Wollaston wire

Platinum in the forms detailed above and in its more usual alloys with other noble metals is available as sheet, foil down to 0-0064 mm thick, tube, rod, wire down to 0-0064 mm diameter, Wollaston wire down to 0-001 mm diameter, and clad on thin sections of base metals, e.g. copper, nickel. Inconel, etc. 

Fig. 5.19 Electrodes used in voltammetry. A—dropping mercury electrode (DME). R denotes the reservoir filled with mercury and connected by a plastic tube to the glass capillary at the tip of which the mercury drop is formed. B—ultramicroelectrode (UME). The actual electrode is the microdisk at the tip of a Wollaston wire (a material often used for UME) sealed in the glass tube...

Medium Energy EBW Detonator w/Wolla-ston Wire Bridge, shown in Fig 72. Wollaston wire is a coaxial bimetallic material made by inserting a wire of one material (usually gold or platinum) in a tube of another (.usually silver) after which the combination of tube and core is drawn thru dies to a smaller size. The outer tube may be dissolved by an acid leaving the core, which may be much smaller than a wire could be drawn by any other process. High temperature double-bore thermo-... 

Temperature (may be measured by a Wollaston wire not influenced by radiation)... 

A photomicrograph of a Ihcrmal probe is shown in Figure 31-16. The most common type of thermal probe is the resistive probe based on a Wollaston wire. This... 

Figure 2. Schematic diagrams of resistive SThM probes a) Wollaston wire type [34,35], b) micro-machined coated Si cantilever [37] and c) data storage doped Si probe [55].

Buzin Al, KamasaP, PydaM, Wunderlich B (2002) Application of Wollaston Wire Probe for Quantitative Thermal Analysis, Thermochim Acta, 381, 9-18. 

Hammiche and co-workers [285] described a technique in which a miniaturized Wollaston wire resistive thermometer is used as a probe to record IR absorption spectra by detecting photothermally induced temperature fluctuations at the sample surface. These authors claimed that such an approach opens the way to spatial resolution extended beyond the diffraction limit by a few hundred nanometers. As an alternative, Palanker et al. [280] suggested to use tipless probing. 

This procedure can also be applied to 5 and 10 pm platinum and gold wires (where the use of soft glass capillaries is sometimes preferred). For smaller tips (1-2 pm diameter), a Wollaston wire (a metal wire covered by a silver layer) is first placed in weak nitric acid solution to dissolve the silver layer prior to sealing the tip (Section 6.3.2). A laser puller can also be used with small diameter quartz capillaries to make submicron size electrodes (Section 6.3.3). Such sealing techniques require much practice and patience. 

Figure 6.3.2.1 Schematic of Pt or Au UMEs with Wollaston wires, (a) Insert a 2-cm long Pt or Au Wollaston wire into one end of a glass capillary, (b) Remove the silver coating with 50% nitric acid. (3) Seal the wire into glass and polish it.

A photomicrograph of a thermal probe is shown in Figure 31-16. The most common type of thermal probe is the resistive probe based on a Wollaston wire. Thb wire has a thick coating of silver on top of a thin core of platinum or a platinum-rhodium alloy. At the tip of the probe, the silver is etched away to expose the bare wire. Micromachined probes have also been developed. With these probes, almost all of the electrical resistance is located at the tip. As a result, when an electric current is applied, only the tip becomes hot. The electrical resistance of the tip is also a measure of the temperature. 

Cantilever mount Wollaston wire Platinum core Probe tip... 

The form of SThM most relevant to the subject of this discussion is carried out using near-field electrical resistance thermometry, and this method has been adopted in the work reported in this chapter. This is because miniaturized resistive probes have the considerable advantage that they can be used both in passive mode as a thermometer and as an active heat source. This enables local thermal analysis (L-TA see text below) as well as SThM to be carried out. At present the most common type of resistive probe available is the Wollaston or Wollaston Wire probe, developed by Dinwiddle et al. (1994) and first used by Balk et al. (1995) and Hammiche et al. (19%a) The construction details of this probe are illustrated in Fig. 7.3. A loop of 75-pm-diameter coaxial bimetallic Wollaston wire is bent into a sharp V-shaped loop. The wire consists of a central 5-pm-diameter platinum/10% rhodium alloy core surrounded by silver. The loop is stabilized with a small bead of epoxy resin deposited approximately 500 pm from its apex. The probe tip or sensor is made... 

Figure 7.5. Diagrams illustrating effects of shape of probe tip on spatial resolution (a) Wollaston wire (b) low-aspect-ratio pyramidal tip (c) high-aspect-ratio pyramidal tip.

SThM was carried out in the laboratory of H. Pollock and A. Hammiche in the Physics Department of the University of Lancaster, Lancaster, UK using a modified Topometrix Explorer SPM (Topometrix Corporation, Santa Clara, CA). The microscope uses a small Wollaston wire, bent and etched to form a contact mode AFM tip with a nominal radius of about 200 nm. The tip is used both as a heat source and a heat sensor. A second, reference, tip is held in air in close proximity to the sample for differential measurements. The heat to the tip can be modulated and the material response to the modulated heating can be monitored during imaging via lock-in techniques. For the work described here the microscope was operated in three imaging modes (1) constant deflection (for topography) (2) constant temperature (DC) and (3) modulated temperature (AC). In an unscanned mode, the tip can be positioned on the surface for local differential thermal analysis (DTA) or local modulated temperature-DTA and local thermomechanical (TMA) measurements (4,22). 

The potential of scanning thermal microscopy (SThM) to provide new property information regarding polymer surfaces has been investigated over the past year with the Pollock group in the UK. In the SThM experiment a small Wollaston wire... 

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