Mid-infrared photonics enables a large number of applications in chemical sensing, medical diagnostics, environmental monitoring, and optical communications, but widespread adoption of this technology is hindered by the lack of compact, CMOS-compatible photodetectors capable of room-temperature operation. This work presents an Al-Si-Al planar heterostructure acting as a plasmonic photodetector that leverages an electrostatically tunable Schottky barrier to detect sub-bandgap mid-infrared photons (5-7 μm) in silicon with a responsivity ∼0.9 mA/W, <0.4 mA/cm2 dark current density, and a broad and uniform spectral response that does not require cooling. Fast internal dynamics with time constants of 3.7 ps and 1.4 ns are observed at 1560 nm, suggesting the potential for high-speed operation. Our monolithic and crystalline Al-Si heterostructure features abrupt interfaces obtained without epitaxy, ensuring CMOS compatibility and scalability. We demonstrate the potential of this device for mid-infrared sensing by detecting and spectrally characterizing water molecule absorption lines. By leveraging plasmonically generated hot-carriers combined with the inherent scalability of silicon-based technology, our work opens new pathways for cost-effective and high-speed infrared photodetectors suitable for next-generation integrated photonic systems.

Water is omnipresent in nanoscale systems, yet its collective dynamics and impact on emerging electronics remain poorly understood. Here, we investigate the role of water molecule dynamics in the ferroelectric response of graphene nanoribbon devices. Our findings demonstrate that the collective dynamics of water molecules stabilize the ferroelectric effect. We find that a minimum bi-layer thickness is required for the temperature stability of the ferroelectric effect. In contrast, mono-layer ribbons show a 70% shrinkage of the hysteresis window between 120 and 400 K. Using a combination of electrical transport measurements and molecular dynamics simulations, we conclude that water molecules bridging between graphene nanoribbon layers stabilize the formation of water clusters via intermolecular Coulomb interactions, driving a robust ferroelectric behavior and remnant polarization observed at the device level. This work lays the foundations for exploiting water dynamics in next-generation ferroelectric heterostructures, with direct implications for neuromorphic computing and memory devices.

Germanium (Ge) is recognized as a highly promising substrate for a broad spectrum of electronic, optical, and quantum applications, owing to its exceptional properties, including high charge carrier mobility, strong spin-orbit coupling, and its behavior as a quasi-direct semiconductor. However, the electron transfer effect in Ge, similar to the Gunn effect in GaAs, which induces negative differential resistance, has received relatively little attention thus far. This is likely due to the requirement for a well-defined material system and device architecture for its realization and usually at low temperatures.

Ge-based bolometers are widely used for near-infrared detection for a broad range of applications such as thermography or chemical analysis. Notably, for the thermometers used in bolometers, integration, scaling, and sensitivity as well as functionality are of utmost importance. In this regard, Ge exhibits a favorable temperature sensitivity due to the relatively low bandgap and a high intrinsic charge carrier concentration. In this work, we demonstrate a nanoscale thermometer for bolometric applications on the base of Ge-on-insulator nanosheets with monolithic Al source/drain contacts envisioned for future wafer-scale integration. Importantly, electrostatic gating of the nanosheets allows the operation as a Schottky barrier field-effect transistor, providing tunability of the energy landscape and the involved charge carrier injection in interaction with the metal-semiconductor junctions. In this approach, the top-gate electrode and drain contact are connected, thus resembling a two-terminal device with bias-tunable temperature coefficient of resistance (TCR) values between 0%/K and −3.8%/K in the temperature range of T = 125–150 K. Moreover, in this configuration, even at room temperature, a maximum TCR value of −1.6%/K is achieved. The bias-tunable TCR exhibited in these devices may enable advanced concepts for room temperature bolometric applications and allow co-integration with nanoelectronics.

Control of water ice formation on surfaces is of key technological and economic importance, but the fundamental understanding of ice nucleation and growth mechanisms and the design of surfaces for controlling water freezing behaviour remain incomplete. Graphene is a two-dimensional (2D) material that has been extensively studied for its peculiar wetting properties with liquid water incl. a heavily debated wetting transparency. Furthermore, graphene is the parent structure of soot particles that are heavily implicated as nuclei in atmospheric ice formation and consequently graphene is often used as a model surface for computational ice nucleation studies. Despite this, to date experimental reports on ice formation on scalable graphene films remain missing. Towards filling this gap, we here report on the water freezing behaviour on scalably grown chemical vapour deposited (CVD) graphene films on application-relevant polycrystalline copper (Cu). We find that as-grown CVD graphene on Cu can be (as we term it) freezing transparent i.e. the graphene presence does not change the freezing temperature curves of liquid water to solid ice on Cu in our measurements. Such freezing transparency has to date not been considered. We also show that chemical functionalization of the graphene films can result in controllable changes to the freezing behaviour to lower/higher temperatures and that also the observed freezing transparency can be lifted via functionalization. Our work thereby introduces the concept of freezing transparency of graphene on a metal support and also introduces scalable CVD graphene/Cu as an ultimately thin platform towards control of ice nucleation behaviour on a technologically highly relevant metal.

In this work, we explore the effect of ultrahigh tensile strain on electrical transport properties of silicon. By integrating vapor-liquid-solid-grown nanowires into a micromechanical straining device, we demonstrate uniaxial tensile strain levels up to 9.5%. Thereby the triply degenerated phonon dispersion relation at the Γ-point of silicon disentangle and the longitudinal phonon modes are used to precisely determine the extent of mechanical strain. Simultaneous electrical transport measurements showed a significant enhancement in the electrical conductance. Aside from considerable reduction of the Si bulk resistivity due to strain-induced band gap narrowing, comparison with quasi-particle GW calculations further reveals that the effective Schottky barrier height at the electrical contacts undergoes a substantial reduction. For these reasons, nanowire devices with ultrastrained channels may be promising candidates for future applications of high-performance silicon-based devices.

In this paper, we exploit the nanometer scale properties of Ge based Schottky barrier field-effect transistors (SBFETs) with monocrystalline Al contacts, fusing the concept of reconfiguration and negative differential resistance (NDR) in a single device. Temperature dependent bias spectroscopy is used to investigate the electronic transport in the NDR regime leading to profound understanding of the involved physical transport mechanisms. Importantly, the obtained SBFETs are capable of shifting the NDR-peak by electrostatic gating. Thus, a cascode of such devices results in overlapping NDR regions, which allows the realization of new circuit topologies beyond the capabilities of conventional CMOS.

2D materials provide a rapidly expanding platform for the observation of novel physical phenomena and for the realization of cutting-edge optoelectronic devices. In addition to their peculiar individual characteristics, 2D materials can be stacked into complex van der Waals heterostructures, greatly expanding their potential. Moreover, thanks to their excellent stretchability, strain can be used as a powerful control knob to tune or boost many of their properties. Here, we present a novel method to reliably and repeatedly apply a high uniaxial tensile strain to suspended van der Waals heterostructures. The reported device is engineered starting from a silicon-on-insulator substrate, allowing for the realization of suspended silicon beams that can amplify the applied strain. The strain module functionality is demonstrated using single- and double-layer graphene layers stacked with a multilayered hexagonal boron nitride flake. The heterostructures can be uniaxially strained, respectively, up to ∼1.2% and ∼1.8%.

In this work, Al2O3-passivated, monolithic, and crystalline Al–Ge–Al heterostructure nanowire field effect transistors (FETs) with Ge channel lengths ranging from 18 to 826 nm are analyzed from a low-frequency noise perspective. 1/f and random telegraph noise (RTN) are analyzed in an accumulation mode, where the hole channel is formed by applying a back-gate potential VG. The normalized power spectral density of drain current fluctuations of 1/f noise (SID/ID2) at medium currents follows nearly an 1/ID trend. 1/f noise is analyzed within both the mobility and carrier number fluctuation models (MFM and CNFM), respectively. Taking the MFM into account, the Hooge noise parameter α spreads in the interval of 1.5 × 10−4 to 4 × 10−2, with lower values for shorter devices. Using the same data and the CNFM, the density of interface states Dit in the Al2O3/GexOy/Ge system was estimated using the transconductance extracted from the quasi-static transfer I/V characteristics. The extracted Dit values range from 5 × 109 to 3 × 1012 cm−2 eV−1. Contact noise has also been observed in some devices at high currents. RTN analyzed in time domain exhibits a relative RTN amplitude in the 0.3%–20% range. Capture and emission time constants as a function of VG exhibit a typical behavior for metal oxide semiconductor FETs. The extracted noise parameters are comparable with Ge and III–V nanodevices of top-down and bottom-up technologies.

The generation of hot carriers by Landau damping or chemical interface damping of plasmons is of particular interest to the fundamental aspects of extreme light-matter interactions. Hot charge carriers can be transferred to an attached acceptor for photochemical or photovoltaic energy conversion. However, these lose their excess energy and relax to thermal equilibrium within picoseconds and it is difficult to extract useful work thereof with thermodynamic efficiencies that are of interest for practical devices. Without a detailed understanding of the underlying plasmon decay processes and transfer mechanisms, proper material matching and design considerations for novel plasmonic devices are extremely challenging. Here, a multifunctional AlSiAl heterostructure device with tunable Schottky barriers is presented to control plasmon-induced hot carrier injection at an abrupt metal-semiconductor interface. Light absorption, surface plasmon generation, and separation of hot carriers arising from the non-radiative decay of surface plasmons are realized in a monolithic Schottky barrier field effect transistor. Aside from barrier modulation, a virtual p-n junction can be emulated in the semiconductor channel with the distinct merit that carrier concentration and polarity are tunable by electrostatic gating. The investigations are carried out with a view to possible use for CMOS-compatible plasmonic photovoltaics, with versatile implementations for autonomous nanosystems.

The interaction mechanisms of water with nanoscale geometries remain poorly understood. This study focuses on behaviour of water clusters under varying external electric fields with a particular focus on molecular ferroelectric devices. We employ a two-fold approach, combining experiments with large-scale molecular dynamics simulations on graphene nanoribbon field effect transistors. We show that bilayer graphene nanoribbons provide stable anchoring of water clusters on the oxygenated edges, resulting in a ferroelectric effect. A molecular dynamics model is then used to investigate water cluster behaviour under varying external electric fields. Finally, we show that these nanoribbons exhibit significant and persistent remanent fields that can be employed in ferroelectric heterostructures and neuromorphic circuits.

Abstract With the emerging transition from programmed to learning computing, traditional electronic ICs are unlikely to be able to match the massive perceptual data that will need to be processed in real-time. Neuromorphic engineering may surmount the von Neumann bottleneck by creating high-performance hardware for distributed and parallel processing with low power consumption. Nowadays, most of high-efficiency neuromorphic hardware is based on artificial synapsis and neuronal devices, utilizingelectrical or optical platforms and thus correspondingly limited in terms of bandwidth or footprint, respectively. In this work, we introduce a plasmon-stimulated synaptic transistor concept that may combine the high bandwidth of a photonic network with the compactness of electronic circuits. The actual synaptic characteristic, including excitatory postsynaptic current and paired-pulse facilitation, is achieved utilizing charge trapping effects to control the conductivity of a monolithic Al-Ge-Al Schottky barrier field-effect transistor. The population of traps is thereby controlled by hot electrons arising from the non-radiative decay of deliberately applied surface plasmon polariton spikes. The temporal dynamics of the trapping process and thus the plasticity of the synaptic transistor can be set by the geometry and operation mode of the synaptic transistor as well as the intensity and duration of the plasmon spikes.

Conventional field‐effect transistor (FET) concepts are limited to static electrical functions and demand extraordinarily steep and reproducible doping concentration gradients. Reaching the physical limits of scaling, doping‐free reconfigurable field‐effect transistors (RFETs) capable of dynamically altering the device operation between p‐ or n‐type, even during runtime, are emerging device concepts. In this respect, Ge has been identified as a promising channel material to enable reduction of power consumption and switching delay of RFETs. Nevertheless, its use has been limited to simulations and bottom‐up demonstrators not compatible with complex circuit technology. In this work, a deterministic top‐down fabrication scheme is demonstrated to realize a Ge‐based RFET architecture and exploring realizations with three independent gates. Polarity control and leakage current suppression are enabled by the specific injection of charge carriers through gated Al‐Ge heterojunctions and the introduction of a blocking electrostatic energy barrier. Further, the choice of monolithic Al/Ge contacts alleviates process variability compared to Ni‐germanide contacts presenting a top‐down technology platform for Ge‐based RFETs. Our device concept is a first step toward future integrated high‐performance and low‐power reconfigurable circuits, providing a platform for future energy‐efficient systems as well as hardware security integrated circuits.

Near-infrared detection is widely used for nondestructive and non-contact inspections in various areas, including thermography, environmental and chemical analysis as well as food and medical diagnoses. Common room temperature bolometer-type infrared sensors are based on architectures in the mu m range, limiting miniaturization for future highly integrated 'More than Moore' concepts. In this work, we present a first principle study on a highly scalable and CMOS compatible bolometer-type detector utilizing Ge nanowires as the thermal sensitive element. For this approach, we implemented the Ge nanowires on top of a low thermal conducting and highly absorptive membrane as a near infrared (IR) sensor element. We adopted a freestanding membrane coated with an impedance matched platinum absorber demonstrating wavelength independent absorptivity of 50% in the near to mid IR regime. The electrical characteristics of the device were measured depending on temperature and biasing conditions. A strong dependence of the resistance on the temperature was shown with a maximum temperature coefficient of resistance of -0.07 K-1 at T = 100 K. Heat transport simulations using COMSOL were used to optimize the responsivity and temporal response, which are in good agreement with the experimental results. Further, lock-in measurements were used to benchmark the bolometer device at room temperature with respect to detectivity and noise equivalent power. Finally, we demonstrated that by operating the bolometer with a network of parallel nanowires, both detectivity and noise equivalent power can be effectively improved.

Silicene is one of the most promising 2D materials for the realization of next-generation electronic devices, owing to its high carrier mobility and bandgap tunability through the imposition of an external electric field. To exploit this fundamental characteristic, it is necessary to engineer an insulating layer that can be interfaced directly to silicene without perturbing its bidimensional nature. At the same time, this insulating layer should exhibit low leakage currents even when highly scaled, to fully exploit the advantages of using a 2D material at the core of the device. CaF$_2$ is known to form a quasi van der Waals interface with 2D materials, as well as to maintain its insulating properties even at ultrathin scales. Here we investigate the growth of CaF$_2$ layers on silicene by molecular beam epitaxy: diffraction images show that CaF$_2$ grows epitaxially on silicene/Ag(111), with its domains fully aligned to the 2D silicon lattice. In-situ XPS analysis evidences that no changes in the chemical state of the silicon atoms can be detected upon CaF$_2$ deposition, excluding the formation of covalent bonds between Ca, F and Si. Polarized Raman analysis shows that silicene undergoes a structural change upon interaction with CaF$_2$, however retaining a bidimensional character and without transitioning to a sp3-hybridized, bulk-like silicon.

Many of graphene's remarkable properties arise from its linear dispersion of the electronic states, forming a Dirac cone at the K points of the Brillouin zone. Silicene, the 2D allotrope of silicon, is also predicted to show a similar electronic band structure, with the addition of a tunable bandgap, induced by spin-orbit coupling. Because of these outstanding electronic properties, silicene is considered as a promising building block for next-generation electronic devices. Recently, it has been shown that silicene grown on Au(111) still possesses a Dirac cone, despite the interaction with the substrate. Here, to fully characterize the structure of this 2D material, we investigate the vibrational spectrum of a monolayer silicene grown on Au(111) by polarized Raman spectroscopy. To enable a detailed ex situ investigation, we passivated the silicene on Au(111) by encapsulating it under few layers hBN or graphene flakes. The observed spectrum is characterized by vibrational modes that are strongly red-shifted with respect to the ones expected for freestanding silicene. By comparing low-energy electron diffraction (LEED) patterns and Raman results with first-principles calculations, we show that the vibrational modes indicate a highly (>7%) biaxially strained silicene phase.

To establish high-bandwidth chip-to-chip interconnects in optoelectronic integrated circuits, requires high-performance photon emitters and signal receiving components. Regarding the photodetector, fast device concepts like Schottky junction devices, large carrier mobility materials and shrinking the channel length will enable higher operation speed. However, integrating photodetectors in highly scaled ICs technologies is challenging due to the efficiency-speed trade-off. Here, we report a scalable and CMOS-compatible approach for an ultra-scaled germanium (Ge) based photodetector with tunable polarity. The photodetector is composed of a Ge Schottky barrier field effect transistor with monolithic aluminum (Al) source/drain contacts, offering plasmon assisted and polarization-resolved photodetection. The ultra-scaled Ge photodetector with a channel length of only 200 nm shows high responsivity of about R = 424 A W−1 and a maximum polarization sensitivity ratio of TM/TE = 11.

Low-dimensional Ge is perceived as a promising building block for emerging optoelectronic devices. Here, we present a wafer-scale platform technology enabling monolithic Al-Ge-Al nanostructures fabricated by a thermally induced Al-Ge exchange reaction. Transmission electron microscopy confirmed the purity and crystallinity of the formed Al segments with an abrupt interface to the remaining Ge segment. In good agreement with the theoretical value of bulk Al-Ge Schottky junctions, a barrier height of 200 ± 20 meV was determined. Photoluminescence and μ-Raman measurements proved the optical quality of the Ge channel embedded in the monolithic Al-Ge-Al heterostructure. Together with the wafer-scale accessibility, the proposed fabrication scheme may give rise to the development of key components of a broad spectrum of emerging Ge-based devices requiring monolithic metal-semiconductor-metal heterostructures with high-quality interfaces.