Second-harmonic generation from electron beam deposited SiO films

Abstract

It is demonstrated that as-grown e-beam deposited SiOx thin films on fused silica substrates show a second-order nonlinear response that is dependent on film thickness. Using a Maker fringes method the effective nonlinear coefficient for a SiO thin film is estimated to be comparable to that of crystalline quartz. Variation of process parameters has been used to investigate the origin of the nonlinear response. The second-harmonic signal is very sensitive to annealing of the film and can be totally removed by annealing at a few hundred degrees. It is also demonstrated that a retarding grid that traps charged particles between the crucible and the sample reduces the nonlinear signal from a SiO thin film significantly. It is suggested that oriented dipoles arise during deposition due to a negatively charged film from oxygen ions, thus, resulting in a non-centrosymmetric film. Finally, using e-beam lithography, well-defined nonlinear 2D structures can be synthesized, thus opening the door to a new and practical way to create nonlinear structures for planar waveguide technology.

Magnesiothermic reduction of silica glass substrate—Chemical states of silicon in the generated layers

“…Silicon-related compounds are composed of silicon atoms in intermediate oxidation states, i.e., between +4 and 0, or 0 and −4 in the formal charge. Among them, nonstoichiometric SiO x (x < 2) and stoichiometric SiO have received much attention, and the structure and electronic states have been research subject for practical application [20][21][22][23][24][25][26]. Thus, it is also interesting to clarify the relationship between the reaction conditions and the chemical states of silicon in the reaction products.…”

Growth direction of oblique angle electron beam deposited silicon monoxide thin films identified by optical second-harmonic generation

“…For films grown at normal deposition direction, the field from ionized atoms orients Si-H bonds perpendicular to the surface resulting in rotationally isotropic SHG. 14 In this Letter, it is shown that through oblique angle deposition the formation of a columnar structure can be used to control the orientation of the Si-H bonds in the SiO films and that the orientation of the columns can be determined from SHG experiments. By analyzing a series of samples grown with varying deposition angle, a correlation between the angle of incidence (AOI) dependence of the SH signal and growth direction is found.…”

“…13 The present authors have recently shown that SiO films grown by electron beam (e-beam) deposition have a nonlinear response comparable to that of non-centrosymmetric crystals. 14 It was suggested that the nonlinearity arises from Si-H bonds oriented by ions during the e-beam deposition process. For films grown at normal deposition direction, the field from ionized atoms orients Si-H bonds perpendicular to the surface resulting in rotationally isotropic SHG.…”

“…For details on the optical setup, see our previous work. 14 It was found by Rutherford backscattering spectrometry (RBS) that porous oblique angle deposition SiO films tended to oxidize partly to a SiO x film in the ambient atmosphere. This is due to water vapor reacting with Si-H and -Si-Sibonds.…”

Second harmonic generation from Ge doped SiO2 (Gex(SiO2)1−x) thin films grown by sputtering

“…For example, strong SHG signals were observed from SiN thin films prepared by plasma enhanced chemical vapor deposition, and silicon monoxide (SiO) thin films prepared by an electron beam deposition. 12,13 In these amorphous thin films, the origin of the second order nonlinearity has not been elucidated.…”