High Electron Affinity Research Articles

Nitrogen-doped graphene oxide as a catalyst for the oxidation of Rhodamine B by hydrogen peroxide: application to a sensitive fluorometric assay for hydrogen peroxide.

The authors report that nitrogen-doped graphene oxide (NGO) catalyzes the oxidative decomposition of the fluorophore Rhodamine B (RhB) by hydrogen peroxide. The catalytic decomposition of hydrogen peroxide yields free hydroxyl radicals that destroy RhB so that the intensity of the yellow fluorescence is reduced. Nitrogen doping enhances the electronic and optical properties and surface chemical reactivities of GO such as widening of bandgap, increase in conductivity, enhanced quenching and adsorbing capabilities etc. The catalytic properties of NGO are attributed to its large specific surface and high electron affinity of nitrogen atoms. The chemical and structural properties of GO and NGO were characterized by XRD, FTIR, SEM, UV-visible and Raman spectroscopies. The method was optimized by varying the concentration of RhB, nitrogen dopant and hydrogen peroxide. The fluorescent probe, best operated at excitation/emission wavelengths of 554/577nm, allows hydrogen peroxide to be determined in concentrations as low as 94 pM with a linear range spanning from 1nM to 1μM. Graphical abstract Schematic illustration of a fluorescence quenching method for the determination of H2O2. Upon addition of H2O2, nitrogen-doped graphene oxide (NGO) catalyzes the oxidation of Rhodamine B dye due to hydroxyl radical generation, which leads to a sensitive quenchometric methd for H2 O2.

Autonomous Self-Healing of Electrical Degradation in Dielectric Polymers Using In Situ Electroluminescence

Summary Dielectric polymers are ubiquitous as electrical insulation in electrical power systems and electronic devices. Electrical treeing is typically regarded as an irreversible degradation process of dielectric polymers subjected to high electric stresses, which significantly limits their lifespan and endangers the reliability of electronics and electrical power systems. Here, we report self-healing polymers consisting of microcapsules that are capable of completely restoring the dielectric properties as a direct response to electrical tree degradation. We design the microcapsules with a relatively higher dielectric constant than polymer matrix to guide the propagation of electrical trees. The electroluminescence generated in situ during electrical treeing of polymers triggers crosslinking of the healing agents released from the capsules to repair the electrically damaged areas under ambient conditions. Notably, the breakdown strength of the mended region is largely enhanced upon healing, which was initiated at different locations. The integration of autonomous healing capability into dielectric materials opens new avenues to smart polymers for electronics and energy applications.

Tunable high workfunction contacts: Doped graphene

Contact electrodes with high work functions can enable significant enhancement in optoelectronic device performance due to their important role in efficient extracting/injecting carriers especially from optically active materials with high electron affinity or deep valence band edge, such as CdTe and some perovskites. With such materials becoming increasingly important in emerging solar cell technologies, the need for high work function electrodes has become of timely importance. In this work, p-doped graphene is investigated using first principle calculations, as a potential high work function contact electrode material for optoelectronic device applications. We found that chemical doping based on the adsorption of different non-metallic adatoms on graphene allows tuning the work function which can reach as high as 5.76 eV. A range of p-dopant adatoms, with varying doping concentrations, was investigated and we showed that the largest change of the work function is caused by chlorine and bromine dopants: a 4% concentration of Cl and Br dopants results in an increase of the work function of graphene from 4.38 eV to 5.76 eV and 5.71 eV, respectively. Furthermore, the calculations show that this significant increase in graphene’s work function is mainly due to the charge transfer from graphene to p-dopant adatoms, which increases the concentration of holes at the graphene surface, and hence, increases its work function. We also analyzed the stability conditions for absorbed halogen adatoms on graphite. In particular, we found that halogen molecules formation process should be significantly inhibited by electrostatic repulsion between charged adatoms which provides additional barrier for them to get closer to react. These findings provide valuable guidance to experimental efforts towards the realization of tunable high work function graphene-based electrodes.

MoO3 induces p-type surface conductivity by surface transfer doping in diamond

Surface transfer doping of diamond using high electron affinity transition metal oxides (TMOs), such as MoO3, has emerged as a key enabling technology for the development of diamond-based surface two-dimensional (2D) electronics. However, the omission of a critical pre-annealing step in the device fabrication process to remove atmospheric adsorbates prior to TMO deposition, as seen in numerous studies, makes the role of TMOs ambiguous in light of air-induced surface conductivity, preventing a full understanding of the intrinsic surface transfer doping behavior of TMO-based surface acceptors. Here, using in-situ four-probe electrical measurements we explicitly show the insulating-to-conducting transition in diamond surface driven by MoO3 induced surface transfer doping. Variable-temperature Hall-effect measurements reveal weak temperature-dependence down to 250 mK, evidencing the 2D Fermi liquid nature of the resulting surface conducting channel on diamond. Using first-principles calculations, we confirm the interfacial charge exchange upon MoO3 adsorption leading to a degenerate hole conducting layer on diamond. This work provides significant insights into understanding the surface transfer doping of diamond induced by TMOs, and paves the way for the investigations of many interesting quantum transport properties in the resulting 2D hole conducting layer, such as phase-coherent magnetotransport, on diamond surface.

Infrared Spectra of CH3CN→M, M-η2-(NC)-CH3, CH3-MNC Prepared by Reactions of Laser-Ablated Fe, Ru, and Pt Atoms with Acetonitrile in Excess Argon.

Reactions of laser-ablated Fe, Ru, and Pt atoms with acetonitrile have been carried out in excess argon, and the products identified in the matrix spectra. CH3CN→Fe and Fe-η2-(NC)-CH3 observed in the original deposition spectra converted to CH3-FeNC on uv irradiation. CH3CN→Ru, the only product detected in the Ru system, dissociated on uv irradiation, but was partly reproduced on subsequent visible irradiation and annealing. Similar behavior was found for CH3CN→Pt. The major products (CH3-FeNC, CH3CN→Ru, and CH3CN→Pt) are the most stable constituents in the previously proposed reaction path for Group 4, 5, 6, and 7 metal atoms and acetonitrile, parallel with the previous results. The Group 8 metal π-coordination products are weakly bound complexes due to limited back-donation to the π*-orbitals of CH3CN. Calculations show that the Fe insertion product has a much less bent structure than the Ru analogue, in line with its higher s-character from the first row transition-metal to the C-Fe bond, and the group 8 metal methylidenes are not agostically distorted. The Pt to N bond in CH3CN→Pt is the strongest of all the metals we have investigated owing in large part to its higher electron affinity, which prevents nitrogen lone pair density from entering the pi* orbitals of the C-N group.

Development of A High-performance Amorphous Fluorinated Polymer Electret Based on Quantum Chemical Analysis

In the present study, for the first time, a novel high-performance amorphous fluorinated polymer electret based on quantum chemical analysis is proposed. Density functional theory is adopted to analyse the electron affinity of CYTOP polymers with different end groups. In analysis of CYTOP series with different end groups, it is found that the amide bond at the end of CYTOP chain attract electron, leading to high electron affinity of the molecule. Based on the DFT results, a new electret material has been developed by adding Tris(2-aminoethyl)amine (TAA) into CYTOP CTX-A. With a 15 µm-thick film, a record-high surface charge density of -4 mC/m2 has been obtained. It is also found from the thermally stimulated discharge experiment that the electron trapped in the CTX-A/TAA have higher thermal stability than CYTOP EGG, which is known as the best fluorinated polymer electret.

Synthesis of Conjugated Polymers Containing B←N Bonds with Strong Electron Affinity and Extended Absorption.

The B←N is isoelectronic to the C–C, with the former having stronger dipole moment and higher electron affinity. Replacing the C–C bonds in conjugated polymers with B←N bonds is an effective pathway toward novel polymers with strong electron affinity and adjustable optoelectronic properties. In this work, we synthesize a conjugated copolymer, namely, BNIDT-DPP, based on a B←N embedded unit, BNIDT, and a typical electron-deficient unit, diketopyrrolopyrrole (DPP). For comparison, the C–C counterpart, i.e., IDT-DPP, is also synthesized. In contrast to IDT-DPP, the B←N embedded polymer BNIDT-DPP shows an extended absorption edge (836 versus 978 nm), narrowed optical bandgap (1.48 versus 1.27 eV), and higher electron affinity (3.54 versus 3.74 eV). The Gaussian simulations reveal that the B←N embedded polymer BNIDT-DPP is more electron-deficient in contrast to IDT-DPP, supporting the decreased bandgap and energy levels of BNIDT-DPP. Organic thin-film transistor (OTFT) tests indicate a well-defined p-type characteristic for both IDT-DPP and BNIDT-DPP. The hole mobilities of IDT-DPP and BNIDT-DPP tested by OTFTs are 0.059 and 0.035 cm2/V·s, respectively. The preliminary fabrication of all-polymer solar cells based on BNIDT-DPP and PBDB-T affords a PCE of 0.12%. This work develops a novel B←N embedded polymer with strong electron affinity and extended absorption, which is potentially useful for electronic device application.

Rational molecular design of polymeric materials toward efficient triboelectric energy harvesting

In the periodic table, halogenic elements have a larger electron affinity (EA = −270~−349 kJ/mol) than any other group, allowing them to accommodate extra electrons for triboelectric energy harvesting. However, because halogenic elements are not homopolymerizable, carbon (EA = −122 kJ/mol)-based polymers (i.e. PTFE, PVDF) are often employed for structural use and mechanical integrity at the expense of reduced electron affinity, intrinsically sacrificing triboelectric energy harvesting. Herein, we report the first example of triboelectric energy harvesting with sulfur backbone-based inorganic polymers synthesized via inverse-vulcanization process of elemental sulfur, a by-product of petroleum refining process. Fluorinated polymeric sulfur demonstrated 6-fold and 3-fold increase in triboelectric energy outputs in voltage and currents respectively in comparison with commercial PTFE film. Such high energy harvesting was achieved by high electron affinity of sulfur (−200 kJ/mol) and by its hypervalency via expanded-octet which provided coordination of two additional bonds with halogens compared to carbon. The triboelectric open-circuit voltage output reached 1366 V and demonstrated direct powering of 630 LEDs under the minimal force of ~30 N. This yellow chemistry-based molecular engineering paves a way for a new class of triboelectric materials toward low-cost, eco-friendly, and scalable triboelectric energy harvesting applications.

Quadruply B←N-Fused Dibenzo-azaacene with High Electron Affinity and High Electron Mobility.

For many years, organoboron compounds have been expected to show excellent electron-injecting and -transporting properties. However, lowest unoccupied molecular orbital (LUMO) energy levels (ELUMO) of B-containing π-conjugated molecules are mostly higher than -4.0 eV and their electron mobilities are usually less than 10-2 cm2 V-1 s-1. In this work, we experimentally prove the remarkably high electron affinity and high electron mobility of organoboron compounds. Our strategy is to incorporate multiple boron-nitrogen coordination bonds (B←N) into azaacenes. We synthesized quadruply B←N-fused dibenzo-azaacene (QBNA) through one-pot multifold borylation cyclization reaction. The incorporation of four B←N units greatly changes the electronic structures and properties and significantly downshifts the electronic energy levels of QBNA. QBNA shows a ELUMO of as low as -4.58 eV, which is among the lowest for n-type organic semiconductors. Single-crystal organic field-effect transistors of QBNA display unipolar n-type characteristic with an electron mobility of up to 1.60 cm2 V-1 s-1 together with excellent ambient stability. This study thus provides a design strategy for high-performance n-type organic semiconductors and high electron-affinity π-systems based on organoboron chemistry.

Interfacial and Bulk Nanostructures Control Loss of Charges in Organic Solar Cells.

Organic solar cells (OSCs) have emerged as one promising sustainable energy resource since the introduction of state-of-the-art bulk heterojunction (BHJ) device structure in early 1990s. Impressively developed molecular design methodologies in the past decade have led researchers toward utilizing more suitable pairs of low (p-type) and high (n-type) electron affinity organic semiconducting materials. Among other attributes, versatile absorption capabilities of these materials highlight their favorable utilization in a single layer BHJ structure. Interaction of these verstile organic materials may lead to explicit interfaces, phase distributions, and crystalline nanostructures. Structural characterization techniques involving soft and hard X-rays have enabled us to measure these morphology parameters quantitatively including their string correlation with photovoltaic (PV) parameters. Favorable processing techniques have been adopted to realize auspicious interfacial areas and charge percolations in bulk toward efficient short circuit current (JSC) and fill factor (FF) values. Collaborative efforts in the fields of chemical structure design of materials, device characterization, and engineering have pushed the power conversion efficiencies (PCEs) of OSCs to 16%. However, the single layer BHJ structure still requires further optimizations for the extension of their PCEs toward the theoretical limit. Maximum utilization of solar energy by organic blend films is the key to match their potential with inorganic/perovskite solar cells. Having comparable JSC and FF values in organic versus inorganic photovoltaic devices, open circuit voltage (VOC) is the only PV parameter limiting the development of OSCs in comparison to their inorganic competitors. This is due to unfavorable competition between rates of charge generation and recombination. Loss of charges during these generation and recombination processes account for the energy loss of the device, ranging from 0.6 to 1.0 V in state-of-the-art OSCs. Highly efficient (14-16%) single layer BHJ devices usually suffer from high energy loss with VOC limited to 0.9 V. Comparatively, devices with reported VOC > 0.9 V suffer from poor JSC and FF values due to unfavorable interfacial ordering and bulk crystalline nanostructures. First part of the Account will address the charge losses during their transfer (interfacial losses) and influential role of interfacial nanostructures in controlling them toward efficient JSC and VOC values. Later, we will discuss losses during exciton diffusion and free charge transport (bulk losses) toward limited charge extraction. We will debate about the role of donor/acceptor nanostructures in correlation with influential photophysics studies to control these losses in small molecule (SM) acceptor based devices. We search for exaggerated crystalline phases of SM acceptor in competition with polymer donor to realize balanced and more efficient charge percolations. These improved diffusion and transport bulk nanostructures will suppress nonradiative (NR) pathways and bulk charge losses toward simultaneous enhancement of FF and VOC values. Favorable interfacial and bulk morphology will drive efficient diffusion, transfer, transport, and extraction of charges in organic blend films. This Account will guide chemists and engineers to optimize chemical structure design and blend film nanostructures toward suppressed energy loss of OSCs.

Highly Selective and Scalable Fullerene-Cation-Mediated Synthesis Accessing Cyclo[60]fullerenes with Five-Membered Carbon Ring and Their Application to Perovskite Solar Cells

Cyclo[60]fullerenes are widely used in many applications including photovoltaic devices owing to their high electron affinity and mobility for an organic molecule. However, their synthesis has been...

Enhanced thermoelectric performance from self-assembled alkyl chain-linked naphthalenediimide/single walled carbon nanotubes composites

Naphthalenediimide (NDI) derivatives with high electron affinity and strong π–π stacking interactions have been frequently used as electro-active materials in the field of organic optoelectronic materials. However, the out of control feature of the aggregate states of NDI derivatives often lead to their poor performance for thermoelectric applications. Herein, taking the advantage of van der Waals forces intermolecular interactions, alkyl chain-linked NDIs with H-(J-) aggregates through self-assembly were successfully achieved. The NDI-based polymer linked with a decyl chain (NDI-10) showed J-aggregate, in which the intrachain electronic coupling was dominated and the polymer linked with a butyl chain (NDI-4) and a hexyl chain (NDI-6) reviewed H-aggregate, in which interchain coupling was dominated, the hypothesis was confirmed by results of fluorescence, SAXS, and XRD. The different H-(J-) aggregates affects carrier transport in a two-dimensional transmission channel in our polymers. Moreover, by utilizing the high electrical conductivity of single-walled carbon nanotubes (SWCNTs), we achieved high-performance thermoelectric (TE) composites containing SWCNTs and the polymers based on the alkyl chain-linked NDIs. The obtained composites displayed enhanced TE performance with a high power factor of 238 ± 21 μW m−1 K−2 at 300 K. The corresponding TE module consisting of ten p-type junctions reaches a large output voltage of 5.82 mV and an output power of 28 nW under a 30 K temperature difference. This design strategy promotes the future fabrication of high-performance TE materials and modules.

A DFT study of the surface charge transfer doping of diamond by chromium trioxide

In this study, a density functional theory method is employed to investigate the surface charge transfer doping of diamond by chromium trioxide (CrO3) with high electron affinity. Superior surface charge transfer of the hydrogenated diamond surface is demonstrated using CrO3 as an electron acceptor. The charge density difference and Bader charge analysis reveal that the electrons are transferred from the diamond surface to CrO3 molecule, leading to the formation of two-dimensional hole gas, and the holes left in the diamond surface increase the conductivity of the diamond surface. The analysis of electronic structure indicates that areal hole density as large as 9.85 × 1013cm−2 for CrO3-doped diamond surface can be achieved. Besides, the optical absorption near infrared region of the hydrogenated diamond surface is greatly enhanced upon CrO3 doping, which implies that this CrO3-doped diamond surface is a promising candidate for optoelectronic materials. The present study provides an in-depth theoretical understanding of the formation of two-dimensional hole gas on diamond surface induced by a new transition metal oxide, and predicts that the CrO3-doped diamond surface may have important implications in electronic and optoelectronic devices.

Asymmetric Aqueous Supercapacitor Based on p- and n-Type Conducting Polymers

We demonstrated an asymmetric aqueous supercapacitor made of p- and n-type conducting polymer electrodes. We used the high electron affinity (EA) n-type polymer poly(benzimidazobenzophenanthroline)...

Stable Tetra- and Penta-Anions in the Gas Phase.

The quest for stable gas-phase anions in highly negative charge states has been a great challenge. While multiply charged anions are stabilized in solids and liquids by compensating cations and solvation cells, respectively, stable anions containing less than a hundred atoms in the gas phase and capable of carrying charge beyond -3 is unknown. Here, we report the discovery of thermodynamically stable tetra- and penta-anions, containing less than 50 and 80 atoms, respectively, in the gas phase. A universal model is developed that explains their stability in terms of the synergy between closed shell, high electron affinity, and size and predicts new highly-charged anions by using the known charged clusters as building blocks. Synthesis of these species can open a new chapter in materials chemistry.

Stable Tetra‐ and Penta‐Anions in the Gas Phase

AbstractThe quest for stable gas‐phase anions in highly negative charge states has been a great challenge. While multiply charged anions are stabilized in solids and liquids by compensating cations and solvation cells, respectively, stable anions containing less than a hundred atoms in the gas phase and capable of carrying charge beyond −3 is unknown. Here, we report the discovery of thermodynamically stable tetra‐ and penta‐anions, containing less than 50 and 80 atoms, respectively, in the gas phase. A universal model is developed that explains their stability in terms of the synergy between closed shell, high electron affinity, and size and predicts new highly‐charged anions by using the known charged clusters as building blocks. Synthesis of these species can open a new chapter in materials chemistry.

Integration of Fullerenes as Electron Acceptors in 3D Graphene Networks: Enhanced Charge Transfer and Stability through Molecular Design.

Here, we report a concept that allows the integration of the characteristic properties of [60]fullerene in 3D graphene networks. In these systems, graphene provides high electrical conductivity and surface area while fullerenes add high electron affinity. We use molecular design to optimize the interaction between 3D graphene networks and fullerenes, specifically in the context of stability and charge transfer in an electrochemical environment. We demonstrated that the capacity of the 3D graphene network is significantly improved upon the addition of C60 and C60 monoadducts by providing additional acceptor states in the form of low-lying lowest unoccupied molecular orbitals of C60 and its derivative. Guided by experimental results and first-principles calculations, we synthesized and tested a C60 monoadduct with increased stability by strengthening the 3D graphene-C60 van-der-Waals interactions. The synthesis method and stabilization strategy presented here is expected to benefit the integration of graphene-C60 hybrid materials in solar cell and charge storage applications.

Recent Progress on Fabrication of Zinc Oxide Nanorod-based Field Effect Transistor Biosensors

Zinc oxide is a unique n-type semiconducting material, owing to wide bandgap of ~3.37 eV, non-toxic, bio-safe and biocompatible with high isoelectric point of ~9.5, make it as promising biomaterial to be utilized as sensing matrix in biosensor applications. In addition, ZnO that possess high electron affinity provide a good conduction pathway for the electrons hence result in significant electrical signal change upon detection to target biomolecules. Moreover, high surface area of ZnO nanorod enhance immobilization of enzymes, hence, increase the device performance. Field effect transistor (FET)-based biosensor offer simplicity in handling and label-free, has also become research topic among researchers for novel biosensor development. This review aims to explore the preparation of ZnO nanorod using hydrothermal method and investigate the fabrication of ZnO nanorod-based FET biosensor. Thus, contribute to enhance understanding towards biosensor development for health monitoring, especially based on FETs structure devices.

Adsorption behaviors of gas molecules on the surface of ZnO nanocrystals under UV irradiation

A UV-activated room temperature chemiresistive gas sensor based on ZnO nanocrystals film was fabricated. Its gas sensing properties under various conditions were also investigated in detail. The results shed new insight into the adsorption behaviors of gas molecules on the surface of ZnO nanocrystals under UV irradiation. The chemisorbed oxygen species (O2(ads)−(hv)) induced by UV light govern the adsorption and desorption ways of other gas molecules on the surface of ZnO nanocrystals, which is dependent on the electron affinity of gas molecules. Gas molecules with higher electron affinity than oxygen molecules can be adsorbed on the surface by the competitive adsorption way, extracting electrons from the surface. Gas molecules with lower electron affinity than oxygen molecules are attracted by the adsorbed O2(ads)−(hv) layer, releasing electrons to the surface. These processes can influence the gas sensing properties of the sensor. Our findings will pave the way for the fundamental understanding and design of UV-activated gas sensor in the future.

Long‐Range Ordered Crystals of 3D Inorganic–Organic Heterojunctions via Colloidal Lithography

AbstractColloidal lithography (CL) has evolved as an alternative to conventional photo‐ and electron‐beam lithography to pattern surfaces with nanometer range resolution. As CL offers substrate‐independent precise positioning and patterning of nanomaterials as long‐range ordered crystals, this has seen new opportunities in optoelectronics. Herein, the scope of CL is expanded to fabricate for the first time, 3D organic–inorganic heterojunction photocatalysts with well‐controlled spacing and coverage density. To achieve this, monodisperse polystyrene (PS) beads of different sizes are used as colloidal masks on a ZnO substrate. Electron beam assisted silver deposition onto these PS masks, and subsequent removal of PS lead to the formation of patterns of silver nanostars on the ZnO thin film. The solid–vapor reaction of silver nanostars with a metal‐coordinating charge‐transfer complex of 7,7,8,8‐tetracyanoquinodimethane (TCNQ) allows spontaneous conversion of Ag nanostars to the large aspect ratio nanowires of metal–organic AgTCNQ semiconductors. This strategy, combining the strengths of CL with high electron affinity of TCNQ molecules allows facile fabrication of long‐range patterns of the heterojunctions of organic (AgTCNQ) and inorganic (ZnO) semiconductors. These surface‐supported 3D heterojunctions act as outstanding photocatalysts through their ability to efficiently separate the electron–hole pairs and thus increasing the electron–hole life times.