Local Anodic Oxidation Research Articles

Nanographene device fabrication using atomic force microscope

A report is presented on the local anodic oxidation of graphene film prepared by chemical vapour deposition using contact mode atomic force microscopy. Raman spectroscopy was used to check the uniformity and thickness of large area graphene film. Various kinds of patterns such as lines, ribbons and further, more complex structures, such as hexagons, two-terminal bar-like devices, were written by varying the tip voltage from −6 to −12 V and the tip speed from 60 to 200 nm/s. It was found that one can easily write any kind of patterns by just manipulating the tip voltage and tip speed instead of concentrating on other factors such as controlled humidity conditions, applied force on the tip and tip current. Also, it is confirmed that with an increase in tip voltage and by slowing the tip movement during lithography, one can write very narrow and sharp patterns which are important factors for the fabrication of graphene-based electronic devices.

Impact of Parameter Variation in Fabrication of Nanostructure by Atomic Force Microscopy Nanolithography

In this letter, we investigate the fabrication of Silicon nanostructure patterned on lightly doped (1015 cm−3) p-type silicon-on-insulator by atomic force microscope nanolithography technique. The local anodic oxidation followed by two wet etching steps, potassium hydroxide etching for silicon removal and hydrofluoric etching for oxide removal, are implemented to reach the structures. The impact of contributing parameters in oxidation such as tip materials, applying voltage on the tip, relative humidity and exposure time are studied. The effect of the etchant concentration (10% to 30% wt) of potassium hydroxide and its mixture with isopropyl alcohol (10%vol. IPA ) at different temperatures on silicon surface are expressed. For different KOH concentrations, the effect of etching with the IPA admixture and the effect of the immersing time in the etching process on the structure are investigated. The etching processes are accurately optimized by 30%wt. KOH +10%vol. IPA in appropriate time, temperature, and humidity.

Impact of KOH Etching on Nanostructure Fabricated by Local Anodic Oxidation Method

Impact of KOH Etching on Nanostructure Fabricated by Local Anodic Oxidation Method

Method for Fabricating Micro/Nanostructures via Scanning Probe Microscope and Anisotropic Wet Etching

The direct modification of silicon, other semiconductors and metal surfaces by the process of local anodic oxidation via electric field from scanning probe microscope (SPM) in conjunction with the absorbed water in atmosphere as the electrolyte is a promising method for fabricating micro/nanostructures. We demonstrated that the process of SPM oxidation and anisotropic wet chemical etching is a low cost and reliable method to produce smooth and uniform etched structures on silicon substrates. Using silicon oxide nanopatterns produced on H-passivated (110) Si surfaces as etching masks, and due to the large (110)/(111) anisotropic ratio of etching rate and the large Si/SiO2 etching selectivity at a relatively low etching temperature and an optimal concentration of aqueous KOH etchant, high-aspect-ratio grating structures have been fabricated by anisotropic wet etching. The approach of combining scanning probe lithography (SPL) with etching technique provides an alternative lithography route to fabricate functional nanophotonic or nanoelectronic devices.

Preparation and Mechanics of Nanotextures on Adapting a Low Adhesive Surface Using Local Oxidation Nanolithography

This paper describes an application for atomic force microscopy to the fabrication of nanotextures with various features on a GaAs surface by local oxidation nanolithography (LON). By controlling the geometrical shapes and surface coverage of the nanotexture, the surface adhesion can be adjusted to a low adhesive surface. The influence of environmental conditions, such as relative humidity and temperature on adhesion behavior, was studied. An optic heater was employed to minimize thermal effect on an atomic force microscope (AFM) cantilever and PbZrTiO3 scanner. In our study, AFM is used for both fabrication and characterization. LON allows the fabricated nanotextures to be altered in situ without the need to change masks or repeat the entire fabrication process. Furthermore, the nanoadhesion characterization of nanotextures on a GaAs surface was investigated with a colloidal probe method.

Submicron Wire Fabrication on Silicon Substrate Based on Atomic Force Microscopy Technique

This article presents on a simple sub-micron wire fabrication by means of local anodic oxidation atomic force microscopy technique. The silicon-based structure consists of two adjacent terminals serve as probing pads and connected with a wire width less than 200 nm. The pad dimension and wire length are 49 μm2 and 11 μm each, respectively. The fabrication process is conducted at room temperature 24–27 °C with 50–60% relative humidity and operated by commercial atomic force microscopy without any modification done. Furthermore, the local oxidation is performed using gold coated AFM probe tip and assisted by the used of special language supported by the equipment software. In addition, 9.0 V applied voltage with 2 μm / sec writing speed is used to realize the oxidation process. I-V characteristic of bare device shows there is a current flow through the device when a range of voltage is applied. By using this local anodic oxidation technique, the silicon wire-based structure is fabricated and used as gas sensor sensing part. The silicon device demonstrates an increase in resistance as introduced to gas environment. The silicon wire device shows relative sensitivity of 35% to the oxygen gas.

Rapid synthesis of gallium oxide resistive random access memory by atomic force microscopy local anodic oxidation

The fabrication of gallium oxide nanodots for the application of resistive random access memory (RRAM) using a process of atomic force microscopy (AFM) local anodic oxidation on an indium tin oxide conductive glass substrate is reported. In the atmospheric environment, an AFM probe tip contacts the gallium film locally. This gallium oxide nanodot acts as the insulator layer in a single unit of the RRAM. The structure describes the insulator layer (GaOx) sandwiched by the top (AFM tip) and bottom (Ga film) electrodes. Using current and voltage biased methods, the device switches from a high-resistance state (HRS) to a low-resistance state (LRS) and reset from LRS to HRS. Low read-voltage is used to distinguish the high/low resistance to present the digital data. Presented results show the ability of atomic force microscopy anodic oxidation to produce 300 nm diameter gallium oxide nanodots on glass substrates for potentially high density RRAMs.

Formation of double ring patterns on Co2MnSi Heusler alloy thin film by anodic oxidation under scanning probe microscope

Double ring formation on Co2MnSi (CMS) films is observed at electrical breakdown voltage during local anodic oxidation (LAO) using atomic force microscope (AFM). Corona effect and segregation of cobalt in the vicinity of the rings is studied using magnetic force microscopy and energy dispersive spectroscopy. Double ring formation is attributed to the interaction of ablated material with the induced magnetic field during LAO. Steepness of forward bias transport characteristics from the unperturbed region of the CMS film suggest a non equilibrium spin contribution. Such mesoscopic textures in magnetic films by AFM tip can be potentially used for memory storage applications.

Role of electric field distribution in local anodic oxidation

Local electric-field-induced anodic oxidation is one of the earliest and most extensively studied techniques in bias-assisted AFM nanolithography. Except the water bridge created between the tip and the sample surface, local anodic oxidation (LAO) process strongly depends on the tip-sample voltage and especially on the electric field distribution under the tip apex centre. Once electric field is formed, its distribution and intensity can be modified by changing the tip-sample voltage and separation. The electric field provides the oxidation kinetics of nanoscale electrochemical reaction and controls the spacial resolution of the fabricated structures. In this paper, the s-wave tip quantum model, the influence of the bias voltage and the electric field strength on oxide structures and the theory of electric-field-induced LAO have been analysed. In addition, dot-array nanogratings, one-dimensional nanogratings and two-dimensional nanogratings are fabricated by using electric-field-induced LAO process with AFM in the ambient atmosphere.

Characterization of Metal Oxide-Based Gas Nanosensors and Microsensors Fabricated via Local Anodic Oxidation Using Atomic Force Microscopy

This work reports on nanoscale and microscale metal oxide gas sensors, consisting of metal-semiconductor-metal barriers designed via scanning probe microscopy. Two distinct metal oxides, molybdenum and titanium oxides, were tested at different temperatures using CO2and H2as test gases. Sensitivities down to ppm levels are demonstrated, and the influence of dry and humid working atmospheres on these metal oxide conductivities was studied. Furthermore, the activation energy was evaluated and analyzed within working sensor temperature range. Finally, full morphological, chemical, and structural analyses of the oxides composites are provided allowing their identification as MoO3and Ti.

Fabrication of p-Type Double Gate and Single Gate Junctionless Silicon Nanowire Transistor by Atomic Force Microscopy Nanolithography

In this work, we have investigated the fabrication of Double gate and Single gate Junctionless silicon nanowire transistor using silicon nanowire patterned on lightly doped (105 cm-3) p-type Silicon on insulator wafer fabricated by Atomic force microscopy nanolithography technique. Local anodic oxidation followed by two wet etching steps, Potassium hydroxide etching for Silicon removal and Hydrofluoric acid etching for oxide removal, were implemented to reach the structures. Writing speed and applied tip voltage were held in 0.6 µm/s and 8 volt respectively for Cr/Pt tip. Scan speed was held in 1.0 µm/s. The etching processes were elaborately performed and optimized by 30%wt. Potassium hydroxide + 10%vol. Isopropyl alcohol in appropriate time, temperature and humidity. The structure is a gated resistor turned off based on a pinch-off effect principle, when essential positive gate voltage is applied. Negative gate voltage was unable to make significant effect on drain current to drive the device into accumulation mode.

Nanofabrication of TaS2 conducting layers nanopatterned with Ta2O5 insulating regions via AFM

It is demonstrated how local oxidation nanolithography performed with an atomic force microscope (AFM-LON) may be successfully employed for the nanopatterning of insulating regions of Ta2O5 on TaS2 ultrathin metallic layers. This provides a simple approach for the fabrication of electronic devices, such as single-electron transistors, at the nanoscale.

Investigation of the nanoscale features fabricated on the HOPG surface induced by STM electric lithography under different voltage regions in ambient conditions

Carbon-based materials have attracted more and more interests in the nanotechnology and high attention has been paid to their fabrication and application. In this work, the nanofabrication of the highly oriented pyrolytic graphite (HOPG) surface was carried out by means of STM direct lithography under voltage pulse. Distinct characteristics of the fabricated features were obtained under different voltage magnitudes. Specifically, we observed the phenomena of exfoliation and folding of the graphite flakes on the HOPG surface above 5 V or so. Detailed study of the process parameters, such as the feedback, the driving of the sample platform, the current value was also performed. Moreover, the segmented current density of the tunnel junction was calculated from J.G. Simmons's equations. Local anodic oxidation and nano explosive damage caused by the electrical breakdown of dielectric gap were put forward as the possible mechanisms to explain the fabricated results.

Local anodic oxidation kinetics of chemical vapor deposition graphene supported on a thin oxide buffered silicon template

Study of local anodic oxidation (LAO) of single layer graphene (SLG) supported on thin oxide buffered silicon template is reported. Centimeter scaled SLG sheet grown through chemical vapor deposition on Cu foil is transferred onto patterned silicon template covered with thin oxide steps. LAO are performed on the supported SLG through contact mode atomic force microscopy in ambient condition. LAO bumps with heights exceed physical carbon–oxygen stacking are formed on thin oxide buffered samples. Micro-Raman spectroscopy reveals the coexistence of surface graphene oxide formation and local strain near the LAO patterns. The writing speed dependence of LAO bump shows a multi-exponent behavior, indicating inhomogeneous chemical profiles involved in the LAO process. The observation points to a sequential kinetics of surface SLG oxidation prior to subsurface silicon oxide protrusion formation. Our work shows the necessity to consider oxidation of substrate through the subsurface buffer layer during nano-scaled field effect device fabrication with LAO method. The strain generation from the subsurface protrusion suggests possible tuning knob for local distortion of SLG structure.

A study of the formation modes of nanosized oxide structures of gallium arsenide by local anodic oxidation

Results obtained in a study of the influence exerted by the technological modes of local anodic oxidation (LAO) on the process in which nanosized oxide structures (NOSs) are formed on the surface of gallium arsenide are reported. The effect of the amplitude and duration of voltage pulses applied to the probesubstrate system, relative air humidity in the technological chamber, and amplitude of cantilever oscillations on the geometric parameters of gallium arsenide NOSs has been examined. It was found that raising the relative humidity from 60 to 90% results in a decrease in the threshold LAO voltage from 7.0 to 6.0 V. It is shown that raising the oscillation amplitude from 0.1 to 2.8 nm leads to a decrease in the NOS height from 3.20 ± 0.34 to 1.10 ± 0.13 nm and in the NOS diameter from 218.4 ± 29.5 to 78.1 ± 10.3 nm.

Selective formation of novel fluorescent aggregates of rhodamine dyes: contribution of surface SiO2 layer and underlying Si layer

AbstractRhodamine (Rh) 6G aggregates were formed on a silicon substrate with a varying thickness surface SiO2 layer utilizing a dewetting process of Rh ethanol solution. Sufficient thickness of 30 nm SiO2 layer gave rise to fluorescent aggregates selectively, similar to those formed on a hydrophilic glass surface. Annealing at 200 oC forced a phase transition of those aggregates to fluorescence quenched state, which was also common with those formed on a hydrophilic glass surface. In contrast, sufficiently thin, e.g. naturally formed at ambient condition, 2 nm thick SiO2 layer gave rise to quenched aggregates, that was spectroscopically identical with the annealed aggregates formed on thick SiO2 layer. Whereas the quenching on sufficiently thin SiO2 layer may be partially due to a nonradiative energy transfer to underlying Si, the majority of the quenching was attributed to specific Rh molecular ordering that is thermodynamically stable than the quasi‐stable fluorescent Rh aggregates. This quasi‐stable aggregates were formed only on sufficiently thick SiO2 layer or on hydrophilic glass substrate. This finding will shed light on the disputed discrepancy of fluorescence quenching of Rh dyes deposited on SiO2 nanostripes that were formed on a Si substrate by local anodic oxidation using a conductive AFM tip. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ordered rippling of polymer surfaces by nanolithography: influence of scan pattern and boundary effects

We demonstrate how AFM nanolithography, with a proper choice of scan pattern, can induce an exceptionally ordered alignment of ripples on the surface of polymer films on the first scan. By analogy with the manipulation of nanoparticles, the orientation of the ripples is determined by the material flow, which is ultimately fixed by the direction of motion of the probing tip. This makes a raster scan pattern the best choice for orienting the ripples, as opposed to the zigzag scan pattern commonly adopted by most AFM setups. Our hypothesis is substantiated by a series of measurements on a solvent-enriched ultrathin film of PET, which allowed ripple formation on the first scan. We also show how the ripple orientation is significantly modified by the boundary conditions appearing when nanolithography is performed on circular, triangular and L-shaped areas on the polymer surface.

Using local anodic oxidation to create storage nanodevices

Possibilities of local anodic oxidation (LAO) for superdense information recording using a negative potential on probe of atomic force lithographer (AFL) are investigated in this paper. It is shown that the intensity of LAO surface of metals and semiconductors significantly depends on parameters such as time of oxidation, humidity, type of oxidizable material and anode-cathode potential difference. The possibility of obtaining structures for storage nanodevices is experimentally proved.

Electric Field Based Simulations of Local Oxidation Nanolithography Using Atomic Force Microscopy in a Level Set Environment

During the last decades it has been shown that non-contact AFM can be used as an efficient lithographic technique capable of manufacturing nanometer sized devices on the surface of a silicon wafer. The AFM nanooxidation approach is based on generating a potential difference between a cantilever needle tip and a silicon wafer. A water meniscus builds up between the tip and the wafer, resulting in a medium for oxyions to move due to the high electric field in the region. A simulator for nanooxidation with non-contact AFM tools, implemented in a Level Set environment, was developed. The presented model uses empirical equations for the height and half-width of an AFM nanodot or nanowire with a physics based shape model. The shape model uses a particle distribution directly derived from the surface charge density, generated on the silicon surface due to the strong electric field.

Electrical property comparison and charge transmission in p-type double gate and single gate junctionless accumulation transistor fabricated by AFM nanolithography

The junctionless nanowire transistor is a promising alternative for a new generation of nanotransistors. In this letter the atomic force microscopy nanolithography with two wet etching processes was implemented to fabricate simple structures as double gate and single gate junctionless silicon nanowire transistor on low doped p-type silicon-on-insulator wafer. The etching process was developed and optimized in the present work compared to our previous works. The output, transfer characteristics and drain conductance of both structures were compared. The trend for both devices found to be the same but differences in subthreshold swing, ‘on/off’ ratio, and threshold voltage were observed. The devices are ‘on’ state when performing as the pinch off devices. The positive gate voltage shows pinch off effect, while the negative gate voltage was unable to make a significant effect on drain current. The charge transmission in devices is also investigated in simple model according to a junctionless transistor principal.