Networking Behavior in Thin Film and Nanostructure Growth Dynamics

Thin film coatings have been essential in development of several micro and nano-scale devices. To realize thin film coatings various deposition techniques are employed, each yielding surface morphologies with different characteristics of interest. Therefore, understanding and control of the surface growth is of great interest. In this paper, we devise a novel network-based modeling of the growth dynamics of such thin films and nano-structures. We specifically map dynamic steps taking place during the growth to components (e.g., nodes, links) of a corresponding network. We present initial results showing that this network-based modeling approach to the growth dynamics can simplify our understanding of the fundamental physical dynamics such as shadowing and re-emission effects

Network Behavior in Thin Film Growth Dynamics

Understanding patterns and components in thin film growth is crucial for many engineering applications. Further, the growth dynamics (e.g., shadowing and re-emission effects) of thin films exist in several other natural and man-made phenomena. Recent work developed network science techniques to study the growth dynamics of thin films and nanostructures. These efforts used a grid network model (i.e. viewing of each point on the thin film as an intersection point of a grid) via Monte Carlo simulation methods to study the shadowing and re-emission effects in the growth. These effects are crucial in understanding the relationships between growth dynamics and the resulting structural properties of the film to be grown. In this dissertation, we use a cluster-based network model with Monte Carlo simulation method to study these effects in thin film growth. We use image processing to identify clusters of points on the film and establish a network model of these clusters. Monte Carlo simulations are used to grow films and dynamically track the trajectories of re-emitted particles. We treat the points on the film substrate and cluster formations from the deposition of adatoms / particles on the surface of the substrate as the nodes of network, and movement of particles between these points or clusters as the traffic of the network. Then, graph theory is used to study various network statistics and characteristics that would explain various important phenomena in the thin film growth. We compare the cluster-based results with the grid-based results to determine which method is better suited to study the underlying characteristics of the thin film. Based on the clusters and the points on the substrate, we also develop a network traffic model to study the characteristics and phenomena like fractal behavior in the count and inter-arrival time of the particles. Our results show that the network theory of the growth process explains some of the underlying phenomena in film growth better than the existing theoretical and statistical models

Network Behavior in Thin Film Growth Dynamics

We present a new network modeling approach for various thin film growth techniques that incorporates re-emitted particles due to the non-unity sticking coefficients. We model re-emission of a particle from one surface site to another one as a network link, and generate a network model corresponding to the thin film growth. Monte Carlo simulations are used to grow films and dynamically track the trajectories of re-emitted particles. We performed simulations for normal incidence, oblique angle, and chemical vapor deposition (CVD) techniques. Each deposition method leads to a different dynamic evolution of surface morphology due to different sticking coefficients involved and different strength of shadowing effect originating from the obliquely incident particles. Traditional dynamic scaling analysis on surface morphology cannot point to any universal behavior. On the other hand, our detailed network analysis reveals that there exist universal behaviors in degree distributions, weighted average degree versus degree, and distance distributions independent of the sticking coefficient used and sometimes even independent of the growth technique. We also observe that network traffic during high sticking coefficient CVD and oblique angle deposition occurs mainly among edges of the columnar structures formed, while it is more uniform and short-range among hills and valleys of small sticking coefficient CVD and normal angle depositions that produce smoother surfaces.Comment: 11 pages, 9 figures, revtex

Polyelectrolyte nanostructures formed in the moving contact line: fabrication, characterization and application: Polyelectrolyte nanostructures formed in the moving contact line: fabrication, characterization and application

Having conducted the research described in this thesis I found that there exists a possibility to produce polyelectrolyte nanostructures on hydrophobic surfaces by application of the moving contact line approach. It was demonstrated that the morphology of nanostructures displays a range of structure variations from root-like to a single wire structure with a high anisotropy and aspect ratio (providing diameters of several nanometers and the length limited by the sample surface dimensions). Such nanostructures can be produced exactly on the spot of interest or can be transferred from the surface where they were produced to any other surfaces by the contact printing technique. A model describing the polymer deposition during the moving contact line processes on hydrophobic surfaces has been proposed. The application of this model provides the ground for an explanation of all the obtained experimental data. Utilizing moving contact line approach aligned one-dimensional polycation structures were fabricated and these structures were used as templates for assembling amphiphile molecules. Quasiperiodic aligned and oriented nanostructures of polyelectrolyte molecules formed in moving droplets were utilized for fabrication of electrically conductive one-dimensional nanowires

Flexomagnetism and vertically graded Néel temperature of antiferromagnetic Cr2O3 thin films

Antiferromagnetic insulators are a prospective materials platform for magnonics, spin superfluidity, THz spintronics, and non-volatile data storage. A magnetomechanical coupling in antiferromagnets offers vast advantages in the control and manipulation of the primary order parameter yet remains largely unexplored. Here, we discover a new member in the family of flexoeffects in thin films of Cr2O3. We demonstrate that a gradient of mechanical strain can impact the magnetic phase transition resulting in the distribution of the Néel temperature along the thickness of a 50-nm-thick film. The inhomogeneous reduction of the antiferromagnetic order parameter induces a flexomagnetic coefficient of about 15 μB nm−2. The antiferromagnetic ordering in the inhomogeneously strained films can persist up to 100 °C, rendering Cr2O3 relevant for industrial electronics applications. Strain gradient in Cr2O3 thin films enables fundamental research on magnetomechanics and thermodynamics of antiferromagnetic solitons, spin waves and artificial spin ice systems in magnetic materials with continuously graded parameters

Annual Report 2015 - Institute of Ion Beam Physics and Materials Research

After the successful evaluation in 2015 we started research and further development of our largescale facilities, in particular the Ion Beam Center (IBC), in the framework of Helmholtz’s Programmeoriented Funding scheme (POF) which coordinates scientific cooperation on a national and international scale. Most of our activities are assigned to the Helmholtz program “From Matter to Materials and Life” within the research area “Matter”, in cooperation with several other German Helmholtz Centers. Our in-house research is performed in three so-called research themes, as depicted in the schematic below. What is missing there for simplicity is a minor part of our activities in the program “Nuclear Waste Management and Safety” within the research area “Energy”. A few highlights which have been published in 2015 are reprinted in this annual report in order to show the variety of the research being performed at the Institute, ranging from self-organized pattern formation during ion erosion or DNA origami patterning, over ferromagnetism in SiC and TiO2 to plasmonics and THz-spectroscopy of III-V semiconductors. A technological highlight published recently is the demonstration of nanometer scale elemental analysis in a Helium ion microscope, making use of a time-of-flight detector that has been developed at the IBC. In addition to these inhouse research highlights, also users of the IBC, in particular of the accelerator mass spectrometry (AMS), succeeded in publishing their research on geomorphology in Nepal in the high-impact journal Science (W. Schwanghart et al., Science 351, 147 (2015)), which demonstrates impressively the added value of transdisciplinary research at the IBC. In order to further develop the IBC, we have started in 2015 the design and construction of our new low energy ion nanoengineering platform which was highly recommended by the POF evaluators. It will consist of two-dimensional materials synthesis and modification, high-resolution ion beam analysis and high-resolution electron beam analysis and will come into full operation in 2019

Utilisation of microbiosensors for monitoring phenols in whisky fermentation process

Biosensors for the specific, sensitive and rapid detection of analytes could play an important role in fermentation industries such as the whisky industry. Long-standing challenges remain unmet and these are associated with the establishment of low-cost, easy-to-use, miniaturised, robust, reliable and highly specific biosensors. In this paper, an optical method, and more specifically fluorescence, is used for the development of a portable biosensor in combination with enzyme technology and microfabrication for the determination of phenols in smoked whisky. At present, chromatographic techniques are utilised by taking a single sample from the fermentation vessel, which may not be totally representative, so an in situ biosensor can improve the quality control during the fermentation process. The enzyme tyrosinase and a fluorescence ruthenium complex oxygen indicator were used for the detection of different phenol percentage. The enzyme and the indicator were immobilised in polymeric films during the microfabrication process. Furthermore, a comparative assessment of the enzyme and the aptamer technologies are discussed. During the last 20 years since the SELEX method developed, over 2000 papers related to aptamers or SELEX have been published and the aptamer biosensors have been enchanced and many new DNA aptamers have been developed. The utilisation of aptamer technology is discussed and advantages over the enzyme biosensor are highlighted for future work