An in-situ thermoelectric measurement apparatus inside a thermal-evaporator

At the ultra-thin limit below 20 nm, a film's electrical conductivity, thermal conductivity, or thermoelectricity depends heavily on its thickness. In most studies, each sample is fabricated one at a time, potentially leading to considerable uncertainty in later characterizations. We design and build an in-situ apparatus to measure thermoelectricity during their deposition inside a thermal evaporator. A temperature difference of up to 2 K is generated by a current passing through an on-chip resistor patterned using photolithography. The Seebeck voltage is measured on a Hall bar structure of a film deposited through a shadow mask. The measurement system is calibrated carefully before loading into the thermal evaporator. This in-situ thermoelectricity measurement system has been thoroughly tested on various materials, including Bi, Te, and Bi$_2$Te$_3$, at high temperatures up to 500 K

Growth of single crystals of methylammonium lead mixedhalide perovskites

We report the growth and characterization of different bulk single crystals of organo lead mixed halide perovskites CH3NH3PbI3−xBrx by two different crystal growth approaches: (i)anti-solvent diffusion, and (ii) inverse temperature crystallization. In order to control the size and the shape of crystals, we have investigated different experimental growth parameters such as temperature and precursor concentration. The morphology of obtained crystals was observed by optical microscope, whereas their intrinsic crystalline properties were characterized by single crystal as well as powder X-ray diffraction. The results illustrated that the growth and crystalline structure of mixed halide perovskites CH3NH3PbI3−xBrx could be easily tuned

Fabrication of Organolead Iodide Perovskite Solar Cells with Niobium-doped Titanium Dioxide as Compact Layer

Organometal halide perovskite materials have shown high potential as light absorbers for photovoltaic applications. In this work, perovskite planar solar cells were fabricated on corning substrates with the structure as follows: the first layer made of tantalum-doped tin oxide as transparent contact material, followed by sputtering niobium-doped titanium oxide as the compact electron transport layer; covered with perovskite CH3NH3PbI3 as the light harvester by combination between spin-coating and dipping methods; CuSCN was evaporated as the hole transport layer; the final thin Al/Ag electrodes were deposited. This configuration is shortly described as Al/TTO/NTO/CH3NH3PbI3/CuSCN/Ag. Such heterojunctions are expected to be suitable for the development of efficient hybrid solar cells. The fabricated cells were measured under the air mass 1.5 illumination condition, showed the rectification effect and exhibited a power conversion efficiency of 0.007%, with a open circuit voltage of 53.2 mV, a short circuit current of 0.36 mA/cm2, and a form factor of 37%. The power conversion efficiency will be further optimized in near future

Characterization of ZnO:Al deposited by co-sputtering for transparent conductive electrodes

Aluminum doped zinc oxide was prepared by magnetron sputtering methods at room temperature using a ZnO ceramic target doped 2%wt by Al2O3. The optical transmittance of the films is higher than 80% in the visible range. A direct bandgap type was reached by controlling deposition conditions; the bandgap value was in the range between 3.2 eV and 4.2 eV. Good electrical and optical properties were obtained for the films deposited by an appropriate co-sputtering of ZnO and Al targets. These films with a resistivity, about 1.3´10-2W.cm, and a transmittance, higher than 80%, can be applicable for transparent conducting electrodes

Synthèse et contrôle de la taille de nanocristaux de silicium par plasma froid. Application dans les domaines de l'optoélectronique et de la nanoélectronique.

In this thesis we have shown that one can synthesize silicon nanocrystals by using square- wave-modulated plasmas in silane-hydrogen gas mixtures. In our experimental conditions, by varying the growth time, we could control the size of silicon nanocrystals (from 4 nm to 12 nm). By measuring the size of the nanocrystals by transmission electron microscopy, we could calculate their radial growth rate. This later is proportional to the silane partial pressure in the gas mixture. By studying two types of plasmas, we have demonstrated the important role of atomic hydrogen for the obtaining of crystallized of nanoparticles. The precise control of size of the silicon nanocrystals has opened two fields of applications: (i) the fabrication of light emitting devices and (ii) the realisation of single electron transistors. For the first type of applications, a preliminary study has shown a blue shift of the photoluminescence peak when decreasing the size of silicon nanocrystals. It has been discussed on the basis of a quantum confinement effect combined with the passivation of the surface of the nanocrystals by a SiOx shell. We elaborated also light emission PIN diodes based on silicon nanocrystals. After the optimization of the PIN structure and of the deposition conditions of the intrinsic layer, we obtained an electroluminescence diode emitting in the range of infrared-visible at room temperature. For the second type of applications, we have studied the injection of charges in the silicon nanocrystals by AFM/KFM. Qualitative observations of injected charges were realized. Quantitative estimation of this charge as well as the effects of doping on the charge of the nanocristals deserves further studies.Dans cette thèse nous avons montré que l'on peut on peut synthétiser des nanocristaux de silicium en utilisant des plasmas pulsés de silane dilué dans l'hydrogène. Dans nos conditions de dépôt, en changeant le temps de croissance entre 100 msec et 1 seconde, nous avons pu contrôler la taille des nanocristaux (de 4 nm à 12 nm). A partir de la mesure de la taille des nanocristaux sur les images MET, nous avons pu calculer la vitesse de croissance radiale. Cette vitesse est proportionnelle à la pression partielle de silane dans le mélange gazeux. Nous avons également montré le rôle important de l'hydrogène atomique pour le processus de cristallisation des nanoparticules dans le plasma. La maîtrise de la synthèse des nanocristaux de silicium ouvre la voie à deux champs d'applications : (i) la fabrication de diodes électroluminescences et (ii) la réalisation de transistors à un électron. Pour la première application, une étude préalable de photoluminescence a montré un déplacement vers le bleu du pic de photoluminescence lorsque la taille des nanocristaux diminue. Cela est interprété à la fois comme un effet de confinement quantique et de passivation de la surface des nanocristaux par une coquille de SiOx. Nous avons également élaboré des diodes électroluminescence PIN basées sur les nanocristaux de silicium. Après une optimisation de la structure PIN et des conditions de dépôt de la couche intrinsèque, nous avons obtenu une électroluminescence dans la gamme infrarouge-visible à température ambiante. En vue de l'application aux transistors, nous avons fait des expériences préalables d'injection de charge dans les nanocristaux par AFM/KFM. L'observation qualitative des charges injectées a été réalisée. L'estimation quantitative de ces charges ainsi que l'étude de charges résiduelles dans des nanocristaux dopés est un domaine qui mérite d'être exploré dans l'avenir

Synthèse et contrôle de la taille nanocristaux de silicium par plasma froid. Application dans les domaines de l'optoélectronique et de la nanoélectronique

PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Synthesis of organo tin halide perovskites via simple aqueous acidic solution-based method

Organometal halide perovskites have been studied extensively during the last ten years for their interesting applications in solar cells and optoelectronics. One drawback of these materials is the presence of lead inside the compound, thus limiting their practical applications. Replacing lead with tin has been one of the implemented approaches for lead-free perovskites. In this paper, we report on the synthesis of organo tin mixed halide perovskites CH3NH3SnBrxCl3-x at room temperature in an aqueous acidic mixture between HCl and H3PO2 without the need of protecting perovskites against moisture. X-ray diffraction patterns show that the tin mixed halide perovskites adopt the trigonal phase. A detailed analysis of Raman scattering measurements has identified several low frequency Sn-Cl and Sn-Br modes of these perovskites. These results show that the high-quality CH3NH3SnBrxCl3-x crystals have been successfully synthesized by this aqueous solution-based method, demonstrating a low-cost approach to replace lead in organo metal halide perovskites for photovoltaic and optoelectronic applications. Keywords: Lead free, Sn-based halide perovskite, Raman, Aqueous acid solution, Low-cost precurso

Stimulated absorption of light in bosonic cascades of excitons

In bosonic cascades of excitons or exciton-polaritons the absorption of electromagnetic radiation resonant to the energy spacing between neighboring quantization levels may be stimulated by the initial state occupation number. This opens way to realization of ultrasensitive detectors of infrared or terahertz radiation. The stimulated absorption of light by bosonic condensates has also a high potentiality for photovoltaic applications

Charge transfers from doped silicon nanocrystals probed by non-contact atomic force microscopy

International audienc

Fabrication of superhydrophobic surfaces for applications in total internal reflection effects

International audienceSuperhydrophobic surfaces have attracted significant attention in the applied science community. This paper presents three different methods for fabricating superhydrophobic surfaces, which can be applied in liquid light guides with the total internal reflection effect playing a central role. The selective bi-polymer etching only produces a hydrophobic porous poly(methyl methacrylate) surface but is simple and versatile for use on an arbitrary surface. In metal-assisted chemical etching, wet etching of a silver layer on a silicon sample creates porous silicon with superhydrophobicity, characterized by a water contact angle of 160 and DEG;. The metal-assisted chemical etching method modified with the presence of polystyrene nanoparticles further improved the water contact angle to 164 and DEG; by creating a nanopillar silicon structure. The metal-assisted chemical etching methods are more complicated but can produce superhydrophobic surfaces with very high water contact angles. These results show that superhydrophobic surfaces fabricated by methods in this study can be used for total internal reflection effect at the interface between water with huge potential applications in liquid light guides