PNNL

Abstract

A novel charged-particle sensitive, pixel based detector array is described and its usage is demonstrated for a variety of applications, from detection of elemental particles (electrons) to hyper-thermal large biomolecular positive and negative ions including keV light atomic and molecular ions. The array detector is a modified light-sensitive charged coupled device (CCD). The IonCCDTM was engineered for direct charged particle detection by replacing the semi-conductor part of the CCD pixel by a conductor1. In contrast with the CCD, where the semi-conductive pixel is responsible for electron-hole pair formation upon photon bombardment, the IonCCD uses a capacitor coupled to the conductive electrode for direct charge integration. The detector can be operated from atmospheric pressure to high vacuum since no high voltages are needed. The IonCCD, presented in this work is an array of 2126 active pixels with 21 um pixel width and 3 um pixel gap. The detection area is 1.5x51mm2 where 1.5 mm and 51 mm are pixel and detector array length, respectively. The result is a one-dimensional position-sensitive detector with 24 um spatial resolution and 88 % pixel area ratio (PAR). In this work we demonstrate the capabilities and the performance of the detector. For the first time we show the direct detection of 250 eV electrons providing linearity response and detection efficiency of the IonCCD as function of electron beam current. Using positive ions from and electron impact source (E-I), we demonstrate that the detection efficiency of the IonCCD is virtually independent of particle energy [250 eV, 1250 eV], particle impact angle [45o, 90o] and particle flux. By combining the IonCCD with a double focusing sector field of Mattauch-Herzog geometry (M-H), we demonstrate fast acquisition of mass spectra in direct air sniffing mode. A first step towards fast in vivo breath analysis is presented. Detection of hyper-thermal biomolecular ions produced using an electrospray ionization source (ESI) is presented. The IonCCD was used as beam profiler to characterize the beam shape and intensity of 15 eV protonated and deprotonated biomolecular ions at the exit of an RF only collisional quadrupole. We present simultaneous detection of 140 eV doubly protonated biomolecular ions when the IonCCD is combined with the M-H analyzer. The latter, demonstrates the possibility of simultaneous separation and micro-array deposition of biological material using a miniature sector field.