Prevalence of oxygen defects in an in-plane anisotropic transition metal dichalcogenide
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-11-09 |
| Journal | Physical review. B./Physical review. B |
| Authors | Ryan Plumadore, Mehmet BaĆkurt, Justin Boddison-Chouinard, Gregory P. Lopinski, M. Modarresi |
| Institutions | WrocĆaw University of Science and Technology, Izmir Institute of Technology |
| Citations | 14 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation: Defect Engineering in 2D Semiconductors
Section titled âTechnical Analysis and Documentation: Defect Engineering in 2D SemiconductorsâReference: Plumadore et al., âPrevalence of oxygen defects in an in-plane anisotropic transition metal dichalcogenideâ (2020)
Executive Summary
Section titled âExecutive SummaryâThis research utilizes advanced scanning probe techniques and theoretical calculations to characterize defects in the anisotropic 2D semiconductor Rhenium Disulfide ($\text{ReS}_2$). The findings are critical for the development of next-generation opto-electronic and quantum devices, areas where 6CCVDâs highly controlled MPCVD diamond materials offer unparalleled performance and integration capabilities.
- Material Focus: Anisotropic van der Waals layered semiconductor $\text{ReS}_2$ was analyzed using STM/STS and XPS.
- Key Finding: The most common atomic-scale defect is identified as an oxygen atom adsorbed at a sulfur vacancy site, confirming the materialâs susceptibility to atmospheric contamination.
- Electronic Properties: The material is confirmed to be semiconducting with a measured band gap of $1.35 \pm 0.1 \text{ eV}$ and is intrinsically n-doped.
- Methodology: Non-invasive STM/STS was performed under Ultrahigh Vacuum (UHV) conditions across a temperature range of 80K-300K.
- Relevance to 6CCVD: The study highlights the necessity of precise defect control for 2D materials, mirroring the stringent requirements for defect engineering in MPCVD Single Crystal Diamond (SCD) for solid-state quantum applications.
- Sales Driver: 6CCVD provides ultra-high purity, highly polished SCD substrates, ideal for integrating 2D materials or serving as the foundation for quantum emitters, offering superior thermal and chemical stability compared to traditional substrates.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental and theoretical results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Measured Energy Gap ($\text{E}_{\text{gap}}$) | $1.35 \pm 0.1$ | eV | STS measurement (Averaged over multiple samples/tips) |
| Calculated Energy Gap (DFT) | $1.3$ | eV | 3-layer $\text{ReS}_2$ slab (Kohn-Sham gap at $\Gamma$ point) |
| Calculated Energy Gap (GOW0) | $2.3$ | eV | Quasiparticle correction (DFT underestimates gap) |
| Crystal Doping Type | n-doped | N/A | Fermi level ($\text{E}{\text{F}}$) found close to Conduction Band ($\text{E}{\text{c}}$) |
| STM Operating Temperature Range | $80$ to $300$ | K | Variable temperature UHV system |
| STM Bias Voltage ($\text{V}_{\text{b}}$) Range | $-1.60$ to $+0.80$ | V | Used for topographic imaging and defect contrast analysis |
| XPS $\text{Al K}\alpha$ Source Energy | $1486.69$ | eV | Used for core level spectra analysis |
| Re 4f Core Level Positions | $42.6$ and $45$ | eV | $\text{Re } 4\text{f } 7/2$ and $4\text{f } 5/2$ doublets |
| Defect Analysis Area | $4.7$ | $\mu\text{m}^2$ | Total area scanned for defect histogram |
Key Methodologies
Section titled âKey MethodologiesâThe structural, electronic, and defect properties of $\text{ReS}_2$ were determined using a combination of advanced experimental and computational techniques:
- Sample Preparation: Commercial bulk $\text{ReS}_2$ crystals were mechanically cleaved in air and immediately transferred into an Ultrahigh Vacuum (UHV) environment to minimize further atmospheric contamination.
- Scanning Tunneling Microscopy/Spectroscopy (STM/STS): A commercial RHK Pan Freedom system was used under UHV conditions (80K-300K) to visualize the anisotropic lattice structure (Re chains) and measure the local density of states ($\text{dI}/\text{dV}$) to determine the semiconducting gap.
- X-ray Photoelectron Spectroscopy (XPS): XPS spectra were collected using $\text{Al K}\alpha$ radiation (1486.69 eV) to confirm the presence of Rhenium (Re), Sulfur (S), and critically, Oxygen (O) contamination, supporting the defect identification.
- Density Functional Theory (DFT) Calculations: Ab initio calculations (Quantum Espresso, VASP) were performed on single-layer and 3-layer $\text{ReS}_2$ slabs to model band structure, Density of States (DOS), and simulate STM images of various defects (S-vacancy, Re-antisite, O-adsorption).
- Defect Identification: Experimental STM/STS signatures (bright center, dark halo, absence of mid-gap states) were compared directly against simulated images and DOS profiles for theoretical defect models, confirming oxygen adsorption at S-vacancy sites as the dominant defect.
- Stacking Analysis: DFT was used to verify the effect of layer number and stacking configuration (AAA, ABA, ABC) on the calculated energy gap, finding the lowest energy configuration to be ABC stacking.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research on $\text{ReS}_2$ underscores the critical role of material quality and defect control in realizing functional 2D electronic and quantum devices. 6CCVD provides MPCVD diamond materials that are essential for advancing research in these high-stakes fields, offering unmatched purity, thermal management, and surface precision.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Material Recommendation | Rationale and Application |
|---|---|---|
| Quantum Emitters / Opto-electronics (Requires stable, controlled defects) | Single Crystal Diamond (SCD), Optical Grade | SCD is the premier host material for solid-state quantum defects (NV, SiV centers). 6CCVD controls nitrogen/boron incorporation during growth, enabling precise defect engineering, unlike the uncontrolled oxygen defects found in $\text{ReS}_2$. |
| High-Stability Substrates for 2D Transfer (Requires ultra-flat, inert surfaces) | Polycrystalline Diamond (PCD) or SCD Wafers | Diamond offers superior thermal conductivity and chemical inertness. Our polishing achieves $\text{R}{\text{a}} < 1\text{ nm}$ (SCD) and $\text{R}{\text{a}} < 5\text{ nm}$ (PCD), providing the atomically flat surface necessary for high-resolution STM/STS or vdW material transfer. |
| Semiconductor Doping / Electrochemical Studies (Analogous to $\text{ReS}_2$ n-doping) | Boron-Doped Diamond (BDD) | 6CCVD supplies BDD films with tunable p-type conductivity, ideal for electrochemical applications, high-power electronics, or as a highly stable electrode material in complex heterostructures. |
Customization Potential
Section titled âCustomization PotentialâThe integration of 2D materials into functional devices often requires non-standard geometries and precise electrical contacts. 6CCVD specializes in meeting these exact specifications:
- Custom Dimensions: We provide plates and wafers up to 125mm in diameter (PCD) and custom-cut SCD pieces, allowing researchers to scale up device fabrication or utilize unique substrate sizes.
- Thickness Control: We offer precise thickness control for both SCD and PCD films, ranging from $0.1\text{ ”m}$ to $500\text{ ”m}$, and substrates up to $10\text{ mm}$ thick.
- Advanced Metalization: To facilitate device integration and electrical measurements (like those requiring precise tunneling contacts), 6CCVD offers in-house deposition of critical metals including Au, Pt, Pd, Ti, W, and Cu. This capability ensures reliable, low-resistance contacts for complex 2D heterostructures.
Engineering Support
Section titled âEngineering SupportâThe identification of oxygen defects in $\text{ReS}_2$ highlights the challenges inherent in working with air-sensitive 2D materials. 6CCVDâs in-house PhD team provides expert consultation to mitigate material challenges:
- Material Selection: Our experts assist researchers in selecting the optimal diamond grade (SCD, PCD, BDD) and surface termination for specific applications, such as integrating 2D materials or developing stable solid-state quantum platforms.
- Defect Control: We offer specialized growth recipes to control the density and type of defects (e.g., nitrogen vacancies) in diamond, crucial for projects involving atomic-scale opto-electronic devices and quantum emitters, providing a level of control far exceeding that achievable in naturally occurring vdW materials.
- Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of sensitive, high-value materials directly to UHV labs and cleanroom facilities worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Atomic scale defects in semiconductors enable their technological\napplications and realization of novel quantum states. Using scanning tunneling\nmicroscopy and spectroscopy complemented by ab-initio calculations we determine\nthe nature of defects in the anisotropic van der Waals layered semiconductor\nReS$_2$. We demonstrate the in-plane anisotropy of the lattice by directly\nvisualizing chains of rhenium atoms forming diamond-shaped clusters. Using\nscanning tunneling spectroscopy we measure the semiconducting gap in the\ndensity of states. We reveal the presence of lattice defects and by comparison\nof their topographic and spectroscopic signatures with ab initio calculations\nwe determine their origin as oxygen atoms absorbed at lattice point defect\nsites. These results provide an atomic-scale view into the semiconducting\ntransition metal dichalcogenides, paving the way toward understanding and\nengineering their properties.\n