Abstract
We developed thermocouple probes consisting of constantan and chromel segments with nanoscale sharpness. The ends of wires made of these alloys were polished utilizing a single step drop-off electrochemical procedure in a H3PO4 solution. The macroscopic shapes of the etched wires were designed to detect ultra-small heat inputs with high sensitivity after assembling a thermocouple. After electrochemical treatment, ultimately smooth, mirror-polished wire surfaces were observed. The etched wires were then assembled in a transmission electron microscope (TEM) to create a miniature thermocouple by using which we successfully detected a small temperature increase induced by focused TEM electron beam irradiation. Judging from high- resolution TEM imaging, a thermocouple with the tip-end of only ~5 nm in diameter was fabricated.
Highlights
Nowadays the preparation of sharpened probes, down to the nanoscale dimensions, becomes essential for many fundamental physical chemistry and application fields
STAM was conducted in a scanning transmission electron microscopy mode (STEM)-compatible instrument because the tips were able to be assembled under precise position control using real-time transmission electron microscopy (TEM) observation
We investigated the characteristics of many thermocouple types and concluded that the E-type thermocouple, a combination of constantan and chromel, had a desired nonmagnetic character and possessed the high Seebeck coefficient
Summary
Nowadays the preparation of sharpened probes, down to the nanoscale dimensions, becomes essential for many fundamental physical chemistry and application fields. Scanning tunneling microscopy (STM), one of the scanning probe microscopy techniques, is the most powerful method to observe single-molecules at nanoscale via utilizing atomically-sharp metal tips. For STM measurements, the tip quality, such as its geometry, shape and cleanness, is the most important factor to achieve atomic resolution. Sharp tips are needed for tipenhanced Raman spectroscopy (TERS) to characterize biomolecules [3]. Numerous studies have been conducted to design the right tip preparation technique. Several reproducible and reliable methods have been reported to prepare W tips having diameters of ~5 nm or less [4, 5]. To enhance Raman scattering efficiency, gold [6] or silver [7] tips have conventionally been used, which are prepared by utilizing the regarded electrochemical procedure
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