Atomic Lithography Research Articles

Nanogap-enhanced infrared spectroscopy with template-stripped wafer-scale arrays of buried plasmonic cavities.

We have combined atomic layer lithography and template stripping to produce a new class of substrates for surface-enhanced infrared absorption (SEIRA) spectroscopy. Our structure consists of a buried and U-shaped metal-insulator-metal waveguide whose folded vertical arms efficiently couple normally incident light. The insulator is formed by atomic layer deposition (ALD) of Al2O3 and precisely defines the gap size. The buried nanocavities are protected from contamination by a silicon template until ready for use and exposed by template stripping on demand. The exposed nanocavity generates strong infrared resonances, tightly confines infrared radiation into a gap that is as small as 3 nm (λ/3300), and creates a dense array of millimeter-long hotspots. After partial removal of the insulators, the gaps are backfilled with benzenethiol molecules, generating distinct Fano resonances due to strong coupling with gap plasmons, and a SEIRA enhancement factor of 10(5) is observed for a 3 nm gap. Because of the wafer-scale manufacturability, single-digit-nanometer control of the gap size via ALD, and long-term storage enabled by template stripping, our buried plasmonic nanocavity substrates will benefit broad applications in sensing and spectroscopy.

Squeezing millimeter waves through a single, nanometer-wide, centimeter-long slit.

We demonstrate broadband non-resonant squeezing of terahertz (THz) waves through an isolated 2-nm-wide, 2-cm-long slit (aspect ratio of 107), representing a maximum intensity enhancement factor of one million. Unlike resonant nanogap structures, a single, effectively infinitely-long slit passes incident electromagnetic waves with no cutoff, enhances the electric field within the gap with a broad 1/f spectral response, and eliminates interference effects due to finite sample boundaries and adjacent elements. To construct such a uniform, isolated slit that is much longer than the millimeter-scale spot of a THz beam, we use atomic layer lithography to pattern vertical nanogaps in a metal film over an entire 4-inch wafer. We observe an increasing field enhancement as the slit width decreases from 20 nm to 2 nm, in agreement with numerical calculations.

Quantum atomic lithography via cross-cavity optical Stern–Gerlach setup

We present a fully quantum scheme to perform 2D atomic lithography based on a cross-cavity optical Stern-Gerlach setup: an array of two mutually orthogonal cavities crossed by an atomic beam perpendicular to their optical axes, which is made to interact with two identical modes. After deriving an analytical solution for the atomic momentum distribution, we introduce a protocol allowing us to control the atomic deflection by manipulating the amplitudes and phases of the cavity field states.

Atomic Force Microscopy Characterization and Lithography of Cu-Ligated Mercaptoalkanoic Acid “Molecular Ruler” Multilayers

Hybrid chemical patterning strategies that combine the sophistication of lithography with the intrinsic precision of molecular self-assembly are of broad interest for applications including nanoelectronics and bioactive surfaces. This approach is exemplified by the molecular-ruler process where the sequential deposition of mercaptoalkanoic acid molecules and coordinated metal ions is integrated with conventional lithographic techniques to fabricate registered, nanometer-scale spacings. Herein, we illustrate the capabilities of atomic force microscopy characterization and lithography to investigate the morphology, quality, and local thickness of Cu-ligated mercaptohexadecanoic acid multilayers on Au{111} substrates. These multilayers are a key component utilized in the molecular-ruler process. The rich and varied topographic features of each layer are investigated via contact-mode atomic force microscopy. Using nanoshaving, an atomic force microscopy lithographic strategy that reveals the underlying Au{111} substrate via tip-induced desorption of a molecular film, the local thicknesses of these multilayers are ascertained; these thicknesses are consistent with the anticipated heights for Cu-ligated mercaptohexadecanoic acid multilayers as well as previous ensemble surface analytical measurements. By regulating the force set point utilized during nanoshaving, the upper layer of a Cu-ligated mercaptohexadecanoic acid bilayer is removed, revealing the carboxyl moiety of the lower mercaptohexadecanoic acid layer. This selective nanoshaving demonstrates a simple and practical means to generate three-dimensional multilayers and to reveal buried chemical functionalities within metal-ligated multilayers.

Atomic layer lithography of wafer-scale nanogap arrays for extreme confinement of electromagnetic waves

Squeezing light through nanometre-wide gaps in metals can lead to extreme field enhancements, nonlocal electromagnetic effects and light-induced electron tunnelling. This intriguing regime, however, has not been readily accessible to experimentalists because of the lack of reliable technology to fabricate uniform nanogaps with atomic-scale resolution and high throughput. Here we introduce a new patterning technology based on atomic layer deposition and simple adhesive-tape-based planarization. Using this method, we create vertically oriented gaps in opaque metal films along the entire contour of a millimetre-sized pattern, with gap widths as narrow as 9.9 Å, and pack 150,000 such devices on a 4-inch wafer. Electromagnetic waves pass exclusively through the nanogaps, enabling background-free transmission measurements. We observe resonant transmission of near-infrared waves through 1.1-nm-wide gaps (λ/1,295) and measure an effective refractive index of 17.8. We also observe resonant transmission of millimetre waves through 1.1-nm-wide gaps (λ/4,000,000) and infer an unprecedented field enhancement factor of 25,000.

Tunable atomic force microscopy bias lithography on electron beam induced carbonaceous platforms

Tunable local electrochemical and physical modifications on the carbonaceous platforms are achieved using Atomic force microscope (AFM) bias lithography. These carbonaceous platforms are produced on Si substrate by the technique called electron beam induced carbonaceous deposition (EBICD). EBICD is composed of functionalized carbon species, confirmed through X-ray photoelectron spectroscopy (XPS) analysis. AFM bias lithography in tapping mode with a positive tip bias resulted in the nucleation of attoliter water on the EBICD surface under moderate humidity conditions (45%). While the lithography in the contact mode with a negative tip bias caused the electrochemical modifications such as anodic oxidation and etching of the EBICD under moderate (45%) and higher (60%) humidity conditions respectively. Finally, reversible charge patterns are created on these EBICD surfaces under low (30%) humidity conditions and investigated by means of electrostatic force microscopy (EFM).

Oxide-based platform for reconfigurable superconducting nanoelectronics

We report quasi-1D superconductivity at the interface of LaAlO3 and SrTiO3. The material system and nanostructure fabrication method supply a new platform for superconducting nanoelectronics. Nanostructures having line widths w ∼ 10 nm are formed from the parent two-dimensional electron liquid using conductive atomic force microscope lithography. Nanowire cross-sections are small compared to the superconducting coherence length in LaAlO3/SrTiO3, placing them in the quasi-1D regime. Broad superconducting transitions versus temperature and finite resistances in the superconducting state well below Tc ≈ 200 mK are observed, suggesting the presence of fluctuation- and heating-induced resistance. The superconducting resistances and V–I characteristics are tunable through the use of a back gate. Four-terminal resistances in the superconducting state show an unusual dependence on the current path, varying by as much as an order of magnitude. This new technology, i.e., the ability to ‘write’ gate-tunable superconducting nanostructures on an insulating LaAlO3/SrTiO3 ‘canvas’, opens possibilities for the development of new families of reconfigurable superconducting nanoelectronics.

Molecular simulation of pattern formation in electron beam lithography

We performed molecular simulation to investigate the pattern formation in electron beam lithography. We introduced the effect of electron exposure by the chain scission of the polymer molecules. In the development process, the small segments of polymer molecules are removed from the resist structure. Our present simulation reveals the typical structure of atomic scale line edge roughness, i.e., the prominences of a molecular chain superimposed on an undulating molecular network. It also indicates that electron scattering in the resist is more dominant for determining the line edge roughness than the molecular behavior for PMMA resist even in atomic scale lithography.

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.

Polymer Brush Electrets

AbstractThe charge storage properties of polymer brushes are reported for the first time. Poly(methyl methacrylate) (PMMA) brushes are explored as electrets to store electrostatic charges. Micrometer‐ and nanometer‐scale patterns of electrostatic charges are successfully fabricated on planar and non‐planar PMMA brush films by means of conductive microcontact printing and atomic force microscope lithography, where the charge storage density and stability are studied in detail with Kelvin force microscopy. Importantly, because PMMA brushes are chemically tethered on the substrate, their charge storage properties can be studied in various organic solvents, in which their bulk counterparts will be dissolved. It is found that patterned charges on PMMA brushes are stable enough in organic media, such as hexane and toluene, for guiding the assembly of Au nanoparticles in organic media and the dewetting of polymer thin films with solvent annealing. The electrets properties shall add a new dimension of functionality, apart from the conventional chemical and physical properties, to polymer brushes for a wide range of applications in materials science, nanotechnology, and electronic devices.

Detection of real-time dynamics of drug–target interactions by ultralong nanowalls

Detecting drug-target interactions in real-time is a powerful approach for drug discovery and analytics. We show here for the first time the ultra fast electrical real-time detection and quantification of antibiotics using a novel biohybrid nanosensor. The biomolecular sensing is performed on ultralong (mm range) high aspect ratio nanowall (50 nm width) surfaces functionalized with operator DNA tetO which is specifically bound by the sensor protein TetR. This sensor protein is released from the operator DNA in a dose dependent manner by exposing the device functionalized with this bound DNA-protein complex to tetracycline antibiotics. As a result, the electrical conductance is accordingly modulated by these surface net charge changes. The switching mechanism of sensor proteins attached at the functionalized surfaces and releasing them again by antibiotics is demonstrated. With the here presented device the detection limit is below the limits of prevailing detection methods. Moreover, the study is extended to detect antibiotic residues in spiked organic milk from cows far below the maximum residual level of the European Union. In spiked milk samples a detection limit for tetracycline concentrations in the 100 fM level was achieved. The nanowall devices are fabricated by atomic layer deposition-based spacer lithography on full wafer scale which is a simple approach capable for mass production.

Single-Mode Superconductivity in LaAlO3/SrTiO3 Nanostructures

ABSTRACTThe properties of superconductors at the extreme limits of dimensionality are of fundamental interest. The interface of LaAlO3 and SrTiO3 hosts a quasi-two-dimensional superconductor below Tc≈200 mK. Here we report superconductivity in nanowire-shaped structures created at the LaAlO3/SrTiO3 interface using conductive atomic force microscope lithography. Nanowire cross-sections are small compared to the superconducting coherence length in LaAlO3/SrTiO3 (w <<ξSC∼100 nm), placing them in the quasi-1D regime. The ability to “write” fully superconducting nanostructures on an insulating LaAlO3/SrTiO3 “canvas” opens possibilities for the development of new families of superconducting nanoelectronics. Four-terminal transport measurements suggest that in some devices both the normal and superconducting states are confined to a single quantum channel.

Covalent poly(methyl methacrylate) nanostructures on functionalized Si(100) surfaces

Material properties are strongly affected by the presence of surface chemical functionalities. In this study we show a platform for fabricating robust poly(methyl methacrylate) molecular architectures covalently bound to silylated Si(100) substrates, by an atom transfer radical polymerization approach. Infrared attenuated total reflectance spectra have shown increasing poly(methyl methacrylate) signals upon increasing reaction time and can be used to monitor the growth of these hybrid inorganic/organic structures. The chemical composition of these surface structures was investigated by X-ray photoelectron spectra. Surface morphology studies were carried out by atomic force microscopy and lithography. In our reaction conditions, the thickness of poly(methyl methacrylate) on Si(100) can be modulated in the nanometer range. Quantum mechanical DFT calculations have been performed to estimate the growth rate.

213 nm pitch standards fabricated using atomic lithography

Atomic lithography is a technique in which nearly resonant light is used to pattern an atom beam periodically. In this article, a 425 nm laser light standing wave is used to focus a beam of chromium atoms to fabricate the period of the nanoscale pitch standards of 213 ± 0.1 nm. The height was 4 nm. The (FWHM) width is 64 ± 6 nm. And this result will be analysed theoretically. The tracing of atoms is numerical simulated based on particle-optics and the factors of affecting deposition result will be found in this article.

Formation of Ni-Silicide Nanowires on Silicon-on-Insulator Substrates by Atomic Force Microscope Lithography and Solid Phase Reaction

Nickel silicide nanowires were fabricated by atomic force microscopy nano-oxidation on silicon-on-insulator substrates, selective wet etching, Ni deposition and a solid phase reaction. Si nanowires with various widths can be fabricated using oxide lines with various widths, which can be controlled by tuning the sample bias during nano-oxidation. When the ratio of the thickness of Ni films to the height of Si nanowires was 1.8, the Ni-rich silicide phases were obtained and were depended on the width of the Si nanowires. Ni atoms on top of and around the Si nanowires participated in the formation of silicide. NiSi nanowires were fabricated by measuring the width of nanowires accurately and tuning the thickness of Ni films that were estimated on the basis of 1 of Ni/Si atomic ratio. Resistivity of the NiSi nanowires increased as their width decreased, mainly because of the polycrystalline structure of nanowires and the electron scattering by grain boundaries.

Field emission in lateral silicon diode fabricated by atomic force microscopy lithography

A novel vacuum lateral silicon diode was fabricated using atomic force microscopy (AFM) lithography to characterise field emission. The silicon diode was approximately 100 nm thick, with an exceptionally smooth surface, and included a finger-like emitter with a gap width of 35 nm. From the Fowler-Nordheim, equation, the field enhancement factor (β) and the field emitting area (A) were assessed to ascertain the high emission current and the low turn-on voltage. The very small emitting area was obtained due to the extremely sharp cathode and very small radius of the anode tip curvature. The turn-on voltage of the diode was 8 V, the smallest value ever reported for lateral silicon field emission diodes.

Multitip atomic force microscope lithography system for high throughput nanopatterning

An atomic force microscope (AFM) system with multiple parallel lithography probes of equal heights on a single cantilever was created in order to improve the throughput of AFM lithography. The multitip probe was fabricated by electron-beam (e-beam) lithography and a dry silicon etching process. Several carbon islands were made on a single cantilever in a straight line by e-beam lithography and were used as an etch mask, whereas the silicon pedestal structure of the multitip probe was fabricated by reactive ion etching (RIE). Finally the carbon islands were sharpened by a RIE process using oxygen gas. The multitip probe was successfully applied to form multidot pattern arrays on a negative resist film coated on silicon by low electric field induced AFM lithography. A pedestal nanopillar structure was utilized as a convenient support feature that enabled better control of multiple nanotip arrays for AFM writing. The authors fabricated such a nanopedestal array with extremely sharp nanoneedle tips.

Study the Characteristic of P-Type Junction-Less Side Gate Silicon Nanowire Transistor Fabricated by Atomic Force Microscopy Lithography

Problem statement: Nanotransistor now is one of the most promising fields in nanoelectronic in order to less energy consuming and application to create developed programmable information processors. Most of Computing and communications companies invest hundreds of millions of dollars in research funds every year to develop smaller transistors. Approach: The Junction-less side gate silicon Nano-wire transistor has been fabricated by Atomic Force Microscopy (AFM) and wet etching on p-type Silicon On Insulator (SOI) wafer. Then, we checked the characteristic and conductance trend in this device regarding to semi-classical approach by Semiconductor Probe Analyser (SPA). Results: We observe in characteristic of the device directly proportionality of the negative gate voltage and Source-Drain current. In semi classical approach, negative Gate voltage falling down the energy States of the Nano-wire between the source and the drain. The graph for positive gate voltage plotted as well to check. In other hand, the conductance will be following characteristic due to varying the gate voltage under the different drain-source voltage. Conclusion: The channel energy states are supposed to locate between two electrochemical potentials of the contacts in order to transform the charge. For the p-type channel the transform of the carriers is located in valence band and changing the positive or negative gate voltage, make the valence band energy states out of or in the area between the electrochemical potentials of the contacts causing the current reduced or increased.

Controlling the function of carbon nanotube devices with re-writable charge patterns

We use atomic force microscopy lithography to write charge patterns in close proximity to carbon nanotube field-effect transistor devices. The silicon dioxide substrate retains the charge for days, allowing various charge configurations to be tested. We show that the written charge can move the Fermi level in the nanotube by 1 eV and we use this charge lithography to reconfigure a field-effect transistor into a pn junction. The substrate charge can be erased and rewritten, offering a new tool for prototyping nanodevices and optimizing electrostatic doping profiles.

Nanoscale Lithography on Monolayer Graphene Using Hydrogenation and Oxidation

Monolayer graphene is one of the most interesting materials applicable to next-generation electronic devices due to its transport properties. However, realization of graphene devices requires suitable nanoscale lithography as well as a method to open a band gap in monolayer graphene. Nanoscale hydrogenation and oxidation are promising methods to open an energy band gap by modification of surface structures and to fabricate nanostructures such as graphene nanoribbons (GNRs). Until now it has been difficult to fabricate nanoscale devices consisting of both hydrogenated and oxidized graphene because the hydrogenation of graphene requires a complicated process composed of large-scale chemical modification, nanoscale patterning, and etching. We report on nanoscale hydrogenation and oxidation of graphene under normal atmospheric conditions and at room temperature without etching, wet process, or even any gas treatment by controlling just an external bias through atomic force microscope lithography. Both the lithographically defined nanoscale hydrogenation and oxidation have been confirmed by micro-Raman spectroscopy measurements. Patterned hydrogenated and oxidized graphene show insulating behaviors, and their friction values are several times larger than those of graphene. These differences can be used for fabricating electronic or electromechanical devices based on graphene.