Significant progress has been made in integrating novel materials into silicon photonic structures in order to extend the functionality of photonic circuits. One of these promising optical materials is BaTiO or barium titanate (BTO) that exhibits a very large Pockels coefficient as required for high-speed light modulators. However, all previous demonstrations show a noticable reduction of the Pockels effect in BTO thin films deposited on silicon substrates compared to BTO bulk crystals. Here, we report on the strong dependence of the Pockels effect in BTO thin films on their microstructure, and provide guidelines on how to engineer thin films with strong electro-optic response. We employ several deposition methods such as molecular beam epitaxy and chemical vapor deposition to realize BTO thin films with different morphology and crystalline structure. While a linear electro-optic response is present even in porous, polycrystalline BTO thin films with an effective Pockels coefficient r = 6 pm V, it is maximized for dense, tetragonal, epitaxial BTO films (r = 140 pm V). By identifying the key structural predictors of electro-optic response in BTO/Si, we provide a roadmap to fully exploit the linear electro-optic effect in novel hybrid oxide/semiconductor nanophotonic devices.

SrTiO3 is a widely used substrate for the growth of other functional oxide thin films. The reactivity of the substrate with respect to the film during deposition, particularly with regard to redox reactions, has typically been glossed over. We demonstrate by depositing a variety of metals (Ti, Al, Nb, Pt, Eu, and Sr) and measuring the in situ core level spectra of both the metal and SrTiO3 that, depending on the oxide formation energy and work function of the metal, three distinct types of behavior occur in thin metal films on SrTiO3 (100). In many cases, there will be an interfacial layer of oxygen-deficient SrTiO3 formed at the interface with the overlying film. We discuss how this may affect the interpretation of the well-known two-dimensional electron gas present at the interface between SrTiO3 and various oxides.

a b s t r a c tHigh-quality epitaxial BaTiO 3 (BTO) on Si has emerged as a highly promising material for future electrooptic (EO) devices based on BTO's large effective Pockels coefficient. We report on the EO response of BTO films deposited on Si by molecular beam epitaxy (MBE), and characterize the structure of these films by reflection high-energy electron diffraction and X-ray diffraction. O 2 rapid thermal anneal at 600°C for 30 min ensures full oxidation of BTO for minimal leakage current with minimal change in crystalline structure.

We report strategies to achieve both high assembly yield of carbon nanotubes at selected positions of the circuit via dielectrophoresis (DEP) and field effect transistor (FET) yield using an aqueous solution of semiconducting-enriched single-walled carbon nanotubes (s-SWNTs). When the DEP parameters were optimized for the assembly of individual s-SWNTs, 97% of the devices showed FET behavior with a maximum mobility of 210 cm2 V(-1) s(-1), on-off current ratio ∼10(6) and on-conductance up to 3 µS, but with an assembly yield of only 33%. As the DEP parameters were optimized so that one to five s-SWNTs are connected per electrode pair, the assembly yield was almost 90%, with ∼90% of these assembled devices demonstrating FET behavior. Further optimization gave an assembly yield of 100% with up to 10 SWNTs per site, but with a reduced FET yield of 59%. Improved FET performance including higher current on-off ratio and high switching speed were obtained by integrating a local Al2O3 gate to the device. Our 90% FET with 90% assembly yield is the highest reported so far for carbon nanotube devices. Our study provides a pathway which could become a general approach for the high yield fabrication of complementary metal oxide semiconductor (CMOS)-compatible carbon nanotube FETs.

The development of novel nano-oxide spintronic devices would benefit greatly from interfacing with emergent phenomena at oxide interfaces. In this paper, we integrate highly spin-split ferromagnetic semiconductor EuO onto perovskite SrTiO3 (001). A careful deposition of Eu metal by molecular beam epitaxy results in EuO growth via oxygen out-diffusion from SrTiO3. This in turn leaves behind a highly conductive interfacial layer through generation of oxygen vacancies. Below the Curie temperature of 70 K of EuO, this spin-polarized two-dimensional t2g electron gas at the EuO/SrTiO3 interface displays very large positive linear magnetoresistance (MR). Soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES) reveals the t2g nature of the carriers. First principles calculations strongly suggest that Zeeman splitting, caused by proximity magnetism and oxygen vacancies in SrTiO3, is responsible for the MR. This system offers an as-yet-unexplored route to pursue proximity-induced effects in the oxide two-dimensional t2g electron gas.