Microfabrication milling

Micro milling was applied frequently in many early applications of micro structuring. Microfabrication of the parallel channels was performed by micro milling of metal tapes at the Karlsruhe Research Center (Forschungszentrum Karlsruhe) [138], In the case of aluminum alloys, ground-in monocrystalline diamonds were used [139], In the case of iron alloys, ceramic micro tools have to be used owing to the incompatibility of diamonds with that material [44], It is certainly a useful tool for experimental work and rapid prototyping, but not a choice with respect to future mass production. 

FIGURE 7.39 Schematic representation of three types of ESI emitter tips, which were microfabricated on PC or PMMA. I, machine-milled 3D tip II, machine-milled 2D tip III, hand-polished 3D tip [213]. Reprinted with permission from the American Chemical... 

Microfabricated MALDI sample targets were also prepared from PMM A by computer numerical control (CNC) milling. In this case, enzyme functionalized cylindrical posts (360 p,m x 360 p,m) served as individual sample targets on the MALDI plate and were used for on-probe characterization of nucleic acids. The advantages of this device included reduced sample consumption and handling and reduced analysis times. Alternatively, MALDI targets with twin anchors (400 p.m) were prepared from silicon wafers by anisotropic dry etching in an inductively coupled plasma. 

Fundamentals on the physical properties of the substrates and on the microfabrication technologies can be found elsewhere [23-25]. First, it has to be considered that the metallic surfaces contacting the process fluids do not catalyze reactions at any appreciable rate. Mills and Nicole [26,27] have shown that the natme of the metal substrate affects combustion reactions. AISI 316 stainless steel, titanium or iron, results in hydrocarbon and oxygen conversions of up to 50% depending on the natme of the metallic material. Similar effects have been found using Cu-based alloys. For these alloys the oxide layer formed upon brass pretreatment results in active ethyl acetate combustion or ethanol dehydrogenation [28,29]. 

---