Resistive-type palladium structures for hydrogen sensing remains as a research focus for their simplicity in device construction. We demonstrate that a siloxane self-assembled monolayer placed between a substrate and an evaporated ultrathin Pd film promotes the formation of small Pd nanoclusters and reduces the stiction between the palladium and the substrate. The resulting Pd nanocluster film can detect 2 % H 2 with a rapid response time of ϳ70 ms and is sensitive to 25 ppm hydrogen, detectable by a 2% increase in conductance due to the hydrogen-induced palladium lattice expansion.

Artificial ices enable the study of geometrical frustration by design and through direct observation. However, it has proven difficult to achieve tailored long-range ordering of their diverse configurations, limiting both fundamental and applied research directions. We designed an artificial spin structure that produces a magnetic charge ice with tunable long-range ordering of eight different configurations. We also developed a technique to precisely manipulate the local magnetic charge states and demonstrate write-read-erase multifunctionality at room temperature. This globally reconfigurable and locally writable magnetic charge ice could provide a setting for designing magnetic monopole defects, tailoring magnonics, and controlling the properties of other two-dimensional materials.

Porous alumina membranes are commercially available and have been widely used in recent nanoscale research, for example, as templates in nanowire fabrication through electrodeposition. In this report, we present a new use for porous alumina membranes in the fabrication of alumina nanotubes/nanowires desired in electrochemical devices and catalytic applications. A high yield of alumina nanotubes/nanowires is obtained by etching porous alumina membranes in an aqueous sodium hydroxide solution. We studied the effects of etching time and solution concentration and characterized the alumina nanotubes/nanowires using a scanning electron microscope (SEM). A discussion of the possible mechanism for the formation of nanotubes/nanowires is given. Our results also imply that in nanowire fabrication through the template approach where alumina membranes are removed with sodium hydroxide solution to release the nanowires special attention is needed in characterizing the nanowires with the SEM because alumina nanotubes/nanowires can be easily mistaken for electrodeposited nanowires.

When the dimension of materials decreases to mesoscale, their properties can change dramatically, depending on the boundary conditions imposed by the sample architecture including geometry, morphology, and hierarchical structures. Here we show that electrodeposition, a method for reducing materials from a solution onto a substrate, can provide a versatile pathway to tailor the architecture of mesostructures. Novel lead (Pb) structures ranging from nanowires, mesoparticles with octahedral, decahedral, and icosahedral shapes to porous nanowires, multipods, nanobrushes, and even snowflake-shaped structures were synthesized through systematically exploring electrodeposition parameters including reduction potentials, solution concentration, starting materials, supporting electrolytes, and surfactants.

We report an anomalous matching effect in MoGe thin films containing pairs of circular holes arranged in such a way that four of those pairs meet at each vertex point of a square lattice. A remarkably pronounced fractional matching was observed in the magnetic field dependences of both the resistance and the critical current. At the half matching field the critical current can be even higher than that at zero field. This has never been observed before for vortices in superconductors with pinning arrays. Numerical simulations within the nonlinear Ginzburg-Landau theory reveal a square vortex ice configuration in the ground state at the half matching field and demonstrate similar characteristic features in the field dependence of the critical current, confirming the experimental realization of an artificial ice system for vortices for the first time.PACS numbers: 74.78. Na, 74.40.Gh Artificial ice systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14] that can have properties similar to atomic spin ices [15][16][17][18][19][20] have been gaining tremendous interest in recent years in areas ranging from solid state systems, magnetism, and soft matter. Among them the two-dimensional (2D) artificial spin ices created using e.g., nanomagnetic arrays [1-8] and charged colloidal particle assemblies [9][10][11][12][13][14] have opened a new avenue in the study of novel phenomena such as geometrical frustration [7,8,[15][16][17][18][19][20][21][22][23][24] which can elucidate, e.g., exotic spin states, [16] charge quantization in magnetic monopoles, [21,22] and mechanisms of high-T c superconductivity. [24] In artificial nanomagnetic square spin ices, [1,8] however, the ice rule states with spin arrangements following "two spins in, two spins out" orders [17] have been only partially observed, which could be due to the weak interactions between the magnetic islands.Vortex matter in a superconductor has much stronger interactions relative to the pinning strength due to the much smaller size scale of the pinning array and could therefore permit a true ice rule obeying ground state. In a recent theoretical work Libal et al. proposed to create artificial square and Kagome ices with vortices in superconductors containing nanostructured arrays of pinning centers.[25] Using elongated double-well pinning sites arranged in a square lattice, for example, they were able to obtain the ground state of a square vortex ice which follows the "two vortices in, two vortices out" rule at each vertex, where the state of each double-well site is defined as "in" if the vortex sits close to the vertex and "out" otherwise. Such vortex systems can offer several advantages over the other artificial ices: [25] i) the ground state can be reached more rapidly as compared to nanomagnet systems due to the larger vortex-vortex interaction strength; ii) defect formation processes can be studied by changing the magnetic field to create vacancies or interstitials that locally break the ice rules; iii) different dynamical annealing protocols can be real...

Nb films containing extended arrays of holes with 45-nm diameter and 100-nm spacing have been fabricated using anodized aluminum oxide (AAO) as substrate. Pronounced matching effects in the magnetization and Little-Parks oscillations of the superconducting critical temperature have been observed in fields up to 9 kOe. Flux pinning in the patterned samples is enhanced by two orders of magnitude as compared to unpatterned reference samples in applied fields exceeding 5 kOe. Matching effects are a dominant contribution to vortex pinning at temperatures as low as 4.2 K due to the extremely small spacing of the holes.

Large area nickel antidot arrays with density up to 10 10 /cm 2 have been fabricated by depositing nickel onto anodic aluminum oxide membranes that contain lattices of nanopores. Electron microscopy images show a high degree of order of the antidot arrays. Various sizes and shapes of the antidots were observed with increasing thickness of the deposited nickel. New features appear in the antidot arrays in both magnetization and transport measurements when the external magnetic field is parallel to the current direction, including an enhancement and a nonmonotonous field dependence of the magnetoresistance, larger values of the coercive field and remanence moment, and smaller saturation field.

The newly developed hydrogen sensor, based on a network of ultrasmall pure palladium nanowires sputter-deposited on a filtration membrane, takes advantage of single palladium nanowires' characteristics of high speed and sensitivity while eliminating their nanofabrication obstacles. However, this new type of sensor, like the single palladium nanowires, cannot distinguish hydrogen concentrations above 3%, thus limiting the potential applications of the sensor. This study reports hydrogen sensors based on a network of ultrasmall Cr-buffered Pd (Pd/Cr) nanowires on a filtration membrane. These sensors not only are able to outperform their pure Pd counterparts in speed and durability but also allow hydrogen detection at concentrations up to 100%. The new networks consist of a thin layer of palladium deposited on top of a Cr adhesion layer 1-3 nm thick. Although the Cr layer is insensitive to hydrogen, it enables the formation of a network of continuous Pd/Cr nanowires with thicknesses of the Pd layer as thin as 2 nm. The improved performance of the Pd/Cr sensors can be attributed to the increased surface area to volume ratio and to the confinement-induced suppression of the phase transition from Pd/H solid solution (α-phase) to Pd hydride (β-phase).