh-deposited cerium oxide thin films under UHV conditions using temperature-programmed desorption and synchrotron soft X-ray photoelectron spectroscopy. The methanol behavior was examined as a function of the Ce oxidation state, methanol exposure, and Rh particle size and coverage. When Rh nanoparticles were deposited on the ceria films, methanol decomposed on Rh to CO and H below 200 K. H atoms recombined and desorbed between 200 and 300 K. CO evolved from Rh deposited on fully oxidized ceria between 400 and 500 K. However, on reduced ceria films, the CO on Rh further decomposed to atomic C. Methanol adsorbed on the ceria films deprotonated to form methoxy as the only intermediate on the surface. This methoxy decomposed and desorbed as CO and H2 at higher temperatures regardless of the ceria oxidation state. Compared with the methanol reaction on Rh-free ceria thin films, formaldehyde formation from methoxy was completely suppressed after Rh deposition. Our results indicate that Rh can promote the decomposition of methoxy adsorbed on the ceria and that decomposition of methoxy intermediates occurred at the metal/oxide interfaces. On the other hand, the reduced ceria can promote total methanol decomposition on Rh.     

Nitridation of niobium films by rapid thermal processing: different behaviour of films on oxydized silicon and monocrystalline sapphire substrates

By electron beam evaporation and RF magnetron sputtering 500 nm thick niobium films were deposited on thermally oxidized Si-(100)-wafers and by RF magnetron sputtering on monocrystalline sapphire-(1-102)-wafers. Investigations by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed differences of the film morphology depending on the substrate used: films deposited on SiO₂ exhibited an even surface with small crystallites, films on sapphire showed parallel surface structures with relatively large and well-shaped crystallites pointing at regular crystal growth influenced by the substrate. These differences in film morphology were also reflected in different reflection intensities of the films in XRD patterns, indicating that the films deposited on sapphire were strongly textured. In a first set of experiments nitridation in molecular nitrogen and ammonia was investigated. In a second set of experiments, it was tried to form oxynitrides of niobium by annealing the nitrided films in molecular oxygen. Particularly by X-ray-diffraction the formation of different nitride and oxide phases in dependence of the reaction temperature was examined. Further, elemental depth profiles were recorded by secondary ion mass spectrometry (SIMS) to track the position of the phases formed in the film. The different substrates led to disparate film reactivities, resulting in different nitridation grades of the films at similar reaction temperatures. In general, larger crystallite sizes resulted in less chemical reactivity of the films: even after nitridation at 1000 °C metallic niobium was still present in films deposited on sapphire. However, no evidence was obtained for the formation of oxynitrides by the process sequence observed.     

Energetically driven reorganization of a modified catalytic surface under reaction conditions

The compositional and structural rearrangements at the catalyst surface during chemical reactions are issues of great importance for understanding and modeling the catalytic processes. Low-energy electron microscopy and photoelectron spectromicroscopy studies of the real-space structure and composition of a Au-modified Rh(110) surface during water formation reveal reorganization processes due to Au mass transport triggered by the propagating reaction fronts. The temporal evolution of the surface reaction results in a 'patterned' surface consisting of separated Au-rich and Au-poor phases with different oxygen coverage, Rh surface structure, and reactivity. The experimental results are complemented by ab initio electronic-structure calculations of the O and Au adsorption phases, which demonstrate that the reorganization of the Au adlayer by the propagating reaction fronts is an energetically driven process. Our findings suggest that reaction-induced spatial inhomogeneity in the surface composition and structure is a common feature of metal catalysts modified with adatoms which become mobile under reaction conditions.     

Nitridation of niobium oxide films by rapid thermal processing

The possibility of forming niobium oxynitride through the nitridation of niobium oxide films in molecular nitrogen by rapid thermal processing (RTP) was investigated. Niobium films 200 and 500 nm thick were deposited via sputtering onto Si(100) wafers covered with a thermally grown SiO₂ layer 100 nm thick. These as-deposited films exhibited distinct texture effects. They were processed in two steps using an RTP system. The as-deposited niobium films were first oxidized under an oxygen atmosphere at 450 °C for various periods of time and subsequently nitridated under a nitrogen atmosphere at temperatures ranging from 600 to 1000 °C for 1 min. Investigations of the oxidized films showed that samples where the start of niobium pentoxide formation was detected at the surface and the film bulk still consisted of a substoichiometric NbO_x phase exhibited distinctly lower surface roughness and microcrack densities than samples where complete oxidation of the film to Nb₂O₅ had occurred. The niobium oxide phases formed at the Nb/substrate interface also showed distinct texture. Zones of niobium oxide phases like NbO and NbO₂, which did not exist in the initial oxidized films, were formed during the nitridation. This is attributed to a “snow-plough effect” produced by the diffusion of nitrogen into the film, which pushes the oxygen deeper into the film bulk. These oxide phases, in particular the NbO₂ zone, act as barriers to the in-diffusion of nitrogen and also inhibit the outdiffusion of oxygen from the SiO₂ substrate layer. Nitridation of the partially oxidized niobium films in molecular nitrogen leads to the formation of various niobium oxide and nitride phases, but no indication of niobium oxynitride formation was found. Figure Schematic representation of the phase distribution in 200 nm Nb film on SiO₂/Si substrate after two steps annealing using an RTP system. The plot below represents the SIMS depth profiles of the nitridated sample with the phase assignment     

Model reaction studies on vanadium oxide nanostructures on Pd(111)

Deuterium desorption and reaction between deuterium and oxygen to water has been studied on ultrathin vanadium oxide structures prepared on Pd(111). The palladium sample was part of a permeation source, thus enabling the supply of atomic deuterium to the sample surface via the bulk. Different vanadium oxide films have been prepared by e-beam evaporation in UHV under oxygen atmosphere. The structure of these films was determined using low energy electron diffraction and scanning tunneling microscopy. The mean translational energy of the desorption and reaction products has been measured with a time-of-flight spectrometer. The most stable phases for monolayer and submonolayer VOx are particular surface-V2O3 and VO phases at 523 and 700 K, respectively. Thicker films grow in the form of bulk V2O3. The mean translational energy of the desorbing deuterium species corresponds in all cases to the thermalized value. Apparent deviations from this energy distribution could be attributed to different adsorption/desorption and/or accommodation behaviors of molecular deuterium from the gas phase on the individual vanadium oxide films. The water reaction product shows a slightly hyperthermal mean translational energy, suggesting that higher energetic permeating deuterium contributes with higher probability to the water formation.     

Nitridation of Niobium Pentoxide Films in Ammonia by Rapid Thermal Processing

The feasibility of niobium oxynitride formation through nitridation of niobium pentoxide films in ammonia by rapid thermal processing (RTP) was investigated. Niobium films 200 and 500 nm thick were deposited by sputtering on Si(100) wafers covered by a 100 nm thick thermally grown SiO₂ layer. These as‐deposited films exhibited distinct texture effects. They were processed in three steps using an RTP system. The as‐deposited niobium films were first nitridated in an ammonia atmosphere at 1000 °C for 1 min and then oxidised in molecular oxygen at temperatures ranging from 400 to 600 °C. Those samples in which a single Nb₂O₅ phase was determined after oxidation were additionally nitridated in ammonia at 1000 °C for 1 min. Investigations show that surface roughness of the samples after oxidation of niobium films first nitridated in ammonia is lower than after direct oxidation of as‐deposited films in oxygen, although the niobium pentoxide phase formed after annealing was the same in both cases. We explain this result as being due to the large expansion of the niobium lattice during the direct oxidation of the niobium film in molecular oxygen and also to the high oxidation rate of the as‐deposited niobium film in oxygen. By incorporation of oxygen in the crystal lattice of niobium and rapid formation of niobium pentoxide, substantial intrinsic stress was built up in the film, frequently resulting in delamination of the film from the substrate. Nitrogen hinders the diffusion of oxygen in nitridated films, which leads to a decrease of the oxidation rate and thus slower formation of Nb₂O₅. Nitridation of the completely oxidised niobium films in ammonia leads to the formation of niobium oxynitride and niobium nitride phases.     

苯乙烯在Ag(111)和Ag(110)表面环氧化反应结构敏感性的理论研究

采用密度泛函理论(DFT)对苯乙烯在Ag(110)表面和Ag(111)表面的环氧化反应进行了计算研究. 经计算, 在Ag(110)表面预吸附氧原子更易吸附在3 重穴位(3h), 吸附能为-3.59 eV; 在Ag(111)表面预吸附氧原子的最稳定吸附位是fcc 位, 吸附能为-3.69 eV. 苯乙烯的环氧化反应过程首先经过一个金属中间体, 然后再进一步反应变为产物, 其中经过直链中间体较支链中间体更加有利. Ag(110)面的反应活化能一般大于Ag(111)面的, 并且微观动力学模拟结果表明, Ag(111)表面生成环氧苯乙烷的选择性要明显高于Ag(110)表面(0.38 与 0.003), 原因是Ag(111)面环氧化反应活化能小于苯乙醛及燃烧中间体的活化能, 而在Ag(110)上正相反.     

Influence of stoichiometry and charge state on the structure and reactivity of cobalt oxide clusters with CO

Cationic and anionic cobalt oxide clusters, generated by laser vaporization, were studied using guided-ion-beam mass spectrometry to obtain insight into their structure and reactivity with carbon monoxide. Anionic clusters having the stoichiometries Co2O3(-), Co2O5(-), Co3O5(-) and Co3O6(-) were found to exhibit dominant products corresponding to the transfer of a single oxygen atom to CO, indicating the formation of CO 2. Cationic clusters, in contrast, displayed products resulting from the adsorption of CO onto the cluster accompanied by the loss of either molecular O 2 or cobalt oxide units. In addition, collision induced dissociation experiments were conducted with N 2 and inert xenon gas for the anionic clusters, and xenon gas for the cationic clusters. It was found that cationic clusters fragment preferentially through the loss of molecular O 2 whereas anionic clusters tend to lose both atomic oxygen and cobalt oxide units. To further analyze how stoichiometry and ionic charge state influence the structure of cobalt oxide clusters and their reactivity with CO, first principles theoretical electronic structure studies within the density functional theory framework were performed. The calculations show that the enhanced reactivity of specific anionic cobalt oxides with CO is due to their relatively low atomic oxygen dissociation energy which makes the oxidation of CO energetically favorable. For cationic cobalt oxide clusters, in contrast, the oxygen dissociation energies are calculated to be even lower than for the anionic species. However, in the cationic clusters, oxygen is calculated to bind preferentially in a less activated molecular O 2 form. Furthermore, the CO adsorption energy is calculated to be larger for cationic clusters than for anionic species. Therefore, the experimentally observed displacement of weakly bound O 2 units through the exothermic adsorption of CO onto positively charged cobalt oxides is energetically favorable. Our joint experimental and theoretical findings indicate that positively charged sites in bulk-phase cobalt oxides may serve to bind CO to the catalyst surface and specific negatively charged sites provide the activated oxygen which leads to the formation of CO 2. These results provide molecular level insight into how size, stoichiometry, and ionic charge state influence the oxidation of CO in the presence of cobalt oxides, an important reaction for environmental pollution abatement.     

Adsorption state and morphology of anthraquinone-2-carboxylic acid deposited from solution onto the atomically-smooth native oxide surface of Al(111) films studied by infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy.

The adsorption state and morphology of anthraquinone-2-carboxylic acid (AQ-2-COOH) deposited from acetone solutions (0.02 - 1.00 mg ml(-1)) onto atomically-smooth native oxide surfaces of Al(111) films were investigated by infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. The atomically-smooth oxide surfaces were prepared by vacuum evaporation of Al on mica substrates at 350 degrees C, followed by oxidation in an oxygen-dc glow discharge at room temperature. It was found that AQ-2-COOH is adsorbed on the film surfaces in both the neutral and ionized state, where the amount of the neutral molecules increases with increasing concentration. This molecule is adsorbed as both a uniform nanometer-scale film, and as micrometer-sized particles with heights ranging from 10 to 200 nm above the film surface. The volumes of the particles of deposited AQ-2-COOH increased with increasing concentration. It is concluded that the particles are microcrystallites of neutral AQ-2-COOH and that the thin uniform film results from AQ-2-COOH anion formation on the film surfaces. A comparison of the results obtained by use of these surface analytical techniques clearly shows the features and advantages of these tools.     

纳米金催化一氧化碳氧化反应的理论研究

近年来,纳米金催化剂独特的催化性质,特别是其优异的低温催化氧化活性,引起了人们极大的研究热情.除低温选择氧化外,在精细化学品合成、大气污染物消除、氢能的转换和利用等领域也开发出了一系列有广泛应用前景的金催化反应.此外,体相金的化学惰性和纳米金的超高活性之间差异的“鸿沟”也引起了理论工作者浓厚兴趣,试图从原理上理解体相金和纳米金活性差异的根源. CO催化氧化是最具有代表性的研究金催化活性的化学反应,本文主要综述了近十多年来金催化 CO氧化反应理论计算方面的研究工作.一般认为, CO在纳米金表面的吸附是 CO氧化反应的初始步骤.密度泛函理论研究表明, CO在金表面的吸附强度主要与被吸附金原子的配位数有关：金配位数越低, CO的吸附能越强,部分研究结果表明两者之间存在近似的线性关系.我们研究发现, CO吸附强度也与被吸附金周围配位金原子的相对位置有关,其中位于正下方的配位金原子加强 CO吸附,而位于侧位的配位金原子则弱化 CO吸附,这显然削弱了 CO吸附与金配位数线性关系的可靠性.理论研究表明,在纯金表
　　面上 O2吸附强度一般很弱,只有在一些特殊结构的金团簇上才有较强的吸附,但在 Au/TiO2界面及 CeO2表面上 O2吸附较强.金表面原子氧的吸附和金的表面结构有关.我们发现,原子氧倾向于在金的表面形成一种线性的 O–Au–O结构以增加其稳定性.当金表面的氧覆盖度增大时,会形成一种金氧化物薄膜结构,其结构依赖于氧的化学势和金的表面结构.纳米金催化 CO氧化反应机理可能因体系、载体等的差异而不同.大部分理论计算结果表明,在纯金表面上 O2很难直接解离形成原子氧,因此反应机理可能是吸附的 CO先与 O2反应形成了一种 CO–O2中间体,然后解离形成 CO2.在 Au/TiO2和 Au/CeO2催化剂上 CO催化氧化机理争议很大,均有计算结果支持 LH机理和 M–vK机理.另外,根据实验上观察到了负载型纳米金能直接活化分子氧的结果,理论上也提出了分子氧先解离为原子氧再与 CO反应的氧解离机理.针对如何解离分子氧问题,人们分别提出了低配位金模型、正方形金结构模型、Ti5c模型及 Au/Ti5c模型等.我们也提出了一种独特的双直线 O–Au–O模型来理解 Au/TiO2或 Au/CeO2界面解离活化分子氧.理论计算结果表明,低配位的金,金和载体之间的电荷转移,以及金所表现出的强相对论效应对于纳米金的活性影响很大.需要特别指出的是,金的强相对论效应有助于理解金表面的 CO吸附与金配位的关系、金表面原子氧的吸附特性、金氧化物薄膜的结构和分子氧的活化等过程.我们认为,金的强相对论作用导致了体相金的化学惰性以及纳米金的活性,因此相对论效应的深入研究将有助于理解金催化 CO氧化反应机理,从而有助于深层次理解纳米金催化活性来源.     

Carbon Monoxide Oxidation on Metal‐Supported Monolayer Oxide Films: Establishing Which Interface is Active

Ultrathin (monolayer) films of transition metal oxides grown on metal substrates have recently received considerable attention as promising catalytic materials, in particular for low‐temperature CO oxidation. The reaction rate on such systems often increases when the film only partially covers the support, and the effect is commonly attributed to the formation of active sites at the metal/oxide boundary. By studying the structure and reactivity of FeO(111) films on Pt(111), it is shown that, independent of the film coverage, CO oxidation takes place at the interface between reduced and oxidized phases in the oxide film formed under reaction conditions. The promotional role of a metal support is to ease formation of the reduced phase by reaction between CO adsorbed on metal and oxygen at the oxide island edge.     

热辅助存储磁盘硅掺杂非晶碳薄膜氧化的ReaxFF反应力场分子动力学模拟

Heat-assisted magnetic recording (HAMR) is one of the promising ways to extend the magnetic recording area density to 1 Tb·in^-2 in hard disk drives (HDDs).High temperature induced by laser heating can cause carbon overcoat (COC) oxidation.Reactive molecular dynamics (MD) simulations are performed to investigate the oxidation process of silicon-doped amorphous carbon (a-C:Si) films for HAMR application.The atomic details of the structure evolution and oxidation process are investigated, and, the oxidation mechanism of the a-C:Si film is clarified.The effect of the duration of laser irradiation on the oxidation of the a-C:Si film is investigated.The oxidation occurs during heating and the beginning of cooling process.Both volume expansion during heating process and cluster of carbon atoms during cooling process increase the rate of sp² carbon.Because of the decrease in the amount of unsaturated silicon atoms and low diffusion coefficient of atomic oxygen, the oxidation rate of the a-C:Si film decreases with laser irradiation cycles.The molecular oxygen is the oxidant due to surface defect of a-C:Si film.The atomic strains break the O-O bonds in Si-O-O-Si linkages and rearrange the surface oxide layers, and process the oxidation of the a-C:Si film.     

Epitaxial growth of pentacene films on Cu110

The molecular structure of thin pentacene (C(22)H(14)) films grown on a Cu(110) surface has been studied by means of He atom scattering, low energy electron diffraction, thermal desorption spectroscopy, x-ray photoelectron spectroscopy, and x-ray absorption spectroscopy. Depending on the actual film thickness three different crystalline phases have been identified which reveal a characteristic reorientation of the molecular plane relative to the substrate surface. In the monolayer regime the molecules form a highly ordered commensurate (6.5x2) structure with a planar adsorption geometry. For thin multilayers (thickness <2 nm) a second phase is observed which is characterized by a lateral ((-0.65 5.69) ( 1.90 1.37)) structure and a tilting of the molecular plane of about 28 degrees around their long axis which remains parallel to the surface. Finally, when exceeding a thickness of about 2 nm subsequent growth proceeds with an upright molecular orientation and leads to the formation of crystalline films which are epitaxially oriented with respect to the substrate. The present study thus demonstrates that also on metal substrates highly ordered pentacene films with an upright orientation of the molecular planes can be grown. Photoelectron spectroscopy data indicate further that thick films do not grow in a layer-by-layer mode but reveal a significant degree of roughness.     

含氮磷酸锂薄膜在空气中的稳定性

利用射频(RF)磁控溅射方法制备了含氮磷酸锂(LiPON)薄膜. 采用SEM、XRD、XPS等技术以及交流阻抗法和电位线性扫描法, 研究了空气湿度对LiPON薄膜形貌、组成和性能的影响. 结果表明, LiPON薄膜在湿度为40%的空气环境中放置24 h后, 将发生明显的水解反应, 使LiPON薄膜表面形貌变得疏松、局部突起; PH3和NH3的产生, 使薄膜中磷元素和氮元素含量减少, 而Li2CO3的生成, 则使薄膜中碳元素和氧元素含量有明显的增加. LiPON电解质薄膜形貌和组成的变化, 造成了薄膜电化学性能的严重恶化.