Jin-Hao Jhang

This study investigates the effects of atmospheric pressure plasma jet on diamond surface functionalization, which is key for plasma-assisted polishing. By varying plasma parameters including voltage waveforms, substrate temperature, reactive gas composition, and flow rate, we identify conditions that enhance hydroxyl and atomic oxygen radical formation and promote sp3-to-sp2 carbon conversion. Pulsed and sinusoidal waveforms are compared, along with the influence of pulse rise and fall times. Optical emission spectroscopy and x-ray photoelectron spectroscopy analyses show that pulsed voltages with short rise and fall times and higher substrate temperature significantly enhance surface oxidation. Increasing gas flow facilitates the generation of excited species, producing more oxygen and hydroxyl terminations. Oxygen addition quenches plasma, and the maximum hydroxyl radical yield is observed at 1500 ppm humidity.

The polarization of ZnO films on Cr ₂ O ₃ /ZnO shows that substrate polarization affects a non-polar material for <3 atomic layers.

Two-dimensional (2D) silica (SiO₂) and aluminosilicate (AlSi₃O₈) bilayers grown on Pd(111) were fabricated and systematically studied using ultrahigh vacuum surface analysis in combination with theoretical methods, including Auger electron spectroscopy, X-ray photoelectron spectroscopy, low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory. Based on LEED results, both SiO₂ and AlSi₃O₈ bilayers start ordering above 850 K in 2 × 10⁻⁶ Torr oxygen. Both bilayers show hexagonal LEED patterns with a periodicity approximately twice that of the Pd(111) surface. Importantly, the SiO₂ bilayer forms an incommensurate crystalline structure whereas the AlSi₃O₈ bilayer crystallizes in a commensurate structure. The incommensurate crystalline SiO₂ structure on Pd(111) resulted in a moiré pattern observed with LEED and STM. Theoretical results show that straining the pure SiO₂ bilayer to match Pd(111) would cost 0.492 eV per unit cell; this strain energy is reduced to just 0.126 eV per unit cell by replacing 25% of the Si with Al which softens the material and expands the unstrained lattice. Furthermore, the missing electron created by substituting Al³⁺ for Si⁴⁺ is supplied by Pd creating a chemical bond to the AlSi₃O₈ bilayer, whereas van der Waals interactions predominate for the SiO₂ bilayer. The results reveal how the interplay between strain, doping, and charge transfer determine the structure of metal-supported 2D silicate bilayers and how these variables may potentially be exploited to manipulate 2D materials structures.

We investigated the adsorption and reaction of methanol on continuous and discontinuous films of samarium oxide (SmO_x) grown on Pt(111) in ultrahigh vacuum. The methanol decomposition was studied by temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS), while structural changes of the oxide surface were monitored by low-energy electron diffraction (LEED). Methanol dehydrogenates to adsorbed methoxy species on both the continuous and discontinuous SmO_x films, eventually leading to the desorption of CO and H₂ which desorbs at temperatures in the range 400–600 K. Small quantities of CO₂ are also detected mainly on as-prepared Sm₂O₃ thin films, but the production of CO₂ is limited during repeated TPD runs. The discontinuous film exhibits the highest reactivity compared to the continuous film and the Pt(111) substrate. The reactivity of methanol on reduced and reoxidized films was also investigated, revealing how SmO_x structures influence the chemical behavior. Over repeated TPD experiments, a SmO_x structural/chemical equilibrium condition is found which can be approached either from oxidized or reduced films. We also observed hydrogen absence in TPD which indicates that hydrogen is stored either in SmO_x films or as OH groups on the SmO_x surfaces.

Binary and ternary PrO_xand CeO_xfilms grown on Si(111) are most versatile systems available in a variety of stoichiometries and surface structures.