Using low-contrast negative-tone PMMA at cryogenic temperatures for 3D electron beam lithography

Electron Energy Loss Processes in Methyl Methacrylate: Excitation and Bond Breaking

Details of electron-induced chemistry of methyl methacrylate (MMA) upon complexation are revealed by combining gas-phase 2D electron energy loss spectroscopy with electron attachment spectroscopy of isolated MMA and its clusters. We show that even though isolated MMA does not form stable parent anions, it efficiently thermalizes the incident electrons via intramolecular vibrational redistribution, leading to autodetachment of slow electrons. This autodetachment channel is reduced in clusters due to intermolecular energy transfer and stabilization of parent molecular anions. Bond breaking via dissociative electron attachment leads to an extensive range of anion products. The dominant OCH₃^- channel is accessible via core-excited resonances with threshold above 5 eV, despite the estimated thermodynamic threshold below 3 eV. This changes in clusters, where M_nOCH₃^- anions are observed in a lower-lying resonance due to neutral dissociation of the ¹(n, π*) state and electron self-scavenging. The present findings have implications for electron-induced chemistry in lithography with poly(methyl methacrylate).

Production and Patterning of Fluorescent Quantum Dots by Cryogenic Electron-Beam Writing

Graphene quantum dots (GQDs) have emerged as a promising type of functional material with distinguished properties. Although tremendous effort was devoted to the preparation of GQDs, their applications are still limited due to a lack of methods for processing GQDs from synthesis to patterning smoothly. Here, we demonstrate that aromatic molecules, e.g., anisole, can be directly converted into GQD-containing nanostructures by cryogenic electron-beam writing. Such an electron-beam irradiation product exhibits evenly red fluorescence emission under laser excitation at 473 nm, and its photoluminescence intensity can be easily tuned with the electron-beam exposure dose. Experimental characterizations on the chemical composition of the product reveal that anisole undergoes a carbonization and further graphitization process during e-beam irradiation. With conformal coating of anisole, our approach can create arbitrary fluorescent patterns on both planar and curved surfaces for concealing information or anticounterfeiting applications. This study provides a one-step method for production and patterning of GQDs, facilitating their applications in highly integrated and compact optoelectronic devices.

High-performance deterministic in situ electron-beam lithography enabled by cathodoluminescence spectroscopy

The application of solid-state quantum emitters in real-world quantum information technologies requires precise nanofabrication platforms with high process yield. Self-assembled semiconductor quantum dots with excellent emission properties have proven to be among the best candidates to meet the needs of a number of novel quantum photonic devices. However, their spatial and spectral positions vary statistically on a scale that is far too large for their system integration via fixed lithography and inflexible processing schemes. We solve this severe problem by introducing a flexible and deterministic manufacturing scheme based on precise and convenient cathodoluminescence spectroscopy followed by high-resolution electron-beam lithography. The basics and application examples of this advanced in situ electron-beam lithography are described in this article. Although we focus here on quantum dots as photon emitters, this nanotechnology concept is very well suited for the fabrication of a variety of quantum nanophotonic devices based on quantum emitters that exhibit suitably strong cathodoluminescence signals.

Quantitative mechanics of 3D printed nanopillars interacting with bacterial cells

One of the methods to create sub-10 nm resolution metal-composed 3D nanopillars is electron beam-induced deposition (EBID). Surface nanotopographies (e.g., nanopillars) could play an important role in the design and fabrication of implantable medical devices by preventing the infections that are caused by the bacterial colonization of the implant surface. The mechanical properties of such nanoscale structures can influence their bactericidal efficiency. In addition, these properties are key factors in determining the fate of stem cells. In this study, we quantified the relevant mechanical properties of EBID nanopillars interacting with Staphylococcus aureus (S. aureus) using atomic force microscopy (AFM). We first determined the elastic modulus (17.7 GPa) and the fracture stress (3.0 ± 0.3 GPa) of the nanopillars using the quantitative imaging (QI) mode and contact mode (CM) of AFM. The displacement of the nanopillars interacting with the bacteria cells was measured by scanning electron microscopy (50.3 ± 9.0 nm). Finite element method based simulations were then applied to obtain the force-displacement curve of the nanopillars (considering the specified dimensions and the measured value of the elastic modulus) based on which an interaction force of 88.7 ± 36.1 nN was determined. The maximum von Mises stress of the nanopillars subjected to these forces was also determined (3.2 ± 0.3 GPa). These values were close to the maximum (i.e., fracture) stress of the pillars as measured by AFM, indicating that the nanopillars were close to their breaking point while interacting with S. aureus. These findings reveal unique quantitative data regarding the mechanical properties of nanopillars interacting with bacterial cells and highlight the possibilities of enhancing the bactericidal activity of the investigated EBID nanopillars by adjusting both their geometry and mechanical properties.

Electron beam lithography of poly(glycidol) nanogels for immobilization of a three-enzyme cascade

Nanogels devices with spatial confinement of multiple enzymes resulted in retention of bioactivity after 30 days with a 5 fold higher chromogenic output compared to free enzyme cascade devices.

Triggered high-purity telecom-wavelength single-photon generation from p-shell-driven InGaAs/GaAs quantum dot

We report on the experimental demonstration of triggered single-photon emission at the telecom O-band from In(Ga)As/GaAs quantum dots (QDs) grown by metal-organic vapor-phase epitaxy. Micro-photoluminescence excitation experiments allowed us to identify the p-shell excitonic states in agreement with high excitation photoluminescence on the ensemble of QDs. Hereby we drive an O-band-emitting GaAs-based QD into the p-shell states to get a triggered single photon source of high purity. Applying pulsed p-shell resonant excitation results in strong suppression of multiphoton events evidenced by the as measured value of the second-order correlation function at zero delay of 0.03 (and ~0.005 after background correction).

Combination photo and electron beam lithography with polymethyl methacrylate (PMMA) resist

We describe techniques for performing photolithography and electron beam lithography in succession on the same resist-covered substrate. Larger openings are defined in the resist film through photolithography whereas smaller openings are defined through conventional electron beam lithography. The two processes are carried out one after the other and without an intermediate wet development step. At the conclusion of the two exposures, the resist film is developed once to reveal both large and small openings. Interestingly, these techniques are applicable to both positive and negative tone lithographies with both optical and electron beam exposure. Polymethyl methacrylate, by itself or mixed with a photocatalytic cross-linking agent, is used for this purpose. We demonstrate that such resists are sensitive to both ultraviolet and electron beam irradiation. All four possible combinations, consisting of optical and electron beam lithographies, carried out in positive and negative tone modes have been described. Demonstration grating structures have been shown and process conditions have been described for all four cases.