7103

448 دكتري

دكتري

فيزيك ماده چگال محاسباتي

1391

هشت،122ص:مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

هادي اكبرزاده

جواد هاشمي فر

1391/7/25

حسن سبزيان، علي مختاري

1397/08/22

كتابنامه

مهندسي برق و كامپيوتر

ID448 دكتري

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

012 First principle study of 1 Adsorption of poly para phenylene polymer on the graphene 2 Bulk and narrow MnSe nanowires in the Rock salt structure Peiman Amiri p amiri@ph iut ac ir Date of Submission 2012 09 18 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree Ph D Language Farsi Supervisor Hadi Akbarzadeh akbarzad@cc iut ac ir Advisor Seyed Javad Hashemifar Hashemifar@cc iut ac irAbstract Our goal in this first principle study is two folded Firstly we study the adsorption of poly para phenylenepolymer on the graphene and secondly we investigated the bulk and narrow MnSe nanowires In the firstpart many body perturbation theory at the G0W0 level was employed to study the electronic properties ofphysisorbed poly para phenylene PPP on graphene Analysis of charge density and electrostatic potentialshows that the polymer surface interaction gives rise to formation of weak surface dipoles with no chargetransfer between the polymer and the surface Within the local density approximation LDA of densityfunctional theory the band structure of combined system appears as a superposition of the band structuresof isolated constituents Consequently the LDA band gap of PPP remains unchanged upon adsorption on thegraphene layer G0W0 calculations however renormalize the electronic levels of the weakly physisorbedpolymer Thereby its band gap is considerably reduced compared to isolated PPP chain This effect can beunderstood in terms of image charges induced in the graphene layer which allows us to explain the quasi particle gap of PPP versus polymer graphene distance by applying a classical image potential model Fromthe other side we demonstrate that the polymer significantly affects the band structure of graphene byopening the gap at the Dirac point At the LDA level the amount of gap is very small while in the G0W0approach due to image charge effects arising from anisotropic polarizability of the polymer chain theamount of gap is remarkable In the second part we employed first principles pseudopotential calculationsto study the structural stability electronic and magnetic properties of bulk free chain free 100 and 110 surfaces and narrow 001 nanowires of MnSe in the rock salt structure In the case of nanowires amongthe various possible cross sections corresponding to 001 growth direction we focused on the highestsymmetry ones which are dipole free and constructed from low index 100 and 110 facets Thenanowires with 100 facets are called square nanowires SQNWs while those with 110 facets are calledlonzenge nanowires LZNWs In order to increase on site correlation of Mn d electrons we applied theGGA U scheme to our calculations This approach improves our results toward better agreement withexperiment The obtained cohesive energies indicate higher stability of narrow MnSe nanowires with 100 facets and sharp square cross sections A phenomenological model is applied to measure the energy costsfor the creation of facet and edge MnSe chains in MnSe nanowires To study the effect of surface danglingbonds on the electronic properties of nanowires we passivate the first radius of SQNWs with pseudohydrogen atoms Comparing the electronic band structures and cohesive energies of the pristine andpassivated MnSe 001 nanowires justifies the efficient surface rehybridization upon structural relaxationand consequently the absence of surface dangling bonds in various MnSe nanostructures Keywords Ab initio G0W0 many body perturbation theory Energy gap Pseudo particle Poly para phenylene Polymer Nanowire Dangling bond Formation energy Phenomenologicalmodel

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