The formation mechanisms of evaporated Pd islands on the reconstructed Au(111) $22 /times /sqrt{3}$ herringbone surface have been here studied by Scanning Tunneling Microscopy (STM) at room temperature. Atomically resolved STM images at the very early stages of growth provide a direct observation of the mechanisms involved in preferential Pd islands nucleation at the elbows of the herringbone structure. At low Pd coverage the Au(111) herringbone structure remains substantially unperturbed and isolated Pd atoms settled in hollow sites between Au atoms are found nearby the elbows and the distortions of the reconstructed surface. In the same regions, at extremely low coverage (0.003 ML), substituted Pd atoms in lattice sites of the Au(111) surface are also observed, revealing the occurrence of a place exchange mechanism. Substitution seems to play a fundamental role in the nucleation process, forming aggregation centers for incoming atoms and thus leading to the ordered growth of Pd islands on Au(111). Atomically resolved STM images of Pd islands reveal a close-packed arrangement with lattice parameter close to the interatomic distance between gold atoms in the fcc regions of the Au(111) surface. Distortion of the herringbone structure for Pd coverages higher than 0.25 ML indicates strong interaction between the growing islands and the topmost Au(111) layer.
Al-induced layer exchange crystallization of amorphous Ge thin films has been demonstrated recently, and provides a suitable system to characterize, model and control Ge crystal growth on non-crystalline substrates. Direct observation of Ge transfer to the surface of Al through an interposed GeOx interfacial layer allows independent measurement of the density and average area of crystalline Ge islands formed on the surface. Based on these experimental observations, the Johnson-Mehl-Avrami-Kologoromov phase transformation theory is extended to model nanoscale nucleation and growth of Ge islands…
The thermodynamics of the Stranski-Krastanov mode of epitaxial growth and the effect of the sign of the lattice misfit are discussed. The Stranski-Krastanov mode of growth represents a sequence of layer-by-layer or Frank-van der Merwe growth followed by the formation of three-dimensional (3D) islands or Volmer-Weber growth. The occurrence of both growth modes mentioned above is in compliance with the wettability criterion of Bauer. The positive wetting function required for the occurrence of the Volmer-Weber growth is originated by the vertical displacements of the atoms close to the edges of …
This work describes morphological and crystalline properties of the InAs islands grown on templates created by focused ion beam (FIB) on indium phosphide (InP) substrates. Regular arrangements of shallow holes are created on the InP (001) surfaces, acting as preferential nucleation sites for InAs islands grown by Metal-Organic Vapor Phase Epitaxy. Ion doses ranging from $10^{15}$ to $10^{16}$ $Ga^{+}$/$cm^{2}$ were used and islands were grown for two sub-monolayer coverages. We observe the formation of clusters in the inner surfaces of the FIB produced cavities and show that for low doses temp…
我们开发了一个理论上的成核的岛屿上的外延生长的基础上推导的寿命和速率管理个人的微观过程。这些过程强烈地受到下降原子的附加台阶边势垒E_S的影响。如果不稳定团簇的解离时间可以忽略，理论预测，对于尺寸i<=2的小临界核，成核受涨落控制，在此期间，i+1个原子偶然出现在岛上。相比之下，对于i>=3的大临界核，成核过程可以以平均场类型的方式描述，对于大E_S，这对应于Tersoff等人[Phys. Rev. Lett. 72，266（1994）]。在波动主导和平均场的情况下，各种标度制度被确定，其中典型的岛的大小在开始的成核显示依赖于吸附原子的扩散速率，传入的原子通量，和步骤边缘交叉概率exp（-E_S/k_B T）的幂律。对于亚稳态团簇的解离速率作为附加参数进入问题的情况，我们建立了一个基于新颖速率方程的半解析方法，该方法可以很容易地在数值上求解。理论计算结果与MonteCarlo实验结果符合得很好。指出了各种应用的影响。
A seed layer-free growth of HfO$_2$ on commercially available CVD graphene from various suppliers is investigated. It is revealed that the samples of monolayer graphene transferred from Cu to SiO$_2$/Si substrates have different coverage with bi- and multi-layer graphene islands. We find that the distribution and number of such islands impact the nucleation and growth of HfO$_2$ by CVD. In particular, we show that the edges and surface of densely distributed bi-layer graphene islands provide good nucleation sites for conformal CVD HfO$_2$ layers. Dielectric constant of 16 is extracted from mea…
It is known in thin-film deposition that the density of nucleated clusters $N$ varies with the deposition rate $R$ as a power law, $N \sim R^α$. The exponent $α$ is a function of the critical nucleus size $i$ in a way that changes with the aggregation-limiting process active in a given system. We extend here to generic aggregation-limiting processes the derivation of the analytical capture-zone distribution function $P_β(s) = a_βs^β\exp(-b_βs^2)$ of Pimpinelli and Einstein [Phys. Rev. Lett. 99, 226102 (2007)]. We show that the exponent $β$ is generally related to the critical nucleus size $i$ …
The ability to pattern the location of pillars in epitaxial matrix-pillar nanocomposites is a key challenge to develop future technologies using these intriguing materials. One such model system employs a ferrimagnetic CoFe$_{2}$O$_{4}$ (CFO) pillar embedded in a ferroelectric BiFeO$_{3}$ (BFO) matrix, which has been proposed as a possible memory or logic system. These composites self-assemble spontaneously with pillars forming through nucleation at a random location when grown via physical vapor deposition. Recent results have shown that if an island of the pillar material is pre-patterned on…
The distributions of inter-island gaps and captures zones for islands nucleated on a one-dimensional substrate during submonolayer deposition are considered using a novel retrospective view. This provides an alternative perspective on why scaling occurs in this continuously evolving system. Distributional fixed point equations for the gaps are derived both with and without a mean field approximation for nearest neighbour gap size correlation. Solutions to the equations show that correct consideration of fragmentation bias justifies the mean field approach which can be extended to provide close…
In the electrochemical deposition of thin films the measurement of the current-time curve does not allow for a direct determination of the nucleus growth law, electrode surface coverage and mean film thickness. In this work we present a theoretical approach suitable to gain insight into these quantities from the knowledge of nucleation density, solution parameters and current-time behavior. The model applies to both isotropic and anisotropic growth rates of nuclei and a study on the effect of nucleus shape and aspect ratio on the kinetics is presented. Experimental results from literature are …
We have studied the monolayer-bilayer transformation in the case of the coherent Stranski-Krastanov growth. We have found that the energy of formation of a second layer nucleus is largest at the center of the first-layer island and smallest on its corners. Thus nucleation is expected to take place at the corners (or the edges) rather than at the center of the islands as in the case of homoepitaxy. The critical nuclei have one atom in addition to a compact shape, which is either a square of i*i or a rectangle of i*(i-1) atoms, with i>1 an integer. When the edge of the initial monolayer island i…
The nucleation and growth of point islands during submonolayer deposition on a one-dimensional substrate is simulated for critical island size $i=0,1,2,3$. The small and large size asymptotics for the gap size and capture zone distributions (GSD and CZD) are studied. Comparisons to theoretical predictions from fragmentation equation analyses are made, along with those from the recently proposed Generalised Wigner Surmise (GWS). We find that the simulation data can be fully understood in the framework provided by the fragmentation equations, whilst highlighting the theoretical areas that requir…
We have demonstrated that the island nucleation in the initial stage of epitaxial thin film growth can be tuned by substrate surface charge doping. This charge effect was investigated using spin density functional theory calculation in Fe-deposition on graphene substrate as an example. It was found that hole-doping can apparently increase both Fe-adatom diffusion barrier and Fe inter-adatom repulsion energy occurring at intermediate separation, whereas electron-doping can decrease Fe-adatom diffusion barrier but only slightly modify inter-adatom repulsion energy. Further kinetic Monte Carlo si…
We report the results of x-ray scattering studies of AlN on c-plane sapphire during reactive radiofrequency magnetron sputtering. The sensitivity of in situ x-ray measurements allowed us to follow the structural evolution of strain and roughness from initial nucleation layers to fullyrelaxed AlN films. A growth rate transient was observed, consistent with the initial formation of non-coalesced islands with significant oxygen incorporation from the substrate. Following island coalescence, a steady state growth rate was seen with a continuous shift of the c and a lattice parameters towards the r…
In this work, the nucleation and growth mechanism of aluminum oxide (Al2O3) in the early stages of the direct atomic layer deposition (ALD) on monolayer epitaxial graphene (EG) on silicon carbide (4H-SiC) has been investigated by atomic force microscopy (AFM) and Raman spectroscopy. Contrary to what is typically observed for other types of graphene, a large and uniform density of nucleation sites was observed in the case of EG and ascribed to the presence of the buffer layer at EG/SiC interface. The deposition process was characterized by Al2O3 island growth in the very early stages, followed …
我们研究了岛形核的动力学在吸附物的存在下，使用动力学蒙特卡罗模拟的两种生长模型。原子（A-原子）和杂质（B-原子）共沉积，扩散和聚集受到吸引AA-和AB-相互作用。吸附原子与杂质的活化交换被认为是维持生长过程中杂质修饰岛边缘的关键过程。虽然杂质的存在强烈地增加了岛密度，但由附着限制生长的速率方程理论预测的岛密度随通量的缩放的变化[D. Kandel，Phys. Rev. Lett. 78，499（1997）]，未观察到。我们认为，在本模型中，即使是完全覆盖的岛屿边缘不提供有效的附着障碍。
Graphene, a flat monolayer of carbon atoms packed tightly into a two dimensional hexagonal lattice, has unusual electronic properties which have many promising nanoelectronic applications. Recent Low Energy Electron Microscopy (LEEM) experiments show that the step edge velocity of epitaxially grown 2D graphene islands on Ru(0001) varies with the fifth power of the supersaturation of carbon adatoms. This suggests that graphene islands grow by the addition of clusters of five atoms rather than by the usual mechanism of single adatom attachment. We have carried out Kinetic Monte Carlo (KMC) simul…
Understanding surface dynamics during epitaxial film growth is key to growing high quality materials with controllable properties. X-ray photon correlation spectroscopy (XPCS) using coherent x-rays opens new opportunities for in situ observation of atomic-scale fluctuation dynamics during crystal growth. Here, we present the first XPCS measurements of 2D island dynamics during homoepitaxial growth in the layer-by-layer mode. Analysis of the results using two-time correlations reveals a new phenomenon - a memory effect in island nucleation sites on successive crystal layers. Simulations indicat…
The distribution of capture zones formed during the nucleation and growth of point islands on a one-dimensional substrate during monomer deposition is considered for general critical island size $i$. A fragmentation theory approach yields the small and (for $i=0$) large size asymptotics for the capture zone distribution (CZD) under the assumption of no neighbour-neighbour gap size correlation. These CZD asymptotic forms are different to those of the Generalised Wigner Surmise which has recently been proposed for island nucleation and growth models, and we discuss the reasons for the discrepanc…
We study how FeO wüstite films on Ru(0001) grow by oxygen-assisted molecular beam epitaxy at elevated temperatures (800-900 K). The nucleation and growth of FeO islands are observed in real time by low-energy electron microscopy (LEEM). When the growth is performed in an oxygen pressure of 10-6 Torr, the islands are of bilayer thickness (Fe-O-Fe-O). In contrast, under a pressure of 10-8 Torr, the islands are a single FeO layer thick. We propose that the film thickness is controlled by the concentration of oxygen adsorbed on the Ru. More specifically, when monolayer growth increases the adsorbe…
Using scanning tunneling microscopy (STM), we investigate oxide-induced growth pits in Si thin films deposited by molecular beam epitaxy. In the transition temperature range from 2D adatom islanding to step-flow growth, systematic controlled air leaks into the growth chamber induce pits in the growth surface. We show that pits are also correlated with oxygen-contaminated flux from Si sublimation sources. From a thermodynamic standpoint, multilayer growth pits are unexpected in relaxed homoepitaxial growth, whereas oxidation is a known cause for step pinning, roughening, and faceting on element…
Graphene films grown by vapor deposition tend to be polycrystalline due to the nucleation and growth of islands with different in-plane orientations. Here, using low-energy electron microscopy, we find that micron-sized graphene islands on Ir(111) rotate to a preferred orientation during thermal annealing. We observe three alignment mechanisms: the simultaneous growth of aligned domains and dissolution of rotated domains, i.e., "ripening"; domain-boundary motion within islands; and continuous lattice-rotation of entire domains. By measuring the relative growth velocity of domains during ripeni…
The GaAs(0 0 1) surface is observed to evolve from being perfectly flat to a surface half covered with one-monolayer high spontaneously formed GaAs islands. The dynamics of this process are monitored with atomic-scale resolution using scanning tunneling microscopy. Surprisingly, pit formation dominates the early stages of island formation. Insight into the nucleation process is reported.
The nucleation and growth of single-layer molybdenum disulfide single domain islands is investigated by in situ low-energy electron microscopy. We study the growth of micron-sized flakes and the correlated flattening process of the gold surface for three different elevated temperatures. Furthermore, the influence of surface step edges on the molybdenum disulfide growth process is revealed. We show that both island and underlying terrace grow simultaneously by pushing the surface step in the expansion process. Our findings point to an optimized growth procedure allowing for step-free single-dom…
Ice formation is one of the most common and important processes on earth and almost always occurs at the surface of a material. A basic understanding of how the physicochemical properties of a material's surface affect its ability to form ice has remained elusive. Here, we use molecular dynamics simulations to directly probe heterogeneous ice nucleation at a hexagonal surface of a nanoparticle of varying hydrophilicity. Surprisingly, we find that structurally identical surfaces can both inhibit and promote ice formation and analogous to a chemical catalyst, it is found that an optimal interact…
The basic physics of nucleation in solid \hl{single-crystal} nanoparticles is revealed by a phase-field theory that includes surface energy, chemical reactions and coherency strain. In contrast to binary fluids, which form arbitrary contact angles at surfaces, complete "wetting" by one phase is favored at binary solid surfaces. Nucleation occurs when surface wetting becomes unstable, as the chemical energy gain (scaling with area) overcomes the elastic energy penalty (scaling with volume). The nucleation barrier thus decreases with the area-to-volume ratio and vanishes below a critical size, a…
An in-situ nanoscopic investigation of the prototypical surface alloying system Ag/Pt(111) is reported. The morphology and the structure of the ultrathin Ag-Pt film is studied using Low Energy Electron Microscopy during growth at about 800 K. An amazingly rich dynamic behaviour is uncovered in which stress relieve plays a governing role. Initial growth leads to surface alloying with prolonged and retarded nucleation of ad-islands. Beyond 50% coverage de-alloying proceeds, joined by partial segregation of Pt towards the centre of large islands in violent processes. Upon coalescence the irregula…
The evolution of surface morphology during the growth of N-polar (000-1) GaN under N-rich condition is studied by kinetic Monte Carlo (kMC) simulations for two substrates miscuts 2deg and 4deg. The results are compared with experimentally observed surface morphologies of (000-1) GaN layers grown by plasma-assisted molecular beam epitaxy. The proposed kMC two-component model of GaN(000-1) surface where both types of atoms: nitrogen and gallium attach the surface and diffuse independently, explains that at relatively high rates of the step flow (miscut angle <2deg) the low diffusion of gallium a…
A basic kinetic model that incorporates a coupled dynamics of the carbon atoms and dimers on a copper surface is used to compute growth of a single-layer graphene island. The speed of the island's edge advancement on Cu[111] and Cu[100] surfaces is computed as a function of the growth temperature and pressure. Spatially resolved concentration profiles of the atoms and dimers are determined, and the contributions provided by these species to the growth speed are discussed. Island growth in the conditions of a thermal cycling is studied.
We present a combined experimental and theoretical study to get insight into both memory and negative differential resistance (NDR) effect in organic memory devices. The theoretical model we propose is simply a one-dimensional metallic island array embedding within two electrodes. We use scattering operator method to evaluate the tunneling current among the electrode and islands to establish the basic bistable I-V curves for several devices. The theoretical results match the experiments very well, and both memory and NDR effect could be understood comprehensively. The experimental corresponden…
Graphene, a hexagonal sheet of $sp^2$-bonded carbon atoms, has extraordinary properties which hold immense promise for future nanoelectronic applications. Unfortunately, the popular preparation methods of micromechanical cleavage and chemical exfoliation of graphite do not easily scale up for application purposes. Epitaxial graphene provides an attractive alternative, though there are many challenges, not least of which is the absence of an understanding of the complex atomistic assembly kinetics of graphene. Here, we present a simple rate theory of epitaxial graphene growth on close-packed me…
