Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Plasma etching of superconducting Niobium tips for scanning tunneling
  microscopy   We report a reproducible technique for the fabrication of sharp
superconducting Nb tips for scanning tunneling microscopy (STM) and scanning
tunneling spectroscopy. Sections of Nb wire with 250 $\mu$m diameter are dry
etched in an SF$_6$ plasma in a Reactive Ion Etcher. The gas pressure, etching
time and applied power are chosen to produce a self-sharpening effect to obtain
the desired tip shape. The resulting tips are atomically sharp, with radii of
less than 100 nm, and generate good STM images and spectroscopy on single
crystal samples of Au(111), Au(100), and Nb(100), as well as a doped
topological insulator Bi$_2$Se$_3$ at temperatures ranging from 30 mK to 9 K.

30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
37
The categories of this paper are: supr-con
1
The categories of this paper are: cs
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
36
The categories of this paper are: cmp-lg
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
23
The categories of this paper are: solv-int
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math