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Graphene oxide (GO) nano-powder is synthesized by the modified Hummer's method, and further thin films are deposited by using the water solution of GO through spin-coating. These films are thermally reduced along with the synthesized GO nano-powder at 50 to 200 °C in a high vacuum. Microstructural, electrical, and optical properties are expectedly controlled by thermal reduction. The electronic properties of GO are investigated by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure. The reduction is confirmed by Raman spectroscopy. The work function and band gap of GO are tuned with the thermal reduction. The changes in properties of GO are not linear, and anomalous changes are observed for the reduction around 150 °C. Pristine and reduced GO nano-powder is incorporated into TiO 2 paste to be the photoanode for dye-sensitized solar cells (DSSCs). It is observed that the performance of the fabricated cells is significantly enhanced for the GO reduced at 150 °C, and the cell exhibited a significant increment of ∼23% for the power conversion efficiency in comparison to DSSC based on an unmodified TiO 2 photoanode., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Two-dimensional molybdenum disulfide (MoS 2 ) has emerged as a promising material for optoelectronic applications because of its superior electrical and optical properties. However, the difficulty in synthesizing large-scale MoS 2 films has been recognized as a bottleneck in uniform and reproducible device fabrication and performance. Here, we proposed a radio-frequency magnetron sputter system, and post-treatments of electron beam irradiation and sulfurization to obtain large-scale continuous and high-quality multilayer MoS 2 films. Large-area uniformity was confirmed by no deviation of electrical performance in fabricated MoS 2 thin-film transistors (TFTs) with an average on/off ratio of 10 3 and a transconductance of 0.67 nS. Especially, the photoresponsivity of our MoS 2 TFT reached 3.7 A W -1 , which is a dramatic improvement over that of a previously reported multilayer MoS 2 TFT (0.1 A W -1 ) because of the photogating effect induced by the formation of trap states in the band gap. Finally, we organized a 4 × 4 MoS 2 phototransistor array with high photosensitivity, linearity, and uniformity for light detection, which demonstrates the great potential of 2D MoS 2 for future-oriented optoelectronic devices.

Multilayer MoS 2 has been gaining interest as a new semiconducting material for flexible displays, memory devices, chemical/biosensors, and photodetectors. However, conventional multilayer MoS 2 devices have exhibited limited performances due to the Schottky barrier and defects. Here, we demonstrate poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) doping effects in multilayer MoS 2 , which results in improved electrical characteristics (∼4.6× higher on-current compared to the baseline and a high current on/off ratio of 10 6 ). Synchrotron-based study using X-ray photoelectron spectroscopy and grazing incidence wide-angle X-ray diffraction provides mechanisms that align the edge-on crystallites (97.5%) of the PDPP3T as well as a larger interaction with MoS 2 that leads to dipole and charge transfer effects (at annealing temperature of 300 °C), which support the observed enhancement of the electrical characteristics. Furthermore, we demonstrate a complementary metal-oxide-semiconductor inverter that uses a p-type MoSe 2 and a PDPP3T-doped MoS 2 as charging and discharging channels, respectively.

The growth characteristics of Ta 2 O 5 thin films by atomic layer deposition (ALD) were examined using Ta(N t Bu)(NEt 2 ) 3 (TBTDET) and Ta(N t Bu)(NEt 2 ) 2 Cp (TBDETCp) as Ta-precursors, where t Bu, Et, and Cp represent tert-butyl, ethyl, and cyclopentadienyl groups, respectively, along with water vapor as oxygen source. The grown Ta 2 O 5 films were amorphous with very smooth surface morphology for both the Ta-precursors. The saturated ALD growth rates of Ta 2 O 5 films were 0.77 Å cycle -1 at 250 °C and 0.67 Å cycle -1 at 300 °C using TBTDET and TBDETCp precursors, respectively. The thermal decomposition of the amido ligand (NEt 2 ) limited the ALD process temperature below 275 °C for TBTDET precursor. However, the ALD temperature window could be extended up to 325 °C due to a strong Ta-Cp bond for the TBDETCp precursor. Because of the improved thermal stability of TBDETCp precursor, excellent nonuniformity of ∼2% in 200 mm wafer could be achieved with a step coverage of ∼90% in a deep hole structure (aspect ratio 5:1) which is promising for 3-dimensional architecture to form high density memories. Nonetheless, a rather high concentration (∼7 at. %) of carbon impurities was incorporated into the Ta 2 O 5 film using TBDETCp, which was possibly due to readsorption of dissociated ligands as small organic molecules in the growth of Ta 2 O 5 film by ALD. Despite the presence of high carbon concentration which might be an origin of large leakage current under electric fields, the Ta 2 O 5 film using TBDETCp showed a promising resistive switching performance with an endurance cycle as high as ∼17 500 for resistance switching random access memory application. The optical refractive index of the deposited Ta 2 O 5 films was 2.1-2.2 at 632.8 nm using both the Ta-precursors, and indirect optical band gap was estimated to be ∼4.1 eV for both the cases.

Graphene is currently at the forefront of cutting-edge science and technology due to exceptional electronic, optical, mechanical, and thermal properties. However, the absence of a sizeable band gap in graphene has been a major obstacle for application. To open and control a band gap in functionalized graphene, several gapping strategies have been developed. In particular, hydrogen plasma treatment has triggered a great scientific interest, because it has been known to be an efficient way to modify the surface of single-layered graphene and to apply for standard wafer-scale fabrication. Here we show a monolayer chemical-vapour-deposited graphene hydrogenated by indirect hydrogen plasma without structural defect and we demonstrate that a band gap can be tuned as wide as 3.9 eV by varying hydrogen coverage. We also show a hydrogenated graphene field-effect transistor, showing that on/off ratio changes over three orders of magnitude at room temperature.

Ambipolar organic electronics offer great potential for simple and low-cost fabrication of complementary logic circuits on large-area and mechanically flexible substrates. Ambipolar transistors are ideal candidates for the simple and low-cost development of complementary logic circuits since they can operate as n-type and p-type transistors. Nevertheless, the experimental demonstration of ambipolar organic complementary circuits is limited to inverters. The control of the transistor polarity is crucial for proper circuit operation. Novel gating techniques enable to control the transistor polarity but result in dramatically reduced performances. Here we show high-performance non-planar ambipolar organic transistors with electrical control of the polarity and orders of magnitude higher performances with respect to state-of-art split-gate ambipolar transistors. Electrically reconfigurable complementary logic gates based on ambipolar organic transistors are experimentally demonstrated, thus opening up new opportunities for ambipolar organic complementary electronics.

We describe robustly anchored triblock copolymers that adopt loop conformations on surfaces and endow them with unprecedented lubricating and antifouling properties. The triblocks have two end blocks with catechol-anchoring groups and a looping poly(ethylene oxide) (PEO) midblock. The loops mediate strong steric repulsion between two mica surfaces. When sheared at constant speeds of ∼2.5 μm/s, the surfaces exhibit an extremely low friction coefficient of ∼0.002-0.004 without any signs of damage up to pressures of ∼2-3 MPa that are close to most biological bearing systems. Moreover, the polymer loops enhance inhibition of cell adhesion and proliferation compared to polymers in the random coil or brush conformations. These results demonstrate that strongly anchored polymer loops are effective for high lubrication and low cell adhesion and represent a promising candidate for the development of specialized high-performance biomedical coatings.

Mussels survive by strongly attaching to a variety of different surfaces, primarily subsurface rocks composed of metal oxides, through the formation of coordinative interactions driven by protein-based catechol repeating units contained within their adhesive secretions. From a chemistry perspective, catechols are known to form strong and reversible complexes with metal ions or metal oxides, with the binding affinity being dependent on the nature of the metal ion. As a result, catechol binding with metal oxides is reversible and can be broken in the presence of a free metal ion with a higher stability constant. It is proposed to exploit this competitive exchange in the design of a new strategy for the formation, removal, and reformation of surface coatings and self-assembled monolayers (SAM) based on catechols as the adhesive unit. In this study, catechol-functionalized tri(ethylene oxide) (TEO) was synthesized as a removable and recoverable self-assembled monolayer (SAM) for use on oxides surfaces. Attachment and detachment of these catechol derivatives on a variety of surfaces was shown to be reversible and controllable by exploiting the high stability constant of catechol to soluble metal ions, such as Fe(III). This tunable assembly based on catechol binding to metal oxides represents a new concept for reformable coatings with applications in fields ranging from friction/wettability control to biomolecular sensing and antifouling.

The molecular order of organic semiconductors at the gate dielectric is the most critical factor determining carrier mobility in thin film transistors since the conducting channel forms at the dielectric interface. Despite its fundamental importance, this semiconductor-insulator interface is not well understood, primarily because it is buried within the device. We fabricated dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) thin film transistors by thermal evaporation in vacuum onto substrates held at different temperatures and systematically correlated the extracted charge mobility to the crystal grain size and crystal orientation. As a result, we identify a molecular layer of flat-lying DNTT molecules at the semiconductor-insulator interface. It is likely that such a layer might form in other material systems as well, and could be one of the factors reducing charge transport. Controlling this interfacial flat-lying layer may raise the ultimate possible device performance for thin film devices.

We report the first case of the successful measurements of a localized spin antiferromagnetic transition in delafossite-type PdCrO2 by angle-resolved photoemission spectroscopy (ARPES). This demonstrates how to circumvent the shortcomings of ARPES for investigation of magnetism involved with localized spins in limited size of two-dimensional crystals or multi-layer thin films that neutron scattering can hardly study due to lack of bulk compared to surface. Also, our observations give direct evidence for the spin ordering pattern of Cr(3+) ions in PdCrO2 suggested by neutron diffraction and quantum oscillation measurements, and provide a strong constraint that has to be satisfied by a microscopic mechanism for the unconventional anomalous Hall effect recently reported in this system.

The adsorption geometry of cis-2-butene-1,4-diol (BEDO, HOCH(2)CH=CHCH(2)OH) on Si(100)-2 x 1 was studied using scanning tunneling microscopy (STM), high resolution X-ray photoemission spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Bias-voltage-dependent STM images exhibited features characteristic of two distinct BEDO adsorption geometries. One feature was a bright protrusion located on the center of a single dimer, indicating an on-top configuration. The low bias-voltage STM image clearly showed dark features indicative of the formation of Si-H bonds on adjacent dimers in the same dimer row. The other feature was a bright protrusion bridged on end between two adjacent dimers in the same dimer row, indicating an end-bridge configuration. Accompanying this feature, two dark features attributed to Si-H bonds were observed on opposite positions to the bridged protrusion. From the XPS results, the Si 2p core level spectra revealed that the dimer atoms are involved in the formation of Si-O and Si-H bonds. On the other hand, carbon K-edge NEXAFS spectra showed that the C=C bond does not participate in the adsorption reaction and remains as an unreacted group. Collectively, the experimental results indicate that the adsorption of BEDO on Si(100)-2 x 1 occurs through the formation of two Si-O bonds via nucleophilic reaction between the two OH groups of BEDO and two Si-Si dimers. Importantly, the maintenance of the C=C bond means that the C=C functional group can be utilized as a new reaction site for further surface chemical reactions.