James G. Partridge

Neuromorphic signal processing has been performed by lateral metal‐semiconductor‐metal photodetectors supported on wide‐bandgap thin‐film amorphous gallium oxide (a‐Ga ₂ O ₃ ). Paired pulse facilitation (PPF) observed in the photocurrents of the devices was attributed to charge trapping and de‐trapping in the a‐Ga ₂ O ₃ and depended systematically on the amplitude, duration, and interval of the pulsed ultraviolet‐C (UVC) input. Four‐bit UVC binary pulse sequences of optimized power were input to the device, and these produced separable electrical output currents (conductance states), measured after the pulse sequences. A simple resistor‐capacitor (RC) equivalent circuit model replicated the neuromorphic device responses, and this model was used with and incorporated into single‐ and multi‐node reservoir computers. Classification of electrocardiograms (ECGs) was performed in simulations using an RC model whose parameters were extracted from and validated against measured device responses. The single‐node reservoir with virtual nodes achieved limited accuracy in classification depending on the heartbeat type, while the composite multi‐node reservoir (consisting of eight RC sub‐reservoirs with different time constants) exhibited significantly improved classification capability, achieving an average accuracy of ∼95%. These results highlight the potential of the a‐Ga ₂ O ₃ detectors as artificial synapses for neuromorphic signal processing and temporal pattern recognition.

Transactive response DNA binding protein (TDP-43) is a biomarker for neurodegenerative diseases, including motor neuron disease. We report an electrolyte channel neuromorphic biosensor that detects the presence of TDP-43 antigen at physiologically realistic concentrations within HEPES buffer solution. Detection occurs when the target antigen binds to a TDP-43 antibody covalently immobilized on a thin polymer gate insulating layer exposed to the solution. A current between source and drain electrodes is passed through the electrolyte and causes electric double layers to form at the source, gate, and drain electrodes in the device. The formation/decay dynamics of these double layers result in a current output resembling a spiking postsynaptic signal. The postsynaptic signal is sensitive, in several ways, to the presence of biomolecules. The paired-pulse index, postsynaptic current decay, and charge passed in tailored pulse sequences enable detection of TDP-43 antigen–antibody binding. The device is simple in architecture, easy to fabricate, and, thus, suitable for disposable use. The results suggest potential for application in population screening by monitoring TDP-43 concentration within blood or cerebrospinal fluid samples.

We present the discovery of a co-operative effect between water and oxygen molecules on the (110) surfaces of perfectly square SnO₂ nanotubes that results in a dramatic reduction in their persistent photoconductivity to above-bandgap UV radiation.

The ultraviolet photo-responses of metal–semiconductor–metal (MSM) devices formed on RF sputtered thin film gallium oxide have been investigated as a function of the stoichiometry and crystallinity of the films and the ambient conditions during illumination. Stoichiometry was altered via the oxygen pressure during growth, and crystallinity was altered via the growth surface; amorphous Ga2O3 films were grown on Si3N4, while polycrystalline β-Ga2O3 films were grown on a-plane sapphire. Interdigitated Pt–Ga2O3–Pt MSM photodetectors were fabricated on the Ga2O3 films, and selective UV-C detection was consistently observed. Under an incident optical power of 0.09 mW/cm2, on/off current ratios (IUV-C:Idark) in the best devices exceeded 103:1. Other figures of merit included responsivity as high as 2.0 A/W and detectivity up to 1.2 × 1013 Jones. Operation in air of 90% relative humidity produced the fastest UV-C response times but the highest dark current, attributed to interaction between water and oxygen surface adsorbates, which affected surface band-bending. Comparison with encapsulated devices enabled identification of trap and surface adsorbate limited components of the device response and recovery. Finally, a self-powered (zero bias) interdigitated Pt–Ga2O3–C UV-C photodetector was tested, and this device exhibited a responsivity of 1.1 × 10−2 A/W and a detectivity of 3.7 × 1010 Jones under 0.09 mW/cm2 UV-C illumination.

The nitrogen‐vacancy (NV) center is a photoluminescent defect in diamond that exists in different charge states, NV ^‐ and NV ⁰ , that are sensitive to the NV's nanoscale environment. Here, all‐optical voltage sensing with NV centers in fluorescent nanodiamonds (FNDs) is demonstrated in a solid‐state device based on electric field‐induced NV charge state modulation. More than 95% of FNDs integrated into a polymer‐based capacitor device show a transient increase in NV ⁻ PL intensity up to 31% within 0.1 ms after application of an external voltage, accompanied by a simultaneous decrease in NV ⁰ PL. The NV ⁻ PL signal increases with increasing electric field from 0 to 619 kV cm ⁻¹ . The best electric field sensitivity for a single FND is 18 V cm ⁻¹ Hz ^−½ . The NV charge state photodynamics are investigated on the millisecond timescale. The change in NV PL is found to strongly depend on the rate of photoexcitation. A model is proposed that qualitatively explains the results based on an electric field‐induced redistribution of photoexcited electrons from substitutional nitrogen to NV centers, leading to a transient conversion of NV ⁰ to NV ⁻ centers. These results contribute to the development of FNDs as reliable, all‐optical, nanoscale electric field sensors in solid‐state systems.

Analytical models for investigating Metal–Semiconductor (M–S) ohmic contacts in test structures have conventionally included resistive-only contact interfaces. Given that M–S contacts are fundamentally governed by electron tunnelling across the potential energy barrier at the M–S interface, this simplified approach may result in misinterpretation. This paper describes, in detail, a novel Resistor-to-Schottky (RSB) barrier analytical model that enables a more in-depth exploration of the physics underlying ohmic contacts. The proposed model is analysed and compared with models constructed using the semiconductor device simulator tool TCAD. The study reveals significant differences in outcomes when employing the RSB model rather than the conventional Transmission Line model and contributes to a more comprehensive understanding of M–S ohmic contacts in test structures.

We have synthesized hydrogenated and deuterated amorphous carbon materials that have a density, 2.7 ± 0.1 g/cm3, consistent with almost entirely tetrahedral bonding. In hydrogen-free tetrahedral amorphous carbon, the presence of a minority of sp2 bonded atoms leads to localized states that could be passivated with hydrogen by analogy with hydrogenated amorphous silicon. Neutron diffraction analysis demonstrated that the local bonding environment is consistent with ab initio models of high density hydrogenated tetrahedral amorphous carbon and with the related tetrahedral molecular structure neopentane. The optical bandgap of our material, 4.5 eV, is close to the bandgap in the density of states determined by scanning tunneling spectroscopy (4.3 eV). This bandgap is considerably larger than that of hydrogen-free tetrahedral amorphous carbon, confirming that passivation of sp2 associated tail-states has occurred. Both the structural and electronic measurements are consistent with a model in which the tetrahedrally bonded carbon regions are terminated by hydrogen, causing hopping conductivity to dominate.

Layered chiral magnets with broken spatial inversion symmetry (SIS) enable chiral spin textures to occur in atomically thin layers. However, most layered materials retain SIS during their crystallization. Here, we demonstrate that SIS can be broken in a layered transition metal dichalcogenide TaS₂ by intercalating Mn atoms. A chiral magnetic phase in Mn_1/3TaS₂ has, thus, been realized. This phase enables a nonzero Dzyaloshinskii–Moriya interaction, which in turn gives rise to large topological Hall effects (THEs) below 50 K. Both the ferromagnetism and THE can be tuned at low temperatures by modulating the carrier density via a protonic gate. Measured at 20 K with V_g = −4.7 V applied to the gate and electron doping density of 1.7 × 10²² cm⁻³, the maximum THE was almost double that recorded with no gate voltage applied. By further reducing the sample thicknesses, both the Curie temperature T_c and the longitudinal magnetoresistance can be significantly modulated. This is consistent with the theory of critical behavior. Our work highlights the ability to control both magnetism and chiral spin textures in Mn_1/3TaS₂ nanoflakes. Applying this discovery may lead to a variety of practical van der Waals heterostructure devices.