Atomic Force Microscopy Nanolithography Research Articles

Investigation of Mode-Induced Spin Wave Transmission Blockage by In Situ Nanoscale Grooves.

In the pursuit of advancing spin-wave optics, the propagation of magnetostatic surface spin-waves is investigated in a uniform permalloy waveguide with in-situ nanopatterned grooves created through Atomic Force Microscopy nanolithography and Focused Ion Beam etching. The study unveils that the introduction of narrow constrictions and grooves leads to a non-monotonic reduction of the transmitted spin-wave signal intensity as the spin-wave pathway is shrinked. The remarkable feature that a stronger signal extinction is obtained for a narrow groove compared to a spin-waveguide interrupted by a full gap, where only inefficient transport through dipolar coupling is allowed, is highlighted. Combining experimental and numerical analyses, the intricate interplay between spin-wave diffraction and reflection at the waveguide edges is unraveled, being at the origin of a transverse-mode variation responsible for the signal extinction when detected using coplanar antennas. The findings offer insights into the controllable manipulation of detected spin-wave intensity, thereby opening promising avenues for the improvement of spin-wave switches and interferometers, and for the nanopatterning of graded indexmagnonics.

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.

Electric-Field and Mechanical Vibration-Assisted Atomic Force Microscope-Based Nanopatterning

Abstract Atomic force microscope (AFM)-based nanolithography is a cost-effective nanopatterning technique that can fabricate nanostructures with arbitrary shapes. However, existing AFM-based nanopatterning approaches have limitations in the patterning resolution and efficiency. Minimum feature size and machining performance in the mechanical force-induced nanofabrication process are limited by the radius and sharpness of the AFM tip. Electric-field-assisted atomic force microscope (E-AFM) nanolithography can fabricate nanopatterns with features smaller than the tip radius, but it is very challenging to find the appropriate input parameter window. The tip bias range in E-AFM process is typically very small and varies for each AFM tip due to the variations in tip geometry, tip end diameter, and tip conductive coating thickness. This paper demonstrates a novel electric-field and mechanical vibration-assisted AFM-based nanofabrication approach, which enables high-resolution (sub-10 nm toward sub-5 nm) and high-efficiency nanopatterning processes. The integration of in-plane vibration with the electric field increases the patterning speed, broadens the selectable ranges of applied voltages, and reduces the minimum tip bias required for nanopatterning as compared with E-AFM process, which significantly increases the versatility and capability of AFM-based nanopatterning and effectively avoids the tip damage.

Electric-Field-Assisted Contact Mode AFM-Based Nanolithography with Low Stiffness Conductive Probes

Abstract Electric-field-assisted atomic force microscope (E-AFM) nanolithography is a novel polymer-patterning technique that has diverse applications. E-AFM uses a biased AFM tip with conductive coatings to make patterns with little probe-sample interaction, which thereby avoids the tip wear that is a major issue for contact-mode AFM-based lithography, which usually requires a high probe-sample contact force to fabricate nanopatterns; however, the relatively large tip radius and large tip-sample separation limit its capacity to fabricate high-resolution nanopatterns. In this paper, we developed a contact mode E-AFM nanolithography approach to achieve high-resolution nanolithography of poly (methyl methacrylate) (PMMA) using a conductive AFM probe with a low stiffness (~0.16 N/m). The nanolithography process generates features by biasing the AFM probe across a thin polymer film on a metal substrate. A small constant force (0.5-1 nN) applied on the AFM tip helps engage the tip-film contact, which enhances nanomachining resolution. This E-AFM nanolithography approach enables high-resolution nanopatterning with feature width down to ~16 nm, which is less than one half of the nominal tip radius of the employed conductive AFM probes.

External-energy-assisted nanomachining with low-stiffness atomic force microscopy probes

Thermal atomic force microscope (AFM) nanolithography enables many nanofabrication applications, but it requires special thermal probes. In this paper, we developed a vibration-assisted sample heating approach to implement the nanomachining of poly(methyl methacrylate) (PMMA) with a regular AFM probe with low stiffness (~0.16 N/m). The joule heating softens the PMMA, which lowers the normal force. The in-plane vibration with high frequency was applied to reduce the adhesion force between the AFM tip and the PMMA with elevated temperature, which enhances nanomachining performances. By using this approach, uniform nanopatterns with controllable dimensions were fabricated on PMMA films with small setpoint force.

Plowing-Induced Structuring of Compliant Surfaces.

The structures produced by a sharp tip scraping a compliant surface are modeled in the illustrative case of scan patterns formed by a series of parallel lines. This is made possible by a modified version of the Prandtl model for stick-slip friction, with an interaction energy landscape replicating the morphology of the evolving surface. As a result, a ripple motif emerges with a tilt angle increasing linearly with the distance between the scan lines, except for the region close to the left boundary of the scanned area, where the ripples are oriented at 90°. This region can penetrate considerably to the right, forming a complex branched pattern. These predictions are substantiated by atomic force microscopy nanolithography experiments on polystyrene surfaces at room temperature. A simple and robust theoretical protocol for reproducing early-stage wear processes (potentially going beyond single contacts) is thus made available.

Tuning phospholipid bilayer permeability by flavonoid apigenin: Electrochemical and atomic force microscopy study

The ability to tune the permeability of cell membranes might have significant implications in targeted drug delivery applications. In this work we employ electrochemical methods as well as nanolithography realized in the environment of in-situ atomic force microscopy (AFM) to demonstrate that bioactive compound apigenin is capable of altering the permeability of a model phospholipid dipalmitoylphosphatidylcholine bilayer supported by a gold surface. The electron transfer rate through the bilayer was investigated employing [Fe(CN)6]4−/[Fe(CN)6]3− redox couple as an electroactive probe. The value of the standard heterogeneous rate constant obtained in the absence of apigenin (k0 = 6.60∙10−5 cm·s−1) indicates that the electron transfer through the bilayer is rather sluggish confirming its compactness. The addition of apigenin to the system leads to a considerable increase of the electron transfer rate to k0 = 5.74∙10−3 cm·s−1 being virtually identical to the value obtained at the bare electrode/electrolyte interface (k0 = 2.24∙10−3 cm·s−1). This suggests that apigenin induces a significant rearrangement of the supported lipid bilayer increasing thus its permeability. The AFM nanolithography performed in-situ in the presence of apigenin confirmed that the supported lipid bilayer reorganizes itself to a monolayer of molecules laying parallel to the electrode surface.

Electronic Transport and Anisotropic Conductivity Behavior on PEDOT:PSS Nanoribbons and Nanostructuring Modification by Atomic Force Microscope Nanoshaving

Nanoribbons of organic semiconductor salts, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS), were deposited on silicon dioxide (SiO2) by the electrospinning technique. It is possible to “shave” or mechanically displace small regions of the polymer nanoribbon by using atomic force microscopy (AFM) nanolithography techniques such as nanoshaving, leaving swaths of the surface cut to the depth of thickness of the nanoribbon. By placing the nanoribbon between two electrode pads with a 10 μm gap, for the first time was performed nanoshaving on the nanoribbon by removing portions of PEDOT-PSS and simultaneously in-situ transport measurement properties of the nanoribbon's dependence on the remaining cross section, showed evidence of anisotropic nature of the conductivity of PEDOT-PSS nanoribbons.

Site accessibility tailors DNA cleavage by restriction enzymes in DNA confined monolayers.

Density-tunable nanografted monolayers (NAMs) of short oligonucleotide sequences on gold surfaces show novel properties that make them suitable for advanced biosensing applications, and in particular to study the effects of crowding and confinement on biomolecular interactions. Here, combining atomic force microscopy nanolithography, topography measurements and coarse-grained molecular dynamics simulations, we investigated restriction enzyme reaction mechanisms within confined DNA brushes highlighting the role played by the DNA sequence conformation and restriction site position along the chain, respectively, in determining the accessibility of the enzyme, and its consequent cleavage efficiency.

Bias-assisted atomic force microscope nanolithography on NbS2 thin films grown by chemical vapor deposition

Niobium disulfide, one of the metallic transition metal dichalcogenides, has a high potential as an electrode material for electronic devices made of 2D materials. Here, we investigated the bias-assisted atomic force microscope nanolithography of NbS2 thin films synthesized by chemical vapor deposition. We analyzed the lithographed pattern using Raman spectroscopy, transmission electron microscopy and friction force microscopy. These analyses showed that lines having various widths and thicknesses could be generated using the lithography technique by simply varying the scan speed and applied voltage. These analyses also revealed that the NbS2 film transformed from a layered crystalline structure into an amorphous structure upon being lithographed. By generating four line segments forming a square and measuring I/V curves inside and outside of the square, the electrical properties of the lithographed material were characterized. These analyses indicate that NbS2 became hydrogenated and an insulator upon being lithographed.

NO gas sensing at room temperature using single titanium oxide nanodot sensors created by atomic force microscopy nanolithography

In this work, the fabrication of single titanium oxide nanodot (ND) resistive sensors for NO gas sensing at room temperature is reported. Two atomic force microscopy nanolithography methods, nanomachining and nano-oxidation, are employed. A single titanium nanowire (NW) is created first along with contact electrodes and a single titanium oxide ND is subsequently produced in the NW. Gas sensing is realized by the photo-activation and the photo-recovery approaches. It is found that a sensor with a smaller ND has better performance than a larger one. A response of 31%, a response time of 91 s, and a recovery time of 184 s have been achieved at a concentration of 10 ppm for a ND with a size of around 80 nm. The present work demonstrates the potential application of single metal oxide NDs for gas sensing with a performance that is comparable with that of metal oxide nanowire gas sensors.

Substrate Effect on Atomic Force Microscopy-Based Nanolithography of Graphene

Atomic force microscopy (AFM)-based nanolithography is one of the commonly used techniques to fabricate graphene devices on different substrates. However, the patterned graphene varies with different substrate materials. We demonstrate, both experimentally and theoretically, that the required force to pattern graphene and the trench morphology is highly dependent on the substrate hardness and the interfacial adhesion energy between graphene and the substrate. A strong correlation is seen between the cutting force and the average width of the fractured graphene on a variety of substrates. In our experiments, we show that graphene trenches with ultrasmooth edges and narrow width down to 30 nm can be created on soft substrates like gold under small applied forces, while only rough and wide trenches can be obtained on hard substrates (Si and SiO2). Our studies reveal the effect of graphene-substrate interactions on the mechanics of AFM nanolithography process, thus paving the way for achieving controllable fabrication of graphene-based devices through an appropriate control of applied forces for the target substrate materials.

Mechano‐ and Photochromism from Bulk to Nanoscale: Data Storage on Individual Self‐Assembled Ribbons

A Pt(II) complex, bearing an oligo‐ethyleneoxide pendant, is able to self‐assemble in ultralong ribbons that display mechanochromism upon nanoscale mechanical stimuli, delivered through atomic force microscopy (AFM). Such observation paves the way to fine understanding and manipulation of the mechanochromic properties of such material at the nanoscale. AFM allows quantitative assessment of nanoscale mechanochromism as arising from static pressure (piezochromism) and from shear‐based mechanical stimuli (tribochromism), and to compare them with bulk pressure‐dependent luminescence observed with diamond‐anvil cell (DAC) technique. Confocal spectral imaging reveals that mechanochromism only takes place within short distance from the localized mechanical stimulation, which allows to design high‐density information writing with AFM nanolithography applied on individual self‐assembled ribbons. Each ribbon hence serves as an individual microsystem for data storage. The orange luminescence of written information displays high contrast compared to cyan native luminescence; moreover, it can be selectively excited with visible light. In addition, ribbons show photochromism, i.e., the emission spectrum changes upon exposure to light, in a similar way as upon mechanical stress. Photochromism is here conveniently used to conceal and eventually erase information previously written with nanolithography by irradiation.

Study of the side gate junctionless transistor in accumulation region

PurposeThe purpose of this paper is to analyse the operation of p-type side gate junctionless silicon transistor (SGJLT) in accumulation region through experimental measurements and 3-D TCAD simulation results. The variation of electric field components, carrier’s concentration and valence band edge energy towards the accumulation region is explored with the aim of finding the origin of SGJLT performance in the accumulation operational condition.Design/methodology/approachThe device is fabricated by atomic force microscopy nanolithography on silicon-on-insulator wafer. The output and transfer characteristics of the device are obtained using 3-D Technology Computer Aided Design (TCAD) Sentaurus software and compared with experimental measurement results. The advantages of AFM nanolithography in contact mode and Silicon on Insulator (SOI) technology were implemented to fabricate a simple structure which exhibits the behaviour of field effect transistors. The device has 200-nm channel length, 100-nm gate gap and 4 μm for the distance between the source and drain contacts. The characteristics of the fabricated device were measured using an Agilent HP4156C semiconductor parameter analyzer (SPA). A 3-D TCAD Sentaurus tool is used as the simulation platform. The Boltzmann statistics is adopted because of the low doping concentration of the channel. Hydrodynamic model is taken to be as the main transport model for all simulations, and the quantum mechanical effects are ignored. A doping dependent Masetti mobility model was also included as well as an electric field dependent model with Shockley–Read–Hall (SRH) carrier recombination/generation.FindingsWe have obtained that the device is a normally on state device mainly because of the lack of work functional difference between the gate and the channel. Analysis of electric field components’ variation, carrier’s concentration and valence band edge energy reveals that increasing the negative gate voltage drives the device into accumulation region; however, it is unable to increase the drain current significantly. The positive slope of the hole quasi-Fermi level in the accumulation region presents mechanism of carriers’ movement from source to drain. The influence of electric field because of drain and gate voltage on charge distribution explains a low increasing of the drain current when the device operates in accumulation regime.Originality/valueThe proposed side gate junctionless transistors simplify the fabrication process, because of the lack of gate oxide and physical junctions, and implement the atomic force microscopy nanolithography for fabrication process. The optimized structure with lower gap between gate and channel and narrower channel would present the output characteristics near the ideal transistors for next generation of scaled-down devices in both accumulation and depletion region. The presented findings are verified through experimental measurements and simulation results.

A Nano-Immunoassay Based on Fluorescence and Atomic Force Spectroscopy for the Detection of Circulating Cancer Biomarkers: The Case of Her2 Positive Breast Cancer

A promising strategy in clinical practice for cancer prevention is to perform an early non-invasive population screening. The detection and quantitative analysis of “new generation” cancer biomarkers, released in the bloodstream from tumor tissues, can be effectively exploited in primary and metastatic cancer diagnosis, prognosis and therapeutic drug monitoring.The main goal of this work is to set-up a highly sensitive Atomic Force Microscopy-based Nano-immunoassay capable to perform the parallel analysis of different cancer biomarkers in a small sample volume and with a label-free technique.We focused here on the specific biomarker Human Epidermal Growth Factor Receptor 2 (Her2), relevant antigen found in some human cancers. For biorecognition we tested two monoclonal mouse Antibodies and a camelid Nanobody, specific for different epitopes of the extracellular domain of Her2 (ECD-Her2).We used Nanografting, a tip assisted Atomic Force Microscopy (AFM) nanolithography technique, to fabricate DNA nanossemblies, functionally exploited then to immobilize DNA-antibody conjugates that recognize specific proteins of interest. The determination of the antigen content of a biological sample was obtained from the analysis of AFM topographic profiles of the nanopatches before and after the sample incubation.By measuring spot height variation we detected up to picomolar concentrations of ECD-Her2 and optimized device sensitivity by correlating the density of the DNA-antibody conjugates on the surface to their target binding capability. In order to characterize the binders suitable for the Nanoarray we also performed Fluorescence, ELISA and Surface Plasmon Resonance assays.Exploiting DNA barcoding of our protein binders, preliminary results have been also obtained in the multiplexing detection of other biomarkers related to ECD-Her2 simultaneously on the same nanoarray; this evidence increases the prognostic value of the test.

Fabrication of single titanium oxide nanodot ultraviolet sensors by atomic force microscopy nanolithography

We report on the fabrication of single titanium oxide nanodot (ND) ultraviolet sensors by atomic force microscopy (AFM) nanolithography. A single titanium nanowire is first fabricated by AFM nanomachining and gold contact electrodes are then created by photolithography. By subsequent AFM nano-oxidation, a single titanium oxide ND sensor is produced. Two types of ND sensors, namely ohmic contact and Schottky contact, have been obtained and the sensitivities are around 0.25 and 320, respectively, under ultraviolet illumination. The rise and the reset times of the Schottky contact sensor are also significantly faster.

Junctionless Silicon-based Device for CO2 and N2O Gas Detection at Room Temperature

This article presents a fabrication of junctionless sub-micron silicon wire based device by means of atomic force microscope nanolithography for carbon dioxide and nitrous oxide gas detection. The final product was obtained after a sequence step of silicon and silicon dioxide etching process. The device consisted of three parallel sub-micron silicon wires which connected to two adjacent contact pads. The obtained silicon wires width ranging between 233nm to 340nm which fabricated under a controlled environment. This experiment utilized the use of silicon-on-insulator wafer as a raw material and atomic force microscope nanolithography as a method to fabricate the device structure. The bare device was electrically characterized using semiconductor parameter analyzer and behaved as a resistor where there was a current flow from one contact point to another contact point. The functionality of the fabricated junctionless device was prolonged by tested the device under gaseous environment at room temperature. The device resistivity was increased upon exposure to both target gases compared with before gas exposure. The response time and recovery time of the device was observed to be less than 1minute for both target gases. The fabricated junctionless sub-micron silicon device showed higher sensitivity to carbon dioxide gas which calculated to be 138%.

Size dependent bipolar resistance switching of NiO nanodots for low-power and multi-state operation

NiO nanodots of various sizes were fabricated via anodic oxidation induced through atomic force microscopy (AFM) nanolithography on an 18 nm thick Ni thin film, and their resistance switching properties were investigated using conductive AFM. We found that NiO nanodots with a medium size of around 15 nm height showed clear bipolar resistance switching. A threshold switching was observed in the NiO nanodots with a larger size due to having a much thinner bottom Ni layer left after oxidation. By adjusting the range of the sweeping voltage, the high resistance state can be controlled to realize multi-state switching. The power consumption during the switching process induced by the AFM tip was found to be lower than the reported power values of the NiO thin film- or NiO nanowires-based resistance switching devices.

Fabrication and simulation of single crystal p-type Si nanowire using SOI technology

Si nanowires (SiNWs) as building blocks for nanostructured materials and nanoelectronics have attracted much attention due to their major role in device fabrication. In the present work a top-down fabrication approach as atomic force microscope (AFM) nanolithography was performed on Si on insulator (SOI) substrate to fabricate a single crystal p-type SiNW. To draw oxide patterns on top of the SOI substrate local anodic oxidation was carried out by AFM in contact mode. After the oxidation procedure, an optimized solution of 30wt.% KOH with 10vol.% IPA for wet etching at 63°C was applied to extract the nanostructure. The fabricated SiNW had 70–85nm full width at half maximum width, 90nm thickness and 4μm length. The SiNW was simulated using Sentaurus 3D software with the exact same size of the fabricated device. I–V characterization of the SiNW was measured and compared with simulation results. Using simulation results variation of carrier's concentrations, valence band edge energy and recombination generation rate for different applied voltage were investigated.

Fabrication of Peptide Self-assembled Monolayer on Mica Surface and its Application in Atomic Force Microscopy Nanolithography

Fabrication of Peptide Self-assembled Monolayer on Mica Surface and its Application in Atomic Force Microscopy Nanolithography