Mn-intercalated MoSe2 under pressure - Electronic structure and vibrational characterization of a dilute magnetic semiconductor

At a Glance

Metadata	Details
Publication Date	2020-09-22
Journal	The Journal of Chemical Physics
Authors	Shunda Chen, Virginia L. Johnson, Davide Donadio, Kristie J. Koski, Shunda Chen
Institutions	University of California, Davis, George Washington University
Citations	9
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Pressure 2D Material Characterization

Executive Summary

This research investigates the electronic and vibrational properties of Mn-intercalated Molybdenum Diselenide (MoSe₂) under high pressure, a study critically dependent on high-quality diamond components.

Core Application: Development of dilute magnetic semiconductors (DMS) and new materials for spintronic applications by chemically and thermodynamically tuning 2D layered materials.
Methodology: Pressure-dependent Raman scattering was performed using a Diamond Anvil Cell (DAC) up to 7 GPa, requiring robust, high-purity diamond anvils for optical access and mechanical integrity.
Key Material Modification: Intercalation of manganese (Mn) into the van der Waals gap of MoSe₂ shifts the Fermi level into the conduction band, resulting in an n-type semiconductor with significant spin polarization.
Pressure Effects: High pressure activates previously Raman-inactive phonon modes (A₂u) and induces a new Mn-Se collective vibrational mode (~250 cm⁻¹) upon decompression, suggesting pressure-induced bonding and structural transitions.
Mechanical Enhancement: Mn intercalation increases the material’s stiffness, raising the isothermal bulk modulus (B_T) from 45.7 GPa (pristine MoSe₂) to 51.3 GPa (Mn_0.125MoSe₂).
Strategic Advantage: The technique of intercalation combined with high pressure offers a route to bypass concentration limitations typically found in dilute magnetic doping, enabling high concentrations of spin-polarized carriers (up to ~2 x 10²⁰ cm⁻³).

Technical Specifications

Hard data extracted from the research paper detailing experimental and calculated parameters.

Parameter	Value	Unit	Context
Maximum Applied Pressure	7	GPa	Hydrostatic conditions maintained in the DAC
DAC Anvil Culet Diameter	0.6	mm	Size of the Boehler anvils used for compression
Gasket Hole Diameter	250	µm	Sample containment area within the DAC
MoSe₂ Platelet Size	1 - 100	µm	Single-crystal platelets used for intercalation
MoSe₂ Thickness Range	Tens of nm to microns	µm	Thickness of the layered material
Intercalant Concentration (Experimental)	~1 - 2	atomic %	Mn_0.02MoSe₂
Experimental Lattice Parameter ‘a’ (Mn_0.02MoSe₂)	3.336 (±0.005)	Å	1.5% in-plane expansion upon intercalation
Experimental Lattice Parameter ‘c’ (Mn_0.02MoSe₂)	12.940 (±0.005)	Å	Cross-plane expansion upon intercalation
Ambient Magnetic Moment (Mn_0.03MoSe₂)	5.00	µ_B	Total magnetic moment at 0 GPa
Calculated Bulk Modulus (Pristine MoSe₂)	47.9	GPa	DFT calculation (Experimental: 45.7 GPa)
Calculated Bulk Modulus (Mn_0.125MoSe₂)	51.3	GPa	DFT calculation, indicating increased stiffness
New Mn-Se Raman Mode Frequency	~250	cm⁻¹	Observed post decompression
Spin-Polarized Carrier Concentration (2H Phase)	Up to ~2 x 10²⁰	cm⁻³	Predicted maximum for spintronic applications

Key Methodologies

A concise, ordered list detailing the experimental and computational recipe parameters.

Host Material Preparation: Molybdenum diselenide (MoSe₂) single-crystal platelets were deposited onto fused silica substrates.
Manganese Intercalation: Zero-valent manganese was intercalated via the decomposition of dimanganese decacarbonyl (C₁₀O₁₀Mn₂) in dilute acetone.
Reaction Conditions: The reaction was conducted under an inert N₂ atmosphere at a controlled temperature of 48 °C for approximately 1.5 to 2.5 hours.
High-Pressure Setup: Pressures up to 7 GPa were generated using an Alamax EasyLab mini-Bragg Diamond Anvil Cell (DAC) equipped with 0.6 mm culets.
Pressure Medium: A 4:1 v/v methanol:ethanol solution was used to ensure relatively hydrostatic pressure conditions.
Raman Excitation: Raman spectra were acquired using a 532 nm Coherent Sapphire laser operating at <1 mW power on the sample, utilizing an 1800 groove/mm grating for high resolution.
Structural Confirmation: Intercalation and structural integrity were confirmed using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Transmission Electron Microscopy (TEM), and X-ray Diffraction (XRD).
Computational Modeling: Density Functional Theory (DFT) calculations were performed using the LSDA+U method (Hubbard U_eff = 4 eV for Mo and Mn) and Density-Functional Perturbation Theory (DFPT) to model phonon frequencies under pressure.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-performance optical components capable of withstanding extreme mechanical stress while maintaining optical clarity. 6CCVD specializes in the MPCVD diamond materials necessary to replicate and advance high-pressure studies in spintronics and 2D materials.

Applicable Materials for High-Pressure Research

Application Requirement	6CCVD Material Recommendation	Technical Justification
Diamond Anvil Cell (DAC) Anvils	Optical Grade Single Crystal Diamond (SCD)	SCD offers the highest mechanical strength and lowest defect density, essential for achieving and maintaining hydrostatic pressures up to 7 GPa and far beyond. Our SCD is Type IIa, ensuring excellent transparency for the 532 nm Raman laser used in this study.
High-Resolution Optical Measurements	Ultra-Low Birefringence SCD	Critical for polarized Raman scattering and minimizing signal distortion under high strain. 6CCVD’s SCD is grown and processed to achieve Ra < 1 nm polishing, ensuring minimal light scattering and superior optical performance.
High-Pressure Substrates	SCD Substrates (up to 10 mm thick)	For future experiments requiring integrated electrical contacts or thermal management, our thick SCD substrates provide unmatched thermal conductivity and mechanical stability.
Integrated Spintronic Devices	Boron-Doped Diamond (BDD)	For electrical resistivity studies mentioned in the conclusions, BDD offers a stable, conductive platform for creating electrodes or active layers in high-pressure environments.

Customization Potential for Advanced Spintronics

The complexity of 2D material research often demands non-standard geometries and integrated functionalities. 6CCVD is uniquely positioned to support the next generation of high-pressure spintronic experiments:

Custom Dimensions and Shaping: While the paper used 0.6 mm culets, 6CCVD can supply SCD plates and wafers up to 125 mm in size, which can be custom-cut and shaped using our in-house laser processing capabilities to meet precise DAC anvil geometries, including specific culet sizes and bevels.
Advanced Metalization: The development of spintronic devices requires precise electrode deposition. 6CCVD offers internal metalization services, including deposition of Au, Pt, Pd, Ti, W, and Cu, allowing researchers to integrate electrical contacts directly onto diamond substrates or protective layers for in situ resistivity measurements under pressure.
Surface Finish: Our SCD polishing capability achieves surface roughness (Ra) < 1 nm, ensuring optimal optical coupling and minimal scattering losses, crucial for sensitive Raman and optical measurements.

Engineering Support

6CCVD’s in-house PhD team can assist with material selection for similar High-Pressure 2D Material Intercalation projects. We provide consultation on optimizing diamond grade, orientation, and geometry to maximize experimental pressure limits and optical throughput for DAC applications.

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

View Original Abstract

Intercalation offers a promising way to alter the physical properties of two-dimensional (2D) layered materials. Here, we investigate the electronic and vibrational properties of 2D layered MoSe2 intercalated with atomic manganese at ambient and high pressure up to 7 GPa by Raman scattering and electronic structure calculations. The behavior of optical phonons is studied experimentally with a diamond anvil cell and computationally through density functional theory calculations. Experiment and theory show excellent agreement in optical phonon behavior. The previously Raman inactive A2u mode is activated and enhanced with intercalation and pressure, and a new Raman mode appears upon decompression, indicating a possible onset of a localized structural transition, involving the bonding or trapping of the intercalant in 2D layered materials. Density functional theory calculations reveal a shift of the Fermi level into the conduction band and spin polarization in MnxMoSe2 that increases at low Mn concentrations and low pressure. Our results suggest that intercalation and pressurization of van der Waals materials may allow one to obtain dilute magnetic semiconductors with controllable properties, providing a viable route for the development of new materials for spintronic applications.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0018716

References

2010 - First-principles theory of dilute magnetic semiconductors [Crossref]
2010 - A ten-year perspective on dilute magnetic semiconductors and oxides [Crossref]
2010 - A window on the future of spintronics [Crossref]
2014 - Dilute ferromagnetic semiconductors: Physics and spintronic structures [Crossref]
2013 - Mn-doped monolayer MoS2: An atomically thin dilute magnetic semiconductor [Crossref]
2013 - Long-range ferromagnetic ordering in manganese-doped two-dimensional dichalcogenides [Crossref]
2016 - Robust ferromagnetism in Mn-doped MoS2 nanostructures [Crossref]
2015 - Manganese doping of monolayer MoS2: The substrate is critical [Crossref]
2018 - Tunable magnetic coupling in Mn-doped monolayer MoS2 under lattice strain [Crossref]
2017 - Intrinsic ferromagnetism in Mn-Substituted MoS2 nanosheets achieved by supercritical hydrothermal reaction [Crossref]