A direct experimental comparison of single-crystal CVD diamond and silicon carbide X-ray beam position monitors

At a Glance

Metadata	Details
Publication Date	2023-07-13
Journal	Journal of Synchrotron Radiation
Authors	C. Houghton, Chris Bloomer, Lorraine Bobb
Institutions	Diamond Light Source
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: Single-Crystal CVD Diamond for X-ray Beam Position Monitors

Executive Summary

This analysis compares Single-Crystal CVD Diamond (SCD) and 4H-Silicon Carbide (4H-SiC) detectors for use as X-ray Beam Position Monitors (XBPMs) in synchrotron facilities. The findings confirm SCD diamond’s status as the superior material for high-resolution, high-flux beam diagnostics, while highlighting 6CCVD’s capability to supply and customize these critical components.

Superior Resolution: SCD XBPMs demonstrated significantly better position resolution (29 nm horizontal, 14 nm vertical @ 20 kHz) compared to 4H-SiC (187 nm horizontal, 76 nm vertical).
Excellent Uniformity: The 20 µm SCD detector exhibited outstanding spatial uniformity (0.47% RMS variation), crucial for accurate intensity monitoring, whereas 4H-SiC showed non-uniformity issues related to fabrication gaps.
High Transmission: Both 20 µm SCD and 2.3 µm 4H-SiC windows achieved >99% transmission at 12.4 keV, validating the use of thin SCD films for non-intrusive diagnostics. 6CCVD specializes in optimizing this thickness.
Temporal Performance: Both materials showed excellent temporal response, tracking synchrotron top-up pulses simultaneously at 20 kHz sampling rates, confirming their suitability for real-time monitoring.
6CCVD Advantage: While 4H-SiC offers larger apertures, 6CCVD addresses this need by offering large-area Polycrystalline Diamond (PCD) plates up to 125 mm for applications requiring high transmission and large fields of view, alongside high-purity SCD for ultimate resolution.
Customization Ready: 6CCVD can replicate the specific 20 µm SCD thickness and 100 nm Titanium (Ti) metalization used in this study, ensuring direct applicability for researchers.

Technical Specifications

Parameter	Value	Unit	Context
SCD Detector Thickness	20	µm	Uniform thickness across the plate
4H-SiC Detector Thickness	2.3 / 362	µm	Thin window / Thick frame
SCD Position Resolution (H)	29	nm	Standard deviation @ 20 kHz sampling, 5V bias
SCD Position Resolution (V)	14	nm	Standard deviation @ 20 kHz sampling, 5V bias
4H-SiC Position Resolution (H)	187	nm	Standard deviation @ 20 kHz sampling, 5V bias
4H-SiC Position Resolution (V)	76	nm	Standard deviation @ 20 kHz sampling, 5V bias
SCD Spatial Uniformity (RMS)	0.47	%	RMS variation of signal current across the active area
4H-SiC Spatial Uniformity (RMS)	1.5	%	RMS variation (excluding quadrant gaps)
X-ray Photon Energy Tested	12.4	keV	Typical Diamond Light Source beamline energy
SCD Transmission @ 12.4 keV	99.2	%	Non-intrusive performance
SCD Metalization Used	100	nm	Titanium (Ti) quadrant electrodes
SCD Bias Requirement	≥ 1	V	Required for >90% Charge Collection Efficiency

Key Methodologies

The experiment utilized simultaneous, in-line testing of commercially sourced SCD and 4H-SiC XBPMs at the I22 beamline at Diamond Light Source.

Detector Configuration:
- SCD: 20 µm thick, uniform single-crystal diamond.
- 4H-SiC: 362 µm thick substrate with a 2.3 µm thin central window (4.0 mm diameter).
- Both devices featured four quadrant electrodes (A, B, C, D) for position measurement via the difference-over-sum method.
Material Structure & Doping:
- SCD: Bulk sc-diamond, requiring external bias (5 V applied in tests) due to difficulty in doping.
- 4H-SiC: Doped epitaxial layers (2 µm n-nitrogen-doped, 0.3 µm p+ phosphorous-doped) forming a p-n junction, enabling operation at 0 V bias (built-in electric field).
Metalization:
- SCD: 100 nm Titanium (Ti) contacts.
- 4H-SiC: 100 nm Aluminium (Al) contacts.
Measurement Techniques:
- Raster Scanning: Two-dimensional scans (9 mm x 7 mm and fine 0.33 mm x 0.33 mm) were performed using a motorized X-Y stage to quantify spatial uniformity.
- Temporal Response: Signal currents were recorded simultaneously at 20 kHz using low-impedance electrometers (TetrAMM) during shutter opening/closing and synchrotron top-up pulses.
- Flux Linearity: Measured by attenuating the X-ray beam using various filter thicknesses.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-performance SCD materials required for next-generation synchrotron diagnostics, offering customization that exceeds standard commercial availability.

Applicable Materials

Research Requirement	6CCVD Material Solution	Customization & Advantage
High Position Resolution (nm scale)	Optical Grade Single Crystal Diamond (SCD)	We provide high-purity SCD plates (Type IIa) with thicknesses precisely controlled from 0.1 µm up to 500 µm, allowing researchers to match the optimal thickness (e.g., 20 µm) for specific X-ray energy ranges and transmission targets.
Large Aperture / High Throughput	High-Purity Polycrystalline Diamond (PCD)	While the paper notes SCD size limitations, 6CCVD offers PCD wafers up to 125 mm in diameter. This is ideal for large-area XBPMs, initial beamline commissioning, or applications where the 4H-SiC size advantage is sought without sacrificing diamond’s radiation hardness.
Uniformity & Surface Quality	Precision Polished SCD	We guarantee surface roughness of Ra < 1 nm for SCD, ensuring the high spatial uniformity (0.47% RMS) observed in the study is maintained or improved, especially critical for thin films.
Doped Detectors (Bias-Free Operation)	Boron-Doped Diamond (BDD)	For applications requiring a built-in electric field (similar to the 4H-SiC p-n junction) to operate without external bias, 6CCVD supplies custom BDD films, enabling diode-like functionality in a diamond platform.

Customization Potential

The research utilized specific dimensions and metal contacts that 6CCVD can replicate or improve upon:

Custom Dimensions: We supply SCD plates in custom sizes, addressing the 5 mm x 5 mm limitation cited in the paper. For larger requirements, our PCD plates are available up to 125 mm diameter.
Thickness Optimization: The 20 µm SCD thickness was key to achieving 99.2% transmission at 12.4 keV. 6CCVD offers precise thickness control (± 1 µm tolerance typical) to optimize transmission for any target X-ray energy (8 keV to 20 keV range).
Advanced Metalization: The paper used 100 nm Ti contacts. 6CCVD offers in-house metalization services including Ti, Pt, Au, Pd, W, and Cu. We can deposit custom electrode patterns (e.g., the four-quadrant design) and thicknesses (e.g., 100 nm) directly onto the SCD surface.
Laser Cutting and Shaping: We offer precision laser cutting for creating custom apertures, holes, or complex shapes required for mounting or integration into existing PCB assemblies (like those shown in Figure 2).

Engineering Support

The comparison between SCD and 4H-SiC highlights a trade-off between ultimate position resolution (SCD) and large aperture/bias-free operation (4H-SiC). 6CCVD’s in-house PhD team specializes in material science and detector physics and can assist researchers in selecting the optimal diamond material:

Resolution vs. Aperture: We provide consultation on whether high-resolution SCD or large-area PCD is the best fit for specific Synchrotron XBPM projects based on required beam size, flux, and resolution targets.
Bias Optimization: Our team can advise on the necessary thickness and bias voltage required for SCD to achieve maximum Charge Collection Efficiency (CCE) for specific applications, ensuring performance exceeds the minimum 90% CCE threshold.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Single-crystal chemical vapour deposition (CVD) diamond detectors are an established transmissive synchrotron beamline diagnostic instrument used for beam position and beam intensity monitoring. A recently commercialized alternative is silicon carbide (4H-SiC) devices. These have the potential to provide the same diagnostic information as commercially available single-crystal CVD diamond X-ray beam position monitors, but with a much larger transmissive aperture. At Diamond Light Source an experimental comparison of the performance of single-crystal CVD diamond and 4H-SiC X-ray beam position monitors has been carried out. A quantitative comparison of their performance is presented in this paper. The single-crystal diamond and 4H-SiC beam position monitors were installed in-line along the synchrotron X-ray beam path enabling synchronous measurements at kilohertz rates of the beam motion from both devices. The results of several tests of the two position monitors’ performance are presented: comparing signal uniformity across the surface of the detectors, comparing kHz intensity measurements, and comparing kHz beam position measurements from the detectors. Each test is performed with a range of applied external bias voltages. A discussion of the benefits and limitations of 4H-SiC and single-crystal CVD diamond detectors is included.

Tech Support

Original Source

DOI: https://doi.org/10.1107/s1600577523005623