Electron exchange between an H ion and a spherical cluster of aluminum atoms

The resonant charge transfer (RCT) between a hydrogen anion and a cluster of aluminum atoms is investigated by means of the wave-packet propagation method that does not exploit the perturbation theory. The RCT on a spherical cluster is found to exhibit quantum size effects due to the finite size of the cluster. The survival amplitude of an ion state has been calculated as a function of the distance to the ion-surface in a normal collision. It is shown that depending on the velocity of the impinging particle, the cluster can behave either as a bulk metal or as a quantum structure with discrete energy states existing over two coordinates.     

Adhesion of proton beam written high aspect ratio hydrogen silsesquioxane (HSQ) nanostructures on different metallic substrates

Hydrogen silsesquioxane (HSQ) behaves as a negative resist under MeV proton beam exposure. HSQ is a high-resolution resist suitable for production of tall (<1.5 μm) high aspect ratio nanostructures with dimensions down to 22 nm. High aspect ratio HSQ structures can be used in many applications, e.g. nanofluidics, biomedical research, etc. Isolated HSQ nanostructures, however, tend to detach from substrates during the development process due to the weak adhesive forces between the resist and the substrate material. Larger proton fluences were observed to promote the adhesion. To determine an optimal substrate material and the proton irradiation doses for HSQ structures, a series of 2 μm long and 60-600 nm wide free-standing lines were written with varying fluences of 2 MeV protons in 1.2 μm thick HSQ resist spun on Ti/Si, Cr/Si and Au/Cr/Si substrates. The results indicate that the Ti/Si substrate is superior in terms of adhesion, while Au/Si is the worst. Cr/Si is not suitable as a substrate for HSQ resist because debris was formed around the structures, presumably due to a chemical reaction between the resist and Cr.     

Formation and evolution of oxygen vacancies in ZnO white paint during proton exposure

The formation and evolution of oxygen vacancies in ZnO white paint during <200 keV protons exposure was investigated using photoluminescence spectroscopy. After irradiation, the shape of photoluminescence spectra changes little, but the peak height decreases. With increasing fluence, the amount of doubly ionized oxygen vacancies decreases, while that for the singly ionized oxygen vacancies increases. The former can trap electrons in the conduction bands to become the singly ionized oxygen vacancies, leading to that the latter gradually becoming the major defects induced by irradiation. The increase in content of singly ionized oxygen vacancies due to the irradiation can also promote an increase in the amount of absorbed oxygen in the paint, enhancing the quenching effect of photoluminescence and thus decreasing the photoluminescence peak.     

Competition of terrace and step-edge sputtering under oblique-incidence ion impact on a stepped Pt(1 1 1) surface

Using molecular-dynamics simulation, we study the sputtering of a Pt(1 1 1) surface under oblique and glancing incidence 5 keV Ar ions. For incidence angles larger than a critical angle ?_c, the projectile is reflected off the surface and the sputter yield is zero. We discuss the azimuth dependence of the critical angle ?_c with the help of the surface corrugation felt by the impinging ion. If a step exists on the surface, sputtering occurs also for glancing incidence ?>?_c. We demonstrate that for realistic step densities, the total sputtering of a stepped surface may be sizable even at glancing incidence.     

An analysis on optical degradation of ZnO/silicone white paint under proton exposure

The optical degradation mechanism of ZnO/silicone white paint caused by 50 keV protons was investigated in terms of X-ray photoelectron spectroscopy (XPS). The results show that the change in solar absorptance Δα_s increases with increasing proton fluence, and the variation of Δα_s has a good relationship with the formation of the oxygen vacancies in ZnO and the Si-CO functional groups in silicone binder. With increasing the proton fluence, both the area ratio of lattice oxygen peak to XPS O_1s spectrum and the peak area in Zn_3d spectra decrease, indicating that the percentage of lattice oxygen decreases and the amount of oxygen vacancies increases. Meanwhile, the area ratio of the Si-CO peak to XPS Si_2p spectrum increases, demonstrating the formation of Si-CO chromophores in silicone binder. Both the oxygen vacancies and the Si-CO chromophores can lead to an optical degradation of ZnO/silicone white paint under proton exposure.