-
[show abstract]
[hide abstract]
ABSTRACT: The growth of indium and aluminum nanostructures on molybdenum disulphide (MoS2)(0001) substrate has been studied using scanning tunneling microscopy in ultra-high vacuum. At low coverage and room temperature (RT), mostly ultra-thin (approximately 1.2-2 nm) triangular In islands were observed on MoS2. With increasing coverage or high flux, large coalesced irregular islands along with triangular and round-shaped ones of increased average height were found. Triangular and round-shaped islands were obtained after annealing the RT-deposited In on MoS2 sample at 450 K. At approximately 375 K, exclusively triangular In islands were observed. Al nanoparticles with diameter in 4-16 nm range were obtained after a low-flux deposited whereas ramified islands were observed in a high flux at RT. Ultra-thin (approximately 1.20-2 nm) Al islands and films were obtained on MoS2 after deposition at 500 K. These results demonstrate that the shape of In and Al nanostructures grown on MoS2 can be controlled in self-assembly by adjusting substrate temperature, deposition flux and amount.
Journal of Nanoscience and Nanotechnology 06/2008; 8(5):2707-12. · 1.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The phase transition process from the Si(1 1 1)-(7 × 7) surface to the Cu/Si(1 1 1)-(5 × 5) surface structure has been studied by scanning tunnelling microscopy and synchrotron radiation photoemission spectroscopy. The nucleation and growth of Cu/Si(1 1 1)-(5 × 5) on the Si(1 1 1)-(7 × 7) surface progress gradually with the increase in Cu coverage. Cu deposition on the Si(1 1 1)-(7 × 7) surface at room temperature may only involve the saturation of the surface dangling bonds, whereas a new surface phase of Cu/Si(1 1 1)-(5 × 5) is formed upon annealing, which saturates at a Cu coverage of 0.9 ML. Our experiments clearly show the surface phase transition process of the (5 × 5) structure as a function of the Cu coverage and provide useful insight into the Cu/Si(1 1 1)-(5 × 5) structure.
Journal of Physics D Applied Physics 04/2008; 41(9):095306. · 2.54 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Thiophene molecule selectively binds to the adjacent adatom-rest atom pair on the Si(111)-(7x7) surface through its alpha-carbon atoms, leading to the covalent attachment of a C-S-C linkage and remaining C=C (beta-carbon) bond onto the surface. Photoemission studies show that Cu atom readily adsorbs onto the S atom of the functional group to form the Cu-S molecular anchor in two forms: one points away from the thiophene C=C group; the other points toward the C=C group.
The Journal of Chemical Physics 02/2008; 128(4):044706. · 3.33 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: When antimony (mostly Sb4) is deposited on highly oriented pyrolytic graphite (HOPG), in situ scanning tunneling microscopy images reveal that three-dimensional
(3D) spherical islands, quasi-2D films and 1D nanowires (NWs) are formed. The spherical islands develop into faceted crystallites
in the later growth stage. The lattice parameters of the 2D and 3D structures are close to those of α-Sb bulk, whereas the
NWs appear in a compressed state. The Laplace pressure, which can reach the GPa range in a nanostructure, is considered the
driving force for the compressive lattice structures of Sb NWs. We found conditions of controlling the dimensionality of Sb
nanostructures in their self-assembly on HOPG to a certain extent. At room temperature and with a low Sb flux, 3D islands
grow exclusively. At a substrate temperature of 100°C, 2D and 1D structures are dominant when a high deposition flux is used,
whereas only NWs are formed initially when a low flux is used. These results are explained in terms of different activation
energies for Sb4 diffusion and conversion to a chemisorption or dissociation state on HOPG. As the temperature increases, the rate of conversion
to the chemisorption or dissociation state increases more rapidly than that of diffusion since the chemisorption activation
energy is much higher than the diffusion barrier of physisorbed Sb4, resulting in enhanced 2D and 1D structural nucleation and growth, which are further favored with the increase in deposition
flux. The bonding nature of various Sb structures with a graphite surface and the conditions for growing aligned Sb NWs exclusively
are discussed.
Applied Physics A 07/2007; 88(2):299-307. · 1.63 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: MnSb nanoparticles with average lateral diameters 〈d〉 from 5 to 30 nm are synthesized on ultra thin silicon nitride covered Si(111) by codeposition of Mn and Sb. These MnSb particles possess sharp interfaces and a NiAs-type lattice. The Mn 2p x-ray absorption spectroscopy analysis shows broad line shapes due to the itinerant Mn 3d states. The particles with 〈d〉 = 5 and 8.5 nm are superparamagnetic at room temperature, while those of 〈d〉 = 15 and 30 nm exhibit ferromagnetic behavior.
Applied Physics Letters 05/2007; 90(20):202503-202503-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The growth of Ge, Sb and Al nanostructures on highly oriented pyrolytic graphite (HOPG) have been studied comparatively using scanning tunnelling microscopy in ultra-high vacuum. Clusters and crystallites of these elements were grown along HOPG steps in the initial stage. But the nanoparticles of these three elements show quite different size distributions and morphological evolution in later growth stages. Using different deposition flux and amount, Ge clusters with self-limiting height, cluster chains and double-layer ramified cluster islands were obtained on HOPG at room temperature (RT). Compact crystalline Ge islands with high-index facets were observed after annealing at 600 K following RT deposition. Three-dimensional (3D) spherical islands, 2D thin films and 1D nanorods of Sb have been synthesized using different fluxes on HOPG at RT. With higher flux and a substrate temperature of 375 K, only crystalline 2D and 1D structures of Sb were obtained. When Al was deposited on HOPG at RT, the growth and coalescence of clusters formed initially result in flat Al crystallites with (111) top facet. After more deposition, craters were observed on top of the flattened Al islands resulting from a few smaller islands merging together. The mobile Al islands on HOPG can be pinned by Sb. The morphology difference of observed nanostructures reflects unique energetic and kinetic properties of atoms and clusters of each element.
Nanotechnology 03/2007; 18(14):145501. · 3.98 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present a scanning tunnelling microscopy (STM) investigation of Co silicide cluster and island formation on Si(111)-(7 × 7). We identify sub-nanometre clusters, which we propose to be the precursors to Co silicide nucleation and growth. The observation of metastable phases and various domains on the surface suggest significant Si rearrangement during silicide formation. Surface diffusion of both Si and type-1 clusters plays a vital role in the nucleation of Co silicide islands. With the help of density functional theory calculations, we propose a model for the surface structure of atomically flat CoSi2(111)-(2 × 2) islands.
Journal of Physics Condensed Matter 07/2006; 18(30):6987. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: One-dimensional (1D) semimetals (e.g., antimony and bismuth) are excellent thermoelectric materials. We demonstrate the self-assembly of 1D Sb nanowires on highly oriented pyrolytic graphite, along with structures of other dimensionality. Comparing with an Sb crystal in ambient condition, our scanning tunneling microscopy analysis indicates that these Sb nanowires have a compressed lattice structure, which is likely formed under the Laplace pressure that can be quite large in a nanostructure. The conditions for growing aligned semimetal nanowires exclusively are discussed.
Applied Physics Letters 06/2006; 88(23):233105-233105-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Thiophene selectively binds to the pair of adjacent Si adatom and Si rest atom on the Si(111)-(7×7) surface, leading to the covalent attachment of C–S–C linkages onto the surface. Cu atoms are found to preferentially adsorb onto the S atoms of the functional C–S–C groups in the formation of copper nanoclusters on the thiophene-mediated Si(111)-(7×7) surface.
Applied Physics Letters 03/2006; 88(12):123106-123106-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Antimony islands of different shapes and dimensions were grown on highly oriented pyrolytic graphite (HOPG) at room temperature in ultrahigh vacuum. Three-dimensional (3D) spherical, 2D thin films and 1D nanorods of Sb on graphite were studied using in situ scanning tunnelling microscopy. Sb was evaporated in the form of Sb4, which interacts with HOPG weakly and exhibits a high surface mobility, resulting in preferential nucleation of 3D spherical islands at defect sites. Surface diffusion and aggregation lead to the formation of nanoparticles with various shapes and sizes. The shape and size of islands depend on growth parameters, i.e. flux and deposition time. The 3D and 2D structures of Sb on graphite have the same bulk crystalline rhombohedral (α-Sb) structure, but the 1D nanorods show a highly compressed structure different from the α-Sb lattice.
Journal of Physics Condensed Matter 03/2006; 18(13):3425. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have studied the size, shape transition, and nucleation sites of self-assembled cobalt silicide clusters on Si(111)−7×7 using scanning tunneling microscopy. Step decoration of solid-phase-epitaxy grown clusters (350–1000 °C) is observed on surfaces with narrow terrace widths (25–40 nm). Experiments repeated on surfaces with wide (>70 nm) terraces reveal significant differences with respect to shape, size, and growth morphology; a bimodal size distribution is observed due to cluster shape transition from irregular clusters to flat-top islands. The control of silicide island nucleation could have potential applications in electrode formation for molecular electronics and nanodevice fabrication.
Applied Physics Letters 01/2006; 88(2):023121-023121-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The well-defined and patterned copper clusters formed on the Si(111)-(7×7) surface have been employed as a template for selective binding of molecules, forming ordered molecular nanostructures. Scanning tunneling microscopic studies show that thiophene molecules preferentially bind to the copper clusters through the S–Cu interaction involving S lone-pair electrons. Large-scale two-dimensional thiophene molecular nanostructures can be obtained using this patterned assembly technique. Our experiments demonstrate the feasibility for controllable growth of ordered molecular nanostructures on Si(111) surface.
Applied Physics Letters 10/2004; 85(14):2926-2928. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The formation of self-assembled one-dimensional molecular nanostructures on Si(100) is studied by scanning tunneling microscopy. Using the Ge-covered Si(100)-2×n surface as a tempting template, we have obtained large-scale one-dimensional styrene molecular nanostructures. The styrene molecules selectively bond to the Ge/Si(100)-2×n surface through the interactions between one C=C bond of the vinyl group and a Ge=Ge dimer to form C–Ge linkages via a [2+2] cycloaddition. This result may provide a pathway for forming controlled organic nanostructures on the Si(100) surfaces. © 2004 American Institute of Physics.
Applied Physics Letters 01/2004; 84(3):401-403. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present a study on the adsorption and thermal decomposition of C60 on Co covered Si(111)-7 × 7 using scanning tunneling microscopy and X-ray photoelectron spectroscopy. Co-induced magic clusters grown on Si(111)-7 × 7 are identified as a possible adsorption site where 51 ± 3% of C60 molecules adsorb at room temperature. On Co/Si(111)-7 × 7, C60 molecules start to decompose at 450 °C, and are completely dissociated to form SiC by 720 °C. This temperature is significantly lower than 910 °C at which C60 completely dissociates on clean Si(111)-7 × 7. This is a possible low temperature method for growing crystalline SiC films using C60 as a precursor molecule.
Applied Surface Science.
