Silver electrodeposition on nanostructured gold: from nanodots to nanoripples

Silver nanodots and nanoripples have been grown on nanocavity-patterned polycrystalline Au templates by controlled electrodeposition. The initial step is the growth of a first continuous Ag monolayer followed by preferential deposition at nanocavities. The Ag-coated nanocavities act as preferred sites for instantaneous nucleation and growth of the three-dimensional metallic centres. By controlling the amount of deposited Ag, dots of ∼50 nm average size and ∼4 nm average height can be grown with spatial and size distributions dictated by the template. The dots are in a metastable state. Further Ag deposition drives the dot surface structure to nanoripple formation. Results show that electrodeposition on nanopatterned electrodes can be used to prepare a high density of nanostructures with a narrow size distribution and spatial order.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Electrochemical Deposition onto Self-Assembled Monolayers

Pattern transfer with high resolution is a frontier topic in the emerging field of nanotechnologies. Electrochemical molding is a possible route for nanopatterning metal, alloys and oxide surfaces with high resolution in a simple and inexpensive way. This method involves electrodeposition onto a conducting master covered by a self-assembled alkanethiolate monolayer (SAMs). This molecular film enables direct surface–relief pattern transfer from the conducting master to the inner face of the electrodeposit, and also allows an easy release of the electrodeposited film due their excellent anti-adherent properties. Replicas of the original conductive master can be also obtained by a simple two-step procedure. SAM quality and stability under electrodeposition conditions combined with the formation of smooth electrodeposits are crucial to obtain high-quality pattern transfer with sub-50 nm resolution.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Oxidation Induced Doping of Nanoparticles Revealed by in Situ X-ray Absorption Studies

Doping is a well-known approach to modulate the electronic and optical properties of nanoparticles (NPs). However, doping at nanoscale is still very challenging, and the reasons for that are not well understood. We studied the formation and doping process of iron and iron oxide NPs in real time by in situ synchrotron X-ray absorption spectroscopy. Our study revealed that the mass flow of the iron triggered by oxidation is responsible for the internalization of the dopant (molybdenum) adsorbed at the surface of the host iron NPs. The oxidation induced doping allows controlling the doping levels by varying the amount of dopant precursor. Our in situ studies also revealed that the dopant precursor substantially changes the reaction kinetics of formation of iron and iron oxide NPs. Thus, in the presence of dopant precursor we observed significantly faster decomposition rate of iron precursors and substantially higher stability of iron NPs against oxidation. The same doping mechanism and higher stability of host metal NPs against oxidation was observed for cobalt-based systems. Since the internalization of the adsorbed dopant at the surface of the host NPs is driven by the mass transport of the host, this mechanism can be potentially applied to introduce dopants into different oxidized forms of metal and metal alloy NPs providing the extra degree of compositional control in material design.Fil: Kwon, Soon Gu. Argonne National Laboratory; Estados UnidosFil: Chattopadhyay, Soma. Argonne National Laboratory; Estados Unidos. Illinois Institute of Technology; Estados UnidosFil: Koo, Bonil. Argonne National Laboratory; Estados UnidosFil: Dos Santos Claro, Paula Cecilia. Argonne National Laboratory; Estados UnidosFil: Shibata, Tomohiro. Argonne National Laboratory; Estados UnidosFil: Requejo, Felix Gregorio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Giovanetti, Lisandro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Liu, Yuzi. Argonne National Laboratory; Estados UnidosFil: Johnson, Christopher. Argonne National Laboratory; Estados UnidosFil: Prakapenka, Vitali. University of Chicago; Estados UnidosFil: Lee, Byeongdu. Argonne National Laboratory; Estados UnidosFil: Shevchenko, Elena V.. Argonne National Laboratory; Estados Unido

Characterization of titania inverse opals prepared by two distinct infiltration approaches

Titanium dioxide inverse opals were prepared by the typical method of infiltration with a liquid precursor (LP-IOs) and by an improved method in which the infiltration step is done with a suspension of TiO2 nanoparticles (NP-IOs). A thorough characterization study was performed on both types of preparations in order to highlight the differences between the resulting inverse opal samples. The formation of a compact overlayer in LP-IO samples inherent to the use of a liquid precursor proved to be detrimental for the optical and photonic properties of the inverse opals. NP-IO samples, on the other hand, showed improved optical, photonic, and mechanical properties. The photocatalytic degradation of a model compound (a well-known dye, methylene blue) revealed that NP-IO samples are able to degrade the model compound at a higher rate due to the absence of the compact overlayer which acts as a mass and light blocking barrier.Fil: Curti, Mariano. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: López Robledo, Germán. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Química; ArgentinaFil: Dos Santos Claro, Paula Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. YPF - Tecnología; ArgentinaFil: Ubogui, Joaquín H.. YPF - Tecnología; ArgentinaFil: Mendive, Cecilia Beatriz. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Direct Imaging of Long-Range Exciton Transport in Quantum Dot Superlattices by Ultrafast Microscopy

Long-range charge and exciton transport in quantum dot (QD) solids is a crucial challenge in utilizing QDs for optoelectronic applications. Here, we present a direct visualization of exciton diffusion in highly ordered CdSe QDs superlattices by mapping exciton population using ultrafast transient absorption microscopy. A temporal resolution of ∼200 fs and a spatial precision of ∼50 nm of this technique provide a direct assessment of the upper limit for exciton transport in QD solids. An exciton diffusion length of ∼125 nm has been visualized in the 3 ns experimental time window and an exciton diffusion coefficient of (2.5 ± 0.2) × 10–2 cm2 s–1 has been measured for superlattices constructed from 3.6 nm CdSe QDs with center-to-center distance of 6.7 nm. The measured exciton diffusion constant is in good agreement with Förster resonance energy transfer theory. We have found that exciton diffusion is greatly enhanced in the superlattices over the disordered films with an order of magnitude higher diffusion coefficient, pointing toward the role of disorder in limiting transport. This study provides important understandings on energy transport mechanisms in both the spatial and temporal domains in QD solids.Fil: Yoon, Seog Joon. University of Notre Dame-Indiana; Estados UnidosFil: Guo, Zhi. Purdue University; Estados UnidosFil: Dos Santos Claro, Paula Cecilia. Argonne National Laboratory; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Shevchenko, Elena V.. Argonne National Laboratory; Estados UnidosFil: Huang, Libai. Purdue University; Estados Unido

Graphene Grown on Ni Foam: Molecular Sensing, Graphene-Enhanced Raman Scattering, and Galvanic Exchange for Surface-Enhanced Raman Scattering Applications

The growing of graphene on irregular 3D Ni structure demonstrates to be aninteresting platform for, molecular sensing, GERS, and SERS applications after galvanicexchange of Ag + ions. Raman, SEM (EDS), optical images, and diffuse reflectance exhibitthat graphene grows in multilayer (MLG) fashion with different stacking configurations.Statistics performed employing Raman show that as-grown graphene can be classified intwo main stacking configurations: AB (or Bernal stacking) and rotated graphene which areseparated by a 2D full-width half maximum (fwhm) threshold of ~30 cm -1 . Rotatedstacking senses low concentrations of methylene blue (MB) at 10 -6 M concentration,whereas AB-stacking seems to be much less sensitive upon molecular adsorption. Galvanicexchange of Ag leads to agglomerates preferentially formed on top graphene wrinkleswhich ultimately became target-spots for performing SERS. Our experiments demonstratethat as-grown graphene, comprised of different stacking configurations, can be used as amolecular sensor and detect nanomolar concentrations of MB and thiram (by SERSapplications), after galvanic exchange with Ag.Fil: Messina, María Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Picone, Andrea Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Dos Santos Claro, Paula Cecilia. YPF - Tecnología; ArgentinaFil: Ruiz, Remigio. YPF - Tecnología; ArgentinaFil: Saccone, Fabio Daniel. YPF - Tecnología; ArgentinaFil: Romano, Rosana Mariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Ibañez, Francisco Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Simultaneous detection and photocatalysis performed on a 3D graphene/ZnO hybrid platform

The synergy between graphene foam (Gf) and ZnO nanoparticles (NPs) allows the detection of analytes at low conentrations, which can be subsequently photocatalyzed on the hybrid surface as well as in the liquid phase upon illumination with low-power UV-vis light-emitting diode (LED) lamps. Detection of methylene blue (MB) and bisphenol A (BPA) is monitored either by graphene-enhanced Raman scattering (GERS) or molecular doping/sensing upon analyte adsorption. Using GERS, we were able to detect concentrations as low as 0.3 ppm of MB, which remained adsorbed on the graphene surface after a photocatalytic conversion of 88% (total conversion). The photocatalysis performances of BPA and MB performed in the liquid phase were lower and corresponded to 73 and 33% as indicated by gas chromatography-mass spectrometry (GC/MS) and UV-vis, respectively. The kinetics of photocatalysis was fitted with a quasi-first-order reaction, and the apparent rate constant (kapp) was calculated according to the Langmuir-Hinshelwood model. The fastest kinetics was achieved with the hybrid platform named "Gf-ZnO400", which was thermally treated at high temperatures and with most of the Ni etched away. This is consistent with the excellent electronic interaction between ZnO and graphene foam as indicated by photoelectrochemistry analysis. We mainly employed Raman scattering and UV-vis spectroscopy analyses for detection and photocatalysis applications; however, we also used other complementary techniques such as focused ion-beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance, GC/MS, and photoelectrochemistry to explore the synergetic behavior of these two nanomaterials. This work brings about new insights into the detection of analyte molecules followed by photocatalysis performed in the solid and liquid states.Fil: Messina, María Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Coustet, Marcos Eduardo. YPF - Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ubogui, Joaquin Hernán. YPF - Tecnología; ArgentinaFil: Ruiz, Remigio. YPF - Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Saccone, Fabio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física; ArgentinaFil: Dos Santos Claro, Paula Cecilia. YPF - Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ibañez, Francisco Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Graphene Grown on Ni Foam: Molecular Sensing, Graphene-Enhanced Raman Scattering, and Galvanic Exchange for Surface-Enhanced Raman Scattering Applications

The growing of graphene on irregular 3D Ni structure demonstrates to be aninteresting platform for, molecular sensing, GERS, and SERS applications after galvanicexchange of Ag + ions. Raman, SEM (EDS), optical images, and diffuse reflectance exhibitthat graphene grows in multilayer (MLG) fashion with different stacking configurations.Statistics performed employing Raman show that as-grown graphene can be classified intwo main stacking configurations: AB (or Bernal stacking) and rotated graphene which areseparated by a 2D full-width half maximum (fwhm) threshold of ~30 cm -1 . Rotatedstacking senses low concentrations of methylene blue (MB) at 10 -6 M concentration,whereas AB-stacking seems to be much less sensitive upon molecular adsorption. Galvanicexchange of Ag leads to agglomerates preferentially formed on top graphene wrinkleswhich ultimately became target-spots for performing SERS. Our experiments demonstratethat as-grown graphene, comprised of different stacking configurations, can be used as amolecular sensor and detect nanomolar concentrations of MB and thiram (by SERSapplications), after galvanic exchange with Ag.Centro de Química InorgánicaInstituto de Investigaciones Fisicoquímicas Teóricas y AplicadasConsejo Nacional de Investigaciones Científicas y Técnica

Graphene and Carbon Dots for Photoanodes with Enhanced Performance

The way graphene (GDs) and carbon dots (CDs) are synthesized and combined with TiO2determine their photoelectrochemical efficiency upon UV and visible LED lights. GDs and CDs are obtained by relatively unexplored top-down methods and conventional bottom-up methods, respectively. Top-down methods consist in the seedless growth of ZnO nanoparticles on the surface of graphene and the electrochemical cleavage of graphene grown on Ni foam. These carbon nanoparticles are later combined with TiO2by different approaches such as solution mixing, adsorption via APTES linkers, and drop-casting on an already formed TiO2film. Once the films are formed, they are placed into a photoelectrochemical Zahner cell and irradiated with LED lights at 450 and 360 nm. It is determined that CDs and GDs perform as efficient photosensitizers as demonstrated by an increase of ∼19- and 20-fold net photocurrent density when irradiated with UV and visible LED lights, respectively. We encountered that CDs are more sensitive upon visible light, whereas GDs promptly respond to UV light due to their difference in size-dependent band gap. Importantly, GDs obtained from seedless growth of ZnO are sensitive to both: UV and Vis LED irradiation. The combination of both nanocarbons would expand the absorption range and may be potentially used as cosensitizers toward the construction of more effective and advanced photoanodes.Fil: Messina, María Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Barrionuevo, Santiago. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Coustet, Marcos Eduardo. Universidad Nacional de La Plata; ArgentinaFil: Kreuzer, Mark P.. YPF - Tecnología; ArgentinaFil: Saccone, Fabio Daniel. YPF - Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Dos Santos Claro, Paula Cecilia. YPF - Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ibañez, Francisco Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin