Photomodulation of Charge Transport in All-Semiconducting 2D-1D van der Waals Heterostructures with Suppressed Persistent Photoconductivity Effect

Lattice-guided assembly of optoelectronically active π-conjugated peptides on 1D van der Waals single crystals

The deployment of organic molecules in high-performance devices strongly relies on the formation of well-ordered domains, which is often complicated by the dynamic and sensitive nature of supramolecular interactions. Here, we engineered the assembly of water-processable, optoelectronic π-conjugated peptides into well-defined organic-inorganic heterointerfaced assemblies by leveraging the long-range anisotropic ordering of 1D van der Waals (vdW) crystals composed of subnanometer-thick transition metal sulfide chains (MS3; M = Nb, Ta) as assembly templates. We found that the monomers can readily form 1D supramolecular assemblies onto the underlying crystal surface, owing to the structural correspondence between the π-π interactions of the quaterthiophene (4T)-based peptide units (DDD-4T) and sulfur atom ordering along the NbS3 (100) surface. The heterointerfaced assemblies exhibited substantially red-shifted photoluminescence and enhanced visible-range photocurrent generation compared to solution-assembled films. Our results underscore the role of lattice matching in forming ordered supramolecular assemblies, offering an emergent approach to assembling organic building blocks endowed with improved physical properties.

Spin Polarization: A New Frontier in Efficient Photocatalysis for Environmental Purification and Energy Conversion

As a promising strategy to improve photocatalytic efficiency, spin polarization has attracted enormous attention in recent years, which could be involved in various steps of photoreaction. The Pauli repulsion principle and the spin selection rule dictate that the behavior of two electrons in a spatial eigenstate is based on their spin states, and this fact opens up a new avenue for manipulating photocatalytic efficiency. In this review, recent advances in modulating the photocatalytic activity with spin polarization are systematically summarized. Fundamental insights into the influence of spin-polarization effects on photon absorption, carrier separation, and migration, and the behaviors of reaction-related substances from the photon uptake to reactant desorption are highlighted and discussed in detail, and various photocatalytic applications for environmental purification and energy conversion are presented. This review is expected to deliver a timely overview of the recent developments in spin-polarization-modulated photocatalysis for environmental purification and energy conversion in terms of their practical applications.

Rational Design of Stimuli-Responsive Inorganic 2D Materials via Molecular Engineering: Toward Molecule-Programmable Nanoelectronics

The ability of electronic devices to act as switches makes digital information processing possible. Succeeding graphene, emerging inorganic 2D materials (i2DMs) have been identified as alternative 2D materials to harbor a variety of active molecular components to move the current silicon-based semiconductor technology forward to a post-Moore era focused on molecule-based information processing components. In this regard, i2DMs benefits are not only for their prominent physiochemical properties (e.g., the existence of bandgap), but also for their high surface-to-volume ratio rich in reactive sites. Nonetheless, since this field is still in an early stage, having knowledge of both i) the different strategies for molecularly functionalizing the current library of i2DMs, and ii) the different types of active molecular components is a sine qua non condition for a rational design of stimuli-responsive i2DMs capable of performing logical operations at the molecular level. Consequently, this Review provides a comprehensive tutorial for covalently anchoring ad hoc molecular components-as active units triggered by different external inputs-onto pivotal i2DMs to assess their role in the expanding field of molecule-programmable nanoelectronics for electrically monitoring bistable molecular switches. Limitations, challenges, and future perspectives of this emerging field which crosses materials chemistry with computation are critically discussed.

Reversible Photomodulation of Two-Dimensional Electron Gas in LaAlO3/SrTiO3 Heterostructures

Long-lived photoinduced conductance changes in LaAlO₃/SrTiO₃ (LAO/STO) heterostructures enable their use in optoelectronic memory applications. However, it remains challenging to quench the persistent photoconductivity (PPC) instantly and reproducibly, which limits the reversible optoelectronic switching. Herein, we demonstrate a reversible photomodulation of two-dimensional electron gas (2DEG) in LAO/STO heterostructures with high reproducibility. By irradiating UV pulses, the 2DEG at the LAO/STO interface is gradually transformed to the PPC state. Notably, the PPC can be completely removed by water treatment when two key requirements are met: (1) the moderate oxygen deficiency in STO and (2) the minimal band edge fluctuation at the interface. Through our X-ray photoelectron spectroscopy and electrical noise analysis, we reveal that the reproducible change in the conductivity of 2DEG is directly attributed to the surface-driven electron relaxation in the STO. Our results provide a stepping-stone toward developing optically tunable memristive devices based on oxide 2DEG systems.

Small Size, Big Impact: Recent Progress in Bottom-Up Synthesized Nanographenes for Optoelectronic and Energy Applications

Bottom-up synthesized graphene nanostructures, including 0D graphene quantum dots and 1D graphene nanoribbons, have recently emerged as promising candidates for efficient, green optoelectronic, and energy storage applications. The versatility in their molecular structures offers a large and novel library of nanographenes with excellent and adjustable optical, electronic, and catalytic properties. In this minireview, recent progress on the fundamental understanding of the properties of different graphene nanostructures, and their state-of-the-art applications in optoelectronics and energy storage are summarized. The properties of pristine nanographenes, including high emissivity and intriguing blinking effect in graphene quantum dots, superior charge transport properties in graphene nanoribbons, and edge-specific electrochemistry in various graphene nanostructures, are highlighted. Furthermore, it is shown that emerging nanographene-2D material-based van der Waals heterostructures provide an exciting opportunity for efficient green optoelectronics with tunable characteristics. Finally, challenges and opportunities of the field are highlighted by offering guidelines for future combined efforts in the synthesis, assembly, spectroscopic, and electrical studies as well as (nano)fabrication to boost the progress toward advanced device applications.

Janus 2D materials via asymmetric molecular functionalization

Janus two-dimensional materials (2DMs) are a novel class of 2DMs in which the two faces of the material are either asymmetrically functionalized or are exposed to a different local environment. The diversity of the properties imparted to the two opposing sides enables the design of new multifunctional materials for applications in a broad variety of fields including opto-electronics, energy storage, and catalysis. In this perspective, we summarize the most enlightening experimental methods for the asymmetric chemical functionalization of 2DMs with tailored made (macro)molecules by means of a supratopic binding (one side) or antaratopic binding (two sides) process. We describe the emergence of unique electrical and optical characteristics resulting from the asymmetric dressing of the two surfaces. Representative examples of Janus 2DMs towards bandgap engineering, enhanced photoresponse and photoluminescence are provided. In addition, examples of Janus 2DMs for real applications such as energy storage (batteries and supercapacitors) and generation (photovoltaics), opto-electronics (field-effect transistors and photodetectors), catalysis, drug delivery, self-healing materials, chemical sensors and selective capture and separation of small molecules are also described. Finally, we discuss the future directions, challenges, and opportunities to expand the frontiers of Janus 2DMs towards technologies with potential impact in environmental science and biomedical applications.

Nanoconfined synthesis of conjugated ladder polymers

This review highlights recent advances in controlled synthesis of conjugated ladder polymers using templates.

Molecular Approach to Engineer Two-Dimensional Devices for CMOS and beyond-CMOS Applications

Two-dimensional materials (2DMs) have attracted tremendous research interest over the last two decades. Their unique optical, electronic, thermal, and mechanical properties make 2DMs key building blocks for the fabrication of novel complementary metal-oxide-semiconductor (CMOS) and beyond-CMOS devices. Major advances in device functionality and performance have been made by the covalent or noncovalent functionalization of 2DMs with molecules: while the molecular coating of metal electrodes and dielectrics allows for more efficient charge injection and transport through the 2DMs, the combination of dynamic molecular systems, capable to respond to external stimuli, with 2DMs makes it possible to generate hybrid systems possessing new properties by realizing stimuli-responsive functional devices and thereby enabling functional diversification in More-than-Moore technologies. In this review, we first introduce emerging 2DMs, various classes of (macro)molecules, and molecular switches and discuss their relevant properties. We then turn to 2DM/molecule hybrid systems and the various physical and chemical strategies used to synthesize them. Next, we discuss the use of molecules and assemblies thereof to boost the performance of 2D transistors for CMOS applications and to impart diverse functionalities in beyond-CMOS devices. Finally, we present the challenges, opportunities, and long-term perspectives in this technologically promising field.

CdSe 1D/2D Mixed-Dimensional Heterostructures: Curvature-Complementary Self-Assembly for Enhanced Visible-Light Photocatalysis

Mixed-dimensional heterostructures (MDHs), which combine nanomaterials of different dimensionalities deliver on the promise to bypass intrinsic limitations of a given low-dimensional material. Here, a strategy to engineer MDHs between two low-dimensional materials by curvature-complementary self-assembly is described. CdSe nanotubes rolled from 2D nanosheets and 1D CdSe nanorods, with negative and positive curvatures, respectively, are selected to illustrate complementary curvature self-assembly. The assembly process, optical, and photoelectrical properties of the CdSe MDHs are thoroughly investigated. Several remarkable features of CdSe MDHs, including increased light absorption, efficient charge separation, and appropriate bandgap structure are confirmed. The MDHs significantly alleviate the sluggish kinetics of electron transfer in the quantum sized CdSe subunits (onset potential of 0.21 V vs RHE for MDHs; 0.4 V lower than their low-dimensional building blocks), while the spatial nano-confinement effect in the CdSe MDHs also assists the interfacial reaction kinetics to render them ideal photocatalysts for benzylamine oxidation (conversion > 99% in 4 h with a two times higher rate than simple mixtures). The results highlight opportunities for building MDHs from low-dimensional building blocks with curvature-complementary features and expand the application spectrum of low dimensional materials in artificial photosynthesis.

Recent advances in optical and optoelectronic data storage based on luminescent nanomaterials

The substantial amount of data generated every second in the big data age creates a pressing requirement for new and advanced data storage techniques. Luminescent nanomaterials (LNMs) not only possess the same optical properties as their bulk materials but also have unique electronic and mechanical characteristics due to the strong constraints of photons and electrons at the nanoscale, enabling the development of revolutionary methods for data storage with superhigh storage capacity, ultra-long working lifetime, and ultra-low power consumption. In this review, we investigate the latest achievements in LNMs for constructing next-generation data storage systems, with a focus on optical data storage and optoelectronic data storage. We summarize the LNMs used in data storage, namely upconversion nanomaterials, long persistence luminescent nanomaterials, and downconversion nanomaterials, and their applications in optical data storage and optoelectronic data storage. We conclude by discussing the superiority of the two types of data storage and survey the prospects for the field.