Flexible, Transparent, and Noncytotoxic Graphene Electric Field Stimulator for Effective Cerebral Blood Volume Enhancement

Enhancing cerebral blood volume (CBV) of a targeted area without causing side effects is a primary strategy for treating cerebral hypoperfusion. Here, we report a new nonpharmaceutical and nonvascular surgical method to increase CBV. A flexible, transparent, and skin-like biocompatible graphene electrical field stimulator was placed directly onto the cortical brain, and a noncontact electric field was applied at a specific local blood vessel. Effective CBV increases in the blood vessels of mouse brains were directly observed from <i>in vivo</i> optical recordings of intrinsic signal imaging. The CBV was significantly increased in arteries of the stimulated area, but neither tissue damage nor unnecessary neuronal activation was observed. No transient hypoxia was observed. This technique provides a new method to treat cerebral blood circulation deficiencies at local vessels and can be applied to brain regeneration and rehabilitation

Mixed Copper States in Anodized Cu Electrocatalyst for Stable and Selective Ethylene Production from CO₂ Reduction

Oxygen–Cu (O–Cu) combination catalysts have recently achieved highly improved selectivity for ethylene production from the electrochemical CO₂ reduction reaction (CO₂RR). In this study, we developed anodized copper (AN-Cu) Cu­(OH)₂ catalysts by a simple electrochemical synthesis method and achieved ∼40% Faradaic efficiency for ethylene production, and high stability over 40 h. Notably, the initial reduction conditions applied to AN-Cu were critical to achieving selective and stable ethylene production activity from the CO₂RR, as the initial reduction condition affects the structures and chemical states, crucial for highly selective and stable ethylene production over methane. A highly negative reduction potential produced a catalyst maintaining long-term stability for the selective production of ethylene over methane, and a small amount of Cu­(OH)₂ was still observed on the catalyst surface. Meanwhile, when a mild reduction condition was applied to the AN-Cu, the Cu­(OH)₂ crystal structure and mixed states disappeared on the catalyst, becoming more favorable to methane production after few hours. These results show the selectivity of ethylene to methane in O–Cu combination catalysts is influenced by the electrochemical reduction environment related to the mixed valences. This will provide new strategies to improve durability of O–Cu combination catalysts for C–C coupling products from electrochemical CO₂ conversion

Modulating Electronic Properties of Monolayer MoS₂ <i>via</i> Electron-Withdrawing Functional Groups of Graphene Oxide

Modulation of the carrier concentration and electronic type of monolayer (1L) MoS₂ is highly important for applications in logic circuits, solar cells, and light-emitting diodes. Here, we demonstrate the tuning of the electronic properties of large-area 1L-MoS₂ using graphene oxide (GO). GO sheets are well-known as hole injection layers since they contain electron-withdrawing groups such as carboxyl, hydroxyl, and epoxy. The optical and electronic properties of GO-treated 1L-MoS₂ are dramatically changed. The photoluminescence intensity of GO-treated 1L-MoS₂ is increases by more than 470% compared to the pristine sample because of the increase in neutral exciton contribution. In addition, the A_1g peak in Raman spectra shifts considerably, revealing that GO treatment led to the formation of p-type doped 1L-MoS₂. Moreover, the current <i>vs</i> voltage (<i>I–V</i>) curves of GO-coated 1L-MoS₂ field effect transistors show that the electron concentration of 1L-MoS₂ is significantly lower in comparison with pristine 1L-MoS₂. Current rectification is also observed from the <i>I–V</i> curve of the lateral diode structure with 1L-MoS₂ and 1L-MoS₂/GO, indicating that the electronic structure of MoS₂ is significantly modulated by the electron-withdrawing functional group of GO

Large Work Function Modulation of Monolayer MoS₂ by Ambient Gases

Although two-dimensional monolayer transition-metal dichalcogenides reveal numerous unique features that are inaccessible in bulk materials, their intrinsic properties are often obscured by environmental effects. Among them, work function, which is the energy required to extract an electron from a material to vacuum, is one critical parameter in electronic/optoelectronic devices. Here, we report a large work function modulation in MoS₂ via ambient gases. The work function was measured by an <i>in situ</i> Kelvin probe technique and further confirmed by ultraviolet photoemission spectroscopy and theoretical calculations. A measured work function of 4.04 eV in vacuum was converted to 4.47 eV with O₂ exposure, which is comparable with a large variation in graphene. The homojunction diode by partially passivating a transistor reveals an ideal junction with an ideality factor of almost one and perfect electrical reversibility. The estimated depletion width obtained from photocurrent mapping was ∼200 nm, which is much narrower than bulk semiconductors