A Versatile Method for Nano‐Fabrication on Diamond Film - Flexible Diamond Metasurfaces as a Demonstration
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2025-04-19 |
| Journal | Advanced Optical Materials |
| Authors | Yi‐Cheng Wang, Jixiang Jing, Yumeng Luo, Linjie Ma, Xiaomin Wang |
| Institutions | Peking University, Dongguan University of Technology |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research introduces a novel and versatile nano-fabrication technique, “mask-transferring by sugar,” specifically designed for ultrathin and flexible diamond films. This method addresses critical limitations associated with conventional lithography on diamond materials.
- Novel Fabrication Method: The sugar-transfer technique enables high-precision, large-scale, and repeatable pattern definition on diamond films, bypassing issues like charge accumulation and proximity effects inherent to direct E-beam lithography (EBL).
- Material Foundation: The method utilizes scalable, ultrathin (approx. 600 nm) diamond films acquired via edge-exposed exfoliation, which possess an extremely low buried surface roughness (Ra: approx. 1.18 nm).
- Overcoming Limitations: The transfer process avoids direct spin-coating on fragile or curved diamond films, preventing shattering, cracking, and uneven resist distribution.
- High Resolution and Accuracy: Masks fabricated via sugar transfer exhibit superior geometrical resolution and accuracy compared to those produced by conventional direct lithography on diamond.
- Device Demonstration: The technique successfully fabricated the first flexible all-diamond metasurfaces on a PET substrate, functioning as structural colors.
- Optical Performance: The resulting structural colors demonstrate ultra-high reflectance (up to 88.78%), wide color gamut (spanning the entire visible range), and robust stability under mechanical bending deformation.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Film Thickness | approx. 600 | nm | Grown by MPCVD on Si substrate. |
| Buried Surface Roughness (Ra) | approx. 1.18 | nm | Ultra-flat surface achieved after exfoliation. |
| As-Grown Surface Roughness (Ra) | 44.58 | nm | Roughness of the top, as-grown surface. |
| CVD Microwave Power | 3400 | W | Diamond membrane growth parameter. |
| CVD Temperature | 900 | °C | Diamond membrane growth parameter. |
| EBL Dose (Mask Preparation) | 750 | µC cm-2 | Used for patterning the ITO template. |
| Sugar Solidification Temperature | 70 | °C | Heating temperature for mask transfer. |
| ICP Etching Gas Flow (O2) | 80 | sccm | Inductive Coupled Plasma etching flow rate. |
| ICP Etching RF Power | 200 | W | Inductive Coupled Plasma etching power. |
| ICP Etching Bias Voltage | 60 | W | Inductive Coupled Plasma etching bias. |
| ICP Etching Cavity Pressure | 10 | mTorr | Inductive Coupled Plasma etching pressure. |
| Max Metasurface Reflectance | 88.78 | % | Achieved at p=370 nm, g=100 nm. |
| Metasurface Period (p) Range | 280 to 400 | nm | Adjusted for color tuning (blue to red). |
| Metasurface Gap (g) Range | 90 to 140 | nm | Adjusted for color tuning. |
| Substrate Material | PET | 1.25 mm thick | Flexible substrate for metasurface device. |
Key Methodologies
Section titled “Key Methodologies”The fabrication process is divided into three main stages: Diamond Film Acquisition, Mask Preparation and Sugar Transfer, and Diamond Etching.
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Diamond Film Growth and Exfoliation:
- Diamond film (approx. 600 nm thick) was grown heteroepitaxially on a 2-inch silicon wafer using Microwave Plasma Chemical Vapor Deposition (MPCVD).
- Growth parameters included 3400 W microwave power, 900 °C temperature, and 15 sccm CH4 flow.
- The film was peeled off the Si substrate using edge-exposed exfoliation with sticky tape, yielding a freestanding, transferable film with an ultra-flat buried surface (Ra approx. 1.18 nm).
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Mask Preparation (on ITO Template):
- A conductive Indium-Tin-Oxide (ITO) film on a PET substrate was used as the template for the mask.
- Hydrogen Silsesquioxane (HSQ) resist was spin-coated and patterned using E-beam lithography (EBL) at a dose of 750 µC cm-2.
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Mask Transferring by Sugar:
- A sugar solution (corn syrup, cane sugar, deionized water) was dropped onto the patterned ITO template.
- The solution was solidified in a heating oven at 70 °C for several hours.
- The solid sugar mask was peeled off the PET template (assisted by residual stress) and gently placed onto the diamond film.
- The sugar was subsequently dissolved using deionized water, leaving the defined mask pattern directly on the diamond surface.
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Diamond Etching and Cleaning:
- Diamond etching was performed using Inductive Coupled Plasma (ICP) etching with O2 gas.
- Key ICP parameters were set to 80 sccm O2 flow, 200 W RF power, 60 W bias voltage, and 10 mTorr cavity pressure.
- The remaining mask material was removed using a KOH solution, resulting in the final all-diamond metasurface structure.
Commercial Applications
Section titled “Commercial Applications”The development of a versatile, high-precision nano-fabrication method for ultrathin, flexible diamond films unlocks potential in several high-tech sectors:
- Flexible and Wearable Displays: The stability of the all-diamond structural colors under bending, combined with the flexible PET substrate, makes this ideal for durable, high-quality wearable display applications.
- Advanced Photonics and Optics: Enables the fabrication of high-performance diamond photonic devices, including:
- Metasurfaces (structural colors, high-efficiency light manipulation).
- Waveguides and Resonators.
- Metalenses and Diffractive Optics.
- Information Security and Encryption: The high saturation and wide gamut of the structural colors are suitable for advanced optical encryption and anti-counterfeiting technologies.
- Next-Generation Electronics: The ability to pattern ultra-flat, transferable diamond films supports the development of diamond-based transistors, P-N junctions, and other high-power/high-frequency electronic devices.
- Quantum Sensing: Precise nanofabrication is crucial for creating structures (like NV centers) used in diamond-based quantum sensors, including thermometers and magnetometers.
- Harsh Environment Devices: Diamond’s exceptional chemical and mechanical durability ensures the longevity of devices (e.g., displays or sensors) in extreme operating conditions.
View Original Abstract
Abstract Diamond exhibits unique performance across a wide range of applications due to its enormous presentable properties in electronic, photonic, and quantum fields. Yet heterogeneous integration of diamonds for on‐chip functionalities, like 2D materials, remains challenging due to the hard acquisition of scalable, transferable, and ultrathin diamond samples. Recently, edge‐exposed exfoliation is demonstrated as an effective way to produce wafer‐scale, freestanding, and ultrathin diamond films. However, the incompatibility of the newly developed diamond film with conventional nano‐fabrication methods makes it difficult to fabricate diamond film into practical devices. Herein, the mask‐transferring by sugar is demonstrated as a versatile method for pattern‐definition on diamond films, which shows satisfying geometrical resolution and accuracy comparing to conventional approaches. Additionally, based on this method, the flexible all‐diamond metasurfaces functioning as structural colors are achieved, which indicates its wide potential for fabricating more diamond‐related devices.