Graphene/perovskite Oxide Hybrid Heterostructures Fabricated Directly on Insulating Substrates Via Atmospheric Chemical Vapor Deposition

Graphene and perovskite oxides together offer exciting potential for new materials with enhanced properties, but creating these hybrid structures has traditionally been a difficult and flawed process. Yeongju Choi, Seungjin Lee, and Dongwon Shin, along with colleagues at their institutions, now demonstrate a significantly improved method for directly growing graphene on insulating perovskite oxide substrates. The team achieves this catalyst-free fabrication using atmospheric chemical vapor deposition on materials including strontium titanate, lanthanum aluminate, and lanthanum strontium aluminum tantalate, avoiding the time-consuming and defect-prone transfer processes of previous approaches. This work establishes a reliable, transfer-free route to create these hybrid heterostructures and reveals that graphene growth conditions are remarkably consistent across different perovskite oxide materials, paving the way for more efficient and reproducible materials design.

This innovative approach directly grows graphene on insulating substrates, streamlining fabrication and minimizing defects. Researchers utilized atmospheric pressure chemical vapour deposition, employing gases such as argon, hydrogen, and methane to facilitate graphene formation at high temperatures, exceeding 1050°C. This high temperature promotes the decomposition of carbon sources and initiates graphene nucleation. The team systematically investigated strontium titanate, lanthanum aluminate, and lanthanum strontium tantalate as potential substrates, all precisely oriented for optimal growth.

These materials were chosen for their ability to withstand the high temperatures required for the process. Precise control of temperature and gas flow rates proved essential, establishing conditions for achieving uniform graphene coverage. The researchers successfully demonstrated graphene growth across a substantial area on each material. Comprehensive characterization using techniques such as Raman spectroscopy, X-ray spectroscopy, scanning probe microscopy, and electron microscopy confirmed the quality and uniformity of the graphene films. The study revealed that the optimal growth conditions remained largely consistent regardless of the substrate used, suggesting a universal approach for fabricating these hybrid heterostructures. This method provides a reliable route for creating high-quality graphene/perovskite oxide interfaces, paving the way for exploring novel synergistic phenomena and advanced device applications. Low-temperature measurements of graphene on strontium titanate demonstrated thermo-mechanical and electron-phonon interactions, providing strong evidence for synergistic behaviour within the hybrid material.

Graphene Growth on Titanate Substrates

This research focuses on growing high-quality, single-layer graphene using chemical vapour deposition on three different substrates: strontium titanate, lanthanum aluminate, and lanthanum strontium tantalate. Scientists meticulously optimized growth parameters, including temperature, gas flow rates, and growth time, to achieve uniform, large-area graphene coverage. A temperature of approximately 1070°C proved optimal for achieving the best results. The study demonstrates that the substrate significantly influences graphene quality and growth characteristics. While all three substrates support graphene growth, subtle differences in surface structure and chemistry affect wrinkle formation, defect density, and overall uniformity.

Maintaining a clean substrate surface is critical, as particulate contamination leads to multilayer graphene nucleation and defects. Hydrogen plays a crucial role in the growth process, likely influencing precursor decomposition and graphene layer control. Importantly, the researchers found no evidence of significant oxygen vacancy formation in the strontium titanate substrate during the growth process, suggesting the substrate remains relatively inert. Detailed analysis revealed that the optimal growth temperature is around 1070°C, with higher temperatures potentially leading to additional graphene layers and lower temperatures resulting in incomplete coverage.

The flow rate of methane, a key precursor gas, also requires careful control to minimize defects. Optimizing growth time is crucial, as longer durations do not necessarily improve quality and can lead to unwanted layer formation. Characterization techniques such as Raman spectroscopy, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and near-edge X-ray absorption fine structure spectroscopy were used to assess graphene quality, wrinkle formation, defect density, and substrate properties. These measurements confirm the growth of single-layer graphene and demonstrate the absence of significant oxygen vacancy formation in the strontium titanate substrate. The research highlights the importance of precise process control and substrate cleanliness for achieving high-quality graphene growth, opening up potential applications in electronics, sensors, and energy storage.

Graphene Growth on Perovskite Insulators

This research demonstrates a broadly applicable method for fabricating hybrid materials composed of graphene and perovskite oxides, overcoming the limitations of traditional transfer-based techniques. Scientists successfully grew uniform, continuous monolayers of graphene directly on three insulating substrates, strontium titanate, lanthanum aluminate, and lanthanum strontium tantalate, using atmospheric pressure chemical vapour deposition. A key achievement is the identification of a robust set of growth conditions that consistently yields high-quality heterostructures, suggesting this approach can be extended to other insulating materials stable at high temperatures. Detailed spectroscopic and microscopic characterization confirmed the quality of the fabricated heterostructures and revealed cooperative phenomena at the graphene-substrate interface.