Nanoscale Periodic Structures Research Articles

Friction Properties of the DLC Film with Periodic Structures in Nano-scale

Reduction of friction at very low normal loads and for very small contact areas is important for the development of micro devices. High performance hard coatings such as diamond-like carbon (DLC) films and improved surfaces with nanostructures are being investigated with respect to their friction reduction properties. Previously, difficulties associated with the production of nano-scale periodic structures in DLC films have prohibited the study of such films.In the present study, the friction properties of the DLC film with periodic structures were investigated at the nano-scale using an atomic force microscope (AFM). These periodic structures were generated on the surface of the DLC film by means of a femtosecond (fs) laser having the fluence near the ablation threshold. Friction tests were carried out under normal loads ranging from 20 nN to 130 nN, and the frictional directions were 0º, 45º and 90º (relative to the line along which the periodic structures were created). The lateral force of the DLC film with the periodic structures was lower than that of the film without the periodic structures. We have concluded that decreases in adhesive forces produce significant decreases in lateral forces for the same normal loads.

Surface nanoscale periodic structures in congruent lithium niobate by domain reversal patterning and differential etching

We report on the fabrication and characterization of one- and two-dimensional periodic structures down to 200 nm size, in congruent lithium niobate crystal samples. Periods from 2μm to 530 nm are investigated. Interference photolithography is used to obtain short pitch insulating gratings, and subsequent electric-field poling, at the overpoling regime, is performed for periodic domain inversion. Nanoscale structures are obtained by selective chemical etching, and topographic investigations are performed by atomic force microscope. The fabricated structures are attractive in nonlinear optics for short-wavelength conversion and in the field of photonic crystals for Bragg and band-gap applications.

Nanoscale periodic and faceted structures formation on Si(1 0 0) by oblique angle oxygen ion sputtering

The dynamics of ripple topography on silicon surfaces generated by oxygen ion bombardment with increasing fluences have been investigated by atomic force microscopy (AFM). At the early stages of sputtering, periodic ripples with the wave vector parallel to ion beam direction are developed. At the late stages of sputtering, the ripple structure tends to break down and the surface becomes faceted. The growth rate of the ripples and the scaling exponents of the faceted surface have been determined. The results are discussed with reference to the Bradley–Harper theory and its nonlinear extension. Finally, the ripple wavelength is found to be a linear function of the bombarding energy.

Novel tunable optical properties of liquid crystals, conjugated molecules and polymers in nanoscale periodic structures as photonic crystals

AbstractTunability of optical properties such as transmission and reflection by temperature and applied voltage has been demonstrated in synthetic opals and inverse opals like three‐dimensional photonic crystals infiltrated with liquid crystals, conjugated molecules and polymers, in accordance with theoretical calculation. A new type of tunability based on uncoupled mode in a two‐dimensional photonic band gap influenced by the field‐dependent anisotropy in liquid crystals has also been demonstrated theoretically. Spectral narrowing and lasing have been observed in these opals infiltrated with conducting polymers and fluorescent dyes like three‐dimensional photonic crystal and fluorescent dye‐doped cholesteric and ferroelectric liquid crystal as one‐dimensional photonic crystal. These lasing wavelength can be controlled by the applied voltage. Laser emission was also realized with conducting polymer on a surface relief grating formed on an azo‐polymer film by interference optical beam.

Nanolithography with metastable helium atoms in a high-power standing-wave light field

We have created periodic nanoscale structures in a gold substrate with a lithography process using metastable triplet helium atoms that damage a hydrophobic resist layer on top of the substrate. A beam of metastable helium atoms is transversely collimated and guided through an intense standing-wave light field. Compared to commonly used low-power optical masks, a high-power light field (saturation parameter of 107) increases the confinement of the atoms in the standing wave considerably, and makes the alignment of the experimental setup less critical. Due to the high internal energy of the metastable helium atoms (20 eV), a dose of only one atom per resist molecule is required. With an exposure time of only eight minutes, parallel lines with a separation of 542 nm and a width of 100 nm (one-eleventh of the wavelength used for the optical mask) are created.

Open problems in the optics of crystals: the role of multiple scattering.

The thickness b of the transition boundary layer, always present in crystals and giving still unsolved problems for the boundary conditions, is shown to be essentially determined by the multiple scattering of light, due to the inhomogeneity of any periodic structure. The parameter b depends on the orientation theta of the boundary plane with respect to the crystal lattice, and diverges for some critical orientations where strong macroscopic effects are found, which cannot be interpreted by any macroscopic model based on bulk and boundary equations. Our analysis exhaustively defines the limits of validity of macroscopic models for periodic nanoscale structures and solid crystals.

Nanoscale Pattern Formation in Langmuir−Blodgett Films of a Semifluorinated Alkane and a Polystyrene−Poly(Ethylene Oxide) Diblock Copolymer

A novel example of the self-assembling capabilities of semifluorinated n-alkanes is presented: nanoscale periodic structures were revealed in mixed Langmuir−Blodgett films of a semifluorinated n-alkane with a polystyrene−poly(ethylene oxide) diblock copolymer by atomic force microscopy. The surface structures, resembling honeycombs with a hump at the center, have a periodicity of ∼40 nm. The same qualitative morphological features were found in all mixed films, independently of the polymer grafting density. Evidence suggests these structures arise from the organization of the semifluorinated alkane molecules segregated to the surface of the polymer layer.

Electrical and Optical Properties of Conducting Polymer and Carbons in Nano-Scale Periodic Structure and their Intercalation Effects

Nano-scale periodic structures of conducting polymer and carbons, which were prepared by infiltration of polymers and carbons in nano-scale interconnected periodic pores in synthetic opals made of regular array of SiO2 spheres and then removing SiO2 by etching, have been found to exhibit novel electrical and optical properties. Their electrical and optical properties in thus fabricated conducting polymer and carbon replicas change drastically upon pyrolysis due to progress of carbonization and graphitization. That is, due to the changes in periodicity, pore size, carbonization degree and crystal structure, electrical conductivity, magnetoconductance and their temperature dependences and optical reflection spectra have changed drastically. These replicas with porous nature can be infiltrated and also intercalated with various materials, resulting in also remarkable changes of properties. The synthetic opal infiltrated with conducting polymer can be electrochemically doped, with which remarkable change of optical properties have been observed due to the shift of the diffraction peak accompanying with the change in refractive index. Alkali metal intercalated carbon and graphite with nano-scale periodic structures have been also studied. The applications of these nano-scale periodic structures of conducting polymer and carbon are also discussed.

Optical properties of conducting polymers in nano-scale periodic structure, microcavities and photonic crystals

Properties of conducting polymers such as photoluminescence (PL) and electroluminescence (EL) depend on the molecular structure of the main chain and also substituents which influences on dimensionality, effective conjugation length and therefore electronic energy schemes and dynamics of excitons. Conducting polymers in nano-scale periodic structures such as multilayers, microcavities and photonic crystals exhibit novel optical characteristics such as unique EL and PL characteristics. Spectral narrowing of PL and lasing with low threshold of excitation intensity have been observed in conducting polymer films in microcavities and also in photonic crystals, synthetic opals with periodicity of several hundreds nano-meter, infiltrated with conducting polymers. Lasing characteristics in synthetic opals are found to be dependent on the periodicity of opalsand also refractive index of the solvent used for infiltration. Polymer replica of synthetic opals with periodic structures also exhibits novel electrical and optical characteristics.

Novel properties of nanoscale organic–inorganic systems and photonic crystals — conducting polymers in nanoscale periodic structures, microcavities and photonic crystals

Conducting polymer/C60and C60doped conducting polymer/C60heterojunctions have been fabricated and found to exhibit remarkably enhanced photoresponse due to the highly effective photoinduced charge transfer at the interface. In conducting polymer/C60alkali metal nanoscale composite systems, multiphase superconductivity has been clarified and explained by taking the coupling of nanoscale grains by Josephson junctions into consideration. As examples of intramolecular organic-inorganic combined systems, unique electrical and optical characteristics have been revealed in oligosilanylene oligophenylene polymers. Electroluminescence has been demonstrated in organic-inorganic junction devices such as conducting polymer/porous Si and conducting polymer/diamond junctions. Conducting, polymer-based nanoscale multilayer systems have been studied utilizing molecular self-assembly method and novel photosensitive characteristics have been revealed. \\indent Novel optical and electrical properties of conducting polymers infiltrated in a photonic crystal, synthetic opal made of SiO2spheres of several hundred nm in diameter, and also a conducting polymer replica have been revealed. A clear diffraction pattern was observed in a photonic crystal infiltrated with conducting polymers, and transmission spectra are dependent on various ambient conditions. Their photoluminescence (PL) spectra, spectral narrowing of PL and lasing characteristics at relatively low optical excitation have also been clarified. Novel conducting characteristics of conducting polymers in a photonic crystal that was prepared by pyrolysis of a polymer replica of opal have also been observed.