When we say generally TiO2 band gap energy, does it mean direct or indirect band energy? I am looking for some papers and if it's possible to find both possibilities!
there are different phases for tio2. each with different band gaps. the band gap referred is generally the indirect band gap.anatase and brookite are indirect semiconductors. this reference might help Nanotechnology 19 (2008) 145605.
there are different phases for tio2. each with different band gaps. the band gap referred is generally the indirect band gap.anatase and brookite are indirect semiconductors. this reference might help Nanotechnology 19 (2008) 145605.
Anatase TiO2 is Indirect band gap but in some references you may find band energy calculation by both method direct and indirect as well
TiO2 Anatase is an indirect band gap semiconductor and possesses a band gap value of ~3.2-3.35 eV if it is in the thin film state. The following refs. might be of help to you:
i) Z. Wang, U. Helmersson, P.O. Ka¨ll, Thin Solid Films 405 (2002) 50.
ii) S. Sen et al.,Thin Solid Films 474 (2005) 245–249
If you study of TiO2 nanoparticles this paper will be useful for you.
Mathias do u got the band gap using both direct and indirect method. I am a litle bit confused. Is both types of transition is favourable in one phase.
Vijayan.P. , No, both direct and indirect optical transitions are not possible in the same phase of a material.
Anatase Tio2 has both direct and indirect band gap and according to some papers direct band gap will be greater than indirect band gap.For AnataseTio2 direct band gap can be of 3.65 range and indirect can be of 3.20ev
can anyone tell me that how can I determine cut off wavelength in absorbance spectra of tio2 in uv-1800 spectroscopy ?
Yes, I think Anatase can have both direct and indirect band gap.
In principle, the band gap value strongly depends on crystal structure, morphology, and chemical composition of the material. First you need to perform optical spectra measurements to get:
1. Direct Band Gap from the linear fit of [a(hv)]2 vs (hv) plot.
2. Indirect Band Gap from the linear fit of [a(hv)]1/2 vs (hv) plot.
Plot 1 and Plot 2 are well fitted at higher photon energy range and lower energy photon range, respectively. Something that intrigues why Direct Gap Energy is higher than Indirect Gap Energy.
Further details can be seen here: https://www.researchgate.net/post/Why_is_direct_band_gap_energy_always_greater_than_indirect_band_gap_energy
Based on the phase structure of the TiO2 it can exhibit both direct and indirect bandgap. Therefore, its necessary to explore the phase of the grown TiO2 film before determining the bandgap. More details are here ( Article Investigation of structural, optical and photocatalytic prop...
)
Yes, i agree with comment " Based on the phase structure of the TiO2 it can exhibit both direct and indirect bandgap. " Experimentally i have found the band gap of TiO2 spin coated thin film 3.2 eV for 300 C from absorbance data using Tauc plot.
For direct transition n=2 and for indirect transition n=0.5 substitute in Tauc expression
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