Extremely Large Magnetic-Field-Effects on the Impedance Response of TiO2 Quantum Dots

Abstract

Here, we report large magnetoresistance and magnetocapacitance response of undoped TiO 2 quantum dots weighting the contribution of both grain and grain boundaries by means of impedance spectroscopy. We also performed a complete characterization of the TiO 2 quantum dots (~5 nm) prepared by sol-gel via water vapor diffusion method, using X-ray diffraction, small angle X-ray scattering, transmission electron microscopy and Raman spectroscopy. In addition, we showed a complete theoretical study on the electronic properties of TiO 2 surface and subsurface oxygen and titanium vacancies to shed some light in their electronic and magnetic properties. Based in our study, we can conclude that the presence of defects, mainly at the grain boundary of these undoped TiO 2 quantum dots, could be responsible for the large positive magnetoresistance (+1200%) and negative magnetocapacitance (−115%) responses at low applied magnetic fields (1.8 kOe) and room temperature.

On the Donor: Acceptor Features for Poly(3-hexylthiophene): TiO2 Quantum Dots Hybrid Materials Obtained via Water Vapor Flow Assisted Sol-Gel Growth

“…The preparation of P3HT:TiO 2 nanocomposites was based on the sol-gel synthesis via water vapor flow diffusion, as it was previously reported for other polymers [ 27 , 28 , 29 ]. In total, 0.3 g of regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) polymer, purchased from Sigma-Aldrich with a M w of 50,000–100,000 and a regioregularity above 90%, were suspended in 50 mL of tetrahydrofuran (THF) and kept stirred at T = 70 °C.…”

Hybrid Organic-Inorganic Materials and Interfaces With Mixed Ionic-Electronic Transport Properties: Advances in Experimental and Theoretical Approaches

“…For instance, DFT studies on the electronic interactions of tetrafluoro-tetracyanoquinodimethane (F4-TCNQ)/ZnO surfaces ( Xu et al, 2013 ), hexafluoro-tetracyano-naphthoquinodimethane (F6-TCNNQ)/ZnO surfaces ( Schöttner et al, 2020 ), oligothiophenes and ZnO (and In-doped SnO 2 ) surfaces ( Timpel et al, 2020 ) has shed some light on the work function and other relevant electronic properties of these h OI interfaces. Other DFT studies on the electronic interactions between larger and more complex systems such as polyaniline oligomer/graphene oxide quantum dots (GQD) including edge functionalization ( Mombrú et al, 2017c ) and vinyl carbazole monomer/TiO 2 surfaces including oxygen and titanium vacancy defects ( Mombrú et al, 2019a ; Mombrú et al, 2019b ) has shown interesting features on the electronic properties evidencing the relevance of using more realistic models as depicted in Figure 2B . For instance, the difference between the LUMO level of vinyl carbazole and the conduction band of TiO 2 surface with oxygen vacancies decreases thus favoring the energy barrier associated with the charge injection at this h OI interface ( Mombrú et al, 2019b ).…”