We show that gallium-ion-implanted silicon serves as an etch mask for fabrication of high aspect ratio nanostructures by cryogenic plasma etching (deep reactive ion etching). The speed of focused ion beam (FIB) patterning is greatly enhanced by the fact that only a thin approx. 30 nm surface layer needs to be modified to create a mask for the etching step. Etch selectivity between gallium-doped and undoped material is at least 1000:1, greatly decreasing the mask erosion problems. The resolution of the combined FIB-DRIE process is 20 lines microm(-1) with the smallest masked feature size of 40 nm. The maximum achieved aspect ratio is 15:1 (e.g. 600 nm high pillars 40 nm in diameter).

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A disposable electrochemical test strip for the quantitative point-of-care (POC) determination of acetaminophen (paracetamol) in plasma and finger-prick whole blood was fabricated. The industrially scalable dry transfer process of single-walled carbon nanotubes (SWCNTs) and screen printing of silver were combined to produce integrated electrochemical test strips. Nafion coating stabilized the potential of the Ag reference electrode and enabled the selective detection in spiked plasma as well as in whole blood samples. The test strips were able to detect acetaminophen in small 40 μL samples with a detection limit of 0.8 μM and a wide linear range from 1 μM to 2 mM, well within the required clinical range. After a simple 1:1 dilution of plasma and whole blood, a quantitative detection with good recoveries of 79% in plasma and 74% in whole blood was achieved. These results strongly indicate that these electrodes can be used directly to determine the unbound acetaminophen fraction without the need for any additional steps. The developed test strip shows promise as a rapid and simple POC quantitative acetaminophen assay.

In this paper, we demonstrate silicon microdevice fabrication by a combination of focused ion beam (FIB) and cryogenic deep reactive ion etching (DRIE). Applying FIB treatment only to a thin surface layer enables very high writing speed compared with FIB milling. The use of DRIE then defines the micro-and nanodevices utilizing the FIB-modified silicon as a mask. We demonstrate the ability to create patterns on highly 3D structures, which is extremely challenging by other nanofabrication methods. The alignment of optically made and FIB-defined patterns is also demonstrated. We also show that complete microelectromechanical systems (MEMS) can be fabricated by this method by presenting a double-ended tuning fork resonator as an example. Extremely short process time is achieved as the full fabrication cycle from mask design to electrical measurements can be completed during one working day.

Corrosion protection of steel obtained with physical vapor deposition (PVD) coatings can be further improved by sealing the intrinsic pinholes with atomic layer deposition (ALD) coatings. In this work, the effect of surface wear on corrosion protection obtained by a hybrid PVD CrN/ALD Al2O3/TiO2 nanolaminate coating was studied. The samples were investigated by alternating surface wear steps and exposure to salt solution and consecutively the progression of corrosion after each wear and each corrosion step was evaluated. Optical microscopy, scanning electron microscopy (SEM), and energy-dispersive spectroscopy showed that the rust spots were almost exclusively located on positions at which the wear steps had removed the top surface of the PVD CrN coating. Nevertheless, even after complete removal of the ALD nanolaminate from the top of the CrN surface by sandpaper grinding, the corrosion current density was less than half compared to the PVD CrN coating alone without surface wear. Cross-sectional SEM images obtained with focused ion beam milling showed not only the presence of the ALD coating at the CrN defects but also the opening of new pathways for the corrosion to attack the substrate. A mechanism for the effect of wear on the structure and corrosion protection of hybrid PVD/ALD coatings is proposed on the basis of this investigation.

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A novel method for fabricating dual-type nanowire (NW) arrays is presented. Two growth steps, selective-area epitaxy (SAE) in the first step and vapor-liquid-solid (VLS) in the second step, are used to grow two types of NWs on the same GaAs substrate. Different precursors can be used for the growth steps, resulting in sophisticated compositional control, as demonstrated for side-by-side grown GaAs and InP NWs. It was found that parasitic growth occurs on the NWs already present on the substrate during the second growth step and that the SAE NWs shadow the growth of the VLS NWs. Optical reflectance measurements revealed the dual-type array having improved light trapping properties compared to single-type arrays. Dual-type NW arrays could be practical for thermoelectric generation, photovoltaics and sensing where composition control of side-by-side NWs and complex configurations are beneficial.

Nafion is a widely used polymer membrane in various applications ranging from advanced energy solutions to sensing of biomolecules. Despite the intensive research carried out over the years to reveal and understand the fine structure of Nafion, its structural features, especially as nanometer-scale films, are not unambiguously known. In this paper, we use room temperature scanning transmission electron microscopy (STEM) tomography complemented by glancing incidence small-angle X-ray scattering (GISAXS) and TEM at low temperatures to reveal the fine structure of thin (10−100 nm) unannealed Nafion films. The results from the detailed three-dimensional reconstructions obtained show that (i) the phase fractions of the hydrophobic and hydrophilic parts of the polymer are somewhat thickness-dependent, changing from 0.65/0.35 to about 0.7/0.3 when moving from 100 to 10 nm thick films; (ii) the channel diameters show a range of values from 3 to 6 nm in all the films independent of their thickness; (iii) the average distances between the hydrophilic channels inside the film have distributions centered around 12 nm (in 10 nm films), 15 nm (in 30 nm films), and 7 nm (in 100 nm films); (iv) in the thickest films, the hydrophilic channels exhibit higher interconnectivity and some of the channels appear to end within the Nafion film instead of going through the films; and (v) there are some confinement effects caused by the hydrophilic SiO 2 surface in the case of 10 and 30 nm thick films shown by the tendency of the hydrophilic channels to move horizontally near the substrate. Furthermore, a stable room temperature STEM tomography imaging method for Nafion films and a sample preparation method that preserves the characteristics of the hydrated morphology of Nafion in the dry state are demonstrated. These results provide a deeper understanding of the fine structure of Nafion thin films and provide a better means to characterize and understand their properties in different applications.