Multimodal X-ray probe station at 9C beamline of Pohang Light Source-II

Abstract

In this study, the conceptual design and performance of a multimodal X-ray probe station recently installed at the 9C coherent X-ray scattering beamline of the Pohang Light Source-II are presented. The purpose of this apparatus is to measure coherent X-ray diffraction, X-ray fluorescence and electrical properties simultaneously. A miniature vacuum probe station equipped with a four-point probe was mounted on a six-axis motion hexapod. This can be used to study the structural and chemical evolution of thin films or nanostructures, as well as device performance including electronic transport properties. This probe station also provides the capability of varying sample environments such as gas atmosphere using a mass-flow-control system and sample temperatures up to 600°C using a pyrolytic boron nitride heater. The in situ annealing of ZnO thin films and the performance of ZnO nanostructure-based X-ray photodetectors are discussed. These results demonstrate that a multimodal X-ray probe station can be used for performing in situ and operando experiments to investigate structural phase transitions involving electrical resistivity switching.

Keywords: beamline; electrical property; four-point probe station; in situ X-ray diffraction; multimodal X-ray probe.

Figure 1

Conceptual design of the miniature X-ray probe station. (a) Top view and (b) perspective view. It mainly consists of a miniature vacuum chamber and motion stages for the probe holder.

Figure 2

(a, b) Photographs of the multimodal X-ray probe station that includes the miniature probe station, hexapod manipulator and six-circle X-ray diffractometer. The X-ray diffractometer operates in ‘2 + 2’ mode to access Q space by combining motions of two detector circles and two sample circles. Panels (c) and (d) show intensity profiles at the focal point for estimating the focus size in the horizontal (c) and vertical (d) directions, respectively.

Figure 3

(a) Powder XRD and (b) GIXS profiles of ZnO nanorods along the out-of-plane Q _z and in-plane Q _x directions, respectively. The GIXS profile is measured at an incident angle of 0.2°. The scan directions in Q _x –Q _z reciprocal space are illustrated in the in-set. The (0001) and atomic planes of hexagonal wurtzite ZnO are aligned with the Q _z and Q _x directions, respectively.

Figure 4

(a) Schematic of the operation of four-point probe and XRD measurements. (b) X-ray probe station, which weighs approximately 8 kg. Probe holders are adjusted by x-y-z stages. (c) Example of sample loaded for multimodal measurements. The probe tips are in contact with metal electrodes.

Figure 5

(a) In situ electrical I–V curves recorded at 25, 100, 200, 300, 400 and 500°C. (b) Variation of electrical conductance as a function of annealing temperature. (c) In situ microbeam XRD profiles of ZnO thin film at 25, 100, 200, 300, 400 and 500°C. The ZnO(0002) Bragg peak with interference fringes is clear. (d) c-lattice constant and crystalline domain size of ZnO thin film as a function of annealing temperature. Strain relaxation significantly affects structural and electrical properties after 400°C during annealing.

Figure 6

(a) Metal–semiconductor–metal type X-ray photodetector. Width and spacing of the metal grids are 200 µm. Top-view SEM image denotes the morphology of the ZnO nanostructures. (b) XRD profile of the ZnO nanostructure-based X-ray photodetector. (c) X-ray-induced photocurrent and dark current profiles as a function of applied voltage. The photo-to-dark-current ratio at 10 V is approximately 250. (d) Sensing profiles for applied voltage of 10 V during repeated X-ray on/off.

Figure 7

A series of diffraction patterns near the off-specular Au( ) Bragg peak. The diffraction patterns of Au nanocrystals were recorded during annealing at 500°C. The interval is Δt ≃ 13 min. Data contain 161  ×  161 pixels corresponding to ΔQ = ±0.0237 Å⁻¹.

Figure 8

The diffraction patterns of Au nanocrystals were recorded while rotating the sample through Bragg diffraction conditions near the off-specular Au( ) Bragg peak. Actually, the θ-rocking angle is ±0.5° with a step of 0.01°. The values shown in the figure represent the rocking angle. Data contain 161 × 161 pixels corresponding to ΔQ = ±0.0237 Å⁻¹.