Advanced Electronic Materials最新文献

The termination of surface-dangling bonds on silicon through hydrogen atoms, also known as Si–H, can achieve chemical passivation and reduce surface states in the electronic bandgap, thus altering electronic properties. Through a comprehensive study of doping levels (10¹⁴–10²⁰ cm⁻³) and types (n and p), a consistent surface dipole trend induced by Si–H termination is discovered. It is achieved by redistributing surface charges and establishing thermal equilibrium with the chemical bond. To resolve this, the surface work function, surface electron affinity, and the energy difference between the valence band and the Fermi level are measured by employing the Kelvin probe, X-ray photoelectron spectroscopy, and photoelectron yield spectroscopy methods. These findings are further validated through ab initio simulations. This finding has immense implications not only for eliminating electronic defects at semiconductor interfaces, which is crucial in microelectronics but also for developing and engineering hybrid interfaces and heterojunctions with controlled electronic properties.

Low-power nonvolatile memories operating down to deep cryogenic temperatures are important for a large spectrum of applications from high-performance computing, electronics interfacing quantum computing hardware to space-based electronics. Despite the potential of Hf_0.5Zr_0.5O₂ (HZO), thanks to its compatibility with complementary metal-oxide-semiconductor (CMOS) back-end-of-line processing, only few studies of HZO-based memory devices down to cryogenic operation temperatures exist. Here, analog ferroelectric memory stack fabrication with 10 nm HZO and their detailed characterization under wide range of pulse amplitudes and frequencies down to 4 K are reported. When operated at temperatures below 100 K, HZO devices can support high amplitude voltage pulses, yielding record high P_r of up to 75µC cm⁻² at ±7 V_p (14 V_pp) pulse amplitudes accompanied with frequency-dependent memory window between 6 and 8 V. Devices show excellent endurance exceeding 10⁹ cycles of ±5 V_p (10 V_pp) and P_r of 30 µC cm⁻² without significant degradation of coercive voltages or loss of polarization at cryogenic temperatures. At least 20 reproducible analog states for temperatures below 100 K with almost ideal linearity of intermediate polarization states in both pulse directions is observed, demonstrating the high potential of analog cryogenic ferroelectric memories, essential for on-line training in in-memory-computing architecture.

Solution-processed inorganic perovskites cause chemical and structural defects unfavorable for photodetector application. Using a binary solvent, defects in CsPbI_xBr_y (CPIB) perovskite are passivated with poly 4-vinylpyridine (PVP) and Poly methyl methacrylate (PMMA) polymers. X-ray photoelectron spectroscopy and FTIR spectra reveal a Lewis base-acid interaction between Pb²⁺ and polymer, confirming the passivation of CPIB perovskite. Scanning electron microscopy analysis shows a dual-surface morphology with microribbons and microcrystals in perovskites. After PMMA treatment, CPIB perovskite exhibits a blue shift in the bandgap (1.8 to 1.95 eV), while the PVP induced a redshift, reducing the bandgap to 1.7 eV. Blue shift in PL analysis indicates modification of grain boundaries. A higher lifetime obtained for CPIB/PVP confirms the restraint of non-radiative recombinations. Photodetectors are fabricated with pristine CPIB, CPIB/PVP, and CPIB/PMMA perovskites. The passivated CPIB/PVP-based photodetector exhibits a quick rise time of ≈23 ms and a decay time of ≈17 ms. It also demonstrates a remarkable photoresponsivity of 23 mA W⁻¹, an internal quantum efficiency of 4.9%, and a detectivity of 15.0 × 10¹⁰ Jones at 10 mW cm⁻² light intensity. This approach shows the potential for environmentally stable polymers to passivate inorganic perovskites for high photodetection performance.

Memristors, being prospective work-horses of future electronics offer various types of memory (volatile and nonvolatile) along with specific computational functionalities. Further development of memristive technologies depends on the availability of suitable materials. These materials should be easily available, stable, and preferably of low toxicity. Commonly used materials are lead halide perovskites, however, they are highly toxic and unstable under ambient conditions. Therefore a novel material is developed on the basis of bismuth iodide. In reaction with butylammonium iodide, it yields a novel compound, butylammonium iodobismuthate (BABI). Here, a diffusive memristor is introduced based on this compound and evaluates its memristive and neuromorphic properties. In contrast to nonvolatile memristors, the BABI memristors exhibit diffusive dynamics, which enable them to store the information only for short periods of time. This property is utilized to mimic the short-term synaptic plasticity described by the leaky integrate-and-fire model of a biological neuron. Combined with high switching uniformity and self-rectifying behavior, these devices show high classification accuracy for MNIST handwritten datasets, paving the way for their application in neuromorphic computing systems.

Flexible thermoelectric generators are leading candidates for next-generation energy-harvesting devices. Although SiGe, an environmentally-friendly semiconductor, is the most reliable and widely tested thermoelectric material, it is difficult to form a SiGe layer with high thermoelectric performance at temperatures lower than the heat-proof temperature of flexible plastic films. In this article, the synthesis of SiGe thermoelectric thin films via the metal-induced layer exchange phenomenon is reviewed, from its mechanism to device performance. The selection of metal species allows low-temperature formation (≤500 °C) of p- and n-type SiGe on insulating substrates. Currently, the maximum power factors near room temperature are 850 µW m⁻¹ K⁻² for p-type Si_0.4Ge_0.6 and 1000 µW m⁻¹ K⁻² for n-type Si_0.85Ge_0.15. These values are the highest among those of Group IV semiconductor thin films formed at low temperatures. The flexible thermoelectric generator consisting of these p- and n-type SiGe exhibits cross-sectional and planar power densities of ≈3.0 mW cm⁻² and 0.50 µW cm⁻², respectively, at a temperature difference of 30 K. Finally, the future challenges of layer exchange for improving the performance of flexible thermoelectric generators based on Group IV semiconductors are discussed.

Recently, superconductivity at high temperatures is observed in bulk La₃Ni₂O_7−δ under high pressure. However, the attainment of high-purity La₃Ni₂O_7−δ single crystals remains a formidable challenge. Here, the crystal structure and physical properties of single crystals of Sr-doped La₃Ni₂O₇ synthesized at high pressure (20 GPa) and high temperature (1400 °C) are reported. Through single crystal X-ray diffraction, it is shown that high-pressure-synthesized paramagnetic Sr-doped La₃Ni₂O₇ crystallizes in an orthorhombic structure with Ni─O─Ni bond angles of 173.4(2)° out-of-plane and 175.0(2)°and 176.7(2)°in plane. The substitution of Sr alters in band filling and the ratio of Ni²⁺/Ni³⁺ in Sr-doped La₃Ni₂O₇, aligning them with those of “La₃Ni₂O_7.05”, thereby leading to significant modifications in properties under high pressure relative to the unsubstituted parent phase. At ambient pressure, Sr-doped La₃Ni₂O₇ exhibits insulating properties, and the conductivity increases as pressure goes up to 10 GPa. However, upon further increasing pressure beyond 10.7 GPa, Sr-doped La₃Ni₂O₇ transits back from a metal-like behavior to an insulator. The insulator–metal–insulator trend under high pressure dramatically differs from the behavior of the parent compound La₃Ni₂O_7−δ, despite their similar behavior in the low-pressure regime. These experimental results underscore the considerable challenge in achieving superconductivity in nickelates.

MXenes, a promising family of 2D transition metal carbides/nitrides, are renowned for their exceptional electronic conductivity and mechanical stability, establishing them as highly desirable candidates for advanced electromagnetic interference (EMI) shielding material. Despite these advantages, challenges persist in optimizing MXene synthesis methods and improving their oxidation resistance. Surface defects on MXenes significantly impact their electronic properties, impeding charge transport and catalyzing the oxidation process. In this study, a novel synthesis protocol derived from the conventional, minimally invasive layer delamination (MILD) method, is presented. Two additional steps are introduced aiming at enhancing process yield, addressing a crucial issue as conventional methods often yield high-quality individual MXene flakes but struggle to generate sufficient quantities for bulk material production. This approach successfully yields Ti₃C₂T_x films with excellent conductivity (3973.72 ±121.31 Scm⁻¹) and an average EMI shielding effectiveness (SE) of 56.09 ± 1.60 dB within the 1.5 to 10 GHz frequency range at 35% relative humidity (RH). Furthermore, this investigation delves into the long-term oxidation stability of these films under varying RH conditions. These findings underscore the effectiveness of this innovative synthesis approach in elevating both the conductivity and EMI shielding capabilities of MXene materials. This advancement represents a significant step toward harnessing MXenes for practical applications requiring robust EMI shielding solutions. Additionally, insights into long-term stability offer critical considerations for implementing MXenes in real-world environments.

Second-order memristors with their internal short-term dynamics display behavioral similarities with biological neurons and constitute an ideal basis unit for hardware neuromorphic networks, aims at treating spatio-temporal tasks. Here, La_0.7Sr_0.3MnO₃/BaTiO₃/La_0.7Sr_0.3MnO₃ second-order memristive devices are investigated whose resistances and temperature dependencies range, on the same chip, from semiconductor to metal, but exhibit a universal neuromorphic plasticity. All devices may be described using a compact phenomenological model of current conduction, showing that resistive switching originates from interfaces, through charge trapping. Remarkably, the processes of short-term memory gain/loss and long-term consolidation/forgetting are the same whatever the device type. Only the synaptic transmission weights and the excitation/relaxation times with respect to stimuli differ, as it occurs for synapses/neurons in the brain. The weights may be tuned by the sole use of the frequency of stimuli (the activity rate), their evolution being dependent on previous activities (the history). Metal and semiconductor devices display the same in-operando dynamics of potentiation or of depression, the transition from one regime to another being history-dependent. The threshold frequencies are slightly lower in semiconducting devices. This work contributes to better understanding of memristive switching and plasticity and is relevant for the development of brain-mimetic neural networks with new programming paradigms.

A nanostructured copper oxide (nCO) coating which can be electrochemically reduced to copper metal is demonstrated as an anti-reflection coating, enabling interference lithography of three-dimensionally structured templates on a surface compatible with subsequent electrodeposition steps. The nCO presents a black needle-like structure which effectively absorbs the incident radiation during interference lithography. Specular and diffused reflectivity measurements confirm nCO has near-zero reflectivity from at least UV (350 nm) to near IR (700 nm) wavelengths. A particularly important aspect of the nCO is its ability to be reduced to copper metal, enabling electrodeposition inside porous templates fabricated on the nCO. It is demonstrated electrodeposition of copper within 3D templates defined by interference lithography and proximity field nano-patterning processes, forming mesostructured metals which enhance two-phase cooling. The resultant 5 µm thick structures exhibited up to 3 times the critical heat flux and 2 times heat transfer coefficient of bare silicon. The structures are optimized via computational tools including Finite Difference Time Domain (FDTD) and COMSOL Multiphysics. The use of the approach demonstrated here can potentially find application in many areas given the broad importance of mesostructured metals for energy, biomedical, and mechanical applications.

The development of intrinsically stretchable polymer semiconductor holds substantial promise in the field of wearable electronics. However, charge transport mobility is typically compromised in existing stretchable semiconductors to achieve the desired stretchability. Herein, a novel “regional conjugation” strategy is proposed to design an intrinsically stretchable polymer semiconductor oligo-diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPTT)–urethane, in which oligo-DPPTT conjugated units and alkyl urethane nonconjugated units are introduced. The regional conjugation of oligo-DPPTT in the polymer backbone endows DPPTT–urethane with good molecular packing, leading to a high mobility of up to 1.7 cm² V⁻¹ s⁻¹. Additionally, incorporating alkyl urethane nonconjugated units in the backbone can reduce film crystallinity and chain aggregation, which contribute to the stretchability of the polymer thin film. Consequently, fully stretchable transistors retain carrier mobility even at 100% biaxial tensile strain. Furthermore, the fully stretchable organic field-effect transistor arrays show remarkable charge transport reversibility and durability after 1000 stretch–release cycles at 25% strain. Additionally, the device exhibits extraordinary electrical stability in air atmosphere. Overall, these results indicate that the “regional conjugation” strategy provides an effective and promising methodology to design intrinsically stretchable and high-performance polymer semiconductor that can advance the development of soft and wearable electronics.