Film Growth And Property Investigation Of Antiperovskitetype Compounds

Over the past a few decades,antieprovskite compounds have drawn much attention from researchers in both applied physics and material science.It has been reported that such compounds can exhibit a varity of intriguing physical properties.In a perovskite oxide ABO₃?A=rare earth or alkaline element,B=transition metal?,the oxygen atoms are situated at the adjacent face-centers,A atoms on the corners of the cubic unit cell and B atoms at the body-center.The antiperovskite compound M₃AN?M=Cu,Mn,Co,Ni,Fe,Ti,A=transition metal?is isostructural with the perovskite oxide ABO₃,as the M atoms are positioned at the adjacent face-centers,while A atoms on the corners and N atom at the body-center.Particularly in manganese-based antiperovskite compounds Mn₃AN,a diversity of physical properties arise from the interplay of lattice,charge,spin and orbital degrees of freedoms.In present thesis,we devote ourselves to the metal-doped copper nitride and?phase manganese nitride antiperovskite compounds.With the magnetron co-sputtering method,the antiperovskite thin films are successfully deposited after many attempts,whose structural,electrical and magnetic properties are investigated systematically.First,the metal-doped copper nitride antiperovskite thin films are grown and investigated.Ternary copper nitride-based Cu₃NM_x?M=Mg,Ta?films with preferred orientation were successfully deposited on silicon and quartz substrates by a custom-designed magnetron sputtering system.The binary compound Cu₃N in cubic anti-ReO₃structure is a semiconductor with a narrow indirect band gap.In the cubic unit cell,the N atoms are situated at the corner of the cubic cell and the copper atoms are positioned at the middle of the edges.With the rather open structure of Cu₃N,the empty center of the cubic cells can be occupied by extrinsic metal atoms.This will bring about metallic ternary compound Cu₃NM_x and cause remarkable changes in the electronic structure compared with the original matrix Cu₃N.To exploit the new lattice sites in addition to the lattice of the original matrix is a novel way of doping,which can radically modify the electronic structure of the solids,it thus hold the promise to give rise to new materials with a tunable band gap.With increasing doping level,the band gap becomes narrower and even overlap,resulting in metal-semimetal or metal-semiconductor transition.According to the temperature dependence of electrical resistivity,all the Cu₃NMg_x antiperovskite films display the semiconducting behavior,whose electrical resistivity drops four orders of magnitude with increasing doping level.The narrowing band gap can be drawn from the variation of optical band gap of the deposits,which decreases from 0.76 eV to 0.07 eV.In Ta-doped copper nitride films,the Ta atoms are believed not to occupy the empty center of the cubic cell.The Ta atoms maybe aggregate at the grain boundary in the form of nitride compound,playing a dominate role in the electronic transport property of the deposits.In contrast,the optical band gap of Cu₃NTa_x films increase with increasing doping level x.Second,the manganese-based antiperovskite films are fabricated and studied systematically.There are a diversity of phases in the manganese nitride compounds.Among them,the conditions of nucleation and growth for?phase manganese nitride film with antiperovskite structure are quite narrow.The Mn-based antiperovskite Mn₃Mn_1-xA_xN?A=Pd,Au,Ni?films were successfully deposited on silicon and other substrates by the co-sputtering means.In addition,we also make attempt to grow the nearly stoichiometric Mn₃CuN antiperovskite film.The matrix material Mn₃MnN antiperovskite compound is a ferrimagnetic metal with the magnetic moment of the corner Mn atom lying antiparallel to that of face-center Mn atom.In the antiperovskite structure,the Mn atoms at the face-centers and N atom at the body-center can form a chemically stable Mn₆N octahedron,which means that the Mn atoms at the corners of the cubic cell are more likely to be replaced by the foreign metal atoms.The largely partial substitution in original matrix can radically modify the electronic structure of the matrix material.With the partial replacement of the corner Mn atoms by Pd atoms,a tunable metal-semiconductor transition can be induced with increasing doping level in Mn₃Mn_1-xPd_xN antiperovskite films,which surprisingly maintain at a comparable resistivity level.In the whole measuring temperature zone,the matrix material Mn₃MnN reveals no evident magnetoresistance?MR?effect while the Pd-doped Mn₃Mn_1-xPd_xN antiperovskite films displays MR effect at high temperature range.The MR effect is believed to be correlated to the external filed induced magnetic phase transition.A broader maximum is observed in the temperature dependence of resistivity for the Mn₃Mn_1-xAu_xN antiperovskite compounds with low doping level x.A dopant addition induced metal-semiconductor transition arises in the low temperature zone below the resistivity maximum point,the same as Mn₃Mn_1-xNi_xN antiperovskite compounds.The Mn₃Mn_1-xNi_xN antiperovskite films deposited on N-type silicon substrate also invokes a metal-semiconductor transition with decreasing temperature in the high temperature zone above the resistivity maximum point.Moreover,an abrupt increment for the resistivity can be observed with decreasing temperature in the corresponding temperature zone.The abrupt increment is more likely to correlated to some certain structural and magnetic transitions.Lastly,we try to grow nearly stoichiometric Mn₃CuN antiperovskite film by using the alloy target?Mn₃Cu?.Since the selective sputtering,the resulting Mn₃CuN antiperovskite films are copper-rich.The copper-rich Mn₃CuN antiperovskite films manifest magnetoelectric effect.