Jiuxiang Dai

Light: Science & Applications, Published online: 26 July 2023; doi:10.1038/s41377-023-01231-1

This work demonstrates a novel negative photoconductance (NPC) detector based on organic-gated carbon nanotube field-effect transistor. With the light-controlled electrostatic coupling mechanism, the NPC device shows high responsivity (72.6 A W⁻¹ at 880 nm), fast response (7 ms), and good stability. Besides, gate-tunable switching between NPC and positive photoconductance (PPC) is observed, which is promising for future multifunctional optoelectronic systems.

Abstract

Negative photoconductance (NPC) detectors have attracted continuous attention for constructing advanced and novel optoelectronic devices, including reconfigurable image sensors and optosynaptic systems, especially by combining NPC with positive photoconductance (PPC). However, NPC devices suffer from much lower photosensitivity, slower response speed, and poor stability, especially in the infrared range. In this work, controllable NPC detectors based on organic-gated carbon nanotube field-effect transistors (OG-CNT FETs) are reported and the strong influence of light-induced electrostatic doping on the nonconventional photoresponse is demonstrated. The PM6/Y6-based heterojunction allows efficient near-infrared light absorption and facilitates exciton diffusion. By introducing a floating gate structure with an ultrathin dielectric layer, the OG-CNT FET shows an enhanced NPC effect owing to in situ signal amplification. Compared to other device configurations, the optimal  OG-CNT FETs exhibit high responsivity of 72.6 A W⁻¹ at 880 nm, along with improved response/recovery times of 7 and 5 ms. Impressively, gate-tunable switching between NPC and PPC is observed under the same light illumination. The reversible switching can be attributed to the competition between the light-controlled electrostatic coupling and the PM6/Y6 photovoltaic effect, which offers a new approach to achieve bidirectional photoresponses and paves the way for the development of future multifunctional optoelectronic systems.

A new type of ferromagnetic semiconductor is obtained by exploiting the perovskite structure. The obtained (4ampy)CuCl₄ exhibits a remarkably saturated magnetization up to 18.56 emu g⁻¹, which is one of the highest-ever-reported values for organic/inorganic hybrid intrinsic ferromagnetic semiconductors.

Abstract

Ferromagnetic semiconductors (FMS) enable simultaneous control of both charge and spin transport of charge carriers, and they have emerged as a class of highly desirable but rare materials for applications in spin field-effect transistors and quantum computing. Organic–inorganic hybrid perovskites with high compositional adjustability and structural versatility can offer unique benefits in the design of FMS but has not been fully explored. Here, a series of molecular FMSs based on the 2D organic–inorganic hybrid perovskite structure, namely (2ampy)CuCl₄, (3ampy)CuCl₄, and (4ampy)CuCl₄, is demonstrated, which exhibits high saturation magnetization, dramatic temperature-dependent conductivity change, and tunable ferromagnetic resonance. Magnetic measurements reveal a high saturation magnetization up to 18.56 emu g⁻¹ for (4ampy)CuCl₄, which is one of the highest value among reported hybrid FMSs to date. Conductivity studies of the three FMSs demonstrate that the smaller adjacent octahedron distance in the 2D layer results in higher conductivity. Systematic ferromagnetic resonance investigation shows that the gyromagnetic ratio and Landau factor values are strongly dependent on the types of organic cations used. This work demonstrates that 2D hybrid perovskite materials can simultaneously possess both tunable long-range ferromagnetic ordering and semiconductivity, providing a straightforward strategy for designing and synthesizing high-performance intrinsic FMSs.

2D ferroic materials with ultrathin thickness and atomically smooth interface are promising candidates for constructing novel memory devices. This review surveys recent progress and proposes future prospects on 2D ferroic materials for nonvolatile memory applications, including 2D spintronic devices, 2D ferroelectric devices, and 2D multiferroic devices.

Abstract

The emerging nonvolatile memory technologies based on ferroic materials are promising for producing high-speed, low-power, and high-density memory in the field of integrated circuits. Long-range ferroic orders observed in 2D materials have triggered extensive research interest in 2D magnets, 2D ferroelectrics, 2D multiferroics, and their device applications. Devices based on 2D ferroic materials and heterostructures with an atomically smooth interface and ultrathin thickness have exhibited impressive properties and significant potential for developing advanced nonvolatile memory. In this context, a systematic review of emergent 2D ferroic materials is conducted here, emphasizing their recent research on nonvolatile memory applications, with a view to proposing brighter prospects for 2D magnetic materials, 2D ferroelectric materials, 2D multiferroic materials, and their relevant devices.

Two new heteroleptic Hf precursors are synthesized, combining reactive dialkyamido with stabilizing formamido ligands. [Hf(DPfAMD)₂(NMe₂)₂] is employed for the deposition of high-quality HfO₂ in a tunable plasma-enhanced atomic layer deposition process. Investigation of metal-insulator semiconductor structures with HfO₂ as the dielectric layer reveals a strong relation between the plasma pulse time and dielectric properties such as permittivity and trap density.

Abstract

HfO₂ thin films are appealing for microelectronic applications such as high-κ dielectric layers, memristors, and ferroelectric memory devices. To fulfill the different requirements of each application, the properties of the deposited material need to be tuned accordingly. In this context, plasma-enhanced atomic layer deposition (PEALD) is a powerful processing route to tailor the properties of HfO₂ thin films, especially at low temperatures. Herein, a comprehensive bottom-up approach is presented, ranging from the synthesis of molecularly engineered Hf precursors to the development of a HfO₂ PEALD process and a detailed evaluation where plasma can be exploited to tune the dielectric properties. With the example of the newly synthesized bis-(dialkylamido)-bis-(formamidinato) Hf(IV) precursor, [Hf{η²-(ⁱPrN)₂CH}₂(NMe₂)₂] which is reactive, thermally robust and volatile, successful implementation in a PEALD process for HfO₂ at low temperatures is demonstrated. The typical atomic layer deposition (ALD) characteristics of precursor saturation, linearity, and ALD temperature window are demonstrated with constant growth of 0.7 Å per cycle from 125 to 200 °C, yielding high-purity layers. The effect of plasma pulse duration on the chemical composition alongside structural, topographical, as well as dielectric properties of the films is investigated. For the latter, the films are incorporated in metal-insulator semiconductor (MIS) structures.

Light: Science & Applications, Published online: 25 July 2023; doi:10.1038/s41377-023-01225-z

npj 2D Materials and Applications, Published online: 25 July 2023; doi:10.1038/s41699-023-00414-z

Author(s): Leonardo Galliano, Michael E. Cates, and Ludovic Berthier

Crystals cannot form in two-dimensional particle systems at equilibrium. A new study has found a regime where a crystal can form if the system is driven out of equilibrium.

[Phys. Rev. Lett. 131, 047101] Published Tue Jul 25, 2023

Abstract

The large size of lasers limits their applications in confined spaces, such as in biosensing and in vivo brain tissue imaging. In this regard, micron-sized lasers have been developed. They exhibit great potential for biological detecting, remote sensing, and depth tracking due to their small sizes, sensitive properties of their spectral fingerprints, and flexible positional modulation in the microenvironment. Lanthanide-based luminescent materials that possess long excited-state lifetime, narrow emission bandwidth, and upconversion behaviors are promising as gain mediums for novel microlasers. In addition, lanthanide-based microlasers could be generated under natural ambient conditions with pumped or continuous light sources, which significantly promotes the practical applications of microlasers. Recent progress in the design, synthesis, and biomedical applications of lanthanide-based microlasers has been outlined in this review. Lanthanide ions doped and upconverted lanthanide-based microlasers are highlighted, which exhibit advantageous structures, miniaturized dimensions, and high lasing performance. The applications of lanthanide-based microlasers are further discussed, the upconverted microlasers show great advantages for biological applications owing to their tunable excitation and emission characteristics and excellent environmental stability. Moreover, perspectives and challenges in the field of lanthanide-based microlasers are presented.

Nature Nanotechnology, Published online: 24 July 2023; doi:10.1038/s41565-023-01454-8

Light: Science & Applications, Published online: 24 July 2023; doi:10.1038/s41377-023-01223-1

This investigation with friction force microscopy reveals that transition metal dichalcogenides (MoS₂ and MoTe₂) in 1T’ phase exhibit friction levels that are 5 to 10 times greater than those in the 2H phase. With density functional theory calculations, this friction increase is attributed to the enhanced electron and phonon dissipation and increased potential energy surface barrier at the tip-sample interface.

Abstract

The fundamental aspects of energy dissipation on 2-dimensional (2D) atomic layers are extensively studied. Among various atomic layers, transition metal dichalcogenides (TMDs) exists in several phases based on their lattice structure, which give rise to the different phononic and electronic contributions in energy dissipation. 2H and 1T’ (distorted 1T) phase MoS₂ and MoTe₂ atomic layers exfoliated on mica substrate are obtained and investigated their nanotribological properties with atomic force microscopy (AFM)/ friction force microscopy (FFM). Surprisingly, 1T’ phase of both MoS₂ and MoTe₂ exhibits ≈10 times higher friction compared to 2H phase. With density functional theory analyses, the friction increase is attributed to enhanced electronic excitation, efficient phonon dissipation, and increased potential energy surface barrier at the tip-sample interface. This study suggests the intriguing possibility of tuning the friction of TMDs through phase transition, which can lead to potential application in tunable tribological devices.

A novel full-van der Waals two-terminal optoelectronic neuristor based on α-In₂Se₃/SnSe ferroelectric p–n heterojunction is proposed. Utilizing co-modulation of the polarization-reconfigurable p–n junction built-in electric field and photo-induced ferroelectric polarization switching, the ultra-high paired-pulse facilitation index (457%), the optical adaptation, and the simulation of the classical Pavlovian conditioned reflexes are realized well.

Abstract

Photoelectric synaptic devices with optical sensing capability are of great importance in simulating human vision systems. Especially realizing all-in-one vision neuristor on silicon based new materials and principles is being pursued. 2D van der Waals (vdW) materials have the unique advantage of arbitrary stacking on demand. Herein, a full-vdW two-terminal 2D ferroelectric α-In₂Se₃/SnSe p–n heterojunction is proposed to construct an optoelectronic neuristor to simulate visual synaptic functions. Implementation of these simulations is attributed to the co-modulation of the electrical polarization reconfigurable built-in electric field caused by p–n junction and photo-inducing ferroelectric polarization switching. These functions include ultra-high paired-pulse facilitation  index (457%), short synaptic plasticity, long synaptic plasticity, and retina-like optical adaptations. The high PPF is crucial for high-precision decoding and processing of visual information. Meanwhile, the classical Pavlovian conditioned reflexes associated with associative learning are also emulated showing the ability of the device to handle complex electrical and optical inputs. This study demonstrates that two-terminal ferroelectric p–n heterojunctions have great potential in high-precision multifunctional optoelectronic visual synaptic devices.

2D transition metal dichalcogenides (TMDCs) are promising for next-gen optoelectronics. Their sensitivity to surroundings affects electronic behavior. Substrate surfaces are chemically engineered to locally dope and adjust properties of monolayer TMDCs employing self-assembled monolayers arranged in patterns. Understanding these factors enables accurate prediction and advanced device design.

Abstract

2D transition metal dichalcogenides (TMDCs) are atomically-thick semiconductors with great potential for next-generation optoelectronic applications, such as transistors and sensors. Their large surface-to-volume ratio makes them energy-efficient but also extremely sensitive to the physical-chemical surroundings. The latter must be carefully considered when predicting the electronic behavior, such as their energy level alignment, which ultimately affects the charge carrier injection and transport in devices. Here, local doping is demonstrated and thus adjusting the opto-electronic properties of monolayer TMDCs (WSe₂ and MoS₂) by chemically engineering the surface of the supporting substrate. This is achieved by decorating the substrate by microcontact printing with patterns of two different self-assembled monolayers (SAMs). The SAMs posses distinct molecular dipoles and dielectric constants, significantly influencing the TMDCs electronic and optical properties. By analyzing (on various substrtates), it is confirmed that these effects arise solely from the interaction between SAMs and TMDCs. Understanding the diverse dielectric environments experienced by TMDCs allows for a correlation between electronic and optical behaviours. The changes primarily involve alteration in the electronic band gap width, which can be calculated using the Schottky-Mott rule, incorporating the dielectric screening of the TMDCs surroundings. This knowledge enables accurate prediction of the (opto-)electronic behavior of monolayer TMDCs for advanced device design.

A new Hg-based sulfide Zn₂HgP₂S₈ with wide bandgap and large SHG response is presented. It shows an unprecedented wide bandgap of 3.37 eV in Hg-based chalcogenide IR NLO materials, and first breaks the 3.0 eV bandgap “wall” in this system. Such a wide bandgap can attribute to the strong s-p hybridization between Hg-S bonding in distorted [HgS₄] units.

Abstract

Hg-based chalcogenides, as good candidates for the exploration of high-performance infrared (IR) nonlinear optical (NLO) materials, usually exhibit strong NLO effects, but narrow bandgaps. Herein, an unprecedented wide bandgap Hg-based IR NLO material Zn₂HgP₂S₈ (ZHPS) with diamond-like structure is rationally designed and fabricated by a tetrahedron re-organization strategy with the aid of structure and property predictions. ZHPS exhibits a wide bandgap of 3.37 eV, which is the largest one among the reported Hg-based chalcogenide IR NLO materials and first breaks the 3.0 eV bandgap “wall” in this system, resulting in a high laser-induced damage threshold (LIDT) of ≈2.2 × AgGaS₂ (AGS). Meanwhile, it shows a large NLO response (1.1 × AGS), achieving a good balance between bandgap (≥3.0 eV) and NLO effect (≥1 × AGS) for an excellent IR NLO material. DFT calculations uncover that, compared to normal [HgS₄]_n, highly distorted [HgS₄]_d tetrahedral units are conducive to generating wide bandgap, and the wide bandgap in ZHPS can be attributed to the strong s-p hybridization between Hg─S bonding in distorted [HgS₄]_d, which gives some insights into the design of Hg-based chalcogenides with excellent properties based on distorted [HgS₄]_d tetrahedra.

This study demonstrates that GaN/Ga₂O₃ heterojunctions can be fabricated by utilizing laser writing to transform the surface of GaN into Ga₂O₃. Moreover, an 8 × 8 GaN/Ga₂O₃ heterojunction photodetector array is fabricated via laser writing, which can be utilized for ultraviolet imaging. This report offers a versatile and scalable approach for the production of large-area heterojunction photodetector arrays.

Abstract

Photodetectors play a crucial role in converting light signals into electrical signals and have significant applications in various fields such as communications, imaging, and sensing. However, the fabrication of a photodetector is a complex process that involves precise control of surface preparation, lithography, and deposition techniques. Here the study demonstrates that GaN/Ga₂O₃ heterojunctions can be fabricated utilizing laser processing to transform the surface of GaN into Ga₂O₃. The GaN/Ga₂O₃ heterojunctions exhibit good reproducibility, uniformity, and ability to operate under zero bias, with a responsivity of 110.22 mA W⁻¹, a detection rate of 5.56 × 10¹¹ jones, and an external quantum efficiency of 42.34%. Moreover, an 8 × 8 photodetector array based on GaN/Ga₂O₃ heterojunction is fabricated via laser writing and is demonstrated to have ultraviolet imaging capabilities. This report presents the pioneering fabrication of a photodetector array using laser writing. The findings offer a versatile and scalable approach for the production of large-area heterojunction photodetector arrays.

Nature Communications, Published online: 21 July 2023; doi:10.1038/s41467-023-40123-1

High-speed optoelectronic nonvolatile memory is constructed based on van der Waals heterostructure. This device exhibits exceptional characteristics, including a large storage window ratio (≈75.5%), an extremely high on/off ratio (10⁷), long retention time >10000 s, abundant endurance (>1000 writing/erasing cycles) and ultrafast electrical writing/erasing speed (40 ns). Additionally, the device displays outstanding optoelectronic storage performance. This high-speed nonvolatile optoelectronic memory has potential applications in the next generation of high-performance nonvolatile memory.

Abstract

High-performance optoelectronic nonvolatile memory is promising candidate for next-generation information memory devices. Here, a floating-gate memory is constructed based on van der Waals heterostructure, which exhibits a large storage window ratio (≈75.5%) and an extremely high on/off ratio (10⁷), as well as an ultrafast electrical writing/erasing speed (40 ns). The enhanced performance enables as-fabricated devices to present excellent multilevel data storage, robust retention, and endurance performance. Moreover, stable optical erasing operations can be achieved by illuminating the device with a laser pulse, showcasing outstanding optoelectronic storage performance (optical erasing speed ≈ 2.3 ms). The nonvolatile and high-speed characteristics of these devices hold significant potential for the integration of high-performance nonvolatile memory.

A combination of HCl-based wet chemical pretreatment and surface doping of p-type InP with magnesium is a potential low-temperature method to decrease the losses due to contact resistance (R_C) in InP devices. Computational and experimental surface studies suggest that the presence of the interfacial InPO₄ and In_xNi_y-containing phases increases the In outdiffusion, which enhances the Mg doping.

Manufacturing a low-resistive Ohmic metal contact on p-type InP crystals for various applications is a challenge because of the Fermi-level pinning via surface defects and the diffusion of p-type doping atoms in InP. Development of wet-chemistry treatments and nanoscale control of p-doping for InP surfaces is crucial for decreasing the device resistivity losses and durability problems. Herein, a proper combination of HCl-based solution immersion, which directly provides an unusual wet chemical-induced InP(100)c(2 × 2) atomic structure, and low-temperature Mg-surface doping of the cleaned InP before Ni-film deposition is demonstrated to decrease the contact resistivity of Ni/p-InP by the factor of 10 approximately as compared to the lowest reference value without Mg. Deposition of the Mg intermediate layer on p-InP and postheating of Mg/p-InP at 350 °C, both performed in ultrahigh-vacuum (UHV) chamber, lead to intermixing of Mg and InP elements according to X-ray photoelectron spectroscopy. Introducing a small oxygen gas background (O₂ ≈ 10⁻⁶ mbar) in UHV chamber during the postheating of Mg/p-InP enhances the indium outdiffusion and provides the lowest contact resistivity. Quantum mechanical simulations indicate that the presence of InP native oxide or/and metal indium alloy at the interface increases In diffusion.

This article presents the high-performance sound detection of nanoscale-thick and large-area graphene oxide (GO) films in liquids. Nanoscale-thick and large-area GO films are manufactured using a facile and controllable method. Performance testing results indicate that the nanoscale-thick and large-area GO films can achieve high-performance sound detection in liquids, providing a competitive solution for developing sensors.

This article presents nanoscale-thick and large-area graphene oxide (GO) films manufactured by a facile method to enable high-performance sound detection in liquids. A Fabry–Perot (F–P) cavity consisting of a GO film, whose vibration diameter is ≈4.4 mm, and a single-mode fiber (SMF) is used as the sensing core for sound detection in liquids. A sound-transparent cap, consisting of a support sleeve and a sound-transparent sleeve, is used to protect the GO-sensing diaphragm to resist liquid pressure to enable long-term stability. The sensing probes with GO diaphragms of ≈100 and 200 nm thickness are placed in ultra-pure water for performance testing. Test results show that they maintain a linear sound pressure response, a flat frequency response, and a uniform directional response from 1 to 100 kHz. They have sensitivities of ≈630 mV Pa⁻¹ and about 84 mV Pa⁻¹, respectively, in the range of 1–100 kHz in all directions in different liquids. These results demonstrate the suitability of the nanoscale-thick and large-area GO films for sound detection in liquids with high performance.

The latest emerging trends of luminescence (nano)thermometry are reviewed from a perspective that has not been considered so far. The theoretical framework covering ratiometric and lifetime-based luminescent thermometers, recommendable standardization practices, reliability, and reproducibility, as well as the advancing use of algorithms for thermal readout improvement are discussed. These backgrounds are complemented by cutting-edge applications, current challenges, and future directions.

Abstract

Luminescence (nano)thermometry is a remote sensing technique that relies on the temperature dependency of the luminescence features (e.g., bandshape, peak energy or intensity, and excited state lifetimes and risetimes) of a phosphor to measure temperature. This technique provides precise thermal readouts with superior spatial resolution in short acquisition times. Although luminescence thermometry is just starting to become a more mature subject, it exhibits enormous potential in several areas, e.g., optoelectronics, photonics, micro- and nanofluidics, and nanomedicine. This work reviews the latest trends in the field, including the establishment of a comprehensive theoretical background and standardized practices. The reliability, repeatability, and reproducibility of the technique are also discussed, along with the use of multiparametric analysis and artificial-intelligence algorithms to enhance thermal readouts. In addition, examples are provided to underscore the challenges that luminescence thermometry faces, alongside the need for a continuous search and design of new materials, experimental techniques, and analysis procedures to improve the competitiveness, accessibility, and popularity of the technology

Publication date: October 2023

Source: Progress in Materials Science, Volume 139

Author(s): Avishek Dey, Silvia Varagnolo, Nicholas P Power, Naresh Vangapally, Yuval Elias, Lois Damptey, Bright N. Jaato, Saianand Gopalan, Zahra Golrokhi, Prashant Sonar, Vimalnath Selvaraj, Doron Aurbach, Satheesh Krishnamurthy

2D Cr₂O₃–CrN mosaic heterostructures consisting of a Cr₂O₃ flake with embedded CrN subdomains are synthesized by a designed chemical vapor deposition method. These mosaic heterostructures exhibit room-temperature ferromagnetism that correlates with the interface. By changing the component ratio of CrN and Cr₂O₃ in mosaic heterostructures, the magnetic properties can be modulated.

Abstract

2D magnets have generated much attention due to their potential for spintronic devices. Heterostructures of 2D magnets are interesting platforms for exploring physical phenomena and applications. However, the controlled growth of 2D room-temperature ferromagnetic heterostructures is challenging. Here, one-pot chemical vapor deposition growth of stable 2D Cr₂O₃–CrN mosaic heterostructures (MHs) is reported with a controlled ratio of components that possess robust room-temperature ferromagnetism. The 2D MHs consist of Cr₂O₃ flakes with embedded CrN subdomains and the CrN:Cr₂O₃ ratio can be tuned from 0% to 100% during growth. By changing the CrN:Cr₂O₃ ratio, the ferromagnetism of the MHs (e.g., saturation magnetization, coercive field), which originates from the interfacial coupling between Cr₂O₃ and CrN, can be controlled. Importantly, the obtained Cr₂O₃–CrN MHs are stable in air at elevated temperatures and have robust ferromagnetism with Curie temperature >400 K. This work presents a facile method for fabricating 2D MHs with tunable magnetism which will benefit high-temperature spintronics.

Light: Science & Applications, Published online: 24 July 2023; doi:10.1038/s41377-023-01206-2