Hexagonally ordered arrays of non‐close‐packed nanoscaled spherical polystyrene (PS) particles are prepared exhibiting precisely controlled diameters and interparticle distances. For this purpose, a newly developed isotropic plasma etching process is applied to extended monolayers of PS colloids (starting diameters <300 nm) deposited onto hydrophilic silicon. Accurate size, shape, and smoothness control of such particles is accomplished by etching at low temperatures (−150 °C) with small rates not usually available in standard reactive ion etching equipment. The applicability of such PS arrays as masks for subsequent pattern transfer is demonstrated by fabricating arrays of cylindrical nanopores into Si.
Among the many phenomena revealed and provided by nanoscience, the functionalization of a surface by nanopatterning certainly holds promise for a large number of attractive applications. A prominent example is the deposition of self-assembled monolayers by microcontact printing in order to control wettability, adhesion, friction, and wear. [1,2] In this context, the well-known lotus effect should be mentioned. This effect is based on a strong reduction of the adhesion of water droplets by nanopatterning a surface with, for example, dense arrays of statistically distributed nanopillars. [3,4] A further application of such nanopillars is their use as effective electron field emitters, as has been demonstrated for Si, [5,6] a material which is also at the focus of the present work, or, more recently, for diamond. [7] Moreover, highly ordered arrays of nanopillars are extremely helpful for the characterization of individual emitters by scanning tunneling microscopy (STM) or scanning tunneling spectroscopy (STS).For an inverted pattern of nanopillars, that is, ordered arrays of cylindrical nanopores with a high aspect ratio, a similar wealth of possible applications can be thought of. For instance, they can serve as contact holes in semiconductors. According to the present semiconductor technology roadmap, they should exhibit diameters well below 80 nm for the "65 nm node generation".[8] Similarly, applications in nanooptics appear attractive; nanopores based on colloidal masks were fabricated into Si with a diameter of 60 nm. [9] Smaller diameters of the order of 30 nm should be obtainable by nanomachining a poly(methyl methacrylate) PMMA resist with an atomic force microscope and subsequent metal-coating and lift-off, thereby accepting the disadvantage of a nonparallel process. [10] Note that the recently developed technique of controlling the diameter of nanopores in ultrathin Si/SiO 2 membranes by the electron beam of a transmission electron microscope is still a nonparallel procedure.[11] Another approach to preparing nanoholes in Si is based on self-organized porous alumina masks in combination with anisotropic Cl 2 reactiveion etching (RIE). [12] In this way, holes with diameters > 13 nm and an aspect ratio of 3 could be obtained. Similar diameters are obtained by a recently reported technique based on the self-organization of inverse spherical micelles formed from diblock copolymers dissolved in an apolar solvent, such as toluene, and selectively loaded in the micellar core with a metal salt, such as HAuCl 4 .[13-16] By dip-coating such solutions onto practically any sufficiently flat substrate, hexagonally ordered arrays of Au nanodots can be prepared by an ashing process.[17] They can be used as nanomasks in a subsequent anisotropic etching step, resulting in corresponding arrays of nanopillars. In this way, hexagonally ordered pillars with a diameter of 14 nm and an aspect ratio of 5 were obtained in Si. This micellar preparation technique offers a number of impressive advantages, such as the control of the...
Plasma etching of densely packed arrays of polystyrene particles leads to arrays of spherical nanostructures with adjustable diameters while keeping the periodicity fixed. A linear dependence between diameter of the particles and etching time was observed for particles down to sizes of sub-50 nm. Subsequent deposition of Co/Pt multilayers with perpendicular magnetic anisotropy onto these patterns leads to an exchange-decoupled, single-domain magnetic nanostructure array surrounded by a continuous magnetic film. The magnetic reversal characteristic of the film-particle system is dominated by domain nucleation and domain wall pinning at the particle locations, creating a percolated perpendicular media system.
Trap centers and minority carrier lifetimes are investigated in InAs/(GaIn)Sb superlattices used for photodetectors in the far-infrared wavelength range. In our InAs/(GaIn)Sb superlattice photodiodes, trap centers located at an energy level of about 1/3 band gap below the effective conduction band edge could be identified by simulating the current-voltage characteristics of the diodes. The simulation includes diffusion currents, generation-recombination contributions, band-to-band coherent tunneling, and trap assisted tunneling. By including the contributions due to trap-assisted tunneling, excellent reproduction of the current voltage curves is possible for diodes with cut-off wavelength in the whole 8-32 µm spectral range at temperatures between 140 K and 25 K. The model is supported by the observation of defect-related optical transitions at about 2/3 of the band-to-band energy in the spectra of the low temperature electroluminescence of the devices. With the combination of Hall- and photoconductivity measurements, minority carrier lifetimes are extracted as a dependence of temperature and carrier density
The dewetting process, which appears upon laserinduced melting of flat nanostructures and leads to a jumping of the droplets off the surface, is used for deposition of nano-particles onto a second substrate. Limitations in materials and particle sizes are discussed and experimentally verified. The experiments show that a variety of metals can be deposited in a size ranging from tens up to several hundreds of nanometers.
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