Nanoscale Corrugation Research Articles

Nanoscale periodic corrugation to dimple transition due to “beat” in a bulk metallic glass

We report an intriguing observation that the interaction of brittle nanoscale periodic corrugations (NPCs) can lead to the formation of ductile dimples on the dynamic fracture surface of a tough Vit 1 bulk metallic glass (BMG) under high-velocity plate impact. A “beat” phenomenon due to superposition of simple harmonic vibrations, approximately characterizing NPCs, is proposed to explain this unusual brittle-to-ductile transition. The present results agree well with our previously revealed energy dissipation mechanism in the fracture of BMGs.

Tuning the electrical resistivity of semiconductor thin films by nanoscale corrugation

The low-temperature electrical resistivity of corrugated semiconductor films is theoretically considered. Nanoscale corrugation enhances the electron-electron scattering contribution to the resistivity resulting in a stepwise resistivity development with increasing corrugation amplitude. The enhanced electron scattering is attributed to the curvature-induced potential energy that affects the motion of electrons confined to a thin curved film. Geometric conditions and microscopic mechanism of the stepwise resistivity are discussed in detail.

Nanoscale morphologies on the fracture surface of bulk metallic glasses in the supercooled liquid region

We report the observations of nanoscale corrugation, nanowave and its branching structures on the fracture surface of tough Vit.1 bulk metallic glass (BMGs) in the supercooled liquid region. Wavelike behaviors of corrugations are observed as well. A shear band-based fracture model is proposed to interpret the formation of nanoscale morphologies in the fracture surfaces of bulk metallic glasses. The results might provide a new insight into the origin of fracture surface roughening in BMGs.

Ductile Fe–Nb–B bulk metallic glass with ultrahigh strength

The authors report a simple Fe-based Fe71Nb6B23 ternary bulk metallic glass with a record high strength of 4.85GPa as well as an appreciable compressive plastic strain of 1.6%. This finding is associated with the unique attribute of the alloying element Nb, which favors the formation of a networklike structure and holds high Poisson’s ratio. A fracture feature with a combination of vein pattern and nanoscale corrugations under compression is clearly characterized in this glass. The fractographic observations correlate well with the observed improvements in plasticity.

Energy dissipation in fracture of bulk metallic glasses via inherent competition between local softening and quasi-cleavage

Compression, tension and high-velocity plate impact experiments were performed on a typical tough Zr41.2Ti13.8Cu10Ni12.5Be22.5 (Vit 1) bulk metallic glass (BMG) over a wide range of strain rates from ∼10−4 to 106 s−1. Surprisingly, fine dimples and periodic corrugations on a nanoscale were also observed on dynamic mode I fracture surfaces of this tough Vit 1. Taking a broad overview of the fracture patterning of specimens, we proposed a criterion to assess whether the fracture of BMGs is essentially brittle or plastic. If the curvature radius of the crack tip is greater than the critical wavelength of meniscus instability [F. Spaepen, Acta Metall. 23 615 (1975); A.S. Argon and M. Salama, Mater. Sci. Eng. 23 219 (1976)], microscale vein patterns and nanoscale dimples appear on crack surfaces. However, in the opposite case, the local quasi-cleavage/separation through local atomic clusters with local softening in the background ahead of the crack tip dominates, producing nanoscale periodic corrugations. At the atomic cluster level, energy dissipation in fracture of BMGs is, therefore, determined by two competing elementary processes, viz. conventional shear transformation zones (STZs) and envisioned tension transformation zones (TTZs) ahead of the crack tip. Finally, the mechanism for the formation of nanoscale periodic corrugation is quantitatively discussed by applying the present energy dissipation mechanism.

Nanopatterned Contacts to GaN

The effect of nanoscale patterning using a self-organized porous anodic alumina (PAA) mask on the electrical properties of ohmic and Schottky contacts to n-GaN was investigated with the aim of evaluating this approach as a method for reducing the specific contact resistance of ohmic contacts to GaN. The electrical characteristics of contacts to these nanopatterned GaN samples were compared with contacts to planar, chemically prepared ("as-grown") GaN samples and reactive ion etched (RIE) GaN films without any patterning. The specific contact resistivities to unintentionally doped n-GaN using a Ti/Al bilayer metallization were determined to be 7.4 × 10 -3 Ω cm 2 for the RIE sample and 7.0 x 10 -4 Ω cm 2 for the PAA patterned sample. Schottky metal contacts with Pt and Ni were prepared on the three samples to validate the effects of RIE and nanopatterning on electrical behavior. The effective barrier height was decreased and the reverse current was increased significantly in the PAA patterned sample. The radius of curvature of the nanoscale corrugation in the patterned interface was smaller than the depletion width. The reduction of the depletion width at sharp corners enhanced the local tunneling current, reducing the specific contact resistivity and decreasing the effective barrier height. These results suggest that nanopatterning with PAA on GaN can significantly lower the contact resistance.

Mechanism for hierarchical self-assembly of nanoparticles on scaffolds derived from block copolymers

Lithographically patterned substrates can direct the self-assembly of block copolymer films into aligned structures that, in turn, template the self-organization of colloidal nanoparticles. Deposition on pristine diblock copolymer films does not lead to reproducible selective decoration, but films modified to have nanoscale corrugation act as scaffolds for highly selective nanoparticle adsorption. The mechanism for this selectivity relies on the lateral forces inherent to spin casting to remove all of the nanoparticle suspension not confined within the nanoscopic trenches. This technique does not rely on interactions between the surfactant capping molecules and the polymer and is therefore general to a wide class of nanoparticle materials. Prospects to obtain long-range ordering and associated potential applications are discussed.

Impact of interface relaxation on the nanoscale corrugation in Pb/Si(1 1 1) islands

The nanoscale hexagonal pattern observed in scanning tunneling microscopy (STM) for 3-layer and 4-layer Pb islands on Si(1 1 1) is studied theoretically. We found that besides thickness the atomic rearrangement at the Pb/Si interface plays an important role in determining the STM patterns. Electronic structures of the Pb film on Si(1 1 1) obtained from fully relaxed and unrelaxed Pb films are qualitatively different. Simulated STM images for Pb films with different stacking also show that the corrugation patterns are sensitive to the buried Pb–Si interfacial structure.

Decay Kinetics of Nanoscale Corrugation Gratings on Polymer Surface: Evidence for Polymer Flow below the Glass Temperature

The near-surface rheology of polystyrene films at temperatures around Tg was probed via the decay kinetics of shallow, nanoscale surface corrugation gratings. The gratings were created via hot embossing with a stepped silicon template. The wavelengths are distributed in a range between 25 and 60 nm and have a modulation depth of about 0.8 nm peak-to-peak. Upon heating, one observes a surface tension-driven decay of the surface corrugation at temperatures more than 30 deg below the bulk Tg. Such a fast decay is unexpected and indicates a strongly lowered glass temperature near the surface.

Growth of ordered, single-domain, alumina nanopore arrays with holographically patterned aluminum films

Highly-ordered, single-domain (∼cm2), alumina nanopore arrays with controlled symmetry were obtained by anodizing prepatterned aluminum films that were deposited on silica substrates. Holographic lithography, in conjunction with a conformal deposition process, was utilized to form nanoscale corrugations on aluminum film surface prior to anodization. Both the order and symmetry of pore arrays were found to be well controlled and guided by the periodic surface corrugations from the initial stage of pore growth. Ordered nanopore arrays grown on foreign substrates are promising as a host or template for forming various nanodevices and their on-chip integration.

RESONANT LIGHT TRANSMISSION IN METALLIC PHOTONIC CRYSTAL SLABS

Light transmission through an opaque nanoscale metallic photonic crystal slabs (MPCS) are investigated. The experimental results show that it is possible to get the extraordinary transmission in visible region even without the presence of holes, which is different from the perforated nanoholes or nanoslits in metallic system. The observed phenomenon can be understood in terms of surface plasmon-enhanced resonant emission of light through a metal structure with a nanoscale corrugation rather than light penetration through tiny holes. It is the periodicity of the interface corrugation that is important for the plasmon as a radiative channel rather than loss. The study suggests that a wide range of photonic applications is possible for such system.

Spontaneous nanoscale corrugation of ion-eroded SiO2: the role of ion-irradiation-enhanced viscous flow.

Grazing incidence x-ray scattering was used to determine the temperature and ion-energy dependence of nanoscale corrugations that form on an amorphous SiO2 surface eroded by Ar+ ions. The corrugation wavelength lambda* shows a nearly linear dependence on ion energy. Between room temperature and approximately 200 degrees C, lambda* depends weakly on temperature and above approximately 200 degrees C it shows an Arrhenius-like increase. Ion-assisted viscous relaxation in a thin surface layer is shown to be the dominant smoothing process during erosion; the rate of viscous smoothing scales as (lambda*)(-4).