Resistive Switching Characteristics of NiO Thin Films Influenced by Changes in the Diameter of Nanometer-Scale Top Electrodes.

We investigated the forming, set, and reset voltages affected by the area of the top electrodes of a resistive random access memory (RRAM) capacitor fabricated by epitaxial NiO thin films. NiO RRAM capacitors with Au top electrode with a diameter of 100 μm showed typical unipolar switching characteristics. Au top electrodes with diameters of 10, 20, and 30 nm were formed on the surface of epitaxial NiO thin films by e-beam lithography.

A comparative study of PMMA/PEG polymer nanocomposites doped with different oxides nanoparticles for potential optoelectronic applications.

PMMA/PEG and PMMA/PEG doped with SiO, TiO and AlO were fabricated using the solution-casting technique. The composites were characterized by X-ray diffraction and scanning electron microscopy (FE-SEM), which revealed that the amorphous nature of PMMA/PEG blend doped with AlO was hindered by the crystalline nature of those doped with SiO and TiO. The absorption of PMMA/PEG blend doped with AlO is higher, band gap energies were decreased from 4.

Conducting atomic force microscopy studies on domain wall currents of BiTiFeO nanodots fabricated by anodic aluminum oxide nanotemplate and sol-gel process.

We investigated the local current characteristics of BiTiFeO (BTFO) nanodots on Nb-doped SrTiO substrates affected by their ferroelectric domain structures and domain walls. The BTFO nanodots with a diameter of about 50 nm were fabricated by anodic aluminum oxide nanotemplates and a BTFO sol-gel process. Based on a piezoresponse force microscope, it was confirmed that domain walls were formed in the ferroelectric domain structures of the epitaxial BTFO nanodots.

A conducting atomic force microscopy study of conducting filament nanobits in the epitaxial NiO thin film prepared precisely controlled by the oxidation time of the single crystalline Ni substrates.

We report on the formation of conducting filament (CF) nanodots and the resistive random access memory (RRAM) characteristics of epitaxial NiO thin films with good crystallinity obtained by oxidation of the single crystal Ni substrates. The thickness of the epitaxial NiO thin films with good crystallinity was precisely controlled by the oxidation time. The local current mapping using conducting atomic force microscope (CAFM) showed that the NiO thin films had uniform resistance without conducting defects inside.

Ferroelectric properties and piezoresponse force micoroscopy study of BiTaTiO thin films.

We investigate the ferroelectric properties and crystal structures of BiTaTiO (BTTO) thin films deposited on single-crystal Nb-doped (100) SrTiO substrates via pulsed laser deposition. The BTTO films exhibited either a (001)-epitaxial crystalline structure or a mixed a- and c-oriented polycrystalline structure depending on the substrate temperature. The ferroelectric polarization and piezoelectric coefficient of the mixed a- and c-oriented film were larger than those of the (001)-epitaxial film because its polar axis was perpendicular to the c-axis.

Effects of a Nb nanopin electrode on the resistive random-access memory switching characteristics of NiO thin films.

We report the effects of bottom electrode shapes on resistive random-access memory (RRAM) devices composed of Nb (bottom electrode)/NiO (dielectric)/Nb (top electrode) structures. By adopting a nano-fabrication process using an anodic aluminum oxide (AAO) nanotemplate, a well-aligned Nb nanopin array bottom electrode was formed on the surface of a Si substrate. For comparison, a Nb thin film was employed as a different type of bottom electrode.

Anomalous domain periodicity observed in ferroelectric PbTiO3 nanodots having 180° stripe domains.

Nanometer-scale ferroelectric dots and tubes have received a great deal of attention owing to their potential applications to nonvolatile memories and multi-functional devices. As for the size effect of 180° stripe domains in ferroelectric thin films, there have been numerous reports on the thickness-dependent domain periodicity. All these studies have revealed that the domain periodicity (w) of 180° stripe domains scales with the film thickness (d) according to the classical Landau-Lifshitz-Kittel (LLK) scaling law (w ∝ d(1/2)) down to the thickness of ~2 nm.

Thermal curing of a self-assembled monolayer at the nanoscale.

On fabrication by contact printing, a nanostructured self-assembled monolayer (SAM) of alkanethiol contains a substantial fraction of unbound molecules that are either inverted among other upright molecules or piled on top of the SAM. The molecular dynamics simulation in the present study demonstrates that thermal annealing cures these defects for a SAM island of octadecanethiol. The SAM island melted partially as a result of heating, so the unbound molecules that had piled on top of the SAM island penetrated down to make contact with the surface, and the inverted molecules flipped to achieve adsorption.

Confinement of ferroelectric domain-wall motion at artificially formed conducting-nanofilaments in epitaxial BiFeO3 thin films.

We report confinement of ferroelectric domain-wall motion at conducting-nanofilament wall in epitaxial BiFeO3 thin film on Nb-doped SrTiO3 substrate. The BiFeO3 film exhibited well-defined ferroelectric response and unipolar resistive switching behavior. We artificially formed conducting-nanofilaments in the BiFeO3 via conducting atomic force microscope techniques.

Four-states multiferroic memory embodied using Mn-doped BaTiO3 nanorods.

Multiferroics that show simultaneous ferroic responses have received a great deal of attention by virtue of their potential for enabling new device paradigms. Here, we demonstrate a high-density four-states multiferroic memory using vertically aligned Mn-doped BaTiO3 nanorods prepared by applying the dip-pen nanolithography technique. In the present nanorods array, the polarization (P) switching by an external electric field does not influence the magnetization (M) of the nanorod owing to a negligible degree of the P-M cross-coupling.

Colors of graphene and graphene-oxide multilayers on various substrates.

We investigated the colors of graphene and graphene-oxide multilayers that were deposited on various dielectric layers. In particular, the effects of the material thickness, the types of dielectric layers, and the existence of a back silicon substrate were analyzed. The colors of graphene-oxide layers on a SiO2/Si substrate were found to periodically change as the material thickness increased.

Spin-canting-induced improper ferroelectricity and spontaneous magnetization reversal in SmFeO3.

SmFeO3, a family of centrosymmetric rare-earth orthoferrites, is known to be nonferroelectric. However, we have found that SmFeO3 is surprisingly ferroelectric at room temperature with a small polarization along the b axis of Pbnm. First-principles calculations indicate that the canted antiferromagnetic ordering with two nonequivalent spin pairs is responsible for this extraordinary polarization and that the reverse Dzyaloshinskii-Moriya interaction dominates over the exchange-striction mechanism in the manifestation of the improper ferroelectricity.

High-mobility graphene nanoribbons prepared using polystyrene dip-pen nanolithography.

Graphene nanoribbons (GNRs) are fabricated by dip-pen nanolithography and polystyrene etching techniques on a SrTiO(3)/Nb-doped SrTiO(3) substrate. A GNR field-effect transistor (FET) shows bipolar FET behavior with a high mobility and low operation voltage at room temperature because of the atomically flat surface and the large dielectric constant of the insulating SrTiO(3) layer, respectively.

A nonvolatile memory device made of a ferroelectric polymer gate nanodot and a single-walled carbon nanotube.

We demonstrate a field-effect nonvolatile memory device made of a ferroelectric copolymer gate nanodot and a single-walled carbon nanotube (SW-CNT). A position-controlled dip-pen nanolithography was performed to deposit a poly(vinylidene fluoride-ran-trifluoroethylene) (PVDF-TrFE) nanodot onto the SW-CNT channel with both a source and drain for field-effect transistor (FET) function. PVDF-TrFE was chosen as a gate dielectric nanodot in order to efficiently exploit its bipolar chemical nature.

NiO resistive random access memory nanocapacitor array on graphene.

In this study, a NiO RRAM nanocapacitor array was fabricated on a graphene sheet, which was on a Nb-doped SrTiO(3) substrate containing terraces with a regular interval of about 100 nm and an atomically smooth surface. For the formation of the NiO RRAM nanocapacitor (Pt/NiO/graphene capacitor) array, an anodic aluminum oxide (AAO) nanotemplate with a pore diameter of about 30 nm and an interpore distance of about 100 nm was used. NiO and Pt were subsequently deposited on the graphene sheet.

Self-formed exchange bias of switchable conducting filaments in NiO resistive random access memory capacitors.

We report on the ferromagnetism of conducting filaments formed in a NiO thin film, which exhibited a typical bistable resistive switching characteristic. The NiO thin film showed an antiferromagnetic hysteresis loop for a high resistive state (R(OFF)). However, for a low resistive state (R(ON)), the conducting filaments exhibited a ferromagnetic hysteresis loop for the field cooling.

Dip-pen lithography of ferroelectric PbTiO(3) nanodots.

Dip-pen nanolithography of ferroelectric PTO nanodots is described. This position-controlled dip-pen nanolithography using a silicon nitride cantilever produced an array of ferroelectric nanodots with a minimum lateral dimension of approximately 37 nm on a Nb-doped SrTiO(3) substrate. This minimum-sized PTO dot is characterized by single-domain epitaxial growth with an enhanced tetragonality (c/a ratio) of 1.

Heteroepitaxial ferroelectric ZnSnO3 thin film.

We investigated the ferroelectric characteristics of an epitaxial perovskite ZnSnO(3) thin film on a (111) SrRuO(3)/(111) SrTiO(3) substrate fabricated by pulsed laser deposition. We confirmed that the ZnSnO(3) thin film was epitaxially grown on the substrate, forming large terraces on the surface of the ZnSnO(3) thin film. The ZnSnO(3) thin film exhibited a high ferroelectric polarization of approximately 47 microC/cm(2), which was further supported by first-principles calculations.

Formation of self-assembled polyelectrolyte multilayer nanodots by scanning probe microscopy.

We demonstrate that patterned nanodots can be obtained from alternatively self-assembled polyelectrolytes which consist of poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) by using atomic force microscopy. The surface potentials are easily reversible as positive or negative depending on the kind of the top polyelectrolyte layer. With the layer by layer growth, the nanodots are formed exactly on the charged area and their thicknesses proportionally increase to the total number of monolayers with a uniform thickness of about 0.

Spontaneous formation of vertical magnetic-metal-nanorod arrays during plasma-enhanced atomic layer deposition.

A novel fabrication method of Co and Ni metal nanorods (NRs) without catalyst or template, based on the spontaneous formation of NRs during plasma-enhanced atomic layer deposition (PE-ALD) is developed. Pure Co and Ni NRs 9-10 nm in diameter are synthesized on SiO(2) and Si substrates by using metal-organic precursors and an NH(3) plasma mixed with a suitable amount of SiH(4) as a reactant. The lengths of the NRs are controlled on the nanometer scale by changing the number of PE-ALD growth cycles.

Ru nanostructure fabrication using an anodic aluminum oxide nanotemplate and highly conformal Ru atomic layer deposition.

We fabricated metallic nanostructures directly on Si substrates through a hybrid nanoprocess combining atomic layer deposition (ALD) and a self-assembled anodic aluminum oxide (AAO) nanotemplate. ALD Ru films with Ru(DMPD)(EtCp) as a precursor and O(2) as a reactant exhibited high purity and low resistivity with negligible nucleation delay and low roughness. These good growth characteristics resulted in the excellent conformality for nanometer-scale vias and trenches.