Metal-insulator phase transition in aVO2thin film observed with terahertz spectroscopy

Abstract

We investigate the dielectric properties of a thin VO 2 film in the terahertz frequency range in the vicinity of the semiconductor-metal phase transition. Phase-sensitive broadband spectroscopy in the frequency region below the phonon bands of VO 2 gives insight into the conductive properties of the film during the phase transition. We compare our experimental data with models proposed for the evolution of the phase transition. The experimental data show that the phase transition occurs via the gradual growth of metallic domains in the film, and that the dielectric properties of the film in the vicinity of the transition temperature must be described by effective-medium theory. The simultaneous measurement of both transmission and phase shift allows us to show that Maxwell-Garnett effective-medium theory, coupled with the Drude conductivity model, can account for the observed behavior, whereas the widely used Bruggeman effective-medium theory is not consistent with our findings. Our results show that even at temperatures significantly above the transition temperature the formation of a uniform metallic phase is not complete.

Review of Near-Field Terahertz Measurement Methods and Their Applications

“…The ANSOM probe was placed over the sample; a THz beam was focus on the apex of the tip and the modulated scattered THz radiation could be collected in the far field. Because the local conductivity of VO 2 can abruptly change when a bias is applied or when the temperature is changing, the measured THz will also be affected [117]. They could conclude from their measurement that micron length scale islands with different conductivity appear below the transition voltage of the film.…”

The influence of polarizability on the dielectric spectrum of the ionic liquid 1-ethyl-3-methylimidazolium triflate

“…The dried IL was stored in a nitrogen-filled glove box and all measurements were conducted under a dry N 2 atmosphere. Broadband dielectric spectra, S Ã 0 ðnÞ þ 1 ¼ e 0 ðnÞ À ie 00 ðnÞ, were obtained by combining data from a frequency-domain reflectometer based on an Agilent E8364B vector network analyzer (VNA) and Agilent 85070E-020 (0.2-20 GHz) and 85070E-050 (0.5-50 GHz) probes, a wave guide interferometer covering 60-89 GHz, 74 a transmission/reflection terahertz time-domain spectrometer (THz-TDS) at 0.3 to 3 THz, 75 and a Bruker Vertex 70 FTIR spectrometer covering the far-infrared (FIR, 0.9 to 12 THz) region. All measurements were conducted at (25.00 AE 0.05) 1C, except for the THz-TDS and FIR spectra, which were recorded at (25.0 AE 0.5) 1C.…”

Tunable Fermi acceleration in a nondissipative driven magnetic billiard

“…4. We plot only the last iteration, i.e., the The red line is a nonlinear fitting given by the classic fourparametric sigmoid Boltzmann function, commonly used for sigmoidal datasets and phase transition models [24], obtained with an adjusted rate of 99.4%, and here it can be described as…”