2023 - Multifunctional SPM probe of the new generation
relevant to TAČR Trend FW03010504
Multifunctional SPM probe of the new generation
The aim of the development of the functional sample is a multifunctional SPM probe of the new generation, which enables the measurement of physical properties of materials and nanostructures, but also allows these properties to be influenced in-situ by applied light, electric field and working gas.
Description
The basic part of the multifunctional SPM probe of the new generation is a quartz tuning fork, which is used as a force sensor in the field of SPM microscopy. A quartz tuning fork is a commercially available electronic component that is commonly used as a frequency normal in real-time circuits (e.g. pocket watches). After being removed from the original case, the tuning fork is equipped with a sharp tip, oscillated to its resonance frequency by an electrical signal, and changes in this resonance frequency due to the force interaction between the sample and the tip are then used for SPM feedback.
In the case of a multifunctional probe (Fig. 1), the SPM tip is fitted in the form of a unique extension at the end of an optical fiber glued along one prong of the quartz tuning fork. The optical fiber is used to guide the light to/from the sample. If a photonic crystal fiber is used, with hollow capillaries running through its core, the working gas can also be supplied to the tip area. Furthermore, the entire probe is coated with a thin layer of gold. The coating of the probe has several functions: it prevents the charging of the probe and the subsequent deformation of the image during simultaneous SEM and SPM measurement, it allows the application of electrical voltage to the SPM tip, and it confines the illumination and collection of light only to the end aperture of the tip.
Figure 1.: Schematic of multifunctional SPM probe of the new generation.
Applications
The multifunctional SPM probe of the new generation is designed to be compatible with the SPM LiteScope intended for correlative measurement using SPM and SEM. In addition, the unique concept of a multifunctional probe based on a photonic crystal fiber extends the capabilities of this SPM/SEM combination with additional imaging and characterization techniques. Thanks to the possibility of illumination and detection of light through the optical fiber of the probe, the investigated samples can thus be characterized using Raman spectroscopy, photoluminescence or by the detection of cathodoluminescence radiation excited by an electron beam. Moreover, these characterization techniques can be performed simultaneously and in a correlated form together with SPM topography measurement and SEM imaging. Figure 2 presents an example of a correlative SPM/SEM measurement together with cathodoluminescence detection. Figure 2a and is an SEM image of the tip of the multifunctional probe scanning over a gold grid on a ruby substrate. The obtained cathodoluminescence map is shown in Figure 2b. Figure 2c shows the SPM topography of the interface of the active electroluminescence (emitter) and the inactive part (electrode) of a GaN LED irradiated with an electron beam. The resulting cathodoluminescence map is shown in Figure 2d.
Figure 2: Cathodoluminescence measurement using a multifunctional probe: a) colored SEM image of a multifunctional SPM probe scanning over a gold grid on a ruby substrate. The yellow rectangle in the image marks the scanned area. b) Cathodoluminescence map obtained during scanning. c) SPM topography and d) cathodoluminescence map of the interface between the emitter and the electrode of the GaN LED, e) 3D SPM topography and 3D topography colored by the cathodoluminescence signal.
The multifunctional SPM probe is not only used for correlative imaging and characterization but can also be directly used to modify the physical properties of the material under investigation or to create nanostructures. And this is mainly due to the possibility of illuminating the sample with the intense laser light, by supplying of working gas and by applying of electric voltage to the tip of the probe. Modification of the surface of the sample can be performed, for example, by techniques such as local anodic oxidation (electric voltage + H2O), hydrogenation (H2 + light), oxidation (O2 + light), electron beam-induced deposition (precursor + electron beam), melting (light) and phase transition of material (light).