Research On Humidity Sensor Based On The Negative Photoconductivity Effect Of Nanodiamonds

Diamond has a wide range of applications in oil and gas exploration,aerospace,precision machining,optoelectronic devices,computer chips and other fields due to its extremely high hardness,good chemical stability,wide band gap,high carrier mobility,and high thermal conductivity.However,the cost of diamond production is currently high and the growth of large-size diamonds still faces difficulties,thus limiting the practical application of diamond.As the nanometer-sized form of diamond,nanodiamonds(NDs)have received increasing attention owing to their low toxicity,stable fluorescence,facile functionalization,and good biocompatibility.A large number of studies have already demonstrated their appealing applications in bioimaging,drug delivery,biosensing and catalysis.However,up to now there are almost no reports on pure NDs photoelectronic devices.Based on this,this thesis investigated the optoelectronic properties of NDs by preparing NDs-based optoelectronic device through a conventional photolithographic microfabrication process.The main contents are as follows:(1)Preparation and characterization of NDs.The selected NDs were characterized by XRD,FT-IR,UV-Vis absorption spectroscopy,and thermogravimetry.It was found that NDs have amorphous surfaces,and these amorphous surfaces adsorb water molecules in the air.(2)Negative photoconductivity phenomenon of NDs-based device and its causes.The NDs-based optoelectronic device was prepared through a conventional photolithographic microfabrication process.The NDs-based device was tested for its photoconductivity performance in an air environment at room temperature,and by analyzing the I-t and I-V curves,it was found that the NDs-based device exhibited a negative photoconductivity phenomenon.Investigated the cause of negative photoconductivity.First,the NDs-based photovoltaic device was tested under vacuum,oxygen,and nitrogen,which showed positive photoconductivity in these three different environments where water molecules were absent.Second,this device was tested for its photoconductivity performance at different temperatures,which showed a transition from negative photoconductivity to positive photoconductivity as the temperature increased.Finally,the device was tested under different humidity,and it was found that the negative photoconductivity phenomenon of the device was more obvious in the environment with higher humidity.The above results illustrated that water is the decisive factor for the appearance of negative photoconductivity.(3)Preparation and performance study of the humidity sensor based on NDs.The effect of humidity on the performance of this NDs-based optoelectronic device was investigated,and the test results showed that the conductivity of the device kept improving with the increase of humidity,which was expected to be applied to humidity sensors.The sensitivity of the NDs-based humidity sensor can reach 10~6%,which is the highest value ever reported for carbon based humidity sensors.