Carbon fibers, etching

Figure 1. Scanning electron micrograph of fracture surface of a mesophase pitch carbon fiber etched with chromic acid to reveal the radial arrangement of constituent lamellar molecules.

The processes involved in the production of these electrodes involve mounting the carbon fibers, etching them to produce a sharp tip, and subsequent insulation of the tip so that only the very end of the tip is exposed (1, 2). Testing of the electrode is then performed to determine whether there are any pinholes in the insulation. 

X.J. Zhang, B. Ogorevc, and J. Wang, Solid-state pH nanoelectrode based on polyaniline thin film elec-trodeposited onto ion-beam etched carbon fiber. Anal. Chim. Acta 452, 1-10 (2002). 

A critical factor here is the reactivity of the hydrogen by-product that is not only able to gasify the initial surface termination of the carbon fiber but also to etch away the newly formed pyrolytic carbon. This effect is desirable for optimization of the growing structure but additionally slows down the reaction. 

Surface treatments of carbon fibers can in general be classified into oxidative and non-oxidative treatments. Oxidative treatments are further divided into dry oxidation in the presence of gases, plasma etching and wet oxidation the last of which is carried out chemically or electrolytically. Deposition of more active forms of carbon, such as the highly effective whiskerization, plasma polymerization and grafting of polymers are among the non-oxidative treatments of carbon fiber surfaces. 

Figure 12.8 Light micrograph of a bovine adrenal medullary cell in culture with etched and glass-encased carbon-fiber electrodes (r = 5 /xm) placed adjacent to it. Magnification is 450x. [From Ref. 88, reproduced with permission of the copyright holder.]...

Most electrode materials that are employed in LCEC can also be used for CEEC. The most commonly employed working electrode is a carbon fiber. Carbon fibers come in many different sizes and can also be etched to smaller diameters. Common applications of CEEC with carbon fiber electrodes are the detection of catecholamines in single neuronal cells and amino acids in brain microdialysis samples following derivatization with NDA/CN. 

The acid-base properties of polyaniline can be utilized to produce solid-state pH sensors where polyaniline works both as the pH-sensitive material and as the ion-to-electron transducer. An excellent example is the electrodeposition of polyaniline on an ion-beam etched carbon fiber with a tip diameter of ca. 100-500 nm resulting in a solid-state pH nanoelectrode with a linear response (slope ca. — 60mV/pH unit) in the pH range of 2.0-12.5 and a working lifetime of 3 weeks [104]. The response time vary from ca. 10 s (around pH 7) to ca. 2 min (at pH 12.5). 

As far as we know, apart from a preliminary report about mercerization of cotton fibers (3) and a recent paper about chemically etched PETP filaments (4), high modulus aramide fibers and carbon fibers are practically the only systems with detailed (recently) published work on electron diffraction and dark field of ultrathin sections of textile or paratextile fibers (5, 6,... 

A single neuron-like PC 12 cell was trapped in an etched glass (30 pm deep) pocket sealed against a PDMS channel layer (20 pm). Quantal release of dopamine (in transient exocytosis) from the cell as stimulated by nicotine was amper-ometrically detected with a carbon fiber electrode. The cells flow into the channels caused by the liquid pressure which was provided by a liquid height at the sample reservoir (e.g., 0.5-2 mm). To facilitate transport of cells in the microchannels, the cell density should not be higher than lOVmL. Serious cell adhesion occurred if the transport speed was low (as provided by liquid height below 0.5 mm),... 

Using the plasmachemical method [3] of etching it was possible to receive the corresponding structure of carbon fibers bundle. 

The carbon fibers bundles structures of the raw cathode and the cathode etched by the plasmachemical method are represented in Fig. 3. Their corresponding field emission images are also presented there. 

At plasmachemical etching process the carbon fibers bundle gets the rounded form prominent fibers are absent, and peripheral — are short. At that time the uniformity of the luminescent screen radiation essentially improves. 

Figure 3. The non-forming carbon fibers bundle (a) and its field emission image (c). The carbon fibers bundle etched by plasma-chemical method (b) and its field emission image (d).

Figure 2. Scanning electron micrograph of a polished surface subsequently etched with chromic acid, of a carbon fiber-pitch carbon composite showing the orientation of a constituent lamellar molecules of pitch carbon parallel to surfaces of the carbon fiber.

Nanosensors for electrochemical detection have been made for years using more traditional fabrication methods, e.g., pulled platinum strings and carbon fibers. Carbon fibers can be purchased with diameters in the low /am range. These can subsequently be etched in an Ar beam until conically shaped tips are produced with tip diameters between 100 and 500 nm [61]. Similarly, a platinum wire can be heated and pulled in order to create tips of similar diameters. Thick film electrodes made by screen printing [62] have also been shown to find application as transducer in microchaimel systems [63]. 

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