The transfer of monolayer molybdenum disulfide (1L‐MoS2) onto any target substrates is inevitable for the next generation of optoelectronic devices such as flexible electronics. However, the existing ...post‐transfer treatments are ineffective for the complete removal of poly(methyl methacrylate) (PMMA) polymer, which is usually used as carrier polymer in the wet‐transfer method. The presence of PMMA residues seriously degrades the intrinsic properties of any 2D materials. Several new cleaning methods such as annealing, ozone cleaning, and acetone treatment adopted in this report are found to be ineffective for the complete removal of PMMA residues on the transferred 1L‐MoS2 film. A new chemical route is developed and demonstrated with a PMMA nonsolvent, ethanol, and ultraclean transferred 1L‐MoS2 is obtained after 96 h hot ethanol treatment. An interfacial diffusion model is proposed for the mechanism of PMMA removal from the 1L‐MoS2 surface. To observe the effect of cleaning process on electrical properties, 1L‐MoS2 field‐effect transistor (FET) devices are fabricated. An enhancement of 80%–85% in the electron mobility is achieved for ultraclean 1L‐MoS2. One order improvement in the FET parameters such as ON/OFF ratio and the subthreshold slope is also observed. It is believed that this novel method can also be applicable for other 2D materials.
Several new cleaning methods such as ozone cleaning, annealing, and acetone treatment are found to be ineffective for the complete removal of poly(methyl methacrylate) (PMMA) residues from wet‐transferred monolayer MoS2. In this context, a simple yet effective chemical treatment, 96 h of hot ethanol cleaning, is found to remove the PMMA residues completely. The ultraclean monolayer MoS2 has shown improved field‐effect transistor performance.
Understanding the effect of the intrinsic properties of monolayer MoS2 (1L-MoS2) on the photoluminescence quantum yield (QY) is indispensable before seeking surface treatments for its improvement. ...Here, the effects of localized heat and heat-dissipation on the QY of 1L-MoS2 grown by chemical vapour deposition (CVD) are reported. The experimentally measured QY increases with an increase in the flake area of 1L-MoS2. The QY of the large-area flake is increased by more than one order as compared to the small-area flake, and this is attributed to a significant reduction in the local temperature rise with laser irradiation. The localized heating effects are substantially reduced in large-area flakes because of efficient heat dissipation. The reduced localized heating effects with flake area are established by power-dependent Raman and PL studies, which are further corroborated by Stokes and anti-Stokes Raman analysis. In the case of small-area (∼33 μm2) 1L-MoS2, there is an additional rise in the local temperature by ∼94 K as compared to the large-area case (∼5778 μm2) for the same laser power. A QY of ∼1.8% is achieved for the large-area 1L-MoS2, which is one order higher than that of the mechanically exfoliated 1L-MoS2 and two orders higher than that of CVD grown 1L-MoS2. The role of carrier density and defect passivation in the PL intensity enhancement was ruled out with the observation of the simultaneous enhancement of integrated PL intensities associated with the trions and excitons. In addition, the PL intensity of the large-area MoS2 monolayers was found to be influenced by the grain size. The role of grain size is understood by invoking the heat-dissipation mechanism at the grain boundaries. The reported results establish the importance of efficient heat-dissipation in realizing the potential of 1L-MoS2 and other 2D monolayer materials.
The crystalline aluminium nitride (AlN) thin films were isothermally annealed at 850 °C in a controlled oxygen environment. The oxidation process has led to significant enhancement in lattice ...parameters and degradation in the crystallinity of as-grown AlN film. The AlN bonding at the film’s surface was systematically reduced and finally vanished when the film was annealed at 20% oxygen mixed with an argon environment. During annealing, nitrogen in AlN is replaced by oxygen, and a fraction of replaced nitrogen is trapped at the interstitial sites in AlN, which systematically enhances with an increment in oxygen content. Magnetic measurements exhibit dilute ferromagnetism induced in as-grown AlN film at 300 K after annealing. Density functional theory (DFT) calculation reveals interaction between N 2p orbitals of interstitial nitrogen and first neighbouring nitrogen atoms contributing to observed magnetic properties.
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•Annealing in O2 environment elongates lattice and alleviates crystallinity of AlN.•O2 ingress in AlN by replacing N along c-axis in AlN matrix.•N replaced by O gets trapped at interstitial site into the AlN matrix.•Annealing in O2 environment instigates dilute FM and weak paramagnetism in AlN.•DFT calculation reveals that N at interstitial site in AlN has moments of 2 μB.
This paper deals with adsorption behavior of ruthenium on Tri-n-butyl phosphate functionalized Multi Walled Carbon Nanotubes (MWCNTs-COO-TBP) from aqueous solution. Adsorption method is significant ...for trace levels (expected level) removal of ruthenium in bioassay (urine) samples which is mandatory requirement of radiation workers in nuclear environment. Multi Walled Carbon Nanotubes (MWCNTs) were initially converted to carboxylated Multi Walled Carbon nanotubes (MWCNTs-COOH) and subsequently treated with Tri-n-butyl phosphate to MWCNTs-COO-TBP. The synthesized MWCNTs-COOH and MWCNTs-COO-TBP were confirmed by Fourier Transform Infrared Spectroscopy (FTIR). Spectroscopic and microscopic techniques such as X-Ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS) and High Resolution Transmission Electron Microscopy (HR-TEM) were used for its characterization before and after adsorption. Various adsorption parameters such as contact time, pH, metal ion concentration and temperature were studied. Langmuir adsorption isotherm model and Pseudo second order kinetics model were found to be best fitted in terms of standard deviation and regression coefficient. Thermodynamics parameters such as enthalpy (ΔH°), entropy (ΔS°), Gibbs energy (ΔG°), activation energy (Ea) and sticking probability (SP*) were calculated. The adsorption capacity was calculated and found to be 141.23 mg.g−1.Moreover, quantification of defects, strains with charge doping states were calculated from Raman mapping and correlation plot.
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•Synthesis and characterization of Tri-n-Butyl Phosphate functionalized Multi Walled Carbon Nanotubes (MWCNTs-COO-TBP).•Detailed study on adsorption of ruthenium on MWCNTs-COO-TBP and its kinetics, thermodynamics and isotherm.•Functionalization of MWCNTs by TBP and its adsorption for ruthenium, confirmed by FTIR and EDS analysis.•Quantification of defects and strains with charge doping states were calculated from Raman mapping and correlation plot.•The potential application of MWCNTs-COO-TBP for adsorption of Ru from aqueous solution was explored.
We fabricated the 1D nanoscrolled monolayer MoS2 (1L-MoS2) with superior characteristics from 1L-MoS2 film in a facile route, using a suitable organic solvent with optimum surface tension, ...evaporation rate and dielectric constant, which facilitates the controlled scroll formation. These nanoscrolls behave as multilayers in morphology and monolayer electronically. The nanoscrolls exhibited a direct optical gap with enhanced photoluminescence quantum yield stemming from the weak interlayer coupling among constituent layers and were corroborated by low-frequency Raman measurements and Kelvin probe force microscopy measurements. Furthermore, enhanced photoluminescence emission after annealing uncovers the thermal stability of nanoscrolls. In addition, conducting atomic force microscopy results exhibit a significantly higher photocurrent in the nanoscrolled 1L-MoS2 compared to the 1L-MoS2. We also realized significantly improved field effect transistor device parameters in nanoscrolled 1L-MoS2 devices. In nanoscrolled devices, we report the highest mobility value of 2400 cm2V-1s-1 reported in any form of 1L-MoS2.
Abstract
The transfer of monolayer molybdenum disulfide (1L‐MoS
2
) onto any target substrates is inevitable for the next generation of optoelectronic devices such as flexible electronics. However, ...the existing post‐transfer treatments are ineffective for the complete removal of poly(methyl methacrylate) (PMMA) polymer, which is usually used as carrier polymer in the wet‐transfer method. The presence of PMMA residues seriously degrades the intrinsic properties of any 2D materials. Several new cleaning methods such as annealing, ozone cleaning, and acetone treatment adopted in this report are found to be ineffective for the complete removal of PMMA residues on the transferred 1L‐MoS
2
film. A new chemical route is developed and demonstrated with a PMMA nonsolvent, ethanol, and ultraclean transferred 1L‐MoS
2
is obtained after 96 h hot ethanol treatment. An interfacial diffusion model is proposed for the mechanism of PMMA removal from the 1L‐MoS
2
surface. To observe the effect of cleaning process on electrical properties, 1L‐MoS
2
field‐effect transistor (FET) devices are fabricated. An enhancement of 80%–85% in the electron mobility is achieved for ultraclean 1L‐MoS
2
. One order improvement in the FET parameters such as ON/OFF ratio and the subthreshold slope is also observed. It is believed that this novel method can also be applicable for other 2D materials.
Understanding the effect of the intrinsic properties of monolayer MoS
2
(1L-MoS
2
) on the photoluminescence quantum yield (QY) is indispensable before seeking surface treatments for its improvement. ...Here, the effects of localized heat and heat-dissipation on the QY of 1L-MoS
2
grown by chemical vapour deposition (CVD) are reported. The experimentally measured QY increases with an increase in the flake area of 1L-MoS
2
. The QY of the large-area flake is increased by more than one order as compared to the small-area flake, and this is attributed to a significant reduction in the local temperature rise with laser irradiation. The localized heating effects are substantially reduced in large-area flakes because of efficient heat dissipation. The reduced localized heating effects with flake area are established by power-dependent Raman and PL studies, which are further corroborated by Stokes and anti-Stokes Raman analysis. In the case of small-area (∼33 μm
2
) 1L-MoS
2
, there is an additional rise in the local temperature by ∼94 K as compared to the large-area case (∼5778 μm
2
) for the same laser power. A QY of ∼1.8% is achieved for the large-area 1L-MoS
2
, which is one order higher than that of the mechanically exfoliated 1L-MoS
2
and two orders higher than that of CVD grown 1L-MoS
2
. The role of carrier density and defect passivation in the PL intensity enhancement was ruled out with the observation of the simultaneous enhancement of integrated PL intensities associated with the trions and excitons. In addition, the PL intensity of the large-area MoS
2
monolayers was found to be influenced by the grain size. The role of grain size is understood by invoking the heat-dissipation mechanism at the grain boundaries. The reported results establish the importance of efficient heat-dissipation in realizing the potential of 1L-MoS
2
and other 2D monolayer materials.
The photoluminescence quantum yield (QY) of monolayer MoS
2
is dependent on its heat-dissipating area, which elucidates that it is essential to understand the effect of intrinsic properties on QY before seeking surface treatments for its improvement.
Understanding the effect of the intrinsic properties of monolayer MoS 2 (1L-MoS 2 ) on the photoluminescence quantum yield (QY) is indispensable before seeking surface treatments for its improvement. ...Here, the effects of localized heat and heat-dissipation on the QY of 1L-MoS 2 grown by chemical vapour deposition (CVD) are reported. The experimentally measured QY increases with an increase in the flake area of 1L-MoS 2 . The QY of the large-area flake is increased by more than one order as compared to the small-area flake, and this is attributed to a significant reduction in the local temperature rise with laser irradiation. The localized heating effects are substantially reduced in large-area flakes because of efficient heat dissipation. The reduced localized heating effects with flake area are established by power-dependent Raman and PL studies, which are further corroborated by Stokes and anti-Stokes Raman analysis. In the case of small-area (∼33 μm 2 ) 1L-MoS 2 , there is an additional rise in the local temperature by ∼94 K as compared to the large-area case (∼5778 μm 2 ) for the same laser power. A QY of ∼1.8% is achieved for the large-area 1L-MoS 2 , which is one order higher than that of the mechanically exfoliated 1L-MoS 2 and two orders higher than that of CVD grown 1L-MoS 2 . The role of carrier density and defect passivation in the PL intensity enhancement was ruled out with the observation of the simultaneous enhancement of integrated PL intensities associated with the trions and excitons. In addition, the PL intensity of the large-area MoS 2 monolayers was found to be influenced by the grain size. The role of grain size is understood by invoking the heat-dissipation mechanism at the grain boundaries. The reported results establish the importance of efficient heat-dissipation in realizing the potential of 1L-MoS 2 and other 2D monolayer materials.
The defect-free transfer of chemical vapour deposition (CVD) grown monolayer MoS2 is important for both fabrication of 2D devices and fundamental point of view for various studies where substrate ...effects need to be minimized. Among many transfer techniques, two well-known techniques that use the polymer as carriers are wet-transfer technique and the surface-energy-assisted transfer technique. In this work, we transferred a single CVD grown monolayer MoS2 by these two transfer methods on a similar substrate, and the intervention of strain and defects in the transfer process is probed by Raman and photoluminescence (PL) spectroscopy, respectively. We found that the conventional and commonly used wet transfer technique degraded the monolayer due to KOH contamination. In contrast, monolayers transferred using the surface-energy-assisted transfer method possess structural integrity and optical quality on a par with the as-grown MoS2 layers. As compared to the wet process a strain-free transfer was recorded in the surface-energy-assisted technique using Raman spectroscopic studies.
