Abstract: A method of etching a substrate includes placing a substrate in a process zone. The substrate has a material with a thickness, and the material has exposed regions between features of a patterned mask. An etchant gas is introduced into the process zone. The etchant gas is energized to etch the material. An endpoint of etching the material of the substrate is determined by (i) reflecting a light beam from the substrate, the light beam having a wavelength selected to have a coherence length in the substrate of from about 1.5 to about 4 times the thickness of the material, and (ii) detecting the reflected light beam to determine an endpoint of the substrate etching process. Additionally, the wavelength of the light beam can be selected to maximize an absorption differential that is a difference between the absorption of the light beam in the patterned mask and the absorption of the light beam in the material.

Abstract: An apparatus for tuning and/or matching a RF coil in a NMR probe comprising a first variable capacitor electrically connected to the coil and a first motor capable of coupling to the first variable capacitor. The first motor when coupled to the first capacitor adjusts a capacitance associated with the first capacitor. The first motor is capable of operating in a strong magnetic field and is capable of not disturbing homogeneity of said magnetic field when said motor is not operating. The apparatus may further include a second variable capacitor and a second motor. The first motor is further capable of coupling to the second capacitor for adjusting a capacitance associated with the second capacitor. The second motor moves the first motor between coupling with the first capacitor and coupling with the second capacitor. The mechanism may be employed to manipulate variable inductive loads for tuning and/or matching.