Advanced Electronic Materials

2D transition metal carbide Ti₃C₂T_x (T stands for surface termination), the most widely studied MXene, has shown outstanding electrochemical properties and promise for a number of bulk applications. However, electronic properties of individual MXene flakes, which are important for understanding the potential of these materials, remain largely unexplored. Herein, a modified synthetic method is reported for producing high‐quality monolayer Ti₃C₂T_x flakes. Field‐effect transistors (FETs) based on monolayer Ti₃C₂T_x flakes are fabricated and their electronic properties are measured. Individual Ti₃C₂T_x flakes exhibit a high conductivity of 4600 ± 1100 S cm⁻¹ and field‐effect electron mobility of 2.6 ± 0.7 cm² V⁻¹ s⁻¹. The resistivity of multilayer Ti₃C₂T_x films is only one order of magnitude higher than the resistivity of individual flakes, which indicates a surprisingly good electron transport through the surface terminations of different flakes, unlike in many other 2D materials. Finally, the fabricated FETs are used to investigate the environmental stability and kinetics of oxidation of Ti₃C₂T_x flakes in humid air. The high‐quality Ti₃C₂T_x flakes are reasonably stable and remain highly conductive even after their exposure to air for more than 24 h. It is demonstrated that after the initial exponential decay the conductivity of Ti₃C₂T_x flakes linearly decreases with time, which is consistent with their edge oxidation.

Sự phát triển nhanh chóng của các công nghệ hữu cơ mới đã dẫn đến những ứng dụng quan trọng của thiết bị điện tử hữu cơ như đi-ốt phát sáng, pin năng lượng mặt trời và bóng bán dẫn hiệu ứng trường. Yêu cầu lớn hiện nay là chất dẫn điện có độ dẫn cao và tính trong suốt để có thể hoạt động như lớp chuyển tải điện tích hoặc kết nối điện trong các thiết bị hữu cơ. Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS), được biết đến như là chất dẫn điện nổi bật nhất, đã đảm nhận vai trò này nhờ vào khả năng tạo màng tốt, tính trong suốt cao, độ dẫn điện điều chỉnh được và độ ổn định nhiệt tuyệt vời. Bài tổng quan này tóm tắt các phương pháp hóa học và vật lý thú vị có thể nâng cao hiệu quả độ dẫn điện của PEDOT:PSS một cách hiệu quả, đặc biệt tập trung vào cơ chế nâng cao độ dẫn cũng như ứng dụng của các màng PEDOT:PSS. Những triển vọng cho các nỗ lực nghiên cứu trong tương lai cũng được đề cập. Dự kiến rằng các màng PEDOT:PSS với độ dẫn cao và tính trong suốt có thể là trọng điểm cho những đột phá vật liệu điện tử hữu cơ trong tương lai.

Ferroelectric polymers are the most promising electroactive materials with outstanding properties that can be integrated into a variety of flexible electronic devices. Their multifunctional capabilities, ability to bend and stretch, ease of processing, chemical stability, and the high biocompatibility of polyvinylidene fluoride (PVDF)‐based polymers make them attractive for applications in flexible memories, energy transducers, and electronic skins. Here, recent advance in the research of PVDF‐based flexible electronic devices is reviewed, including nonvolatile memories, energy‐harvesting devices, and multifunctional portable sensors.

Current microfabrication of micro‐supercapacitors often involves multistep processing and delicate lithography protocols. In this study, simple fabrication of an asymmetric MXene‐based micro‐supercapacitor that is flexible, binder‐free, and current‐collector‐free is reported. The interdigitated device architecture is fabricated using a custom‐made mask and a scalable spray coating technique onto a flexible, transparent substrate. The electrode materials are comprised of titanium carbide MXene (Ti₃C₂T_x) and reduced graphene oxide (rGO), which are both 2D layered materials that contribute to the fast ion diffusion in the interdigitated electrode architecture. This MXene‐based asymmetric micro‐supercapacitor operates at a 1 V voltage window, while retaining 97% of the initial capacitance after ten thousand cycles, and exhibits an energy density of 8.6 mW h cm⁻³ at a power density of 0.2 W cm⁻³. Further, these micro‐supercapacitors show a high level of flexibility during mechanical bending. Utilizing the ability of Ti₃C₂T_x‐MXene electrodes to operate at negative potentials in aqueous electrolytes, it is shown that using Ti₃C₂T_x as a negative electrode and rGO as a positive one in asymmetric architectures is a promising strategy for increasing both energy and power densities of micro‐supercapacitors.

The hysteretic behavior of organic–inorganic halide perovskites (OHPs) are exploited for application in neuromorphic electronics. Artificial synapses with 2D and quasi‐2D perovskite are demonstrated that have a bulky organic cation (phenethylammonium (PEA)) to form structures of (PEA)₂MA_n‐1Pb_nBr_3n+1. The OHP films have morphological properties that depend on their structure dimensionality (i.e., n value), and artificial synapses fabricated from them show synaptic responses such as short‐term plasticity, paired‐pulse facilitation, and long‐term plasticity. The operation mechanism of OHP artificial synapses are also analyzed depending on the dimensionality and it is found that quasi‐2D (n = 3–5) OHP artificial synapses show much longer retention than 2D and 3D OHP counterparts. The calculated energy consumption of a 2D OHP artificial synapse (≈0.7 fJ per synaptic event) is comparable to that of biological synapses (1–10 fJ per synaptic event). These OHP artificial synapses may enable development of neuromorphic electronics that use very little energy.

Silicon doped hafnium oxide was the material used in the original report of ferroelectricity in hafnia in 2011. Since then, it has been subject of many further publications including the demonstration of the world's first ferroelectric field‐effect transistor in the state‐of‐the‐art 28 nm technology. Though many studies are conducted with a strong focus on application in memory devices, a comprehensive study on structural stability in these films remains to be seen. In this work, a film thickness of about 36 nm, instead of the 10 nm used in most previous studies, is utilized to carefully probe how the concentration range impacts the evolution of phases, the dopant distribution, the field cycling effects, and their interplay in the macroscopic ferroelectric response of the films. Si:HfO₂ appears to be a rather fragile system: different phases seem close in energy and the system is thus rich in competing phenomena. Nonetheless, it offers ferroelectricity or field‐induced ferroelectricity for elevated annealing conditions up to 1000 °C. Similar to the measures taken for conventional ferroelectrics such as lead zirconate titanate, engineering efforts to guarantee stable interfaces and stoichiometry are mandatory to achieve stable performance in applications such as ferroelectric memories, supercapacitors, or energy harvesting devices.

2D materials are considered promising candidates for developing next‐generation high‐performance energy efficient electronic, optoelectronic, and valley‐tronic devices. Though metal oxides are widely used in the fabrication of many advanced devices, very little work has been reported on their properties in 2D limit. This article reports the discovery of a new 2D materials system, 2D tin monoxide (SnO). Layer by layer growth of SnO on sapphire and SiO₂ substrates is demonstrated using a pulsed laser deposition method. The number of SnO layers is controlled by controlling the number of laser shots during the deposition process. Raman spectroscopic and X‐ray photoelectron spectroscopic analysis confirms the formation of phase pure SnO layers. Field effect transistors (FETs) using few layer SnO channels grown on SiO₂ substrates are successfully fabricated. These FETs show typical p‐channel conduction with field effect mobility ranging from 0.05 to 1.9 cm² V⁻¹ s⁻¹. Field effect mobility varies with the number of SnO layers and decreases on either sides of the optimum layer numbers (12), which is explained based on charge screening and interlayer coupling in layered materials.

A flexible version of traditional thin lead zirconium titanate ((Pb_1.1Zr_0.48Ti_0.52O₃)‐(PZT)) based ferroelectric random access memory (FeRAM) on silicon shows record performance in flexible arena. The thin PZT layer requires lower operational voltages to achieve coercive electric fields, reduces the sol‐gel coating cycles required (i.e., more cost‐effective), and, fabrication wise, is more suitable for further scaling of lateral dimensions to the nano‐scale due to the larger feature size‐to‐depth aspect ratio (critical for ultra‐high density non‐volatile memory applications). Utilizing the inverse proportionality between substrate's thickness and its flexibility, traditional PZT based FeRAM on silicon is transformed through a transfer‐less manufacturable process into a flexible form that matches organic electronics' flexibility while preserving the superior performance of silicon CMOS electronics. Each memory cell in a FeRAM array consists of two main elements; a select/access transistor, and a storage ferroelectric capacitor. Flexible transistors on silicon have already been reported. In this work, we focus on the storage ferroelectric capacitors, and report, for the first time, its performance after transformation into a flexible version, and assess its key memory parameters while bent at 0.5 cm minimum bending radius.

Bismuth ferrite (BFO)‐based ceramics with large electromechanical response are important in electronic device applications. To better understand their physical mechanisms, a new phase diagram established by temperature dependence of dielectric properties, temperature dependence of piezoelectric coefficient, and the evolution of their properties is proposed to explain the contribution of piezoelectric and strain response by comparing ferroelectric (FE) and relaxor ferroelectric (RFE) compositions. The FE components with macrodomains have large piezoelectric constant (d₃₃ of 412 pC/N) at high temperature. The RFE components with nanodomains possess giant strain response (S_uni = 0.37%) at 180 °C. Combined with in situ and ex situ techniques, the physical mechanisms behind the enhancement of these properties are explored. Macrodomains and multipolar phase coexistence contribute to the piezoelectricity improvement. Nanodomains and an unstable depolarization temperature (T_d) region engineer the strain enhancement, which can promote electric‐field‐induced domain switching, lattice strain, and irreversible phase transition. In particular, the T_d region of BiFeO₃‐based ceramics has been ignored for several years, although it is actually an effective medium to engineer properties. The proposed phase diagram and dynamic model can be used to well understand the structural origins of large electromechanical properties in BFO‐based ceramics, which can give some guidance to explore materials with excellent properties for different applications.