Kaltenpoth G, Schnabel P, Menke E, Walter E C, Grunze M, Penner R M
Department of Chemistry, University of California, Irvine, California 92697-2025, USA.
Anal Chem. 2003 Sep 15;75(18):4756-65. doi: 10.1021/ac034507e.
Palladium was electrodeposited onto lithographically patterned Si(100) "micro-channels" with dimensions of 2 microm (width) x 100 microm (length). The properties of these Pd-covered Si micro-channels for detecting dihydrogen gas were then evaluated. Pd electrodeposition was carried out under conditions favoring an instantaneous nucleation and growth mechanism. This strategy produced size-similar Pd particles at a coverage of (4-6) x 10(9) cm(-2) within the confines of the Si micro-channel. When the mean particle radius, ro, was smaller than a critical value (ro < rc = 70-85 nm), each Pd particle was well separated on the surface from adjacent particles, on average, and no response to H2 gas attributable to the micro-channel was observed. As Pd particles were grown larger, to a mean radius of ro approximately equal to rc, adjacent particles on the surface touched and the electrical resistance of the micro-channel dropped by several orders of magnitude. These "type 2" H2 sensors exhibited a rapid (< 1 s), reversible decrease in their resistance in response to exposure to H2 above 0.5%, but a minimum resistance was observed at 1-2%, and a resistance increase was seen at higher H2 concentration. This complex behavior resulted from the existence of three mechanisms for charge transport across the micro-channel. If still larger quantities of Pd were deposited, the Pd particle ensemble coalesced into an electrically continuous film. These "type 3" sensors became more resistive in the presence of H2, not more conductive as seen for sensors of types 1 and 2, but the amplitude of this response was smaller than seen for type 2 sensors.
钯被电沉积到光刻图案化的尺寸为2微米（宽）×100微米（长）的硅（100）“微通道”上。然后评估了这些覆盖钯的硅微通道检测氢气的性能。钯的电沉积是在有利于瞬时成核和生长机制的条件下进行的。该策略在硅微通道范围内以（4 - 6）×10⁹ cm⁻² 的覆盖率产生尺寸相似的钯颗粒。当平均颗粒半径ro小于临界值（ro < rc = 70 - 85纳米）时，平均而言，每个钯颗粒在表面上与相邻颗粒充分分离，并且未观察到归因于微通道的对氢气的响应。随着钯颗粒长大到平均半径ro约等于rc，表面上相邻颗粒接触，微通道的电阻下降几个数量级。这些“2型”氢气传感器在暴露于高于0.5%的氢气时，其电阻迅速（< 1秒）、可逆地降低，但在1 - 2%时观察到最小电阻，在更高氢气浓度下电阻增加。这种复杂行为是由三种跨微通道电荷传输机制的存在导致的。如果沉积更多的钯，钯颗粒聚集体会合并成一个电连续膜。这些“3型”传感器在氢气存在下电阻变得更大，不像1型和2型传感器那样更具导电性，但其响应幅度比2型传感器小。
