Direct growth of graphene films without catalyst on flexible glass substrates by PECVD

A hydrogen-plasma-etching-based plasma-enhanced chemical vapor deposition(PECVD)synthesis route without metal catalyst for preparing the graphene films on flexible glass is developed.The quality of the prepared graphene films is evaluated by scanning electron microscopy,x-ray photoelectron spectroscopy,high-resolution transmission electron microscopy,ultraviolet-visible spectroscopy,and electrochemical measurements.In a radio frequency(RF)power range of 50 W-300 W,the graphene growth rate increases with RF power increasing,while the intensity ratio of D-to G-Raman peak(I_(D)/I_(G))decreases.When the RF power is higher than 300 W,the I_(D)/I_(G)rises again.By optimizing experimental parameters of hydrogen plasma etching and RF power,the properties of as-prepared flexible graphene on glass are modulated to be able to achieve the graphene's transparency,good electrical conductivity,and better macroscopic uniformity.Direct growth of graphene film without any metal catalyst on flexible glass can be a promising candidate for applications in flexible transparent optoelectronics.

Electronic structure and optical properties of Ge-and F-doped α-Ga2O3:First-principles investigations

The prospect ofα-Ga2O3 in optical and electrical devices application is fascinating.In order to obtain better performance,Ge and F elements with similar electronegativity and atomic size are selected as dopants.Based on density functional theory(DFT),we systematically research the electronic structure and optical properties of dopedα-Ga2O3 by GGA+U calculation method.The results show that Ge atoms and F atoms are effective n-type dopants.For Ge-dopedα-Ga2O3,it is probably obtained under O-poor conditions.However,for F-dopedα-Ga2O3,it is probably obtained under O-rich conditions.The doping system of F element is more stable due to the lower formation energy.In this investigation,it is found that two kinds of doping can reduce theα-Ga2O3 band gap and improve the conductivity.What is more,it is observed that the absorption edge after doping has a blue shift and causes certain absorption effect on the visible region.Through the whole scale of comparison,Ge doping is more suitable for the application of transmittance materials,yet F doping is more appropriate for the application of deep ultraviolet devices.We expect that our research can provide guidance and reference for preparation ofα-Ga2O3 thin films and photoelectric devices.

Annealing effects on the optical and electrochemical properties of tantalum pentoxide films

Tantalum pentoxide(Ta_(2)O_(5)) has attracted intensive attention due to their excellent physicochemical properties.Ta_(2)O_(5) films were synthesized via electron beam evaporation(EBE)and subsequently annealed at different temperatures ranging from 300 to 900℃.X-ray diffraction(XRD)results show that amorphous Ta_(2)O_(5) thin films form from 300 to 700℃ and then a phase transition to polycrystalline β-Ta_(2)O_(5) films occurs since 900℃.The surface morphology of the Ta_(2)O_(5) films is uniform and smooth.The resulted Ta_(2)O_(5)films exhibit excellent transmittance properties for wavelengths ranging from 300 to 1100 nm.The bandgap of the Ta_(2)O_(5) films is broadened from 4.32 to 4.46 eV by annealing.The 900℃ polycrystalline film electrode has improved electrochemical stability,compared to the other amorphous counterparts.