Unraveling the microscopic origins of non-Fermi liquid behavior near a quantum critical point (QCP) remains a central puzzle in condensed matter physics. A key challenge lies in disentangling the often-coexisting roles of Coulomb interactions and disorder. Here, we use transition metal dichalcogenides (TMDs)─PdSe2, WSe2, and MoS2─as prototypes to understand how Coulomb interactions and disorder govern the electrical resistivity of metals near the QCP. We show that resistivity exhibits Fermi liquid behavior at low temperatures and T-linear resistivity at intermediate temperatures in the deep metallic phase of these systems. As the metal-insulator boundary approaches, the low-temperature Fermi liquid phase turns into the T-linear resistivity in PdSe2 and transitions to an electron glass in WSe2 and MoS2 by increasing the strength of Coulomb interactions and degree of disorder. Further, resistivity develops distinct nonmonotonic T-dependencies in these systems while approaching the metal-insulator boundary, suggesting different microscopic origins of resistivity. This dichotomy is corroborated by quantum critical scaling, which reveals divergent universality classes. This study establishes TMDs as a promising platform for understanding the interplay between Coulomb interactions and disorder in the quantum critical regime.

Even though atomically thin 2D semiconductors have shown great potential for next‐generation electronics, the low carrier mobility caused by poor metal–semiconductor contacts and the inherently high density of impurity scatterings remains a critical issue. Herein, high‐mobility field‐effect transistors (FETs) by introducing few‐layer PdSe 2 flakes as channels is achieved, via directly depositing semimetal antimony (Sb) as drain–source electrodes. The formation of clean and defect‐free van der Waals (vdW) stackings at the Sb–PdSe 2 heterointerfaces boosts the room temperature transport characteristics, including low contact resistance down to 0.55 kΩ µm, high on‐current density reaching 96 µA µm −1 , and high electron mobility of 383 cm 2 V −1 s −1 . Furthermore, metal–insulator transition (MIT) is observed in the PdSe 2 FETs with and without hexagonal boron nitride (h–BN) as buffer layers. However, the layered h–BN/PdSe 2 vdW stacking eliminates the interference of interfacial disorders, and thus the corresponding device exhibits a lower MIT crossing point, larger mobility exponent of γ ∼ 1.73, significantly decreased hopping parameter of T 0 , and ultrahigh electron mobility of 2,184 cm 2 V −1 s −1 at 10 K. These findings are expected to be significant for developing high mobility 2D‐based quantum devices.

Palladium diselenide (PdSe2), as an emerging two-dimensional (2D) layered material, is gaining growing attention in nanoelectronics and optoelectronics due to its thickness-dependent band gap, high carrier mobility, and good air stability. However, its asymmetric pentagon structure is inclined to breed defects. Herein, the intrinsic Se vacancy-induced trap states and their influence on the hopping transport in PdSe2 are systematically investigated. We provide direct evidence that Se vacancies exist in the fresh PdSe2 samples, which results in the localized trapping states inside the band gap. For the few-layer PdSe2, at 77 K, the trap density (Dit) near the midgap is about 2.2 × 1013 cm-2 eV-1, whereas at 295 K, the Dit value increases to ∼7.1 × 1013 cm-2 eV-1. By comparison, the multilayer PdSe2 shows nonobvious temperature-dependent trap behaviors with almost unchanged Dit values of ∼8.1 × 1012 cm-2 eV-1 at midgap in the temperature range between 77 and 295 K. Thus, trap states in the few-layer PdSe2 are more vulnerable to temperature effect. Transport measurements demonstrated that both few-layer and multilayer PdSe2 field-effect transistor (FET) devices show n-type dominant ambipolar behaviors. The electron mobility in the multilayer PdSe2 FET is nearly 15-fold higher than that in the few-layer PdSe2 FET at 315 K, probably owing to the decreased effective mass and suppression of charge impurity scattering in the thicker channel material. However, both FET devices exhibit variable-range hopping over a temperature range from 77 to 240 K and thermally activated hopping at temperatures above 240 K. The hopping transport mechanism is strongly associated with the Se vacancy-induced localized states with poor screening and strong potential fluctuations. This study reveals the important role of structural defects in tailoring and improving the charge transport properties of PdSe2.

Achieving tunable optoelectronic properties and clarifying interlayer interactions are key challenges in the development of 2D heterostructures. Herein, we report the feasible modulation of the optoelectronic properties of monolayer MoS2 (1L-MoS2) on three different graphene monolayers with varying ability in extracting electrons. Monolayer oxygen-functionalized graphene (1L-oxo-G, a high amount of oxygen of 60%) with a work function (WF) of 5.67 eV and its lowly oxidized reduction product, namely reduced-oxo-G (1L-r-oxo-G, a low amount of oxygen of 0.1%), with a WF of 5.85 eV serving as hole injection layers significantly enhance the photoluminescence (PL) intensity of MoS2, whereas pristine monolayer graphene (1L-G) with a work function (WF) of 5.02 eV results in PL quenching of MoS2. The enhancement in the PL intensity is due to increase of neutral exciton recombination. Furthermore, 1L-r-oxo-G/MoS2 exhibited a higher increase (5-fold) in PL than 1L-oxo-G/MoS2 (3-fold). Our research can help modulate the carrier concentration and electronic type of 1L-MoS2 and has promising applications in optoelectronic devices.

In recent years, graphene oxide has been considered as a soluble precursor of graphene for electronic applications. However, the performance lags behind that of graphene due to lattice defects. Here, the relation between the density of defects in the range of 0.2 % and 1.5 % and the transport properties is quantitatively studied. Therefore, the related flakes of monolayers of graphene were prepared from oxo-functionalized graphene (oxo-G). The morphologic structure of oxo-G was imaged by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Field-effect mobility values were determined to range between 0.3 cm(2) V-1 s(-1) and 33.2 cm(2) V-1 s(-1), which were inversely proportional to the density of defects. These results provide the first quantitative description of the density of defects and transport properties, which plays an important role for potential applications.

Hybridizing graphene and molecules possess a high potential for developing materials for new applications. However, new methods to characterize such hybrids must be developed. Herein, the wet-chemical non-covalent functionalization of graphene with cationic pi-systems is presented and the interaction between graphene and the molecules is characterized in detail. A series of tricationic benzimidazolium salts with various steric demand and counterions was synthesized, characterized and used for the fabrication of graphene hybrids. Subsequently, the doping effects were studied. The molecules are adsorbed onto graphene and studied by Raman spectroscopy, XPS as well as ToF-SIMS. The charged pi-systems show a p-doping effect on the underlying graphene. Consequently, the tricationic molecules are reduced through a partial electron transfer process from graphene, a process which is accompanied by the loss of counterions. DFT calculations support this hypothesis and the strong p-doping could be confirmed in fabricated monolayer graphene/hybrid FET devices. The results are the basis to develop sensor applications, which are based on analyte/molecule interactions and effects on doping.

The thermal decomposition of graphene oxide (GO) is a complex process at the atomic level and not fully understood. Here, a subclass of GO, oxo-functionalized graphene (oxo-G), was used to study its thermal disproportionation. We present the impact of annealing on the electronic properties of a monolayer oxo-G flake and correlated the chemical composition and topography corrugation by two-probe transport measurements, XPS, TEM, FTIR and STM. Surprisingly, we found that oxo-G, processed at 300 °C, displays C-C sp3 -patches and possibly C-O-C bonds, next to graphene domains and holes. It is striking that those C-O-C/C-C sp3 -separated sp2 -patches a few nanometers in diameter possess semiconducting properties with a band gap of about 0.4 eV. We propose that sp3 -patches confine conjugated sp2 -C atoms, which leads to the local semiconductor properties. Accordingly, graphene with sp3 -C in double layer areas is a potential class of semiconductors and a potential target for future chemical modifications.

The substrate effect on the electronic transport of graphene with a density of defects of about 0.5% (0.5%G) is studied. Devices composed of monolayer 0.5%G, partially deposited on SiO2 and h-BN were used for transport measurements. We find that the 0.5%G on h-BN exhibits ambipolar transfer behaviours under ambient conditions, in comparison to unipolar p-type characters on SiO2 for the same flake. While intrinsic defects in graphene cause scattering, the use of h-BN as a substrate reduces p-doping.

Die Entwicklung vielseitiger Funktionalisierungskonzepte für Graphen steht derzeit im Fokus der Forschung. Mittels Oxo‐Funktionalisierung von Graphit wird die gesamte Oberfläche von Graphen für die C‐C‐Bindungsbildung zugänglich, um Addenden einzuführen. Hier stellen wir die Arylierung von Graphen durch Arylazocarbonsäure‐ tert ‐butylester vor, die nach Aktivierung durch Säuren Arylradikale erzeugen. Überraschenderweise korreliert der Funktionalisierungsgrad mit der Konzentration der Strukturdefekte im Graphengitter. Folglich ist Graphen inert, wenn es frei von Defekten ist. Die Reaktion kann auch auf in Lösemitteln dispergiertes Graphen angewendet werden und führt zu einer bitopen Funktionalisierung. Ist Graphen auf Oberflächen abgeschieden wird eine monotope Funktionalisierung erreicht. Da Arylazocarbonsäure‐ tert ‐butylester vielfältig an verschiedene Moleküle gebunden werden kann, ebnet das vorgestellte Verfahren den Weg zu funktionellen Graphenderivaten, wobei die Defektdichte im Graphen den Grad der Funktionalisierung bestimmt.

The development of versatile functionalization concepts for graphene is currently in the focus of research. Upon oxo-functionalization of graphite, the full surface of graphene becomes accessible for C-C bond formation to introduce out-of-plane functionality. Herein, we present the arylation of graphene with arylazocarboxylic tert-butyl esters, which generates aryl radicals after activation with an acid. Surprisingly, the degree of functionalization is related to the concentration of lattice vacancy defects in the graphene material. Consequently, graphene materials that are free from lattice defects are not reactive. The reaction can be applied to graphene dispersed in solvents and leads to bitopic functionalization as well as monotopic functionalization when the graphene is deposited on surfaces. As the arylazocarboxylic tert-butyl ester moiety can be attached to various molecules, the presented method paves the way to functional graphene derivatives, with the density of defects determining the degree of functionalization.

Graphene-based materials have attracted increasing attention due to their atomically-thick two-dimensional structures, high conductivity, excellent mechanical properties, and large specific surface areas. The combination of biomolecules with graphene-based materials offers a promising method to fabricate novel graphene-biomolecule hybrid nanomaterials with unique functions in biology, medicine, nanotechnology, and materials science. In this review, we focus on a summarization of the recent studies in functionalizing graphene-based materials using different biomolecules, such as DNA, peptides, proteins, enzymes, carbohydrates, and viruses. The different interactions between graphene and biomolecules at the molecular level are demonstrated and discussed in detail. In addition, the potential applications of the created graphene-biomolecule nanohybrids in drug delivery, cancer treatment, tissue engineering, biosensors, bioimaging, energy materials, and other nanotechnological applications are presented. This review will be helpful to know the modification of graphene with biomolecules, understand the interactions between graphene and biomolecules at the molecular level, and design functional graphene-based nanomaterials with unique properties for various applications.

By specifically binding with various inorganic nanomaterials through their functional groups or introducing special reactivity, the nanostructures and biofunctions of designed peptides can be enriched. This review provides a brief discussion on the design, composition, and biomedical applications of bioinspired peptideinorganic nanomaterial hybrids. The attaching mechanisms of different peptide-inorganic nanomaterials are discussed from the viewpoint of the functional group, nanostructure, and conformational freedom. Particularly, the structures and functions of the obtained hybrids based on different nanomaterials are described in detail. In addition, we highlight some examples of self-assembled peptide-inorganic nanomaterial systems with relevance to biomedical applications, including biosensors, cell targeting, bioimaging, biomineralization, biocatalysts, and drug delivery. We also give a short outlook on the broad prospects of the fabrication and applications of peptide-inorganic nanomaterial hybrids.

Three-dimensional Ag nanoparticle/GNs (Ag/GNs) hybrids as highly efficient counter electrode (CE) materials for dye sensitized solar cells (DSSCs) is described, highlighting the Ag nanoparticles as zero-dimensional nanospacers inserting into GNs to lift the interspacing layer between individual GNs. It is demonstrated that, when the hybrids are used as CE materials for DSSCs, compared to their pure GNs, Ag/GNs hybrids without agglomerates have a significant improvement in their electrochemical properties such as high current density, narrow peak-to-peak separation (Epp) and low charge transfer resistance (RCT). The enhancement of electrochemical performance can be attributed to the increased electrode conductivity, an extended interlayer distance and the reduction of the restacking of graphene sheets due to the insertion of metallic Ag nanoparticles into GNs. The DSSC with this hybrid CE exhibited an energy conversion efficiency (η) of 7.72% with an open circuit voltage (VOC), short circuit photocurrent density (JSC), and fill factor (FF) of 732 mV, 14.67 mA cm(-2), and 71.8%, respectively.

Reduced graphene oxide (RGO) has proven to be effective in trace gas detection at room temperature ambient conditions. However, the slow response-recovery characteristic is a major hurdle for the RGO-based gas sensors. Herein, we report a gravure-printed chemoresistor-type NO2 sensor based on sulfonated RGO (S-RGO) decorated with Ag nanoparticles (Ag-S-RGO). Large amounts of silver nanoparticles with an average particle size of 10-20 nm were uniformly assembled on flat S-RGO surfaces. The printed Ag-S-RGO sensor possesses a high sensitivity and fast response-recovery characteristic over NO2 concentrations ranging from 0.5 to 50 ppm. Upon exposure to 50 ppm NO2 at room temperature, the Ag-S-RGO sensor shows a sensitivity of 74.6%, a response time of 12 s and a recovery time of 20 s. In addition, the Ag-S-RGO sensors exhibit satisfactory flexibility with an almost constant resistance after 1000 bending cycles. The printed and high-performance Ag-S-RGO sensors described here will be a good prospect in environmental monitoring of NO2.

The paper shows the gravure printing technology is used as deposition method to pattern a graphene film on flexible polyimide substrates for a wireless strain sensor (WSS). According to the inductive coupling between the reader antenna and the graphene pattern (GP), a change in the GP characteristic can be detected wirelessly by a corresponding change in the complex impedance of the reader antenna. The WSS overcomes the inadequacy of the existing conventional sensors limited monitoring locations. And the WSS also exhibits a high sensitivity of 51% under a load of 100 N.