Question

Write a three page report on the recent advancements in the area of plasma in engineering

The paper will be in 12 point times new roman single spaced and will be three pages long (not inlcuding the references. It will include the following elements:

1) Title

2) Your name.

3) Introduction paragraph

4) Your analysis.

5) conclusion.

6) references.

Answer 1

Precise tunability of electronic properties of two-dimensional (2D) nanomaterials is a key goal of current research in this field of materials science. Chemical modification of layered transition metal dichalcogenides leads to the creation of heterostructures of low-dimensional variants of these materials. In particular, the effect of oxygen-containing plasma treatment on molybdenum disulfide (MoS2) has long been thought to be detrimental to the electrical performance of the material. We show that the mobility and conductivity of MoS2 can be precisely controlled and improved by systematic exposure to oxygen/argon plasma and characterize the material using advanced spectroscopy and microscopy. Through complementary theoretical modeling, which confirms conductivity enhancement, we infer the role of a transient 2D substoichiometric phase of molybdenum trioxide (2D-MoOx) in modulating the electronic behavior of the material. Deduction of the beneficial role of MoOxwill serve to open the field to new approaches with regard to the tunability of 2D semiconductors by their low-dimensional oxides in nano-modified heterostructures

he recent decade has produced intense research into layered two-dimensional (2D) nanomaterials, with transition metal dichalcogenides (TMDs), such as MoS2, being the prime focus in the area of novel nanoelectronics (1–5). Progress demands that a nanofabrication methodology is developed to control the structure and properties of semiconducting layered crystals so that desired functionalities are obtained for these materials in the future. These may include phase transitions (6, 7) or conductivity modulation for next-generation data storage (8, 9). In particular, the interaction of low-energy radio frequency–generated plasma ions with MoS2 has already led to the creation of a multitude of devices, including rectifying diodes, photovoltaics, and nonvolatile memories (10–12). Plasma power and exposure time have emerged as key variables to delineate between chemical etching and physical sputtering regimes (13–16). Treatment with oxygen-containing plasma leads to the formation of molybdenum trioxide (MoO3) centers, which have been reported to increase the resistivity of the material and inhibit carrier transport, while retaining relative structural integrity of the now oxide-containing MoS2 heterostructure (17, 18). Here, we demonstrate the tuning of electrical resistivity of few-layer MoS2 by treatment with O2/Ar (1:3) plasma. The field-effect mobility, ?FE, of the MoS2 channel is seen to deteriorate initially but recovers to above-original levels after 6 s of exposure to the plasma. The associated electrical conductivity of the device is noted to increase by an order of magnitude at this stage. Upon further treatment, the conductivity and mobility drop again and no subsequent recovery is seen. In the limited literature regarding this phenomenon, the reason for the apparent recovery remains under debate (19–21). Although other means of doping MoS2 have recently facilitated mobility improvement (22, 23), a molybdenum oxide–mediated n-type doping scheme has not yet been demonstrated. Here, we propose a mechanism of impurity-mediated electrical tuning facilitated by a 2D phase of MoOx, with advanced spectroscopic and microscopic studies to support electrical characterization. We infer the presence of this substoichiometric 2D molybdenum trioxide phase, which serves to screen charges associated with plasma-created sulfur vacancies (SVs), enhancing mobility in underlying MoS2 layers after 6 s of plasma treatment, which increases the channel conductivity. Complementary mathematical modeling of conductive networks reveals the beneficial effect of the freshly incorporated oxide in the MoS2 matrix. Recent theoretical work has predicted the 2D phase of MoO3 to be a material with a distinctly high acoustic phonon-limited carrier mobility (>3000 cm2 V?1 s?1) (24), whereas experimental 2D field-effect transistors (FETs) made of substoichiometric exfoliated MoO3 have reported mobilities far exceeding those of MoS2(>1100 cm2 V?1 s?1) (25, 26). The advantageous effect of the 2D phase of MoOx on the electrical properties of MoS2 may play a key role in the applications of planar heterostructures of layered TMDs in novel electronic devices. Future research into this area must consider the benefits of defect-mediated transport in 2D nanoelectronics.

RESULTS AND DISCUSSION

Recovery of field-effect mobility in plasma-treated MoS2

For the initial plasma exposures, the level of drain-source current for a four-layer (4L) device varies slightly up until 6 s, when a significant rise in output current is noted, indicating an increase in the conductivity of the channel (Fig. 1A). Subsequent exposures cause a continuing drop in current level until the noise floor of the instrument (10?11 A) is reached after 12 s of plasma treatment (for a closer analysis of device stability, see fig. S4). The gate characteristics (Fig. 1B) of the n-type MoS2 change significantly after 6 s. The level of output current at negative gate values increases by several orders of magnitude at 6 s, implying a drastic shift in the threshold voltage (VTH) to negative gate biases. Correlated with this is the change in the sensitivity of the output current to the applied gate-source bias (VGS), with a much more gradual increase in output current throughout the sweep. Figure 1 (C and D) tracks the evolution of the threshold gate voltage (VTH) and the subthreshold swing (Ssub) over plasma exposure time. The threshold voltage is seen to shift from ??21 V for the untreated device to ??37 V at 6 s of exposure and subsequently to large positive gate biases after 10 s. The shift toward negative threshold voltages at 6 s implies increased depletion mode functionality for n-type devices, whereas the upshift of VTH after further exposure denotes an increase of p-type doping. Ssub, in turn, initially shows little change until it increases fivefold at 6 s and up to eightfold at 10 s relative to the values before treatment. Upon further exposure, it drops again to ?25 volts per decade as VTH is shifted to large positive gate biases. At 6 s, the sample shows a marked increase in Ssub, indicating that it is less sensitive to variations in the gate field around the region where the FET conductive channel is formed. This is expected to occur if the now-doped few topmost layers of the device have an increased charge trap density (22), originating from the plasma treatment.

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