ACS Applied Electronic Materials最新文献

We present a sub-μm spatial resolution Raman mapping study of strain-engineered germanium (Ge) micro-bridge structures, fabricated on a 220 nm silicon-on-insulator (Ge-SOI). Revision of the analytical geometric-strain model for such structures, to account for partial under-etching, provides good agreement with the uniaxial tensile strain, inferred from Raman peak shifts, over a wide range of geometries. The additional mechanical support, provided by the partial under-etch, leads to improved yield while still achieving a significant degree of up to ∼2.5% strain. We reveal that even relatively small variations in geometry lead to inhomogeneous strain profiles, including regions of locally enhanced strain at points of high radii of curvature. Our observation of a strongly correlated Raman intensity–strain relation is due to the strain-shifted E₁ critical point coming into resonance with our 1.96 eV pump laser. A simple model for this provides an estimate of the electron–hole lifetime, τ_e–h ∼35 fs, and exciton binding energy, E_b ∼15 meV, which are consistent with efficient coupling of the Raman process to quasi-two dimensional (2D) van Hove (vH) excitons in a region of the Ge band structure exhibiting nonparabolicity and a saddle-point topology with a logarithmic joint density of states (JDOS).

Two-dimensional (2D) semiconductors are sensitive to mechanical stress due to their atomic thickness, weak van der Waals interfaces, and ultra-high sensitivity to the surrounding dielectric environment. While the effects of in-plane strain in transition-metal dichalcogenides (TMDs) have been extensively studied, the influence of locally generated out-of-plane compressive stress—commonly introduced during fabrication, packaging, and 3D integration—remains largely unexplored. Here, we apply controlled GPa-level perpendicular stress to monolayer WS₂ field-effect transistors (FETs) using a nanoindenter integrated with in situ electrical measurements. Vertical compression reduces the on-state current by up to ∼74.2%, with partial recovery after unloading. Finite element modeling and electro-mechanical TCAD simulations indicate that mobility degradation is dominated by stress-induced enhancement of WS₂–oxide interfacial coupling rather than intrinsic band-structure modification. Photoluminescence and Raman spectroscopy reveal that the WS₂ lattice remains intact and show ∼0.5% relaxation of intrinsic tensile strain. These results establish a quantitative framework for understanding vertical-stress-driven transport degradation and highlight out-of-plane compression as an emerging reliability challenge for 2D materials in future stacked and heterogeneous device architectures.

This paper presents a dual-tube actuated plastic optical fiber (POF) end-face coupling sensor integrated into a dual-channel mattress for non-invasive monitoring of thoracic and abdominal respiratory motions. The sensing unit employs a three-segment fiber architecture within a nested tube assembly: the middle POF segment is embedded in a flexible inner tube, while the input and output fibers are inserted into the ends of this inner tube with well-defined gaps from the middle fiber’s end faces. This inner assembly is further sheathed in a rigid outer tube. When subjected to cyclic compression from human respiration, the rigid outer tube bears the pressure and drives the middle segment to undergo overall vertical displacement, while the input/output fibers remain stationary. This induces simultaneous lateral misalignment at both end-face pairs (input–middle and middle–output), which magnifies the change in optical coupling efficiency and results in enhanced output intensity variations with signal stability. The transmission loss of the sensor exhibited good linearity with applied force over the range of 0–8 N, yielding R² = 0.9824 and a sensitivity of 1.362 dB/N. In dynamic tests with simulated respiratory signals, real-time extraction of respiratory rate and amplitude using a peak detection algorithm gave maximum relative errors of 2.6% and 5.2%, respectively. After integration into the mattress, the system was evaluated in a human-subject experiment during respiratory measurements. The thoracic and abdominal channels showed high measurement accuracy, close agreement with a reference respiratory belt, and robust signal quality. Furthermore, several simulated abnormal respiratory states were recorded, and the acquired waveforms captured key features of these abnormal respiratory patterns. These results demonstrate that the proposed mattress can provide respiratory rate, amplitude, and thoracoabdominal phase difference data, offering multidimensional parameters for the assessment of abnormal respiratory patterns.

The widespread adoption of flexible electronics has driven the development of all-solid-state energy storage materials. However, the limited single-functionality and unsatisfactory low-temperature tolerance of conventional hydrogel electrolytes remain critical challenges for wearable applications. Thus, a Cu@Fe₃O₄-PANI/PVA/PA/LiCl (CPPALi) hydrogel was fabricated via a freeze–thaw approach. Through hydrogen bonding, physical cross-linking, and electrostatic interactions, the one-pot incorporation of PA, Cu@Fe₃O₄-PANI (CFP) hybrids, and LiCl significantly enhanced the conductivity, water retention, and adhesion, and anti-freezing performance. The above as-obtained CPPALi_0.6 hydrogel strain sensor exhibited linear strain sensing characteristics (GF = 1.95) for human motion monitoring with high conductivity (2.74 S m^–1) and outstanding freeze resistance (–47 °C) and good water retention capacity. The all-solid-state CPPALi_0.6 supercapacitor devices were assembled with CPPALi_0.6 hydrogel as electrolyte and activated carbon as electrodes. Importantly, they delivered a specific capacitance of 310.8 mF cm^–2 at 1 mA cm^–2, achieved an energy density of 45.6 μWh cm^–2 at a power density of 255.1 μW cm^–2, and retained stable electrochemical stability even at –30 °C. Series-connected CPPALi_0.6 supercapacitor devices could power a light bulb and drive a timer for 60 min. After 3000 charge–discharge cycles, the capacitance retention remained as high as 94.4%, and the performance remained stable after 21 days. Thus, this multifunctional hydrogel integrates structural stability, adhesion, anti-freezing, energy storage, and sensing functionalities, demonstrating significant potential in the field of wearable all-solid-state electronic devices.

MXenes have demonstrated strong potential across a wide range of applications due to their outstanding properties, evidenced by the impressive performance of MXene-based devices reported to date. As the field moves toward commercialization, identifying methods and technologies compatible with scalable manufacturing has become increasingly important. In this context, direct-write printing has emerged as a transformative approach in printed and flexible electronics because it enables the deposition of functional metallic, semiconducting, and dielectric films with controlled thickness from tailored inks. Printing is also cost-effective because it simplifies processing and reduces infrastructure and logistical requirements. Printing is especially attractive for wearable devices because it can produce thin films on both rigid and flexible substrates. Although researchers have prepared MXene active layers using a wide variety of techniques, direct-write printing has shown considerable promise in recent studies. This spotlight article highlights recent advances in MXene applications in energy storage and harvesting, electromagnetic interference shielding, and antennas, along with background on ink formulation and thin-film fabrication using common printing methods.

The relentless pursuit of higher efficiency, power density, and temperature capability in power electronics has positioned 4H-silicon carbide (4H-SiC) as a cornerstone semiconductor for next-generation devices. While the existence of a native SiO₂ layer had facilitated the development of 4H-SiC metal-oxide-semiconductor (MOS) technology, this insulator was ultimately identified as a constraint on its ultimate performance. The significant dielectric constant (k) mismatch between SiO₂ (k = 3.9) and 4H-SiC (k = 9.7) results in a much higher electric field within the oxide, thereby limiting the full exploitation of the high critical field of 4H-SiC. Furthermore, the inherently high interface trap density (D_it) at the SiO₂/SiC interface severely degraded channel mobility and device reliability. This review comprehensively charted the trajectory of advanced high-k passivation layers designed to surmount these fundamental limitations. This review presented a critical assessment of a wide spectrum of alternative dielectrics, including Al₂O₃, AlN, HfO₂, ZrO₂, and rare-earth oxides, based on stringent criteria such as band alignment, thermodynamic stability, and interface quality. The pivotal role of post-deposition annealing in passivating interface states and modulating electrical properties was thoroughly examined. By synthesizing the current state of the art and highlighting emerging materials and interface engineering strategies, this review provided a roadmap for the development of robust high-k dielectrics on 4H-SiC, which is crucial for unlocking the full potential of ultra-high-voltage, high-temperature, and radiation-hardened power devices.

The photodetection capabilities of RF sputtered amorphous thin-film gallium oxide have been studied as a function of their growth temperature. Specifically, X-ray photoelectron spectroscopy (XPS) and dark/UV-C illuminated temperature-dependent current–voltage measurements were used to reveal the relationships among growth temperature, stoichiometry, and photoresponse characteristics. XPS O 1s analysis revealed that an optimum growth temperature of 600 °C yielded the lowest concentration of oxygen vacancies. Devices on this film exhibited the best overall photosensitivity to 254 nm UV-C light, with the highest responsivity (R = 13 A/W) and specific detectivity (D^* = 3.7 × 10¹³ Jones) alongside fast transient response times (τ_r ∼ 0.51 s, τ_d ∼ 0.16 s). Lower growth temperatures resulted in films that exhibited increased persistent photoconductivity and proved thermally unstable, failing to recover their original characteristics after heating to 200 °C. Increasing the growth temperature above 600 °C caused increased oxygen deficiency in the films when compared with films grown at 600 °C, likely due to increased out-diffusion of oxygen during deposition. These findings demonstrate that cost-effective, scalable RF sputtering at an optimized growth temperature can produce amorphous gallium oxide with comparable UV-C sensitivity to that achieved with more complex deposition methods.

Ion irradiation offers a generalizable route for engineering functional materials through defect formation. Here, we demonstrate robust optical memory in GaScN thin films enabled by low-energy Ar⁺ ion irradiation. The irradiation-induced defect states give rise to persistent photoconductivity and support a range of brain-inspired functionalities, including synaptic plasticity, activity-dependent memory transition, and higher-order learning. The cumulative photoresponse further enables optoelectronic logic operations, including AND and OR Boolean functions. These results establish ion irradiation as an effective strategy for realizing optical memory in nitrides, providing a versatile platform for programmable neuromorphic optoelectronics.

Location-selective engineering of chemically identical areas of a complex substrate by the deposition of several different self-assembled monolayers (SAMs) represents a challenge of interfacial nanotechnology. These areas cannot be distinguished by tailoring the anchoring group of the different SAM-forming molecules, since this group, dictated by surface chemistry, should be the same for all these molecules. However, as shown in the present study, such engineering can be potentially performed electrochemically, by the successive assembly of one of the SAMs on all the areas, its controlled removal from selected areas by applying a system-specific reductive desorption potential, and the deposition of the second SAM onto these areas, while the first SAM is preserved in all other regions. The approach was tested with individual samples and several aromatic SAM-forming molecules with either thiolate or selenolate anchoring to the substrate (Au). It worked well for most combinations of these molecules, which provides a reliable basis for its extension to real-life heterogeneous templates, such as circuit boards hosting different types of organic transistors, requiring type-specific interface engineering.

Tungsten oxide (WO₃) is a promising electrochromic (EC) material, yet its low electrical conductivity and sluggish ion-transport limit its switching kinetics and cycling stability. Herein, we construct a hierarchical two-dimensional/zero-dimensional (2D/0D) Ti₃C₂T_x MXene/WO₃ composite film via interfacial self-assembly and electrochemical deposition. Interconnected Ti₃C₂T_x nanosheets serve as a conductive scaffold, and their excellent electrical conductivity significantly reduces the charge transport barrier, while uniformly distributed WO₃ nanoparticles (≈65 nm) provide abundant electroactive interfaces and shortened ion-transport pathways. By optimizing the tungsten-ion concentration, deposition voltage, and deposition time, the Ti₃C₂T_x/WO₃ composite film exhibits an optical modulation of 50.93% at 600 nm, with coloration and bleaching times of 12.06 and 13.29 s, respectively. The film retains 98.15% of its initial optical modulation after 1200 s of continuous cycling, compared with 58.41% for neat WO₃. These improvements originate from the synergistic effect of Ti₃C₂T_x and WO₃. Ti₃C₂T_x facilitates charge transport, whereas nanoscale WO₃ enhances electrolyte accessibility and facilitates ion diffusion, collectively accelerating the electrochemical reaction kinetics. This work establishes a rational 2D/0D architecture for coupling rapid electron and ion transport and offers a viable strategy for high-performance electrochromic devices.