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Self-assembled Ag(111) nanostructures induced by Fermi surface nesting
摘要： Scanning tunneling microscopy measurements on Ag(111)/MoS2 reveal atomically ?at preferred, or “magic,” heights occurring at 6, 10, and 14 atomic layers. These results are consistent with Ag growth on a variety of semiconducting substrates and correlate with electronic energy savings in electronic structure calculations of freestanding Ag(111) ?lms. Thus, under certain conditions, Ag will spontaneously form quantized structures independent of the substrate. To explain this, we have found Fermi surface nesting vectors in the bulk Ag band structure which account for these results and the fact Ag that is gapped along the surface normal. This model extends to a range of metallic systems which exhibit electronic con?nement, epitaxial growth, and minimal strain. As with Au/MoS2, the Ag/MoS2 system exhibits this behavior at unusually high temperatures so that these principles might be used for control over device features at the nanometer scale under standard fabrication conditions.
关键词： quantum size effects,MoS2,Fermi surface nesting,Ag(111),scanning tunneling microscopy
更新于2025-09-16 10:30:52
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Electrons and Phonons Cooperate in the Laser-Induced Desorption of CO from Pd(111)
摘要： Femtosecond laser induced desorption of CO from a CO-covered Pd(111) surface is investigated with ab initio molecular dynamics with electronic friction that incorporates effects due to the excited electronic and phononic systems, as well as out-of-phase coadsorbate interactions. Our simulations show evidence of an important electron-phonon synergy in promoting CO desorption that has largely been neglected in other similar systems. At the saturated coverage of 0.75 ML, effects due to CO-CO interadsorbate energy exchange are also important. Our dynamics simulations, in concert with site-specific desorption energy calculations, allow us to understand the large coverage dependence of the desorption yields observed in experiments.
关键词： electron-phonon synergy,Pd(111),desorption,femtosecond laser,CO,electronic friction,ab initio molecular dynamics
更新于2025-09-16 10:30:52
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Self-decoupled tetrapodal perylene molecules for luminescence studies of isolated emitters on Au(111)
摘要： Self-decoupled tetrapodal perylene molecules were designed, synthesized, and deposited on the Au(111) surface through the electrospray ionization technique. Photoluminescence and lifetime measurements show that the chromophore groups of the designed molecules are well decoupled from the gold substrate. Preliminary scanning tunneling microscopy induced luminescence measurements indicate the observation of molecule-specific emissions from isolated single tetrapodal perylene molecules adsorbed directly on Au(111). The emergence of significant emission when the tip is positioned at the molecular center suggests that there is a considerable vertical component of the transition dipole of the designed molecule along the tip axial direction. Our results may open up a route for the realization of nanolight sources and plasmonic devices based on organic molecules.
关键词： tetrapodal perylene,Au(111),isolated emitters,self-decoupled,luminescence
更新于2025-09-12 10:27:22
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Terahertz intersubband absorption of GaN/AlGaN step quantum wells grown by MOVPE on Si(111) and Si(110) substrates
摘要： We demonstrate terahertz intersubband absorptions in nitride step quantum wells (SQWs) grown by metal organic vapor phase epitaxy simultaneously on two different substrate orientations [Si(111) and Si(110)]. The structure of the SQWs consists of a 3 nm thick Al0.1Ga0.9N barrier, a 3 nm thick GaN well, and an Al0.05Ga0.95N step barrier with various thicknesses. This structure design has been optimized to approach a ?atband potential in the wells to allow for an intersubband absorption in the terahertz frequency range and to maximize the optical dipole moment. Structural characterizations prove the high quality of the samples. Intersubband absorptions at frequencies of 5.6 THz (k (cid:2) 54 lm), 7 THz (43 lm), and 8.9 THz (34 lm) are observed at 77 K on both substrate orientations. The observed absorption frequencies are in excellent agreement with calculations accounting for the depolarization shift induced by the electron concentration in the wells.
关键词： Si(111),GaN/AlGaN,step quantum wells,intersubband absorption,Si(110),MOVPE,terahertz
更新于2025-09-12 10:27:22
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Formation of Highly Ordered Terminal Alkyne Self-Assembled Monolayers on the Au{111} Surface through Substitution of 1-Decaboranethiolate
摘要： The reaction aimed at completing and closing the open cages of 1-decaboranethiol self-assembled monolayers (SAMs) on Au{111} with 4-phenyl-1-butyne results in highly ordered monolayers of 4-phenyl-1-butyne. The initially disordered 1-decaboranethiolate changed into ordered (√3×√3)R 30° lattices on Au{111} typical of alkyne SAMs, indicating the complete substitution of 1-decaboranethiolate moieties, as determined by nanoscale imaging with scanning tunneling microscopy and X-ray photoelectron spectroscopy. Vibrational spectroscopy results indicate that the process happens gradually and that alkynyl groups are not totally oxidized in the ordered 4-phenyl-1-butyne monolayer.
关键词： Au{111},self-assembled monolayers,vibrational spectroscopy,scanning tunneling microscopy,X-ray photoelectron spectroscopy,4-phenyl-1-butyne,1-decaboranethiol
更新于2025-09-11 14:15:04
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Effects of Gas-Phase Conditions and Particle Size on the Properties of Cu(111)-Supported Zn <sub/>y</sub> O <sub/>x</sub> Particles Revealed by Global Optimisation and Ab Initio Thermodynamics
摘要： The characterisation of the interaction between nano- or sub-nano- particles with a support nowadays increasingly relies on computational modelling by means of the density functional theory calculations. These provide valuable atomic-detail understanding of the structure and energetics of supported clusters, but it is still challenging to find (or design) structural models that are representative of real systems in terms of size, structure, and composition. In this study, we have applied an extensive and systematic approach combining global optimisation based on an evolutionary algorithm with atomistic ab initio thermodynamics for finding stable structures of a relevant material for catalytic methanol synthesis: Cu(111)-supported ZnyOx clusters. We identify the ZnO3 motif as the elementary building block of such clusters, on which we recently have investigated the full catalytic process for methanol synthesis. With the collection of global minima of Cu(111)-supported ZnyOx clusters resulting from this large-scale global optimisation effort, we assess the effect of size, gas-phase conditions, and support interactions on the phase diagrams, reactivity, and structural properties of the ZnyOx particles. We find moderate size-effects that are mostly related to the differences in stable Zn:O ratios of the identified global minima and to the formation of different sites in larger clusters. In contrast, large differences in the oxidation state of the clusters as defined by the gas-phase conditions significantly affect the geometry, electronic structure, and reactivity of the ZnyOx particles. This highlights the importance of thoroughly sampling structures with different stoichiometry and appropriately assessing their stability using a detailed thermodynamics analysis.
关键词： global optimisation,Cu(111)-supported ZnyOx clusters,ab initio thermodynamics,density functional theory,methanol synthesis
更新于2025-09-11 14:15:04
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Au Nanocluster Growth on Graphene Supported on Ni(111)
摘要： Low energy alkali ion scattering is used to investigate the deposition of Au onto a single layer of graphene grown onto Ni(111) by chemical vapor deposition. The yield of 3.0 keV Na+ singly scattered from Au as a function of coverage indicates that it grows in a Volmer-Weber mode forming nanoclusters that increase in size with the amount of deposition. The neutralization probability of the scattered Na+ is high for the smallest clusters and decreases as they increase in size. This is presumably caused by the cluster edge atoms being positively charged combined with the fact that the ratio of edge to center atoms decreases with size, which is similar to the behavior of Au nanoclusters on oxide substrates. In addition, oxygen is intercalated under the graphene film to decouple it from the substrate, but no changes in the growth mode or neutralization probability are observed.
关键词： Au nanoclusters,Ni(111),graphene,Volmer-Weber growth mode,charge transfer,low energy alkali ion scattering
更新于2025-09-11 14:15:04
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Pb phases on Si(111)
摘要： We present here a combined experimental Raman spectroscopy and ab initio theoretical study of the (√3×√3) reconstructed SIC phase of Pb on Si(111) and discuss their relation to the atomic surface structure. The Raman response of the surface localized vibrational modes, in particular, is identified in the low-frequency spectral range (down to 15 cm?1). We demonstrate that Raman spectroscopy is a very powerful approach to test atomic structures of surfaces and a valuable complement to standard surface analytics. While the calculated spectra of H3 and T4 are too similar to allow a discrimination of these phases, the good overall agreement to the measured Raman spectra enables a classification of the observed vibrational modes.
关键词： surface vibrations,Pb/Si(111),atomic structure,ab initio,Raman spectroscopy
更新于2025-09-10 09:29:36
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Formation of a Graphene-Like SiN Layer on the Surface Si(111)
摘要： The kinetics of the formation and thermal decomposition of a two-dimensional SiN-(8 × 8) nitride layer on a Si(111) surface is studied. The SiN-(8 × 8) structure is a metastable intermediate phase formed during the nitridation of silicon before the formation of a stable amorphous Si3N4 phase. Studying the SiN-(8 × 8) structure by scanning tunneling microscopy shows its complex structure: it consists of an adsorption (8/3 × 8/3) phase, with the lateral period 10.2 ?, and a honeycomb structure with a ~6 ? side of a hexagon that is turned 30° with respect the adsorption phase. The band gap of the SiN-(8 × 8) phase is measured and found to be ~2.8 eV, which is smaller compared to the band gap of the β-Si3N4 crystal phase 5.3 eV. The interplanar spacings in the (AlN3)/(SiN)2 structure on the Si(111) surface are measured. The spacings are 3.3 and 2.86 ? in SiN and AlN, respectively. Such interplanar spacings are indicative of weak van der Waals interaction between the layers. A model of the SiN-(8 × 8) structure as a flat graphene-like layer is suggested. The model is consistent with the diffraction and microscopy data.
关键词： nitride layer,van der Waals interaction,Si(111) surface,SiN-(8 × 8),graphene-like
更新于2025-09-10 09:29:36
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Structure and properties of Mn3O4 thin films grown on single crystal substrates by chemical vapor deposition
摘要： Mn3O4 thin films were fabricated on SrTiO3(111) and Y3Al5O12(100) substrates by chemical vapor deposition (CVD) under O2 atmospheres, starting from a fluorinated Mn(II) diketonate-diamine adduct. The obtained systems were investigated by a multi-technique characterization in order to elucidate the interplay between preparation conditions and their chemico-physical properties. The results highlighted the formation of phase-pure and homogeneous a -Mn3O4 (haussmannite) films, characterized by a smooth morphology, an appreciable Vis light absorption and structural features directly dependent on the used substrate. The target systems were uniformly doped with fluorine, due to the used Mn compound acting as a single-source precursor for both Mn and F. In addition, magnetic force microscopy measurements revealed the formation of spin domains and long-range magnetic order in the target materials, paving the way to their future implementation as magnetic media toward device integration for data storage.
关键词： Y3Al5O12(100),SrTiO3(111),Mn3O4 thin films,chemical vapor deposition,magnetic materials
更新于2025-09-10 09:29:36