Enhanced Field Ionization Enabled by Metal Induced Surface States on Semiconductor Nanotips

Abstract

Recent progress in the realization of material structures with quantum confi nement and high surface to volume ratio in nanoscale interwoven metal and semiconductor building blocks offers a strong potential to build highly functional nanodevices. Ultra-sharp tips with distinct material dependent properties of metal and semiconductor exhibit important functionalities in devices including gas ionization sensors, fi eld emission devices, and ion-mobility spectrometry. Herein, a dramatically enhanced fi eld ionization process and a device based on charged particle beams for which the geometrical and surface properties of the constituent semiconductor nanotips are engineered with controlled introduction of metallic impurities to realize close to three orders of magnitude reduction in the ionization electric-fi eld strength are described. Experimentally observed low voltage fi eld ionization phenomenon is explained using the geometrical fi eld enhancement, surface states induced by controlled introduction of metallic impurities, and polarizabilities of gas particles at the nanotips. The nanotips are employed to design fi eld ionization gas sensors whose nanoscale pristine semiconductor tips are controllably decorated with atomic metal impurities to boost the electron tunneling properties under extremely low bias voltages. These devices also outperform their solid-state macroscopic counterparts in terms of simplicity of their construction and higher selectivity.

An enhanced gas ionization sensor from Y-doped vertically aligned conductive ZnO nanorods

“…For Si NRs GIS, metal encapsulation can also decrease the breakdown voltages significantly [55], which is in a good agreement with our conclusion. However, we would expect that the superior chemical and mechanical stability of conductive metal oxide could offer a more reliable GIS performance suitable for industrial applications.…”

Metal Decoration and Magnetic Field Effect on the Electrical Breakdown Voltage for ZnO Nanorods Gas Ionization Sensor

“…The role of metal decoration is to produce small size protuberances on the surface of nanorods and then creates a higher electric field at the surface of protuberances . Besides the change in surface roughness, the surface states created by decoration are also important in reducing the ionization voltage (Karaagac and Islam, 2014). The decoration may unintentionally introduce impurity into the semiconductor and create high density of surface states (Karaagac and Islam, 2014).…”

“…Besides the change in surface roughness, the surface states created by decoration are also important in reducing the ionization voltage (Karaagac and Islam, 2014). The decoration may unintentionally introduce impurity into the semiconductor and create high density of surface states (Karaagac and Islam, 2014). However, the effect of sole metal decoration on the electrical field enhancement is not enough to decrease V EB to a safe handle level.…”

Nanofabricated Low-Voltage Gated Si Field-Ionization Arrays

“…8), after the third sweep are due to the increase in the anode current and the high voltage (+1100 V) leading to Joule heating of the anode, and hence, out-gassing in the measurement chamber. The slow FE recovery after FI experiments could be ascribed to either surface adsorption of gas molecules during FI, which prevented electron emission in the initial sweeps in FE mode, or unfilled surface states between the valence and conduction bands, which are depleted during FI [33]. A possible solution was investigated by using of a thin coating of Pt.…”