Thermal Scanning Probe Lithography Research Articles

Assembly and Bilayer Liftoff of Periodic Nanostructures with Sub-20 nm Resolution Using Thermal Scanning Probe Lithography

Assembly and Bilayer Liftoff of Periodic Nanostructures with Sub-20 nm Resolution Using Thermal Scanning Probe Lithography

Thermal scanning probe and laser lithography for patterning nanowire based quantum devices

Semiconductor nanowire (NW) quantum devices offer a promising path for the pursuit and investigation of topologically-protected quantum states, and superconducting and spin-based qubits that can be controlled using electric fields. Theoretical investigations into the impact of disorder on the attainment of dependable topological states in semiconducting nanowires with large spin–orbit coupling and g-factor highlight the critical need for improvements in both growth processes and nanofabrication techniques. In this work, we used a hybrid lithography tool for both the high-resolution thermal scanning probe lithography and high-throughput direct laser writing of quantum devices based on thin InSb nanowires with contact spacing of 200 nm. Electrical characterization demonstrates quasi-ballistic transport. The methodology outlined in this study has the potential to reduce the impact of disorder caused by fabrication processes in quantum devices based on 1D semiconductors.

Fabrication of a hybrid device for the integration of light-triggered proton pumps

Biological ion pumps, such as bacteriorhodopsin (bR), utilize photons to move ions against concentration gradients, offering energy harvesting and spatiotemporal control of chemical gradients. This capability goes far beyond the capabilities of today's synthetic devices, suggesting a hybrid approach to embed bRs in synthetic devices in order to direct the proton flow towards useful system applications. In this study, a hybrid silicon-based nanochannel network with integrated purple membranes (PM) containing bR was fabricated. The fabrication method combines thermal scanning probe lithography, etching techniques, atomic layer deposition, plasma-enhanced chemical vapor deposition, and photolithography to create devices with buried nanochannels on silicon substrates. PM patches were deposited onto specified sites by a tunable nanofluidic confinement apparatus. The resulting device holds the potential for locally controlling directed ion transport in micrometer scale devices, a first step towards applications, such as locally affected proton catalyzed chemical reaction networks. Furthermore, this fabrication strategy, employing a maskless overlay, is a tool for constructing intricate nanofluidic network designs which are mechanically robust and straightforward to fabricate.

Combining thermal scanning probe lithography and dry etching for grayscale nanopattern amplification

Grayscale structured surfaces with nanometer-scale features are used in a growing number of applications in optics and fluidics. Thermal scanning probe lithography achieves a lateral resolution below 10 nm and a vertical resolution below 1 nm, but its maximum depth in polymers is limited. Here, we present an innovative combination of nanowriting in thermal resist and plasma dry etching with substrate cooling, which achieves up to 10-fold amplification of polymer nanopatterns into SiO2 without proportionally increasing surface roughness. Sinusoidal nanopatterns in SiO2 with 400 nm pitch and 150 nm depth are fabricated free of shape distortion after dry etching. To exemplify the possible applications of the proposed method, grayscale dielectric nanostructures are used for scalable manufacturing through nanoimprint lithography and for strain nanoengineering of 2D materials. Such a method for aspect ratio amplification and smooth grayscale nanopatterning has the potential to find application in the fabrication of photonic and nanoelectronic devices.

Multi- and Gray-Scale Thermal Lithography of Silk Fibroin as Water-Developable Resist for Micro and Nanofabrication.

Silk fibroin (SF) is a natural material with polymorphic structures that determine its water solubility and biodegradability, which can be altered by exposing it to heat. Here, a hybrid thermal lithography method combining scalable microscale laser-based patterning with nanoscale patterning based on thermal scanning probe lithography is developed. The latter enables in addition grayscale patterns to be made. The resolution limit of the writing in silk fibroin is studied by using a nanoscale heat source from a scanned nanoprobe. The heat thereby induces local water solubility change in the film, which can subsequently be developed in deionized water. Nanopatterns and grayscale patterns down to 50nm lateral resolution are successfully written in the silk fibroin that behaves like a positive tone resist. The resulting patterned silk fibroin is then applied as a mask for dry etching of SiO2 to form a hard mask for further nano-processing. A very high selectivity of 42:1 between SiO2 and silk fibroin is obtained allowing for high-aspect ratio structure to be fabricated. The fabricated nanostructures have very low line edge roughness of 5±2nm. The results demonstrate the potential of silk fibroin as a water-soluble resist for hybrid thermal lithography and precise micro/nanofabrication.

Nanoscale-localized multiplexed biological activation of field effect transistors for biosensing applications.

The rise in antibiotic-resistant pathogens, highly infectious viruses, and chronic diseases has prompted the search for rapid and versatile medical tests that can be performed by the patient. Field-effect transistor (FET)-based electronic biosensing platforms are particularly attractive due to their sensitivity, fast turn-around time, potential for parallel detection of multiple pathogens, and compatibility with semiconductor manufacturing. However, an unmet critical need is a scalable, site-selective multiplexed biofunctionalization method with nanoscale precision for immobilizing different types of pathogen-specific bioreceptors on individual FETs, preventing parallel detection of multiple targets. Here, we propose a paradigm shift in FET biofunctionalization using thermal scanning probe lithography (tSPL) with a thermochemically sensitive polymer. This polymer can be spin-coated on fully-fabricated FET chips, making this approach applicable to any FET sensor material and technology. Crucially, we demonstrate the spatially selective multiplexed functionalization capability of this method by immobilizing different types of bioreceptors at prescribed locations on a chip with sub-20 nm resolution, paving the way for massively parallel FET detection of multiple pathogens. Antibody- and aptamer-modified graphene FET sensors are then realized, achieving ultra-sensitive detection of a minimum measured concentrations of 3 aM of SARS-CoV-2 spike proteins and 10 human SARS-CoV-2 infectious live virus particles per ml, and selectivity against human influenza A (H1N1) live virus.

Selective placement of functionalised DNA origami via thermal scanning probe lithography patterning

We developed a precise nanopatterning method using thermal scanning probe lithography (t-SPL) to organize functionalised DNA origami into nanoarrays, achieving single-molecule control.

Achieving Reliable and Ultrafast Memristors via Artificial Filaments in Silk Fibroin.

The practical implementation of memristors in neuromorphic computing and biomimetic sensing suffers from unexpected temporal and spatial variations due to the stochastic formation and rupture of conductive filaments (CFs). Here, the biocompatible silk fibroin (SF) is patterned with an on-demand nanocone array by using thermal scanning probe lithography (t-SPL) to guide and confine the growth of CFs in the silver/SF/gold (Ag/SF/Au) memristor. Benefiting from the high fabrication controllability, cycle-to-cycle (temporal) standard deviation of the set voltage for the structured memristor is significantly reduced by ≈95.5% (from 1.535 to 0.0686 V) and the device-to-device (spatial) standard deviation is also reduced to 0.0648 V. Besides, the statistical relationship between the structural nanocone design and the resultant performance is confirmed, optimizing at the small operation voltage (≈0.5 V) and current (100 nA), ultrafast switching speed (sub-100 ns), large on/off ratio (104 ), and the smallest switching slope (SS < 0.01 mV dec-1 ). Finally, the short-term plasticity and leaky integrated-and-fire behavior are emulated, and a reliable thermal nociceptor system is demonstrated for practical neuromorphic applications.

Generating smooth potential landscapes with thermal scanning-probe lithography

Scanning probe microscopy (SPM) uses a sharp tip to interrogate surfaces with atomic precision. Inputs such as mechanical, electrical, or thermal energy can activate highly localized interactions, providing a powerful class of instruments for manipulating materials on small length scales. Thermal scanning-probe lithography (tSPL) is an advanced SPM variant that uses a silicon tip on a heated cantilever to locally sublimate polymer resist, acting as a high-resolution lithography tool and a scanning probe microscope simultaneously. The main advantage of tSPL is the ability to electrically control the temperature and applied force of the tip, which can produce smooth topographical surfaces that are unattainable with conventional nanofabrication techniques. Recent investigations have exploited these surfaces to generate potential landscapes for enhanced control of photons, electrons, excitons, and nanoparticles, demonstrating a broad range of experimental possibilities. This paper outlines the principles, procedures, and limitations of tSPL for generating smooth potentials and discusses the prospective impact in photonics, electronics, and nanomaterials science.

Thermal Scanning-Probe Lithography for Broad-Band On-Demand Plasmonic Nanostructures on Transparent Substrates.

Thermal scanning-probe lithography (t-SPL) is a high-resolution nanolithography technique that enables the nanopatterning of thermosensitive materials by means of a heated silicon tip. It does not require alignment markers and gives the possibility to assess the morphology of the sample in a noninvasive way before, during, and after the patterning. In order to exploit t-SPL at its peak performances, the writing process requires applying an electric bias between the scanning hot tip and the sample, thereby restricting its application to conductive, optically opaque, substrates. In this work, we show a t-SPL-based method, enabling the noninvasive high-resolution nanolithography of photonic nanostructures onto optically transparent substrates across a broad-band visible and near-infrared spectral range. This was possible by intercalating an ultrathin transparent conductive oxide film between the dielectric substrate and the sacrificial patterning layer. This way, nanolithography performances comparable with those typically observed on conventional semiconductor substrates are achieved without significant changes of the optical response of the final sample. We validated this innovative nanolithography approach by engineering periodic arrays of plasmonic nanoantennas and showing the capability to tune their plasmonic response over a broad-band visible and near-infrared spectral range. The optical properties of the obtained systems make them promising candidates for the fabrication of hybrid plasmonic metasurfaces supported onto fragile low-dimensional materials, thus enabling a variety of applications in nanophotonics, sensing, and thermoplasmonics.

Phase Nanoengineering via Thermal Scanning Probe Lithography and Direct Laser Writing (Adv. Mater. Technol. 16/2023)

Phase Nanoengineering via Thermal Scanning Probe Lithography and Direct Laser Writing (Adv. Mater. Technol. 16/2023)

Phase Nanoengineering via Thermal Scanning Probe Lithography and Direct Laser Writing

AbstractNanomaterials derive their electronic, magnetic, and optical properties from their specific nanostructure. In most cases, nanostructured materials and their properties are defined during the materials growth, and nanofabrication techniques, such as lithography, are employed subsequently for device fabrication. Herein, a perspective is presented on a different approach for creating nanomaterials and devices where, after growth, advanced nanofabrication techniques are used to directly nanostructure condensed matter systems, by inducing highly controlled, localized, and stable changes in the electronic, magnetic, or optical properties. Then, advantages, limitations, applications in materials science and technology are highlighted, and future perspectives are discussed.

Spectral tuning of Bloch Surface Wave resonances by light-controlled optical anisotropy

Abstract Fostered by the recent advancements in photonic technologies, the need for all-optical dynamic control on complex photonic elements is emerging as more and more relevant, especially in integrated photonics and metasurface-based flat-optics. In this framework, optically-induced anisotropy has been proposed as powerful mean enabling tuning functionalities in several planar architectures. Here, we design and fabricate an anisotropic two-dimensional bull’s eye cavity inscribed within an optically-active polymeric film spun on a one-dimensional photonic crystal sustaining Bloch surface waves (BSW). Thanks to the cavity morphology, two surface resonant modes with substantially orthogonal polarizations can be coupled within the cavity from free-space illumination. We demonstrate that a dynamic control on the resonant mode energies can be easily operated by modulating the orientation of the optically-induced birefringence on the surface, via a polarized external laser beam. Overall, reversible blue- and red-shifts of the resonant BSWs are observed within a spectral range of about 2 nm, with a moderate laser power illumination. The polymeric structure is constituted by a novel blend of an azopolymer and a thermally-sensitive resist, which allows a precise patterning via thermal scanning probe lithography, while providing a significant structural integrity against photo-fluidization or mass-flow effects commonly occurring in irradiated azopolymers. The proposed approach based on tailored birefringence opens up new pathways to finely control the optical coupling of localized surface modes to/from free-space radiation, particularly in hybrid organic–inorganic devices.

Non-invasive fabrication of plasmonic nanostructures on dielectric substrates coated with transparent-conductive oxide

Modern photonics demands for high-resolution (HR) and deterministic lithography on transparent substrates. Thermal scanning-probe lithography (t-SPL) is a mask-less approach that couples a nanoscopic patterning resolution with the possibility to perform morphological characterizations without damaging delicate substrates unlike it happens for other techniques of similar resolution. In order to operate at its maximum performances, an electric bias between the scanning micromachined cantilever and the sample is needed thereby preventing, in principle, the patterning of transparent materials (that are usually insulators). In this work we demonstrate that by intercalating an ultrathin layer of a transparent conductive oxide (TCO) between an insulating and transparent substrate and the polymeric thin layer it is possible to exploit all the benefits of t-SPL also on challenging optically transparent substrates. Taking advantage of this particular lithographic configuration, we were effectively able to obtain a family of different gold plasmonic nanostructures resonating in the spectral range from the Visible to the Near-Infrared. The ensemble of the different resonators shows optical properties that encourage their exploitation in fields like sensing and thermoplasmonics.

(Student Award, 1st Place, Invited) Rapid Nanometer Scale Patterning Using New High-Sensitivity, Dry-Develop Resists

A family of high-resolution, photo-thermal resists based on low ceiling temperature copolymers has been developed and used in a nanometer scale, direct-write thermal patterning tool. The polymer resists are composed of cyclic, low ceiling temperature (Tc) poly(aldehydes). Tc is the thermodynamic temperature which separates polymer from monomer. The Tc of the polymers is below room temperature making the polymer meta-stable at room temperature. The resists very rapidly and cleanly decompose into monomer only when triggered during patterning because the mechanism of depolymerization is suppressed. Cleaving a single bond in the polymer chain initiates the spontaneous and complete depolymerization of the polymer. The use of these low Tc polymers in thermal scanning probe lithography to resolve nanometer size features will be described. Laser ablation of the same polymers has been demonstrated in thermal scanning probe tools allowing for the rapid removal of large areas of the resist adding speed to the hot-tip thermal patterning capability. A particular advantage of the laser assisted thermal scanning probe patterning tools is the ability to form three-dimensional features both by hot-tip patterning and laser ablation.

Edge-Contact MoS2 Transistors Fabricated Using Thermal Scanning Probe Lithography.

The science and engineering of two-dimensional materials (2DMs), in particular, of 2D semiconductors, is advancing at a thriving pace. It is well known that these delicate few-atoms thick materials can be damaged during the processing toward their integration into final devices. Thermal scanning probe lithography (t-SPL) is a gentle alternative to the typically used electron beam lithography to fabricate these devices avoiding the use of electrons, which are well known to deteriorate the 2DMs’ properties. Here, t-SPL is used for the fabrication of MoS2-based field effect transistors (FETs). In particular, the use of t-SPL is demonstrated for the first time for the fabrication of edge-contact MoS2 FETs, combining the hot-tip patterning and Ar+ milling to etch the 2DM. To avoid contamination of the contact interface by atmospheric gas molecules, etching and metal deposition are performed without breaking the vacuum conditions in between. With this process, edge-contact MoS2 FETs are successfully fabricated and characterized. On/off ratios up to 108 and 109 are obtained at room temperature in air and vacuum, respectively, i.e., comparable with the best values reported in the literature.

Thermal scanning probe lithography

Thermal scanning probe lithography

Thermal scanning probe lithography

Thermal scanning probe lithography

Thermal scanning probe lithography using Parylene C as thermal resist

Thermal scanning probe lithography is a direct-write patterning method that uses a heated scanning probe tip to remove thermal resist. The most widely used thermal resist is polyphthalaldehyde. Another alternative thermal resist, Parylene C is introduced in this letter. It has been found that Parylene C has a wide process latitude as a thermal resist under our experimental conditions. A high resolution of ∼40 nm can be achieved in our optimised process. In addition, patterns in parylene layer can be transferred directly into the substrate with deep reactive ion etching without an additional hard mask, thus simplifying the fabrication process.

Controlling resonant surface modes by arbitrary light induced optical anisotropies

In this work the sensitivity of Bloch Surface Waves to laser-induced anisotropy of azo-polymeric thin layers is expe rimentally shown . The nanoscale reshaping of the films via thermal-Scanning Probe Lithography allows to couple light to circular photonic nanocavities, tailoring on-demand resonant BSW confined within the nanocavity.