Thomas Pucher

Hand-drawn nail-polish microfiber shadow masks enable low-cost, lithography-free fabrication of sub-micrometer electrode gaps and functional MoS ₂ devices on rigid and flexible substrates.

Freestanding ferroelectric oxides integrated with 2D semiconductors offer a platform for reconfigurable electronic functionalities beyond conventional dielectric gating. However, once released from epitaxial constraint and transferred directly onto metallic gates, the BaTiO ₃ (BTO) membranes under study preferentially adopt an in‐plane polarization configuration, suppressing out‐of‐plane ferroelectric coupling at room temperature. Here, we demonstrate that single‐layer MoS ₂ field‐effect transistors gated by 25 nm freestanding BTO exhibit excellent electrostatic control at room temperature, with subthreshold swings down to 85 mV dec ^{− 1} and high on/off ratios, yet negligible hysteresis, highlighting the effectiveness of depolarized BTO as an ultrahigh‐κ dielectric. Upon cooling, robust counter‐clockwise ferroelectric hysteresis emerges, with memory windows of ∼0.4 V, stable over 500 cycles and retention times exceeding 10 ⁵ s. Temperature‐dependent x‐ray diffraction reveals structural signatures consistent with the bulk phase transitions sequence of BTO and confirms a predominant in‐plane lattice orientation near room temperature. The combined electrical and structural analysis indicates that phase‐dependent polarization anisotropy, together with domain‐wall dynamics and interfacial screening processes, stabilizes an out‐of‐plane polarization component at low temperature in the rhombohedral and orthorhombic phases.

The integration of natural layered minerals into van der Waals heterostructures offers a scalable and earth-abundant route to high-performance 2D electronics. Here, we explore biotite, an ion-rich member of the mica family, as a multifunctional building block in ultrathin device architectures. Mechanically exfoliated biotite flakes are incorporated as gate dielectrics in monolayer MoS ₂ field-effect transistors, yielding low transfer hysteresis (20 mV) and field-effect mobilities around 10 cm ² V ⁻¹ s ⁻¹ in all-van der Waals configurations with graphite contacts. The same platform supports high-performance photodetection, with responsivities up to 392 AW ⁻¹ and rise times of ~20 ms. Biotite is also implemented as an active switching material in metal-insulator-metal memristors, where silver filament formation drives reproducible bipolar resistive switching across more than 10 ⁴ cycles with memory windows of 10 ² –10 ⁴ Ω. By inverting the electrode bias configuration, the same device transitions from non-volatile to volatile threshold switching, which is especially relevant for neuromorphic device applications. Switching voltages scale with flake thickness, reaching below 0.5 V for 6 nm devices. Together, these findings reveal biotite as a promising natural layered 2D dielectric, unlocking new device functionalities in 2D transistors and memristors.

Fabricating microelectronic devices for two-dimensional (2D) materials research is essential but often limited by the high cost and need for specialized facilities. This study establishes a practical method for cleaning and reusing substrates with pre-patterned electrodes. The cleaning protocol involves the use of an ultrasonic bath in warm N -methyl-2-pyrrolidone (NMP), enabling the removal of 2D materials without damaging the electrodes. Electrical measurements, Raman analysis, and Kelvin probe force microscopy measurements collectively confirm the feasibility of repeatedly reusing the same pre-patterned chip, showing that the cleaned regions exhibit no detectable Raman signatures of the transferred 2D material, retain a largely homogeneous surface-potential distribution, and preserve comparable electrical performance after reuse. By extending the lifetime of pre-patterned chips, this approach can reduce substrate consumption and lower the cost of 2D device prototyping.

Fabricating microelectronic devices for two-dimensional (2D) materials research is essential but often limited by the high cost and need for specialized facilities. This study presents an efficient and sustainable method for cleaning and reusing substrates with pre-patterned electrodes. The cleaning protocol involves the use of an ultrasonic bath in warm N-methyl-2-pyrrolidone (NMP), enabling the removal of 2D materials without damaging the electrodes. This method significantly reduces costs and encourages more responsible use of resources in 2D materials device fabrication.

Anisotropic 2D materials such as black phosphorus (BP), GeS or CrSBr, exhibit direction‐dependent optical and electronic properties that are highly desirable for polarization‐sensitive detection, waveguiding, and directionally tuned transport. However, scalable fabrication of large‐area films with preserved in‐plane crystallographic alignment remains a key challenge. Here, a roll‐to‐roll‐inspired mechanical exfoliation technique as a general, low‐cost, and scalable strategy to produce large‐area films of in‐plane anisotropic van der Waals nanosheets is presented. Polarized transmittance measurements confirm the presence of predominant optical anisotropy across centimeter‐scale areas, and scanning transmission electron microscopy (STEM) reveals that individual nanosheets exhibit consistent in‐plane orientation at the nanoscale. Furthermore, anisotropic electronic devices are fabricated and demonstrate that the films inherit the direction‐dependent conductivity of their constituent flakes. This method offers a broadly applicable route for integrating anisotropic nanosheets of 2D materials into scalable optoelectronic and sensing technologies.

A cost‐effective and flexible approach is presented to maskless photolithography using a commercial Liquid Crystal Display (LCD)‐based Masked Stereolithography Apparatus (MSLA) 3D printer. This method enables rapid and flexible patterning of photoresist‐coated silicon wafers without the need for traditional photomasks, as well as the fabrication of large‐area wafer‐scale electrode arrays, offering a highly accessible alternative for microdevice fabrication. The process achieves spatial resolution approaching 20 µm and is demonstrated in the fabrication of gold electrodes for two‐dimensional (2D) material‐based transistors. The electrodes are used to integrate MoS ₂ flakes, transferred via an all‐dry deterministic method to fabricate field effect transistors and photodetectors. The results confirm that LCD‐based lithography can produce high‐quality devices comparable to those fabricated with conventional photolithography equipment, making it an attractive solution for low‐cost, high‐precision microfabrication.

The integration of high-dielectric-constant (high-κ) materials with two-dimensional (2D) semiconductors is promising to overcome performance limitations and reach their full theoretical potential. Here, we show that naturally occurring phlogopite mica, exfoliated into ultrathin flakes, can serve as a robust high-κ dielectric layer for transition metal dichalcogenide-based 2D electronics and optoelectronics. The wide band gap (∼4.8 eV), high dielectric constant (∼11), and large breakdown field (>10 MV cm^-1) of phlogopite enable transistors with subthreshold swings down to 100 mV dec^-1, minimal hysteresis (∼30-60 mV), and interface trap densities comparable to those of state-of-the-art oxide dielectrics. Moreover, phototransistors built upon monolayer molybdenum disulfide (MoS₂) and phlogopite exhibit responsivities up to 3.3 × 10⁴ AW^-1 and detectivities close to 10¹⁰ Jones, surpassing devices based on conventional gate insulators. We further demonstrate the versatility of this natural dielectric by integrating phlogopite/MoS₂ heterostructures into NMOS inverters, showcasing robust voltage gains and low-voltage operation. Our findings establish phlogopite as a promising, earth-abundant dielectric for next-generation 2D transistor technologies and high-performance photodetection.

We present adaptive, strain-engineered photodetectors based on 2D semiconductors. Our devices present a footprint of only about 40 × 20 μm², and they are fabricated on transparent polypropylene substrates and integrate lithographically designed microheaters that induce controllable biaxial strain via thermal actuation, thus leading to a red shift in their spectral response. This strain-induced tunability is combined with a machine learning-based spectral reconstruction approach, where a neural network is trained on an extensive data set of synthetic spectra and corresponding photocurrents generated from measured device responsivities under varying strain conditions. Although the system demonstrates spectral reconstruction over a relatively narrow range, it provides a compelling proof-of-concept for a miniaturized adaptive spectrometer.

Two-dimensional van der Waals heterostructures offer a versatile platform for developing multifunctional optoelectronic devices, as their tuneable electronic and optical properties enable a wide range of applications. Among them, WS₂/PdSe₂ heterostructures exhibit attractive features, making them promising candidates for the realisation of broadband photodetectors and pressure optoelectronic sensors. In this study, WS₂/PdSe₂ heterostructures were fabricated and electrically characterised under different environmental and light conditions. WS₂/PdSe₂ heterostructures exhibit n-type conduction with an impressive ON/OFF current ratio up to 10⁸, demonstrating their suitability for high-performance electronic devices. Their electrical properties were extensively investigated under different pressure conditions, from ambient pressure to high vacuum (10³–10⁻⁴ mbar), both in the dark and under illumination. The results reveal that the adsorption and desorption of water and oxygen molecules on the materials’ surface play a crucial role in modulating the electrical response of the WS₂/PdSe₂ heterostructure. Analysis of the light response in the visible spectrum reveals a responsivity of up to 1.2 A W⁻¹ at a wavelength of 620 nm. WS₂/PdSe₂-based devices were further tested as pressure optoelectronic sensors, monitoring the photocurrent evolution during transitions between high vacuum and ambient pressure. These findings open the way for various applications in the field of optoelectronics and sensing.