Zno Contaminado Con Pd

Wang et al. Nanoscale Research Letters 2011, 6:534
http://www.nanoscalereslett.com/content/6/1/534

NANO EXPRESS

Open Access

A novel gas ionization sensor using Pd
nanoparticle-capped ZnO
Hongjun Wang1, Changwei Zou2, Canxin Tian1, Lin Zhou1, Zesong Wang1 and Dejun Fu1,3*

Abstract
A novel gas ionization sensor using Pd nanoparticle-capped ZnO (Pd/ZnO) nanorods as the anode isproposed.
The Pd/ZnO nanorod-based sensors, compared with the bare ZnO nanorod, show lower breakdown voltage for
the detected gases with good sensitivity and selectivity. Moreover, the sensors exhibit stable performance after
more than 200 tests for both inert and active gases. The simple, low-cost, Pd/ZnO nanorod-based field-ionization
gas sensors presented in this study have potentialapplications in the field of gas sensor devices.
1. Introduction
Gas sensors have attracted considerable attention in
recent years because of their huge potential applications,
such as pollution detection, environment protection, gas
detection for counter-terrorism, etc. [1]. There are two
types of gas sensors, chemical type operated by gas
adsorption-desorption and physical type operated by
fieldionization. In different gas varies and concentrations atmosphere, the chemical type gas sensor can
detect the modifications of the electronic properties in
the active layer, such as carbon nanotubes (CNTs) [2-4],
porous silicon [5], and metal oxides [6]. However, the
application of the chemical type gas sensor is limited by
several disadvantages, such as the potential difficulties indetecting gases with low adsorption energies, the high
working temperature (except for the CNTs based sensors), and the higher power consumption.
Recent efforts have been directed to the physical type
of gas senor based on the field ionization, which works
by fingerprinting the ionization characteristics of distinct
gases. This type sensor can detect gases regardless of
their adsorption energies. Anovel physical gas sensor
based on CNTs has been demonstrated with low breakdown voltage due to its extremely sharp radii [7,8]. This
sensor can detect many gases, such as Air, He, Ar, and
gas mixtures, by the strong electric fields generated at
the tips to strip electrons from the various gas molecules [7]. However, the CNTs show poor stability

* Correspondence: balu7015@hotmail.com
1Department of Physics, Wuhan University, Wuhan 430072, China
Full list of author information is available at the end of the article

because it could easily be oxidized and degraded in the
oxygen-contained atmosphere [9,10].
Recently, gas ionization sensors using a sparse array of
vertically aligned gold nanorods as substitutes for CNTs
have successfully been prepared for the first time[11-14]. Owing to the chemical stability of one-dimensional ZnO (1D ZnO) nanowires at room temperature,
they also have been used for stable field-ionization gas
sensors instead of CNTs [10]. However, 1D ZnO nanostructures with relatively smooth surface and larger tip
radii, compared with CNTs, need higher breakdown voltage. Therefore, the modification of the surface of 1D
ZnO nanostructures toobtain lower breakdown voltage
is one of the key issues for gas sensor applications. In
this study, we introduce a physical gas sensor using palladium (Pd) nanoparticle-capped ZnO (Pd/ZnO) nanorods as the anode. The results show that the breakdown
voltage decreases for the Pd/ZnO nanorod-based sensor,
compared with the bare ZnO nanorod. This study investigates the potential applications of suchphysical ionization gas sensors.

2. Experimental section
ZnO nanorods were grown on silicon substrates through
a reactive vapor deposition method as reported in detail
elsewhere [15]. The Pd nanoparticles were deposited by
a dc sputtering system at a fixed current of 40 mA for
120 s. The morphology of ZnO nanorods was characterized by a Sirion FEG scanning electron microscopy
(SEM) and...