Pre-patterned Films Research Articles

Role of deposition noise in nanostructure formation: A theoretical investigation of quantum dots and quantum dotmolecules

Quantum dots (QDs) and quantum dot molecules (QDMs) are nanostructures that spontaneously self-assemble under different heteroepitaxial growth conditions to reduce the strain in the system. In the silicon–germanium system, QDs form when the rate of deposition is low, whereas QDMs form at higher deposition rates. In this work, the theoretical model of silicon–germanium heteroepitaxy is modified by explicitly incorporating noise in a continuum theory for surface evolution in molecular beam epitaxy. Using the connection between higher deposition flux and a higher noise amplitude, it is possible to explain how changing flux can lead to a transition from QD to QDM formation, as seen in experiments. In these systems, increasing the noise amplitude leads to formation of pits on the surface, as opposed to QDs. These pits serve as nucleation sites for eventual QDM formation and subsequent refinement during annealing. On the other hand, in the case of pre-patterned films with existing pits, QDMs form under low stochasticity, whereas QDs form when the noise amplitude is large. Thus, we illustrate a dual role of noise in nanostructure growth: one where it promotes formation of QDMs via pit nucleation and another where it curtails QDM formation due to stochastic effects.

Swelling-induced surface instability patterns guided by pre-introduced structures.

Swelling-induced, spontaneously generated surface instability patterns in substrate-attached hydrogel films can be harnessed for advanced applications, however, methods to control their formation and morphology are missing. Here we propose that their generation may be guided by intentionally pre-introduced line structures. While uniform gel films produce irregular polygonal instability patterns, instability patterns generated in pre-patterned films with hexagonal line structures are regular hexagons with long-range order. The pre-introduced line structures act as defects in the generation of the surface instability patterns, which determine the position of the creases, regulate their rearrangement and determine their final morphology. The contrast between the pre-introduced structures and the surrounding area should be high enough for the pre-introduced structures to act as defects. Only when the characteristic wavelength of the pre-introduced pattern matches with the one of the gel film, perfect hexagonal patterns can be obtained. The gel films with uniform topographic features may find various advanced applications.

Structural, magnetic, and mechanical properties of 5μm thick SmCo films suitable for use in microelectromechanical systems

5 μ m thick SmCo films were deposited onto Si substrates using triode sputtering. A study of the influence of deposition temperature (Tdep⩽600°C) on the structural, magnetic, and mechanical properties has shown that optimum properties [highest degree of in-plane texture, maximum in-plane coercivity and remanence (1.3 and 0.8T, respectively), and no film peel-off] are achieved for films deposited at the relatively low temperature of 350°C. This temperature is compatible with film integration into microelectromechanical systems. The deposition rate was increased from 3.6to18μm∕h by increasing the surface area of the target from 7to81cm2 while keeping the target potential fixed. Mechanically intact films could be prepared by deposition onto prepatterned films or deposition through a mask.

Preparation of micropatterned poly(silsesquioxane) thin films using adamantylphenol molecules

Poly(methyl silsesquioxane) (PMSSQ) thin films with micropatterned surface structures have been prepared by use of adamantylphenol molecules as a photo-thermal sensitive moiety together with UV lithographic technique and mild heating process. Initially, PMSSQ films form positive patterns of micronscale due to the film densification triggered by photooxidation and photopolymerization of doped moieties within UV exposed region. With thermal treatment, negative patterns from these pre-patterned films are formed by the difference of polycondensation rates between non-exposed regions and irradiated areas without additional developing or etching steps. This structural transformation of PMSSQ thin films was investigated using Fourier-transformed infrared spectroscopy, ultraviolet visible spectroscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, and field emission scanning electron microscopy.

Comparison of excimer laser recrystallized prepatterned and unpatterned silicon films on SiO2

The laser recrystallization of unpatterned and prepatterned silicon films on SiO2 is compared. For the prepatterned films, multiple-pulse laser irradiation at certain energy densities produces three well defined zones containing different microstructure. Two of these zones appear as bands along the edges of the prepatterned islands. The first zone, or “chill zone,’’ is found at the outer edge of the island, and consists of an ∼250-nm-wide band of heterogeneously nucleated fine grains. The second zone, or “columnar zone,’’ is found next to the chill zone, and is made up of large elongated grains, measuring about 1.5×0.5 μm, with their boundaries running perpendicular to the island edges. Finally, the third zone, or “equiaxed zone,’’ includes the remainder of the prepatterned island, and has a grain microstructure identical to the recrystallized unpatterned films. The creation and identification of these three zones for laser irradiated prepatterned Si films is presented. The laser conditions that create these zones, and the recrystallization mechanisms and resulting microstructure of each zone are presented in detail.