本文基于密度泛函理论(DFT)的第一性原理计算了W、Mn、V、Ti替位掺杂二维MoSi_(2)N_(4)后的几何结构、电子结构以及光学性质的变化.电子结构分析表明W、Mn、W、Ti替位掺杂二维MoSi_(2)N_(4)后的禁带宽度分别为1.806 e V、1.003 e V、1.2...本文基于密度泛函理论(DFT)的第一性原理计算了W、Mn、V、Ti替位掺杂二维MoSi_(2)N_(4)后的几何结构、电子结构以及光学性质的变化.电子结构分析表明W、Mn、W、Ti替位掺杂二维MoSi_(2)N_(4)后的禁带宽度分别为1.806 e V、1.003 e V、1.218 e V和1.373 e V;四种过渡金属掺杂后MoSi_(2)N_(4)的带隙类型没有发生改变,均为间接带隙半导体;W掺杂后的杂质能级靠近价带顶,费米能级靠近价带顶,为p型半导体,杂质能级为受主能级;Mn掺杂后的杂质能级靠近导带底,费米能级靠近导带底,为n型半导体;V和Ti掺杂后杂质能级位于费米能级附近,为复合中心;光学性质分析表明,在2 e V~4 e V的能量区间内,W掺杂结构的吸收波长为336 nm,体系发生红移;Mn、V和Ti替位掺杂后的吸收波长分别为320 nm、358 nm和338 nm,且掺杂体系均发生蓝移.展开更多
Barium metaborate (BaB 2O 4) exists in two forms the high temperature for m α phase and the low temperature form β phase,with the phase transition poi nt at around 925℃.The low temperature phase (β BBO) is an exce...Barium metaborate (BaB 2O 4) exists in two forms the high temperature for m α phase and the low temperature form β phase,with the phase transition poi nt at around 925℃.The low temperature phase (β BBO) is an excellent NLO cryst al for UV region,while the high temperature one (α BBO) is known as a good bir efringent material.α BBO crystal possesses better transparency in the ultravio let region compared with commonly used YVO 4 and CaCO 3 crystals.However,due t o phase transition problem,it is difficult to grow single α BBO crystals by D CZ method,which restricts its wider application.α BBO crystal usually cracks upon cooling resulted from phase transition to β phase.Therefore,it is difficult to grow β BBO single crystals directly from pure BaB 2O 4 mel t;however,to grow single crystals of α BBO is not easy,either. Our recent experiments showed that one could avoid cracking of α BBO cryst als by Sr 2+ doping.This minute amount of Sr 2+ plays the role of structure stabilizer,which inhibits structural reconstruction. In this way,Sr 2+ d op ed BBO single crystals do not subject to phase transition from 925℃ down to roo m temperature. We have mow successfully grown out α BBO single crystals 30mm in diameter by D CZ method from Sr x Ba 1- x BO 4 melt with Sr concentration 0.3 0 .5%.The ratation rate is 10 15r/min,pulling speed is 1 2mm/h.Preliminary tests revealed that its structure and physic chemical properties were almost identic al to those grown from pure melts.These Sr 2+ doped α BBO crystals are no w being widely used in optical isolators.展开更多
文摘本文基于密度泛函理论(DFT)的第一性原理计算了W、Mn、V、Ti替位掺杂二维MoSi_(2)N_(4)后的几何结构、电子结构以及光学性质的变化.电子结构分析表明W、Mn、W、Ti替位掺杂二维MoSi_(2)N_(4)后的禁带宽度分别为1.806 e V、1.003 e V、1.218 e V和1.373 e V;四种过渡金属掺杂后MoSi_(2)N_(4)的带隙类型没有发生改变,均为间接带隙半导体;W掺杂后的杂质能级靠近价带顶,费米能级靠近价带顶,为p型半导体,杂质能级为受主能级;Mn掺杂后的杂质能级靠近导带底,费米能级靠近导带底,为n型半导体;V和Ti掺杂后杂质能级位于费米能级附近,为复合中心;光学性质分析表明,在2 e V~4 e V的能量区间内,W掺杂结构的吸收波长为336 nm,体系发生红移;Mn、V和Ti替位掺杂后的吸收波长分别为320 nm、358 nm和338 nm,且掺杂体系均发生蓝移.
文摘Barium metaborate (BaB 2O 4) exists in two forms the high temperature for m α phase and the low temperature form β phase,with the phase transition poi nt at around 925℃.The low temperature phase (β BBO) is an excellent NLO cryst al for UV region,while the high temperature one (α BBO) is known as a good bir efringent material.α BBO crystal possesses better transparency in the ultravio let region compared with commonly used YVO 4 and CaCO 3 crystals.However,due t o phase transition problem,it is difficult to grow single α BBO crystals by D CZ method,which restricts its wider application.α BBO crystal usually cracks upon cooling resulted from phase transition to β phase.Therefore,it is difficult to grow β BBO single crystals directly from pure BaB 2O 4 mel t;however,to grow single crystals of α BBO is not easy,either. Our recent experiments showed that one could avoid cracking of α BBO cryst als by Sr 2+ doping.This minute amount of Sr 2+ plays the role of structure stabilizer,which inhibits structural reconstruction. In this way,Sr 2+ d op ed BBO single crystals do not subject to phase transition from 925℃ down to roo m temperature. We have mow successfully grown out α BBO single crystals 30mm in diameter by D CZ method from Sr x Ba 1- x BO 4 melt with Sr concentration 0.3 0 .5%.The ratation rate is 10 15r/min,pulling speed is 1 2mm/h.Preliminary tests revealed that its structure and physic chemical properties were almost identic al to those grown from pure melts.These Sr 2+ doped α BBO crystals are no w being widely used in optical isolators.
