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CO and H2 activation over g-ZnO layers and w-ZnO(0001)
摘要： Graphene-like ZnO (g-ZnO) nanostructures (NSs) and thin films were prepared on Au(111) and their reactivities towards CO and H2 were compared with that of wurtzite ZnO (w-ZnO) (0001) single crystal. The interaction and reaction between CO/H2 and the different types of ZnO surfaces were studied using near-ambient-pressure scanning tunneling microscopy (NAP-STM), X-ray photoelectron spectroscopy (XPS) and Density functional theory (DFT) calculations. The reactivity of the w-ZnO(0001) surface towards CO and H2 was found to be more prominent than those on the surfaces of g-ZnO/Au(111). CO oxidation took place primarily at the edge sites of w-ZnO(0001) and the interface between g-ZnO NSs and Au(111), while g-ZnO thin films on Au(111) appeared inert at below 600 K. Similarly, the w-ZnO(0001) surface could dissociate H2 at 300 K, accompanied by a substantial surface reconstruction, while g-ZnO on Au(111) appeared inert for H2 activation at 300 K. DFT calculations showed that the reactivities of ZnO surfaces towards CO could be related to the formation energy of oxygen vacancy (EOvf), which could be related to the charge transfer to lattice oxygen atoms or surface polarity.
关键词： CO oxidation,NAP-STM,ZnO,XPS,surface polarity,oxygen vacancy
更新于2025-09-23 15:23:52
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Mechanism of field-induced manipulation of Cu-phthalocyanines on a Bi surface using scanning tunneling microscope
摘要： We have revisited our hypothesis [K. Nagaoka et al., Jpn. J. Appl. Phys. 57 (2018) 020301] regarding the control of the motion and assembly of copper phthalocyanine (CuPc) molecules on a Bi(001) surface using a scanning tunneling microscope (STM) tip. The proposal that the observed diffusion and condensation are not due to the adsorption/desorption of molecules via the tip by applying a bias voltage was investigated for field-induced manipulation. Our experiments show that CuPc cannot move across steps or condense on different terraces on the Bi(001) surface. When confined to a nano-scale region, the CuPc molecules assemble into ordered single-layer islands. The island position can be manipulated using the STM tip, with an almost constant number of condensed molecules remaining inside the terrace. These results allowed us to rule out the possibility of picking-up and depositing molecules by the STM tip.
关键词： STM,phthalocyanine,self-assembly,field-induced manipulation,bismuth,surface science
更新于2025-09-23 15:23:52
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Defect-associated adsorption of monoethanolamine on TiO2(1 1 0): An alternative way to control the work function of oxide electrode
摘要： Controlling defects is one of the basic strategies for tailoring electronic structure of materials, which has not been explored that much yet for organic-inorganic hybrid systems. In this study, we investigated the control of work function of oxide electrode by defect-associated adsorption of molecules at the single-molecule level by means of scanning tunneling microscopy and first principle calculations. The equilibrium adsorption configuration of monoethanolamine (MEA, HO(CH2)2NH2), an effective coating for lowering the work function of an oxide electrode, varies as a function of surface coverage at TiO2(1 1 0) surfaces. Our results showed that defects at the oxide surface and intermolecular interactions dominate the stable configuration of adsorbates as well as work function of the system. The dissociative adsorption at Ov was found to be more efficient at lowering the work function of TiO2(1 1 0) surface, suggesting that defect control can be used to improve the performance of organic-inorganic hybrid systems.
关键词： STM,Work function,DFT,TiO2(1 1 0),Defect,Monoethanolamine
更新于2025-09-23 15:21:21
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Potassium-Promoted Reduction of Cu <sub/>2</sub> O/Cu(111) by CO
摘要： In situ X-ray photoelectron spectroscopy (XPS), infrared reflection absorption spectroscopy (IRRAS) and scanning tunneling microscopy (STM) were used to study the reduction of Potassium-modified Cu2O/Cu(111) by CO. By following the time evolution of the O 1s peak of Cu2O, we determined that the apparent activation energy for Cu2O reduction by 2 × 10-4 Torr CO is decreased by ~30% in the presence of K. On the K-modified surface, both XPS and IRRAS data show the formation of a surface species identified by IRRAS as carbonate (CO3 2-), likely forming a K+-CO3 2- complex, which is stable up to 500 K. STM images show that K+-CO3 2- complexes form chains around reduced Cu islands, thereby hindering the mass transfer of Cu atoms and preventing the reconstruction of the surface. Theoretical calculations show that the formation of carbonate on the K-modified ‘44’ Cu2O structure is thermodynamically favorable compared to the formation of CO2 on either the bare or K-modified surfaces.
关键词： STM,XPS,copper,catalysis,IRRAS,alkali promoter
更新于2025-09-23 15:21:21
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Imaging empty states on the Ge(100) surface at 12 K
摘要： Our understanding of bias-dependent scanning-tunneling-microscopy (STM) images is complicated not only by the multiplicity of the surface electronic structure, but also the manifold tunneling effects in probing semiconductor surfaces having directional dangling- and covalent-bond orbitals. Here we present a re?ned interpretation of empty-state STM images from the model semiconductor surface, Ge(100), on the basis of measurements at low temperature (12 K) combined with density-functional-theory calculations. In the lower-bias regime ((cid:2)1.6 V), the electron tunneling is found to occur predominantly in antibonding dangling-bond or/and dimer-bond states (π ? 2 , and σ ?) of Ge(100) at the surface-parallel wave vector k(cid:3) = 0, leading to the tunneling current maxima located directly on the dimer rows. At higher biases (e.g., at 2 V), the current maxima are shifted to the position in the troughs between the dimer rows, because the tunneling occurs ef?ciently in the π ? 2 states at k(cid:3) (cid:4)= 0 associated with the dimer-up atoms of two adjacent dimer rows, i.e., because of increased sideways tunneling. Thus, the empty-state STM images of Ge(100), albeit strongly bias-dependent, re?ect the dimer arrangement rather than the backbonds and surface resonances at all experimental conditions used. The results are also discussed in comparison with the counterpart system of Si(100).
关键词： STM,density-functional-theory,Ge(100),tunneling,semiconductor surfaces
更新于2025-09-23 15:21:01
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Redox Properties of Cu <sub/>2</sub> O(100) and (111) Surfaces
摘要： Intense research efforts are directed towards Cu and Cu2O based catalysts as they are viewed as potential replacements for noble metal catalysts. However, applications are hampered by deactivation, e.g. through facile complete oxidation to CuO. Despite the importance of the redox processes for Cu2O catalysts a molecular level understanding of the deactivation process is still lacking. Here we study the initial stages of oxidization of well-defined Cu2O bulk single crystals of (100) and (111) termination by means of synchrotron radiation X-ray photoemission spectroscopy (XPS) and scanning tunneling microscopy (STM). Exposure of the (100) surface to 1 mbar O2 at 25 ℃ result in formation of a 1.0 monolayers (ML) CuO surface oxide. The surface is covered by 0.7 ML OH groups from trace moisture in the reaction gas. In contrast, neither hydroxylation nor oxidation was observed on the (111) surface under similar mild exposure conditions. On Cu2O(111) the initial formation of CuO requires annealing to ～400 ℃ in 1 mbar O2, highlighting the marked different reactivity of the two Cu2O surfaces. Annealing of the (100) surface, under ultrahigh vacuum conditions, to temperatures up to ～225 ℃ resulted in removal of the OH groups (0.46 ML decrease) at a rate similar to a detected increase in CuO coverage (0.45 ML increase), suggesting the reaction path 2OHadsorbed + Cu2Osolid → H2Ogas + 2CuOsolid. STM was used to correlate the observed changes in surface chemistry with surface morphology, confirming the surface hydroxylation and CuO formation. The STM analysis showed dramatic changes in surface morphology demonstrating a high mobility of the active species under reaction conditions.
关键词： XPS,surface oxidation,redox properties,hydroxylation,STM,Cu2O
更新于2025-09-23 15:21:01
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Study on Formation Process and Models of Linear Fe Cluster Structure on a Si(111)-7 × 7-CH3OH Surface
摘要： STM results showed that Fe atoms were deposited on a Si(111)-7 × 7 reconstructed surface, which was saturated with CH3OH molecules. Fe atomic linear structure was composed of stable clusters and in-situ observed by the scanning tunneling microscopy (STM). The aim to improve its application of magnetic memory material, both formation process and models, has been explored in this paper. By combining surface images and mass spectrometer data, an intermediate layer model was established. In terms of thermal stability, the most favorable adsorption sites of CH3OH were further explored. After that, Fe atoms were deposited on the Si(111)-7 × 7-CH3OH surface, forming a linear cluster structure. On the one hand, a new Fe cluster model was put forward in this paper, which was established with height measurement and 3D surface display technology. This model is also affected by the evaporation temperature, which can be consistent with the atomic stacking pattern of face centered cubic structures. On the other hand, the slight height change suggested the stability of linear structures. Even in the condition of thin air introduction, Fe cluster showed a good performance, which suggested the possibility of magnetic memory application in the future. These investigations are believed to have, to a certain extent, increased the probability of forming Fe linear clusters on the surface of silicon substrate, especially according to the models and surface technology we adjusted.
关键词： cluster,CH3OH,STM,linear structure,evaporation
更新于2025-09-23 15:21:01
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Study on Photoemission and Tunneling in Light - Modulated Scanning Tunneling Microscopy
摘要： We propose the utilization of a light-modulated scanning tunneling microscope (LM-STM) to study the plasmon-enhanced photoemission and tunneling effect between metal tip and Au nanostructures on conductive substrate. The periodic Au nanorods are fabricated by electron beam lithography (EBL) and the topography is imaged using atom force microscopy (AFM) and STM. With irradiation of continuous lasers at 532 and 805 nm, the performance of electron tunneling emission is measured under STM’s ramp mode. We show that, by exciting localized surface plasmon resonances (LSPRs), a tiny laser intensity of around 1 W/cm2 along with a bias voltage less than 50 mV can activate a significantly enhanced tunneling current. This method has the potential for analyzing electron energy states and transport characteristics of surface plasmon.
关键词： plasmonics,Au nanostructures,tunneling,photoemission,STM
更新于2025-09-23 15:21:01
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Single Photon Emission from a Plasmonic Light Source Driven by a Local Field-Induced Coulomb Blockade
摘要： A hallmark of quantum control is the ability to manipulate quantum emission at the nanoscale. Through scanning tunneling microscopy induced luminescence (STML) we are able to generate plasmonic light originating from inelastic tunneling processes that occur in the vacuum between a tip and a few-nanometer thick molecular film of C60 deposited on Ag(111). Single photon emission, not of molecular excitonic origin, occurs with a 1/e recovery time of a tenth of a nanosecond or less, as shown through Hanbury Brown and Twiss photon intensity interferometry. Tight-binding calculations of the electronic structure for the combined Ag-C60-tip system results in good agreement with experiment. The tunneling happens through electric field induced split-off states below the C60 LUMO band, which leads to a Coulomb blockade effect and single photon emission. The use of split-off states is shown to be a general technique that has special relevance for narrowband materials with a large bandgap.
关键词： STM induced luminescence,antibunching,Coulomb blockade,plasmon,split-off states
更新于2025-09-23 15:19:57
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Influence of the support on stabilizing local defects in strained monolayer oxide films
摘要： Two-dimensional materials with a honeycomb lattice, such as graphene and hexagonal boron nitride, often contain local defects in which the hexagonal elements are replaced by four, five, seven, and eight-membered rings. An example is the Stone-Wales (S-W) defect, where a bond rotation causes four hexagons to be transformed into a cluster of two pentagons and two heptagons. A further series of similar defects incorporating divacancies results in larger structures of non-hexagonal elements. In this paper, we use scanning tunneling microscopy (STM) and density functional theory (DFT) modeling to investigate the structure and energetics of S-W and divacancy defects in a honeycomb (2 × 2) Ti2O3 monolayer grown on an Au(111) substrate. The epitaxial rumpled Ti2O3 monolayer is pseudomorphic and in a state of elastic compression. As a consequence, divacancy defects, which induce tension in freestanding films, relieve the compression in the epitaxial Ti2O3 monolayer and therefore have significantly lower energies when compared with their freestanding counterparts. We find that at the divacancy defect sites there is a local reduction of the charge transfer between the film and the substrate, the rumpling is reduced, and the film has an increased separation from the substrate. Our results demonstrate the capacity of the substrate to significantly influence the energetics, and hence favor vacancy-type defects, in compressively strained 2D materials. This approach could be applied more broadly, for example to tensile monolayers, where vacancy-type defects would be rare and interstitial-type defects might be favored.
关键词： elastic strain,local structural defects,monolayers,scanning tunneling microscopy (STM),density functional theory (DFT),two-dimensional materials,ultrathin oxide films
更新于2025-09-19 17:15:36