One-dimensional Islands Research Articles

Non-equilibrium island size distribution in one dimension

In this paper, a novel analytical expression for the size distribution of one-dimensional structures at thermodynamic non-equilibrium is derived. The expression is obtained using one-dimensional lattice gas model. Ostwald ripening and decay of short one-dimensional islands is taken into account. The theoretical results are compared with kinetic Monte Carlo simulations and the experimental size distribution of one-dimensional wires. A correct method of extracting the binding energy from the experimental size distribution in one dimension is proposed.

One-dimensional island size distribution: From non-equilibrium to equilibrium

We present a critical view of the analysis of experimental one-dimensional island size distribution as a function of time. We study the processes of island growth using large-scale kinetic Monte Carlo simulations with diffusion barriers calculated within the framework of the density functional theory. We have shown that one-dimensional island size distribution depends significantly on the time of the experiment. Our model predicts that during annealing or cooling, the transition from one state of thermodynamical equilibrium to another occurs through a non-equilibrium state. This transition consists of Ostwald ripening and decay of one-dimensional islands. The results of our work demonstrate that considering experimental one-dimensional island size distribution as an equilibrium is a big misconception.

Fabrication of Highly Oriented Multilayer Films of Picene and DNTT on Their Bulklike Monolayer.

Highly oriented, multilayer molecular films of picene and dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) molecules with the long axis parallel to the substrate (parallel configuration, hereafter) were fabricated on their characteristic bulklike monolayer. These molecules form a dense monolayer with a bulklike molecular arrangement on metal surfaces such as Au(111), which allows further stacking of parallel molecules. Indeed, upon adsorption of picene and DNTT on these dense monolayers, growth of straight islands of multilayer without the dendritic layer was observed. Particularly, in the case of picene, one-dimensional islands with lengths over 100 μm were formed and aligned in 3-fold symmetric directions of the substrate, which was not observed in the case of DNTT. X-ray diffraction measurements revealed the presence of [201̅] and [211̅] planes and the absence of the [001] diffractions, indicating that the one-dimensional islands of picene indeed consist of parallel molecules. The formation of huge crystalline islands in the case of picene, in contrast to the case of DNTT, is likely induced by the stronger intermolecular force, as suggested from the calculation of the vibrational energy.

Size distributions and scaling relations for heterogeneous nucleation and growth of atomic chains

An analytical model for one-dimensional islands growth was developed being inspired by experiments on growth of metallic atomic chains. On the basis of reported observations and simulations we considered the case of heterogeneous nucleation with linear on size rates for growth and decay. In this case the exact solution of the system of rate equation leads to Polya distribution for lengths of chains and corresponding scaling behaviour. These analytically computed dependences demonstrated good matching with experimental results.

Formation of alkaline-earth template layers on Ge(100) for oxide heteroepitaxy: Self-organization of ordered islands and trenches

The first step required for oxide heteroepitaxy with atomically abrupt interfaces on Si and Ge(100) is the formation of an alkaline-earth template layer. The atomic structure of this template layer on Ge(100) was characterized using scanning tunneling microscopy and electron diffraction. At elevated temperatures, Sr immediately roughens the surface; a transition that can be associated with Sr displacing Ge from the surface. With increasing Sr coverage a series of ordered (3 \ifmmode\times\else\texttimes\fi{} 4), (3 \ifmmode\times\else\texttimes\fi{} 2), (9 \ifmmode\times\else\texttimes\fi{} 1), and (6 \ifmmode\times\else\texttimes\fi{} 1) phases were observed. Transitions between these phases were accompanied by morphological changes: formation of the (3 \ifmmode\times\else\texttimes\fi{} 4) phase smoothed surface; transition to a local (3 \ifmmode\times\else\texttimes\fi{} 2) ordering was accompanied by trench formation; ordering of the trenches led to the (9 \ifmmode\times\else\texttimes\fi{} 1) structure; and finally, the (6 \ifmmode\times\else\texttimes\fi{} 1) structure was characterized by atomic rows. For both Sr and Ba, highly ordered arrays of one-dimensional islands could be produced with double-height steps preventing orthogonal domain formation. We associate the morphological transitions with strain relief of the surface phases and interactions of step ledges.

Impact of Substrate Defects on the Equilibrium One-Dimensional Island Size Distribution

As long as only first-neighbour interactions are considered, equilibrium island size distributions of monoatomic islands in one dimension follow an exponential law regardless of the strength and the repulsive or attractive character of the adsorbate–adsorbate interactions. However, one-dimensional atomic wires obtained via nucleation at the step edges have a monomodal island size distribution. In this paper, we present a simple one-dimensional Monte Carlo model that shows how the monomodal distribution observed experimentally can be obtained by including surface defects that only suppress the interaction between two successive adsorbates.

Modeling growth of one-dimensional islands: Influence of reactive defects

Influence of reactive defects on size distribution of one-dimensional islands is studied by means of kinetic Monte Carlo simulations in combination with an analytical approach. Two different models are examined: a model with anisotropically diffusing atoms irreversibly aggregating to islands, and a reversible model close to thermal equilibrium which allows atom detachment from islands during the growth. The models can be used to simulate island growth of group III metals deposited on the Si(100)2 x 1 surface at room temperature: Al, Ga (irreversible model), and In (equilibrium model). We demonstrate that concentration of the reactive defects 0.0025 per site may change the island size distribution from monomodal to monotonically decreasing in the case of the irreversible model. At concentration >or=0.005 defects per site, a difference between results of the studied models is suppressed by the influence of the defects and similar island size distributions are obtained.

Pentagonal ice in chains

One-dimensional islands that grow during ice nucleation at low temperatures on a copper(110) surface are identified as chains of water-molecule pentagons. This unexpected molecular arrangement optimizes oxygen-atom proximity to preferred bonding sites on the metal, while minimizing strain in the hydrogen-bond network.

Heterogeneous nucleation and adatom detachment at one-dimensional growth of In onSi(100)−2×1

Growth of atomic indium chains---one-dimensional islands---on the $\text{Si}(100)\text{\ensuremath{-}}2\ifmmode\times\else\texttimes\fi{}1$ surface was observed by scanning tunneling microscopy (STM) at room temperature and simulated by means of a kinetic Monte Carlo method. Density of indium islands and island-size distribution was obtained for various deposition rates and coverage. STM observation of growth during the deposition of indium provided information on growth kinetics and relaxation of grown layers. Important role of $C$-type defects at adsorption of metal atoms was observed. Measured growth characteristics were simulated using a microscopic model with anisotropic surface diffusion and forbidden zones along the metal chains. An analysis of experimental and simulation data shows that the detachment of indium adatoms from the chains substantially influences a growth scenario and results in monotonously decreasing chain length distribution function at low coverage. Diffusion barriers determined from the simulations correspond to almost isotropic diffusion of indium adatoms on the surface. The results are discussed with respect to data reported in earlier papers for other metals.

Binding and Diffusion of Al Adatoms and Dimers on the Si(100)-2 × 1 Reconstructed Surface: A Hybrid QM/MM Embedded Cluster Study

When group III metals are deposited onto the Si(100)-2 × 1 reconstructed surface they are observed to self-assemble into chains of atoms that are one atom high by one atom wide. To better understand this one-dimensional island growth, ab initio electronic structure calculations on the structures of Al atoms on silicon clusters have been performed. Natural orbital occupation numbers show that these systems display significant diradical character, suggesting that a multireference method is needed. A multiconfiguration self-consistent field (MCSCF) calculation with a 6-31G(d) basis set and effective core potentials was used to optimize geometries. The surface integrated molecular orbital molecular mechanics embedded cluster method was used to take the surface chemistry into account, as well as the structure of an extended surface region. Potential energy surfaces for binding of Al adatoms and Al−Al dimers on the surface were determined, and the former was used to obtain a preliminary assessment of the surface diffusion of adatoms. Hessians were calculated to characterize stationary points, and improved treatment of dynamic electron correlation was accomplished using multireference second order perturbation theory (MRMP2) single-point energy calculations. Results from the MRMP2//MCSCF embedded cluster calculations are compared with those from QM-only cluster calculations, embedded cluster unrestricted density functional theory calculations, and previous Car−Parrinello DFT studies.

Accelerated kinetic Monte Carlo algorithm for diffusion-limited kinetics

If a stochastic system during some periods of its evolution can be divided into noninteracting parts, the kinetics of each part can be simulated independently. We show that this can be used in the development of efficient Monte Carlo algorithms. As an illustrative example, the simulation of irreversible growth of extended one-dimensional islands is considered. The approach allowed us to simulate the systems characterized by parameters superior to those used in previous simulations.

Formation Mechanism of One-Dimensional Si Islands on aH/Si(001)Surface

The formation mechanism of one-dimensional Si islands on a H/Si(001)-(2x1) surface is studied using scanning tunneling microscopy/spectroscopy and first-principles calculations. We observed that one-dimensional islands that are made from dimer chains are formed at the initial growth stages similar to the bare Si(001) surface. It is found that the number of odd-numbered dimer chains is larger than that of even-numbered dimer chains. We propose the growth processes of the two types of growth edges to explain the observation.

Modeling one-dimensional island growth with mass-dependent detachment rates

m+1 b , with constant b. A mapping onto a column problem shows that these systems are zero-range processes, whose steady state properties are exactly calculated under the assumption of independent column heights in the master equation. Simulation provides accurate island size distributions which confirm analytic reductions and are particularly useful whenever the analytical tools cannot provide results in closed form. The shape of island size distributions can be changed from monomodal to monotonically decreasing by tuning the temperature or changing the coverage onedimensional density . In all cases, small values of the scaling variable X �1 / 1� favor the monotonically decreasing ones. However, for large X, rapidly increasing rates m lead to distributions with peaks very close to m and rapidly decreasing tails, while slowly increasing m provide peaks close to m / 2 and fat right tails.

Growth of One-Dimensional Pd Nanowires on the Terraces of a ReducedSnO2(101)Surface

Palladium, vapor-deposited at room temperature on a reduced SnO2(101) surface, forms one-dimensional islands, one atomic layer high, 5 A wide, and up to 350 A long. Scanning tunneling microscopy shows that neighboring islands do not merge. First-principles calculations reveal the atomistic processes that lead to this, for metal oxide substrates unusual, overlayer growth. Formation of 1D islands is mediated by a large anisotropy in surface diffusion, strong Pd-Sn interaction, and the lack of stable binding sites at the sides of the Pd islands. Nucleation is defect mediated, and the initial nucleation site determines the width of the resulting nanocluster.

Surface morphology study of fluorocarbon macromolecule deposited on polyimide substrates

Plasma treatment and polymerization have been widely applied to modify the surface of polymer materials in the last decades. In this paper, fluorocarbon macromolecules were deposited on polyimide (PI) substrates by R.F. magnetron sputtering with argon gas as plasma, and PTFE as targets. The surface morphology of the deposited substance was observed by Scanning Electron Microscopy (SEM). It was found that some segregated grains deposited on the PI substrates tended to be finer, more uniformly dispersed and more round with increasing energy. At certain conditions (1 Pa, 400 W, 60 min), quite uniform nanometer sized particles 40–50 nm have been obtained. Fluorocarbon macromolecules were also observed by Atom Force Microscopy (AFM). They have form of round particles with tendency to grow in vertical direction. They are packed closely to each other. The growth mode of fluorocarbon macromolecule is to be one-dimensional island. The experimental results obtained by Transmission Electron Microscopy (TEM) show that in the range of 60 min, the speed of nanometer sized fluorocarbon macromolecule deposition was constant of approximately 10 nm/min.

Growth and optical characterization of single quantum well structure of submonolayer ZnS/ZnTe

Single quantum wells of submonolayer ZnS/ZnTe were grown between ZnTe layers using hot wall epitaxy method with fast-movable substrate configuration. As ZnS well widths decrease from 1 to 0.15 monolayer, the photoluminescence peaks shift to higher energies from 2.049 to 2.306 eV, and the photoluminescence intensities increase. As ZnS well width decrease, the PL spectra show the lower-energy tails and consequently the increased PL FWHMs. This is a result of a convolution of two PL peaks from two-dimensional and zero-dimensional quantum islands, supported by a still lived lower-energy peaks of zero-dimensional quantum islands above 50 K. The energy shift in the power dependence of photoluminescence spectra is proportional to the third root of the excitation density. These behaviors can be described by the formation of submonolayer type-II ZnS/ZnTe quantum well structure, and the coexistence of two-dimensional and one-dimensional islands in ZnS layers.

Adsorption of di- l-alanine on Cu( [formula omitted]) investigated with scanning tunneling microscopy

Sub-monolayer growth of a small chiral peptide, di- l-alanine, on Cu(1 1 0) was investigated by variable temperature scanning tunneling microscopy (STM). At low coverage and for temperatures above ≈−220 K the molecules nucleate along the [ 3 ̄ 3 2] direction to form short, mainly one-dimensional islands. An increase in coverage leads to the formation of [ 3 ̄ 3 2]-directed, elongated islands. Images with sub-molecular resolution reveal that the orientation of the molecules within one particular island depends on the deposition temperature. At higher coverage, up to one monolayer, the islands coalesce, giving rise to phase boundaries between domains of opposite orientation. An atomic-scale model for di- l-alanine on Cu(1 1 0) is presented.

Epitaxial Growth of CaF2 Films on Si(111) Studied by Scanning Tunneling Microscopy

Using ultrahigh vacuum scanning tunneling microscopy, we have studied the early stages of the epitaxial growth of CaF2 films on Si(111) at 630°C at a slow deposition rate of 0.2 monolayer (ML) per minute. After formation of CaF interface layer, we observe the film grows in the sequence of step edge decoration, one-dimensional islands growth on the terrace, formation of clusters of the islands, coalescence of the island cluster and filling of gaps between the one-dimensional islands in the cluster and between the island clusters to complete a layer. By such a sequence, epitaxial CaF2 films with atomically flat surface could be grown in layer-by-layer fashion up to 3 ML. The growth mode is discussed in relation to kinetic phase diagram [M. A. Olmstead: Thin Films: Heteroepitaxial Systems, eds. W. K. Liu and M. B. Santos (World Scientific, Singapore, 1999) Chap. 5].

Theoretical investigation of the island formation on a hydrogen-terminated Si(001) surface

We report the result of first-principles calculations on the mechanism of the one-dimensional (1D) island formation on the hydrogen terminated Si(001)–(2×1) surface. It is found that the growth at the nonrebonded edge proceeds by capturing two surface Si adatoms and by releasing a H 2 molecule. The growth at the rebonded edge proceeds by capturing two surface Si adatoms and two surface H atoms. The growth at the nonrebonded edges is quicker than that at the rebonded edges. The number of islands having two rebonded edges are larger than those of other types of islands. These results are in good agreement with the experimental results.

Experimental evidence for resonant tunneling in a luttinger liquid

We have measured the low-temperature conductance of a one-dimensional island embedded in a single mode quantum wire. The quantum wire is fabricated using the cleaved edge overgrowth technique and the tunneling is through a single state of the island. Our results show that while the resonance line shape fits the derivative of the Fermi function the intrinsic linewidth decreases in a power law fashion as the temperature is reduced. This behavior agrees quantitatively with Furusaki's model for resonant tunneling in a Luttinger liquid.