Evolution Of Surface States Research Articles

Chemical state and wettability of ion-irradiated diamond surfaces

It is shown that the wettability of diamond can be tailored in a broad range by the surface modification via ion bombardment. The polished MPCVD diamond films were oxidized in air at 550 °C to make the surface hydrophilic and then were irradiated with Ar + ions at 1 keV energy at doses ranging from 1×10 14 to 5×10 16 cm −2. The surface state evolution was monitored in situ with X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES). A progressive sp 3 to sp 2 bond transformation took place with the dose increase, while the irradiated surface becomes hydrophobic with the water contact angle increasing from 24° to 67° as measured with a sessile drop method. The heating of the ion-treated samples in air at 450 °C restores the hydrophilic properties inherent to oxidized diamond surface.

Study of the transition from the ideal Si( [formula omitted])–H(1×1) surface to the (7×7) reconstruction by HREELS, UPS and LEED

The temperature-induced evolution of the Si(1 1 1)–H(1×1) surface towards the (7×7)-reconstruction has been studied by means of UPS, HREELS and LEED techniques. We found that H atom desorption occurs at about 500 °C, and the full development of the (7×7)-phase, checked by both UPS and LEED, occurs around 700 °C. In the valence band spectra, the (7×7)-related restatom peak is present already for annealing temperature of 465 °C, while the adatom-related peak starts to appear only around 600 °C and fully develops at 700 °C. A band bending is detected and its behavior discussed in relation to the surface state evolution. In the first annealing steps, the desorption-induced defects cause the shift of the surface Fermi level and the consequent upwards band bending, which reaches the maximum value of 0.47 eV for annealing to 465 °C. The subsequent evolution of the dangling-bond states into the (7×7) surface states determines the band bending decrease till 0.1 eV.

Analysis of Surface Photoabsorption Spectra of (001) InP Surfaces

We present an in situ surface photoabsorption (SPA) study on surface structures of (001) InP surfaces. Conventional subtraction spectra of SPA on (001) InP showed two peaks at 430 nm and 600 nm, which we assigned as P dimer and In dimer peaks, respectively. By modifying the conventional subtraction equation to separate contributions from In- and P-stabilized surfaces, we could observe another structure at 400 nm which we interpret as related to In-stabilized surface, showing possibility of complementary role of this modified equation. We also observed evolution of surface states from P- to In-stabilized surfaces at 600°C by the change of PH3 partial pressure.

More Than Skin Deep

Electrons normally stay close to surfaces of metals and have a lot to do with what kinds of chemistry can take place on surfaces. In his Perspective, Plummer discusses results published in the same issue by HA¶fer et al. in which the technique of coherent laser excitation was used to put surface electrons into high-lying Rydberg states. The behavior of the excited electrons was then mapped out with angle-resolved photoemission. Knowledge of the time evolution of surface states may help with detailed studies of surface dynamics and chemical reactions.