No abstract

The lateral alignment of [012] habit-modified calcite crystals with respect to a carboxylic acid terminated self-assembled monolayer (SAM) of thiols has been determined. The crystals were grown from a Kitano solution (pH 5.6-6.0), and the samples were investigated with scanning electron microscopy, X-ray diffraction, and polarization microscopy. For the first time, a lattice match in one direction, which is the nearest neighbor direction of the SAM and the calcite <100> direction, has been experimentally shown. The experimental results are in good agreement with the theoretical models proposed in previous work, and it is expected that this method can be applied to similar systems where inorganic crystals nucleate with a preferred orientation to a SAM.

Aligned calcite crystals have been grown in an hexagonal arrangement (see Figure) using highly oriented Au (111) films on monocrystalline mica substrates. This alignment is observed over distances larger than the dimensions of monocrystalline Au(111) domains. A change in nucleation face with pH during growth—reflecting the different orientation of the carboxylate end groups of the SAM with respect to the substrate—is discussed.

We report the direct imaging of electrically active Si dopants near the GaAs(110) surface with a scanning tunneling microscope at a temperature of 4.2 K. In the filled state images, we observe patterns of rings which are centered around the individual doping atoms. We believe these ring patterns are induced by the individual impurities, which, due to their charge, disturb the local potential and cause oscillations in the charge density, also called Friedel oscillations. In the empty state images no Friedel oscillations can be observed.

Nanowires of different nature have been shown to self-assemble as a function of stress at the contact between two macroscopic metallic leads. Here we demonstrate for Au wires that the balance between various metastable nanowire configurations is influenced by the microstructure of the starting materials and we discover a new set of periodic structures, which we interpret as due to the atomic discreteness of the contact size for the three principal crystal orientations.PACS numbers: 73.40. Jn, 61.46.+w, 68.65.La Metallic nanowires have shown rich properties in terms of self-organization phenomena that are controlled by a combination of the quantum nature of the conduction electrons and the atomic-scale surface energy (see review [1] and references therein). Here we report yet another surprising series of stable structures.At the very smallest scale the metals Au, Pt and Ir, spontaneously form into chains of atoms [2,3,4]. For slightly larger diameters further unusual arrangements referred to as 'weird wires' were predicted [5] and later observed in high-resolution transmission electron microscopy (TEM) [6,7,8]. The observed structures for Au have a helical arrangement in the form of concentric shells of atoms.In contrast to these atomic-packing driven structures, electronic shell filling has been shown to lead to an independent series of stable nanowire (NW) diameters for the free-electron-like alkali metals [9,10], and the noble metals [11,12,13]. These NWs were not imaged as in TEM, but their stability was inferred from frequently occurring stable conductance values during gentle breaking of the contacts (see below). The series of stable values has a characteristic period when plotted as a function of the square root of the conductance, √ G, which is a measure of the radius of the wires.Finally, regular bulk-packing of NWs has also been observed, where the surface energy is the driving force, leading to completing of flat facets of the wires. Such effects have been observed in TEM [14,15,16] as remarkably long and stable wires, mostly for Au along the [110] direction. This atomic shell filling series has also been observed in the conductance [17], again as a regular period in √ G. Exactly which of these types of NWs self-assembles appears to depend critically on the experimental conditions, which is not fully understood. We anticipate that the selection of local minima in the free energy is influenced by the dynamics of the wire formation and the boundary conditions imposed by the structure of the leads. Here, we present evidence that the microstructure of the starting material, whether work hardened or annealed, influences the appearance of a new series of stable NWs that are periodic in the conductance, G, as opposed to √ G for the NWs observed previously.Gold is the archetypal metal when investigating quantum transport phenomena in atomic-sized contacts [1]. The initial interest into these systems was in quantization of the conductance, in conjunction with the atomic discreteness of the contacts. The expe...