Light Enhanced Electron Transduction and Amplified Sensing at a Nanostructure Modified Semiconductor Interface

Abstract

Visible and UV light are demonstrated to significantly enhance the sensing properties of an n‐type porous silicon (PS) extrinsic semiconductor interface to which TiO2 and titanium oxynitride (TiO2‐xNx) photocatalytic nanostructures are fractionally deposited. The acid/base chemistry of NH3, a moderately strong base, and NO2, a moderately strong acid, couples to the majority charge carriers of the doped semiconductor as the strong acid (TiO2) enhances the extraction of electrons from NH3, and the more basic TiO2‐xNx decreases the efficiency of electron extraction relative to the untreated interface. In contrast, NO2 and a TiO2 or TiO2‐xNx nanostructure‐decorated PS interface compete for the available electrons leading to a distinct time dependent electron transduction dynamics as a function of TiO2 and TiO2‐xNx concentration. Only small concentrations of TiO2 and its oxynitride and no self‐assembly are required to enhance the response of the decorated interface. With light intensities of less than a few lumens/cm2‐sterad‐nm, responses are enhanced by up to 150% through interaction with visible (and UV) radiation. These light intensities should be compared to the sun's radiation level, ≈500 lumens/cm2‐sterad‐nm suggesting the possibility of solar pumped sensors. The observed behavior in these systems is largely explained by the recently developed Inverse Hard/Soft Acid/Base (IHSAB) concept.

How to Improve the Performance of Porous Silicon‐Based Gas and Vapor Sensors? Approaches and Achievements

“…In contrast, the response to NH 3 increased in the TiO 2− x N x modified PSi sensor for both UV and white light. When detecting NO 2 , Laminack and Gole had the opposite situation. The light had a marked effect on the resistance response to NO 2 for untreated PSi, which was counter to that observed for the PSi microstructure platform deposited with distinct nanostructured island sites of TiO 2 and TiO 2− x N x .…”

“…To measure the change in response to NO 2 , a UV lamp was introduced in the enclosed testing chamber. Laminack and Gole also studied the influence of light on the sensor response of PSi‐based sensors. They found that white light and UV light did not have any effect on the sensor response to NH 3 for untreated PSi.…”

“…Kim et al supposed that UV light activates the response of the oriental polarization which has a slow relaxation time for an AC field. Laminack and Gole believed that the UV and white light excitation causes the TiO 2− x N x to become more acidic, enhancing the electron withdrawing power and thus increasing the sensor response. However, till now, the consistent mechanisms, which can explain the photoassisted gas‐sensing properties of various PSi‐based structures, are absent.…”

Nanostructure directed interfaces created from nanoparticle island sites deposited to microporous arrays and forming sensor platforms

“…The use of low light levels (≤ ! Watt) demonstrates the feasibility for developing Solar Pumped Sensors [13]. The ability to deal with water vapor contamination has been demonstrated [14].…”

New Generation Devices for Gas (Liquid) Sensing

“…In addition, the sensor platforms are capable of operation under extremely small magnetic field control [27]. The devices have the potential for adaptation to solar pumped sensing, micro-reactor, and solar assisted micro-reactors to achieve difficult but important chemical transformations, extending the development of basic heterogeneous catalyst sites and potential acid/base pairing combinations [28]. The technology has now been applied to the characterization of volatile liquids including the alcohols, acetone, chloroform, additional polar and nonpolar solvents, and more complex liquids including isoprene.…”