Search

We present a molecular dynamics simulation scheme that we apply to study the time evolution of the self-organized growth process of metal cluster assemblies formed by sputter-deposited gold atoms on a planar surface. The simulation model incorporates the characteristics of the plasma-assisted deposition process and allows for an investigation over a wide range of deposition parameters. It is used to obtain data for the cluster properties which can directly be compared to recently published experimental data for gold on polystyrene (M. Schwartzkopf \textit{et al}., ACS Appl. Mater. Interfaces \textbf{7}, 13547 (2015)). While good agreement is found between the two, the simulations additionally provide valuable time-dependent real-space data of the surface morphology some of whose details are hidden in the reciprocal-space scattering images that were used for the experimental analysis.

The stress generated during thermal cycling of electron‐beam‐evaporated Cr‐Co and Ti‐Co films on quartz substrates was measured by means of the cantilever bending‐beam technique between 20 and 550 °C. The thickness ratio was selected to correspond to an atom ratio of [Co]/[Cr] and [Co]/[Ti]>3. In the unreacted films, the residual stress after cycling is tensile and comparable with that in pure Co. In Co‐Cr films there is only a slight increase in stress after complete reaction, whereas a marked increase in tensile stress is observed in Co‐Ti films. Phase formation and reaction kinetics were investigated by Rutherford backscattering and x‐ray diffraction. The dominant phases in Co‐Cr are solid solutions of Cr in Co and Co in Cr with the same structure as the original films. In Co‐Ti the main reaction product is the intermetallic compound Co3Ti with the Cu3Au structure. The formation of Co3Ti, which is accompanied by volume shrinkage, is diffusion controlled. The high activation energy of 2.4±0.2 eV suggest...

Recent experiments and kinetic Monte Carlo (KMC) simulations [H. Greve et al., Appl. Phys. Lett. 88, 123103 (2006), L. Rosenthal et al., J. Appl. Phys. 114, 044305 (2013)] demonstrated that physical vapor co-deposition of a metal alloy (Fe-Ni-Co) and a polymer (Teflon AF) is a suitable method to grow magnetic nanocolumns in a self-organized one-step process. While only thermal sources have been used so far, in this work, we analyze the feasibility of this process for the case of a sputtering source. For that purpose, we extend our previous simulation model by including a process that takes into account the influence of ions impinging on the substrate. The simulation results predict that metal nanocolumn formation should be possible. Furthermore, we show that the effect of ions that create trapping sites for the metal particles is to increase the number of nanocolumns.

Metal-polymer nanocomposites have been investigated extensively during the last years due to their interesting functional applications. They are often produced by vapor phase deposition which generally leads to the self-organized formation of spherical metallic nanoparticles in the organic matrix, while nanocolumns are only obtained under very specific conditions. Experiments\cite{Grev+06} have shown that co-evaporation of the metallic and organic components in a simple single-step process can give rise to the formation of ultrahigh-density Fe-Ni-Co nanocolumnar structures embedded in a fluoropolymer matrix. Here we present a kinetic Monte Carlo approach which is based on an new model involving the depression of the melting point on the nanoscale and a critical nanoparticle size required for solidification. In addition we present new experimental results down to a deposition temperature of \cel{-70} and also report the magnetic properties. The simulations provide a detailed understanding of the transition from spherical cluster growth to formation of elongated structures and are in quantitative agreement with the experiments.

We quantitatively assessed the influence of reactive gases on the formation processes of transition metal clusters in a gas aggregation cluster source. A cluster source based on a 2 in. magnetron is used to study the production rate of titanium and cobalt clusters. Argon served as working gas for the DC magnetron discharge, and a small amount of reactive gas (oxygen and nitrogen) is added to promote reactive cluster formation. We found that the cluster production rate depends strongly on the reactive gas concentration for very small amounts of reactive gas (less than 0.1% of total working gas), and no cluster formation takes place in the absence of reactive species. The influence of discharge power, reactive gas concentration, and working gas pressure are investigated using a quartz micro balance in a time resolved manner. The strong influence of reactive gas is explained by a more efficient formation of nucleation seeds for metal-oxide or nitride than for pure metal.

Granular nanocomposite films with embedded metallic particles have been suggested as a promising material class for magnetoelectric (ME) applications. We present a thorough case study of nanogranular aluminum nitride (AlN)/cobalt (Co) composites accompanied by finite element simulations. The present study shows that the use of metallic nanoparticles in 0–3 nanocomposites has fundamental limitations for the development of ME materials. AlN/Co films are deposited by magnetron co-sputtering with a gas aggregation cluster source, allowing the direct investigation of the cluster influence on the structural properties of the matrix under otherwise identical deposition conditions. While commonly leakage currents are perceived as the major challenge of the granular approach, our findings indicate further inherent hindrances. Apart from an increase of dielectric losses tanδ with increasing cobalt content, we find a drastic degradation of matrix crystallinity already at very low filling factors and a pronounced inc...

An improved effective medium approximation (EMA) is presented that accounts for higher order interactions between metal nanoparticles in metal-dielectric composite materials and compared to experimental results. The theoretical results of this formalism are applied to a composite material consisting of spherical gold nanoparticles randomly distributed in a dielectric matrix, which has been extensively characterized with respect to its structural and optical properties. The experimental results and theoretical predictions are compared and the results are discussed. It is shown that the modified theory expands the range to which EMA can be applied to a metal filling fraction of ∼20% at very little additional computational expenses. The improved theory also allows extracting more information from the optical characterization of the composite material such as the distribution of the interparticle distances in a composite.

The stress relaxation behavior during thermal cycling of metal/quartz and metal/polyimide/quartz layered structures has been investigated using a cantilever bending beam technique. The metals chosen for this study include Cu and Cr, two materials with contrasting mechanical and interfacial bonding properties. A finite element analysis, as well as an analytical calculation, has been carried out to deduce the stress distribution in the layered structures. Results indicate that the extent of stress relaxation strongly depends on the intrinsic mechanical property of the metal film with significantly higher stresses residing in the Cr film than in the Cu film. The interfacial polyimide layer has been found to serve as an effective buffering layer to reduce the residual stress in metal films. Observations from transmission electron microscopy suggest that the stress is partially released through the deformation of the polyimide near the metal/polyimide interface.

Adhesion and interfacial failure of Cr, Cu, and Cu/Cr films on a thin pyromellitic dianhydride‐oxydianiline polyimide substrate have been investigated using a recently developed stretch deformation technique. This method directly measures the energy required to separate the interface from the difference in the load versus elongation curves between film/substrate and substrate structures. The failure mode was observed in combination with morphological studies by in situ optical microscopy and scanning and transmission electron microscopies. The stress distribution in the sample upon stretching has been computed by a finite element analysis. The difference in the stress relief modes, film fracture, and delamination behavior for Cu versus Cr films is discussed. The important role of crack formation in the metal overlayer for initiating failure is demonstrated. The effects due to the addition of a brittle Cr interface layer between polyimide and Cu on the buildup of stress and the onset of failure have also b...