Porous 4H-SiC layers were fabricated by photochemical etching of n-type 4H-SiC samples with varying resistivity. An etching solution of Na 2 S 2 O 8 and HF was used while Pt deposited at the 4H-SiC surface served as catalyst for the reduction of Na 2 S 2 O 8 . The contact resistance at the Pt/4H-SiC junction was decreased by annealing and surface near phosphorous doping. This enabled the porosification of 4H-SiC with photochemical etching. © The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0021603jss] All rights reserved.Manuscript submitted November 9, 2015; revised manuscript received December 14, 2015. Published December 24, 2015 Compared to porous silicon, porous silicon carbide has many outstanding properties such as an enhanced chemical inertness, high heat conductivity and a relatively large bandgap. Therefore it offers novel application scenarios as electrode material in super-capacitors, 1 membranes for biomedical devices 2 or in the manufacturing of high temperature gas sensors. Controlling the etching depth for 6H-SiC is still an unresolved issue, while the formation of a porous structure on 4H-SiC is limited to surface regions in the nanometer range. 6,7 In this letter the formation of porous 4H-SiC by MAPCE is presented for samples having different bulk resistivity by decreasing the contact resistance at the Pt/4H-SiC junction. ExperimentalAs substrates, n-type 4H-SiC wafers with low and high resistivity (ρ = 0.02 · cm and ρ = 0.106 · cm respectively) were purchased from CREE. Square samples of these substrates with an area of 1 cm 2 were used for experiments. For cleaning, all samples were consecutively soaked for 5 minutes in acetone, isopropanol and ethanol. Then a 300 nm thin Pt layer was sputter deposited on the samples with a LS730S Von Ardenne sputter machine, while a 0.7 × 0.7 cm 2 silicon piece in the center of the sample served as shadow mask. Prior to Pt deposition, the samples were cleaned in situ using an inverse sputter etching procedure with Argon plasma for 60 s at 1000 W. Finally the samples were placed in an etching solution containing 0.04 mol/L Na 2 S 2 O 8 and 1.31 mol/L HF for 2 hours under UV irradiation. As etching chamber a porous silicon etching cell from AMMT GmbH with a total volume of 1.5 L was used. Front side illumination was z E-mail: markus.leitgeb@tuwien.ac.at done with a 250 Watt ES280LL mercury arc lamp at full spectrum. The distance from the samples to the UV source was approximately 3 cm. In this configuration the effective volume of the etching solution was 150 mL.For electrical characterization the Agilent B2911A Precision Source/Measure Unit was used. An array of circular Pt/TiN/Pt trilayered pads was sputter deposited onto 1 cm 2 square samples. The diameter of the pads was 1 mm and the dist...

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Restenosis after balloon angioplasty or stent placement is characterized by local accumulation of mainly vascular smooth muscle cells and the synthesis of extracellular matrix molecules (ECM).We hypothesized that inhibition of ECM synthesis represents a strategy to prevent trauma-induced neointima formation. Rats were treated with pirfenidone (1 g/kg of body weight orally.), an inhibitor of growth factor-induced collagen synthesis, and subjected to balloon denudation of the carotid artery. Two weeks later, computer-aided morphometry was done and compared with untreated controls (each n = 6). Neointimal proliferative activity was quantified immunohistochemically by counting PCNA-positive nuclei, and collagen deposition was visualized by picrosirius red staining and semi-quantified by Northern blot. Control-injured animals developed marked neointimal thickening within 2 weeks (I/M, mean intima to media ratio: 2.42 +/- 0.15) resulting in an 89.2% luminal narrowing. The neointima mainly consisted of vascular smooth muscle cells embedded in collagen. Neointima formation was strongly reduced when balloon-injured animals had been treated with pirfenidone (I/M ratio 0.22 +/- 0.08, P < 0.001), resulting in a minimal residual narrowing of the lumen (7.9%). I/M ratio did not further increase even after discontinuation of the drug for 14 days (0.35 +/- 0.13). Proliferative activity within the neointima was unaffected by the drug, 4.4% versus 4.8% of neointimal cells stained positive for PCNA in carotid arteries of treated versus untreated animals, respectively. However, picrosirius red staining demonstrated marked attenuation of collagen deposition, a finding that was further confirmed by Northern blot of homogenized vessels. Pirfenidone, currently being investigated clinically for the treatment of various fibrotic diseases, is able to prevent neointimal lesion formation most likely through inhibition of local ECM deposition. Targeting matrix deposition may have an intriguing potential for the prevention of vascular proliferative diseases.

In this article the etch morphology generated by a metal assisted chemical etch process, using silver particles is studied. Temperature, as well as doping concentrations, are varied over a wide range. Especially the results at low temperatures (<0°C) allow insight into the processes itself. Highly doped samples (Nd > 1017 cm−3) show an interesting tendency, by favoring micro pore formation over the usually observed template like etching of the metal coated regions. By considering the properties of the Schottky barrier between metal particle and silicon substrate the observed phenomena are discussed.