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Minimum energy path for the nucleation of misfit dislocations in Ge/Si(001) heteroepitaxy  [PDF]
Oleg Trushin,Emile Maras,Alexander Stukowski,Enzo Granato,See Chen Ying,Hannes Jonsson,Tapio Ala-Nissila
Physics , 2015,
Abstract: A mechanism for the formation of a 90{\deg} misfit dislocation at the Ge/Si(001) interface has been determined from atomic scale simulations based on the Stillinger-Weber interatomic potential function. A minimum energy path connecting the coherent epitaxial state to a final state with a 90{\deg} misfit dislocation was found using the nudged elastic band method with atomic structure generated using a repulsive bias activation procedure. The energy along the path exhibits a first maximum as a 60{\deg} dislocation nucleates. An intermediate minimum along the path corresponds to an extended 60{\deg} dislocation. A subsequent energy maximum then occurs as a second 60{\deg} dislocation nucleates in a complementary, mirror glide plane, simultaneously starting from the surface and from the first 60{\deg} dislocation. The activation energy of the nucleation of the second dislocation is 30% lower than that of the first one showing that the formation of the second 60{\deg} dislocation is aided by the presence of the first one. An understanding of the formation mechanism of 90{\deg} misfit dislocations could help design procedures for growing strain released Ge overlayers on Si(001) surfaces.
High-resolution electron microscopy of misfit dislocations in AlSb/GaAs(001)system

Wen Cai,Li Fang-Hua,Zou Jin,Chen Hong,

物理学报 , 2010,
Abstract: The detailed core structures of misfit dislocations in the AlSb/GaAs(001) hetero structure system were studied by 200 kV LaB_6 filament high-resolution electron microscope. In combination with image deconvolution, the 110] images were transformed into the projected structure maps, and the image resolution was enhan ced up to the information limit of the microscope. To distinguish Al and Sb atoms in the AlSb film, the image contrast change with the sample thickness was analyzed for the perfect region in dec...
Energetics and bonding properties of the Ni/$β$-SiC (001) interface: an ab-initio study  [PDF]
G. Profeta,A. Continenza,A. J. Freeman
Physics , 2001, DOI: 10.1103/PhysRevB.64.045303
Abstract: We investigate the adsorption of a Ni monolayer on the $\beta$-SiC(001) surface by means of highly precise first-principles all-electron FLAPW calculations. Total energy calculations for the Si- and C-terminated surfaces reveal high Ni-SiC adsorption energies, with respect to other metals, confirmining the strong reactivity and the stability of the transition metal/SiC interface. These high binding energies, about 7.3-7.4 eV, are shown to be related to strong $p$-$d$ hybridization, common to both surface terminations and different adsorption sites and despite the large mismatch, can stabilize overlayer growth. A detailed analysis of the bonding mechanism, hybridization of the surface states, charge transfer and surface core level shifts reveals the strong covalent character of the bonding. After a proper accounting of the Madelung term, the core level shift is shown to follow the charge transfer trend.
Reconstruction and thermal stability of the cubic SiC(001) surfaces  [PDF]
A. Catellani,G. Galli,F. Gygi
Physics , 1996, DOI: 10.1103/PhysRevLett.77.5090
Abstract: The (001) surfaces of cubic SiC were investigated with ab-initio molecular dynamics simulations. We show that C-terminated surfaces can have different c(2x2) and p(2x1) reconstructions, depending on preparation conditions and thermal treatment, and we suggest experimental probes to identify the various reconstructed geometries. Furthermore we show that Si-terminated surfaces exhibit a p(2x1) reconstruction at T=0, whereas above room temperature they oscillate between a dimer row and an ideal geometry below 500 K, and sample several patterns including a c(4x2) above 500 K.
Theoretical investigations of a highly mismatched interface: the case of SiC/Si(001)  [PDF]
Laurent Pizzagalli,Giancarlo Cicero,Alessandra Catellani
Physics , 2007, DOI: 10.1103/PhysRevB.68.195302
Abstract: Using first principles, classical potentials, and elasticity theory, we investigated the structure of a semiconductor/semiconductor interface with a high lattice mismatch, SiC/Si(001). Among several tested possible configurations, a heterostructure with (i) a misfit dislocation network pinned at the interface and (ii) reconstructed dislocation cores with a carbon substoichiometry is found to be the most stable one. The importance of the slab approximation in first-principles calculations is discussed and estimated by combining classical potential techniques and elasticity theory. For the most stable configuration, an estimate of the interface energy is given. Finally, the electronic structure is investigated and discussed in relation with the dislocation array structure. Interface states, localized in the heterostructure gap and located on dislocation cores, are identified.
Structural Analysis of Highly Relaxed GaSb Grown on GaAs Substrates with Periodic Interfacial Array of 90° Misfit Dislocations  [cached]
Jallipalli A,Balakrishnan G,Huang SH,Rotter TJ
Nanoscale Research Letters , 2009,
Abstract: We report structural analysis of completely relaxed GaSb epitaxial layers deposited monolithically on GaAs substrates using interfacial misfit (IMF) array growth mode. Unlike the traditional tetragonal distortion approach, strain due to the lattice mismatch is spontaneously relieved at the heterointerface in this growth. The complete and instantaneous strain relief at the GaSb/GaAs interface is achieved by the formation of a two-dimensional Lomer dislocation network comprising of pure-edge (90°) dislocations along both [110] and [1-10]. In the present analysis, structural properties of GaSb deposited using both IMF and non-IMF growths are compared. Moiré fringe patterns along with X-ray diffraction measure the long-range uniformity and strain relaxation of the IMF samples. The proof for the existence of the IMF array and low threading dislocation density is provided with the help of transmission electron micrographs for the GaSb epitaxial layer. Our results indicate that the IMF-grown GaSb is completely (98.5%) relaxed with very low density of threading dislocations (105 cm 2), while GaSb deposited using non-IMF growth is compressively strained and has a higher average density of threading dislocations (>109 cm 2).
Theoretical study of the (3x2) reconstruction of beta-SiC(001)  [PDF]
L. Pizzagalli,A. Catellani,G. Galli,F. Gygi,A. Baratoff
Physics , 1999, DOI: 10.1103/PhysRevB.60.R5129
Abstract: By means of ab initio molecular dynamics and band structure calculations, as well as using calculated STM images, we have singled out one structural model for the (3x2) reconstruction of the Si-terminated (001) surface of cubic SiC, amongst several proposed in the literature. This is an alternate dimer-row model, with an excess Si coverage of 1/3, yielding STM images in good accord with recent measurements [F.Semond et al. Phys. Rev. Lett. 77, 2013 (1996)].
Configuration and local elastic interaction of ferroelectric domains and misfit dislocation in PbTiO3/SrTiO3 epitaxial thin films  [cached]
Takanori Kiguchi, Kenta Aoyagi, Yoshitaka Ehara, Hiroshi Funakubo, Tomoaki Yamada, Noritaka Usami and Toyohiko J Konno
Science and Technology of Advanced Materials , 2011,
Abstract: We have studied the strain field around the 90° domains and misfit dislocations in PbTiO3/SrTiO3 (001) epitaxial thin films, at the nanoscale, using the geometric phase analysis (GPA) combined with high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark field––scanning transmission electron microscopy (HAADF-STEM). The films typically contain a combination of a/c-mixed domains and misfit dislocations. The PbTiO3 layer was composed from the two types of the a-domain (90° domain): a typical a/c-mixed domain configuration where a-domains are 20–30 nm wide and nano sized domains with a width of about 3 nm. In the latter case, the nano sized a-domain does not contact the film/substrate interface; it remains far from the interface and stems from the misfit dislocation. Strain maps obtained from the GPA of HRTEM images show the elastic interaction between the a-domain and the dislocations. The normal strain field and lattice rotation match each other between them. Strain maps reveal that the a-domain nucleation takes place at the misfit dislocation. The lattice rotation around the misfit dislocation triggers the nucleation of the a-domain; the normal strains around the misfit dislocation relax the residual strain in a-domain; then, the a-domain growth takes place, accompanying the introduction of the additional dislocation perpendicular to the misfit dislocation and the dissociation of the dislocations into two pairs of partial dislocations with an APB, which is the bottom boundary of the a-domain. The novel mechanism of the nucleation and growth of 90° domain in PbTiO3/SrTiO3 epitaxial system has been proposed based on above the results.
Interfacial stress field generate by a biperiodic hexagonal network of misfit dislocations in a thin bicristal InAs/(111)GaAs  [cached]
Outtas, T.,Madani, S.,Adami, L.,Bonnet, R.
Boletín de la Sociedad Espa?ola de Cerámica y Vidrio , 2004,
Abstract: The elastic interactions generated by the presence of a biperiodic network, more precisely hexagonal, of misfit dislocations in the interfacing of a thin bicristal have been simulated numerically while considering an anisotropic elasticity for each crystal. The representation of the normal equi-stress near the dislocation segments and near of the triple node of hexagonal cell permits to detect the stress concentration zone du to elastic field for InAs/(111)GaAs system, because, in the category of semiconductors, this is an ideal system which exhibit the presence of edge dislocations type parallels to the free surfaces by S.T.M.[1]. Las interacciones elásticas generadas por la presencia de una red biperiódica, de dislocaciones en la interfase de un bicristal han sido simuladas numéricamente, considerando elasticidad anisotropa para cada cristal. La representación de las tensiones próximas a las dislocaciones y del nodo triple de la celda hexagonal, permite detectar la zona de concentración de tensiones debido al campo elástico para el sistema InAS/(111) GaAS, ya que, en los semiconductores, éste es un sistema ideal que muestra la presencia de dislocaciones paralelas a las superficies libres por S.T.M.[1].
Ab initio Study of Graphene on SiC  [PDF]
Alexander Mattausch,Oleg Pankratov
Physics , 2007, DOI: 10.1103/PhysRevLett.99.076802
Abstract: Employing density-functional calculations we study single and double graphene layers on Si- and C-terminated 1x1-6H-SiC surfaces. We show that, in contrast to earlier assumptions, the first carbon layer is covalently bonded to the substrate, and cannot be responsible for the graphene-type electronic spectrum observed experimentally. The characteristic spectrum of free-standing graphene appears with the second carbon layer, which exhibits a weak van der Waals bonding to the underlying structure. For Si-terminated substrate, the interface is metallic, whereas on C-face it is semiconducting or semimetallic for single or double graphene coverage, respectively.
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