Advances in gas ionization sensors based on nanostructured materials: a review

Crystalline-to-Amorphous Phase Transformation in CuO Nanowires for Gaseous Ionization and Sensing Application

“…After amorphization, the formed surface states can modulate the band bending at the gas–solid interface, as shown in the right diagram. Such a change of band configuration further lowers the potential barrier, which provides additional elevation of the field emission efficiency. ,, …”

“…Such a change of band configuration further lowers the potential barrier, which provides additional elevation of the field emission efficiency. 1,50,51 Gas-Sensing Properties of Amorphous CuO NWs. Lowering the discharge V th after amorphization could enable this CuO NW device to serve as an ionization gas sensor.…”

“…10,11 By ionizing the target gas, a specific current−voltage characteristic can be generated as the "fingerprint" of the gas component. 12,13 The main disadvantages of traditional bulky ionization gas sensors, for example, high power consumption and risky high operation voltage, hinder their practical application. 14−16 Therefore, onedimensional nanomaterials with ultrasharp tips, for example, carbon nanotubes, as well as ZnO, Si, or CuO nanowires (NWs), 17−20 are equipped onto the traditional macroscopic electrodes in order to lower both the operation voltage and the current.…”

“…Field gas ionization system is capable of ionizing the gas molecules by loading a low voltage on the electrodes and is favorable for many potential applications, for example, sensors, , environmental remediation, spectrometry, − and biomedicine . Among them, ionization gas sensors have attracted extensive interest for their advantages like high selectivity and fast response/recovery. , Ionization gas sensing is substantially based on the separation of the positive and negative charges of a gas molecule. , By ionizing the target gas, a specific current–voltage characteristic can be generated as the “fingerprint” of the gas component. , The main disadvantages of traditional bulky ionization gas sensors, for example, high power consumption and risky high operation voltage, hinder their practical application. − Therefore, one-dimensional nanomaterials with ultrasharp tips, for example, carbon nanotubes, as well as ZnO, Si, or CuO nanowires (NWs), − are equipped onto the traditional macroscopic electrodes in order to lower both the operation voltage and the current. Then, intensive studies of decorating the thin film or nanoparticles have been conducted on these nanoelectrodes to further decrease the gas ionization voltages. − However, in contrast to these approaches of additional manufacturing, the study of structural evolution of these microscopic electrodes themselves during the gas ionization is still challenging, and it is worthwhile devoting effort to it, which is strongly associated with the sensing properties of current–voltage ( I – V ) characteristics, repeatability, and stability …”

MEMS-Based Ionization Gas Sensors for VOCs with Array of Nanostructured Silicon Needles

“…Recently many researches are focused on application of nanostructured materials and novel electrode structures. − The silicon-based nanostructure is demonstrated to be one kind of the effective nanomaterials to induce a non-uniform electric field for gas molecule ionization in spite of the low working pressure. , Both the microneedle structure and the nanostructure would both enhance the electric field around the micro gas gap. The side-wall microneedle arrays allow the nanostructures to be arranged as tip to tip, which could provide the maximum effective ionization area of the nanolayers.…”