The electronic state in ultrathin gold nanowires is tuned by careful engineering of the device architecture via a chemical methodology. The electrons are localized to an insulating state (showing variable range hopping transport) by simply bringing them close to the substrate, while the insertion of an interlayer leads to a Tomonaga Luttinger liquid state.

A detailed understanding of structure and stability of nanowires is critical for applications. Atomic resolution imaging of ultrathin single crystalline Au nanowires using aberration-corrected microscopy reveals an intriguing relaxation whereby the atoms in the close-packed atomic planes normal to the growth direction are displaced in the axial direction leading to wrinkling of the (111) atomic plane normal to the wire axis. First-principles calculations of the structure of such nanowires confirm this wrinkling phenomenon, whereby the close-packed planes relax to form saddle-like surfaces. Molecular dynamics studies of wires with varying diameters and different bounding surfaces point to the key role of surface stress on the relaxation process. Using continuum mechanics arguments, we show that the wrinkling arises due to anisotropy in the surface stresses and in the elastic response, along with the divergence of surface-induced bulk stress near the edges of a faceted structure. The observations provide new understanding on the equilibrium structure of nanoscale systems and could have important implications for applications in sensing and actuation.

magnetization, [12,13] magnetocrystalline anisotropy, [14] magnetostriction, [15] Gilbert damping parameter, [16-19] and magnetooptical spectral response, [10,20,21] and the net anisotropy may be varied widely by choice of substrate, which affects the strain state of the film. [22,23] Ferrimagnetic insulators, such as YIG and REIG, are particularly promising for spintronics as they do not contribute Ohmic losses from parasitic current shunting and exhibit fast magnetization dynamics and low losses in the THz regime. [24] Films with perpendicular magnetic anisotropy (PMA) are advantageous for investigation of spin-orbit torque (SOT) effects, chiral magnetic textures such as skyrmions, and for high density information storage based on domain walls. [25,26] It is difficult to grow YIG with PMA, but REIG films with PMA have been grown, and manipulation of their magnetization has been demonstrated via a spin-orbit torque (SOT) from an adjacent heavy metal [3,27] or from a topological insulator [28,29] with a large spin Hall angle. Electrical control of the magnetization using the damping-like SOT offers the potential for memory and logic devices with ultra-low power dissipation. [30-32] Taking advantage of these properties in spintronic devices requires the integration of PMA REIG films onto non-garnet substrates; silicon is of particular interest as a substrate due to its commercial ubiquity. Single crystal garnet thin films have been grown with PMA by selecting a substrate and garnet composition such that the out-of-plane magnetoelastic anisotropy K me originating from epitaxial lattice mismatch overcomes the shape anisotropy K sh. PMA has been demonstrated in samarium-, [33] thulium-, [18] europium-, [19,34] and terbium [19,34] iron garnets on gadolinium gallium garnet (Gd 3 Ga 5 O 12 , GGG) substrates, and bismuthsubstituted yttrium-[7] and thulium-[35,36] iron garnets on substituted GGG (Gd 2.6 Ca 0.4 Ga 4.1 Mg 0.25 Zr 0.65 O 12 , SGGG). For films grown on (111)-oriented garnet substrates the magnetocrystalline anisotropy also contributes to PMA by an amount K 1 /12, which is typically small, where K 1 is the first order magnetocrystalline anisotropy coefficient. For polycrystalline films grown on non-garnet substrates, the elastic anisotropy originates instead from thermal expansion mismatch with the substrate on cooling from the annealing Magnetic insulators, such as the rare-earth iron garnets, are promising materials for energy-efficient spintronic memory and logic devices, and their anisotropy, magnetization, and other properties can be tuned over a wide range through selection of the rare-earth ion. Films are typically grown as epitaxial single crystals on garnet substrates, but integration of these materials with conventional electronic devices requires growth on Si. The growth, magnetic, and spin transport properties of polycrystalline films of dysprosium iron garnet (DyIG) with perpendicular magnetic anisotropy (PMA) on Si substrates and as single crystal films on garnet substrates are reported. PMA orig...

It is well known that metals with higher electron affinity like Au tend to undergo reduction rather than cation-exchange. It is experimentally shown that under certain conditions cation-exchange is dominant over reduction. Thermodynamic calculation further consolidates the understanding and paves the way for better predictability of cation-exchange/reduction reactions for other systems.

Although ultrathin Au nanowires (∼2 nm diameter) are expected to demonstrate several interesting properties, their extreme fragility has hampered their use in potential applications. One way to improve the stability is to grow them on substrates; however, there is no general method to grow these wires over large areas. The existing methods suffer from poor coverage and associated formation of larger nanoparticles on the substrate. Herein, we demonstrate a room temperature method for growth of these nanowires with high coverage over large areas by in situ functionalization of the substrate. Using control experiments, we demonstrate that an in situ functionalization of the substrate is the key step in controlling the areal density of the wires on the substrate. We show that this strategy works for a variety of substrates ranging like graphene, borosil glass, Kapton, and oxide supports. We present initial results on catalysis using the wires grown on alumina and silica beads and also extend the method to lithography-free device fabrication. This method is general and may be extended to grow ultrathin Au nanowires on a variety of substrates for other applications.