A study of the dewetting behavior of platinum-thin-films on silicon was carried out to determine how variation of dewetting parameters affects the evolution of film morphology and to pinpoint which parameters yielded the smallest, most circular features. Platinum film thickness as well as dewetting time and temperature were varied and the film morphology characterized by means of scanning electron microscopy (SEM) analysis. Two different pathways of dewetting predicted in the literature (Vrij 1966 Discuss. Faraday Soc. 42 23, Becker et al 2003 Nat. Mater. 2 59-63) were observed. Depending on the initial criteria, restructuring of the film occurred via hole or droplet formation. With increased annealing time, a transition from an intermediate network structure to separated islands occurred. In addition, the formation of multilayered films, silicide crystals and nanowires occurred for certain parameters. Nevertheless, the dewetting behavior witnessed could be related to physical processes. Droplets with a mean diameter of 9 nm were formed by using a 1.5 nm thick platinum film annealed at 800 °C for 30 s. To demonstrate the suitability of the annealed films for further processing, we then used the dewetted films as masks for reactive ion etching to transfer the pattern into the silicon substrate, forming tapered nanopillars.
ResultsThe median age at diagnosis and the end of the study was 13 (range 1-84) and 82 (range 16-248) months, respectively. Three splenectomised and one non-splenectomised patients died during the total observation period of 436 on 12 May 2018 by guest. Protected by copyright.
We present a novel technique for fabricating nanometre spaced metal electrodes on a
smooth crystal cleavage plane with precisely predetermined spacing. Our method does not
require any high-resolution nanolithography tools, all lateral patterning being based on
conventional optical lithography. Using molecular beam epitaxy we embedded a
thin gallium arsenide (GaAs) layer in between two aluminium gallium arsenide
(AlGaAs) layers with monolayer precision. By cleaving the substrate an atomically
flat surface is obtained exposing the AlGaAs–GaAs sandwich structure. After
selectively etching the GaAs layer, the remaining AlGaAs layers are used as a
support for deposited thin film metal electrodes. We characterized these coplanar
electrodes by atomic force microscopy and scanning electron microscopy; this
revealed clean, symmetric and macroscopically flat surfaces with a maximum
corrugation of less than 1.2 nm. In the case of a device with a 20 nm thick GaAs
layer the measured electrode distance was 22.5 nm with a maximum deviation of
less than 2.1 nm. To demonstrate the electrical functionality of our device we
positioned single colloidal gold nanoparticles between the electrodes by an alternating
voltage trapping method; this resulted in a drop of electrical resistance from
∼11 G Ω to
∼1.5 k Ω
at 4.2 K. The device structure has large potential for the manipulation of nanosized objects
like molecules or more complex aggregates on flat surfaces and the investigation of their
electrical properties in a freely suspended configuration.
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