Effect of solute atoms on dislocation motion in Mg: an electronic structure perspective.

Solution strengthening is a well-known approach to tailoring the mechanical properties of structural alloys. Ultimately, the properties of the dislocation/solute interaction are rooted in the electronic structure of the alloy. Accordingly, we compute the electronic structure associated with, and the energy barriers to dislocation cross-slip. The energy barriers so obtained can be used in the development of multiscale models for dislocation mediated plasticity. The computed electronic structure can be used to identify substitutional solutes likely to interact strongly with the dislocation. Using the example of a-type screw dislocations in Mg, we compute accurately the Peierls barrier to prismatic plane slip and argue that Y, Ca, Ti, and Zr should interact strongly with the studied dislocation, and thereby decrease the dislocation slip anisotropy in the alloy

Compliant substrate epitaxy: Au on MoS2

A theory for the epitaxial growth of Au on MoS2 is developed and analyzed. The theory combines continuum linear elasticity theory with density functional theory to analyze epitaxial growth in this system. It is demonstrated that if one accounts for interfacial energies and strains, the presence of misfit dislocations, and the compliance of the MoS2 substrate, the experimentally observed growth orientation is favored despite the fact that it represents a larger elastic mismatch than two competing structures. The stability of the experimentally preferred orientation is attributed to the formation of a large number of strong Au-S bonds, and it is noted that this strong bond may serve as a means to exfoliate and transfer large single layers sheets of MoS2, as well as to engineer strain within single layers of MoS2. The potential for using a van der Waals-bonded layered material as a compliant substrate for applications in 2D electronic devices and epitaxial thin film growth is discussed

Deterministic Assembly of Arrays of Lithographically Defined WS2 and MoS2 Monolayer Features Directly from Multilayer Sources into Van der Waals Heterostructures

One of the major challenges in the van der Waals (vdW) integration of two-dimensional (2D) materials is achieving high-yield and high-throughput assembly of predefined sequences of monolayers into heterostructure arrays. Mechanical exfoliation has recently been studied as a promising technique to transfer monolayers from a multilayer source synthesized by other techniques, allowing the deposition of a wide variety of 2D materials without exposing the target substrate to harsh synthesis conditions. Although a variety of processes have been developed to exfoliate the 2D materials mechanically from the source and place them deterministically onto a target substrate, they can typically transfer only either a wafer-scale blanket or one small flake at a time with uncontrolled size and shape. Here, we present a method to assemble arrays of lithographically defined monolayer WS2 and MoS2 features from multilayer sources and directly transfer them in a deterministic manner onto target substrates. This exfoliate-align-release process - without the need of an intermediate carrier substrate - is enabled by combining a patterned, gold-mediated exfoliation technique with a new optically transparent, heat-releasable adhesive. WS2/MoS2 vdW heterostructure arrays produced by this method show the expected interlayer exciton between the monolayers. Light-emitting devices using WS2 monolayers were also demonstrated, proving the functionality of the fabricated materials. Our work demonstrates a significant step toward developing mechanical exfoliation as a scalable dry transfer technique for the manufacturing of functional, atomically thin materials

Oriented Growth of Gold Nanowires on MoS2

Layered 2D materials serve as a new class of substrates for templated synthesis of various nanomaterials even with highly dissimilar crystal structures; thus overcoming the lattice constraints of conventional epitaxial processes. Here, molybdenum disulfide (MoS2) is used as a prototypical model substrate for oriented growth of in-plane Au nanowires (NWs) despite the nearly 8% lattice mismatch between MoS2 and Au. Au NWs on the MoS2 surface are oriented along three symmetrically equivalent directions within the substrate arising from the strong Au-S binding that templates the oriented growth. The kinetics of the growth process are explored through experiments and modeling. Strong charge transfer is observed between Au NWs and MoS2, resulting in degenerate p-doping of MoS2

Oriented Growth of Gold Nanowires on MoS2

Layered 2D materials serve as a new class of substrates for templated synthesis of various nanomaterials even with highly dissimilar crystal structures; thus overcoming the lattice constraints of conventional epitaxial processes. Here, molybdenum disulfide (MoS2) is used as a prototypical model substrate for oriented growth of in-plane Au nanowires (NWs) despite the nearly 8% lattice mismatch between MoS2 and Au. Au NWs on the MoS2 surface are oriented along three symmetrically equivalent directions within the substrate arising from the strong Au-S binding that templates the oriented growth. The kinetics of the growth process are explored through experiments and modeling. Strong charge transfer is observed between Au NWs and MoS2, resulting in degenerate p-doping of MoS2

Reversible phase changes in Ge-Au nanoparticles

We demonstrate a reversible phase transition in nanoparticles composed of a binary eutectic alloy, Ge-Au. The structure, 9 nm diameter nanoparticles embedded in silica, can be switched from bilobe to mixed using a 30 ns ultraviolet laser pulse. The structure can be switched back to bilobe by heating at 80 degrees C. The bilobe/mixed switching can be performed on the same sample at least ten times. Synchrotron X-ray diffraction studies reveal that the bilobe structure contains crystalline Ge and Au while the mixed structure consists of crystalline Ge and beta Ge-Au. (C) 2011 American Institute of Physics. [doi:10.1063/1.3584850]status: publishe

Embedded Binary Eutectic Alloy Nanostructures

The properties of binary eutectic alloy nanostructures embedded within a matrix are discussed. It is demonstrated that GeAu and GeSn nanostructures embedded in SiO2 form in a bilobed structure as predicted by a simple theory. Upon heating, the nanostructures melt and assume a nominally compositionally homogeneous structure. Slow cooling of the liquid returns the nanostructure to its equilibrium bilobed morphology. Rapid quenching yields a kinetically limited, nearly compositionally homogeneous solid. Rapid thermal annealing can convert this metastable structure again into the bilobed structure. It is, therefore, possible to switch between the bilobed structure and the homogenous structure. The kinetics of the homogeneous composition to bilobe structure transformation depend on composition. Tuning the composition enables one to tune the transformation temperature. Possible technological applications of these nanostructures are discussed.status: publishe

Effect of solute atoms on dislocation motion in Mg: An electronic structure perspective

Solution strengthening is a well-known approach to tailoring the mechanical properties of structural alloys. Ultimately, the properties of the dislocation/solute interaction are rooted in the electronic structure of the alloy. Accordingly, we compute the electronic structure associated with, and the energy barriers to dislocation cross-slip. The energy barriers so obtained can be used in the development of multiscale models for dislocation mediated plasticity. The computed electronic structure can be used to identify substitutional solutes likely to interact strongly with the dislocation. Using the example of a-type screw dislocations in Mg, we compute accurately the Peierls barrier to prismatic plane slip and argue that Y, Ca, Ti, and Zr should interact strongly with the studied dislocation, and thereby decrease the dislocation slip anisotropy in the alloy