Edge Effect in Electronic and Transport Properties of 1D Fluorinated Graphene Materials

A systematic examination of the electronic and transport properties of 1D fluorine-saturated zigzag graphene nanoribbons (ZGNRs) is presented in this article. One publication (Withers et al., Nano Lett., 2011, 11, 3912–3916.) reported a controlled synthesis of fluorinated graphene via an electron beam, where the correlation between the conductivity of the resulting materials and the width of the fluorinated area is revealed. In order to understand the detailed transport mechanism, edge-fluorinated ZGNRs with different widths and fluorination degrees are investigated. Periodic density functional theory (DFT) is employed to determine their thermodynamic stabilities and electronic structures. The associated transport models of the selected structures are subsequently constructed. The combination of a non-equilibrium Green’s function (NEGF) and a standard Landauer equation is applied to investigate the global transport properties, such as the total current-bias voltage dependence. By projecting the corresponding lesser Green’s function on the atomic orbital basis and their spatial derivatives, the local current density maps of the selected systems are calculated. Our results suggest that specific fluorination patterns and fluorination degrees have significant impacts on conductivity. The conjugated π system is the dominate electron flux migration pathway, and the edge effect of the ZGNRs can be well observed in the local transport properties. In addition, with an asymmetric fluorination pattern, one can trigger spin-dependent transport properties, which shows its great potential for spintronics applications.

The structure and electronic properties of fluorinated graphene

Аннотация. Графен обладает целым рядом уникальных свойств, чем и привлекает внимание многих исследователей. Кроме фундаментального интереса, связанного с «релятивистским» поведением носителей заряда, графен перспективен как материал для приборов нано-, оптоэлектроники и плазмоники. Когда мы говорим о достоинствах приборов на основе графена, в литературе везде упоминаются: высокая подвижность электронов, возможность эффективного управления электрическими и оптическими свойствами с помощью внешнего напряжения. Эффективность в данном случае обусловлена низкой плотностью электронных состояний, которая определяется линейной зависимостью энергетического спектра от волнового вектора. Основным препятствием к применению графена в электронике является отсутствие запрещенной зоны между валентной зоной и зоной проводимости. Химическая модификация графеновых слоев имеет большое значение для разработки новых материалов, поскольку она не только открывает щель между валентной зоной и зоной проводимости, но и позволяет контролировать ее ширину. Поэтому одной из областей исследований таких систем является химическая функционализация, а именно адсорбирование атомами фтора графена. В данной работе мы изучили структурные и электронные свойства фторированного графена в зависимости от концентрации атомов фтора и от их местоположения в кристаллической решетке, используя вычисления из первых принципов, основанные на теории функционала плотности. Результаты показывают, что электронные свойства фторированного графена сильно зависят от степени фторирования и местоположения атомов в кристаллической решетке.

Preparation of Polyimide Films with Ultra-Low Dielectric Constant by Phase Inversion

Due to the high value of its dielectric constant, polyimide does not meet the requirements of the development of integrated circuits and high-frequency printed circuits. The development of novel low dielectric constant polyimide materials for the preparation of flexible copper clad laminates is of theoretical and practical significance in the application of polyimide for 5G communications. In this work, different fluorinated graphene/polyamic acids (FG/PAA) were used as the precursor, and the porous polyimide film was successfully prepared by phase inversion. The dielectric constant of the porous polyimide film is relatively low, being less than 1.7. When the content of fluorinated graphene is 0.5 wt%, the overall dielectric performance of the porous film is the best, with a dielectric constant of 1.56 (10 kHz) and a characteristic breakdown field strength of 56.39 kV/mm. In addition, the mechanical properties of the film are relatively poor, with tensile strengths of 13.87 MPa (0.2 wt%), 13.61 MPa (0.5 wt%), and 6.25 MPa (1.0 wt%), respectively. Therefore, further improving the breakdown resistance and mechanical properties of the porous film is essential for the application of porous ultra-low dielectric polyimide materials.

Preparation of Modified Fluorographene Oxide with Interlayer Supporting Structure

Fluorinated graphene (FGi) is easy to agglomerate, after which it turns into a curly and wavy shape, which results in a great decrease in the properties of the resultant composite materials and coatings. In this study, fluorinated graphene oxide (FGO) modified with p-phenylenediamine (PPD) was prepared, but with a view to avoid its agglomeration and retain a sheet-like structure. Through the reaction between PPD and the epoxy groups of FGO, the modified FGO with an amino group (N-PGO) had a larger interlayer d-spacing than FGO. The stability of N-PGO was also improved, and nitrogen, fluorine, oxygen, and carbon were evenly distributed in the N-PGO sheets. All the results indicate that PPD can act as an effective spacer to separate graphene sheets for good anti-agglomeration properties. This method produced modified graphene with fluorine, amino, and carbonyl groups. It shows potential in introducing N-PGO as a reactive modifier in composite materials and coatings for a variety of industrial applications including waterborne epoxy materials.