Nanolithography Process Research Articles

Fabrication of Lateral Polysilicon Gap of Less than 50 nm Using Conventional Lithography

We report a thermal oxidation process for the fabrication of nanogaps of less than 50 nm in dimension. Nanogaps of this dimension are necessary to eliminate contributions from double-layer capacitance in the dielectric detection of protein or nucleic acid. The method combines conventional photolithography and pattern-size reduction techniques. The gaps are fabricated on polysilicon-coated silicon substrate with gold electrodes. The dimensions of the structure are determined by scanning electron microscopy (SEM). An electrical characterization of the structures by dielectric analyzer (DA) shows an improved conductivity as well as enhanced permittivity and capacity with the reduction of gap size, suggesting its potential applications in the detection of biomolecule with very low level of power supply. Two chrome Masks are used to complete the work: the first Mask is for the nanogap pattern and the second one is for the electrodes. An improved resolution of pattern size is obtained by controlling the oxidation time. The method expected to enable fabrication of nanogaps with a wide ranging designs and dimensions on different substrates. It is a simple and cost-effective method and does not require complicated nanolithography process for fabricating desired nanogaps in a reproducible fashion.

Engineered low-dimensional nanomaterials for sensors, actuators, and electronics

We present an overview of our research on nanoelectronics and nanomechanics based on low-dimensional materials, including carbon nanotubes and graphene. Our primary research focus is on carbon nanotube and graphene architectures for electronics, energy harvesting, and sensing applications. We are also investigating an atomically precise graphene nanomachining method as well as a high-throughput desktop nanolithography process. In addition, we are exploiting nanomechanical actuators and nanoscale measurement techniques for reconfigurable arrayed nanostructures with applications in THz antennas, remote detectors, and biomedical nanorobots. Last, we are studying the effect of antibody functionalized nickel nanowires to improve cell separation techniques. These design, nanofabrication, manipulation, and characterization processes will enable next-generation nanoelectronics that have a wide range of applications including sensors, detectors, system-on-a-chip, system-in-a-package, programmable logic controls, energy storage systems, and all-electronic systems.

Formation of Epitaxial NiSi<SUB>2</SUB> Nanowires on Si(100) Surface by Atomic Force Microscope Nanolithography

Ni nanowries were fabricated by atomic force microscope nanolithography, evaporation, lift-off and annealing processes. Epitaxial NiSi2 nanowires on a Si(100) surface along Si(110) and (100) directions were formed by the rapid thermal annealing treatment of the Ni nanowires at 400 degrees C. The silicide nanowires along the Si(110) direction had coherent type-A Si(111) and Si(100) interfaces, while those along the Si(100) direction had a type-A Si(110) interface. Silicide nanowires were agglomerated when the Ni nanowires were annealed at high temperature (> or = 500 degrees C). The mechanism of formation of a faceted nanowire was discussed based on the minimization of the total surface energy.

Application of Supercritical Fluid in Nanolithographic Processes

The supercritical state provides an energetic environment in which high-aspect-ratio or active surface structures can be reacted, swelled, cleaned, or coated. Due to both low viscosity and low interfacial tension, reagent, solvent, rinsing and drying media of supercritical fluids can be efficiently delivered into the nanointerstices of a substrate. This article summarizes recent patents in the field of using supercritical fluids in nanolithographic processing methods such as drying, removal of lithographic resist, and formation of hybrid structures. Some of our recent efforts on restoring the collapsed on-chip nanotube arrays, and synthesizing zeolite-polymer hybrid membrane materials are exemplified as applications of supercritical fluids. Introducing supercritical effects may guide sustainable technologies for the development of green processes.

Graphene based chemical sensor fabrication by means of Focused Ion Beam

Graphene is a material with surprising properties, that very recently aroused the attention of the scientific world for its potential applications in different fields from electronics to sensors. To date, many works have been already published dealt with graphene-based sensor in which the preparation of the devices involves the use of some lithographic method. It is known, however, that typical nano-lithographic processes leave an uncontrolled residue on graphene. In this work we present a graphene based chemiresistor, where the electrode structure is realized by Ion Beam Induced Deposition technique; the current–voltage characteristics of such a device will be investigated in different environments.

A novel 3D nanolens for sub-wavelength focusing by self-aligned nanolithography

In this work, a novel type of nanolens based on super oscillation theory has been developed and fabricated. A self-aligned nanolithography process is developed to achieve error-free structured nanolens without the need of complex registration which always carries intrinsic errors. This fabrication technique significantly simplifies the process and reduces the production costs consequently. The success of this process will enable us to achieve focusing and imagining beyond diffraction limit, which will be presented in other communications.

Formation Mechanism and Mechanics of Dip-Pen Nanolithography Using Molecular Dynamics

Molecular dynamics simulations are used to investigate the mechanisms of molecular transference, pattern formation, and mechanical behavior in the dip-pen nanolithography (DPN) process. The effects of deposition temperature were studied using molecular trajectories, the meniscus characteristic, surface absorbed energy, and pattern formation analysis. At the first transferred stage (at the initial indentation depth), the conformation of SAM molecules lies almost on the substrate surface. The molecules start to stand on the substrate due to the pull and drag forces at the second transferred stage (after the tip is pulled up). According to the absorbed energy behavior, the second transferred stage has larger transferred amounts and the transfer rate is strongly related to temperature. When molecules were deposited at low temperature (e.g., room temperature), the pattern shape was more highly concentrated. The pattern shape at high temperatures expanded and the area increased because of good molecular diffusion.

Precise voltage contrast image assisted positioning for in situ electron beam nanolithographyfor nanodevice fabrication with suspended nanowire structures

In this paper, we demonstrate precise voltage contrast image positioning for in situ electronbeam (e-beam) nanolithography to integrate nanowires into suspended structures fornanoswitch fabrication. The positioning of the deflection electrodes on the nanowires canbe well controlled using a precise voltage contrast image positioning technique, where theerror can be minimized to about 10 nm. Using such a method, dispersed nanowires can besandwiched between two layers of resist and suspended by one e-beam nanolithographyprocess without any etching. The in situ e-beam nanolithography eliminates the stagemovement error by preventing any movements of the stage during the nanolithographyprocess; hence, a high precision laser stage and alignment marks on the substrate are notneeded, which simplifies the traditional e-beam nanolithography process. Thenanoswitches fabricated using this method show ON and OFF states with the changesof applied voltages. This simplified process provides an easy, low cost and lesstime-consuming route to integrating suspended nanowire based structures using aconverted field emission scanning electron microscope e-beam system, which can alsobe customized to fabricate multi-layer structures and a site-specific nanodevicefabrication.

Direct low-energy electron beam nanolithography

We describe here an alternative approach to direct low-energy electron beam nanolithography process with no conventional deposition of any resist or self-assembled monolayer. The method is based on direct formation of ultrathin dielectric layer on electron irradiated surface, without generation of structural defects. High-quality electron-induced patterns with lateral resolutions of about 10 nm are demonstrated on SiO 2 surface.

Nanoscale patterning of kinesin motor proteins and its role in guiding microtubule motility

Biomolecular motor proteins have the potential to be used as 'nano-engines' for controlled bioseparations and powering nano- and microelectromechanical systems. In order to engineer such systems, biocompatible nanofabrication processes are needed. In this work, we demonstrate an electron beam nanolithography process for patterning kinesin motor proteins. This process was then used to fabricate discontinuous kinesin tracks to study the directionality of microtubule movement under the exclusive influence of surface bound patterned kinesin. Microtubules moved much farther than predicted from a model assuming infinite microtubule stiffness on tracks with discontinuities of 3 mum or less, consistent with a free-end searching mechanism. As the track discontinuities exceeded 3 mum, the measured and predicted propagation distances converged. Observations of partially fixed microtubules suggest that this behavior results from the interaction of the microtubules with the surface and is not governed predominately by the microtubule flexural rigidity.

In Situ Detection of Live Cancer Cells by Using Bioprobes Based on Au Nanoparticles

We fabricate the high-performance probes based on Au nanoparticles (AuNP) for detection of live cancer cell. AuNP were synthesized with narrow sized distribution (ca. 10 nm) by Au salt reduction method and deposited onto the aminated substrate as a cross-linker and hot spot. Herein, AuNP has enabled the easy and efficient immobilization of the antibody (Cetuximab), which can selectively interact with epidermal growth factor receptor (EGFR) on the surface of epidermal cancer, as detecting moiety onto the AuNP-deposited substrate without nanolithography process. After conjugation of Cetuximab with AuNP-deposited substrate, Cetuximab-conjugated probe as a live cancer cell detector (LCCD) could detect EGFR-highexpressed A431 cells related to epithelial cancer with 54-times larger specificity and sensitivity in comparison with EGFR-deficient MCF7 cells. This implies that AuNP-based probes demonstrate abundant potentials for detection and separation of small biomolecules, cells and other chemicals.

A Study on the Dip-pen Nanolithography Process and Fabrication of Optical Waveguide for the Application of Biosensor

Photonic crystal structures have been received considerable attention due to their high optical sensitivity. One of the techniques to construct their structure is the dip-pen lithography (DPN) process, which requires a nano-scale resolution and high reliability. In this paper, we propose a two dimensional photonic crystal array to improve the sensitivity of optical biosensor and DPN process to realize it. As a result of DPN patterning test, we have observed that the diffusion coefficient of the mercaptohexadecanoic acid (MHA) molecule ink in octanol is much larger than that in acetonitrile. In addition, we have designed and fabricated optical waveguides based on the mach-zehnder interferometer (MZI) for application to biosensors. The waveguides were optimized at a wavelength of 1550 nm and fabricated according to the design rule of 0.45 delta%, which is the difference of refractive index between the core and clad. The MZI optical waveguides were measured of the optical characteristics for the application of biosensor.

GaN membrane-supported UV photodetectors manufactured using nanolithographic processes

Membrane GaN metal–semiconductor–metal (MSM) photodetector structures using nanolithographic techniques have been manufactured for the first time. Very low dark currents and unexpected high values for the responsivity have been obtained. It seems that the membrane together with the (submicronic) MSM structure increase the gain of the structure and responsivities in the range of 50–100A/W can be obtained.

Electrically Biased Nanolithography with KOH-Coated AFM Tips

This letter provides the first study aimed at characterizing the desorption and nanolithographic processes for SAM-coated, gold-coated silicon substrates oxidatively patterned with an AFM with a tip under potential control. The process either results in recessed patterns where the monolayer has been removed or raised structures where the monolayer has been removed and silicon oxidation has taken place. Eleven different SAMs have been studied, and the type of pattern formed depends markedly upon SAM chain length, end functional group, and applied bias. We show how local pH and choice of monolayer can be used to very effectively control the type of pattern that is ultimately formed. Interestingly, we show that hydroxide anion accessibility to the substrate surface is one of the most significant factors in determining the pattern topography. Moreover, control over the pattern topography can be achieved by controlling the concentration of the KOH in the water meniscus formed at the point of contact between tip and surface in the context of a bias-controlled DPN experiment with a KOH-coated tip. The work provides important insight into the factors that control SAM desorption and also ways of controlling the topography of features made in a potential-controlled scanning probe nanolithographic process.

Nearfield surface enhanced spectroscopy using targeted nanoparticle deposition

Surface enhanced spectroscopy is demonstrated by depositing gold nanoparticles on a surface using an atomic force microscope. A modified dip pen nanolithography process is used to place particles directly on to a target. Near-field optical enhancement is demonstrated for Raman and infrared spectroscopies and is applicable for fluorescence spectroscopy. This approach provides localized, near-field spectroscopy with subdiffraction limit resolution and a general method for fabricating plasmonic device structures.

Cheap and Robust Ultraflat Gold Surfaces Suitable for High-Resolution Surface Modification

A simple procedure to elaborate robust ultraflat gold surface without clean room facilities is presented. Self-assembled 3-mercaptopropytriethoxysilane (MPTMS) on silicon was used as a buffer layer on which gold was sputtered using a common sputter-coating apparatus. The optimization of the sample position into the chamber of the sputtering machine yielded the formation of a thin (approximately 8 nm) gold layer. The characterization of the resulting gold surface (i.e., AFM, X-ray reflectivity, and diffraction) has demonstrated its high smoothness (<0.7 nm) over a large scale with a preferred (111) orientation. The robustness of the substrate toward organic solvents and thermal treatment was also tested. The ability of these surfaces to be used as substrates for high-resolution surface modification was confirmed by functionalizing the gold surface using the dip pen nanolithography process.

Spin momentum transfer effects observed in electrodeposited Co/Cu/Co nanowires

Spin-transfer torque effects are reported in nanowires consisting in Co/Cu/Co trilayers electrodeposited on an anodic alumina template. Using a nanolithography process based on electrically controlled nanoindentation of the alumina template, we are able to investigate the spin transport properties of single nanowires at room temperature. For small applied magnetic fields, we have measured resistance changes above a critical direct-current (dc) injected current that corresponds to the change in resistance observed in the magnetoresistance curves at low current. We conclude that magnetic reversals are driven by a spin-polarized current. The critical current densities needed for the magnetization reversals are in the 107 A/cm2 range and the dependence of the critical currents with the applied field is consistent with the spin-transfer mechanism. For large applied magnetic fields, the differential resistance exhibits some peaks that we attribute to the onset of high-frequency excitations of the free-layer magnetization. According to the high density of electrodeposited nanowires in alumina templates, our results are promising for synchronized spin-transfer oscillators.

Portable microsensors based on individualSnO2 nanowires

Individual SnO2 nanowires were integrated in suspended micromembrane-based bottom-up devices.Electrical contacts between the nanowires and the electrodes were achieved with the helpof electron- and ion-beam-assisted direct-write nanolithography processes. Thestability of these nanomaterials was evaluated as function of time and appliedcurrent, showing that stable and reliable devices were obtained. Furthermore, thepossibility of modulating their temperature using the integrated microheater placedin the membrane was also demonstrated, enabling these devices to be used ingas sensing procedures. We present a methodology and general strategy for thefabrication and characterization of portable and reliable nanowire-based devices.

Secondary electron imaging at gas pressures in excess of 1kPa

Environmental scanning electron microscopy (ESEM) enables electron imaging of gas-mediated, direct-write nanolithography processes, liquids, and hydrated biomaterials. However, ESEM is limited by poor image quality at gas pressures in excess of ∼600Pa. Here the authors achieve high quality secondary electron imaging at 2kPa of H2O by optimizing boundary conditions that govern beam scatter and the energy distribution of low energy electrons in the gas, dielectric breakdown of the gas, and detector collection efficiency. The presented high pressure imaging method will enable imaging of hydrated materials at close to room temperature, and gas-mediated surface modification processes occurring at high pressures.

Microfluidic device for delivery of multiple inks for dip pen nanolithography

In the dip pen nanolithography (DPN) process, ultra-sharp scanning probe tips ("pens") are coated with chemical compounds (or "ink") and contacted with a surface to produce submicron-sized features. This work describes the design, fabrication, and testing of a microfluidic ink delivery device for delivering multiple species of inks to an array of multiple pens, as well as for maximizing the number of inks for simultaneous patterning by DPN. The microfluidic device (called "Centiwell") consists of a 2-D array of 96 microwells that are obtained by silicon bulk micromachining process. A thermoelectric module is attached to the bottom of the substrate. Microbeads of a hygroscopic material (e.g., polyethylene glycol or PEG) are dispensed into the microwells. The thermoelectric module cools the substrate to below the dew point for condensing water droplets on the microbeads and to create PEG solutions that serve as the ink for DPN. An array of pens is then coated with the ink. Subsequently, nanolithography is performed with the coated pens. Multiple PEG nanopatterns obtained by this method are presented as proof-of-concept. This demonstrates the functionality of the Centiwell microfluidic ink delivery device for nanolithography of multiple inks. Also, fractal nanopatterns are observed in the nanolithography experiments.