Isotope Engineered Fluorinated Single and Bilayer Graphene: Insights into Fluorination Selectivity, Stability, and Defect Passivation

Tailoring the physicochemical properties of graphene through functionalization remains a major interest for next-generation technological applications. However, defect formation due to functionalization greatly endangers the intrinsic properties of graphene, which remains a serious concern. Despite numerous attempts to address this issue, a comprehensive analysis has not been conducted. This work reports a two-step fluorination process to stabilize the fluorinated graphene and obtain control over the fluorination-induced defects in graphene layers. The structural, electronic and isotope-mass-sensitive spectroscopic characterization unveils several not-yet-resolved facts, such as fluorination sites and CF bond stability in partially-fluorinated graphene (F-SLG). The stability of fluorine has been correlated to fluorine co-shared between two graphene layers in fluorinated-bilayer-graphene (F-BLG). The desorption energy of co-shared fluorine is an order of magnitude higher than the CF bond energy in F-SLG due to the electrostatic interaction and the inhibition of defluorination in the F-BLG. Additionally, F-BLG exhibits enhanced light-matter interaction, which has been utilized to design a proof-of-concept field-effect phototransistor that produces high photocurrent response at a time <200 µs. Thus, the study paves a new avenue for the in-depth understanding and practical utilization of fluorinated graphenic carbon.

Organic molecule functionalized lead sulfide hybrid system for energy storage and field dependent polarization performances

A wet chemical route is reported for synthesising organic molecule stabilized lead sulfide nanoparticles. The dielectric capacitance, energy storage performances and field-driven polarization of the organic–inorganic hybrid system are investigated in the form of a device under varying temperature and frequency conditions. The structural analysis confirmed the formation of the monoclinic phase of lead sulfide within the organic network. The band structure of lead sulfide was obtained by density functional theory calculation that supported the semiconductor nature of the material with a direct band gap of 2.27 eV. The dielectric performance of the lead sulfide originated due to the dipolar and the space charge polarization. The energy storage ability of the material was investigated under DC-bias conditions, and the device exhibited the power density values 30 W/g and 340 W/g at 100 Hz and 10 kHz, respectively. The electric field-induced polarization study exhibited a fatigue-free behaviour of the device for 103 cycles with a stable dielectric strength. The study revealed that the lead sulfide-based system has potential in energy storage applications.

Ultra-strong stability of double-sided fluorinated monolayer graphene and its electrical property characterization

Fluorinated graphene has a tunable band gap that is useful in making flexible graphene electronics. But the carbon-fluorine (C-F) bonds in fluorinated graphene can be easily broken by increased temperature or electron beam irradiation. Here, we demonstrate that the stability of fluorinated graphene is mainly determined by its C-F configuration. The double-sided fluorinated graphene has a much stronger stability than the single-sided fluorinated graphene under the same irradiation dose. Density functional theory calculations show that the configuration of double-sided fluorinated graphene has a negative and low formation energy, indicating to be an energetically stable structure. On the contrary, the formation energy of single-sided fluorinated graphene is positive, leading to an unstable C-F bonding that is easily broken by the irradiation. Our findings make a new step towards a more stable and efficient design of graphene electronic devices.

Resistive switching effects in fluorinated graphene films with graphene quantum dots enhanced by polyvinyl alcohol

Two-layer films of partially fluorinated graphene (PFG) with graphene quantum dots and polyvinyl alcohol (PVA) were prepared by means of 2D printing technology. A stable resistive switching effect with the ON/OFF current ratio amounting from one to 4-5 orders of magnitude is found. The decrease in the PVA thickness leads to a change of the unipolar threshold switchings to the bipolar resistive switchings. The crossbar Ag/PFG/PVA/Ag structures retain their performance up to 6.5% deformation. The switching phenomenon is observed for a period about a year. The traps with characteristic activation energies ∼0.05 eV are suggested to be responsible for resistive switching. The time of charge-carrier emission from the localized states was found to be ∼5 μs. A quality model to describe the resistive switching effect in two-layer films implying the conduction over quantum dots proceeding with the participation of active traps at the PFG/PVA interface is proposed. The structures with the design demonstrated threshold resistive switching have their high potential for development of selector devices integrated to sensor or memristors circuits, for information storage and data processing, for flexible and wearable electronics. The structures with lower PVA thickness and the bipolar threshold switching are perspective for non-volatile memory cells for printed and flexible electronics.

Ternary Memristic Effect of Trilayer-Structured Graphene-Based Memory Devices

A tristable memory device with a trilayer structure utilizes poly(methyl methacrylate) (PMMA) sandwiched between double-stacked novel nanocomposite films that consist of 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) doped with graphene oxide (GO). We successfully fabricated devices consisting of single and double GO@PBD nanocomposite films embedded in polymer layers. These devices had binary and ternary nonvolatile resistive switching behaviors, respectively. Binary memristic behaviors were observed for the device with a single GO@PBD nanocomposite film, while ternary behaviors were observed for the device with the double GO@PBD nanocomposite films. The heterostructure GO@PBD/PMMA/GO@PBD demonstrated ternary charge transport on the basis of I–V fitting curves and energy-band diagrams. Tristable memory properties could be enhanced by this novel trilayer structure. These results show that the novel graphene-based memory devices with trilayer structure can be applied to memristic devices. Charge trap materials with this innovative architecture for memristic devices offer a novel design scheme for multi-bit data storage.

Memristic Characteristics from Bistable to Tristable Memory with Controllable Charge Trap Carbon Nanotubes

The incorporation of the one-dimensional carbon nanomaterial carbon nanotubes (CNTs) in poly(methyl methacrylate) (PMMA) was found to successfully develop a resistive switching. It implements memristic characteristics which shift from bistable to tristable memory. The localized current pathways in the organic nanocomposite layers for each intermediate resistive state (IRS) are attributed to the trapping mechanism consistent with the fluorescent measurements. Multi-bit organic memories have attracted considerable interest, which provide an effective way to increase the memory density per unit cell area. This study will be useful for the development and tuning of multi-bit storable organic nanocomposite memory device systems.

Fluorescence turn-off Ag/fluorinated graphene composites with high NIR absorption for effective killing of cancer cells and bacteria

This study establishes FGO–Ag as a novel fluorescence “turn-off” nanocarrier with good targeting efficiency and high NIR absorption and drug loading; it also demonstrates its application in antibacterial and cancer chemo-photothermal treatments.