Photoluminescence Enhancement from Semiconductor Quantum Dot/Polymer Composite Thin Films Using Ag Films

Si thin films are attracted as materials for ultra-large-scale solar cell systems at relatively low cost. Electrodeposition is expected as one fabrication method of Si thin films due to its advantages such as relatively simplicity process, precision control of nanostructure and continuous deposition in large area. Si thin films have been electrodeposited in non-aqueous solvents owing to their large electrochemical windows which allows for the study of Si electrodeposition [1-3]. Among various non-aqueous solvents, organic solvents and ionic liquids, which can be used under low temperature, have been used as electrolytes for the electrodeposition of Si thin films in our laboratory. We have previously succeeded to electrodeposit Si thin films in organic solvents and ionic liquids [4-6]. However, there is a problem for applications to solar cells that some impurities (mainly carbon and oxygen) are incorporated in thin films. We have reported the carbon content can be reduced by annealing treatment [7]. On the other hand, the decrease of oxygen content is still required. Thus, we evaluate the composition of Si thin films electrodeposited in an organic solvent and an ionic liquid without oxygen atoms in order to analysis the effect of bath conditions on the composition of thin films (especially, where the oxygen incorporated in Si thin films comes from). Si thin films were electrodeposited with 3 electrode cell (W.E. : Au, R.E. : Ag/Ag+, C.E. : Pt) in acetonitrile, 0.3 M tetrabutylammonium chloride and 0.5 M SiCl4 was used as an organic solvent, and 1-butyl-3-methylimidazolium hexafluorophosphate and 0.5 M SiCl4 as an ionic liquid. The composition of Si thin films were evaluated by X-ray photoelectron spectroscopy. As a result, the oxygen content in Si thin films were decreased by using the solvents without oxygen atoms in both organic solvent and ionic liquid cases. This results suggest that the reason the oxygen inclusion is derived from the incorporation of solvents themselves in films during electrodeposition, and propose us the way to obtain films with low impurities. In addition, the rotating disk electrode was used in the organic solvent case in order to promote the convection. The usage of this rotating disk electrode showed the decrease of impurities in Si thin films. Therefore, it is indicated that the stable supply of SiCl4 to the electrode surface is important factor to obtain films with low impurities. This study reveals that bath condition significantly affects to the composition of Si thin films, and could help us to fabricate films for applications to solar cells. This study was financially supported in part by the Japan Science and Technology Agency (JST) CREST program, and Y. T. acknowledges the Leading Graduate Program in Science and Engineering, Waseda University, from MEXT, Japan. [1] S. Zein El Abedin, N. Borrissenko, F. Endres, Electrochem. Comm., 6 (2004) 510. [2] T. Munisamy, A. J. Bard, Electrochim. Acta, 55 (2010) 3797. [3] M. Bechelany, J. Elias, P. Brodard, J. Michler, L. Philippe, Thin Solid Films 520 (2012) 1895. [4] Y. Nishimura and Y. Fukunaka, Electrochim. Acta, 53 (2007) 111. [5] T. Homma, J. Komadina, Y. Nakano, T. Ouchi, T. Akiyoshi, Y. Ishibashi, Y. Nishimura, T. Nishida, and Y. Fukunaka, Electrochem. Soc. Trans., 41 (2012) 9. [6] J. Komadina, T. Akiyoshi, Y. Ishibashi, Y. Fukunaka, T. Homma, Electrochim. Acta, 100 (2013) 236. [7] Y. Tsuyuki, A. Pham, J. Komadina, Y. Fukunaka, T. Homma, Electrochim. Acta, 183 (2015) 49.

Plasma polymerized (PP) 2,6-diethylaniline (DEA) and N,N,3, 5 tetramethylaniline (TMA) composite thin films were deposited by dynamic plasma (AC, 50 Hz) polymerization technique using a capacitively coupled reactor of diverse monomer composition. The composite film thickness increased proportionally with the percentage of TMA in the composition. X-ray photoelectron spectroscopy confirmed the uniformity of the film composition, consisting primarily of carbon, nitrogen, and oxygen, with different possible groups such as C–C, C–H, C–N, and C–O. Field emission scanning electron microscopy images revealed smooth and homogeneous surface morphologies in the composite films, which contrast with the thin homopolymer films. The current density (J) vs voltage (V) behaviors of the homopolymer and composite polymer thin films sandwiched between aluminum electrodes demonstrated that the J values could be tailored by adjusting the individual monomer concentration in the PP(DEA:TMA) composite films, as well as by increasing the measurement temperature (298–373 K). The conduction behavior of these composite films exhibited ohmic characteristics in the lower voltage region (below 10 V), while space charge-limited conduction dominated in the higher voltage region (above 10 V) across the entire temperature region. The activation energy was ∼0.019 eV in the ohmic region and 0.260 eV in the non-ohmic region. Changing the composition of two monomers can tune the properties of the as-deposited films, making the film suitable for various electronic and optoelectronic devices.

Semiconductor quantum dots (QDs) with circularly polarized luminescence (CPL) characteristics hold significant promise for a range of applications, including information security, three-dimensional (3D) display, quantum computing, and spintronics. Recent approaches combining QDs with chiral liquid crystal assemblies have demonstrated amplified CPL performance (specifically, luminescence dissymmetry factor, <i>g</i>_lum &gt; 10^–1). However, the inherent fluidity and alignment sensitivity of chiral liquid crystals, along with QD aggregation and phase separation, continue to hinder the uniformity and long-term stability of these systems. In this work, we developed an <i>in-situ</i> helical co-assembly polymerization strategy that covalently incorporated InP-based QDs into chiral liquid crystal polymer templates, forming QD-based polymeric superhelical structures. We synthesized high-quality InP/ZnSeS/ZnS QDs and functionalized their surfaces with polymerizable groups to enable reactivity. By precisely tuning the photonic bandgap of the chiral liquid crystal polymers, we achieved chiral parented templates with high chiroptical activity overlapping full-visible-spectrum. Through covalent crosslinking with the QDs, a polymer network was formed, resulting in a maximum <i>g</i>_lum of 1.0. This polymerization-with-assembly approach offers exceptionally flexible and precise control over both the composition and architecture of superhelical materials, paving the way for high-quality CPL materials with broad applications in advanced technologies.

Fluorescence quenching caused by aggregation of water-soluble CdSe quantum dots

This work is concerned with the synthesis of two types of composites thin films (Sb2O3:WO3 and (Sb2O3:In2O3) with different concentrations (0.0,0.05,0.1, and 0.15). The prepared thin films are characterized with the use of the X-ray diffraction atomic force microscope AFM and UV-Vis–infrared spectrophotometer. The structural examination shows that both composite's thin films were polycrystalline with nano size with cubic phase as majority and orthorhombic phase as minority phase. The crystal size decreases from 34.6 to 24.7 and 21.7 nm for (Sb2O3:WO3) and (Sb2O3:In2O3) thin films, respectively. The average roughness shows non-regular growth by increasing the concentration of both oxides. The optical energy band gap shows a red shift for both types of nanostructure thin films, which populate these composited thin films for solar cell applications.

A review devoted to the theory of excitonic quasimolecules (Biexcitons) (formed of spatially separated electrons and holes) in a nanosystems that consists of semiconductor and dielectric quantum dots synthesized in a dielectric matrix.It is shown that exciton quasimolecules formation is of the threshold character and possible in nanosystems, in with the spacing between the quantum dots surfaces is larger than a certain critical spacing.It was found that the binding energy of singlet ground state of exciton quasimolecules, consisting of two semiconductor quantum dots is a significant large values, larger than the binding energy of the biexciton in a semiconductor single crystal almost two orders of magnitude.

Here, we study the self-aligned asymmetric electrically conductive composite thin film prepared via casting of graphene oxide (GO)/poly (vinylidene-hexafluoropropylene) (PVDF-HFP) dispersion, followed by low temperature hydriodic acid reduction. The results showed that composite thin film revealed the high orientation of graphene sheets along the direction of film surface. However, graphene sheets are asymmetrically distributed along the film thickness direction in the composite film. Both sides of as prepared composite film showed different surface characteristics. The asymmetric surface properties of composite film induced distinction of surface resistivity response; top surface resistivity (21 Ohm) is ∼ 4 times higher than bottom surface resistivity (5 Ohm). This asymmetric highly electrically conducting composite film revealed efficient electromagnetic interference (EMI) shielding effectiveness of ∼ 30 dB. This study could be crucial for achieving aligned asymmetric composite thin film for high-performance EMI shielding radiation.

Recently, mass production and extensive use of novel engineered nanomaterials (e.g., carbon nanotubes, fullerene, nano-TiO2, nano-Au and quantum dots) raise increasing concerns about their potential harmful effects on our environment and human health. Therefore, for better understanding of their environmental and biological fate upon accidental release during their manufacturing and transport processes, increasing number of studies on the toxicities of engineered nanomaterials were conducted during last few years. However, regarding the toxicity of engineered nanomaterials, contradictory results were frequently found in the current literature, probably due to the widely varying physicochemical properties of engineered nanomaterials and inconsistency of the dosage/exposure conditions. Among various engineered nanoparticles, semiconductor quantum dots (QDs) have received significant attention as a new type of fluorophore for the biological and medical imaging. However, they also induced increasing concern as a potential pollutant, due to its unknown toxicity as a nanometer-scale material as well as the toxic components (i.e., Cd, Zn, Se and etc). But, their colloidal stability, photochemical property, dissolution behavior and overall cytotoxic impact of these QD colloids have not been systematically studied and completely understood yet. In this study, using various analytical tools, we have prepared and characterized water-soluble monodisperse QD nanocolloids with well-defined core and hydrodynamic size, functional groups at the interface, impurities, nanoparticle concentration and impurities in aqueous solution. Then, toxicological impacts of QD nanocolloids collected at different stage of preparation (i.e., different degree of impurity) were tested on gram negative bacterial cells (i.e., Escherichia coli). Preparation, surface modification and characterization of QD nanoparticles. From XRD analysis of QD nanoparticles, we confirmed that the QDs synthesized using SiPOP mothod predominantly have the wurtzite CdSe crystal structure (see supporting information, Figure S1). Additionally, absences of CdO or ZnO peaks in the XRD results indicated that negligible degree of oxidations occurred during the preparation of this QD nanoparticle. Furthermore, application of schrrer equation to the width of CdSe (110) peak resulted in the estimated value of CdSe core size, which is 3.25 nm (see supporting information, Figure S2), while estimation of CdSe core size from the position (559 nm) of the first excitonic absorption peak resulted in very similar value (3.24 nm). To make this QD soluble in aqueous solution, ligand exchange reaction of TOPO capped QD (i.e., QD) was performed using MAA (mercaptoacetic acid) and aqueous colloid of carboxylic acid group terminated QD was prepared. Then, several cycles of wash-out procedure were conducted to remove residual MAA from aqueous solution. To assure the monodispersity of this QDs in aqueous solution, hydrodynamic sizes of QDs were also measured by dynamic light scattering methods (QD = 4.56 nm, see Fig. 1) and confirmed that the individual QD particles are well dispersed in solution with least degree of aggregation. Concentrations of QDs in aqueous solutions were determined from the intensities of the first excitonic absorption peak and extinction coefficients based on the method reported by Yu et al. and presented in the units of moles of QD per liter (i.e., [QD]). Fourier Transform Infrared (FT-IR) spectroscopy was used to monitor changes in surface modifying groups of QDs as well as impurities included during ligand exchange process. During surface modification process, the replacement of TOPO and changes in adsorbed MAA molecules were monitored by FT-IR and corresponding spectra were presented in Fig. S3 (In supporting information). The IR spectrum shown in Fig. S3(e) shows spectrum collected from QD solutions after several cycles of wash-out process and showed quite distinct spectral features with that of Fig. S3(d). First of all, absence of thiol peaks around 2570 cm−1 indicate that there is no free MAA with thiol groups and most of the MAA are already lost their hydrogen and

Polaron dephasing processes are investigated in InAs/GaAs dots using far-infrared transient four wave mixing (FWM) spectroscopy. We observe an oscillatory behaviour in the FWM signal shortly (< 5 ps) after resonant excitation of the lowest energy conduction band transition due to coherent acoustic phonon generation. The subsequent single exponential decay yields long intraband dephasing times of 90 ps. We find excellent agreement between our measured and calculated FWM dynamics, and show that both real and virtual acoustic phonon processes are necessary to explain the temperature dependence of the polarization decay. PACS numbers: 78.67.Hc, 78.47.+p, 42.50.Md, 71.38.-k The strong spatial confinement of carriers in semiconductor quantum dots (QDs) leads to striking differences in the carrier-phonon interaction compared with systems of higher dimensionality. In particular, the discrete energy level s tructure in QDs results in long exciton and electron dephasing times [1, 2, 3, 4], making these semiconductor nanostructures highly attractive for implementation in quantum information processing applications. The study of dephasing mechanisms in QDs is commonly carried out using transient four wave mixing (FWM) spectroscopy. Using resonant interband excitation, FWM measurements have revealed the absorption lineshape of single QDs to consist of a narrow zero phonon line (ZPL) and an acoustic phonon-related broadband centred at the same energy. The only intraband FWM study [5] involved resonant excitation of high energy transitions in th e valence band of p-doped QDs yielding dephasing times ∼ 15 ps. However it was not possible to determine the dephasing mechanisms in this case. Intraband studies of the well-resolved lowest energy conduction band electron transitions in InAs/GaAs QDs have provided deep insight into the electron-phonon interaction and carrier relaxation processes in n-doped samples. Clear evidence of strong coupling between electrons and phonons, resulting in polaron formation, has been demonstrated using magneto-transmission measurements [6]. Ultrafast studies [7, 8] of polaron decay have shown that the previously assumed ’phonon bottleneck’ picture is not valid. Compared with semiconductor quantum wells, the intraband population relaxation time in QDs is long (∼ 50 ps) suggesting relatively long dephasing times. However there have been no reports of direct dephasing measurements to date. In the present letter we present the first investigations of i ntraband dephasing in n-doped QDs using degenerate FWM. Our calculations of the absorption lineshape in this case sh ow marked differences in comparison with the interband absorption [9]. The intraband lineshape consists of peaked acoustic phonon sidebands separated by ∼ 1.5 meV from the ZPL, which corresponds to phonons with wavelength close to the dot size, and is reminiscent of the lineshape associated wit h impurity-bound electron transitions [10]. Using pulse durations short enough to excite both the ZPL and acoustic phonon sidebands we find damped oscillations in the FWM signal, indicative of coherent acoustic phonon generation, followed by a single exponential decay. In contrast with the interband case, where the origin of the strong temperature dependence of the excitonic linewidth is still subject to debate, the simple 3 -level structure of the lowest energy conduction band states in InAs QDs permits an accurate simulation of the temperature dependence of the FWM signal. The excellent agreement found between experiment and theory, shows that virtual transitions between the p-states is the dominant dephasing mechanism at high temperature. At low temperature, we have measured an intersublevel dephasing time of T2 ∼ 90 ps. It is also interesting to compare our results with previous intraband dephasing measurements in higher dimensional (quantum well) systems [11]. Here phonon-mediated processes are not significant with the intraband dephasing instead determined by electronelectron interactions, yielding typical dephasing times ∼ 0.3 ps which are approximately 2 orders of magnitude faster than for the QD samples studied here. The relatively long intraband dephasing time in QDs is key to the efficient operation of new types of mid-infrared QD-based devices, such as intersublevel polaron lasers [12] and may be relevant for potential device applications such as qubits for quantum information processors [13]. The investigated samples were grown on (100) GaAs substrates by molecular beam epitaxy in the Stranski-Krastranow mode. They comprise 80 layers of InAs self-assembled QDs separated by 50 nm wide GaAs barriers, thus preventing both structural and electronic coupling between QD layers. The polaron transitions were studied between s-like ground (s) and p-like first excited ( p) states within the conduction band. To populate the s state, the samples were delta-doped with Si 2 nm below each QD layer. The doping density was controlled in such a way that the average doping did not exceed 1 electron per dot (see Ref. [14] for more details). Absorp

Metal oxide composite thin films made by magnetron sputtering for bactericidal application

Sol-gel and coprecipitation methods successfully prepared titanium dioxide (TiO2) powders with anatase structure. The TiO2 powders are then used to fabricate pure TiO2 thin-film or mixed with SnO2 powders for the TiO2/SnO2 composite thin film. Furthermore, the structural, morphological, as well as the optical properties of films were also investigated. The results showed that the synthesized thin-film of TiO2 powders by sol-gel method obtained better crystallinity and microstructure compared to the synthesized thin film by co-precipitation method. In the DSSC system, these features are needed to increase the electron mobility that responsibility for transport and recombination of photoexcited electrons. SEM images exhibited the smooth surface and uniform in particle size obtained by the addition of SnO2 powders in composite films. The composite thin film also indicated a higher transmittance value. Keywords: sol-gel,co-precipitation,anatase, composite.

Effect of substrate temperature on poly(methyl methacrylate) nanocomposite thin films deposited by matrix assisted pulsed laser evaporation

Formation of poly(methyl methacrylate)-ZnO nanoparticle quantum dot composites by dispersion polymerization in supercritical CO2

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pH-dependent aggregation and photoluminescence behavior of thiol-capped CdTe quantum dots in aqueous solutions