Question

it is
possible in Commericial ESR Spectrometers to detect the resonance from
Simple Containing
${10}^{10}$
per
${cm}^{2}$
Calculate
monalar Spin
Concentration
Corresponding to
detection limit. ​

Answer 1

Answer:

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Explanation:

Supplementary Materials

Abstract

X-band rapid-scan EPR was implemented on a commercially available Bruker ELEXSYS E580 spectrometer. Room temperature rapid-scan and continuous-wave EPR spectra were recorded for hydrogenated amorphous silicon powder samples. By comparing the resulting signal intensities the feasibility of performing quantitative rapid-scan EPR is demonstrated. For different hydrogenated amorphous silicon samples, rapid-scan EPR results in signal-to-noise improvements by factors between 10 and 50. Rapid-scan EPR is thus capable of improving the detection limit of quantitative EPR by at least one order of magnitude. In addition, we provide a recipe for setting up and calibrating a conventional pulsed and continuous-wave EPR spectrometer for rapid-scan EPR.

Keywords: rapid-scan EPR, quantitative EPR, sensitivity, amorphous silicon

Abstract

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1. Introduction

For more than four decades, continuous-wave (CW) EPR has been utilized to quantitate the concentration of paramagnetic states in various branches of both science and industry. The most common application fields for quantitative EPR include radiation dosimetry [1–3], archaeological and geological dating [4–6], food analysis [7–9], environmental research [10, 11] and modern electronics, such as thin-film solar-cell materials [12–16]. Present X-band CWEPR spectrometers typically achieve spin sensitivities of about 1012 spins per mT line width [17].1 Despite this already high sensitivity, many examples exist where the number of spins present is close to or even below this detection limit.

A case in point are defect states in thin-film silicon (TFS) solar-cell materials, e. g., dangling Si-Si bonds (DBs) in hydrogenated amorphous silicon (a-Si:H). Such defects can act as recombination centers or trap states for charge carriers, thus impairing the electronic transport. Due to the paramagnetic nature of many of these defects, EPR is routinely employed to quantitate defect concentrations. Quantitative EPR experiments thereby contribute to reveal the impact of defect states on electronic device performance [12–16]. For typical TFS samples, an absolute spin sensitivity of 1012 spins corresponds to a concentration sensitivity of about 1014 spins per cm3.2 With increasing electronic quality, defect densities in state-of-the-art TFS materials are approaching this range [16].

Table 1

Table 1

Summary of electron-spin relaxation times (T1, T2) and absolute number of spins (NS), determined by quantitative CWEPR, and the resulting spin concentration (ρS) of all a-Si:H samples under study.

2.2. EPR set-up

All EPR measurements were carried out at X-band (9.4 GHz to 9.8 GHz) and room temperature on a Bruker ELEXSYS E580 spectrometer. It is equipped with a lock-in amplifier for phase-sensitive detection of CWEPR, and with a quadrature mixer and a SpecJet-II fast digitizer for direct time-domain detection of RS and PEPR. For the PEPR experiments discussed in section 2.3, pulse sequences were generated by a PatternJet-II pulse programmer and amplified by a travelling-wave-tube (TWT) amplifier with a nominal power of 1 kW.