Tunable Photodetectors via In Situ Thermal Conversion of TiS3 to TiO2

Abstract

In two-dimensional materials research, oxidation is usually considered as a common source for the degradation of electronic and optoelectronic devices or even device failure. However, in some cases a controlled oxidation can open the possibility to widely tune the band structure of 2D materials. In particular, we demonstrate the controlled oxidation of titanium trisulfide (TiS3), a layered semiconductor that has attracted much attention recently thanks to its quasi-1D electronic and optoelectronic properties and its direct bandgap of 1.1 eV. Heating TiS3 in air above 300 °C gradually converts it into TiO2, a semiconductor with a wide bandgap of 3.2 eV with applications in photo-electrochemistry and catalysis. In this work, we investigate the controlled thermal oxidation of individual TiS3 nanoribbons and its influence on the optoelectronic properties of TiS3-based photodetectors. We observe a step-wise change in the cut-off wavelength from its pristine value ~1000 nm to 450 nm after subjecting the TiS3 devices to subsequent thermal treatment cycles. Ab-initio and many-body calculations confirm an increase in the bandgap of titanium oxysulfide (TiO2-xSx) when increasing the amount of oxygen and reducing the amount of sulfur.

Borocarbonitride Layers on Titanium Dioxide Nanoribbons for Efficient Photoelectrocatalytic Water Splitting

“…It is clear from the SEM measurements, that there was no significant change in the morphology, apart from a slight increase of the roughness on the TiO 2 surface compared to TiS 3 . We also acquired optical microscopy images to have a deeper understanding of the change on the surface of these nanoribbons (Figure 1b), which allowed us to determine that the material became more transparent to the optical microscope, in good agreement with the results reported by Ghasemi et al [17] and with our optical characterizations shown below (see Figure 4). Structural changes were also monitored via XRD after the oxidation and after growing the BCN on top of this oxidized material (Figure 2).…”

“…TiS 3 nanoribbons were squashed in one direction and oxidized on a hot plate at 300 °C in air (the decomposition temperature of TiS 3 [ 17 ]) for 20–30 s, which allowed us to obtain the desired TiO 2 nanoribbons. Figure S1 shows the change in the color of the samples, from black to white, at a glance.…”

“…The starting TiS 3 material has been obtained by the sulfuration of Ti disks (15 mm diameter, Good Fellow 99.5%) in sealed Pyrex ampoules for 20 h at 550 • C, using sulfur powder as sulfur source [18,19]. TiS 3 nanoribbons were squashed in one direction and oxidized on a hot plate at 300 • C in air (the decomposition temperature of TiS 3 [17]) for 20-30 s, which allowed us to obtain the desired TiO 2 nanoribbons. Figure S1 shows the change in the color of the samples, from black to white, at a glance.…”

“…In this work, BCN was grown, for the first time, on nanostructured TiO 2 samples. In particular, BCN was grown on TiO 2 nanoribbons, obtained by the thermal annealing of TiS 3 [ 17 ]. A deep characterization of TiO 2 nanoribbons, with and without BCN, as well as the starting material, TiS 3 , was made with scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and diffuse reflectance measurements.…”

Nonuniform Debye Temperatures in Quasi-One-Dimensional Transition-Metal Trichalcogenides

“…The shift of ZrS 3 peaks to lower frequencies is attributed to a 1.9 times higher atomic mass of Zr, compared to Ti. The oxidized crystals would be expected to exhibit additional Raman peaks at 225 and 360 cm –1 for ZrS 3 , or at 150 and 395 cm –1 for TiS 3 . The absence of these peaks indicates the high quality of the crystals used in this work.…”