Oxidation Lithography Research Articles

Creation and Characterization of Nanoscale Ribbons on MoS2 by Atomic Force Microscope Nanolithography

The atomic force microscope (AFM) has been widely used for fabricating the nanoscale oxide ribbons on various materials surface. Herein, we first conducted local anodic oxidation (LAO) lithography on two-dimensional nanomaterial (2D), i.e. multilayer MoS2, using AFM. The correlation of patterning behavior on the MoS2 flakes between the lithography conditions was investigated. The height and full width half maximum (FWHM) increase linearly with increasing tip voltage, even at different tip speeds, which is consistent with the results obtained from the Cabrera-Mott oxidation theory. The size of the clear relation decreases linearly with increasing tip speed, indicating that longer tip writing patterns result in more oxidation. The formation mechanism of the patterned oxide lines is presented along with LAO reaction processes.The final LAO lithography products have been demonstrated to be MoO2 and MoO3 by micro-Raman spectroscopy. These results show that LAO lithography using AFM is an effective technique for nanofabrication of nanodevices.

Multicomponent Nanoscale Patterning of Functional Light‐Harvesting Protein Complexes by Local Oxidation Lithography

AbstractLocal oxidation lithography has the potential for patterning proteins on conductive substrates such as silicon with nanometer accuracy, guided by and extending the nanoscale architectures found in native bioenergetic membranes. Such membranes foster energy and electron transfers between two or more types of protein complex, so the potential of this lithographic technique is investigated for copatterning multiple types of protein complex. Composite patterns consisting of light‐harvesting 2 (LH2) and reaction center‐light‐harvesting 1‐PufX (RCLH1) complexes purified from Rhodobacter (Rba.) sphaeroides, and light‐harvesting complex II (LHCII) purified from spinach, are fabricated. Atomic force microscopy (AFM) images demonstrate the successful sequential deposition of single‐molecule layers of RCLH1 and LH2 molecules. In the case of LHCII, a mixture of single‐layer and multilayer patterns is found on the silicon substrate. Experimental conditions are established for the most efficient substrate surface modification and for protein immobilization. Spectral imaging and fluorescence lifetime imaging microscopy (FLIM) show that the immobilized photosynthetic complexes retain their native light‐harvesting and energy transfer functions, and provide evidence for excitation energy transfer from LH2 to RCLH1. Local oxidation lithography has the capacity to pattern proteins singly, or in small domains, for fabricating bioinspired nanoscale architectures for biosensors and solar cells.

Enhanced adhesive strength between SU-8 photoresist and titanium substrate by an improved anodic oxidation method for high aspect-ratio microstructures

This paper presents an anodic oxidation treatment method for improving the adhesive strength between SU-8 photoresist and titanium substrate. The adhesion strengths were measured for the treated titanium substrates by different anodic oxidation techniques, which increased with the enhancement of the surface roughness and thorny structures on the treated substrate. It was found that the adhesion was increased by approximately 86% through anodic oxidation treatment in 3.0 mol l−1 NaOH solution compared to Si wafer substrate. Additionally, the influence of UV dosage and hard bake temperature on the adhesion strength was examined for the anodic oxidation treated substrates. The UV dosage effect, with a range from 0.8 to 2.08 J cm−2, was measured and analyzed for a 300 µm thickness SU-8 cylinder, and the adhesion strength corresponding to the optimal dosage (1.52 J cm−2) was 45.82 ± 3.08 MPa. The adhesion was further strengthened by a hard bake at 110 °C for 60 min and its value was up to 71.64 MPa, which almost approaches the breaking strength of the SU-8 polymer. Using the optimized anodic oxidation and UV lithography conditions, high aspect ratio (24) SU-8 micropillar arrays with 600 µm height were fabricated without any distortion, collapse or delamination. Finally, to evaluate the feasibility of the anodic oxidation treated titanium substrate to serve as a seed layer, the electrochemical properties were measured by polarization curves.

Application of scanning probe oxidation lithography in fabrication of micro-nano devices

Scanning probe lithography technology is mainly used the electrical, mechanical or thermal interaction between the atomic force microscope tip and substrate to perform imaging, manipulation and modification of the nanoscale surface. It is a simple, rapid and accurate nanostructure preparation technique. The scanning probe oxidation lithography technology has a good prospect, using highly localized water bridge formed between the tip and the sample surface to prepare micro-nano scale structures on material surface through electrochemical reactions. It has been widely used to produce nano-scale functionalized patterns and micro-nano devices. The mechanism of the patterning process and influencing factors such as voltage, tip-sample force, duration, relative humidity, and scanning speed are described in detail in this paper. Then, the work on the preparation of micro-nano devices using this technology is summarized. Finally, we discussed the advantages and problems of this technology, as well as the potential solution and development of it.

Atomic Force Microscopy Local Oxidation of GeO Thin Films

Metastable germanium monoxide (GeO) thin-insulating films have been investigated as a new promising material for atomic force microscope (AFM) oxidation lithography. The kinetics of GeO layer oxidation performed in the tapping mode of AFM was found to have a logarithmic relationship to oxide height versus pulse duration. Effect of humidity on oxidation of germanium monoxide thin films was studied at relative humidity 40, 60, 80%. When local anodic oxidation of GeO layer was carried out by AFM operating in the contact mode in high voltage (≥9 V) regime and at high relative humidity (RH = 80%), the size and shape of fabricated oxide was changed drastically.

Local anodic oxidation lithography on organic semiconductor crystals: Oxide depth revealed by conductance tomography

Abstract Nanopatterning electrically insulating oxide lines on organic electronic surfaces can play a role in fabricating future nanoscale devices. Here we write oxide features on rubrene single crystal surfaces by performing local anodic oxidation using the tip of an atomic force microscope. Oxide feature height increases with voltage bias and decreases with tip writing speed, and gaps as small as 22 nm at the surface between two parallel oxide lines were realised. Conductance tomography is employed in a unique way to determine the depths of oxide features, by exposing subsurface layers of the patterned material without using chemical etching while simultaneously mapping material conductance. The oxide line depth exceeds its height, with the depth-to-height ratio frequently being more than 1.6. A critical electric field of ∼3 × 106 V/cm is identified, below which the oxide growth ceases, resulting in a maximum oxide vertical extent of about ∼60 nm at a voltage bias of ∼20 V.

Conductive polycrystalline diamond probes for local anodic oxidation lithography

This is the first report characterizing local anodic oxidation (LAO) lithography performed using conductive monolithic polycrystalline diamond (MD) and conductive polycrystalline diamond-coated (DC) tips and comparing it to the diamond-like carbon-coated and metal-coated silicon tips. The range and the rate of increase in the lithographic linewidth and height with tip bias (dw/dV and dh/dV) differed based on the tip material. The DC tips resulted in wider and taller lines and a higher dw/dV and dh/dV compared to metal-coated tips with a similar force constant (kAvg). The metal-coated and the DC tips with comparable kAvg showed comparable threshold voltages, whereas the MD tips with similar kAvg showed a higher threshold voltage. The MD tips exhibited less than half the height and nearly half the dw/dV and dh/dV obtained with the metal-coated tips with similar kAvg, thus also resulting in a smaller width at −10 V. The linewidths were found to be proportional to the inverse of the log of write speed ( for all the tips; however, the proportionality constant varied with tip material; the DC tips had larger values, and the MD and the metal-coated tips had comparable values. When varying the speed, the height was found to be a sigmoidal function of width, with the MD probes achieving lower height compared to the metal-coated and the DC tips with comparable kAvg. This study expands the application of monolithic conductive polycrystalline diamond (PCD) probes with outstanding wear resistance to fine LAO lithography.

Optimization of Linear Oxide Width Using Local Anodic Oxidation Lithography for Fabrication of Semiconductor and Metal Nanowires

In this study, the response surface methodology was utilized to optimize width of linear oxide for fabrication of Si oxide nanowires using local anodic oxidation lithography. A collection of experiments was designed using central composite design to evaluate the results statistically. The functional relationships were studied between the ambient humidity, applied voltage and tip speed as independent variables. Furthermore, a new approach was indicated by using design of experiment (DOE) to determine the significant parameters that affects on dimensional characteristics of the linear oxide. Numerical optimization was prepared by the DOE software to obtain the optimal conditions of parameters in order to perform the requirements as desired. These results indicate that the technique has a great potential for the fabrication of individual metal and semiconductor nanowires.

Role of re-growth interface preparation process for spectral line-width reduction of single InAs site-controlled quantum dots

We present growth and optical characterization measurements of single InAs site-controlled quantum dots (SCQDs) grown by molecular beam epitaxy on GaAs (001) patterned substrates by atomic force microscopy oxidation lithography. InAs SCQDs directly grown on the patterned surface were used as a seed layer and strain template for the nucleation of optically active single InAs SCQDs. The preservation of the initial geometry of the engraved pattern motifs after the re-growth interface preparation process, the lack of buffer layer growth prior to InAs seed layer deposition and the development of suitable growth conditions provide us an improvement of the SCQDs’ active layer optical properties while retaining a high ratio of single occupation (89%). In this work a fivefold reduction of the average optical line-width from 870 μeV to 156 μeV for InAs SCQDs located 15 nm from the re-growth interface is obtained by increasing the temperature of the initial thermal treatment step of the re-growth interface from 490 °C to 530 °C.

Fabrication of 10-nm-scale nanoconstrictions in graphene using atomic force microscopy-based local anodic oxidation lithography

We performed local anodic oxidation (LAO) lithography on monolayer graphene and highly oriented pyrolytic graphite (HOPG) using atomic force microscope (AFM). Auger electron spectroscopic measurements in the oxidized area formed on the HOPG revealed that the number of oxygen atoms systematically increased with the bias voltage applied to the AFM cantilever |Vtip|, which demonstrates the tunability of the extent of oxidation with |Vtip|. By optimizing the LAO conditions, we fabricated monolayer graphene nanoconstrictions with a channel width as small as 10 nm, which is the smallest graphene nanoconstriction so far achieved by utilizing AFM lithography techniques.

Study of Growth Parameters for Single InAs QD Formation on GaAs(001) Patterned Substrates by Local Oxidation Lithography

This work studies the selective nucleation of InAs within nanoholes on GaAs(001) substrates patterned by atomic force microscopy local oxidation. The effects of substrate temperature and As4 overpressure during InAs deposition directly on the patterned substrate (without a GaAs buffer layer) are considered. It is found that when InAs is deposited at substrate temperature of 510 °C under low As4 overpressure, a single InAs quantum dot per nanohole is obtained for a broad range of sizes of pattern motifs. The use of these InAs quantum dots as seed nuclei for vertical stacking of optically active single InAs site-controlled quantum dots is investigated.

A mass-production-ready anti-wear probe for scanning probe microscopy lithography

In this paper, a mass-production-ready anti-wear probe that has a much higher drawing stability than a conventional probe with a needle-shape tip while keeping the same drawing ability of arbitrary patterns has been proposed. The probe tip with a uniform cuboid-shape consisted of a microscale mechanical contact (width of the cantilever), two nanoscale electrical contacts (thickness of tungsten film) formed on the sidewalls of the mechanical contact, and an eave formed at the end. The microscale mechanical contact reduced tip wear by dispersing the force, while the nanoscale electrical contact enabled the drawing of nanoscale patterns. The uniform shape of the probe tip enabled the probe to maintain its stable performance, even when it had been mechanically worn. The eave played an essential role for mass production during simultaneous metallization of probes; it prevented tungsten film from being deposited on the mechanical contact by creating a shadow during the sputtering process. The results of the local anodic oxidation (LAO) lithography showed that the proposed probe was able to draw arbitrary patterns while maintaining stable performance over a long drawing distance.

Wear-Insensitive Sidewall Microprobe With Long-Term Stable Performance for Scanning Probe Microscopy Lithography

In this paper, a wear-insensitive sidewall microprobe with long-term stable performance is proposed. The proposed microprobe helps to reduce probe-tip wear and improve patterning stability in scanning probe microscopy lithography. The microprobe tip with a uniform cuboid-shape consists of a microscale mechanical contact and two nanoscale electrical contacts formed on the sidewall of the mechanical contact. The microscale mechanical contact reduces tip wear by dispersing the force applied to the tip, while the nanoscale electrical contact enables the sketching of nanoscale features. The uniform shape of the probe tip enables the probe to maintain its stable performance, even when it is mechanically worn. A prototype of the proposed microprobe with an 80-μm long mechanical line contact and a 30-nm long electrical line contact is fabricated using microelectromechanical systems techniques. The patterning stability of the fabricated microprobe in local anodic oxidation (LAO) lithography is investigated in terms of the change in the dimensions of the drawn lines and the shape of the probe tip before and after a 2-m scan. The results of the LAO lithography show that the fabricated microprobe could maintain a stable patterning performance after 2-m scan, which is an improvement of several thousand times over a conventional probe.

Hierarchical, Guided Self-Assembly of Preselected Carbon Nanotubes for the Controlled Fabrication of CNT Structures by Electrooxidative Nanolithography

A fully controllable process for the fabrication of carbon nanotube assemblies is presented on the basis of a sequential electrochemical oxidation lithography process. This approach utilizes the local chemical conversion of a n-octadecyltrichlorosilane self-assembled monolayer into a template featuring polar acid groups. The capability to utilize such chemically active templates for the site-selective assembly of individual carbon nanotubes was demonstrated, and a hierarchical, sequential structuring routine to obtain crossed CNT configurations, formed by preselected carbon nanotubes, was implemented. The introduced process allows the reliable and well-controlled fabrication of tailor-made nanoscopic assemblies of nanomaterials toward their integration into complex device frameworks and could provide control over the electrical properties of the fabricated assemblies.

Effects of ion beam-irradiated Si on atomic force microscope local oxidation

Atomic force microscope oxidation lithography was used to study the effects of low-energy ion beams on a silicon substrate. The oxygen containing layer formed by H+ ion beam irradiation was characterized by Kelvin probe force microscopy. Giant oxide features with heights over 100nm were fabricated by cathodic oxidation. The growth rate of the oxide features increased on the H+ ion-irradiated substrate and the etching selectivity was observed for individual oxide features. The density and oxygen concentration of the oxide features were affected by the chemical etching process. The mechanism of cathodic oxidation by Ohmic current was proposed.

New Design Concepts for the Fabrication of Nanometric Gap Structures: Electrochemical Oxidation of OTS Mono‐ and Bilayer Structures

A reliable nanofabrication concept to engineer metallic nanometric gap structures and to incorporate silver nanoparticles within the gaps utilizing a combination of self-assembly strategies and electrochemical oxidation lithography is developed. The approach uses the differences in oxidation kinetics of n-octadecyltrichlorosilane (OTS) monolayer and bilayer structures. The processes are investigated in detail and form the basis for a new nanofabrication process.

Atomic Force Microscopy Based Tunable Local Anodic Oxidation of Graphene

We have fabricated graphene/graphene oxide/graphene (G/GO/G) junctions by local anodic oxidation lithography using atomic force microscopy (AFM). The conductance of the G/GO/G junction decreased with the bias voltage applied to the AFM cantilever V(tip). For G/GO/G junctions fabricated with large and small |V(tip)|. GO was semi-insulating and semiconducting, respectively. AFM-based LAO lithography can be used to locally oxidize graphene with various oxidation levels and achieve tunability from semiconducting to semi-insulating GO.

A Study on Carbon-Nanotube Local Oxidation Lithography Using an Atomic Force Microscope

In this paper, nanoscale anodic oxidation lithography using an atomic force microscope (AFM) is systematically studied on carbon nanotubes (CNTs). Trends between the produced feature size and the corresponding process parameters, such as applied voltage, water meniscus length, tip speed during oxidation (hold time), and humidity are observed. By methodically varying these process parameters, the appropriate working ranges have been found to create features of various sizes based on the oxidation of the CNT structure. We have obtained feature sizes down to 58 nm by setting oxidation time per pixel to 20 ms corresponding to a tip speed of 1.50 μ m/s. Optimizing the tip speed during line scans was found to be critical in maintaining the presence of the water meniscus, which was often found to break above the tip speeds of 1 μm/s. In addition, a comparison of the results from employing this technique between CNT and graphene patterning is illustrated. Other factors affecting the reproducibility of the results are addressed in an endeavor to make the oxidization process more robust and repeatable.

Fabrication of ring structures by anodization lithography on self-assembled OTS monolayers

A new and rational fabrication concept to obtain ring structures with nanometer dimensions is presented that utilizes a combination of anodization and electrochemical oxidation lithography on a self-assembled monolayer of n-octadecyltrichlorosilane performed with an electrically biased scanning force microscopy tip. During the oxidation process two different chemical areas are created; a silicon oxide core which is surrounded by a chemically active, acid functionalized rim feature. The oxidation conditions, as well as the scaling options of this lithographic process have been investigated and revealed good controllability of the ring dimensions. A straightforward electroless metal deposition process was used to convert the ring structures into metal features.

10 Micrometer-Scale SPM Local Oxidation Lithography

10 micrometer-scale scanning probe microscopy (SPM) local oxidation lithography was performed on Si. In order to realize large-scale oxidation, an SPM tip with a contact length of 15 microm was prepared by focused-ion-beam (FIB) etching. The oxidation was carried out in contact mode operation with the contact force ranging from 0.1 to 2.1 microN. The applied bias voltage was 50 V, and scanning speed was varied from 10 to 200 microm/s. The scan length was 15 microm for one cycle. The influence of contact force on the large-scale oxidation was investigated. At high contact force, the Si oxide with good size uniformity was obtained even with high scanning speed. The SPM tip with larger contact length may increase the spatial dimensions of the water meniscus between the SPM tip and sample surface, resulting in the larger dimensions of the fabricated oxide. Furthermore, the throughput of large-scale oxidation reached about 10(3) microm2/s by controlling the scanning speed and contact force of the SPM tip. It is suggested that SPM local oxidation can be upscaled by using a SPM tip with large contact length.