Materials. Oleic acid (90%, Fisher Chemical), titanium(IV) bis(ammonium lactate)dihydroxide (TiALH, 50% wt in water * , Alfa Aesar), Sr(OH) 2 •8H 2 O (99%, Alfa Aesar), Cr(NO 3 ) 3 •9H 2 O (Crystalline Certified, Fisher Chemical), tetramethylammonium hydroxide (10 M NMe 4 OH, Acros Organics), hydrazine hydrate (N 2 H 4 •H 2 O, 99%, Acros Organics), ethanol (200 proof, PHARMCO-AAPER) and hexanes (optima, Fisher Chemical) were used as received. Synthesis of colloidal SrTiO 3−δ and Cr 3+ -doped SrTiO 3−δ nanocrystals. Colloidal SrTiO 3 NCs were prepared by a modified hydrothermal method. 1-3 In a typical synthesis, 1.25 mmol of titanium(IV) bis(ammonium lactate)dihydroxide and Sr(OH) 2 •8H 2 O were dissolved in 30 mL of distilled H 2 O. The pH was adjusted to 12.1 with NMe 4 OH (10 M). The solution was transferred to a 45-mL Teflon-lined autoclave and N 2 H 4 •H 2 O (5 mmol) and oleic acid (2.5 mmol) were added. 2 The autoclaves were sealed and heated to 200 °C for 24 h. The resulting oleic acid functionalized NCs were washed with ethanol and suspended in hexanes. The synthetic * The batch of TiALH received from Alfa Aesar contains common impurities of TiO 2 at ~14% and pH of the solution ~8.4-8.5. The presence of insoluble TiO 2 indicates that slow hydrolysis is taking place in the TiALH bottle and definitely overestimates [Ti] in the calculation of x nom =[Cr]/([Cr]+[Ti]).

The spin relaxation dynamics of Cr3+ substitutional dopants in ∼10 nm colloidal SrTiO3 nanocrystals (NCs) has been studied by variable-temperature electron paramagnetic resonance (EPR) spectroscopy and continuous wave EPR power saturation measurements between 4.2 and 50 K. The presence of self-trapped electrons introduced by anaerobic ultraviolet irradiation (photodoping) is able to effectively accelerate the spin relaxation dynamics of localized spins of Cr3+ through a cross-relaxation process. The extra electrons introduced during photodoping trap on Ti-sites, creating Ti3+ defects with EPR transitions that are observed only at cryogenic temperatures because of fast spin–lattice relaxation. The change in the spin relaxation upon photodoping the Cr-doped SrTiO3 NCs is totally reversible upon opening the sample to air. This result provides a novel strategy to modulate spin dynamics in individual NCs using photons where long-lived spins on dopant ions couple to the fast-relaxing spins from metastable, transient defects.

Memristors, often comprising an insulating metal oxide film between two metal electrodes (MIM), constitute a class of two-terminal devices that possesses tunable variations in resistance based on the applied bias history. Intense research remains focused on the metal-insulator interface, which serves as the crux of coupled electronic-ionic interactions and dictates the underpinning transport mechanisms at either electrode. Top-down, ultrahigh-vacuum (UVH) deposition approaches for MIM nanostructures yield highly crystalline, heteroepitaxial interfaces but limit the number of electrode configurations due to a fixed bottom electrode. Here we report on the convective self-assembly, removal, and transfer of individual nanoribbons comprising solution-processed, single-crystalline strontium titanate (STO) perovskite oxide nanocrystals to arbitrary metallized substrates. Nanoribbon transferability enables changes in transport models ranging from interfacial trap-detrap to electrochemical metallization processes. We also demonstrate the endurance of memristive behavior, including switching ratios up to 10, after nanoribbon redeposition onto poly(ethylene terephthalate) (PET) flexible substrates. The combination of ambient, aerobic prepared nanocrystals and convective self-assembly deposition herein provides a pathway for facile, scalable manufacturing of high quality, functional oxide nanostructures on arbitrary surfaces and topologies.

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We demonstrate a low-temperature reduction method for exhibiting fine control over the oxidation state of substitutional Mn ions in strontium titanate (SrTiO 3 ) bulk powder. We employ NaBH 4 as the chemical reductant that causes significant changes in the oxidation state and oxygen vacancy complexation with Mn 2+ dopants at temperatures <350°C where lattice reduction is negligible. At higher reduction temperatures, we also observe the formation of Ti 3+ in the lattice by diffuse-reflectance and low-temperature electron paramagnetic resonance (EPR) spectroscopy. In addition to Mn 2+ , Mn 4+ , and the Mn 2+ complex with an oxygen vacancy, we also observe a sharp resonance in the EPR spectrum of heavily reduced Mn-doped SrTiO 3 . This sharp signal is tentatively assigned to surface superoxide ion that is formed by the surface electron transfer reaction between Ti 3+ and O 2 . The ability to control the relative amounts of various paramagnetic defects in SrTiO 3 provides many possibilities to study in a model system the impact of tunable dopant-defect interactions for spin-based electronic applications or visible-light photocatalysis.

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The synthesis and application of environmentally benign, efficient and low cost heterogeneous catalysts is increasingly important for affordable and clean chemical technologies. Nanomaterials have been proposed to have new and exciting properties relative to their bulk counterparts due to the quantum level interactions that exist at nanoscale. These materials also offer enormous surface to volume ratios that would be invaluable in heterogeneous catalysis. Recent studies point at titanium dioxide nanomaterials as having strong potential to be applied in heterogeneous photocatalysis for environmental remediation and pollution control. This work reports the use of surface modified anatase TiO2 nanofibers with rhodium (Rh) nanoparticles in the photodegradation of rhodamine B (RH-B), an organic pollutant. The dimensions of TiO2 nanofibers were 150±50 nm in diameter and the size of the Rh nanoparticles was ~5 nm. The Rh-doped TiO2 catalyst exhibited an enhanced photocatalytic activity in photodegradation of rhodamine B under visible light irradiation, with 95 % degradation within 180 minutes reaction time. Undoped TiO2 did not show any notable phocatalytic activity under visible light.