| Nanoparticles and nanoparticle arrays have potential applictions in many fields, such as optical nanodevices, electronic nanocircuits, and chemical sense, due to their unique physical properties. With their ultrahigh detection ability towards optical, electrical and magnetic field, a significant interest has been developed on metallic nanostructures based sensors for magnetic field, temperature, gases and biomolecules.The physical characteristics of densely packed metal nanoparticle arrays are determined by internanoparticle coupling mechanisms. The electrical optical, electrical and magnetic behaviors of metal nanoparticle arrays can be tuned by varying internanoparticle separations. This is physical basis for development of sensors based on nanoparticle arrays. Palladium is an important hydrogen storage material. The volume expansion, which occurs in Pd nanoclusters at hydrogenation, is exploited to reversibly narrow or even close the inherent nanogaps contained between Pd nanoparticle arrays. Changes in the gap size result in changes in the electron barrier, leading to a measurable change in the conductance of the Pd nanoparticle arrays. The first problem for developing this type sensors is how to realize controllable preparation of Pd nanoparticle arrays. It is also important to tune the electronic transport properties and optimize hydrogen sensing behavior of Pd nanoparticle arrays varying the parameters of nanoparticle arrays.In this thesis, the electronic properties and hydrogen sensing application of Pd nanoparticle arrays are discussed. The evolution characteristic of quantum conductance and variation law of conductance induced by hydrogen absorption is investigated. The beam of Pd clusters was deposited onto gold interdigital electrodes. In order to tune the electronic transport properties and optimize hydrogen sensing behavior of Pd nanoparticle arrays, the coverage of nanoparticles was precisely controlled by monitoring the conductance of nanoparticle arrays.To fabricate the Pd nanoparticle film, Pd clusters was generated with a magnetron plasma gas aggregation cluster source and was deposited onto substrate. Microanalysis shows that the Pd nanoparticles have a mean diameter of about9nm, well-crystallized, the grain size was homogeneous, and the interface is distinguishing. Besides, the Pd nanoparticle arrays presents fractal structure. The morphology and structure of Pd nanoparticle arrays are related to nanoparticle coverage. An architecture of nanoparticle chains is formed in low coverage Pd nanoparticle arrays. High coverage Pd nanoparticle arrays are composed of close-packed particles.Inorder to probe the transport properties of the nanoparticle arrays, we measured the dc Ⅰ-Ⅴ curve at temperatures range from10-300k. Below a certain temperature, the I-V behavior of Pd ananoparticle arrays is excellent agreement with the scaling law I∝(V-Vjf proposed by MW model. There is a threshold voltage(VT) corresponding to coulomb blockade in I-V curve. The threshold voltage, VT, decreases linearly with increasing temperature and vanished at certain temperature, resulting in no Coulomb blockade.The results show that coverage of nanoparticles have an important influence on electronic properties of Pd nanoparticle arrays. Low coverage nanoparticle arrays have a higher threshold voltage than high coverage nanoparticle arrays have and exhibits Coulomb blockade at room temperature. The corresponding switching energy, eVT, at absolute zero temperature is5.4eV, which is50times enhanced compared to an isolated10nm Au particle. The exponent ζ, increases with the increase of nanoparticle coverage. This indicates that there is a dimensional crossover form ID to2D or even to3D in Pd nanoparticle arrays as the temperature rises.Temperature-dependent DC transport measurements are performed to elucidate the electron transport mechanics in the Pd nanoparticle arrays. The Pd nanoparticle arrays display a strong temperature dependence of the resistance with a negative temperature coefficient, which indicated that the conductivity is determined by tunneling between nanoparticles. On lowering the temperature, the temperature-dependent conductance of Pd nanoparticle array shows a crossover from an Arrhenius-type thermal-activated tunneling (ln(g-)∝-T-1behavior) to an Variable range Hopping (VRH) type hopping mechanism (ln(g)∝-T-1/2behavior).The conductance of Pd nanoparticle arrays increase with hydrogen adsorption, as well as recovery after hydrogen deloading. The response is induced by expansion of Pd nanoparticles:The volume expansion narrow or even close the inherent nanogaps. Changes in the gap size result in decrease of the electron barrier, leading to increase of tunneling current.Three typical response regions with different conductance-hydrogen pressure correlations were observed, which is associated with3phase regions of PdHx:α phase region, α to β phase transition region and β phase region. The sensor shows the highest resolution in α to β phase transition region, due to the expansion of the Pd nanoparticles induced by the α to β phase transition of PdHx, which is much larger than that induced by hydrogen absorption in the pure phase α-PdHx or β-PdHx. The sensor showed ppm detection limitation, sub-second response and can be operated in atmospheric environment at room temperature.The response characteristics of the devices are found to depend strongly on the nanoparticle coverage. In the low H2pressure region, properly increasing coverage gives higher sensitivity. In the high H2pressure region, lowering sensitivity is induced by too high. The highest sensitivity was obtained at48.6%coverage.Pd nanoparticle arrays can give a fast response to hydrogen gas. The response time to12kPa and250Pa hydrogen gas are0.8s and5s respectively. As the coverage of this films increase, there is an increase in the response time. Besides, the response is slowed down by several seconds at the hydrogen pressure1000-3000Pa region associated with the α-β phase transition of Pd.We investigated the influence of temperature and humidity on the conductance of Pd nanoparticle arrays. Results showed that the detecting low concentration hydrogen was easy to bring errors caused by change of temperature. So, if the Pd nanoparticle array based sensor is used for low concentration hydrogen detection, a careful temperature compensation is critically required. On the other hand, the influence of humidity can be eliminated by coating a PMMA on the surface of Pd nanoparticle array without substantial changes in sensing mechanism. |
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