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Simulation based on Knudsen's law shows that film thickness uniformity above 99% can be realized on spherical substrates with optimized profiles of shadowing masks. However, a type of optical thickness nonuniformity is revealed when the masks are applied for thickness correction of MgF

Manipulation of artificial molecular rotors/motors is a key issue in the field of molecular nanomachines. Here we assemble non-planar SnPc molecules on an FeO film to form two kinds of rotors with different apparent morphologies, rotational speeds and stabilities. Both kinds of rotors can switch to each other

Monolayer and few layer antimony allotropes fabricated on oxide layers are essential for practical applications in fields of solar cells, electronic and photonic devices. Here the antimony structural phases are systemically studied on corrugated copper oxide of Cu(111) by atomically-resolved scanning tunneling microscopy (STM). We find that initial deposition of Sb atoms causes the structural changes of the underlying oxide layer and sequentially gives rise to the formation of flat (√7 × √7)-Sb and buckled antimonene phases. Finally, a nanoring-like antimony configuration is observed with triangle-shaped atomic arrays closely packing and shows high stabilities for oxygen exposure. The (√7 × √7) phase exhibits the metallic property with energetically continuous electronic states existing near Fermi level. For the antimonene and nanoring phases, band gap signatures are observed, implying the semiconducting features. Our results provide a method for fabricating stable elemental allotropes on oxide surfaces.

Significant work function changes from bare Pt(111) surface to 1 monolayer and 2 monolayers of ultrathin iron oxide (FeO) films on it are investigated by means of scanning tunneling microscopy/spectroscopy (STM/STS). With FeO layer-by-layer growth, a continuous reduction of the work function along with the surface vacuum level (VL) shifting is observed. We found that the compression of the electron spill-out at the metal-oxide interface and the substantial reconstruction of 2 ML FeO film, respectively, make major contributions to the first and the second reductions of the work function. The rectifying effect in FeO films is also observed, which is attributed to the downward shift of band alignment imposed by the total change in surface dipole. Our work shows that the polar oxide films play an important role to adjust surface electronic structures for enhancing device functionality.

Antimony nanostructures fabricated on metal oxide layers are essential for practical applications in fields of solar cells, electronic and photonic devices. Here the antimony phases were systemically studied on the copper oxide of Cu(110). By high-resolution scanning tunneling microscopy (STM), we revealed that a wrinkled antimony phase was formed on the CuO surface regardless of the initial oxide structure. It exhibited an armchair-like configuration making up of protruded and dipped Sb atoms as confirmed by STM and density functional theory calculations. Further Sb deposition caused the armchair-like phase distorting and subsequently gave rise to formation of a c(2 × 2)-Sb phase. Finally, another kind of wrinkled phase was successfully fabricated. It consisted of two zigzagged antimony chains with protruded and dipped Sb atoms alternately distributing. By analysis of the atomically-resolved STM topographies, several kinds of dislocations have been observed and the corresponding geometric models are addressed. The armchair and zigzag phases both exhibited high stabilities for oxygen exposure. Conductance measurements imply that each phase interacts with the underlying layer. Our results might provide a way for fabricating stable ultrathin materials with a well-defined edge structure on oxide surfaces.

Scanning tunneling microscopy at low temperature and low molecular coverage (∼1%) was combined with density-functional theory calculations to investigate the adsorption of isolated perylene-3,4,9,10-tetracarboxyl acid dianhydride (PTCDA) molecules on KCl(100) surfaces. Experimentally, we used epitaxial thin KCl(100) films on Ag(100) of about 3 layers in thickness. After deposition at 100 K, the PTCDA molecules are statistically distributed on the terraces with an azimuthal orientation of the long axis along the polar ⟨110⟩ orientation. After annealing at about 150 to 200 K the molecules are exclusively found at step-edge sites. Thereby, several configurations are observed, the most typical being a site where the PTCDA molecules protrude into the step edge, forming vacancies at the step edge. The total-energy calculations predict this step-edge adsorption site to be energetically favorable compared to the adsorption on terraces. The corrugation of the calculated potential energy surface is below 1 eV, with...

Bias-dependent features of the insulating NaCl layer grown on Cu(001) have been investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The apparent layer thickness of the NaCl film is variable at bias voltages ranging from 2.8 to 3.2 V as well as from 4.0 to 5.0 V. and the Moire pattern induced by NaCl-Cu lattice mismatch also shows bias dependence. The z-V (dz/dV-V) curves and dl/dV mapping measurements reveal that the resonant tunneling between the image potential states (IPSs) on Cu(001) and the Fermi level of the STM tip leads to drastic variations of these features. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.

Molecular rotors, motors and gears play important roles in artificial molecular machines, in which rotor and motor matrices are highly desirable for large-scale bottom-up fabrication of molecular machines. Here we demonstrate the fabrication of a highly ordered molecular rotor matrix by depositing nonplanar dipolar titanyl phthalocyanine (TiOPc, C32H16N8OTi) molecules on a Moire patterned dipolar FeO/Pt(111) substrate. TiOPc molecules with O atoms pointing outwards from the substrate (upward) or towards the substrate (downward) are alternatively adsorbed on the fcc sites by strong lateral confinement. The adsorbed molecules, i.e. two kinds of molecular rotors, show different scanning tunneling microscopy images, thermal stabilities and rotational characteristics. Density functional theory calculations clarify that TiOPc molecules anchoring upwards with high adsorption energies correspond to low-rotational-rate rotors, while those anchoring downwards with low adsorption energies correspond to high-rotational-rate rotors. A robust rotor matrix fully occupied by low-rate rotors is fabricated by depositing molecules on the substrate at elevated temperature. Such a paradigm opens up a promising route to fabricate functional molecular rotor matrices, driven motor matrices and even gear groups on solid substrates.

The adsorption and electronic properties of isolated cobalt phthalocyanine (CoPc) molecule on an ultrathin layer of NaCl have been investigated. High-resolution STM images give a detailed picture of the lowest unoccupied molecular orbital (LUMO) of an isolated CoPc. It is shown that the NaCl ultrathin layer efficiently decouples the interaction of the molecules from the underneath metal substrate, which makes it an ideal substrate for studying the properties of single molecules. Moreover, strong dependence of the appearance of the molecules on the sample bias in the region of relatively high bias (>3.1 V) is ascribed to the image potential states (IPSs) of NaCl/Cu(100), which may provide us with a possible method to fabricate quantum storage devices.

To observe molecular orbitals using scanning tunneling microscopy, well-ordered oxidized layers on Cu(001) were fabricated to screen the individual adsorbed cobalt phthalocyanine (CoPc) molecules from the electronic influence of the metal surface. Scanning tunneling microscope images of the molecule on this oxidized layer show similarities to the orbital distribution of the free molecule. The good match between the differential conductance mapping images and the calculated charge distribution at energy levels corresponding to the frontier orbitals of CoPc provides more evidence of the screening of the oxidized layer from interactions between the metal surface and supported molecules. (C) 2012 Elsevier B.V. Elsevier All rights reserved.

The morphologies, self-assembly structures, and stability of cobalt-phthalocyanines (CoPc) molecules adsorbed on Cu(001) with coverage ranging from 0.2 monolayer (ML) to 1.6 ML are investigated by ultrahigh-vacuum low-temperature scanning tunneling microscopy (UHV LT-STM) at liquid nitrogen temperature. Upon increasing the deposition of CoPc molecules various structures, such as isolated adsorption, quasi-hexagonal structure, square root(29) x square root(29) structure, are well characterized by the corresponding high-resolution STM images. The CoPc-CoPc intermolecular interaction and CoPc-substrate interfacial interaction dominate the structural evolutions. For the coverage higher than 1 ML, CoPc molecules preferentially locate on top of the molecules underneath and organize into square root(58) x square root(58) structure. As more and more CoPc molecules adsorb on the first layer, in some square root(58) x square root(58) regions molecular insertion leads to the formation of the square root(29) x square root(29) domain to effectively decrease the energy of the whole system.

Tailoring of the assembly structure of organic molecular monolayer is of great importance to improve the performance of molecular devices. In this work, a typical ionic compound, namely KCl, was used to mediate the rearrangement of 3, 4, 9, 10-perylene tetracarboxylic dianhydride (PTCDA) monolayer on Ag(100). Combined scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) results indicate that both molecule and molecular superlattice would rotate after the dosing of KCl. The density functional theory calculation shows that KCl would exist in the form of molecules rather than ions on Ag(100) and demonstrates that experimentally observed structural transition induced by KCl molecules is energetically favored.

Molecular orientations and assembled structures of C-60 molecules on Pt(111) have been characterized by low-temperature scanning tunneling microscopy for coverage between 0.1 ML and 1.5 ML. At room temperature, C-60 molecules preferentially decorate the steps and nucleate into single layer islands (SLIs) with hexagonal close-packed structures upon increasing coverage. C-60 islands comprise two differently oriented C-60/Pt(111)-(root 13 x root 13) R13.9 degrees phases, in which five types of molecular orientation of C-60 carbon cage configurations are clearly identified by the high-resolution scanning tunneling microscopy image. Further annealing treatment leads to more uniform molecular orientation without apparent aggregation of C-60 SLIs. As coverage increases above 1 ML, domains corresponding to (2 root 3 x 2 root 3) R30 degrees. superstructure appear. To explain the above transformation, an interfacial reconstruction model is proposed according to the detailed study of the molecular adsorption structures in different domains. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3530289]

Adsorption of NH3 molecules on Si(111)-(7 × 7) has been studied by scanning tunneling microscopy. We find that the dissociative adsorption is site-selective and exhibits two adsorption structures resulting from different reaction channels: [Formula: see text] and [Formula: see text]. To explain the dissociation processes, an adsorption model for these reactions is given. Furthermore, the evolution of the local electronic structures is investigated by means of atomically resolved scanning tunneling spectroscopy to clarify the effect of different fragments on the surface states. Finally, we discuss the adsorption position of H atoms from the NH3 dissociation.