Oxide Nanodots Research Articles

Atomic Force Microscope nanolithography on titanium: Influence of the anodic voltage waveform on the formation of oxide nanodots

We investigate the effect of different voltage waveforms on the growth of titanium oxide nanodots using Atomic Force Microscope (AFM) nanolithography. The resulting oxide features are compared by taking into account the current data detected during oxidation under the application of constant and linear ramp voltages. The experimental analysis of current waveforms during oxidation upon a constant bias voltage gives quantitative criteria to reduce space charge effects. The use of ramp voltages gives higher flexibility on the control of volume and aspect ratio of oxide features by varying the duty cycle.

Floating nanodot gate memory fabrication with biomineralized nanodot as charge storage node

We have demonstrated floating nanodot gate memory (FNGM) fabrication by utilizing uniform biomineralized cobalt oxide (Co3O4) nanodots (Co-BNDs) which are biochemically synthesized in the vacant cavity of supramolecular protein, ferritin. High-density Co-BND array (>6.5×1011cm−2) formed on Si substrate with 3-nm-thick tunnel SiO2 is embedded in metal-oxide-semiconductor (MOS) stacked structure and used as the floating gate of FNGM. Fabricated Co-BND MOS capacitors and metal-oxide-semiconductor field effect transistors show the hysteresis loop due to the electron and hole confinement in the embedded Co-BND. Fabricated MOS memories show wide memory window size of 3–4V under 10V operation, good charge retention characteristics until 104s after charge programming, and stress endurance until 105 write/erase operation. Observed charge injection thresholds suggest that charge injection through the direct tunneling from Si to the energy levels in the conduction and valence bands of Co3O4 and long charge retention characteristics implies prompt charge confinement to the deeper energy level of metal Co which is formed during the annealing in the device processing.

Fabrication and Field-Emission Characteristics of TiN Nanorods with a Concave Top Surface

Well-ordered titanium nitride nanorods were fabricated by reactive ion etch using titanium oxide nanodots as the mask, which were prepared using the anodic aluminum oxide templation method. The TiN nanorods exhibited a concave top surface with a protruding edge. Due to the protruding top edge and a high aspect ratio, the TiN nanorods showed a low turn-on voltage of 1.6 V/μm. The ellipsoidal cylinder model was used to evaluate the field-enhancement effect of the protruding edge, and an underestimation by ∼ 26% was found as compared with the enhancement factor derived from the Fowler-Nordheim plot.

A study of the transient current during the formation of titanium oxide nanodots by AFM anodic oxidation

We analyze transient current data during the formation of titanium oxide nanodots by AFM-tip-induced anodic oxidation with the aim of getting further understanding of local oxidation kinetics. The measured current waveforms show a transition between two distinct regimes, in agreement to what was previously known of the growth process, and their behavior is discussed with respect to the oxide growth rate and to the formation of the space charge. Furthermore, it is shown how the knowledge of the duration of the first transient regime can be exploited to optimize the application of pulsed bias voltages to obtain a substantial improvement in aspect ratio of growing oxides.

Effects of Tip Voltage and Writing Speed on the Formation of Silicon Oxide Nanodots Patterned by Scanning Probe Lithography

Effects of Tip Voltage and Writing Speed on the Formation of Silicon Oxide Nanodots Patterned by Scanning Probe Lithography

Fabrication of ordered Ta2O5 nanodots using an anodic aluminum oxide template on Si substrate

Ordered arrays of Ta2O5 nanodots were prepared using anodic aluminum oxide (AAO) as a template to support localized oxidation of TaN. Films of TaN (50 nm) and Al (1.5 μm) were deposited successively on p-type Si wafers and followed by a two-step anodization process at 40 V using oxalic acid as the electrolyte. The first anodization promoted growth of irregular AAO from overlying Al film. After chemical etching, the second anodization was performed to develop well-organized AAO channels and initiate oxidation of underlying TaN film to form tantalum oxide nanodots at the AAO pore bottoms. X-ray photoelectron spectroscopy results confirmed the chemical nature of nanodots as stoichmetric Ta2O5. X-ray diffraction demonstrated the amorphous characteristic of Ta2O5. As shown in field-emission scanning electron microscopy and transmission electron results, the Ta2O5 nanodots exhibited a hillock structure 80 nm in diameter at the bottom and 50 nm in height. We also synthesized 30-nm nanodots by adjusting AAO formation electrochemistry. This demonstrates the general applicability of the AAO template method for nanodot synthesis from nitride to oxide at a desirable size.

Local Oxide Growth Mechanisms on Nickel Films

The oxidation characteristics of nickel thin films were investigated by atomic force microscopy (AFM) anodization. The anodization parameters, such as anodized voltages, oxidation times, pulse voltage periods and how they affected the creation and growth of the oxide nanostructures were explored. The results showed that the height of the nickel oxide nanodots grew as a result of either the anodization time or the anodized voltage being increased. The oxide growth rate was dependent on the anodized voltage and on the resulting electric field strength. Furthermore, as the electric field strength was at an order of 2×109 Vm−1, the anodization rate decreased quickly and the oxide dots stopped growing.

Size control for two-dimensional iron oxide nanodots derived from biological molecules

We demonstrated the fabrication of size-controlled two-dimensional iron oxide nanodots derived from the heat treatment of ferritin molecules self-immobilized on modified silicon surfaces. Ferritin molecules were immobilized onto 3-aminopropyltrimethoxysilane (3-APMS)-modified silicon surfaces by electrostatic interactions between negatively charged amino acids of ferritin molecules and amino terminal functional groups of 3-APMS. Heat treatments were performed at 400 °C for 60 min to fabricate two-dimensional nanodots based on ferritin cores. XPS and FT-IR results clearly indicate that ferritin shells were composed of amino acids and 3-APMS modifiers on silicon surfaces were eliminated by heat treatment. Nanodots on substrate surfaces corresponded to iron oxides. The size of nanodots was tunable in the range of 0–5 (±0.75) nm by in situ reactions of iron ion chelators with ferritin molecules immobilized on substrates before heat treatment.

Self-aligned tantalum oxide nanodot arrays through anodic alumina template

A novel strategy for fabricating the ordered nanodot arrays of tantalum oxide with anodic alumina film is proposed to serve the template. Anodic oxidation of Al on TaN film has been performed in oxalic acid and sulfuric acid electrolytes at various applied voltages for porous alumina formation. Anodising reaction proceeds in the sequence of growth of porous anodic alumina when the aluminum layer is consumed up to the underlying TaN, and the growth of tantalum oxide under the bottoms of the alumina pores occurred simultaneously. The nanostructure of the nanodot arrays was studied by scanning electron microscopy, and the chemical composition of nanodots was analyzed by X-ray photoelectron spectroscopy. The nanodots are composed of nonstoichiometric TaO x . The nanodot diameter demonstrated here ranges between 15 nm and 70 nm and density ranges between 10 11/cm 2 and 10 10/cm 2.

Formation of epitaxial oxide nanodots on oxide substrate: Cu 2O on SrTiO 3(1 0 0)

X-ray photoelectron spectroscopy analysis during the oxygen plasma assisted molecular beam epitaxy, combined with atomic force microscopy and scanning Auger microscopy have been used to evaluate the mechanism of single-phase Cu 2O nanodot formation on the SrTiO 3(1 0 0) surface. Formation of pure crystalline Cu 2O nanodots occurs rather in a narrow growth parameter window, outside which a coexistence of the multiple phases has been observed. Cuprous oxide nanodots on the SrTiO 3(1 0 0) substrate follow a growth mechanism which differs significantly from the growth modes observed for the majority of semiconductor quantum dots. Growth starts without wetting layer formation with appearance of well-ordered truncated square-based nanodots at submonolayer coverages. At the initial stages of growth, the nanodot size is only weakly changes with coverage and exponentially scales with temperature. After reaching a critical, temperature dependent dot density (∼10 13 cm −2 for 760 K growth temperature), growth of mid-sized nanoclusters starts through coalescence, which is eventually followed by large dome-shaped cluster formation at higher coverages. The coexistence of the different types of the clusters at high coverages results in a multimodal distribution of sizes and shapes.

Selective growth of carbon nanotubes on nickel oxide templates created by atomic force microscope nano-oxidation

The selective growth of carbon nanotubes on nickel oxide templates of square blocks of size 2×2 μm 2 on Si by a microwave-heated CVD has been successfully demonstrated. By applying a negative bias to a conductive tip, nickel oxide patterns were first created by the process of nano-oxidation. The unoxidized nickel film was then removed using a wet chemical etch technique, thereby forming nickel oxide templates over which the carbon nanotubes were grown. We also obtained single carbon nanotubes on nickel oxide nanodots that have diameters as small as 100 nm. The selective growth of CNTs over nickel oxide templates could be also fulfilled on not nickel-etched substrate by appropriately controlling the growth temperature and growth time.

Fabrication and Field Emission Characteristics of Highly Ordered Titanium Oxide Nanodot Arrays

Fabrication and Field Emission Characteristics of Highly Ordered Titanium Oxide Nanodot Arrays

Self-assembled zinc oxide nanodots on silicon oxide

Self assembled ZnO nanodots are grown by electron beam evaporation of Zn on thermally oxidized silicon substrates and subsequent annealing in oxygen. Characterization by TEM and EELS shows that the quantum dots are indeed zinc oxide single crystals grown with their c-axis perpendicular to the substrate; their distribution and size depends on the deposition parameters of zinc onto the substrates.

Solvothermal Routes for Synthesis of Zinc Oxide Nanorods

AbstractControl of the synthesis of nanomaterials to produce morphologies exhibiting quantized properties will enable device integration of several novel applications including biosensors, catalysis, and optical devices. In this work, solvothermal routes to produce zinc oxide nanorods are explored. Much previous work has relied on the addition of growth directing/inhibiting agents to control morphology. It was found in coarsening studies that zinc oxide nanodots will ripen to nanorod morphologies at temperatures of 90 to 120 °C. The resulting nanorods have widths of 9-12 nm average dimension, which is smaller than current methods for nanorod synthesis. Use of nanodots as nuclei may be an approach that will allow for controlled growth of higher aspect ratio nanorods.

Initial stages of oxide nanodot heteroepitaxial growth: Cu2O on SrTiO3(100)

The growth mechanism in a heteroepitaxy of oxide nanodots is investigated by a combination of x-ray photoelectron spectroscopy (XPS), atomic force microscopy, and theoretical modeling. In contrast to the majority of semiconductor systems, in the studied metal oxide system of Cu2O–SrTiO3(100) the growth process starts without wetting layer formation with the appearance of small (∼10nm) square-based planar Cu2O nanodots. Continued deposition leads mainly to increase of the nanodot density, practically, without change of their size. Only after reaching some critical density (∼1013cm−2 for 760K growth temperature), growth of scattered, significantly larger islands starts through the coalescence of small nanodots. XPS analysis suggests that the interface between small nanodots and substrate is abrupt with only weak Cu–O(SrTiO3) interaction.

Formation and kinetics study of cuprous oxide nanodots on LaAlO 3 (0 0 1)

Cu 2O nanodots have been grown on LaAlO 3 (0 0 1) substrates using metalorganic chemical vapor deposition. X-ray diffraction reveals that the nanodots grow epitaxially on the substrate. The dots are hut-shaped islands with {1 1 1} side facets. Evolution of the nanodot shape, density, and size during growth has been analyzed by scanning electron microscopy and atomic force microscopy. It is shown that Ostwald ripening plays an important role in nanodot growth.

Formation and electric property measurement of nanosized patterns of tantalum oxide by current sensing atomic force microscope

Nanosized patterns of tantalum oxide were fabricated on a tantalum substrate by applying a potential pulse utilizing current sensing atomic force microscopy (CSAFM). The dimensions of the dots were strongly dependent on the bias applied, scan rate, and potential pulse duration. By controlling these variables, the minimum size nanodots with full width at half maximum of 35 nm was achieved. Immediately after pattern formation, the electrical properties of the Ta oxide nanodots were measured using CSAFM. The charge transport at the CSAFM tip and the nanosized Ta oxide dot can be described by Poole–Frenkel type conduction. The relative dielectric constant of the nanosized Ta2O5 dots was calculated to be 17.8–24.3, showing that the quality of the oxide was high. In addition, by controlling the substrate bias applied, pulse duration, and tip scan speed, nanosized Ta oxide lines with the desired dimensions were prepared.

Fabrication of nickel oxide nanostructures by atomic force microscope nano-oxidation and wet etching

We report the fabrication of nickel oxide nanostructures by atomic force microscope nano-oxidation and subsequent wet etching. By applying a negative bias to a conductive tip, nickel oxide patterns are first created by the process of nano-oxidation. The unoxidized nickel film is then etched away in a diluted nitric acid solution. Auger electron spectroscopy measurements confirm the complete removal of the nickel film and the preservation of the oxide patterns. Nickel oxide nanodots with diameters as small as 100 nm are reliably produced by the present method.

Self-organized titanium oxide nanodot arrays by electrochemical anodization

Ordered nanodot arrays of titanium oxides were prepared from TiN/Al films on the silicon substrate by electrochemical anodization of a TiN layer using a nanoporous anodic aluminum oxide film as the template. The microstructure of the nanodot arrays was studied by transmission electron microscopy and scanning electron microscopy, and the chemical composition of nanodots was analyzed by electron energy loss spectroscopy. The as-prepared nanodots are basically composed of amorphous TiOx with a hexagonal arrangement and an average diameter of about 60 nm. Using this approach, it is expected that nanodot arrays of various oxide semiconductors can be achieved.

Nano-etching Using Nanodots Mask Fabricated by Bio-nano-process

An array of iron oxide nanodots with 6 nm diameter was used as a nanometer size patterning mask for inductively coupled plasma (ICP) etching process. The array of nanodots was fabricated by biological pathway named bio-nano-process. A cage protein, ferritin, was employed to accommodate an iron oxide core with 6 nm diameter and a two dimensional array of ferritin was made using their self-assembling ability. The array of ferritin was transferred onto a silicon wafer and the protein moiety was selectively eliminated by ozone treatment. The array of nanodots was used as a patterning dry-etching mask. The ICP etching using CHF3 gas at low temperature produced a combination of cone-shape peaks and plateaux. This result demonstrates the possibility that iron oxide nanodots array produced by bio-nano-process can be used as a dry-etching mask and that an array of nano-columns with high density could be produced. Taking a variety of bio-molecules which can accommodate inorganic materials into consideration, this bio-nano-process is expected to lead to a new approach for making nano-scale masks.