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Electrochemical reduction in aqueous graphene oxide (GO) dispersion has emerged as an alternative route to producing a reduced GO (rGO) membrane on Au mesh. Under scanning electron microscopy, an interesting pattern formed by distinct differences was discovered from the deoxidization evolution. Scanning transmission X-ray microscopy shows the chemical composition coordination mixing of C–OH, C–O–C, HO–C O, and C O bonds at nanoscale resolution. The electrochemical reduction of C–OH, new bonding of C–O–C, and structure recovery of C C were obtained from GO transformation into the rGO membrane. In Kelvin probe force microscopy, the same pattern of rGO was also observed for the diversity of work functions ranging from 5.55 to 5.70 eV compared with the uniform distribution of GO of 5.78 eV. Density functional theory calculations predicted that the work function variation originated from the dependence of O atom number and functional group species. A high (low) diversity in work function values was ascribed to the C–O–C (HO–C O) bond even with increasing oxygen numbers, accounting for the peak variation. Controlling the work function holds great significance for photovoltaic behavior and band alignment in photoelectric devices. Thus, growing large-area rGO membranes offers a new route to obtaining membranes for applications requiring transparent materials.

Direct probing of metal–oxygen chemistry at the solid/liquid interface is essential to unravel the reaction mechanism of metal–air batteries. Ambient pressure X-ray photoelectron spectroscopy (APXPS) is an effective tool to study metal–oxygen reactions but has been limited to solid-state environments. Here, for the first time, we demonstrate in situ probing of potassium oxygen reduction/evolution reaction (ORR/OER) via APXPS in ionic liquid-based air batteries. We reveal the formation and oxidation of K2O and K2O2 in K–O2 batteries, highlighting new reaction pathways in addition to the widely established one-electron process in K–O2 batteries. Importantly, we show that the formation and subsequent oxidation of K2O2 trigger irreversible cell chemistry, which could be responsible for capacity decay in K–O2 batteries. We further show that common impurities in air such as H2O and CO2 reduce chemical reversibility of ORR and OER. This study reveals root causes of irreversible cell chemistry in K–air batteries via direct probing of ionic liquid-based air batteries via APXPS, which can be widely applied to study the chemistry of solid/liquid interfaces of metal–air batteries.

Thin Sn films on Ag(111) grown at different Sn coverage and substrate temperature were characterized with low-energy electron diffraction and x-ray photoelectron spectra. The results show that surface alloying of Sn atoms on Ag(111) occurs at a temperature as low as 96 K, indicating a strong tendency to form a surface alloy between Sn and Ag. During the alloying, Sn atoms substitute Ag atoms in random locations, resulting in a disordered Sn/Ag(111) surface. The alloy surface becomes completely ordered with a (√3 × √3) R30° reconstruction (the √3 phase) only when it is annealed above 453 K, but annealing at 403 K converts all Sn atoms on Ag(111) into the alloy state; the surface coverage of Sn is no more than 1/3 monolayer with excess Sn diffusing into the Ag(111) substrate. These observations indicate that the √3 phase with the Sn-Ag surface alloy is the only ordered phase obtainable on Sn/Ag(111) once the Sn-Ag surface alloy is formed. It is consequently impracticable to grow non-alloy ordered phases, such as stanene, on Ag(111) epitaxially at a temperature above 96 K, showing evident discrepancies with the conclusions of the previous computational study.

The holes doping effect on the metal–insulator transition (MIT) behavior of VO2 film is investigated via the tetrafluorotetracyanoquinodimethane (F4TCNQ) molecules adsorption induced surface charge transfer. Comparing with the MIT process of pristine VO2 film, a critical temperature decrease of about 4 °C for the F4TCNQ covered VO2 sample is observed. The MIT depression mechanism is deeply investigated based on detailed experiments including synchrotron radiation photon electronic spectroscopy (SRPES), X-ray absorption near-edge structure (XANES) spectroscopy and variable temperature Raman spectroscopy. Results indicate that the electronic structures of F4TCNQ covered VO2 sample are changed clearly due to the effective holes doping. In addition, the doped holes also change the V 3d orbital occupancy and weaken the electron–electron correlation as well, lowering the crystalline stability energy. Both of the above effects are in favor of triggering the earlier occurrence of MIT, resulting in the decrease of critical temperature.

Highly ordered Ag films grown on cleaved mica with a two-step procedure were characterized in detail with several techniques for surface analysis, including low-energy electron diffraction, X-ray photoemission spectra, a scanning tunneling microscope and angle-resolved photoemission spectra. Silver films of a thickness ≥ 100 nm were deposited on mica substrates at 300 K and stored under ambient conditions. The Ag/mica films became atomically flat and free of contamination when they were transferred into ultra-high vacuum and prepared with sputtering and annealing. The experimental results indicate that the surfaces of the cleaned Ag/mica films have structural and electronic properties resembling those of a Ag(111) single crystal with ordered domains aligned over a macroscopic region, but the surfaces of the Ag/mica films became rough on annealing above 623 K. On the rough surfaces, the surface steps tended to bunch together, yielding flat terraces bound with steps of large heights. With the decreased thermal stability in mind, the Ag/mica film is adoptable as a cheap platform alternative to a Ag(111) single crystal for the growth of highly ordered overlayers.

The uncontrolled lithium dendrite growth during cycling causes safety issues that impede lithium metal batteries from practical applications. In anode-free lithium metal batteries (AFLMBs), the unregulated plating of lithium on bare copper enforces a more severe growth of lithium dendrite. Herein, we guide the direction of lithium (Li) depositions towards the backside of gold sputter perforated polyimide film (PI@Au), which serves as an anode current collector. Thus, Li can deposit on the surface of PI@Au, and subsequently, Li growth takes place in the direction away from the separator face (ASF). This backside deposition and growth tactic allow the battery to operate safely, even when lithium dendrite exists. Remarkably, the dendrite free separator facing (SF) of PI@Au anode demonstrates highly improve cycling stability. Hence, PI@Au//LFP cell is capable of maintaining capacity retention (CR) of 20% for 340 cycles with an average Coulombic efficiency (Av. CE) of 98.7% (0.5 mA/cm2). In contrast, the control cell (Cu//LFP) runs only for 165 cycles under the same value of CR. This work not only proposes an innovative approach in developing ultra-safe AFLMBs but also validates the feasibility of electrically nonconductive substrates as anode current collectors by modifying their lithiophilicity.

In-depth mechanistic understanding of CO2 reduction reaction (CRR) and CO2 evolution reaction (CER) is the prerequisite to develop stable and efficient Li–CO2 batteries. In this study, we investigate the redox reaction of CO2 on the porous carbon surface in ionic liquid electrolyte via synchrotron-based in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) technique. We used ionic liquid to facilitate CO2 capture and stabilize CRR intermediate anions owing to its strong solvation for Li+. We demonstrate that pure CO2 reduction is not electrochemically active at room temperature on porous carbon electrode and its kinetics can be remarkably improved by H2O, which could be responsible for the discrepancy on CRR kinetics in the literature. However, in the presence of H2O, the formed LiOH gradually converted to Li2CO3 leading to severe electrolyte degradation in charging reaction. With the assistance of O2 in the ionic liquid-based electrolyte, we show, for the first time, CRR yields a low-valence amorphous carbon and Li2O2/Li2O in the Li–CO2 batteries. The formed amorphous carbon, Li2O2 and Li2O exhibit higher rechargeability and faster kinetics compared with Li2CO3-oxidation. These new findings provide direct evidence of CRR mechanism and insights in resolving the discrepancy on CRR kinetics in Li–CO2 batteries.

A study of Fe-ion intercalation in Bi2Te3 probed by the x-ray diffraction, magnetization, Hall measurement, and spectra of synchrotron x-ray photoemission spectroscopy is reported, in which a large positive magnetoresistance (MR) and a high carrier mobility for applications have been achieved and probed in the quenched FexBi2Te3 single crystals with x = 0.01 and 0.15. Large positive MR of ∼470% with a Hall mobility of ∼44000 cm2/Vs at 5 K and 6 T has been observed on a quenched Fe0.01Bi2Te3 sample with a quenching temperature Tq of 400 °C, where the electrical parameters can be tuned by Tq. Larger c-axis lattice constants and electron-dominant carriers in the quenched samples lead to the inference that the doped Fe atoms are mostly located at the intercalated van der Waals gap positions and exist as a metallic state of Fe0, which is confirmed by the synchrotron x-ray photoemission spectroscopy (XPS) spectra. Combining the x-ray diffraction, magnetization, and Hall-coefficient studies, here we pave a simple way for probing into the location of Fe dopants in Bi2Te3. In addition, novel magnetotransports of Fe-doped Bi2Te3 associated with the absence of ferromagnetism have been presented, and satisfy the scenario that the topological surface state persists without the loss of topological insulating characteristics of the linear band dispersion, and the large MR may originate from the surface magnetism, even in the presence of Fe impurities. This study also discusses the huge enhancement of Hall mobility arising from the surface Dirac electrons that are accompanied with a modified band structure in quenched Fe0.01Bi2Te3.

For typical organic transistors with a lateral source/drain contact geometry, self-assembled monolayer (SAM) has been extensively applied to modify the organic/dielectric interface state and to improve the in-plane charge transport. Here, we demonstrate that SAM modification can also be applied to improve the out-of-plane charge transport in vertical organic field-effect transistors (VOFETs), leading to a simultaneous increase in the on-current and ON/OFF ratio. We investigate a series of phosphonic acid (PA) SAMs with different alkyl chain length for modification of p-type dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) VOFETs and their corresponding lateral transistors for comparison. The perforated source electrode of VOFETs is fabricated using surfactant-assisted colloidal lithography, which provides excellent control of the perforations fill factor and allows the introduction of an insulating cap layer to eliminate the off-current. Overall, the VOFET modified with dodecyl-PA SAM shows the optimal performance, with a 6 times enhanced mobility (and on-current) and a larger ON/OFF ratio compared to the unmodified device. Similar performance enhancement is also observed in the lateral transistors with SAM modifications. From detailed analyses of DNTT film morphology, crystallinity, and molecular orientation, we demonstrate that SAM modification exerts a strong impact on film morphology not only near the interface but also in the bulk, which plays a major factor for enhancing the mobilities in two types of transistors. The highest mobility obtained in the dodecyl-PA SAM modified VOFET is primarily attributed to the formation of largest grains with a resultant decrease of boundary defect density, despite that the crystallinity and molecular packing are not much improved than the other devices.

The unregulated growth of lithium dendrite upon cycling is hampering the applications of lithium metal batteries. The inherent artificial solid electrolyte interphase (SEI) formed during the first few cycles cannot provide the desired stability of lithium deposition. In the anode free battery (AFB) configuration, uncontrolled lithium plating on bare copper imposes a more serious lithium dendrite growth. Herein, we modify the copper current collector with a binder-free ultra-thin spin-coated graphene oxide (GO). The synchronize smooth and conductive GO-coated artificial SEI with lithium fluoride derived from fluoroethylene carbonate (FEC) electrolyte additive greatly control the lithium deposition. Accordingly, the synergistic effect enables smooth, uniform, and dendrite-free lithium plating. Moreover, the AFB with GO film and 5% FEC in the carbonate-based electrolyte is capable of achieving high coulombic efficiency of an average 98% and attains ~44% of its initial capacity after 50 cycles. In contrast, the full cell with bare Cu//LiNi1/3Mn1/3Co1/3O2 (NMC) has a coulombic efficiency of 89% and retains 26.9% after 20 cycles. Our results demonstrate that the synergy of GO-coated artificial SEI with FEC additive can be a promising approach to impede lithium dendrites growth and result in enhanced electrochemical performance in an AFB.

Ambipolar organic field-effect transistors (OFETs) based on a bilayer structure of highly crystalline small molecules, n-type α,ω-diperfluorohexylquaterthiophene (DFH-4T) and p-type dinaphtho[2,3- b :2′,3′- f ]thieno[3,2- b ]thiophene (DNTT), are investigated. By employing DFH-4T/DNTT as the bottom/top layers and appropriate high work function (WF) electrodes in a bottom-gate, top-contact configuration, the superior ambipolar characteristics with matched electron and hole mobilities of 1–1.1 cm 2 V −1 s −1 are achieved. Intriguingly, this high-performance device exhibits a unique feature of an extremely rough, nonplanar heterojunction in the DFH-4T/DNTT combination and a large electron injection barrier from the high WF electrodes to DFH-4T, suggesting some underlying mechanisms for the effective charge transport and injection. The electrical and structural analyses reveal that the crystal packing of the bottom DFH-4T layer supports the growth of a high-quality DNTT crystal network for high-mobility hole transport upon the nonplanar heterojunction, and also enables the formation of an enlarged organic/metal contact surface for efficient electron injection from the high WF electrodes, as the key attributes leading to an overall excellent ambipolar behavior. The effect of intrinsic charge accumulation at the heterojunction interface on the ambipolar conduction is also discussed. Furthermore, a complementary-like inverter constructed with two DFH-4T/DNTT ambipolar OFETs is demonstrated, which shows a gain of 30.

To explore the possibility of employing thermally generated H atoms to determine the chemical composition of a metallic surface, we investigated the adsorption and desorption of H atoms generated with a thermal cracker on surfaces Au(111) and Ag/Au(111). Angle-resolved photoemission spectra showed that the noble-metallic surfaces deteriorated upon exposure to a flux of H atoms at ~ 100 K. Upon subsequent annealing, the order of the surfaces was mostly recovered when H atoms on the surfaces desorbed, but the recovery was incomplete even with annealing at a temperature much higher than that at which H atoms desorb. X-ray photoemission spectra showed that O-containing contaminants existed on the surfaces after the H dosing. The evolution of O 1s during annealing indicated that the O-containing contaminants were H 2 O and its moieties generated during thermal cracking; the disturbances of the surfaces remaining above the desorption temperature of H atoms were likely caused by chemisorbed O. Our results show that it is possible to employ thermally generated H atoms to determine the chemical composition of a metallic surface, but a small proportion of H 2 O in a H 2 gas line might be unavoidable; precautions against possible O contamination are required when a thermal cracker is employed.

Solvent–vapor annealing was used to increase the field-effect mobility of soluble triethylsilylethynyl anthradithiophene spin-coated on organosilane-terminated silicon dioxide, yielding a high value of 1.2 cm 2 V −1 s −1 . The cause of improvement was investigated by atomic force microscopy, X-ray diffraction, and near-edge X-ray absorption fine structure spectroscopy. Vapor annealing exerts little effect on the molecular tilt and the crystallinity normal to the surface, but improves the film morphology significantly, yielding larger grains with perhaps better in-plane crystallinity.

Mo 2 C@a-C core-shell powders were prepared by reacting Mo powders with gaseous 1-chlorobutane or hexachlorobenzene at 1173 K. The chlorinated reactants acted as the source of carbon for the carburization of Mo and the source of chlorine, which assists the etching of Mo to reduced particle sizes.

Due to its special properties, amorphous carbon (a-C) materials have been reported to display novel functions for many potential optical [1,2], frictional [3] and electronic [2,4] applications. These include protective coating, ultra durable anti-reflection coatings [1,2], mechanical devices [2,3], and electron emitters [4]. The ability to fabricate a-C into desired physical shapes has attracted much attention. For example, anodic aluminum oxide (AAO) has been used as templates to shape a-C into tubular shapes by pyrolyzing propylene inside the AAO channels [5]. In our study herein we report on a process to grow a-C tubes (a-CT) by coupling two fabrication methods we recently developed [6,7]. First, a layer of short aligned a-CT was deposited by LPCVD from SiCl3CCl3 on an AAO substrate [6]. Then, by employing the Na-filled AAO (Na@AAO) reactive template method, we were able to significantly elongate the a-CT [7]. Using a hot-wall LPCVD reactor with a base pressure of 10 1 Pa, SiCl3CCl3 (Aldrich, 97%) was evaporated at 273 K without carrier gas. The precursor was decomposed at 1273 K and 10 Pa to deposit a layer of carbon on AAO substrates (Whatman Anodisc 13, observed pore diameter: 280 nm, thickness: 60 lm). After 3 h, the AAO substrates turned black and the product a-C film on AAO (a-C/AAO) was obtained. As shown by the scanning electron microscope (SEM, JEOL JSM-6330F at 15 kV) images in Fig. 1, the average diameter of the open-ended a-CT, 330–340 nm, is close to the channel diameter in the AAO. The average thickness of the a-CT wall was 30 nm. In Fig. 1(b), the average thickness of the array layer was estimated to be 800 nm, much thinner than the AAO thickness of 60 lm. We speculate that the activated species generated from SiCl3CCl3, :CCl2, cannot diffuse effectively into the AAO channels to form a thick carbon layer. Fig. 1(b) also shows that the a-CT array is connected as a layer of film on top of the AAO. Using energy dispersive spectroscopy (EDS), the composition of the isolated tube array layer was confirmed to be carbon. Thus, the data support the conclusion that we have successfully deposited a-C on AAO (a-C/AAO) in the form of short a-CT array. We also attempted to perform this process on a home-made AAO with a channel diameter of 30 nm. However, :CCl2 apparently could not diffuse into the narrow AAO channels to grow into an a-CT layer. After the short a-C/AAO layer was fabricated by LPCVD, we explored the possibility of extending the tube length by the sodium reactive template method that had been previously developed [6]. By decomposing NaH (Aldrich, 0.2 g, 8 mmol) on a-C/AAO inside a tube furnace at 623 K under 1 atm of Ar (flow rate: 30 sccm) for 0.5 h, Na filled the channels of AAO to generate Na@a-C/AAO. Further reaction of Na@a-C/AAO with Carbon 43 (2005) 2618–2641

Carbon materials with different morphology were prepared by reacting CCl 4 and Mo at 873–1173 K. At 873–973 K, hollow spheres (diameter: 1–3 μm, shell thickness: 50 nm) were obtained. At 1073 K, particles (diameter: 50–100 nm) encapsulated in spherical shells (diameter: 1–5 μm) were collected. At 1173 K, formation of particles (diameter: 200–300 nm) was observed. Mo acted as a reagent to remove chlorine atoms from the carbon source and a template for the formation of the spherical structures. We propose that reaction temperature and polymerization of chlorinated species formed from the pyrolysis of CCl 4 affect the morphology of carbon products greatly.