Tunable Electrical Properties Research Articles

Recent progress in synthesis and properties of two-dimensional boron carbon nitride for application in energy storage devices

Abstract Two-dimensional (2D) Boron Carbon Nitride (BCN) has recently gained significant attention as a convoluted ternary system owing to its remarkable capability to exhibit a wide range of finely tunable physical, chemical, optical, and electrical properties. In this review, we discuss a variety of stable structure forms of BCN nanosheets. In addition, this review provides recent approaches for synthesizing BCN nanostructures, and properties of BCN derivatives. BCN is a promising material for sustainable energy and energy storage devices. Since BCN application is a challenge in the field of energy, we present potential applications of BCN in the field of energy including supercapacitors and batteries, wastewater treatment, electrochemical sensing, and gas adsorption.

Advancing Biosensing and Imaging with DNA-Templated Metal Nanoclusters: Synthesis, Applications, and Future Challenges—A Review

Metal nanoclusters (MNCs) are emerging as a novel class of luminescent nanomaterials with unique properties, bridging the gap between individual atoms and nanoparticles. Among these, DNA-templated MNCs have gained significant attention due to the synergistic combination of MNCs’ properties (such as exceptional resistance to photostability, size-tunable emission, and excellent optical characteristics) with the inherent advantages of DNA, including programmability, functional modification, molecular recognition, biocompatibility, and water solubility. The programmability and biocompatibility of DNA offer precise control over the size, shape, and composition of MNCs, leading to tunable optical, electrical, and magnetic properties. This review delves into the complex relationship between DNA sequence, structure, and the resulting MNC properties. By adjusting parameters such as DNA sequence, length, and conformation, the size, morphology, and composition of the corresponding MNCs can be fine-tuned, enabling insights into how DNA structure influences the optical, electrical, and magnetic properties of MNCs. Finally, this review highlights the remarkable versatility and latest advancements of DNA-templated MNCs, particularly in biosensing and imaging, and explores their future potential to revolutionize biomedical applications.

Study of morphology, phase composition, optical properties, and thermal stability of hydrothermal zirconium dioxide synthesized at low temperatures.

Oxide nanoparticles exhibit unique features such as high surface area, enhanced catalytic activity, and tunable optical and electrical properties, making them valuable to various industry applications as well as for the development of new research projects. Nowadays, ZrO2 nanoparticles are widely used as catalysts and precursors in ceramic technology. Hydrothermal synthesis with metal salts is one of the most common methods for producing stable tetragonal-phase zirconium dioxide nanoparticles. However, hydrothermal synthesis requires relatively high process temperatures (160-200°C) and the use of advanced heat-resistant autoclaves capable of maintaining high pressure. This paper investigates how different precursors (ZrOCl₂·8H₂O and ZrO(NO₃)₂·2H₂O) and synthesis temperatures (110-160°C) affect the phase composition, optical properties, size, and shape of ZrO₂ nanoparticles produced by hydrothermal synthesis without calcination. In addition, the effect of temperature exposure in the range of 100-1000°C on the phase stability of the synthesized nanoparticles was studied. X-ray diffraction and Raman spectroscopy techniques were used to determine the structure and phase composition, while the optical properties were examined through the analysis of transmission and absorption spectra in the visible and UV ranges. It was found that the obtained particles at synthesis temperatures of 110-130°C have predominantly cubic c-ZrO2 phase, which changes to monoclinic phase when heated above 500°C. Analysis of visible and UV spectroscopy data reveals that the experimental samples have pronounced absorption in the middle UV range (200-260nm) and have an energy band gap Eg varying from 4.8 to 5.1eV. The hydrothermal powders synthesized in this study can be used as absorbers in the mid-UV range and as reinforcing additives in the preparation of technical ceramics.

Reduced Graphene Oxide Supported MoSxSe2-X Bifunctional Electrocatalysts for Electrochemical Ammonia Production from Nitrate

Ammonia (NH₃) holds significant importance across various human activities, finding applications in fertilizers, pharmaceuticals, and carbon-free energy fuel. Traditionally, NH₃ production relies on the energy-intensive Haber-Bosch process, leading to substantial CO₂ emissions. As an alternative, there's growing interest in electrochemical NH₃ production. The electrochemical nitrate reduction reaction (NO₃RR) is particularly promising due to its low energy barrier, high nitrogen source solubility, and high activity. Molybdenum dichalcogenides (Mo-based TMDs) have emerged as catalysts for electrochemical NH₃ production, leveraging their 2D structure, large surface area, and tunable electrical properties. However, Mo-based TMDs having 2H crystal structure face challenges like low electrical conductivity and high hydrogen evolution reaction (HER) activity, which competes with NH₃ production. To address this, we developed various 1T-MoSxSe2-x/rGO electrocatalysts. These catalysts exhibited a yield rate exceeding 3511.9 μg h-1 cm-2 (at -0.6 V vs. RHE) and a 70 % faradaic efficiency (at -0.2 V vs. RHE) in a 1 M KOH and 0.1 M NaNO₃ solution. And their bifunctional properties (Oxygen evolution reaction, OER) show a low overpotential of 338.8 mV at 10 mA. Our research aims to enhance NO3RR under ambient conditions and investigate the potential of bifunctional properties (OER) for the commercialization of electrochemical NH₃ production.

Novel HPMC/PEDOT:PSS nanocomposite for optoelectronic and energy storage applications.

This study investigates a class of materials known as polymer nanodielectrics, which are formed by incorporating ceramic fillers into polymers. These materials offer the unique advantage of tunable electrical and optical properties. The research focuses on the incorporation of high-purity stannic oxide nanoparticles (SnO2 NPs) into a ternary blend matrix of hydroxypropyl methylcellulose (HPMC) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) using a solution casting method. Characterization techniques like X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) revealed alterations in the amorphous nature of the HPMC/PEDOT:PSS blend upon the introduction of SnO2 NPs. These analyses also suggest the formation of interactions between the polymer and nanoparticles. Scanning electron microscopy (SEM) images confirmed the successful dispersion of SnO2 NPs on the surface of the polymer blend, particularly at lower concentrations. The optical properties of the nanocomposite films were investigated using UV-vis spectrophotometry. This analysis allowed for the calculation of optical constants like the bandgap and refractive index. The results showed a dual-bandgap structure, with the direct and indirect bandgaps ranging from 4.92 eV to 4.26 eV and 3.52 eV to 1.68 eV, respectively. Electrical characterization using AC conductivity and dielectric permittivity measurements revealed a dependence on the SnO2 NPs concentration within the frequency range of 0.1 Hz to 10 MHz. The relaxation processes and interfacial polarization effects within these nanocomposites are further discussed in the study. At a frequency of 10 Hz, the AC conductivity exhibited a significant increase, rising from 1.85 × 10-12 S m-1 to 1.04 × 10-9 S m-1 upon the addition of 0.7 wt% SnO2 NPs. These findings highlight the multifunctional nature of the developed nanocomposites. They hold promise for various applications, including UV blockers, optical bandgap tuners, and optical coatings in advanced optoelectronic devices. Additionally, their tunable high permittivity suggests potential use as dielectric substrates for next-generation, high-performance energy storage devices.

Nanoarchstructured MoS2-based strain sensor with exceptional gauge factor

Two-dimensional (2D) MoS2, part of the transition metal dichalcogenides family, has emerged as a promising candidate for wearable strain sensors owing to its unique attributes, including mechanical flexibility, low toxicity, tunable and high electrical properties. MoS2-based sensors exhibit higher gauge factors (∼760 for monocrystalline, ∼56.5 for polycrystalline) and a lower limit of detection than conventional metal sensors. We report an advanced strain sensor with ultra-high sensitivity to minute deformations, exploiting a three-dimensional nanostructured-2D MoS2 (3DN-MoS2) with an arch-like configuration. The nanoarchstructured MoS2-based strain sensor (NaM-SS) achieves exceptional gauge factors, exceeding 1500 for tensile strain, using 3DN-MoS2 sensing material in conjunction with a poly-dimethylsiloxane support. This piezo-resistive sensor, fabricated through an eco-friendly and straightforward process, exhibits remarkable gauge factors at three levels: 1500 (ε < 0.55 %), 13,500 (0.55 %< ε ≤ 0.75 %), and 37,000 (0.75 % < ε ≤ 1.2 %). The sensor’s limit of detection stands at a subtle tensile strain ε of 0.02 %. Furthermore, its feasibility is validated by its ability to monitor various human physical motions, including eye blinking, blood pulsation, and muscle activity. Our findings indicate significant potential for precision strain sensors in applications requiring ultra-high sensitivity, such as detecting subtle biomedical signals, meticulous machinery control, and structural health monitoring.

Tuning of electrical properties and persistent photoconductivity of SnO2 thin films via La doping for optical memory applications

This work explored the potential of utilizing Lanthanum doped tin oxide Sn1−xLaxO2 (x = 0.01 to 0.1) based Metal-Semiconductor-Metal Ohmic photoconductors for optical memory applications making use of the persistent photoconductivity (PPC) property. The structural, optical, and electrical properties of Sn1−xLaxO2 thin films deposited on glass substrates using the spray pyrolysis method, with a focus on the impact of lanthanum concentration on the photoresponse characteristics was investigated. Raman spectroscopy confirmed the presence of oxygen vacancies and nanometric grain size in the films along with the typical Raman active modes of tin oxide. The Sn4+ and La3+ oxidation states in Sn1−xLaxO2 as well as the contributions from lattice oxygen and oxygen vacancies were identified using XPS. Photoluminescence studies revealed emissions in the UV, violet, blue, and yellow regions, corresponding to tin interstitials, oxygen vacancies, and other defects, with intensity variations based on La concentration. All films exhibited n-type conductivity, with La content influencing both resistivity and carrier concentration. Photoconductivity measurements demonstrated enhanced photocurrent under UV illumination, with La doping affecting energy levels and defect states. The Sn0.90La0.10O2 film possessed a photocurrent retention of nearly 64 % within a span of 104 s, showing that higher concentration of La favoured the enhancement of retention of photocurrent for a comparatively longer duration. The significant persistent photoconductivity requires the conditions like optically active materials, a built-in electric field to separate electron-hole pairs, and defect states to trap carriers, which are all met by the prepared Sn1-xLaxO2 photoconductor with higher La doping levels, confirming the suitability of these films for practical use as optical non-volatile memory elements.

Nanocomposite superstructure of zinc oxide mesocrystal/reduced graphene oxide with effective photoconductivity

Metal oxide mesocrystals are the alignment of metal oxide nanoparticles building blocks into the ordered superstructure, which have potentially tunable optical, electronic, and electrical properties suitable for practical applications. Herein, we report an effective method for synthesizing mesocrystal zinc oxide nanorods (ZnONRs). The crystal, surface, and internal structures of the zinc oxide mesocrystals were fully characterized. Mesocrystal zinc oxide nanorods/reduced graphene oxide (ZnONRs/rGO) nanocomposite superstructure were synthesized also using the hydrothermal method. The crystal, surface, chemical, and internal structures of the ZnONRs/rGO nanocomposite superstructure were also fully characterized. The optical absorption coefficient, bandgap energy, band structure, and electrical conductivity of the ZnONRs/rGO nanocomposite superstructure were investigated to understand its optoelectronic and electrical properties. Finally, the photoconductivity of the ZnONRs/rGO nanocomposite superstructure was explored to find the possibilities of using this nanocomposite superstructure for ultraviolet (UV) photodetection applications. Finally, we concluded that the ZnONRs/rGO nanocomposite superstructure has high UV sensitivity and is suitable for UV detector applications.

Building Therapies Layer-by-Layer: 2024 Benjamin Franklin Medal in Chemistry presented to Paula T. Hammond, Ph.D

The field of polymer science and materials engineering is advancing with new assembly processes that allow for the implementation of nanoscale structures and orders at a more affordable cost. Layer-by-layer (LbL) adsorption, which was introduced 30 years ago, has revolutionized the understanding and application of electrostatic assembly. This has resulted in a rapid expansion of the field, generating new scientific insights and engineering applications. Chemical engineers have mainly explored its use in reactive and passive membranes, drug delivery systems, and electrochemical and sensing devices. The 2024 Franklin Medal Laureate Professor Paula T. Hammond has been at the forefront of this progress.Professor Paula T. Hammond has been instrumental in the advancement of this field since its inception. The LbL method allows for the sequential and precise assembly of different charged species, from molecules and polymers to colloidal and nano-to-microscale materials. The assembly is driven by alternating charge interactions or complementary bonding, such as hydrogen bonding. LbL offers unprecedented control over materials selection, properties, and architecture by alternatingly adsorbing oppositely charged species from aqueous solutions. This near-molecular control enables the design of functional materials with widely tunable structural, optical, electrical, and chemical properties. The ability to incorporate an array of building blocks into nanoscale thin films allows for control of film composition across its thickness, which is crucial for many emerging applications. Engineering opportunities span biology, medicine, energy conversion, storage (fuel cells, batteries, electrochromic devices, and solar cells), and sensors.Professor Paula T. Hammond is recognized for being at the forefront of developing LbL and related electrostatic polymer assembly techniques that create entire families of nanostructured polymer and composite systems. Her innovative materials display outstanding static properties as well as a range of dynamic (environmentally responsive) properties. LbL offers a multitude of advantages for biological applications and excels in its impact on drug delivery. Cytocompatibility, engineering the drug loading versatility, film stability, and protecting the payload and its controlled release are paramount for the successful translation of LbL drug delivery systems.Professor Hammond has translated her scientific insights into practical applications in medicine and sustainable energy, nurturing their commercial exploration, expanding their technical impact, and inspiring a generation of soft matter nanomaterials scientists and engineers.

Graphene-Based Catalysts: Emerging Applications and Potential Impact.

Carbon nanofillers in general and graphene in particular are considered as promising potential candidates in catalysis due to their two-dimensional (2D) nature, zero bandwidth, single atom thickness with a promising high surface area: volume ratio. Additionally, graphene oxide via result of tunable electrical properties has also been developed as a catalytic support for metal and metal oxide nanofillers. Moreover, the possession of higher chemical stability followed by ultrahigh thermal conductivity plays a prominent role in promoting higher reinforcement of catalytically active sites. In this review we have started with an overview of carbon nanofillers as catalyst support, their main characteristics and applications for their use in heterogeneous catalysis. The review article also critically focusses on the catalytic properties originating from both functional groups as well as doping. An in-depth literature on the various reaction catalysed by metal oxide based nanoparticles supported on GO/rGO has also been incorporated with a special focus on the overall catalytic efficiency with respect to graphene contribution. The future research prospective in the aforementioned field has also been discussed.

In-situ polymerized boehmite/ cashew gum/ polyvinyl alcohol/ polypyrrole blend nanocomposites with tunable structural, electrical, and mechanical properties for enhanced energy storage applications

This study describes the successful synthesis of boehmite (BHM) nanofiller-reinforced ternary blend nanocomposite films composed of polyvinyl alcohol (PVA), cashew gum (CG), and polypyrrole (PPy) using in-situ polymerization with water as the environmentally friendly solvent. The blend nanocomposites were characterized using Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). FTIR analysis revealed chemical bonding between BHM and the biopolymer matrix at1071 cm-1. FE-SEM images exhibited a uniform distribution of BHM nanofillers within the CG/PVA/PPy matrix, particularly at a 10 wt% concentration. The addition of BHM significantly enhanced the thermal stability and the glass transition temperature of the nanocomposites. The temperature-sensitive AC conductivity, activation energy, and dielectric properties were examined using an impedance analyzer. AC conductivity analysis revealed reduced activation energy (1.277 × 10⁻5 eV at 7 wt% BHM) and increased dielectric constant (from 565.28 to 4411.22). The ternary blend nanocomposite demonstrated a significant 60.2 % increase in tensile strength, reflecting enhanced force resistance, while hardness values ranged from 26 to 30, classifying the films as soft and flexible. Overall, the study highlights significant enhancements in the morphological, electrical, thermal, dielectric, and mechanical properties of the nanocomposite films, emphasizing their promising potential for energy storage applications.

The evolution of morphology and structure of spin-coated Zinc Acetate thin films and their impact on ZnO film morphology

The deposition of ZnO thin films using sol-gel technology is a straight forward and widely used method for fabricating ZnO films with diverse morphologies and tunable electrical and optical properties. Notably, the preparation of ZnO compact layers from a zinc acetate and monoethanolamine (ZA:MEA) solution via spin-coating has gained popularity due to its simplicity. The pretreatment of spin-coated ZA:MEA films significantly impacts the morphology and structure of the resulting ZnO films. While the effects of preheating and its rate on ZnO precursor films have been extensively studied, the morphological and structural evolution of ZA:MEA films immediately after spin-coating and its subsequent impact on the final ZnO film have not been previously explored. In this study, we present the topography and phase composition of as-grown ZA:MEA films using atomic force microscopy (AFM). We conduct an in-situ investigation of the morphological evolution of ZA:MEA films. Our results reveal that as-grown ZA:MEA films possess an inhomogeneous structure. AFM phase image shows two distinct domains in the ZA:MEA films. Over time, we observe the growth of crystals in both vertical and perpendicular directions. ZA:MEA film aged for at least 20 h develops arrays of vertically oriented crystals throughout the film covered with sheet-like crystals forming on the film surface. This temporal evolution in the morphology and structure of ZA:MEA films significantly influences the morphology of the final ZnO film.

Highly Porous Particles of Cellulose Derivatives for Advanced Applications.

A chemical modification of cellulose diacetate by phthalate and nitrate was performed to increase solubility in organic solvents and change the electrical properties. The role of substituents on the conductivity, permittivity, and polarizability of cellulose films is revealed. It has been shown that highly porous micro particles can be obtained from cellulose derivatives by a simple and technological freeze-drying method. The resulting micro sized aerogels have a predominantly spherical morphology and amorphous structure. Suspensions of porous particles of nitro- and phthalylated cellulose derivatives in silicone oil have an increased dielectric permittivity compared to cellulose diacetate particles. Produced particles are novel promising material with tunable electrical properties for advanced applications in composites, including for electrorheological fluids.

Characterization of an Environmentally Responsive Organic-Inorganic Hybrid Fe3O4/SiO2/PPy-c Core-Shell Nanocomposite with Magneto-Chromatic Ability for Synergistic Electrical Properties.

The aim of this study was to analyze the properties of a composite that incorporates carbon black and polypyrrole within an Fe3O4/SiO2 core-shell structure, synthesized using the Stöber method under high ultrasonic irradiation conditions (120 W) for Fe3O4/SiO2 nanocomposite. The Fe3O4/SiO2 core-shell indicates magnetochromatic behavior characterized by temperature-dependent coloration and magnetic alignment. Incorporating carbon black and polypyrrole at moderate temperature (5-15 °C) enhanced the electrical conductivity. The electrical resistivity ρ was 7.30 × 106 Ω·cm for Fe3O4, 3.19 × 108 Ω·cm for Fe3O4/SiO2, and 242.56 Ω·cm for Fe3O4/SiO2/PPy-c at room temperature. When it was performed at moderate temperature (5-15 °C), the ρ of the prepared Fe3O4/SiO2 and Fe3O4/SiO2/PPy-c nanocomposite was 1.08 × 108 and 0.00799 Ω·cm, respectively. Current-voltage measurements revealed a linear relationship, with butterfly shaped curves in the forward-bias region for all samples. The Fe3O4/SiO2/PPy-c nanocomposite's tunable synergistic electrical properties at moderate temperatures make it useful for environmental applications, electrical wiring, and circuitry.

Advances in the Fabrication, Properties, and Applications of Electrospun PEDOT-Based Conductive Nanofibers.

The production of nanofibers has become a significant area of research due to their unique properties and diverse applications in various fields, such as biomedicine, textiles, energy, and environmental science. Electrospinning, a versatile and scalable technique, has gained considerable attention for its ability to fabricate nanofibers with tailored properties. Among the wide array of conductive polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) has emerged as a promising material due to its exceptional conductivity, environmental stability, and ease of synthesis. The electrospinning of PEDOT-based nanofibers offers tunable electrical and optical properties, making them suitable for applications in organic electronics, energy storage, biomedicine, and wearable technology. This review, with its comprehensive exploration of the fabrication, properties, and applications of PEDOT nanofibers produced via electrospinning, provides a wealth of knowledge and insights into leveraging the full potential of PEDOT nanofibers in next-generation electronic and functional devices by examining recent advancements in the synthesis, functionalization, and post-treatment methods of PEDOT nanofibers. Furthermore, the review identifies current challenges, future directions, and potential strategies to address scalability, reproducibility, stability, and integration into practical devices, offering a comprehensive resource on conductive nanofibers.

Ceramic/Polymer Nanodielectrics: Towards a Multifunctional or Smart Performance

Ceramic nanoparticles/polymer composite nanodielectrics constitute a novel class of engineering materials, which exhibit tunable mechanical, thermal, electrical and magnetic properties, energy storing/recovering ability in tandem with processability and corrosion resistance. By these means the produced nanocomposites are characterized by multifunctionality since structural components are able to perform a wide range of desirable functions. When the embedded nanoparticles are polar oxides and/or piezo/ferro-electrics, or any kind of stimuli responsive materials additional functional performance is induced in the nanocomposites, providing a suitable basis for the development of smart materials.

On-chip multi-degree-of-freedom control of two-dimensional materials.

Two-dimensional materials (2DM) and their heterostructures offer tunable electrical and optical properties, primarily modifiable through electrostatic gating and twisting. Although electrostatic gating is a well-established method for manipulating 2DM, achieving real-time control over interfacial properties remains challenging in exploring 2DM physics and advanced quantum device technology1-6. Current methods, often reliant on scanning microscopes, are limited in their scope of application, lacking the accessibility and scalability of electrostatic gating at the device level. Here we introduce an on-chip platform for 2DM with in situ adjustable interfacial properties, using a microelectromechanical system (MEMS). This platform comprises compact and cost-effective devices with the ability of precise voltage-controlled manipulation of 2DM, including approaching, twisting and pressurizing actions. We demonstrate this technology by creating synthetic topological singularities, such as merons, in the nonlinear optical susceptibility of twisted hexagonal boron nitride (h-BN)7-10. A key application of this technology is the development of integrated light sources with real-time and wide-range tunable polarization. Furthermore, we predict a quantum analogue that can generate entangled photon pairs with adjustable entanglement properties. Our work extends the abilities of existing technologies in manipulating low-dimensional quantum materials and paves the way for new hybrid two- and three-dimensional devices, with promising implications in condensed-matter physics, quantum optics and related fields.

Ni3C nanosheets and PVA nanocomposite based memristor for low-cost and flexible non-volatile memory devices

Two-dimensional (2D) MXenes have gained extensive attention in the field of memristors due to their high ion mobility, chemical stability and tunable electrical and surface properties. Moreover, MXenes have tunable interlayer bonding which enables enhancement in memristor performance. In this work, we synthesize a novel nanocomposite of Ni3C nanosheets and polyvinyl alcohol (PVA) and fabricate a flexible memristor with Ag/Ni3C-PVA/ITO/PET configuration for non-volatile memory applications. Ni3C nanosheets were synthesized from Ni-MAX (Ni3AlC2) through a solvothermal etching and exfoliation process. The nanosheet like structure of Ni3C is confirmed through Scanning Electron Microscopy (SEM) and Transmission Electron microscopy (TEM). Characterization techniques like X-ray diffraction (XRD), Raman spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR) reveal the crystalline phases, surface functional groups and chemical bonds present in Ni3C nanosheets and Ni3C-PVA nanocomposite. The memristor was fabricated through a facile low cost solution processed based fabrication technique. The Ag/Ni3C-PVA/ITO/PET memristor exhibits bipolar non-volatile switching characteristics. The device with optimised mass ratio of 4:3 (Ni3C: PVA) shows a decent off/on ratio of 2.09 × 102, long retention time of 104 s, and an endurance of 102 DC cycles. The SET voltage of the as-fabricated device is 2.8 V and the RESET voltage is −5.33 V. The flexible memristor exhibits outstanding mechanical robustness over 500 bending cycles. The high charge carrier mobility of Ni3C results in lower switching voltage and the dielectric property of PVA improves data retention and off/on ratio of the memristor. The resistive switching behaviour is explained through conductive metallic bridge mechanism. The conduction mechanism follows Ohmic conduction in ON state and trap controlled space charge limited current (TCSCLC) mechanism in OFF state. The results demonstrate that the nanocomposite with its superior resistive switching effects is suitable for cost-effective, high-performance, flexible non-volatile memory devices.

(Invited) Electronic Doping in Two-Dimensional Semiconductors

Quantum-confined semiconductors provide highly tunable optical and electrical properties for a wide variety of emerging applications. Two-dimensional semiconductors possess tunable bandgaps, high charge carrier mobilities, and strong light-matter interactions that can enable applications in photovoltaics, quantum information processing, and spintronics. Electronic doping, the intentional introduction of controlled charge carrier density and type (electrons or holes) is a fundamental enabler for many emerging applications of two-dimensional semiconductors. While electrostatic doping in transistor geometries is useful for certain applications, it is important to develop additional methods based on e.g. molecular redox doping and substitutional atomic doping that can provide tunable Fermi level control in the absence of an applied bias. In this presentation, I will discuss our efforts to develop such doping strategies for a variety of two-dimensional semiconductors. I will discuss how electronic doping modulates opto-electronic properties, including ground-state absorbance, charge transport, and excited-state dynamics in these 2D semiconductors. These studies provide fundamental insights into the degree to which molecular and substitutional doping strategies can modulate Fermi level, charge transport, and excitonic optical transitions in 2D semiconductors.

(Invited) Exciton Dissociation in Mixed-Dimensionality SWCNT-Based Heterojunctions

Quantum-confined semiconductors provide highly tunable optical and electrical properties for a wide variety of emerging applications. Semiconducting single-walled carbon nanotubes (s-SWCNTs) have shown tremendous potential in applications ranging from digital logic, biological imaging, quantum information processing, photovoltaics, and thermoelectric energy harvesting. Energy harvesting applications rely critically upon the creation of tailored interfaces that enable the movement of energetic species (excitons, electrons, holes) in specified directions. In this talk, I will discuss the use of a variety of rationally designed “mixed-dimensionality” heterojunctions between s-SWCNTs and transition metal dichalcogenide (TMDC) monolayers to harvest visible/near-infrared photons and convert these excitations into long-lived charge-separated states. Type-II heterojunctions between s-SWCNTs and TMDCs enable rapid exciton dissociation and microsecond charge-separated state lifetimes. We have developed new TMDC/SWCNT/TMDC trilayer architectures that enable charge transfer cascades for improving charge separation yield and lifetime. These trilayer architectures allow us to probe out-of-plane carrier diffusion in the nanotube layer and the degree to which bound interfacial excitons impact the photophysics in these mixed-dimensionality heterostructures. I will also discuss the methodology by which we attempt to quantify the photoinduced exciton dissociation quantum yields in these nanoscale heterostructures. Using several heterostructure results, we are attempting to narrow in on appropriate ways to quantify the local dielectric constant and exciton size in both the SWCNT and TMDC components, each of which impact the estimated charge carrier yields. Taken together, these studies provide fundamental insights into the links between ground-state thermodynamics and excited-state dynamics for model nanoscale heterojunctions used to harvest solar energy and produce long-lived charge-separated states.