| 1. |
- Auroux, Etienne, et al.
(författare)
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A metal-free and transparent light-emitting device by sequential spray-coating fabrication of all layers including PEDOT:PSS for both electrodes
- 2023
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 13:25, s. 16943-16951
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Tidskriftsartikel (refereegranskat)abstract
- The concept of a metal-free and all-organic electroluminescent device is appealing from both sustainability and cost perspectives. Herein, we report the design and fabrication of such a light-emitting electrochemical cell (LEC), comprising a blend of an emissive semiconducting polymer and an ionic liquid as the active material sandwiched between two poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) conducting-polymer electrodes. In the off-state, this all-organic LEC is highly transparent, and in the on-state, it delivers uniform and fast to turn-on bright surface emission. It is notable that all three device layers were fabricated by material- and cost-efficient spray-coating under ambient air. For the electrodes, we systematically investigated and developed a large number of PEDOT:PSS formulations. We call particular attention to one such p-type doped PEDOT:PSS formulation that was demonstrated to function as the negative cathode, as well as future attempts towards all-organic LECs to carefully consider the effects of electrochemical doping of the electrode in order to achieve optimum device performance.
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| 2. |
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| 3. |
- La Hera, Vladimir Miranda, et al.
(författare)
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Controlled Synthesis of Tellurium Nanowires
- 2022
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 12:23
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Tidskriftsartikel (refereegranskat)abstract
- One-dimensional tellurium nanostructures can exhibit distinct electronic properties from those seen in bulk Te. The electronic properties of nanostructured Te are highly dependent on their morphology, and thus controlled synthesis processes are required. Here, highly crystalline tellurium nanowires were produced via physical vapour deposition. We used growth temperature, heating rate, flow of the carrier gas, and growth time to control the degree of supersaturation in the region where Te nanostructures are grown. The latter leads to a control in the nucleation and morphology of Te nanostructures. We observed that Te nanowires grow via the vapour–solid mechanism where a Te particle acts as a seed. Transmission electron microscopy (TEM) and electron diffraction studies revealed that Te nanowires have a trigonal crystal structure and grow along the (0001) direction. Their diameter can be tuned from 26 to 200 nm with lengths from 8.5 to 22 μm, where the highest aspect ratio of 327 was obtained for wires measuring 26 nm in diameter and 8.5 μm in length. We investigated the use of bismuth as an additive to reduce the formation of tellurium oxides, and we discuss the effect of other growth parameters.
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| 4. |
- Miranda la Hera, Vladimir, et al.
(författare)
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Controlled synthesis of tellurium nanowires by physical vapor deposition
- 2022
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Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 12:23
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Tidskriftsartikel (refereegranskat)abstract
- One-dimensional tellurium nanostructures can exhibit distinct electronic properties from those seen in bulk Te. The electronic properties of nanostructured Te are highly dependent on their morphology, and thus controlled synthesis processes are required. Here, highly crystalline tellurium nanowires were produced via physical vapour deposition. We used growth temperature, heating rate, flow of the carrier gas, and growth time to control the degree of supersaturation in the region where Te nanostructures are grown. The latter leads to a control in the nucleation and morphology of Te nanostructures. We observed that Te nanowires grow via the vapour–solid mechanism where a Te particle acts as a seed. Transmission electron microscopy (TEM) and electron diffraction studies revealed that Te nanowires have a trigonal crystal structure and grow along the (0001) direction. Their diameter can be tuned from 26 to 200 nm with lengths from 8.5 to 22 μm, where the highest aspect ratio of 327 was obtained for wires measuring 26 nm in diameter and 8.5 μm in length. We investigated the use of bismuth as an additive to reduce the formation of tellurium oxides, and we discuss the effect of other growth parameters.
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| 5. |
- Miranda la Hera, Vladimir, et al.
(författare)
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Electronic properties of hexagonal v-shaped gallium nitride pits
- 2023
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:51, s. 24658-24665
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Tidskriftsartikel (refereegranskat)abstract
- In this work, the morphology, surface composition, and electronic properties of porous GaN films containing hexagonal V-shaped pits were studied. The V-pits are orientated along the [0001] direction of GaN, and we observed a clear relation between the growth time with the surface composition, film thickness, and pit morphology, which in turn had a significant impact on the band gap, valence band maximum, and the work function. The effect on the position of the valence band maximum and work function is explained by the formation of superficial oxygen-rich phases such as Ga2O3 and nonstoichiometric GaNxOy as supported by X-ray photoelectron spectroscopy and density functional theory (DFT). We further show a change in the optical band gap with the thickness of the porous films explained by a change in the tensile strain caused by open-core screw dislocations that gives rise to the formation of V-pits. The correlation between strain and the band gap is supported by DFT calculations. Our study provides insights into the intricate relation between surface states and electronic properties of semiconducting materials and offers directions for designing GaN heterojunctions with specific optical and electronic properties.
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| 6. |
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| 7. |
- Miranda la Hera, Vladimir, 1988-
(författare)
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Surface analysis of low dimensional materials : revealing their electronic properties by advanced spectroscopy
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low-dimensional materials (0D, 1D, 2D) have been widely used to develop modern miniaturized (micro- and nano-) technology. The use of these materials come from their extraordinary optical, electrical, thermal, and mechanical properties, which are very different from the bulk crystal. To understand low-dimensional materials there is a large interest in studying the surface states of such materials, because the topmost few atomic layers possess an atomic arrangement and electronic structure different from the crystal bulk and hence responsible for many of the novel properties. In surface science, the techniques typically probe the topmost 1-10 nm of surfaces exposed to vacuum. X-ray photoemission spectroscopy (XPS) is the most common surface technique used because of its relatively easy handling and good ability to reveal important information on the surface oxidation states. XPS involves radiation of light that penetrates a sample up to 10 nm depth. Ultraviolet photoemission spectroscopy (UPS) is another surface-sensitive technique, with a slightly lower probing depth, on average about 2.5 nm. For the research in this thesis, a vacuum system has been constructed that contains surface analytical equipment for UPS, Angle Resolved Photospectroscopy and Low-electron energy diffraction. Normally, XPS and UPS are used as individual techniques as they both determine different properties of the material. However, hereby for many applications both are used in conjunction because they complement each other and provide a comprehensive analysis of the samples structure and electronic properties.The aim of this thesis is to present surface analytical measurements carried on low-dimensional materials. Among the materials studied is Graphene, used to as a proof-of-principle experiment in the vacuum system constructed as it has been extensively studied and information can be easily found. The second material was Cu2O thin films that shows different chemical and electronic properties depending on the oxidation level. The third material is nanoporous GaN that exhibit V-pits that modify the properties of the material depending on the hole sizes. The fourth material are trigonal Te nanowires, 1D nanostructures that has a narrow direct bandgap, a high-hole mobility, and a high current density. Finally, an application of the constructed setup is show characterizing the electronic properties of NiFeMo solids.
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| 8. |
- Rafei, Mouna, et al.
(författare)
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Non-stoichiometric NiFeMo solid solutions; tuning the hydrogen adsorption energy via molybdenum incorporation
- 2022
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Ingår i: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 9:34
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Tidskriftsartikel (refereegranskat)abstract
- Solution precursor plasma spraying is used to produce catalytic trimetallic coatings containing Ni, Fe and Mo directly onto stainless-steel mesh, Ni foam and carbon paper. The resulting material is mostly comprised of face centered cubic FeNi3 alloy forming a highly porous coating with nanostructured features. The addition of Mo (up to ≈14 at%) generates no new crystal phases but only an increase in the lattice parameter, indicating the formation of FeNi3Mox solid solutions. The FeNi3Mox solid solutions are used as electrocatalyst for the hydrogen evolution reaction (HER) in alkaline media. The addition of Mo increases the HER activity significantly reaching an optimum performance at ≈9 at% Mo (FeNi3Mo0.40) with an overpotential at −10 mA cm−2 of 112 mV and a Tafel slope of 109 mV dec−1. The enhanced HER activity is attributed to the formation of a FeNi3Mox solid solution with an increased work function that is correlated to smaller hydrogen adsorption energies. Theoretical activity maps reveal that sites near superficial Mo atoms forms catalytic hot spots and are responsible for the observed activity.
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| 9. |
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| 10. |
- Rafei, Mouna, et al.
(författare)
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Study on the electronic and structural properties of oxidized copper films
- 2022
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Ingår i: AIP Advances. - : American Institute of Physics (AIP). - 2158-3226. ; 12:10
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the oxidation of Cu substrates was carried out under controlled conditions by regulating the pressure, atmosphere composition, process time, and temperature. By tuning the synthesis conditions, the formation of cuprous oxide (Cu2O) or cupric oxide (CuO) could be preferentially promoted. The oxidation temperature was varied from 400 to 1050 °C, and a gradual oxidation of metallic Cu to Cu2O was achieved at mild oxidation conditions (400-600 °C), while the formation of CuO was only observed at higher temperatures (≥900 °C). The surface morphology was also affected changing from a highly granular texture (400 °C) with grain sizes between 0.59 ± 0.15 μm to smooth large crystallites (≥900 °C) with a size within 2.76 ± 0.97 μm. We also show that by controlling the oxidation temperature (400-1050 °C), it is possible to tune the work function and the ionization potential of the resulting Cu2O/CuO film, properties that are important for various optoelectronic applications.
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