In this study, we prepare the zinc oxide nanotip with aqueous solution on Al doped ZnO/glass substrate. In excess of 6 hours growth, the film-liked layer is obtained in the bottom of ZnO nanotip. In order to study the photoresponse of maximum ZnO nanotip length without film-like layer, we choose 6 hours as the growth time of ZnO nanotip, which the height is almost the same of about 4 £gm. For the fabrication of ZnO nanotip UV photodetector, In-Zn was use as anode and cathode electrodes in digitate type on the top of ZnO nanotip array. The photoresponse which use AZO buffer layer of 300 s is better than others due to the larger surface to volume ratio. We obtain that Ron/off is 10.9, rise time is 280 s, and decay time is 870 s. The thermal annealing at 300 ¢XC in N2, O2, and N2O for 1 hr can improve the photoresponse, because the Zn(OH)2 in the ZnO nanotip gets converted into ZnO. Among annealing ambiences, the annealed ZnO nanotip in N2O show higher performance due to high decomposition of O atoms, which fills in the oxygen vacancy. We obtained that Ron/off is 26.04, rise time is 50 s, and decay time is 70 s at 300 oC in N2O.

In recent years, even though the light output of GaN-related LED continues to increase, the brightness is still low compared to conventional lighting systems and it is necessary to further improve the light extraction of LEDs. In this study, we utilize the ZnO nanotip with aqueous solution and flip-chip technique to increase the light extraction of GaN LEDs. Electroluminescence (EL) and angular optical distribution are used to measure the light output intensity of LED. In the results, ZnO nanotip after thermal annealing with N2O ambiance decrease the ZnO defects. Flip-chip LED has higher light intensity ( 1.25 times) than conventional one in vertical emitting area ( at 0 angles). The enhancement of light output is duo to the reduction of light absorption from the metal contact and Fresnel¡¦s transmission losses. Finally, we fabricate a high brightness LED with above light enhancement design. EL intensity of LED is increased about 1.38 times than conventional one. Therefore, we can manufacture a LEDs array with above designs to obtain high light output for future solid-state illumination.

The length of ZnO nanotip can be controlled by the deposition time, and the crystal of ZnO nanotip can be enhanced by a thermal annealing at 300oC in this study.The thickness of TiO2 on ITO/glass also can be controlled by the deposition time in this investigate. There are three major parts in this study : 1. (1). The control of thickness of TiO2 film and length of ZnO nanotip and (2). the difference of their photocatalytic activities are two major parts. 2. The relationship between the surface area and the photocatalytic activities of TiO2 powder (P25) and film. 3. The improvement of photocatalytic activity was utilized by the hetrojunction of ZnO nanotip/TiO2 and TiO2/ZnO nanotip, and the P25 is used as a reference for all measurements.

In this study, we used two types of materials as working electrode of DSSC, commercial TiO2 (P25) nanoparticle and ZnO nanotip. First part, we sintered TiO2 electrode in nitrogen and treat TiO2 electrode by UV light irradiation, in order to increase dye adsorption onto TiO2. Second part, we used three different buffer layers to grow ASD-ZnO nanotip as working electrode, sputtered-ZnO, sputtered-AZO and spin-coating TiO2. The hetrojuction is formed at the interface of ZnO nanotip/TiO2 buffer layers due to the different materials between ZnO and TiO2, which is beneficial for electron-hole separation. The morphology was measured by field emission scanning electron microscope (FE-SEM, Philip XL-40FEG). The sheet resistivity was measured by four-point probe. The crystallinity was examined by X-Ray diffraction (XRD, Simens D5000). Structural and spectral properties are characterized by ultraviolet-visible spectroscopy (UV-Vis) spectroscopy. The fourier transform infrared spectroscopy (FT-IR spectroscopy, BRUKER 66v/s) deals with the infrared region of absorption spectroscopy. And the Angilent B1500A is used for current-voltage (I-V) characterization of solar cells. In our results, we enhance the performance of TiO2 electrode DSSC, the open circuit voltage can reach to 0.56 V, the short circuit current density can reach to 16.65 mA/cm2, the conversion efficiency can reach to 4.6 % and the fill factor can reach to 49.2 %. On ZnO electrode, the open circuit voltage can reach to 0.57 V, the short circuit current density can reach to 4.43 mA/cm2, the conversion efficiency can reach to 1.21 % and the fill factor can reach to 47.9 %.

In this study, we prepare the zinc oxide nanotip with aqueous solution deposited on ZnO nucleation layer. The thermal annealing with N2 ambiance at 300 oC for 1 hr increase the UV emission and decrease the defects. We use ZnO nanotip as an anti-reflection layer because of surface roughness and optical interference. ZnO nanotip with rough surface decreases reflection, so we use ZnO nanotip as an anti-reflection layer, after grown ZnO nanotip on solar cell the efficiency of solar cell was enhancement. The coordination modes were measured by Fourier-transform infrared spectrometer (FTIR). The physical properties were characterized by X-ray diffraction (XRD). The optical properties were measured by Micro-photoluminescence (Micro-PL). The morphology was observed by field emission scanning electron microscope (FE-SEM). The performance of the cells was measured by a semiconductor device analyzer. In our results, we grow the high performance of ZnO nanotip on solar cell to increase the efficiency. The short-circuit current increased from 42 to 51 mA, and the efficiency increased from 15.7 to 18.8 %.

Cette thèse étudie l'interaction de nanopointes avec des impulsions laser ultracourtes pour observer l'émission photo-assistée d'électrons. Plusieurs mécanismes physiques entrent en jeu, chacun ayant une signature unique identifiable dans le spectre d'énergie des électrons. Nous avons développé une nouvelle expérience pour observer et identifier ces mécanismes d'émission. Ceci inclut le développement complet d'un système laser flexible (notamment un amplificateur optique non colinéaire (NOPA) haute cadence), une chambre ultra-vide avec détecteur d'électrons (mesure de spectre d'électrons et carte 2D de l'émission) et un dispositif de nanopositionnement de la pointe dans le foyer du laser, et enfin la fabrication et caractérisation de pointes diverses (en collaboration avec les laboratoires CEMES (Toulouse) et GPM (Rouen)). Nous avons observé l'émission photo-induite d'électrons à partir de nanopointes de différents matériaux (tungstène, argent, et une nouvelle pointe formée autour d'un nanotube de carbone unique). Nous avons confirmé l'observation de pics ATP (signature de la photoémission au dessus du seuil) sur une pointe de tungstène. Nous avons détecté la première émission induite par laser à partir de nanocône de carbone unique. Enfin, nous avons observé un plateau dans le spectre d'énergie des électrons d'une pointe d'argent, signature de la recollision et rediffusion des électrons sur la pointe. Pour identifier et caractériser ces mécanismes, des études variées ont été faites en fonction de la tension appliquée sur la pointe, du taux de répétition du laser, de sa polarisation, de sa puissance et de sa longueur d'onde. En étudiant la forme du spectre des photoélectrons, nous avons pu extraire des informations sur l'interaction: le facteur d'amplification du champ laser proche de la nanopointe et la probabilité d'absorption d'un photon au dessus du seuil. / This thesis concerns the interaction of a sharp nanotip with an ultrashort laser pulse for the observation of emission of photoelectrons. An electron can be emitted from a sharp nanotip system by many different mechanisms. Each mechanism gives a unique signature that can be identified by the photoelectron energy spectrum. We developed a new experiment to observe and identify these emission mechanisms. This consists of a flexible laser system (including the development of a high repetition rate, variable repetition rate noncollinear optical parametric amplifier (NOPA)), ultra high vacuum chamber, electron detector (electron spectrometer with 2D resolution), nanopositioning of a sharp nanotip in the focus of the laser, and fabrication of these nanotip samples in a variety of materials (in collaboration with CEMES (Toulouse) and GPM (Rouen)). We observed the emission of photoelectrons from various nanotips based on different materials: tungsten, silver, and a new type of carbon-based nanotip formed around a single carbon nanotube. We confirm the observation of above threshold photoemission (ATP) peaks from a tungsten nanotip. We detected the first laser induced electron emission from a carbon cone based on a single carbon nanotube. We observed a plateau in the electron spectra from a silver nanotip, the signature of electron recollision and rescattering in the tip. Various studies were performed in function of the voltage applied, repetition rate of the laser, laser polarization, energy and wavelength of the laser in order to understand these phenomena. From spectral features we were able to extract information about the system such as the enhancement factor of the laser electric field near the nanotip and the probability of above threshold photon absorption. Comparisons of the various spectra observed allowed us to spectrally identify the mechanisms for photoemission for tip based systems.

In this study, zinc oxide (ZnO) nanotip and nanorod were grown on glass substrate by aqueous solution deposition (ASD). Both characteristics of the two nanostructures were investigated. For fabrication of ZnO nanostructure UV photodetector, In-Zn inter-digitated metal electrode was evaporated on the top of the grown ZnO nanostructure to form the contact via. Compared with the common value (375 nm), both the peaks from the PL spectra of ZnO nanotip and nanorod are red-shifted (409 nm) due to the massive defects in nanotip and nanorod. In order to improve the photosensiblity, heterojunction of ZnO nanostructure/TiO2 film was prepared and were made into UV photodetector. Photoresponses of both nanotip and nanorod were improved after N2O annealing at 300oC. With the heterojunction of ZnO 1D nanostructure on TiO2 film, the photoresponses of both ZnO nanotip/TiO2 film can reach to 22.85, and the rise time and decay time are 40 and 82 seconds, respectively. On the other side, the photoresponses of both ZnO nanorod/TiO2 film can reach to 27.44, and the rise time and decay time are 22 and 133 seconds, respectively.

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