Vladimir Tuboltsev

Magnetism in nanocrystalline gold.

While bulk gold is well known to be diamagnetic, there is a growing body of convincing experimental and theoretical work indicating that nanostructured gold can be imparted with unconventional magnetic properties. Bridging the current gap in experimental study of magnetism in bare gold nanomaterials, we report here on magnetism in gold nanocrystalline films produced by cluster deposition in the aggregate form that can be considered as a crossover state between a nanocluster and a continuous film. We demonstrate ferromagnetic-like hysteretic magnetization with temperature dependence indicative of spin-glass-like behavior and find this to be consistent with theoretical predictions, available in the literature, based on first-principles calculations.

Magnetic Properties of Polycrystalline Bismuth Ferrite Thin Films Grown by Atomic Layer Deposition.

The atomic layer deposition (ALD) method was applied to grow thin polycrystalline BiFeO3 (BFO) films on Pt/SiO2/Si substrates. The 50 nm thick films were found to exhibit high resistivity, good morphological integrity, and homogeneity achieved by the applied ALD technique. Magnetic characterization revealed saturated magnetization of 25 emu/cm(3) with temperature-dependent coercivity varying from 5 to 530 Oe within the temperature range from 300 to 2 K. Magnetism observed in the films was found to change gradually from ferromagnetic spin ordering to pinned magnetic domain interactions mixed with weak spin-glass-like behavior of magnetically frustrated antiferromagnetic/ferromagnetic (AFM-FM) spin ordering depending on the temperature and magnitude of the applied magnetic field. Antiferromagnetic order of spin cycloids was broken in polycrystalline films by crystal sizes smaller than the cycloid length (∼60 nm). Uncompensated spincycloids and magnetic domain walls were found to be the cause of the high magnetization of the BFO films.

Binding of deposited gold clusters to thiol self-assembled monolayers on Au(111) surfaces

We study the mechanisms involved in Au nanocluster deposition on thiol self-assembled monolayer modified Au(111) surfaces. Molecular dynamics simulations reveal a wide range of cluster-surface binding configurations within a very narrow deposition energy range (0.2–0.6 eV/atom for ∼2.5 nm diameter clusters). These go from noncovalent to full contact and include surprising intermediate cases in which the clusters are bound to the underlying Au(111) surface via molecular links and nanowires. Experiments show that, subsequently, the clusters are covered by thiols and slightly flattened.

Sculpturing Nanowires with Ion Beams

Mass production in the close and sub-10-nm feature size regime is hindered by the lack of available and suitable tools capable of delivering the required levelofwell-controlledminiaturization. Low-energy ion beams provide a great degree of control when applied to prefabricated nanostructures for gradual downsizing and shaping. The unique sculpturing capability exhibited by energetic ions on the nanometer scale in forming threedimensional (3D) nano-objects enables fabrication of continuousnanowires, of virtuallyanymaterial,macroscopically long, and with an effective diameter of less than 10 nm. Newdevelopments in surface nanostructuring are expected to meet the emerging needs of industry in miniaturization, which currently faces serious difficulties in upholding the trend, particularly in microelectronics. The availability of effective tools for reliable mass production of complex composite nanoscale structures is a necessary prerequisite for successful industrial exploitation of the dramatic developments in nanoscience. Future success in developing 10-nm and sub-10-nm technologies will depend to a great degree on how well the process of nanostructuring is controlled on the nanoscale. In this size regime, morphological non-homogeneities characteristic to thematerial forming thebodyof ananostructure become comparable with its size. Any structural imperfections that are of little concern at the macroscale become absolutely critical when approaching the 10-nm size regime. In nanostructures bearing some functionality, that is, nanodevices, a nanowire is a necessary attribute forming an elemental link enabling charge transfer. The 10-nm feature size domain is of great interest for both fundamental research in the field of low-dimensional nanostructures and developing new nanoelectronic applications where nanostructuring enables new functionalities. New, exiting physics is expected at this scale due to the quantum size effects that, for example, may open a new route towards quantum communication and computation. It was predicted theoretically that a superconducting loop with embedded 10-nm-diameter nanowire

Spin-glass behavior of nanocrystalline multiferroic bismuth ferrite lead titanate

Multiferroic bismuth ferrite lead titanate exhibiting both ferroelectricity and ferromagnetism in a single perovskite phase has been chemically synthesized in the form of nanocrystalline films with large surface/interface to volume atomic ratio. The films show both electric polarization and magnetization hysteresis loops and demonstrate behavior consistent with the existence of a spin-glass state at temperatures well above the room temperature. Anomalous magnetic properties and glassy dynamics are associated with a high degree of magnetic frustration and disorder due to the spatial confinement in nanosized crystalline grains, random distribution of anisotropy axes in the grains, inter-grain interaction and the effects of uncompensated spins on the large effective surface and interface favored by the nanocrystalline morphology of the films.

Composition dependence of Si{sub 1-x}Ge{sub x} sputter yield

Sputtering yields have been measured for unstrained Si{sub 1-x}Ge{sub x} (x=0-1) alloys when bombarded with Ar{sup +} ions within the linear cascade regime. Nonlinear S-shape dependence of the sputter yield as a function of the alloy composition has been revealed. The dependence is analyzed within the frameworks of the cascade theory conventionally accepted to be the most systematic to date theoretical approach in sputtering. In view of a linear composition dependence predicted for the sputter yield by the cascade theory adapted for polyatomic substrates, the nonlinearity observed in our experiments is shown to be related to the alloying effect on the surface binding energies of the alloy components. Based on this analysis, an interpretation is proposed for the experimentally observed nonlinear composition dependence of Si{sub 1-x}Ge{sub x} sputter yield. The yield is expressed by an equation derived from the cascade theory with additional terms of the composition parameter x. The form of the equation implies that for a polyatomic substrate the surface binding energy of an individual atom is determined not only by its own chemical identity but to a considerable degree by the identities of its neighbors.

Spin-glass magnetism of surface rich Au cluster film

The magnetic response of two-dimensional uncapped Au islands tens of nanometers in size was measured using a superconducting quantum interference device magnetometer. The magnetization vs. field was found to exhibit a clear ferromagnetic-like hysteresis loop and a large positive remanent magnetization was acquired after momentary application of a strong magnetic field. The Au magnetic response is assumed to be due to the surface effects in the nanosized islands and the large fraction of canted surface magnetic moments which interaction and mutual orientation differ from the bulk diamagnetic order.

Critical temperature modification of low dimensional superconductors by spin doping

Ion implantation of Fe and Mn into Al thin films was used for effective modification of Al superconductive properties. The critical temperature of the transition to the superconducting state was found to decrease gradually with implanted Fe concentration. It was found that suppression by Mn implantation is much stronger compared to Fe. At low concentrations of implanted ions, suppression of the critical temperature can be described with reasonable accuracy by existing models, while at concentrations above 0.1 at.% a pronounced discrepancy between the models and experiments is observed.

Growth mode-dependent ferromagnetic properties of palladium nanoclusters

Cluster deposited Pd films exhibit ferromagnetism in the temperature range from 1.8 to 400 K. The magnetization properties are found to be dependent on the film thickness. The varying morphology of the resulting Pd film with respect to thickness suggests that cluster size, deposition energy, and substrate type are crucial for the resulting film magnetization. This is demonstrated by the characteristic ferromagnetic hysteresis with the temperature dependent saturation magnetization, remanence, and coercivity of palladium nanocluster aggregates. The temperature dependence of the saturation magnetization, remanence, and coercivity of Pd nanoclusters were measured using an ultra-high-sensitive magnetometer based on a superconducting quantum interference device, and the morphology of the samples was analyzed by tunneling electron microscopy.Cluster deposited Pd films exhibit ferromagnetism in the temperature range from 1.8 to 400 K. The magnetization properties are found to be dependent on the film thickness. The varying morphology of the resulting Pd film with respect to thickness suggests that cluster size, deposition energy, and substrate type are crucial for the resulting film magnetization. This is demonstrated by the characteristic ferromagnetic hysteresis with the temperature dependent saturation magnetization, remanence, and coercivity of palladium nanocluster aggregates. The temperature dependence of the saturation magnetization, remanence, and coercivity of Pd nanoclusters were measured using an ultra-high-sensitive magnetometer based on a superconducting quantum interference device, and the morphology of the samples was analyzed by tunneling electron microscopy.

Silicon-based Coulomb blockade thermometer with Schottky barriers

A hybrid Coulomb blockade thermometer (CBT) in form of an array of intermittent aluminum and silicon islands connected in series via tunnel junctions was fabricated on a thin silicon-on-insulator (SOI) film. Tunnel barriers in the micrometer size junctions were formed by metal-semiconductor Schottky contacts between aluminium electrodes and heavily doped silicon. Differential conductance through the array vs. bias voltage was found to exhibit characteristic features of competing thermal and charging effects enabling absolute temperature measurements over the range of ∼65 to ∼500 mK. The CBT performance implying the primary nature of the thermometer demonstrated for rather trivial architecture attempted in this work paves a route for introduction of Coulomb blockade thermometry into well-developed contemporary SOI technology.