A polycrystalline diamond micro-detector for X-ray absorption fine-structure measurements
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-02-16 |
| Journal | Journal of Synchrotron Radiation |
| Authors | LEI YAO, Yunpeng Liu, Bingjie Wang, Lixiong Qian, Xueqing Xing |
| Institutions | Institute of High Energy Physics, University of Chinese Academy of Sciences |
| Citations | 6 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis focuses on the fabrication and performance validation of a miniaturized X-ray detector utilizing Chemical Vapor Deposited (CVD) polycrystalline diamond film for X-ray Absorption Fine-Structure (XAFS) measurements.
- Core Achievement: Successful development of a highly compact, polycrystalline diamond micro-detector designed to replace bulky Ion Chambers (ICs) in synchrotron applications.
- Miniaturization: The packaged detector is extremely small (15 mm x 7.8 mm x 5.8 mm), making it ideal for integration into complex, combined experimental setups where space is severely limited.
- Material Advantage: Using polycrystalline CVD diamond avoids the intense diffraction spots produced by single-crystal diamond, preventing interference with other detectors used in combined techniques.
- High Response: The CVD diamond micro-detector demonstrated a response current to incident 8 keV X-rays that was approximately fivefold stronger (2.7-3.2 ”A) than the routine IC (0.5-0.6 ”A).
- Accuracy Improvement: XAFS fitting parameters (e.g., near-neighbor bond lengths) derived from the diamond detector data were consistently closer to known crystallographic true values than those obtained using the routine IC.
- Feasibility Confirmed: The detector successfully collected high-quality K-edge XAFS spectra for Cr, Fe, Cu, and Se foils across the 5.5 to 13.5 keV energy range, confirming its reliability for X-ray intensity collection.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Detector Material | Polycrystalline Diamond | N/A | Fabricated via CVD |
| Film Thickness (Initial) | 300 | ”m | Thickness of self-supporting laminae |
| Packaged Dimensions (L x W x H) | 15 x 7.8 x 5.8 | mm | External stainless steel shell size |
| Active Electrode Area | 8 x 5 | mm | Vacuum-evaporated Aluminum electrodes |
| Electrode Thickness | less than 100 | nm | Aluminum layer thickness |
| Operating Energy Range | 5.5 to 13.5 | keV | Tested range for XAFS measurements |
| Incident Photon Flux | ~1012 | photons s-1 | Flux at BSRF beamline 1W2B |
| Dark Current (Stabilized) | ~30 | pA | CVD Diamond Micro-detector |
| Dark Current (Routine IC) | 5.5 to 7.5 | pA | Routine Ion Chamber (IC) |
| Response Current (8 keV) | 2.7 to 3.2 | ”A | CVD Diamond Micro-detector |
| Response Current (8 keV) | 0.5 to 0.6 | ”A | Routine Ion Chamber (IC) |
| Routine IC Working Voltage | 2000 | V | Standard operating voltage for IC |
| Cr-Cr Distance (Second Subshell) | 2.87 | A | Measured by CVD detector (Crystallographic value: 2.88 A) |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication and testing of the polycrystalline diamond micro-detector followed these primary steps:
- Material Preparation: Purchased CVD polycrystalline diamond films (300 ”m thickness) were cut into small pieces (11 mm x 6 mm).
- Surface Cleaning: The diamond pieces underwent chemical cleaning (decarburization and degreasing) using H2SO4 and NH4OH solutions.
- Electrode Masking: Photoresist was applied to the four edges of the diamond piece to ensure electrical isolation between the front and back electrodes.
- Metallization: Aluminum metal was evaporated in vacuum and deposited on both sides of the diamond film to form 8 mm x 5 mm electrodes (<100 nm thickness).
- Mounting and Wiring: The diamond piece was mounted onto a small hollow circuit board (10 mm x 5 mm x 1.5 mm). Gold wires connected the circuit board copper lines to the aluminum electrodes for bias voltage application.
- Encapsulation: The assembly was insulated using a 30 ”m thick polyimide film and housed within a stainless steel shell (15 mm x 7.8 mm x 5.8 mm).
- XAFS Measurement: Transmission XAFS spectra of elemental foils (Cr, Fe, Cu, Se) were collected at BSRF beamlines 1W2B and 4B9A, covering 5.5 to 13.5 keV.
- Signal Acquisition: The current signal was amplified (Keithley Model 428), converted to a pulse frequency (V/F converter), and recorded using a counter (EG&G Model 974).
Commercial Applications
Section titled âCommercial ApplicationsâThe polycrystalline diamond micro-detector technology is highly relevant for applications requiring compact, radiation-hard, and high-performance X-ray detection:
- Synchrotron Research Facilities: Direct replacement for large, routine Ion Chambers (ICs) in transmission XAFS beamlines, offering improved accuracy in structural parameter fitting.
- Combined Spectroscopy Techniques: Essential for advanced experimental setups (e.g., simultaneous XAFS/XRD, XAFS/Raman) where the detector must not obstruct or interfere with other measurement signals.
- High-Flux X-ray Environments: Diamondâs inherent radiation hardness and fast response time make it superior to traditional Si-based detectors in high-intensity synchrotron beams (fluxes â„1011 photons s-1).
- Miniaturized X-ray Instrumentation: Potential use in developing compact, field-deployable X-ray analysis tools (like portable XRF or XAS units) that require stable, low-dark-current detectors.
- Radiation Monitoring and Dosimetry: Diamondâs stability and low dark current (pA range) are beneficial for precise monitoring in high-radiation fields.
View Original Abstract
The microminiaturization of detectors used to record the intensity of X-ray beams is very favorable for combined X-ray experimental techniques. In this paper, chemical-vapor-deposited (CVD) polycrystalline diamond film was used to fabricate a micro-detector owing to its well controlled size, good thermostability, and appropriate conductivity. The preparation process and the main components of the CVD diamond micro-detector are described. The external dimensions of the packaged CVD diamond micro-detector are 15 mm Ă 7.8 mm Ă 5.8 mm. To demonstrate the performance of the detector, K -edge X-ray absorption fine-structure (XAFS) spectra of Cr, Fe, Cu, and Se foils were collected using the CVD diamond micro-detector and routine ion chamber. These XAFS measurements were performed at beamline 1W2B of Beijing Synchrotron Radiation Facility, covering an energy range from 5.5 to 13.5 keV. By comparison, it can be seen that the CVD diamond micro-detector shows a more excellent performance than the routine ion-chamber in recording these XAFS spectra. The successful application of the CVD diamond micro-detector in XAFS measurements shows its feasibility in recording X-ray intensity.