Platinum needle probe

The resistance of membranes can be measured by AC impedance methods [85,86], using the four-point-probe technique. The test membrane is placed in a cell consisting of two Pt-foil electrodes, spaced 3 cm apart, to feed the current to a sample of 3 x 1 cm and two platinum needles placed 1 cm apart, to measure the potential drop (see Fig. 4.3.26). The cell is placed in a vessel maintained at constant temperature by circulating water. The impedance measurements are then carried out at 1-10 kHz using a frequency-response analyzer (e.g., Solatron Model 1255HF frequency analyzer). After ensuring that there are no parasitic processes (from the phase angle measurements, which should be zero), one can measure the resistance directly. The membrane resistance can also be obtained directly from the real part of the impedance (see typical data in Fig. 4.3.27). 

In this study, a platinum (Pt) needle probe covered with cadmium sulfide (CdS) was used to detect the evanescent fields and the needle tip size was about 10pm. And the luminescent light at 652 nm was observed from CdS excited by the evanescent fields due to SP excitations in the ATR configuration using the incident Ar laser beam at 488 nm. The luminescent light at 652... 

Bead thermistors are formed by placing two wires, commonly of platinum, in dose proximity and paralld to each other and bridging them with a drop of slurry, which is then sintered into a hard bead and encapsulated in protective glass. Such thermistors are quite stable, approaching, over narrow temperature limits, the stability of industrial metallic thermometers. However, the resistance tolerance may vary from unit to unit by as much as 20%, and matching or interchangeability is usually achieved by selection. Beads can be made quite small, which may allow application in, eg, temperature probes mounted in intravenous needles. 

Electrochemical functionalization - reductive coupling of diazonium salts The electrochemical functionalization of SWCNTs, deposited on an Si/Si02 substrate, with 4-nitrophenyl groups succeeded by the reduction of 4-nitrobenzene-diazonium salt in a mini-electrochemical cell with platinum counter and (pseu-do-)reference electrodes. A probe needle was used to make contact with one of the Au-Pd bonding pads on the substrate and allowed the application of an electric potential to the electrode (-1.3 V vs. Pt for >30 s) and to any SWCNTs underneath the electrode [177b]. 

Like electron microscopy, scanning probe microscopy (SPM) also opens a window into the world of nanometer-sized specimens and, in some cases, provides details at the atomic level. One version of SPM is scanning tunneling microscopy (STM), in which a platinum-rhodium or tungsten needle is scanned across the surface of a conducting solid. When the tip of the needle is brought very close to the surface, electrons tunnel across the intervening space (Fig. 9.23). 

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