高効率太陽光エネルギー変換を目指したプラズモニック銅カルコゲナイドナノ結晶の開発

京都大学新制・課程博士博士(理学)甲第24180号理博第4871号京都大学大学院理学研究科化学専攻(主査)教授 寺西 利治, 教授 島川 祐一, 教授 倉田 博基学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDGA

Near-infrared plasmonics with vacancy doped semiconductor nanocrystals

Plasmonics with heavily doped semiconductor nanocrystals (NCs) is an emerging field in NC science. However, impurity doping of NCs remains far from trivial and is, as yet, dominated by a low chemical control over the incorporated dopant atoms. An appealing alternative is vacancy doping, where the formation of vacancies in the structure is responsible for an increased carrier density and elegantly circumvents the issues related to impurity doping. Due to high carrier densities of around 10^21cm^(-3) localized surface plasmon resonances (LSPRs) in the near infrared (NIR) are expected, and as such highlighted to close the gap between conventionally doped NCs and noble metal nanoparticles. Copper chalcogenide NCs, namely copper sulfide (Cu2-xS), copper selenide (Cu2-xSe), and copper telluride (Cu2-xTe), are an attractive example of vacancy doped semiconductor NCs, with spectra dominated by intense NIR resonances. Within this study thorough experimental evidence has been given to prove the plasmonic nature of those NIR resonances. By presenting typical plasmonic characteristics, such as refractive index sensitivity of the LSPR, its intrinsic size dependence, plasmon dynamics, or interparticle plasmon coupling, the LSPRs in copper chalcogenide NCs have unambiguously been identified. The chemical nature of vacancy doping turns out to deliver an additional, highly attractive means of control over the LSPR in vacancy doped copper chalcogenide NCs. Through chemical tailoring of the copper vacancy density via controlled oxidation and reduction, as shown in this study, a reversible tuning of the LSPR over a wide range of frequencies in the NIR (1000-2000 nm) becomes feasible. This highlights copper chalcogenide NCs over conventional plasmonic materials. Notably, the complete suppression of the LSPR uncovers the excitonic features present only in the purely semiconducting, un-doped NCs and reveals the unique option to selectively address excitons and highly tunable LSPRs in one material (bandgap Eg~1.2 eV). As such, copper chalcogenide NCs appear to hold as an attractive material system for the investigation of exciton plasmon interactions. Indeed, a quenching of the excitonic transitions in the presence of the developing LSPR is demonstrated within this work, with a full recovery of the initial excitonic properties upon its suppression. A theoretical study on the shape dependent plasmonic properties of Cu2-xTe NCs reveals a deviation from the usual Drude model and suggests that the carriers in vacancy doped copper chalcogenide NCs cannot be treated as fully free. On the other hand, the Lorentz model of localized oscillators appears to account for the weak shape dependence, as observed experimentally, indicating an essential degree of localization of the carriers in vacancy doped copper chalcogenide NCs. Taken together, this work delivers a huge step toward the complete optical and structural characterization of plasmonic copper chalcogenide NCs. The advantages of semiconductor NC chemistry have been exploited to provide access to novel plasmonic shapes, such as tetrapods that have not been feasible to produce so far. A precise size, shape and phase control presents the basis for this study, and together with a thorough theoretical investigation delivers important aspects to uncover the tunable plasmonic properties of vacancy doped copper chalcogenide NCs

Structural, Optical and Transport Properties of Copper Chalcogenide Nanocrystal Superlattices

This cumulative thesis is based on three publications. It investigates the self-assembly of nanocrystal (NC) superlattices, charge transport in NC assembly, and application of these superlattices in optoelectronic and vapor sensing. The materials of choice are copper chalcogenide NCs such as binary copper sulfide Cu1.1S NCs, binary copper selenide Cu2Se NCs and ternary Cu2-xSeyS1-y NCs and the organic semiconductors metal (Cu or Co) centered -4,4′,4″,4″,4‴-tetraaminophthalocyanine (Cu/CoTAPc). Macroscopic superlattices of NCs are prepared by Langmuir-type self-assembly at the air/liquid interface followed by simultaneous ligand exchange with an organic semiconductor. To enhance interparticle coupling, we cross-link the nanocrystals with the organic π-system Cu-4,4′,4″,4″,4‴-tetraaminophthalocyanine and observe a significant increase in electrical conductivity. Ultraviolet-visible-near-infrared (UV-vis-NIR) and Raman spectroscopy are used to track the chemical changes on the nanocrystals’ surface before and after ligand exchange and develop a detailed picture of the various components which dominate the surface chemistry of this material. Grazing-incidence small-angle X-ray scattering (GISAXS) serve to study the importance of electronic conjugation in the organic π-system vs interparticle spacing for efficient charge transport. Transport measurements reveal that Cu4APc provides efficient electronic coupling for neighboring Cu1.1S NCs. The electrical properties of monolayers of this hybrid ensemble are consistent with a two-dimensional semiconductor and exhibit two abrupt changes at discrete temperatures (120 and 210 K), which may be interpreted as phase changes. This material provides the opportunity to apply the hybrid ensemble as a chemiresistor in organic vapor sensing. The vapor sensing experiments exhibits a strong selectivity between polar and nonpolar analytes, which we discuss in light of the role of the organic π-system and its metal center. Next, we choose ternary alloyed Cu-based chalcogenide NCs Cu2SeyS1–y and checked the effect of ligand exchange with the organic π-system Cobalt β-tetraaminophthalocyanine (CoTAPc) along with its binary counterpart Cu2Se NCs. We analysed changes in the structural, optical as well as electric properties of thin films of these hybrid materials. Strong ligand interaction with the surface of the NCs is revealed by UV/vis absorption and Raman spectroscopy. GISAXS studies show a significant contraction in the interparticle distance upon ligand exchange. For copper-deficient Cu2-xSe, this contraction has a negligible effect on electric transport, while for copper-deficient Cu2-xSeyS1-y, the conductivity increases by eight orders of magnitude and 8 results in metal-like temperature-dependent transport. We discuss these differences in the light of varying contributions of electronic vs. ionic transport in the two materials and highlight their effect on the stability of the transport properties under ambient conditions. With photocurrent measurements, we demonstrate high optical responsivities of 200-400 A/W for CoTAPc-capped Cu2SeyS1–y and emphasize the beneficial role of the organic π-system in this respect, which acts as an electronic linker and an optical sensitizer at the same time. Finally, we report on the in-situ monitoring of the formation of conductive superlattices of Cu1.1S nanodiscs via cross-linking with semiconducting Co-4,4′,4″,4″,4‴-tetraaminophthalocyanine (CoTAPc) molecules at the liquid/air interface by real-time grazing incidence small angle X-ray scattering (GISAXS). We determine the structure, symmetry and lattice parameters of the superlattices, formed during solvent evaporation and ligand exchange on the self-assembled nanodiscs. Cu1.1S nanodiscs self-assemble into two-dimensional hexagonal superlattice with a minor in-plane contraction (~ 0.2 nm) in the lattice parameter. A continuous contraction of the superlattice has been observed during ligand exchange, preserving the initial hexagonal symmetry. We estimate a resultant decrement of about 5% in the in-plane lattice parameters. The contraction is attributed to the continuous replacement of the native oleylamine surface ligands with rigid CoTAPc. The successful cross-linking of the nanodiscs is manifested in terms of the high electrical conductivity observed in the superlattices. This finding provides a convenient platform to understand the correlation between the structure and transport of the coupled superstructures of organic and inorganic nanocrystals of anisotropic shape

Structural studies of the silica sol-gel glasses doped with copper selenide nanoparticles with plasmonic resonance absorption

Background: Semiconductor-doped glasses are treated actively through many years and continue to be of great interest because challenged features of nanosized semiconductors of various chemical nature. Copper chalcogenides have discovered the plasmonic properties in line with quantum confinement effects specific for major of semiconductor nanoparticles. Objective: The aim of this work is to study structural and optical features of the sol-gel derived silica glasses with copper selenide nanoparticles demonstrating appearance of the plasmonic light absorption in the near IR range. Method: The samples under study were fabricated through an original sol-gel technique realizing the simultaneous synthesis of copper selenide and sintering of mesoporous silica. The copper selenide glasses were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and optical absorption spectroscopy. Results: Formation of nanocrystalline Cu2-xSe particles of the size range from tens nm through 100-150 nm is established with XRD and TEM techniques. The principal optical properties are presented by the featured absorption in the visible and near-IR ranges. Eg was evaluated for the direct transitions in the range of 2.10-2.36 eV. The plasmonic resonance in the nanoparticles due to increased carrier concentration originated by intrinsic defectness of Cu2-xSe nanoparticles with variable stoichiometry. Its energy can be controlled by Cu/Se ratio in the synthesis procedure.Comment: 16 pages including 5 figure

Colloidal Semiconductor Nanoparticles as Functional Materials: Design, Assembly and Applications

This work summarizes results of about ten years of the author’s own research activities in the field of colloidal synthesis of semiconductor nanoparticles, their postsynthetic chemical modification, assembly, and applications. I attempted to provide a concise yet comprehensive overview presenting my own results as a part of the knowledge framework created in close collaboration with many colleagues from all over the world. This habilitation thesis consists of an introduction, explaining the motivation of the research accomplished, followed by a main part which briefly presents key achievements of the author with links to appropriate annexes, i.e. original published articles in peer review journals which are attached to this cumulative script, and completed by conclusions

Chalcogen Impact on Covalency within Molecular [Cu\u3csub\u3e3\u3c/sub\u3e(μ\u3csub\u3e3\u3c/sub\u3e-E)]\u3csup\u3e3+\u3c/sup\u3e Clusters (E = O, S, Se): A Synthetic, Spectroscopic, and Computational Study

Reaction of the tricopper(I)-dinitrogen tris(β-diketiminate) cyclophane, Cu3(N2)L, with O-atom-transfer reagents or elemental Se affords the oxido-bridged tricopper complex Cu3(μ3-O)L (2) or the corresponding Cu3(μ3-Se)L (4), respectively. For 2 and 4, incorporation of the bridging chalcogen donor was supported by electrospray ionization mass spectrometry and K-edge X-ray absorption spectroscopy (XAS) data. Cu L2,3-edge X-ray absorption data quantify 49.5% Cu 3d character in the lowest unoccupied molecular orbital of 2, with Cu 3d participation decreasing to 33.0% in 4 and 40.8% in the related sulfide cluster Cu3(μ3-S)L (3). Multiedge XAS and UV/visible/near-IR spectra are employed to benchmark density functional theory calculations, which describe the copper-chalcogen interactions as highly covalent across the series of [Cu3(μ-E)]3+ clusters. This result highlights that the metal-ligand covalency is not reserved for more formally oxidized metal centers (i.e., CuIII + O2- vs CuII + O-) but rather is a significant contributor even at more typical ligand-field cases (i.e., Cu3II/II/I + E2-). This bonding is reminiscent of that observed in p-block elements rather than in early-transition-metal complexes

Ag2ZnSnS4 Nanocrystals Expand the Availability of RoHS Compliant Colloidal Quantum Dots

The demonstration of the quantum confinement effect in colloidal quantum dots (QDs) has been extensively studied and exploited mainly in Pb and Cd chalcogenide systems. There has been an urgent need recently for the development of non(less)-toxic colloidal QDs to warrant compliance with current safety regulations (Restriction of Hazardous Substances (RoHS) Directive 2002/95/EC). Herein, we report Pb/Cd-free, solution processed luminescent Ag2ZnSnS4 (AZTS) colloidal QDs. We present a selective and controlled amine and thiol-free synthesis of air stable luminescent AZTS QDs by the hot injection technique. By controlling the reaction conditions we obtain controlled size variation and demonstrate the quantum confinement effect that is in good agreement with the theoretically calculated values. The band gap of the AZTS QDs is size-tunable in the near-infrared from 740 to 850 nm. Finally, we passivate the surface with Zn-oleate, which yields higher quantum yield (QY), longer lifetime, and better colloidal stability.Peer ReviewedPostprint (published version

Tuning and Locking the Localized Surface Plasmon Resonances of CuS (Covellite) Nanocrystals by an Amorphous CuPdxS Shell

[Image: see text] We demonstrate the stabilization of the localized surface plasmon resonance (LSPR) in a semiconductor-based core–shell heterostructure made of a plasmonic CuS core embedded in an amorphous-like alloyed CuPd(x)S shell. This heterostructure is prepared by reacting the as-synthesized CuS nanocrystals (NCs) with Pd(2+) cations at room temperature in the presence of an electron donor (ascorbic acid). The reaction starts from the surface of the CuS NCs and proceeds toward the center, causing reorganization of the initial lattice and amorphization of the covellite structure. According to density functional calculations, Pd atoms are preferentially accommodated between the bilayer formed by the S–S covalent bonds, which are therefore broken, and this can be understood as the first step leading to amorphization of the particles upon insertion of the Pd(2+) ions. The position and intensity in near-infrared LSPRs can be tuned by altering the thickness of the shell and are in agreement with the theoretical optical simulation based on the Mie–Gans theory and Drude model. Compared to the starting CuS NCs, the amorphous CuPd(x)S shell in the core–shell nanoparticles makes their plasmonic response less sensitive to a harsh oxidation environment (generated, for example, by the presence of I(2))

A new application of solvent extraction to separate copper from extreme acid mine drainage producing solutions for electrochemical and biological recovery processes

Over the last decade, AMD waters have gained more attention as a potential source of metals due to the emerging need to recover or recycle metals from secondary resources. Metals recovery supports sustainability and the development of a circular economy with benefits for resource conservation and the environment. In this study, five extractants (Acorga M5640, LIX 54, LIX 622, LIX 622 N, and LIX 864) diluted (15% (v/v)) in Shell GTL with 2.5% (v/v) octanol were compared and evaluated for Cu recovery from an extreme AMD sample (5.3 +/- 0.3 g/L Cu) collected at the inactive Sao Domingos Mine in the Iberian Pyrite Belt of Portugal. Of the five extractants, Acorga M5640 showed the best selective efficiency. Further tests showed that 30% (v/v) of this extractant was able to selectively extract approximate to 96.0% of the Cu from the AMD in one extraction step and all of the remaining Cu (to below detection) in three steps. Among the different stripping agents tested, 2 M sulfuric acid was the most efficient, with approximate to 99% of the Cu stripped, and the recyclability of the organic phase was confirmed in five successive cycles of extraction and stripping. Furthermore, contact time tests revealed that the extraction kinetics allows the transfer of approximate to 97% of the Cu in 15 min, and aqueous to organic phase ratios tests demonstrated a maximum loading capacity of approximate to 16 g/L Cu in the organic phase. Raising the concentration of Cu in the stripping solution (2 M sulfuric acid) to approximate to 46 g/L through successive striping steps showed the potential to recover elemental Cu using traditional electrowinning. Finally, a biological approach for Cu recovery from the stripping solution was evaluated by adding the supernatant of a sulfate-reducing bacteria culture to make different molar ratios of biogenic sulfide to copper; ratios over 1.75 resulted in precipitation of more than 95% of the Cu as covellite nanoparticles.info:eu-repo/semantics/publishedVersio