[Paper Review] Synthesis and electronic structure characterization of diamane

Feng Ke, Lingkong Zhang+14 more|arXiv (Cornell University)|Feb 5, 2019

Graphene research and applicationsMaterials Science3 citations

TL;DR

This study reports the first successful synthesis and electronic characterization of free-standing, trilayer and thicker diamane films via high-pressure compression of graphene above 20 GPa, with stable recovery to ambient conditions. Electrical, XRD, Raman, and optical absorption measurements combined with band structure calculations reveal an indirect bandgap of 2.8 eV, establishing diamane as a promising carbon-based semiconductor with potential for electronic applications.

ABSTRACT

Atomically thin graphite, known as graphene, has been a marvel in material science because of its exceptional properties, novel physics and promising applications. Atomically thin diamond, called diamane, has also attracted considerable scientific interest due to its potential physical and mechanical properties. However, until now there has been no reports of successful synthesis of a free-standing pristine diamane film. Here, we report the synthesis and electronic structure characterization of diamane. Electrical measurements, x-ray diffraction and theoretical simulations reveal that trilayer and thicker graphene transform to hexagonal diamane (h-diamane) when compressed to above 20 GPa, which can be preserved down to few GPa. Raman studies indicate that the sample quenched from high pressure and high temperature also has a h-diamane structure, i.e., h-diamane is recovered back to ambient conditions. Optical absorption and band structure calculations reveal an indirect energy gap of 2.8 eV in the diamane film. Compared to gapless graphene, diamane with sizable bandgap may open up new applications of carbon semiconductors.

Motivation & Objective

• To achieve the synthesis of free-standing, pristine diamane films, which had not been experimentally realized despite theoretical interest.
• To characterize the electronic structure of diamane under ambient conditions following high-pressure synthesis.
• To determine the stability and structural integrity of diamane after decompression to ambient pressure.
• To measure the electronic bandgap of diamane and compare it to gapless graphene.
• To validate the existence of hexagonal diamane (h-diamane) through experimental and theoretical methods.

Proposed method

• High-pressure compression of trilayer and thicker graphene films to above 20 GPa using a large-volume press.
• In situ X-ray diffraction to monitor structural phase transitions during compression.
• Raman spectroscopy to confirm the presence of h-diamane structure after quenching from high-pressure and high-temperature conditions.
• Electrical transport measurements to probe the electronic properties of the recovered diamane films.
• Optical absorption spectroscopy to determine the bandgap of the diamane film.
• Density functional theory (DFT) band structure calculations to interpret the electronic structure and confirm the indirect bandgap.

Experimental results

Research questions

• RQ1 Can free-standing, pristine diamane be synthesized experimentally under high pressure?
• RQ2 Is the hexagonal diamane (h-diamane) phase stable upon decompression to ambient conditions?
• RQ3 What is the electronic band structure and bandgap of the synthesized diamane film?
• RQ4 How does the electronic structure of diamane differ from that of gapless graphene?
• RQ5 Can experimental measurements such as Raman and optical absorption confirm the predicted h-diamane structure?

Key findings

• Trilayer and thicker graphene films transform into hexagonal diamane (h-diamane) under compression above 20 GPa.
• The h-diamane phase is preserved down to a few gigapascals, indicating structural stability upon decompression.
• Raman spectroscopy confirms the recovery of the h-diamane structure after quenching from high-pressure and high-temperature conditions.
• Optical absorption measurements reveal an indirect bandgap of 2.8 eV in the diamane film.
• Theoretical band structure calculations support the presence of an indirect bandgap of 2.8 eV, consistent with experimental observations.
• The results establish diamane as a wide-bandgap semiconductor, contrasting with the gapless nature of graphene.