Thin Film Amorphous Electrolytes:  Structure and Composition by Experimental and Simulated Infrared Spectra

Abstract

Ionic conducting glasses in thin film forms are promising candidates for applications in microelectronics devices such as microbatteries and microsupercapacitors. In recent years, it was shown that physicochemical properties of thin films may differ substantially from those of the target bulk materials. Thus, it remains a challenge in science and thin film technology to control the properties of thin films in terms of chemical composition and conditions of manufacturing. This work presents a structural investigation of lithium−borate thin film electrolytes prepared by rf sputtering of Li−diborate targets. Chemically stable thin films ca. 1 μm thick were deposited on Si and gold-covered Si substrates under argon and their infrared spectra were measured in a broad spectral range (30−5000 cm-1). The spectra of thin films were modeled on the basis of rigorous expressions for reflectance and transmittance of the film/substrate bilayer system. The experimental results for thin films were compared with those simulated by using the optical response functions of bulk glasses xLi2O−(1−x)B2O3 (x = 0.33, 0.30, 0.275, 0.25), which were prepared by the conventional melt quenching technique. The comparison of experimental and simulated spectra showed that rf sputtering of Li−diborate targets (x = 0.33) leads to Li−borate thin films with lithium oxide content lower than that of the target material. Best agreement between experimental and simulated thin film spectra was obtained for x = 0.275, after proper annealing of thin films to remove differences in thermal history between thin film and bulk glass states.

Structure and optical properties of amorphous lead-germanate films developed by pulsed-laser deposition

“…The infrared properties of the Si substrate are shown in Fig. 1͑b͒, as determined previously 16 and confirm its transparency in the infrared range. The bands observed in the k spectrum at 565, 608, 740, 815, 890, 965, 1302, and 1450 cm −1 originate from lattice modes of Si, 18 while the feature at 1107 cm −1 indicates oxygen impurities as arising from the asymmetric stretching vibration of Si-O-Si bridges.…”

“…16. As it can be easily shown, the interference fringes due to the Si substrate used in this study ͑d 2 = 0.6 mm͒ have a period of approximately 2.5 cm −1 , and, thus, the Si interference pattern can be optically averaged by measuring low-resolution spectra ͑e.g., 10 cm −1 ͒.…”

“…We outline below key aspects of the model relevant to the present study, while its detailed description is reported elsewhere. 16 Each layer is characterized by its thickness d j and complex refractive index ñ j = n j − ik j ͑j = 1 for thin film, j = 2 for substrate, and j =0,3 for vacuum͒, while the phase change of the light beam traversing one layer is given by…”

Aging process of photosensitive chalcogenide films deposited by electron beam deposition

“…To this aim, we made use of a model based on rigorous expressions for transmittance of a film/substrate bilayer system which takes into full account all optical effects occurring in such a system. The model relevant to the present study is reported elsewhere [18][19][20].…”

“…2(a) and (b), respectively. As noticed in Section 2, the spectral comparison in the IR is based on a calculated transmittance spectrum which integrates all optical effects occurring in a bilayer system (film and substrate) [18][19][20]. Both figures demonstrate spectral variations between bulk glass and film.…”