Edge-modification Induced Transformation Of Electronics And Magnetism In Armchair MoS₂ Nanoribbons

MoS₂ namoribbons（MoS₂NRs） possess the similar geometry structure with graphene and unique properties depended by the construction. With the superior performance suitable for device applications than other materials, MoS₂ NRs have attracted extensive attention in recent years. In order to explore the potential advantages of MoS₂ NRs in spintronics devices, based on density functional theory, we demonstrate systematically edge-modification induced transformation of electronics and magnetism in armchair nanoribbons.In the first chapter, we mainly describe the research background, basic properties, preparation methods of MoS₂ and electronic properties of MoS₂ NRs. The second chapter mainly introduces the theory methods and simulation tools: density functional theory and ATK software package, VASP. In the third and fourth chapters, we give a brief illustration of the work done during my studies. The contents and conclusions include the following two aspects:（1） Based on ab initio theory, we study systematically how AMoS₂ NRs transforms from nonmagnetic semiconductor to magnetic or/and metallic when being edge-passivated by OH groups. OH groups can be linked by both S and Mo edge atoms of AMoS₂ NRs. However, an S atom can catch one OH group only when each of its neighbor Mo atoms has already been passivated by two. On the whole, the AMoS₂ NR becomes edge magnetic in low passivation density and edge conductive in high density. In the case of uniform edge passivation, if the number i of OH groups per primitive cell satisfies i <1, a non-passivated edge Mo atom may be spin polarized if its neighbor Mo atom has adsorbed one OH group and the nanoribbon becomes magnetic semiconductor. In case 1 ￡i <8 one or both of the edges usually become metallic and nonmagnetic. For i =8 the nanoribbon become nonmagnetic semiconductor again.（2） Compared with egde modificated by hydroxyl anions, With edge adsorpted Li kations, we demonstrate how nonmagnetic semiconductor armchair MoS₂ nanoribbons（AMoS₂NRs） become magnetic semiconductor or semimetal. Li kations can locate on E（edge）, H（Hollow） and T（Top） sites on the edge of AMoS₂ NRs. If the number i of Li kations per primitive cell satisfies i=1, the descending order of the stabilities for AMoS₂ NRs is E, T and H. When Li kation locates on E site, AMoS₂ NRs become semimetal from nonmagnetic semiconductor. The similar properties are performed by AMoS₂ NRs When Li kation locates on H and T sites. They are both magnetic semiconductor. In the case 1< i ≤4, only considering T and H site, Li kations tend to locate on T site. AMoS₂ NR becomes semimetal for i being odd, and magnetic semiconductor for even. When the concentration is diluted, Li kation on T site can transfer spontaneously to H site. Meanwhile, AMoS₂ NR is magnetic semiconductor.