Large Area Fabrication of Semiconducting Phosphorene by Langmuir-Blodgett Assembly - PubMed (original) (raw)

Large Area Fabrication of Semiconducting Phosphorene by Langmuir-Blodgett Assembly

Harneet Kaur et al. Sci Rep. 2016.

Abstract

Phosphorene is a recently new member of the family of two dimensional (2D) inorganic materials. Besides its synthesis it is of utmost importance to deposit this material as thin film in a way that represents a general applicability for 2D materials. Although a considerable number of solvent based methodologies have been developed for exfoliating black phosphorus, so far there are no reports on controlled organization of these exfoliated nanosheets on substrates. Here, for the first time to the best of our knowledge, a mixture of N-methyl-2-pyrrolidone and deoxygenated water is employed as a subphase in Langmuir-Blodgett trough for assembling the nanosheets followed by their deposition on substrates and studied its field-effect transistor characteristics. Electron microscopy reveals the presence of densely aligned, crystalline, ultra-thin sheets of pristine phosphorene having lateral dimensions larger than hundred of microns. Furthermore, these assembled nanosheets retain their electronic properties and show a high current modulation of 104 at room temperature in field-effect transistor devices. The proposed technique provides semiconducting phosphorene thin films that are amenable for large area applications.

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Figures

Figure 1

Figure 1. Characterization of BP crystal and its exfoliated suspension.

(a) X-ray diffraction spectra of BP crystal. (b) Raman spectra of the BP crystal. Inset: Optical image of crystal. (c) Scanning electron microscopy of BP revealing its layered structure. Inset: EDX spectra of BP crystal (left) and magnified SEM revealing the presence of sharp edges (right). (d) Tauc plot of exfoliated BP suspension. Inset: Digital image of exfoliated BP suspension. (e) Atomic force microscopic image of the drop-cast nanosheets of exfoliated BP. Inset: Height profile of phosphorene nanosheets.

Figure 2

Figure 2. Surface morphology of LB assembled phosphorene nanosheets on SiO2/Si substrate.

(a) FESEM of small nanosheets (S-Ex BP) deposited at a surface pressure of 40 mN/m. (b) Magnified FESEM image S-Ex BP. (c) AFM of S-Ex BP. Inset: Height profile of nanosheets. (d) FESEM of large nanosheets (L-Ex BP) deposited at a surface pressure of 40 mN/m. (e) Magnified FESEM image of L-Ex BP. (f) AFM of L-Ex BP. Inset: Height profile of nanosheets.

Figure 3

Figure 3. HRTEM of LB assembled phosphorene on TEM grids.

(a) Thin sheets of phosphorene. Inset (i): Aggregate of thin sheets of phosphorene, (ii): Atomic scale image of nanosheets. (b–e) Selected area electron diffraction patterns. (f) Atomic scale micrograph of phosphorene. (g) Interface between two sheets of phosphorene. Inset (iii): Honeycomb microstructure of phosphorene.

Figure 4

Figure 4. Field effect transistor with LB assembled phosphorene as a conducting channel material.

(a) Digital image of the device. (b) Optical image of channel. (c) Magnified optical image showing a connecting nanosheet between source and drain. (d) AFM of the device. Inset: Height profile of nanosheet. (e) Variation of drain current IDS with gate voltage VGS (left y-axis is the linear scale, and right y-axis is the logarithmic scale). (f) Variation of drain current IDS with the drain voltage VDS for different gate voltages VGS.

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