Electric-Field-Induced Phase Change in Copper Oxide Nanostructures

Abstract

Transition-metal oxides such as cupric and cuprous oxides are strongly correlated materials made of earth-abundant chemical elements displaying energy band gaps of around 1.2 and 2.1 eV. The ability to design nanostructures of cupric and cuprous oxide semiconductors with in situ phase change and morphological transition will benefit several applications including photovoltaic energy conversion and photoelectrochemical water splitting. Here, we have developed a physicochemical route to synthesize copper oxide nanostructures, enabling the phase change of cupric oxide into cuprous oxide using an electric field of 105 V/m in deionized water via a new synthetic design protocol called electric-field-assisted pulsed laser ablation in liquids (EFA-PLAL). The morphology of the nanostructures can also be tuned from a sphere of ∼20 nm to an elongated leaf of ∼3 μm by controlling the intensity of the applied electric field. Futuristically, the materials chemistry occurring during the EFA-PLAL synthesis protocol developed here can be leveraged to design various strongly correlated nanomaterials and heterostructures of other 3d transition-metal oxides.

Data-Driven Predetermination of Cu Oxidation State in Copper Nanoparticles: Application to the Synthesis by Laser Ablation in Liquid

“…Target surface properties like roughness, purity, and contamination are generally unknown. Concerning the choice of using the % of O + Cl + CN + S in solvent and solutes, this is based on the strong empirical evidence in the literature that any of these elements can react with Cu. ,− Hence, this feature was preferred over the % of each single chemical group (O, Cl, CN, S but also C, H, and N) to reduce the already cumbersome list of parameters and facilitate the discovery of mutual correlations with the other features whose role remains more obscure.…”

“…With LAL, Cu, Cu 2 O, CuO, Cu 2 S, and CuCN NPs have been synthesized using a metallic Cu target while varying the laser source, setup, solvent, and solutes. ,− Unfortunately, the LAL of Cu targets usually produces a mixture of these different phases. Picking just a specific compound is a rather empirical endeavor based on changing the LAL synthesis parameters, which is particularly complex in the case of compounds with intermediate oxidation states such as Cu 2 O.…”

“…Picking just a specific compound is a rather empirical endeavor based on changing the LAL synthesis parameters, which is particularly complex in the case of compounds with intermediate oxidation states such as Cu 2 O. In the case of Cu-based NPs, the identification of the appropriate LAL conditions for a specific compound needs accurate quantitative assessment of the products, best achieved by quantitative analysis of the X-ray diffraction (XRD) pattern, and may still lead to misleading results due to aging or manipulation of the products before structural analysis (e.g., heating and air exposure), which ineluctably alter the oxidation state and the morphology of the Cu nanocrystals. ,,, Another critical aspect is the purity and aging of the bulk metal target used for LAL, which may undergo oxidation with a drastic change in the synthesis conditions. , …”

Controlling the Structure and Morphology of Organic Nanofilaments Using External Stimuli

“…To illustrate just a few, chameleons achieve active and rapid color change by tuning the lattice of guanine nanocrystals, cephalopods use reversible soft tissue shape changes for camouflage, and Boquila trifoliolataa vine plant from rainforests in southern Chileis capable of complex leaf mimicry (shape, color, and orientation), potentially using communication through volatile chemicals or acoustic signals to actively imitate the leaf character of surrounding plants of other species . External stimuli to realize structural or morphological changes commonly include changes in pH, changes in temperature, mechanical deformation, exposure to chemicals, irradiation with light at specific wavelengths, − and external electric or magnetic fields. − Considering our ongoing discoveries of nanofilament shapes (morphologies) in the B4 phase of some bent-core liquid crystals (BC-LCs), we were particularly intrigued by the opportunity to alter the nanofilament shape using external stimuli other than the rate of temperature change on cooling from an isotropic liquid. Here, applying an electric field or irradiation with UV light was of particular interest.…”

“…Across the materials and length scale spectrum, these two external stimuli have been extensively employed to afford structural and morphological changes. Applied electric fields have been used to alter (“square”) the shape of giant vesicles, control morphological evolution in thin silicon rubber films, or alter the phase (from CuO to Cu 2 O) and shape (spherical to elongated leaf-like) of copper oxide nanostructures, among others. Light-controlled shape changes are even more prevalent in the literature, largely because of the attractive, non-invasive remote actuation permitted by light irradiation .…”