A Study Of Silicon Photo-electrodes Hydrogen Peroxide Detection

Photo-electrochemical sensor is a new kind of developing analytical devicebased on the photo-electrochemical properties of materials. Because of its remarkablesensitivity, inherent miniaturization, portability and easy integration,photo-electrochemical analysis is becoming a promising analytical technique.Research on the quantitative detection of hydrogen peroxide （H₂O₂） receivedconsiderable attention, because H₂O₂is widely used as an oxidizing agent in chemicaland food industries. It is an essential mediator in food, pharmaceutical, clinical, andenvironmental analysis. Prussian blue （PB, ferric hexacyanoferrate） and its analoguesare the prototype of a number of poly-nuclear transition metal hexacyanometalateshaving an open, zeolite-like structure. PB is usually considered as an“artificialperoxidase”due to its high activity and selectivity toward the reduction of hydrogenperoxide and it has been extensively used in the construction of electrochemicalbiosensors.This thesis mainly investigates three kinds of photoelectrodes based on two kindsof silicon wafers （n-Si and n-n⁺-Si）. About 40 nm three different metals films of Pt, Ni,Pt-Ni alloy were coated onto the front surface of n-Si （111） or n-n⁺-Si wafers in highvacuum evaporating system. Prussian blue （PB） film and nickel hexacyanoferrate（NiHCF） film have been deposited on the surface of metals coated different typessilicon wafer. Cyclic voltammograms and x-ray photoelectron spectroscopy （XPS）were used to characterize the surface of modified electrode. The modified electrodeshave been used for determination of hydrogen peroxide （H₂O₂） with a two-electrodecell in absence of reference electrode by photocurrent measurement at a zero bias butunder irradiation with 50W halogen-tungsten lamp. This work demonstrates thefeasibility of the photo-electrodes, sensitivity of H₂O₂sensors, and provides aneffective approach to detect H₂O₂. Experimental studies include the followingcontent:1. Hydrogen peroxide sensor based on PB modified n-n⁺-Si photo-electrodeA Prussian-blue （PB） film has been deposited on the surface of platinum coatedn-type epitactic silicon （Pt/n-n⁺-Si） wafer. The electro-deposition of PB was achievedby a cyclic scan in a potential range of 0.2 to +0.6 V （vs. SCE） at 50 mV/s for 5cycles in a solution containing 2.5 mM FeCl3, 2.5 mM K3Fe（CN）6, 0.1 M KCl and 0.1 M HCl with an illumination from 50 W bromine-tungsten lamp. The emphasis is laidon that this modified silicon electrodes can be used as sensors for the photocurrentdetermination of hydrogen peroxide only in two-electrode system without referenceelectrode at a zero bias. The use of the PB modified Pt/n-n⁺-Si electrode as ahydrogen peroxide sensor was demonstrated with good stability and selectivity. ThePB film was characterized by cyclic voltammetry measurements and scanningelectronic microscopy （SEM）. A new photo-electrochemical sensor based ontwo-electrode system for determination of hydrogen peroxide has been developed.2. Hydrogen peroxide sensor based on Prussian blue modified and coated withdifferent metals film on the surface of n-Si waferAbout 50 nm two different metals of Ni and Pt-Ni alloy were coated onto the frontsurface of n-Si （111） wafers. The Prussian-blue （PB） film modified Ni/n-Si,Pt-Ni/n-Si electrode was prepared by a simple chemical deposition and cyclicvoltammetry. The PB/Ni-n-Si sensor showed good electro-catalytic activity and goodphotocurrent responses by adding different concentrations of H₂O₂with a definitestability.3. Hydrogen peroxide detection with n-silicon photo-electrodes modified bynickel hexacyanoferrate filmsBy depositing a film of nickel hexacyanoferrate （NiHCF） on platinum film coatedsilicon electrodes, a new photo-electrochemical sensor for the detection of hydrogenperoxide has been developed. The stable film of NiHCF was chemically depositedonto a phosphorus heavy doped silicon （n⁺-Si） with 9μm epitaxial layer （n-n⁺-Si）wafers coated with about 40 nm platinum layer （Pt/n-n⁺-Si）. Cyclic voltammogramsand x-ray photoelectron spectroscopy （XPS） were used to characterize the NiHCFfilm on the Pt/n-n⁺-Si electrode. The NiHCF modified Pt/n-n⁺-Si electrode has beenused for determination of hydrogen peroxide （H₂O₂） with a two-electrode cell inabsence of reference electrode by photocurrent measurement at a zero bias. Thecomposite modified electrode demonstrated good photocurrent responses by addingdifferent concentrations of H₂O₂with a definite stability. The modified electrode wasused as a sensor for H₂O₂, with a linear range from 3.3×10 6to 1.0×10^-4M of H₂O₂,with a detection limit （S/N = 3） of 3.3×10^-6M and with a sensitivity of 42 mA M 1cm 2. This provides a facile way of detecting H₂O₂and succeeds in averting frominconvenient reference electrode.