Electrical and Plasmonic Properties of Ligand-Free Sn4+-Doped In2O3 (ITO) Nanocrystals

Sn4+-doped In2O3 (ITO) is a benchmark transparent conducting oxide material. We prepared ligand-free but colloidal ITO (8nm, 10% Sn4+) nanocrystals (NCs) by using a post-synthesis surface-modification reaction. (CH3)(3)OBF4 removes the native oleylamine ligand from NC surfaces to give ligand-free, positively charged NCs that form a colloidal dispersion in polar solvents. Both oleylamine-capped and ligand-free ITO NCs exhibit intense absorption peaks, due to localized surface plasmon resonance (LSPR) at around =1950nm. Compared with oleylamine-capped NCs, the electrical resistivity of ligand-free ITO NCs is lower by an order of magnitude (approximate to 35mcm(-1)). Resistivity over a wide range of temperatures can be consistently described as a composite of metallic ITO grains embedded in an insulating matrix by using a simple equivalent circuit, which provides an insight into the conduction mechanism in these systems

Halide perovskite quantum dots photosensitized-amorphous oxide transistors for multimodal synapses

Deployment of novel artificial synapses serves as the crucial unit for building neuromorphic hardware to drive data-intensive applications. Emulation of complex neural behaviour through conventional Si-based devices requires a large number of elements which increases fabrication complexity and brings challenges of connectivity. Hence, there is a need to investigate alternative material systems and device architectures for emulating richer neural behaviour comprising of lesser elements. Herein, a thin-film transistor (TFT)-like synaptic device using all-inorganic Cesium lead bromide (CsPbBr3) perovskite quantum dots (QDs) and amorphous Indium Gallium Zinc Oxide (a-IGZO) semiconductor active material is explored for brain-inspired computing. The incorporation of CsPbBr3 QDs as a photosensitizer aids in realizing light-dependent synaptic memory. Furthermore, type II heterostructure can serve as a basis for electro-optical programming. The proposed artificial synapse demonstrates a materials combination that could decouple optical absorption and charge transport property, provides freedom to tune the spectral region. Harnessing the advantages of novel materials, our devices obey spike-timing-dependent plasticity rules, inculcate associative learning and linear non-volatile blind updates. This architecture paves way for efficient building of neuromorphic hardware elements with facile tunability and tailorable plasticity.Ministry of Education (MOE)National Research Foundation (NRF)Accepted versionThis research was funded by National Research Foundation, Prime Minister’s Office, Singapore under its Competitive Research Program (CRP Award No. NRF-CRP14-2014-03), the Intra-CREATE Collaborative Grant (NRF2018-ITC001-001), and Tier 2 Grant Nos. MOE2016-T2-1-100 and MOE2018-T2-2-083

Halide Perovskite Quantum Dots Photosensitized‐Amorphous Oxide Transistors for Multimodal Synapses

Deployment of novel artificial synapses serves as the crucial unit for building neuromorphic hardware to drive data-intensive applications. Emulation of complex neural behaviour through conventional Si-based devices requires a large number of elements which increases fabrication complexity and brings challenges of connectivity. Hence, there is a need to investigate alternative material systems and device architectures for emulating richer neural behaviour comprising of lesser elements. Herein, a thin-film transistor (TFT)-like synaptic device using all-inorganic Cesium lead bromide (CsPbBr3) perovskite quantum dots (QDs) and amorphous Indium Gallium Zinc Oxide (a-IGZO) semiconductor active material is explored for brain-inspired computing. The incorporation of CsPbBr3 QDs as a photosensitizer aids in realizing light-dependent synaptic memory. Furthermore, type II heterostructure can serve as a basis for electro-optical programming. The proposed artificial synapse demonstrates a materials combination that could decouple optical absorption and charge transport property, provides freedom to tune the spectral region. Harnessing the advantages of novel materials, our devices obey spike-timing-dependent plasticity rules, inculcate associative learning and linear non-volatile blind updates. This architecture paves way for efficient building of neuromorphic hardware elements with facile tunability and tailorable plasticity.Ministry of Education (MOE)National Research Foundation (NRF)Accepted versionThis research was funded by National Research Foundation, Prime Minister’s Office, Singapore under its Competitive Research Program (CRP Award No. NRF-CRP14-2014-03), the Intra-CREATE Collaborative Grant (NRF2018-ITC001-001), and Tier 2 Grant Nos. MOE2016-T2-1-100 and MOE2018-T2-2-083

Defect-Mediated Electron–Hole Separation in Colloidal Ag₂S–AgInS₂ Hetero Dimer Nanocrystals Tailoring Luminescence and Solar Cell Properties

Nanoscale heterojunctions with type-II band alignment can efficiently separate a photogenerated electron–hole pair, and therefore find applications in solar cells and photocatalysis. Here, we prepare a nanojunction in the form of Ag₂S–AgInS₂ hetero dimer nanocrystal that does not contain toxic Cd and Pb. A combination of photophysics, cyclic voltammetry, and quantum dot-sensitized solar cell properties shows that the junction/interface has a type-I band alignment, but still electron–hole separation takes place with efficacy across the interface because of defect states. The electron gets localized in a defect state within the AgInS₂ part, and the hole resides in the Ag₂S part of the hetero dimer nanocrystal. This type-II-like defect-mediated electron–hole separation, irrespective of the nature interfacial band alignment, is an interesting phenomenon, and can be utilized to tune optoelectronic properties of heterostructured nanocrystals. For example, very long (13 μS) photoluminescence lifetime has been observed for Ag₂S–AgInS₂ hetero dimer nanocrystals because of this defect-mediated spatial separation of electron and hole wave functions, which in turn improve the solar cell efficiency by more than 3 times as compared to that of AgInS₂ nanocrystals

Colloidal Mn-Doped Cesium Lead Halide Perovskite Nanoplatelets

Strong quantum confinement in Mn-doped semiconductor nanocrystals enhances dopant–carrier exchange interactions. Here, we report the synthesis and optical properties of strongly quantum confined, quasi two-dimensional, Mn-doped CsPbCl₃ nanoplatelets. A room-temperature synthesis was employed to prepare the platelets with thickness 2.2 nm (4 monolayers), which is significantly smaller than the Bohr excitonic diameter of CsPbCl₃ (5 nm). Efficient transfer of excitonic energy from the host to the Mn²⁺ dopant ions leads to a spin-forbidden ⁴T₁–⁶A₁ Mn d-electron emission with the highest quantum yield of ∼20% and exhibits a long lifetime of 1.6 ms. Subsequent anion exchange reactions at room temperature lead to the formation of Mn-doped CsPbBr₃ nanoplatelets, with weak Mn emission. These newly developed Mn-doped cesium lead halide nanoplatelets are suitable candidates for exploring the effects of quantum confinement on dopant–carrier exchange interaction and exhibiting interesting magneto-optic properties

Postsynthesis Doping of Mn and Yb into CsPbX3 (X = CI, Br, or I) Perovskite Nanocrystals for Downconversion Emission

Doping Mn and Yb into CsPbX3 (X = Cl, Br, or I) nanocrystals (NCs) yields luminescence due to de-excitation through d-d (yellow-red emission) and f-f transitions (near-infrared emission), respectively. However, to date, both Mn emission and Yb emission have been obtained from perovskite NCs with a wider band gap (<480 nm). To overcome this problem, we have developed a postsynthesis doping method in which Mn and Yb can be easily doped into preformed CsPbX3 NCs with band gaps in the entire visible region. Different morphologies like nanoplatelets and nanocubes are doped. Because we dope preformed host NCs, the effect of dopants on optical properties can be studied more reliably using the same batch of host NCs for both undoped and doped samples. We find that the problem of the absence of Mn emission from Mn-doped CsPbBr3 NCs can be overcome by suppressing back energy transfer from Mn to host NCs, either by increasing the band gap of the host by quantum confinement or by measuring photoluminescence at lower temperatures. Interestingly, dopants are found to enhance the excitonic emission intensities and reduce the Urbach absorption tail, suggesting a reduced defect density compared to that of undoped NCs. These added functionalities and capability to dope lower-band gap materials can be explored further for near-infrared light-emitting diodes, sensing, and luminescent solar concentrators of desired colors

Colloidal Nanocomposite of TiN and N‑Doped Few-Layer Graphene for Plasmonics and Electrocatalysis

A combination of high carrier density, high surface area, solution processability, and low cost is desired in a material for electrocatalytic applications, including H₂ evolution and a counter electrode of a solar cell. Also, plasmonic-based applications in biological systems can be derived from such material. In this regard, a colloidal nanocomposite of TiN and N-doped few-layer graphene (TiN–NFG) is synthesized from molecular precursors. TiN nanocrystals (NCs) provide free electrons for electrical conductivity and plasmonics, whereas NFG is responsible for charge transport, high surface area, and colloidal stability. Colloidal TiN–NFG nanocomposites exhibit a localized surface plasmon resonance band at around 700 nm. Coatings of the nanocomposite form a counter electrode for efficient (8.9%) dye-sensitized solar cells. Furthermore, the nanocomposite acts as an efficient electrocatalyst for hydrogen evolution reaction, exhibiting an overpotential ∼161 mV at a current density of 10 mA/cm²

Halide perovskite memristors as flexible and reconfigurable physical unclonable functions

Despite the impressive demonstrations with silicon and oxide memristors, realizing efficient roots of trust for resource-constrained hardware remains a challenge. Here, the authors exploit switching behavior in one dimensional perovskite memristors to design security primitives for key generation and device authentication

Stoichiometric Engineering of Cs2AgBiBr6 for Photomultiplication- Type Photodetectors

Photomultiplication (PM)-type photodetectors with a high external quantum efficiency (EQE) can be realized through adequately engineered trap states and trap-assisted charge injection. By strategically introducing slightly rich Bi and highly rich Br stoichiometric conditions, efficient trap states are realized for holes in lead-free Cs1.98AgBi1.15Br7.9 double perovskite (DP). With the diode structure of ITO/SnO2/Cs1.98AgBi1.15Br7.9/poly(3-hexylthiophene) (P3HT)/MoOx/Ag, where SnO2 and P3HT layers are used as the hole-and electron-blocking layers, respectively, successful realization of the selective hole trap and the resulting band bending/electron injection at the anode interface is demonstrated. As a result, a high EQE of similar to 16,000%, responsivity of similar to 50 A W-1, and specific detectivity of over 1012 Jones at -3 V are demonstrated. The origin of the suggested PM mechanism is discussed using photophysical and optoelectronic measurements and theoretical studies. This work ensures the successful demonstration of PM-type photodetectors using lead-free Cs2AgBiBr6 DP through strategic trap engineering

Condado de Treviño: aproximación a una "addenda" al "corpus" epigráfico de la provincia de Burgos

Since some years ago, the collection of epigraphic corpora from the region of Castilla y León was being completed. The corpus corresponding to Burgos' province was one of the last, but, nevertheless, this one isn't complete, because it doesn't show the whole provincial collection, missing the information from a enclave, the Condado de Treviño, in the Alava's province.Desde hace unos años, el conjunto de corpora epigráficos de Castilla y León, ha ido siendo completado. El corpus correspondiente a la provincia de Burgos, ha sido uno de los últimos, pero, sin embargo, éste no está completo, pues no muestra el conjunto epigráfico completo, faltando la información de un enclave, el Condado de Treviño, sito en la provincia de Álava