Yihao Yang's research while affiliated with Taiyuan University of Technology and other places

Highly aligned TiO2 nanoarrays (TNAs) are fabricated on free-standing diamond (FSD) films and Si wafers (for comparison). Different anodizing times (e.g., 5, 15, 25, 45, and 60 min) are used to investigate the morphology morphologies of TNAs and their effect on the electron field emission (EFE) properties. With the increase of the anodizing time, the features of TNAs grown on the FSD film undergo the transition from nanorods to nanopores and then to nanotubes. The XRD, Raman, and TEM results reveal that TNAs synthesized on the FSD film are preferentially oriented rutile phase, while those synthesized on the Si wafers show the anatase structure. Rutile TiO2 has a relatively low work function and is favorable to EFE performance. Importantly, the nanotubes on the FSD substrate with a 45 min anodizing time grow perpendicularly to each crystal face of the diamond grains and exhibit a superior EFE behavior, which can be turned on at a low field of 0.7 V/μm and attain a high current density of 0.6 mA/cm² at an applied field of 1.6 V/μm. The enhanced EFE performance of TNAs/FSD composite film is ascribed to the synergetic effects among the electron acceleration layer played by the FSD film, more electron emission sites provided by the nanotubes with large aspect ratios, and lowlower work function of rutile TiO2. Moreover, the heterogeneity of the FSD substrate and TNAs also can decrease the interface barrier to make electrons transmit effectively.

Diamond films with different grain sizes in the range of ~ 9 nm to ~ 50 μm have been deposited on silicon substrates using a homemade microwave plasma chemical vapor deposition reactor by varying the deposition parameters. The surface morphologies have been examined by scanning electron microscope and atomic force microscope, which show the secondary nucleation intensity and surface defects of the diamond films increase with the decrease of the diamond grain size. Although X-ray diffraction spectra show the absence of graphitic carbon features, the Raman and X-ray photoelectron spectroscopy show the sp2/sp3-bonded carbon ratios increase with the decrease of the diamond grains. The CH4 percentage in plasma during deposition plays a crucial role in the formation of diamond films with different grain sizes and sp2 contents, which in turn determines the electron field emission behavior of the corresponding diamond films. The smaller the grain size of the diamond, the higher is the grain boundary density, which can provide more electron emission sites and form conductive networks for electron transport. The ultra-nanocrystalline diamond film shows needle-like cluster structures and optimum electrical performance. The corresponding electron field emission behavior can be turned on at a field of 6.71 V/μm and attain a current density of 16.28 μA/cm2 at an applied field of 11.31 V/μm.