ISM2019 (Microscopy)


Sreedhara M B 1 C. N. R. Rao 2
1Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel
2International Centre for Material Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India

Atomic layer deposition (ALD) is a unique thin film deposition method, suitable for depositing uniform and conformal films with atomic accuracy.1 Single crystalline materials with specific phases are usually preferable as the active and interfacial films for devices but most of the ALD grown materials are limited to polycrystalline and amorphous.2 Here we present the growth and characteristics of single crystalline films of pristine MoS2 and V2O5 by ALD. Employing thermal ALD, we have grown crystalline MoS2 films on c-axis Al2O3 substrate. Details of the atomic registry between MoS2 and sapphire has been revealed by HRTEM and shows (00l) preferred orientation with c-sapphire. The compressive strain of 2% in the first MoS2 layer and 0.6% in the second layer has been observed at the interface. The crystallographic relationships between the films and the substrate are Al2O3 || MoS2 and Al2O3 || MoS2. Planar faults are observed in the TEM and are due discontinuous Mo and S atomic planes shared between adjacent layers. Interestingly, the films show a high density of nanowalls and exhibit excellent electrochemical characteristics in Na-ion battery.3 Single crystalline epitaxial V2O5 films have been deposited on c-Al2O3 using plasma enhanced ALD. The HRTEM images show the smooth interface between the Al2O3 and V2O5 film with epitaxial growth. The crystallographic relations are found be V2O5||Al2O3 and V2O5|| <11̅02>Al2O3 and undergo compressive strain at the initial few monolayer growth to adjust epitaxially with the substrate. The observed compressive strain is consistent with Raman signatures. Humidity sensor based on the V2O5 film has superior sensitivity relative to other oxide-based sensors.4

  1. Miikkulainen, V.; Leskelä, M.; Ritala, M.; Puurunen, R. L., Appl. Phys. 2013, 113 (2), 021301.
  2. Wen, L.; Zhou, M.; Wang, C.; Mi, Y.; Lei, Y., Energy Mater. 2016, 6, 1600468.
  3. B. Sreedhara, Subhra Gope, Badri Vishal, Ranjan Datta, Aninda J. Bhattacharyya, C. N. R. Rao, J. Mater. Chem. A, 2018, 6, 2302.
  4. B. Sreedhara, J. Ghatak, B. Bharath, and C. N. R. Rao, ACS Appl. Mater. Interfaces 2017, 9, 3178.