Jiuxiang Dai

Oxide semiconductors are being researched for 3D back-end-of-line integration as silicon-based materials reach their limits. This study develops atomically-ordered InGaZnO transistors with high mobility (>100 cm² Vs⁻¹) using plasma-enhanced atomic layer deposition, controlling plasma energy to find out the origin of the ultra-high mobility. These understanding insights the powerful potential of PEALD-OS as a next-generation active material for replacing silicon.

Abstract

As the scale-down and power-saving of silicon-based channel materials approach the limit, oxide semiconductors are being actively researched for applications in 3D back-end-of-line integration. For these applications, it is necessary to develop stable oxide semiconductors with electrical properties similar to those of Si. Herein, a single-crystal-like indium–gallium–zinc–oxide (IGZO) layer (referred to as a pseudo-single-crystal) is synthesized using plasma-enhanced atomic layer deposition and fabricated stable IGZO transistors with an ultra-high mobility of over 100 cm² Vs⁻¹. To acquire high-quality atomic layer deposition-processed IGZO layers, the plasma power of the reactant is controlled as an effective processing parameter by evaluating and understanding the effect of the chemical reaction of the precursors on the behavior of the residual hydrogen, carbon, and oxygen in the as-deposited films. Based on these insights, this study found that there is a critical relationship between the optimal plasma reaction energy, superior electrical performance, and device stability.

2D piezoelectric materials constitute a promising alternative for piezocatalysis due to their inherent advantages, such as high flexibility, large surface area, and abundant active sites. In this review, the state-of-the-art research progresses on 2D piezoelectric materials and their applications in piezocatalysis are summarized. The overall goal is to inspire and accelerate the practical deployment of 2D piezoelectric materials for piezocatalytic applications.

Abstract

Piezocatalysis is an emerging technique that holds great promise for the conversion of ubiquitous mechanical energy into electrochemical energy through piezoelectric effect. However, mechanical energies in natural environment (such as wind energy, water flow energy, and noise) are typically tiny, scattered, and featured with low frequency and low power. Therefore, a high response to these tiny mechanical energies is critical to achieving high piezocatalytic performance. In comparison to nanoparticles or 1D piezoelectric materials, 2D piezoelectric materials possess characteristics such as high flexibility, easy deformation, large surface area, and rich active sites, showing more promise in future for practical applications. In this review, state-of-the-art research progresses on 2D piezoelectric materials and their applications in piezocatalysis are provided. First, a detailed description of 2D piezoelectric materials are offered. Then a comprehensive summary of the piezocatalysis technique is presented and examines the piezocatalysis applications of 2D piezoelectric materials in various fields, including environmental remediation, small-molecule catalysis, and biomedicine. Finally, the main challenges and prospects of 2D piezoelectric materials and their applications in piezocatalysis are discussed. It is expected that this review can fuel the practical application of 2D piezoelectric materials in piezocatalysis.

Addressing the challenge of detecting biomolecules at low concentrations using plasmonic biosensors, a plasmonic biosensor based on ferroelectric 2D Bi₂O₂Se materials is presented, which exhibits an ultralow detection limit of 1 fM for protein molecules.

Abstract

Plasmonic biosensing is a label-free detection method that is commonly used to measure various biomolecular interactions. However, one of the main challenges in this approach is the ability to detect biomolecules at low concentrations with sufficient sensitivity and detection limits. Here, 2D ferroelectric materials are employed to address the issues with sensitivity in biosensor design. A plasmonic sensor based on Bi₂O₂Se nanosheets, a ferroelectric 2D material, is presented for the ultrasensitive detection of the protein molecule. Through imaging the surface charge density of Bi₂O₂Se, a detection limit of 1 fM is achieved for bovine serum albumin (BSA). These findings underscore the potential of ferroelectric 2D materials as critical building blocks for future biosensor and biomaterial architectures.

Annual Review of Materials Research, Volume 53, Issue 1, Page 253-274, July 2023.

Annual Review of Materials Research, Volume 53, Issue 1, Page 25-51, July 2023.

Annual Review of Materials Research, Volume 53, Issue 1, Page 371-397, July 2023.

Abstract

Chemical vapor deposition (CVD) using gaseous hydrocarbon sources has shown great promise for large-scale graphene growth, but high growth temperatures (typically 1000 °C) require sophisticated and expensive equipment, which increases graphene production costs. Here, we demonstrate a new approach to produce graphene at low cost from scrap steel sheets treated by thermal evaporation of copper plating, which is a derivative of traditional CVD technology. Without additional carbon sources, graphene film was successfully prepared on copper-coated scrap steel sheets at 820 °C. The resulting graphene has few defects and uniform morphology, comparable to CVD graphene grown at 1000 °C. Finally, the obtained graphene film is used in combination with an interdigital electrode to detect NO₂ successfully, showing excellent performance. This technology expands the application of graphene in the manufacture of gas sensing devices and is compatible with traditional microelectronics technology.

Magnetic photonic-crystal microrobots consisting of pH-responsive hydrogel microspheres with encapsulated periodically assembled Fe₃O₄ nanoparticles show integrated functions of magnetic propulsion, pH-responsive structural colors, and pH-dependent drug loading/releasing. Thus, they can collectively move toward a specific target with abnormal pH conditions (e.g., tumor cells), and spontaneously perform on-the-fly visual pH detection and self-regulated pH-dependent drug delivery.

Abstract

Swarming magnetic micro/nanorobots hold great promise for biomedical applications, but at present suffer from inferior capabilities to perceive and respond to chemical signals in local microenvironments. Here we demonstrate swarming magnetic photonic-crystal microrobots (PC-bots) capable of spontaneously performing on-the-fly visual pH detection and self-regulated drug delivery by perceiving local pH changes. The magnetic PC-bots consist of pH-responsive hydrogel microspheres with encapsulated one-dimensional periodic assemblies of Fe₃O₄ nanoparticles. By programming external rotating magnetic fields, they can self-organize into large swarms with much-enhanced collective velocity to actively find targets while shining bright “blinking” structural colors. When approaching the target with abnormal pH conditions (e.g., an ulcerated superficial tumor lesion), the PC-bots can visualize local pH changes on the fly via pH-responsive structural colors, and realize self-regulated release of the loaded drugs by recognizing local pH. This work facilitates the development of intelligent micro/nanorobots for active “motile-targeting” tumor diagnosis and treatment.

The development of ultrathin materials and devices in recent years is reviewed. The advantages of ultrathin flexible devices compared with conventional thick devices are emphasized. The size effect of ultrathin materials and the relationship between the thickness of materials and the performance of devices are discussed. Finally, the limitations and perspectives of ultrathin materials and devices are explored.

Abstract

Intelligent technologies based on artificial intelligence and big data hold great potential for health monitoring and human–machine capability enhancement. However, electronics must be connected to the human body to realize this vision. Thus, tissue or skin-like electronics with high stretchability and low stiffness mechanical properties are highly desirable. Ultrathin materials have attracted significant attention from the research community and the industry because of their high performance and flexibility. Over the past few years, considerable progress has been made in flexible ultrathin sensors and devices based on ultrathin materials. Here, we review the developments in this area and examine representative research progress in ultrathin materials fabrication and device construction. Strategies for the fabrication of stretchable ultrathin materials and devices are considered. The relationship between the thin-film structure and performance is emphasized and highlighted. Finally, the current capabilities and limitations of ultrathin devices were explored.

npj 2D Materials and Applications, Published online: 06 July 2023; doi:10.1038/s41699-023-00408-x

Coulomb engineering of two-dimensional Mott materials

Publication date: July–August 2023

Source: Materials Today, Volume 67

Author(s): Qianqian Wang, Yuting Zhou, Xiaolin Wang, Hongqiang Gao, Zhiwen Shu, Ziyu Hu, Peipei Tao, Yasin Ekinci, Michaela Vockenhuber, Yiqin Chen, Huigao Duan, Hong Xu, Xiangming He

This study reports on sputter-deposited ferroelectric sub-5 nm thin Al_0.74Sc_0.26N. Scanning transmission electron microscopy (STEM) investigations reveal the formation of domain walls with a significant horizontal component and in-grain partial switching on lateral dimensions below 10 nm². The impact of the substrate type (silicon and sapphire) as well as a decrease in the coercive field (E_c ) with thickness are discussed in detail and enable switching voltages as low as 1 V.

Abstract

Analog switching in ferroelectric devices promises neuromorphic computing with the highest energy efficiency if limited device scalability can be overcome. To contribute to a solution, one reports on the ferroelectric switching characteristics of sub-5 nm thin Al_0.74Sc_0.26N films grown on Pt/Ti/SiO₂/Si and epitaxial Pt/GaN/sapphire templates by sputter-deposition. In this context, the study focuses on the following major achievements compared to previously available wurtzite-type ferroelectrics: 1) Record low switching voltages down to 1 V are achieved, which is in a range that can be supplied by standard on-chip voltage sources. 2) Compared to the previously investigated deposition of ultrathin Al_1−xSc_xN films on epitaxial templates, a significantly larger coercive field (E _c ) to breakdown field ratio is observed for Al_0.74Sc_0.26N films grown on silicon substrates, the technologically most relevant substrate-type. 3) The formation of true ferroelectric domains in wurtzite-type materials is for the first time demonstrated on the atomic scale by scanning transmission electron microscopy (STEM) investigations of a sub-5 nm thin partially switched film. The direct observation of inversion domain boundaries (IDB) within single nm-sized grains supports the theory of a gradual domain-wall driven switching process in wurtzite-type ferroelectrics. Ultimately, this should enable the analog switching necessary for mimicking neuromorphic concepts also in highly scaled devices.

Designed gradient-relaxor antiferroelectric PbZrO₃-based films with hierarchical domain structure are achieved for a small amount of La/Sr doping at A-site, accounting for the enhanced polarization switching stability and increased antiferroelectric phase stability. Those features endow A-site doped PbZrO₃ films with the greatest potential for low field/voltage energy storage applications including wearable and portable devices.

Abstract

Dielectric capacitors play a vital role in advanced electronics and power systems as a medium of energy storage and conversion. Achieving ultrahigh energy density at low electric field/voltage, however, remains a challenge for insulating dielectric materials. Taking advantage of the phase transition in antiferroelectric (AFE) film PbZrO₃ (PZO), a small amount of isovalent (Sr²⁺) / aliovalent (La³⁺) dopants are introduced to form a hierarchical domain structure to increase the polarization and enhance the backward switching field E _A simultaneously, while maintaining a stable forward switching field E _F. An ultrahigh energy density of 50 J cm⁻³ is achieved for the nominal Pb_0.925La_0.05ZrO₃ (PLZ5) films at low electric fields of 1 MV cm⁻¹, exceeding the current dielectric energy storage films at similar electric field. This study opens a new avenue to enhance energy density of AFE materials at low field/voltage based on a gradient-relaxor AFE strategy, which has significant implications for the development of new dielectric materials that can operate at low field/voltage while still delivering high energy density.

By incorporating electron spin resonance capability in spin-polarized scanning tunneling microscopy, quantum states of individual spins on surfaces can be initialized, controlled, and read out. Individual spins and artificial spin structures built atom-by-atom provide new platforms for sensing magnetic interactions, performing quantum operations, and simulating spin Hamiltonians at the atomic scale.

Abstract

The desire to control and measure individual quantum systems such as atoms and ions in a vacuum has led to significant scientific and engineering developments in the past decades that form the basis of today's quantum information science. Single atoms and molecules on surfaces, on the other hand, are heavily investigated by physicists, chemists, and material scientists in search of novel electronic and magnetic functionalities. These two paths crossed in 2015 when it was first clearly demonstrated that individual spins on a surface can be coherently controlled and read out in an all-electrical fashion. The enabling technique is a combination of scanning tunneling microscopy (STM) and electron spin resonance, which offers unprecedented coherent controllability at the Angstrom length scale. This review aims to illustrate the essential ingredients that allow the quantum operations of single spins on surfaces. Three domains of applications of surface spins, namely quantum sensing, quantum control, and quantum simulation, are discussed with physical principles explained and examples presented. Enabled by the atomically-precise fabrication capability of STM, single spins on surfaces might one day lead to the realization of quantum nanodevices and artificial quantum materials at the atomic scale.

Nature Nanotechnology, Published online: 29 June 2023; doi:10.1038/s41565-023-01432-0

Colloidal quantum dots are a potential source of scalable single-photon emitters, but they typically exhibit broad emission linewidths. Proppe et al. show narrow-linewidth emission from heavy-metal-free InP/ZnSe/ZnS dots with coherence times of up to 250 ps.

Nature Materials, Published online: 29 June 2023; doi:10.1038/s41563-023-01567-4

A two-dimensional atomically flat insulator with large dielectric constant and high breakdown field strength has been successfully grown. This material could serve as the dielectric and encapsulation layers for two-dimensional materials for studying their emergent physics, as well as for next-generation electronics.

Nature Communications, Published online: 29 June 2023; doi:10.1038/s41467-023-39002-6

The isolation of graphene leads to a surge of interest in two dimensional materials, and recently, ferromagnetism has been observed in several two-dimensional materials. However, two-dimensional ferromagnetism remains rare. Here, Gong et al present an alternative approach to achieve two-dimensional ferromagnetism; combining antiferromagnetic FePS3 with non-magnetic WS2 they find a ferromagnetic state forms at the interface of these two materials.

Nature Communications, Published online: 01 July 2023; doi:10.1038/s41467-023-39450-0

The authors demonstrate near-perfect light absorption using only two atomic layers of transition metal dichalcogenides. This is achieved by reducing interlayer interaction which optimizes band nesting, and does not require the use of complex metasurfaces.

Nature Materials, Published online: 06 July 2023; doi:10.1038/s41563-023-01600-6

The authors report the emergence of a transient hexatic state during laser-induced transformation between two charge-density wave (CDW) phases in a thin film of the CDW material 1T-TaS2.

Interlayer interactions of 1T-NbSe₂, a 2D correlated material, are unraveled from geometric and electronic structures of 1T-NbSe₂ bilayers in 28 stacking orders using density-functional-theory. In the interlayer region of each stacking configuration, interfacial Se pz orbitals electronically hybridize while the stacking order varies the hybridization details that modulate the electronic state of the bilayer among four (correlated) insulating states.

Abstract

Correlated 2D layers, like 1T-phases of TaS₂, TaSe₂, and NbSe₂, exhibit rich tunability through varying interlayer couplings, which promotes the understanding of electron correlation in the 2D limit. However, the coupling mechanism is, so far, poorly understood and is tentatively ascribed to interactions among the dz2${{\mathrm{d}}}_{{{\mathrm{z}}}^2}\ $orbitals of Ta or Nb atoms. Here, it is theoretically shown that the interlayer hybridization and localization strength of interfacial Se p_z orbitals, rather than Nb dz2${{\mathrm{d}}}_{{z}^2}\ $orbitals, govern the variation of electron-correlated properties upon interlayer sliding or twisting in correlated magnetic 1T-NbSe₂ bilayers. Each of the layers is in a star-of-David (SOD) charge-density-wave phase. Geometric and electronic structures and magnetic properties of 28 different stacking configurations are examined and analyzed using density-functional-theory calculations. It is found that the SOD contains a localized region, in which interlayer Se p_z hybridization plays a paramount role in varying the energy levels of the two Hubbard bands. These variations lead to three electronic transitions among four insulating states, which demonstrate the effectiveness of interlayer interactions to modulate correlated magnetic properties in a prototypical correlated magnetic insulator.