Ionoluminescence in the Helium Ion Microscope

Abstract

Ionoluminescence (IL) is the emission of light from a material due to excitation by an ion beam. In this work, a helium ion microscope (HIM) has been used in conjunction with a luminescence detection system to characterize IL from materials in an analogous way to how cathodoluminescence (CL) is characterized in a scanning electron microscope (SEM). A survey of the helium ion beam induced IL characteristics, including images and spectra, of a variety of materials known to exhibit CL in an SEM is presented. Direct bandgap semiconductors that luminesce strongly in the SEM, are found not do so in the HIM, possibly due to defect-related non-radiative pathways created by the ion beam. Other materials do, however, exhibit IL, including a cerium-doped garnet sample, quantum dots and rare earth doped LaPO 4 nanocrystals. These emissions are a result of transitions between f electron states or transitions across size dependent band gaps. In all these samples, IL is found to decay with exposure to the beam, fitting well to double exponential functions. In an exploration of the potential of this technique for biological tagging applications, imaging with the IL emitted by rare earth doped LaPO 4 nanocrystals, simultaneously with secondary electron imaging, is demonstrated at a range of magnifications.

Material characterization and modification using helium lon microscopy : various examples

“…However, ionoluminescence studies are significantly complicated by the fact that an ion beam not only induces light emission, but also directly influences the luminescence properties of the target due to defect creation [49,50] …”

“…It is similar to the cathodoluminescence (CL) phenomenon in scanning electron microscopy (SEM). The possibility for IL studies using HIM was previously demonstrated by Boden et al [50] and Ogawa et al [103]. Ionoluminescence is a result of the radiative relaxation of target electrons that have been excited by the incident beam.…”

“…However, the ion beam irradiation introduces defects at a relatively high rate, significantly influencing the luminescent properties of the materials (see Chapter 5). Previous attempts to investigate IL from bulk semiconductors using HIM were not successful [50]. The authors of Ref.…”

“…We use SE throughout this chapter for those electrons, which are generated as a result of an ion impact, actually make it to the surface and are emitted into the vacuum. In addition to SEs and backscattered He signals typically used in HIM, also photon generation and detection is possible for certain materials [50,103]. This phenomenon is called ionoluminescence (IL).…”

“…The authors of Ref. [50] report that no detectable signal was obtained from a series of direct band-gap semiconductor samples. However, later the same authors demonstrated IL of a GaN layer on sapphire [157].…”