Crystal Nattoo

All Publications

• Optoelectronic Properties of Atomic Layer Deposited and Sputtered MoS2 Films. ACS applied materials & interfaces Nattoo, C. A., Peña, T., Nassiri Nazif, K., Wu, X., Rahimisheikh, S., D'Acunto, G., Bent, S. F., Hadermann, J., Pop, E. 2025

  Abstract

  Large-area growth techniques are needed to bring transition metal dichalcogenide (TMD) films into future applications, but some of these methods have not been sufficiently studied. Here, we evaluate and compare few-layer MoS2 films (<3 nm thick) grown by atomic layer deposition (ALD) and radio frequency (RF) sputtering, using optical, topographical, X-ray spectroscopy, transmission electron microscopy, and electrical device characterization. The electron mobility of ALD films improves 3-fold with rapid thermal annealing, and these improvements are correlated with changes in their Raman spectra, such as a decrease in both the shoulder-to-E2g and LA(M)-to-A1g intensity ratios. On the other hand, the sputtered films had lower mobility and lower transistor current on/off ratio than the ALD samples, and the thermal annealing worsened both their surface roughness and electrical behavior. This work illustrates the utility of nondestructive materials characterization (e.g., Raman, with complementary techniques) to obtain a better picture of material quality before performing time-consuming device fabrication and electrical testing on emerging TMD films.

  View details for DOI 10.1021/acsami.5c04483

  View details for PubMedID 40779262

• Biaxial Strain Transfer in Monolayer MoS2 and WSe2 Transistor Structures. ACS applied materials & interfaces Michail, A., Yang, J. A., Filintoglou, K., Balakeras, N., Nattoo, C. A., Bailey, C. S., Daus, A., Parthenios, J., Pop, E., Papagelis, K. 2024

  Abstract

  Monolayer transition metal dichalcogenides are intensely explored as active materials in 2D material-based devices due to their potential to overcome device size limitations, sub-nanometric thickness, and robust mechanical properties. Considering their large band gap sensitivity to mechanical strain, single-layered TMDs are well-suited for strain-engineered devices. While the impact of various types of mechanical strain on the properties of a variety of TMDs has been studied in the past, TMD-based devices have rarely been studied under mechanical deformations, with uniaxial strain being the most common one. Biaxial strain on the other hand, which is an important mode of deformation, remains scarcely studied as far as 2D material devices are concerned. Here, we study the strain transfer efficiency in MoS2- and WSe2-based flexible transistor structures under biaxial deformation. Utilizing Raman spectroscopy, we identify that strains as high as 0.55% can be efficiently and homogeneously transferred from the substrate to the material in the transistor channel. In particular, for the WSe2 transistors, we capture the strain dependence of the higher-order Raman modes and show that they are up to five times more sensitive compared to the first-order ones. Our work demonstrates Raman spectroscopy as a nondestructive probe for strain detection in 2D material-based flexible electronics and deepens our understanding of the strain transfer effects on 2D TMD devices.

  View details for DOI 10.1021/acsami.4c07216

  View details for PubMedID 39226175