Search

Metal–organic frameworks (MOFs) exhibit large surface areas and low thermal conductivity, making them promising for thermoelectric generation. However, their limited electrical conductivity poses a significant hurdle to be practically useful. Traditionally, enhancing the electrical conductivity of MOFs typically comes at the cost of reducing surface area, thereby increasing thermal conductivity. This study introduces an approach to simultaneously boost the electrical conductivity and porosity of a MOF‐based material while maintaining remarkably low thermal conductivity. The electrically conductive poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) is deployed to nucleate the growth of Cu3(BTC)2 (or simply CuBTC, where BTC = benzene‐1,3,5‐tricarboxylic acid), resulting in the synthesis of composites labeled CPP‐y (where y denotes wt% PEDOT:PSS). Predictably, the CPP‐y composites are more electrically conductive than pure CuBTC, achieving an electrical conductivity exceeding 1.40 S cm−1 at room temperature. Furthermore, the CPP‐y composites exhibit consistently high Brunauer–Emmett–Teller (BET) surface areas of ≈1600 m2 g−1, comparable to pristine CuBTC, while maintaining thermal conductivities below 0.04 W m−1 K−1 at room temperature. With a high Seebeck coefficient in the range 180–373 µV K−1, CPP‐15 and CPP‐23 demonstrate a figure‐of‐merit (zT) of 0.25 and 0.11, respectively, at 285 K, marking a substantial achievement for MOF‐based materials. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2), a two‐dimensional (2D) semiconducting material harbors intrinsic defects that can be harnessed to achieve tuneable electronic, optoelectronic, and electrochemical devices. However, achieving precise control over defect formation within monolayer MoS2, remains a notable challenge. Here, an in‐situ defect engineering approach for monolayer MoS2 using a pressure‐dependent chemical vapor deposition (CVD) process is presented. Monolayer MoS2 grown in a low pressure CVD conditions (LP‐MoS2) produces sulfur vacancy (Vs) induced defect‐rich crystals primarily attributed to the oxygen‐deficient growth conditions. Conversely, atmospheric pressure CVD‐grown MoS2 (AP‐MoS2) passivates these defects with oxygen from ambient conditions. This disparity in defect profiles profoundly impacts crucial functional properties and device performance. AP‐MoS2 shows a drastically enhanced photoluminescence, which is significantly quenched in LP‐MoS2 attributed to in‐gap electron donor states induced by the Vs defects. However, the n‐doping induced in LP‐MoS2 generates enhanced photoresponsivity and detectivity in fabricated photodetectors compared to the AP‐MoS2‐based devices. Defect‐rich LP‐MoS2 outperforms AP‐MoS2 as channel layers of field‐effect transistors (FETs), as well as electrocatalytic material for hydrogen evolution reaction (HER). This work presents a single‐step CVD approach for in situ defect engineering in monolayer MoS2 and presents a pathway to control defects in other monolayer 2D materials. [ABSTRACT FROM AUTHOR]

Liquid metal nanodroplets are an emerging class of underexplored materials with significant potential in many applications, including catalysis, bio‐therapeutics, and phase‐change materials. These nanostructures are generally synthesized by mechanical agitation via ultrasonication of low‐melting metals like Ga. Once these materials are successfully synthesized, they can be suspended in a vast array of different solvents. However, one major issue arises specifically with liquid metal alloys which are found to de‐alloy in the sonication process. Here, it is demonstrated that this challenge can be overcome by undertaking sonication at high temperatures, suspending nanodroplets within molten sodium acetate (NaOAc). After cooling, the nanostructures become planet‐like nanodroplets which are covered by an interfacial oxide crust, feature a liquid metal mantle, and a solid core. The molten salt solvent can effectively be removed rendering this approach to be ideal, especially for catalysts. The proof‐of‐concept application is demonstrated by carrying out electrocatalytic ethanol oxidation, using the Cu–Ga system. The superior performance of the Cu–Ga nanodroplets highlights potential in catalyzing a vast array of reactions. Aside from the Cu–Ga system, this facile process can be applied to multiple other systems, including Ag–Ga, Zn–Ga, Bi–Ga, In–Cu, and Sn–Cu. [ABSTRACT FROM AUTHOR]

Amorphous carbon films with an intermediate content of sp3 atoms are finding applications as resistive switches in devices for bio-sensing and for neuromorphic pattern recognition. To understand resistive switching and photoconductivity in amorphous semiconductors dominated by hopping conduction, we present a theory that unifies the optical and electronic properties. The theory considers all of the states to be localized to various extents instead of being extended electronic states. The electronic density of states (eDOS) is modeled with Gaussian functions, symmetric in energy around the Fermi energy. A "hopping mobility" between localized states that is explicitly both energy and temperature dependent is introduced. We describe an example application to amorphous carbon films prepared by using high power impulse magnetron sputtering that have a range of sp3 hybridization fractions of the carbon atoms. The electronic bandgaps of the films are observed to correlate with their optical bandgaps. The eDOS is benchmarked against optical property measurements made by ellipsometry. The theory explains the temperature dependence of the resistivity and predicts that the films should show a temperature dependent hopping photoconductivity. Measurements confirm the presence of the photoconductivity and reveal its spectral dependence. A link is made between persistent hopping photoconductivity and resistive switching. [ABSTRACT FROM AUTHOR]

Angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) is a technique used for depth‐dependent analysis in the near‐surface region of samples. Calculation of a concentration depth profile using ARXPS requires an inverse Laplace transform, which adds considerable complexity to the analysis. In this insight note, the Tikhonov regularization algorithm for depth profile reconstruction from ARXPS data is examined. The steps required to produce a concentration depth profile are provided. The discussion includes strategies that deal with elastic scattering, electron attenuation, choice of regularization terms and optimization of the regularization parameters. The method is implemented in a Microsoft Excel spreadsheet that allows users to calculate a depth profile for data collected at up to five angles for five different peak components. [ABSTRACT FROM AUTHOR]

Reducing CO2 emissions is crucial for the future survival of the planet and the demand for innovative technologies to capture and reduce CO2, focusing on global net-zero carbon emissions is growing significantly. Hence, researchers worldwide are investigating approaches to mitigate the greenhouse effect caused by excessive emissions of CO2. Low melting point liquid metals offer promising opportunities to exploit novel chemistry in negative emission technologies. In this paper, a high-yield, safe and on-demand approach based on Li-containing liquid metal for the reduction of CO2 to solid materials at low temperatures and atmospheric pressure is reported. In this process, Li metal plays a major role in driving the dissociation of CO2 to its elemental constituents, carbon and oxygen. During the CO2 reduction process, Li dissolved in gallium liquid metal, diffuses to the liquid–gas interface and reduces CO2 to carbon, while undergoing an oxidation reaction. The resulting crust that forms on the surface of the Li–Ga liquid metal alloy consists of solid carbonaceous materials that can be directly utilized as a supercapacitor, achieving a sustainable process for CO2 reduction. The use of Li–Ga liquid metal alloys enables CO2 conversion at near room temperature producing carbonaceous materials that can be effectively integrated into energy storage systems. [ABSTRACT FROM AUTHOR]

We report an electrically conductive carbon film with controllable hydrophilic properties that offers a covalent binding surface containing radicals for biomolecule attachment without using chemical linkers. Films were deposited from an acetylene-containing plasma using plasma immersion ion implantation during growth and subsequently annealed under vacuum. Electrical conductivity, spin density, contact angle, surface energy, surface composition, and covalent binding capability were studied as a function of annealing temperature, revealing three distinct regions. In the first region, surface energy is dominated by polar groups. In the second region, the polar groups are expelled, creating unpaired electrons that dominate the polar component of the surface energy. In the third region, the electrical conductivity rises and the polar component of surface energy falls as the unpaired electrons recombine, leading to an optimum combination of surface energy, spin density, and electrical conductivity for biological applications. It is proposed that persistent radicals are responsible for both high wettability and covalent binding properties. Covalently attached enzyme molecules on the C film can resist stringent washing with detergents. The C films offer the functions of conducting polymers, but with the added features of controllable wettability and a covalent binding capability. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive study regarding the impact of the Al electrode on the surface passivation of three TiOx‐based passivating selective contacts: TiOx:Al/LiFx/Al,TiOx/LiFx/Al, and a‐Si/TiOx:Al/LiFx/Al. A deterioration in passivation is recorded after the deposition of the Al electrode at close to room temperature, where the deterioration correlated to the Al thickness. A thin Al (10 nm) electrode resulted in the most severe passivation decline, while samples with a 100 nm Al electrode showed much less passivation deterioration. Furthermore, it is found that a low‐temperature annealing step led to a partial recovery of the passivation, particularly in the case of TiOx:Al/LiFx/Al and a‐Si/TiOx:Al/LiFx/Al contacts. The presented discovery in this article provides crucial insight into the importance of characterization and evaluation of passivating contacts, which is demonstrated here to be highly sensitive to the deposited metal thickness and the interfacial layers, as well as to the post‐deposition annealing. [ABSTRACT FROM AUTHOR]