Etch channel

A note of caution on the use of photo-etched channels has been offered by RAMSHAWfl3 ) who points out that the system is attractive in principle provided that severe practical problems such as fouling are not encountered. With laminar flow in matrices with a mean plate spacing of 0.3-1 mm, volumetric heat transfer coefficients of 7 MW/m3 K have been obtained with modest pressure drops. Such values compare with 0.2 MW/m3 K for shell and tube exchangers and 1.2 MW/m3 K for plate heat exchangers. 

Bnlk wave devices have different tolerances and recently Capelle, Zarka and co-workers have studied bulk waves in qnartz resonators and used stroboscopy to identify unwanted modes associated with defects. They have also performed tine section topography in stroboscopic mode to identify if the interaction between a dislocation and the acoustic wave could be described by simple linear piezoelectric theory. Using simulation of the section topographs to analyse the data, they conclnded that a non-Unear interaction was present near to the dislocation line, linear theory working satisfactorily in the region far from the defect. Etch channels appeared to have more inflnence on the acoustic wave than individnal dislocations. 

Guijt et al. [69] reported four-electrode capacitively coupled conductivity detection in NCE. The glass microchip consisted of a 6 cm etched channel (20 x 70 pm cross-section) with silicon nitride covered walls. Laugere et al. [70] described chip-based, contactless four-electrode conductivity detection in NCE. A 6 cm long, 70 pm wide, and 20 pm deep channel was etched on a glass substrate. Experimental results confirmed the improved characteristics of the four-electrode configuration over the classical two-electrode detection set up. Jiang et al. [71] reported a mini-electrochemical detector in NCE,... 

The mixer was made by wet-chemical etching of glass substrates, following a photolithographic step, yielding channels for the fluid flow and for the electrodes. The electrodes (100 Q resistors) were made by an electron-beam evaporation process generating thin metallic films in the etched channels [92], Holes were drilled into the cover plate for inlet and outlet connection. Fusion bonding was used to seal the plates. 

Continuous-flow microreactors were successfully fabricated by etching channels in silicon and immobilizing urease onto channel surfaces by a layer-by-layer self-assembly technique. Preliminary results show urea conversion. The potential advantages of this surface-coating technique in microreactors warrant continued investigation. 

Fig. 1. Electron micrograph of electrophoresis channels formed into a glass substrate by photolithography and wet chemical etching. Channel dimensions width 50 pm, depth 12 pm (reprinted with permission from [19]. Copyright 1993 American Chemical Society)...

Isopropyl alcohol (IPA) is sometimes added to KOH in order to reduce the etchant surface tension. This in turn assists in releasing H2 bubbles and in dissolving organic contaminants. So the addition of IPA avoids the micromask effect and produces smoothly etched channels [303]. 

FIGURE 2.6 SEM images of etched channels illustrating the dependence of the smoothness of the etched surface on the etching solution. (A) SEM image of the channel etched with a high concentration of buffered HF (32% HF buffered with a 1 1 ratio of HF to ammonium fluoride) (scale bar 150 pm). (B) SEM image of the channel etched with a low concentration of non-buffered HF solution (10% HF) (scale bar 100 pm) [125], Reprinted with permission from Elsevier Science. 

Normally, one-level etching was performed, but in some applications (e.g., pre-channel filter), a two-level etching method was also performed [148]. BOE etch was chosen over HF etch for quartz because BOE produced a smoother etch (0.23 urn RSI )) than did HF (0.55 pm RSI )) [149]. The cross section of an etched channel in a quartz chip is shown in Figure 2.11 [1006]. 

FIGURE 4.4 Slides (a) and (b) are composed of HF etched channels with powder-blasted access holes in (a). The bonding of the two slides gives a cross-shaped channel layout (c) of injection volume of 27 pL [314]. Reprinted with permission from the American Chemical Society. 

Why would the use of sonication during etching help produce smoothly etched channel walls [105] (2 marks)... 

Future applications of CE to PCR product analysis will arise from improvements in CE instrumentation. Advances in miniaturization of CE devices by producing glass chips with etched channels of <1 cm in length... 

M. J. J. Theunissen, Etch channel formation during anodic dissolution of n-type silicon in aqueous hydrofluoric acid, J. Electrochem. Soc. 119, 351, 1972. 

Etched, channel in silicon gives TVF6 access to parorus Si... 

The reaction can be run in a minireactor with a silver catalyst in etched channels.15 However, neighbors to the Rhone-Poulenc plant in Institute, West Virginia are still concerned about the 250,000 lb of methyl isocyanate stored there.16... 

Figure 2.5 Integrated analytical system. A nine-position microfabricated device was coupled to an ITMS instrument via a transfer capillary and a microESI ion source. The inner surface of the transfer capillary (15 cm long, 75 pm i.d., 150 pm o.d.) was derivatized with 3-aminopropylsilane. The etched channels were 30 pm deep and 72-73 pm wide. The diameter of the reservoirs was 1mm. The sample flow was controlled by an array of computer-controlled high-voltage relays which are also schematically represented. The software controlled the sample flow from the different reservoirs, the generation of MS spectra, the selection of potential peptides, the generation of MS-MS spectra and the matching of the MS-MS spectra against a protein sequence database. (Adapted with permission from Ref. 6).

---