Publications by authors named "Leyre Gomez"

15 Publications

  • Page 1 of 1

Direct Visualization and Determination of the Multiple Exciton Generation Rate.

ACS Omega 2020 Sep 19;5(34):21506-21512. Epub 2020 Aug 19.

Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.

Multiple exciton generation (MEG) takes place in competition to other hot carrier cooling processes. While the determination of carrier cooling rates is well established, direct information on MEG dynamics has been lacking. Here, we present a methodology to obtain the MEG rate directly in the initial ultrafast transient absorption dynamics. This method is most effective to systems with slow carrier cooling rates. Perovskite quantum dots exhibit this property and are used to illustrate this approach. They show a delayed carrier concentration buildup following an excitation pulse above the MEG threshold energy, which is accompanied by a faster carrier relaxation, providing a direct evidence of the MEG process. Numerical modeling within a simple framework of two competing cooling mechanisms allows us to extract the MEG rate and carrier energy cooling rates for this material. The presented methodology could provide new insights in carrier generation physics and valuable information for MEG investigations.
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http://dx.doi.org/10.1021/acsomega.0c02067DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7469370PMC
September 2020

Highly Stable Perovskite Supercrystals via Oil-in-Oil Templating.

Nano Lett 2020 Aug 28;20(8):5997-6004. Epub 2020 Jul 28.

Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.

Inorganic perovskites display an enticing foreground for their wide range of optoelectronic applications. Recently, supercrystals (SCs) of inorganic perovskite nanocrystals (NCs) have been reported to possess highly ordered structure as well as novel collective optical properties, opening new opportunities for efficient films. Here, we report the large-scale assembly control of spherical, cubic, and hexagonal SCs of inorganic perovskite NCs through templating by oil-in-oil emulsions. We show that an interplay between the roundness of the cubic NCs and the tension of the confining droplet surface sets the superstructure morphology, and we exploit this interplay to design dense hyperlattices of SCs. The SC films show strongly enhanced stability for at least two months without obvious structural degradation and minor optical changes. Our results on the controlled large-scale assembly of perovskite NC superstructures provide new prospects for the bottom-up production of optoelectronic devices based on the microfluidic production of mesoscopic building blocks.
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http://dx.doi.org/10.1021/acs.nanolett.0c02005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7431010PMC
August 2020

Efficient carrier multiplication in CsPbI perovskite nanocrystals.

Nat Commun 2018 10 10;9(1):4199. Epub 2018 Oct 10.

Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands.

The all-inorganic perovskite nanocrystals are currently in the research spotlight owing to their physical stability and superior optical properties-these features make them interesting for optoelectronic and photovoltaic applications. Here, we report on the observation of highly efficient carrier multiplication in colloidal CsPbI nanocrystals prepared by a hot-injection method. The carrier multiplication process counteracts thermalization of hot carriers and as such provides the potential to increase the conversion efficiency of solar cells. We demonstrate that carrier multiplication commences at the threshold excitation energy near the energy conservation limit of twice the band gap, and has step-like characteristics with an extremely high quantum yield of up to 98%. Using ultrahigh temporal resolution, we show that carrier multiplication induces a longer build-up of the free carrier concentration, thus providing important insights into the physical mechanism responsible for this phenomenon. The evidence is obtained using three independent experimental approaches, and is conclusive.
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http://dx.doi.org/10.1038/s41467-018-06721-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6180104PMC
October 2018

Correction to "Hybridization of Single Nanocrystals of CsPbBr and CsPbBr".

J Phys Chem C Nanomater Interfaces 2018 Feb 9;122(7):4116. Epub 2018 Feb 9.

[This corrects the article DOI: 10.1021/acs.jpcc.7b05752.].
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http://dx.doi.org/10.1021/acs.jpcc.8b00996DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5847119PMC
February 2018

Extraordinary Interfacial Stitching between Single All-Inorganic Perovskite Nanocrystals.

ACS Appl Mater Interfaces 2018 Feb 2;10(6):5984-5991. Epub 2018 Feb 2.

Institute of Physics, University of Amsterdam , Science Park 904, 1098 XH Amsterdam, The Netherlands.

All-inorganic cesium lead halide perovskite nanocrystals are extensively studied because of their outstanding optoelectronic properties. Being of a cubic shape and typically featuring a narrow size distribution, CsPbX (X = Cl, Br, and I) nanocrystals are the ideal starting material for the development of homogeneous thin films as required for photovoltaic and optoelectronic applications. Recent experiments reveal spontaneous merging of drop-casted CsPbBr nanocrystals, which is promoted by humidity and mild-temperature treatments and arrested by electron beam irradiation. Here, we make use of atom-resolved annular dark-field imaging microscopy and valence electron energy loss spectroscopy in a state-of-the-art low-voltage monochromatic scanning transmission electron microscope to investigate the aggregation between individual nanocrystals at the atomic level. We show that the merging process preserves the elemental composition and electronic structure of CsPbBr and takes place between nanocrystals of different sizes and orientations. In particular, we reveal seamless stitching for aligned nanocrystals, similar to that reported in the past for graphene flakes. Because the crystallographic alignment occurs naturally in drop-casted layers of CsPbX nanocrystals, our findings constitute the essential first step toward the development of large-area nanosheets with band gap energies predesigned by the nanocrystal choice-the gateway to large-scale photovoltaic applications of inorganic perovskites.
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http://dx.doi.org/10.1021/acsami.7b17432DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5814954PMC
February 2018

Hybridization of Single Nanocrystals of CsPbBr and CsPbBr.

J Phys Chem C Nanomater Interfaces 2017 Sep 10;121(35):19490-19496. Epub 2017 Aug 10.

Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.

Nanocrystals of all-inorganic cesium lead halide perovskites (CsPbX, X = Cl, Br, I) feature high absorption and efficient narrow-band emission which renders them promising for future generation of photovoltaic and optoelectronic devices. Colloidal ensembles of these nanocrystals can be conveniently prepared by chemical synthesis. However, in the case of CsPbBr, its synthesis can also yield nanocrystals of CsPbBr and the properties of the two are easily confused. Here, we investigate in detail the optical characteristics of simultaneously synthesized green-emitting CsPbBr and insulating CsPbBr nanocrystals. We demonstrate that, in this case, the two materials inevitably hybridize, forming nanoparticles with a spherical shape. The actual amount of these CsPbBr nanocrystals and nanohybrids increases for synthesis at lower temperatures, i.e., the condition typically used for the development of perovskite CsPbBr nanocrystals with smaller sizes. We use state-of-the-art electron energy loss spectroscopy to characterize nanoparticles at the single object level. This method allows distinguishing between optical characteristics of a pure CsPbBr and CsPbBr nanocrystal and their nanohybrid. In this way, we resolve some of the recent misconceptions concerning possible visible absorption and emission of CsPbBr. Our method provides detailed structural characterization, and combined with modeling, we conclusively identify the nanospheres as CsPbBr/CsPbBr hybrids. We show that the two phases are independent of each other's presence and merge symbiotically. Herein, the optical characteristics of the parent materials are preserved, allowing for an increased absorption in the UV due to CsPbBr, accompanied by the distinctive efficient green emission resulting from CsPbBr.
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http://dx.doi.org/10.1021/acs.jpcc.7b05752DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5592650PMC
September 2017

Color-stable water-dispersed cesium lead halide perovskite nanocrystals.

Nanoscale 2017 Jan;9(2):631-636

Institute of Physics, University of Amsterdam, Science Park 904, 1098 HX Amsterdam, The Netherlands.

Cesium lead halide perovskite nanocrystals are being lately explored for optoelectronic applications due to their emission tunability, high photoluminescence quantum yields, and narrow emission bands. Nevertheless, their incompatibility with polar solvents and composition homogenization driven by a fast anion-exchange are still important drawbacks to overcome. Herein we report on a successful encapsulation of colloidal perovskite nanocrystals within solid-lipid structures mainly consisting of stearic acid. The product is water-stable for a period longer than 2 months and anion-exchange is fully arrested when mixing nanocrystals of different halide compositions. This strategy boosts the potential applications of all-inorganic perovskite nanocrystals for ink-printing.
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http://dx.doi.org/10.1039/c6nr08892aDOI Listing
January 2017

Direct Observation of Band Structure Modifications in Nanocrystals of CsPbBr Perovskite.

Nano Lett 2016 11 18;16(11):7198-7202. Epub 2016 Oct 18.

National Institute of Advanced Industrial Science and Technology (AIST) , AIST Central 5, Tsukuba 305-8565, Japan.

We investigate the variation of the bandgap energy of single quantum dots of CsPbBr inorganic halide perovskite as a function of size and shape and upon embedding within an ensemble. For that purpose, we make use of valence-loss electron spectroscopy with Z-contrast annular dark-field (ADF) imaging in a state-of-the-art low-voltage monochromatic scanning transmission electron microscope. In the experiment, energy absorption is directly mapped onto individual quantum dots, whose dimensions and location are simultaneously measured to the highest precision. In that way, we establish an intimate relation between quantum dot size and even shape and its bandgap energy on a single object level. We explicitly follow the bandgap increase in smaller quantum dots due to quantum confinement and demonstrate that it is predominantly governed by the smallest of the three edges of the cuboidal perovskite dot. We also show the presence of an effective coupling between proximal dots in an ensemble, leading to band structure modification. These unique insights are directly relevant to the development of custom-designed quantum structures and solids which will be realized by purposeful assemblage of individually characterized and selected quantum dots, serving as building blocks.
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http://dx.doi.org/10.1021/acs.nanolett.6b03552DOI Listing
November 2016

Magneto-plasmonic nanoparticles as theranostic platforms for magnetic resonance imaging, drug delivery and NIR hyperthermia applications.

Nanoscale 2014 Aug;6(15):9230-40

Department of Chemical Engineering, Aragon Institute of Nanoscience (INA), University of Zaragoza, Campus Río Ebro-Edificio I+D, C/Poeta Mariano Esquillor S/N, 50018-Zaragoza, Spain.

PEGylated magneto-plasmonic nanoparticles with a hollow or semi-hollow interior have been successfully synthesized and their physico-chemical characteristics have been investigated. The hollow interior space can be used to store drugs or other molecules of interest whereas magnetic characterization shows their potential as contrast agents in magnetic resonance imaging (MRI) applications. In addition, their plasmonic characteristics in the near infrared (NIR) region make them efficient in photothermal applications producing high temperature gradients after short irradiation times. We show that by controlling the etching conditions the inner silica shell can be selectively dissolved to achieve a hollow or semi-hollow interior without compromising the magnetic or plasmonic characteristics of the resulting nanoparticles. Magnetic measurements and transmission electron microscopy observations have been used to demonstrate the precise control during the etching process and to select an optimal concentration of the etching reagent and contact time to preserve the inner superparamagnetic iron oxide-based nanoparticles and the plasmonic properties of the constructs. Drug loading capabilities were also evaluated for both semi-hollow and as-synthesized nanoparticles using Rhodamine B isothiocyanate as a model compound. The nanoparticles produced could be potentially used as "theranostic" nanoparticles with both imaging capabilities and a dual therapeutic function (drug delivery and hyperthermia).
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http://dx.doi.org/10.1039/c4nr01588fDOI Listing
August 2014

Temporal and spatial patterning of transgene expression by near-infrared irradiation.

Biomaterials 2014 Sep 21;35(28):8134-8143. Epub 2014 Jun 21.

Hospital Universitario La Paz-IdiPAZ, 28046 Madrid, Spain.

We investigated whether near-infrared (NIR) light could be employed for patterning transgene expression in plasmonic cell constructs. Hollow gold nanoparticles with a plasmon surface band absorption peaking at ∼750 nm, a wavelength within the so called "tissue optical window", were used as fillers in fibrin-based hydrogels. These composites, which efficiently transduce NIR photon energy into heat, were loaded with genetically-modified cells that harbor a heat-activated and ligand-dependent gene switch for regulating transgene expression. NIR laser irradiation in the presence of ligand triggered 3-dimensional patterns of transgene expression faithfully matching the illuminated areas of plasmonic cell constructs. This non-invasive technology was proven useful for remotely controlling in vivo the spatiotemporal bioavailability of transgenic vascular endothelial growth factor. The combination of spatial control by means of NIR irradiation along with safe and timed transgene induction presents a high application potential for engineering tissues in regenerative medicine scenarios.
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http://dx.doi.org/10.1016/j.biomaterials.2014.06.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4101380PMC
September 2014

Plasmon-enhanced photocatalytic water purification.

Phys Chem Chem Phys 2014 Aug;16(29):15111-6

Department of Chemical Engineering, Aragon Institute of Nanoscience (INA), University of Zaragoza, Campus Río Ebro, 50018 Zaragoza, Spain.

Increasing water demand and water scarcity around the world requires the development of robust and efficient methods for water purification in the coming decades. Here, we report a photocatalytic water purification method using visible light (532 nm) utilizing 5 nm gold nanoparticles and their enhancement when attached on the surface of silica nanospheres as an inactive support to prevent nanoparticle coalescence or sintering. This is a non-toxic, low-cost, and easy photocatalytic process which provides high decomposition rates. Decomposition of the methyl orange dye is tested as a reaction model and trichloroethylene is selected as an example of a real water pollutant. When irradiated at their plasmon resonant frequency, the gold nanoparticles generate hydroxyl radicals that degradate organic pollutants into non-toxic molecules representing a basic mechanism of photocatalytic water purification.
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http://dx.doi.org/10.1039/c4cp00229fDOI Listing
August 2014

Near-infrared-actuated devices for remotely controlled drug delivery.

Proc Natl Acad Sci U S A 2014 Jan 13;111(4):1349-54. Epub 2014 Jan 13.

Laboratory for Biomaterials and Drug Delivery, Department of Anesthesiology, Division of Critical Care Medicine, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115.

A reservoir that could be remotely triggered to release a drug would enable the patient or physician to achieve on-demand, reproducible, repeated, and tunable dosing. Such a device would allow precise adjustment of dosage to desired effect, with a consequent minimization of toxicity, and could obviate repeated drug administrations or device implantations, enhancing patient compliance. It should exhibit low off-state leakage to minimize basal effects, and tunable on-state release profiles that could be adjusted from pulsatile to sustained in real time. Despite the clear clinical need for a device that meets these criteria, none has been reported to date to our knowledge. To address this deficiency, we developed an implantable reservoir capped by a nanocomposite membrane whose permeability was modulated by irradiation with a near-infrared laser. Irradiated devices could exhibit sustained on-state drug release for at least 3 h, and could reproducibly deliver short pulses over at least 10 cycles, with an on/off ratio of 30. Devices containing aspart, a fast-acting insulin analog, could achieve glycemic control after s.c. implantation in diabetic rats, with reproducible dosing controlled by the intensity and timing of irradiation over a 2-wk period. These devices can be loaded with a wide range of drug types, and therefore represent a platform technology that might be used to address a wide variety of clinical indications.
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http://dx.doi.org/10.1073/pnas.1322651111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3910641PMC
January 2014

Au-PLA nanocomposites for photothermally controlled drug delivery.

J Mater Chem B 2014 Jan 9;2(4):409-417. Epub 2013 Dec 9.

Department of Industrial Engineering, University of Salerno, Fisciano, SA, Italy.

Stimuli-responsive drug delivery systems were obtained by encapsulating near-infrared (NIR) sensitive hollow gold nanoshells (HGNs) together with the molecule to be released into biodegradable poly-lactic acid (PLA) sub-micron particles. The rapid heating of the PLA particles caused by NIR radiation enabled use of the PLA-HGN composites as a photo-triggered drug release system. Rhodamine was used as a test molecule to obtain release profiles under different irradiation conditions. HGNs (32 nm diameter, 4.5 nm shell thickness) were synthesized via galvanic replacement of cobalt nanoparticles, using poly(vinylpyrrolidone) (PVP) as a stabilizer. PLA-HGN sub-micron particles (with mean diameters around 200 nm) encapsulating rhodamine were obtained using the supercritical emulsion extraction (SEE) technique. A good gold dispersion and a loading efficiency around 50% in the polymeric matrix were obtained for different HGN loadings. The release rate could be tuned by controlling the intensity of NIR exposition. Rhodamine release was completed in less than 10 hours when applying intense NIR irradiation for a few minutes, whereas 12 days of release was necessary in its absence. The system also allowed rhodamine release in a pulsed pattern.
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http://dx.doi.org/10.1039/c3tb21099eDOI Listing
January 2014

Scaled-up production of plasmonic nanoparticles using microfluidics: from metal precursors to functionalized and sterilized nanoparticles.

Lab Chip 2014 Jan 15;14(2):325-32. Epub 2013 Nov 15.

Institute of Nanoscience of Aragon and Department of Chemical Engineering, University of Zaragoza, E-50018, Zaragoza, Spain.

An exquisite control of synthesis parameters is generally required in nanomaterial synthesis to guarantee consistency in the essential characteristics such as size and shape. On the other hand, reliable scaled-up production of nanomaterials is required in order to achieve the production rates required for emerging nanotechnology applications while delivering a consistent product with the intended characteristics, avoiding the traditional batch-to-batch deviations. The continuous production of nanomaterials is challenging because of the difficulties involved in translating the complexity of nanomaterial synthesis into on-line operations. In this regard, microfluidic platforms stand out over conventional batch reactors due to their superior performance, easy scalability and reliability. Here, a continuous, scaled-up synthesis of high quality plasmonic hollow gold nanoparticles is reported for the first time. Not only was the throughput significantly higher than in a batch reactor, but also the microfluidic system allowed the on-line implementation of two new stages in nanomaterial production: surface functionalization and sterilization.
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http://dx.doi.org/10.1039/c3lc50999kDOI Listing
January 2014

Enhancing of plasmonic photothermal therapy through heat-inducible transgene activity.

Nanomedicine 2013 Jul 22;9(5):646-56. Epub 2012 Nov 22.

CIBER de Bioingeniería, Biomateriales y Nanomedicina, CIBER-BBN, Spain.

Unlabelled: We explore the synergistic effect of photothermal therapy and gene therapy, simultaneously triggered by silica-gold nanoshells (NS) or hollow gold nanoparticles (HGNPs) in human HeLa cells following near-infrared (NIR) light irradiation. Thermal transfer from NS was higher than that displayed by HGNPs, owing to a differential interaction of the nanomaterial with the biological environment. Under sublethal photothermal conditions, NS and HGNPs effectively modulated the expression levels of a DsRed-monomer reporter gene controlled by the highly heat-inducible human HSP70B promoter, as a function of nanomaterial concentration and length of laser exposure. Hyperthermia treatments at doses that do not promote cell death generated a lethal outcome in HeLa cells harboring the fusogenic GALV-FMG transgene under the control of the HSP70B promoter. Combination of lethal photothermia with the triggering of the cytotoxic transgene resulted in a dramatic increase of the cell-ablation area as a result of the synergistic activity established.

From The Clinical Editor: In this study photothermal therapy and gene therapy, simultaneously triggered by silica-gold nanoshells or hollow gold nanoparticles, was investigated in human HeLa cells following near-infrared (NIR) light irradiation. It is shown that the combination of lethal photothermia with the triggering of the cytotoxic transgene at sublethal levels results in a synergistic cytotoxic effect in vitro.
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http://dx.doi.org/10.1016/j.nano.2012.11.002DOI Listing
July 2013