X-ray study of the confinement of silver chalcogenide inside mesoporous silica

Overview & Synopsis

Silver chalcogenides such as Ag2Se and Ag2Te are known to be non-magnetic semiconductors for temperatures below ~400K, without significant magnetoresistance. Altering the stoichiometry by adding a small amount of silver, electrical resistance of Ag2+δSe and Ag2+δTe (with δ = 0.01) become very sensitive to magnetic field up to 60 Teslas. Furthermore, this giant magnetoresistance presents a near-linear increase of the resistance with the applied magnetic field, without saturation. Thus silver chalcogenides appear to be attractive as magnetic-field sensors. Our work is to confine this kind of material in an inorganic matrix to make a composite material. The choice of silica is the most appropriate since silica is chemically inert and it has been shown in the case of selenium based particles that interactions between silica and selenium are very weak and that confinement preserves their semi-conducting properties. The method we have used to confine nanoparticles inside silica is the synthesis of silver chalcogenide directly inside the pores of mesoporous silica, presenting an ordered array of pores, with a diameter of about 2 nm. In the case of Ag2Se, after impregnation of a silver ions solution into silica, a selenium ions solution is introduced. The existence of nanocrystalline silver selenide has been confirmed using synchrotron radiation X-ray diffraction. The observed diffraction peaks correspond well to the standard powder diffraction data set of the orthorhombic structure of Ag2Se.