Kinetic growth mechanisms of sputter-deposited Au films on mica: from nanoclusters to nanostructured microclusters

Au nanostructured film was deposited on mica by room temperature RF sputtering. The growth mechanism of the film was studied analyzing the evolution of the film morphology as a function of its thickness by the atomic force microscopy. In the early stages of a growth the film evolution proceeds by the nucleation and growth of nanoclusters. After a critical thickness the growth of microclusters formed by the joining of nanoclusters in preferential nucleation sites, onto a quasicontinuous film, is observed. We quantified the evolution of the mean nanoclusters height and surface density and of the film roughness. This data were analyzed by the dynamic scaling theory of growing interfaces obtaining the scaling and roughness exponents z and β whose values suggest a conservative growth process. We also quantified the growth of the microclusters showing that it is consistent with a coalescence/impingement dynamic. About the formation of the microclusters, furthermore, we speculate that their origin is strongly correlated to the features of the sputtering technique in connection with the deposition on a high-diffusivity substrate.     

Application of Mie theory and fractal models to determine the optical and surface roughness of Ag–Cu thin films

Thin films of Ag/Cu were deposited by reactive DC magnetron sputtering on (001)-oriented Si and glass substrates for various deposition times (4–24 min). These films were characterized by atomic force microscopy (AFM), and a power law scaling was performed on the obtained micrographs to investigate the self-affine nature of the sample morphology, which is indicative of a fractal structure. We applied the Higuchi’s algorithm to the AFM data to determine the fractal dimension of each sample, and the Hurst exponents were computed. The deposition time dependences of these parameters and the grain size distributions estimated from the UV–visible spectra using the Mie theory, allowed us to describe a particle formation mechanism during the deposition process, in which the length of continuous paths of conductive particles increases as the deposition time is increased. In agreement with this explanation, the electrical resistance decreased with the increment of the deposition time.     

Scaling of the interface roughness in Fe-Cr superlattices: self-affine versus non-self-affine

We have analyzed kinetic roughening in Fe-Cr superlattices by energy-filtered transmission electron microscopy. The direct access to individual interfaces provides both static and dynamic roughness exponents. We find an anomalous non-self-affine scaling of the interface roughness with a time dependent local roughness at short length scales. While the deposition conditions affect strongly the long-range dynamics, the anomalous short-range exponent remains unchanged. The different short- and long-range dynamics outline the importance of long-range interactions in kinetic roughening.     

Dynamics of encapsulation and controlled release systems based on water-in-water emulsions: Liposomes and polymersomes

The deformation relaxation behavior of two types of vesicles, liposomes and polymersomes, was investigated using a general nonequilibrium thermodynamics theory based on the interfacial transport phenomena (ITP) formalism. Liposomes and polymersomes are limiting cases of this theory with respect to rheological behavior of the interfaces. They represent respectively viscous, and viscoelastic surface behavior. We have determined the longest relaxation time for a small perturbation of the interfaces for both these limiting cases. Parameter maps were calculated which can be used to determine when surface tension, bending rigidity, spontaneous curvature, interfacial permeability, or surface rheology dominate the response of the vesicles. In these systems up to nine different scaling regimes were identified for the relaxation time of a deformation with droplet size, with scaling exponent n ranging from 0 to 4.     

Multiscale theory of fluctuating interfaces: renormalization of atomistic models

We describe a framework for the multiscale analysis of atomistic surface processes which we apply to a model of homoepitaxial growth with deposition according to the Wolf-Villain model and concurrent surface diffusion. Coarse graining is accomplished by calculating renormalization-group (RG) trajectories from initial conditions determined by the regularized atomistic theory. All of the crossover and asymptotic scaling regimes known from computer simulations are obtained, but we also find that two-dimensional substrates show an intriguing transition from smooth to mounded morphologies along the RG trajectory.     

Roughness scaling and sensitivity to initial conditions in a symmetric restricted ballistic deposition model

In this work, we introduce a restricted ballistic deposition model with symmetric growth rules that favors the formation of local finite slopes. It is the simplest model which, even without including a diffusive relaxation mode of the interface, leads to a macroscopic groove instability. By employing a finite-size scaling of numerical simulation data, we determine the scaling behavior of the surface structure grown over a one-dimensional substrate of linear size L. We found that the surface profile develops a macroscopic groove with the asymptotic surface width scaling as , with . The early-time dynamics is governed by the scaling law , with . We further investigate the sensitivity to initial conditions of the present model by applying damage spreading techniques. We find that the early-time distance between two initially close surface configurations grows in a ballistic fashion as , but a slower Brownian-like scaling () sets up for evolution times much larger than a characteristic time scale . Received 26 May 2000     

Scaling law in the ordering process of quenched thermodynamically unstable systems

The dynamics of phase separation in quenched thermodynamically unstable systems is studied. The scaling law exhibited in the late stage of the ordering process is investigated by the interface model. In the kinetics of the order-disorder transition the motion of random interfaces is shown to be responsible for the scaling law. The scaling form of the scattering function is obtained with particular attention to the fluctuating thermal noises. A droplet picture is used to discuss spinodal decomposition of off-critically quenched binary fluids. The sealing function is calculated explicitly in the region where the Brownian coagulation is most dominant for the phase separation. It is shown that the thermal noises are relevant to the scaling law in the ordering process driven by the Brownian coagulation whereas they are negligible in the kinetics of order-disorder transition.     

Dynamical scaling and kinetic roughening of single valued fronts propagating in fractal media

We consider the dynamical scaling and kinetic roughening of single-valued interfaces propagating in 2D fractal media. Assuming that the nearest-neighbor height difference distribution function of the fronts obeys Lévy statistics with a well-defined algebraic decay exponent, we consider the generalized scaling forms and derive analytic expressions for the local scaling exponents. We show that the kinetic roughening of the interfaces displays intrinsic anomalous scaling and multiscaling in the relevant correlation functions. We test the predictions of the scaling theory with a variety of well-known models which produce fractal growth structures. Results are in excellent agreement with theory. For some models, we find interesting crossover behavior related to large-scale structural instabilities of the growing aggregates. Received 22 May 2002 Published online 19 November 2002     

End-tethered charged chains at surfaces

We present here a short review covering most of the experimental results on tethering charged chains by an end to a surface. A first class of experiments deals with solid surfaces where charged chains are either chemically grafted or adsorbed through a purposely chosen moiety. Structural studies have been carried out by scattering methods, spectroscopic techniques or microscopy. Forces between the polyelectrolyte layers covering the surfaces have also been obtained by using for instance, the surface force apparatus (SFA). A second class of experiments concerns polyelectrolytes, which are end-tethered to flexible surfaces like air–liquid or liquid–liquid interfaces. These experiments are fewer in number and mainly rely on the adsorption or spreading of charged diblock copolymers at the fluid interfaces.     

Study of laser-deposited metallic thin films by a combination of high-resolution ex situ and time-resolved in situ experiments

Laser-deposited metallic alloys and multilayers were studied in detail by a combination of high-resolution ex situ and time-resolved in situ experiments. The purpose of these experiments is to better understand the special properties of laser-deposited metallic films in comparison with conventionally prepared thin films. During deposition, thickness, resistance, and electron diffraction (THEED) experiments show that the film surface is resputtered, local mixing at the interfaces of multilayers on a nanometre scale occurs, and metastable phases up to large film thicknesses are formed. After deposition, a compressive stress of 1-2 GPa was measured using four-circle diffractometry, and growth defects were observed on an atomic scale by electron microscopy (HRTEM) and field ion microscopy (FIM). The obtained structural details of the metallic films can be explained by an implantation model for the laser deposition process.     

Surface roughness analysis and magnetic property studies of nickel thin films electrodeposited onto rotating disc electrodes

Ni films were electrodeposited onto polycrystalline gold substrates mounted on a rotating disc electrode. The effects of rotation speed, film thickness and current density on the kinetic roughening and magnetic properties of the films were investigated. The film surface roughness was imaged using an atomic force microscope (AFM). The results indicate that the film roughness increases as the film thickness or deposition current density increases. We found that the electrodeposited Ni films exhibit anomalous scaling since both local and large-scale roughnesses show a power-law dependence on the film thickness. The effect of electrode rotation speed on the film surface roughness was also investigated. Scanning electron microscopy studies (SEM) had a good agreement with the AFM results. The average crystalline size of the film surfaces is also calculated from X-ray line broadening using (220) peak and Debye–Scherrer formula. The obtained results agree with that of AFM and SEM. The Ni thin films which are grown at different deposition current densities and rotation speeds exhibit in-plane magnetization with coercivities less than 110 Oe.     

Localized excitations at the Mott insulator-superfluid interfaces for confined Bose-Einstein condensates

In this Letter, we derive the dispersion relation of the surface waves at the interfaces between Mott-insulating and superfluid domains for a two-dimensional Bose-Einstein condensate in an optical lattice subjected to a confining potential. We then calculate their contribution to the heat capacity of the system and show how its low-temperature scaling allows an experimental test of the existence and properties of Mott insulator-superfluid domains.     

Epitaxial growth of Au and Pt on Fe3O4(1 1 1) surface

We have studied the epitaxial growth of Au and Pt layers on Fe₃O₄(1 1 1) as a function of the deposition temperature and thickness. The layers were deposited by UHV sputtering and the structural properties were investigated by reflection high energy electron diffraction (RHEED), X-ray experiments and transmission electron microscopy (TEM). The epitaxial growth of both metals was obtained whatever the deposition conditions but the wetting is however different for the two metals. Comparison between the coverage ratios of Au and Pt is correlated with their surface and interfaces energies. The optimum conditions to achieve a 2D flat epitaxial metallic layer are determined.     

遮蔽效应对抛射沉积模型标度性质的影响

在表面粗糙化生长过程中粒子非垂直入射产生的遮蔽效应是一种长程相互作用, 实验发现非垂直入射时生长表面形貌和生长性质都受到遮蔽效应的影响. 本文通过模拟倾斜入射的抛射沉积模型得到了其标度指数、 表面统计的偏度和峰度以及生长体的多孔性与入射角度的关系, 模拟结果显示标度指数与入射角度的关系是非单调的, 而偏度和峰度的有限尺寸效应也取决于入射角度的大小. 同时本文对以上模拟结果进行了定性的分析.     

椭圆偏振技术研究VHF-PECVD高速沉积微晶硅薄膜的异常标度行为

采用VHF-PECVD技术高速沉积了不同生长阶段的微晶硅薄膜,通过椭圆偏振技术研究了生长过程中微晶硅薄膜表面粗糙度的演化.实验结果表明,沉积气压P_g=300 Pa时,β=0.81,其超出标度理论中β最大值为0.5范围,出现异常标度行为.这表明微晶硅薄膜高速生长中还存在其他粗糙化增加的因素,此粗糙化增加的因素与阴影作用有关. 关键词： 微晶硅薄膜 椭偏光谱法 生长机制 表面粗糙度     

Conserved dynamics and interface roughening in spontaneous imbibition: A critical overview

Imbibition phenomena have been widely used experimentally and theoretically to study the kinetic roughening of interfaces. We critically discuss the existing experiments and some associated theoretical approaches on the scaling properties of the imbibition front, with particular attention to the conservation law associated to the fluid, to problems arising from the actual structure of the embedding medium, and to external influences such as evaporation and gravity. Our main conclusion is that the scaling of moving interfaces includes many crossover phenomena, with competition between the average capillary pressure gradient and its fluctuations setting the maximal lengthscale for roughening. We discuss the physics of both pinned and moving interfaces and the ability of the existing models to account for their properties. Received 17 February 1999 and Received in final form 24 November 1999     

Anomalous scaling of the surface width during Cu electrodeposition

Kinetic roughening during thin film growth is a widely studied phenomenon, with many systems found to follow simple scaling laws. We show that for Cu electrodeposition from additive-free acid sulphate electrolyte, an extra scaling exponent is required to characterize the time evolution of the local roughness. The surface width w(l,t) scales as t(beta(loc))lH, when the deposition time t is large or the size l of the region over which w is measured is small, and as t(beta+beta(loc)) when l is large or t is small. This is the first report of such anomalous scaling for an experimental ( 2+1)-dimensional system. When the deposition current density or Cu concentration is varied, only beta(loc) changes, while the other power law exponents H and beta remain constant.     

Two-Dimensional Critical Percolation: The Full Scaling Limit

We use SLE ₆ paths to construct a process of continuum nonsimple loops in the plane and prove that this process coincides with the full continuum scaling limit of 2D critical site percolation on the triangular lattice – that is, the scaling limit of the set of all interfaces between different clusters. Some properties of the loop process, including conformal invariance, are also proved.Research partially supported by a Marie Curie Intra-European Fellowship under contract MEIF-CT-2003-500740 and by a Veni grant of the Dutch Organization for Scientific Research (NWO).Research partially supported by the U.S. NSF under grant DMS-01-04278.     

Dynamics of rough interfaces in chemical vapor deposition: experiments and a model for silica films

We study the surface dynamics of silica films grown by low pressure chemical vapor deposition. Atomic force microscopy measurements show that the surface reaches a scale invariant stationary state compatible with the Kardar-Parisi-Zhang (KPZ) equation in three dimensions. At intermediate times the surface undergoes an unstable transient due to shadowing effects. By varying growth conditions and using spectroscopic techniques, we determine the physical origin of KPZ scaling to be a low value of the surface sticking probability, related to the surface concentration of reactive groups. We propose a stochastic equation that describes the qualitative behavior of our experimental system.