Multifunctional Sensors Based On Doped Indium Oxide Nanocrystals

With the rapid growth of portable devices and the Internet of Things,the need for sensor integration has accelerated research in multifunctional sensing platforms.Multifunctional sensors that can detect light radiation,biological activity,pressure,and gas to monitor environmental changes have huge potential applications for efficient health monitoring,neuromedical devices,human-machine interfaces,and other integrated intelligent microsystems.The development and synthesis of multifunctional materials are the prerequisite for building multifunctional devices and help to understand the design rules for next-generation hybrid functional systems.In addition to multiple functions,sensors also need high sensitivity,low power consumption,and low cost.Silicon materials,currently popular in the semiconductor field,have been successfully used for photodetection,biosensing,gas sensing,etc.However,the inherent difficulty of integrating them onto arbitrary substrates limits their applicability.As an alternative,plasmon excitations have become a popular field for studying lightmatter interactions in recent years.And surface plasmon excitations(SP)resonance in nanomaterials has been successfully applied in photodetection,gas sensing,biosensing,etc.due to their excellent physical and chemical properties,such as abundant chemically active sites,high surface-to-volume ratio,and tunable light absorption.In this regard,ITO nanocrystals(NCs),an alternative type of doped metal oxides,not only diplay well visible transmittance,but also can be controlled to tune their IR plasmon resonance absorption by varying their doping concentration,providing a viable material for the realization of multifunctional sensors.Based on the above scientific issues,in this thesis,ITO NCs were firstly prepared by a rapid esterification reaction to obtain crystals with uniform particle size and good homogeneity.Furthermore,the regulation of the Sn doping concentration in ITO NCs could be achieved by changing the ratio of indium/tin in the precursor solution.Then we have prepared a multifunctional ITO NCs-based device for efficient NO2 gas sensing and ultraviolet(UV)/infrared(IR)photodetection.The details of this thesis are as follows:1.ITO NCs were facily prepared by a rapid esterification reaction.And the ITO NCs with 10%and 12.5%tin doping concentrations were obtained by varying the proportion of indium tin in the precursor solution.It is worth noting that the different doping concentrations have a significant effect on the position of the IR resonance absorption peaks of ITO NCs.The uniform ITO NC films were obtained through a spincoating process,and the conductivity of the films can be adjusted by wrapping the outer layer of the nanocrystals with ligand exchange.2.A photosensitive device of ITO NCs was prepared on silicon substrate with 300 nm oxide layer.And the device can detect both ultraviolet(UV)/infrared(IR)photon signals at room temperature with visible wavelengths blind.We observed that the device using EDT as a ligand,showed a photo-responsivity of 31.3/177.7 mA·W-1 and a normalized detection rate of about 1 × 1010/109 cm·Hz1/2·W-1 at wavelength of 375 nm and 2200 nm,respectively.3.Finally,by testing the light-activated NO2 gas sensing performance,we found that the detectivity of the ITO NCs sensor for low concentrations NO2 was further activated by light illumination.The sensor has a higher response(4.2),shorter response/recovery time(156.8/554.2 s),and lower limit of detection(LOD)(219 ppb)for 1 ppm NO2 compared to a dark environment.Moreover,the sensor’s LOD is below the permissible exposure limit for nitrogen dioxide as specified in the Occupational Safety and Health Administration’s(OSHA)"Air Pollutant Limits".In summary,our work provides an alternative path for the development of low-cost,easily integrated multifunctional devices.