| Nanowires have been fabricated via an alternating electric field in recent dozens of years. Nanowires were deposited and self-assembled from solution through directly applying AC-fields. This method can produce thin, continuous and high-crystal nanowires. The nanowires are formed by connecting nanoparticles through metal bonding. Thus, the nanowires have high mechanical stability and the delicated morphology. The prepareing technique overcomes disadvantage of poor stability of particles self-assembled nanowires. The new nanomaterials can serve as conductive connection, sensor, swich and network on the chip.Au-Pt dentritic nanowires (DNWs) were successfully fabricated from the corresponding ions solution via deposition of an alternating current (AC) in this thesis. The morphology, composition and phase structure of Au-Pt DNWs were characterized by a scanning electron microscopy (SEM), energy-dispersion X-ray (EDX) spectrometer and X-ray diffraction (XRD). The effects of electrolyte on the morphology and composition of Au-Pt were discussed. The optimum composition of electrolyte has confirmed and the effect of AC signal parameters on morphology and composition of alloy nanowires has also been explored, and the different Pt composition of nanowires were assembled into a hydrogen sensors to detect their performance. The main results are gained as follows:(1) The additive in electrolyte had a direct effect in forming aligned alloy denrtitic nanowires. When 0.5 mol·dm-3 H3BO3 was added in electrolyte, the diameters of nanowires were about 100 nm. This is attributed to dual functions of H3BO3,adjusting pH value of the electrolyte to the range of 2—3 and stabilizing electrolyte during DNWs assembled process, and controling the metal deposition rate.(2) In the electrolyte composited of HAuCl4·4H2O、H2PtCl6·6H2O and H3BO3, under the same ratio of [AuCl4]- and [PtCl6]2-, the lower concentration of electrolyte was, the smaller diameter of nanowires and the thinner of nanowires became. The composition of nanowires is unchangeable via changing the total concentration of electrolyte. The results indicates that the optimal electrolyte composition was 0.2 mmol·dm-3 HAuCl4·4H2O,1 mmol·dm-3 H2PtCl6·6H2O and 0.5 mol·dm-3 H3BO3.(3) The alloy composition could be well-controlled via adjusting Pt and Au complex ion molar ratio in the electrolyte. The alloy possessed an extensive composition range from 8 to 95 at% Pt when the ion ratios of Pt/Au varied from 1 to 80. The XRD analysis indicated that AumPt100-mDNWs beared the characteristics of an alloy type compound involving Au and Pt. what is more, the pure Au and Pt dentritic nanowires had been fabricated.(4) The Au-Pt dentritic nanowires could not obtained by only applying single frequency, so we applied varied frequencies to assembling nanowires. The initial frequency 300 Hz lasting 2 s is for nucleation and then quickly adjust to 1MHz for growth and alignment of nanowires along the direction of AC field.(5) During the AC deposition, voltage provided energy to initiate nanowire growth. The applied AC voltage was proportional to FDEP (dielectrophoresis force), which played an important role in the self-assembly and alignment of DNWs. When the gap of Au electrods was between 10 to 40μm, the strength of electric field produced by applying voltage on Au electrods was in the rang of 2.828×105 5.656×105 V·m-1 to fabricate DNWs. The applied voltage depended on the gap of two electrodes. The wider gap of two electrodes was, the bigger applied voltage was, and vice versa. To bridge the gap of two microelectrodes, the deposition time was linearly proportional to the gap of electrode.(6) Pt or Pt alloy dendritic nanowire on Au microelectrodes could be successfully assembled into a hydrogen sensor. The sensors responded to the hydrogen gas of 0.15—4.00%(the volume ratio, V/V) at room temperature, the results shows that the Pt nanowires sensor showed high sensitivity, quick response and recovery. The highest value of sensitivity reached to 86.67% and the shortest response time was about 3 s. Response time decreaseed with the increase of hydrogen concentration.(7) The hydrogen action with Platinum or Platinum alloy dendritic nanowires could be explained by Tafel reaction and Volmer reaction, the mechanism was a process of surface chemical adsorption, dissociation of hydrogen molecules into atoms and followed by a charge transfer step. The probability of collisions between the hydrogen molecules and Pt or Pt alloy favored a dissociation of hydrogen molecules into hydrogen atoms, which form protons by donating the electrons to the conduction band of dendritic nanowires.The electron gain increased the nanowires conductivity, which was reflected in the increase in the initial sensor cerrent. |
PDF Full Text Request