Mechanical Modulation of Phonon-Assisted Field Emission in a Silicon Nanomembrane Detector for Time-of-Flight Mass Spectrometry.

Jonghoo Park,Robert Blick

doi:10.3390/s16020200

Abstract

We demonstrate mechanical modulation of phonon-assisted field emission in a free-standing silicon nanomembrane detector for time-of-flight mass spectrometry of proteins. The impacts of ion bombardment on the silicon nanomembrane have been explored in both mechanical and electrical points of view. Locally elevated lattice temperature in the silicon nanomembrane, resulting from the transduction of ion kinetic energy into thermal energy through the ion bombardment, induces not only phonon-assisted field emission but also a mechanical vibration in the silicon nanomembrane. The coupling of these mechanical and electrical phenomenon leads to mechanical modulation of phonon-assisted field emission. The thermal energy relaxation through mechanical vibration in addition to the lateral heat conduction and field emission in the silicon nanomembrane offers effective cooling of the nanomembrane, thereby allowing high resolution mass analysis.

Highlights

Nanomembranes (NMs) are freestanding structures with thicknesses of on the order of a few hundred nanometers or less with aspect ratio over 1,000,000
We utilized silicon nanomembrane thinner than its phonon mean free path to transform the thermal energy deposited by ion bombardment into the phonon-assisted field emission (PAFE) for ion detection in MALDI TOF mass spectrometry at room temperature
We have found that when the accelerated ions bombard the one side of the silicon nanomembrane and deposit thermal energy on the nanomembrane, it causes PAFE and mechanical vibration of the silicon nanomembrane

Summary

Introduction

Nanomembranes (NMs) are freestanding structures with thicknesses of on the order of a few hundred nanometers or less with aspect ratio over 1,000,000. A measure of the amount of kinetic energy deposited in the detector by ion bombardment is highly independent on the ion mass and can overcome the drawbacks of the conventional ion detectors which stems from the velocity dependent sensitivity. The impact energy measurement in TOF mass spectrometry has been realized by the cryogenic detectors [14] This approach demonstrated a quantum efficiency several orders of magnitude larger than the MCP detectors, but it requires an expensive cryogenic system. We utilized silicon nanomembrane thinner than its phonon mean free path to transform the thermal energy deposited by ion bombardment into the phonon-assisted field emission (PAFE) for ion detection in MALDI TOF mass spectrometry at room temperature. The coupling of these electrical and mechanical phenomenon leads to mechanical modulation of PAFE and it gives better understanding on the operating principle of the detector and how thermal energy dissipates in the silicon nanomembrane detector

Experimental Section

Results and Discussion

Conclusions