Channeling effect in polycrystalline deuterium-saturated CVD diamond target bombarded by deuterium ion beam

At a Glance

Metadata	Details
Publication Date	2015-02-02
Journal	Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
Authors	A. Bagulya, O. D. Dalkarov, M. A. Negodaev, A. S. Rusetskiĭ, A. P. Chubenko
Institutions	National Research Nuclear University MEPhI, P.N. Lebedev Physical Institute of the Russian Academy of Sciences
Citations	20
Analysis	Full AI Review Included

Technical Documentation and Material Sourcing Analysis: Channeling Effect in Polycrystalline Deuterium-Saturated CVD Diamond Targets

This document analyzes the research paper detailing the use of polycrystalline CVD diamond (PCD) as a deuterium-saturated target for D-D nuclear reaction experiments, focusing on the ion channeling effect. This application highlights the demand for highly controlled, thick PCD materials, a core capability of 6CCVD.

Executive Summary

Critical Application Validation: The research validates Polycrystalline CVD (PCD) diamond as a high-efficiency, fixed-target material for low-energy D-D nuclear fusion experiments (d+d → n + ³He).
Significant Anisotropy Observed: A strong angular dependence of neutron yield was measured, demonstrating a yield 3 times higher when the deuterium beam was normal to the target surface (β=0°) compared to oblique incidence (β=±45°).
Ion Channeling Mechanism: This high anisotropy is attributed to the presence of narrow vertical channels (grain boundaries) and aligned crystallites inherent in the columnar growth structure of the CVD diamond film, which facilitate enhanced penetration of the 20 keV D ions.
Material Specifications: Experiments utilized a 400 µm thick, ‘black diamond’ grade PCD film, characterized by a highly defective columnar structure (crystallites up to 100 µm on the growth side).
Specialized Preparation: Targets required advanced post-processing, including substrate removal via complex acid etching, laser cutting (Nd:YAG, 10 nm pulse), and subsequent deuterium saturation via high-voltage electrolysis (50 V, 20-30 mA/cm²).
6CCVD Value Proposition: The requirement for thick, custom-dimensioned PCD targets with controlled columnar morphology directly aligns with 6CCVD’s advanced MPCVD growth and processing services.

Technical Specifications

Parameter	Value	Unit	Context
Target Material	Polycrystalline CVD Diamond (PCD)	N/A	Columnar structure, ‘black diamond’ grade
Diamond Film Thickness	400	µm	Produced by plasma-chemical reactor (STS-100)
Final Target Diameter	18	mm	Cut from larger wafer using Nd:YAG laser
Crystallite Lateral Size (Growth Side)	≈50	µm	Quadratic fragments, evidence of vertical columns
Growth Temperature (T_sub)	920	°C	Substrate temperature during CVD
Growth Pressure	90	Torr	Chamber pressure
Growth Gas Mixture	CH₄ (10%), O₂ (0.9%)	N/A	Total gas flow: 0.5 l/min
Primary Impurity Concentration (H)	Up to 1000	ppm	Located on grain boundaries (C-H connections)
Silicon Admixture	~10	ppm	Contained in layer adjacent to substrate
Deuterium Ion Beam Energy (E_d)	20	keV	Used at HELIS facility
Deuterium Ion Beam Current (I_d)	50-60	µA	Used in target irradiation
D Saturation Voltage	50	V	Applied during electrolysis (D₂O/LiOD solution)
D Saturation Current Density	20-30	mA/cm²	Applied during electrolysis
Max Neutron Yield Ratio	3	N/A	Longitudinal yield at β=0° vs. β=±45°
Neutron Energy (d+d reaction)	2.45	MeV	Primary neutron energy detected

Key Methodologies

The following recipe parameters and process steps were crucial for the fabrication and testing of the high-performance deuterium-saturated PCD target:

CVD Synthesis of PCD Film: The 400 µm film was grown in an STS-100 reactor using 3.3 kW microwave power (2.45 GHz). The recipe utilized a high-pressure (90 Torr) and high-temperature (920 °C) regime with 10% CH₄ and 0.9% O₂ to intentionally induce the high-defect, columnar ‘black diamond’ structure necessary for channeling effects.
Post-Growth Separation: The diamond film was separated from the 3 mm thick, 57 mm diameter silicon substrate using a highly corrosive chemical mixture (hydrofluoric, nitric, and acetic acids).
Target Structuring: The large film was precisely cut into 18 mm diameter discs using a Nd:YAG laser (pulse duration of 10 nm; frequency of 10 kHz).
Graphite Remediation: To remove graphitic edges created by the laser cutting process, the discs underwent a high-temperature oxidation step in air at 580 °C for 1 hour.
Deuterium Loading: Saturation was achieved via electrolysis, immersing the diamond target as a cathode in a 0.3M solution of LiOD in D₂O. Saturation parameters were fixed at 50 V applied voltage and a current density between 20-30 mA/cm².
Nuclear Testing: The target was mounted in a water-cooled, rotating holder and irradiated with a 20 keV deuterium ion beam (50-60 µA). Neutron flux yield was measured longitudinally and transversely using ³He detectors as a function of target angle (β).

6CCVD Solutions & Capabilities

This research demonstrates a critical need for precision-engineered, thick CVD diamond materials for advanced nuclear physics and high-flux target applications. 6CCVD is uniquely positioned to supply the materials required to replicate, scale, or extend this research, offering control over the key material parameters driving the channeling phenomenon.

Applicable Materials

To achieve the columnar structure and thickness required for deep ion penetration and channeling effects, 6CCVD recommends:

Nuclear Grade Polycrystalline CVD Diamond (PCD): Optimized for target applications requiring deep implantation or saturation. We can replicate the columnar growth necessary for the observed channeling effect by controlling substrate temperature and gas phase parameters during synthesis.
Specific Recommendations:
- Thickness Control: We offer PCD layers precisely tailored to the experimental requirements, spanning from 0.1 µm up to 500 µm, matching the 400 µm requirement.
- Substrate/Handle Layer Options: We provide targets pre-separated (free-standing) or mounted on various custom substrates (Si, Mo, W) depending on cooling and mounting needs.

Customization Potential

The experimental setup required tight control over dimensions, geometry, and surface preparation, capabilities that are standard services at 6CCVD:

Requirement in Paper	6CCVD Solution	Advantage for Research
Custom Dimensions (18 mm disc)	Precision laser cutting and shaping services.	Targets can be provided in any custom dimension up to 125 mm diameter.
Substrate Removal (Etching)	Standard chemical or mechanical substrate lift-off capability.	Ensures free-standing target films without Si contamination or mechanical stress.
Polishing Requirements	Polishing services down to Ra < 5 nm for inch-size PCD.	While this application used a rough growth surface, we can supply targets with controlled surface roughness for tailored diffusion studies.
Material Doping/Impurity Control	Capability for controlled Boron-Doped Diamond (BDD) synthesis.	Allows researchers to study D-saturation and channeling in materials with varying conductive properties or intrinsic defect concentrations (e.g., nitrogen or hydrogen).

Engineering Support

The observed channeling effect is highly dependent on the crystal structure and orientation. 6CCVD’s in-house material scientists and PhD-level engineers specialize in tailoring CVD growth parameters to control grain size, grain boundary structure, and crystal orientation (e.g., producing highly [100] textured films).

We offer consultation for projects related to:

High-Energy Physics Targets: Designing optimal diamond targets for neutron generation, beam monitoring, or particle detection.
Fusion Research: Optimizing diamond structure for enhanced hydrogen isotope (H, D, T) retention or release studies.
Microstructure Engineering: Controlling the columnar morphology to maximize ion channeling or, conversely, minimize it for detector applications.

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

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.nimb.2015.01.021