Two-dimensional (2D) materials have been a great interest as high-performance transparent and flexible electronics due to their high crystallinity in atomic thickness and their potential for variety applications in electronics and optoelectronics. The present study explored the wafer scale production of MoS 2 nanosheets with layer thickness modulation from single to multi-layer by using two-step method of metal deposition and CVD process. The formation of high-quality and layer thickness-modulated MoS 2 film was confirmed by Raman spectroscopy, AFM, HRTEM, and photoluminescence analysis. The layer thickness was identified by employing a simple method of optical contrast value. The image contrast in green (G) channel shows the best fit as contrast increases with layer thickness, which can be utilized in identifying the layer thickness of MoS 2. The presence of critical thickness of Mo for complete sulphurization, which is due to the diffusion limit of MoS 2 transformation, changes the linearity of structural, electrical, and optical properties of MoS 2. High optical transparency of >90%, electrical mobility of $12.24 cm 2 V À1 s À1 , and I on/off of $10 6 characterized within the critical thickness make the MoS 2 film suitable for transparent and flexible electronics as compared to conventional amorphous silicon (a-Si) or organic films. The layer thickness modulated large scale MoS 2 growth method in conjunction with the layer thickness identification by the nondestructive optical contrast will definitely trigger development of scalable 2D MoS 2 films for transparent and flexible electronics.

Highly conductive and transparent thin films were prepared using highly purified multi-walled carbon nanotube (MWCNT) sheets. The electrical properties of the MWCNT sheet were remarkably improved by an acid treatment, resulting in densely packed MWCNTs. The morphology of the sheets reveals that continuous electrical pathways were formed by the acid treatment, greatly improving the sheet resistance all the while maintaining an excellent optical transmittance. These results encourage the use of these MWCNT sheets with low sheet resistance (450 Ω/sq) and high optical transmittance (90%) as a potential candidate for flexible display applications.

The scaling down of electromechanical devices from micrometer scales to nano scales is of great interest. This paper presents fabrication and characterization of sub-micron high aspect ratio metallic electrothermal actuators using a combination of electron beam lithography and electroplating techniques. A 1.2 µm thick SU-8 layer was used as a sacrificial layer and a 1 µm thick electron beam lithography-processed polymethyl methacrylate resist was used to form 3:1 aspect ratio sub-micron (minimum feature size of 350 nm) electroplated nickel electrothermal actuators. Such sub-micron electrothermal actuators were characterized by a nanomanipulator system in a scanning electron microscopy system. Electro-thermo-mechanical finite element analysis (FEA) of the actuator using ANSYS was carried out and the FEA results were in good agreement with the measured results. Displacements at the tip of the actuator of 370 nm were reproducibly observed with the applied voltages of 145 mV. This work can be applied to realize more sophisticated nano actuators which can manipulate sub-micron scale objects.

One must control the size distribution of catalyst Fe nano-particles (NPs) very carefully if one is to have any chance of growing "super-aligned" carbon nanotube (CNT) forests which can be spun directly into yarns and pulled directly into long sheets. Control of the Fe Nps size is important during all phases, including: the catalyst deposition, annealing and forest growth. As a result, it is important to understand how NPs are affected by various experimental factors as well as how those catalyst NPs then cause the growth of the forests. This paper focuses on two key experimental factors: The as-deposited thickness of the Fe catalyst film and the use of hydrogen gas (H2) during anneal and growth. We found that the sheet resistance (Rs) of as-deposited Fe films is directly related to the average film thickness and can be used to estimate whether the films can catalyze the growth of super-aligned forests. The height of the CNT forests decrease with decreasing Rs, but only slowly. More importantly, CNTs grown on the largest and the smallest Rs films are less aligned. Instead, they are more curled and wavy due to the Fe NP dynamics. The use of Hydrogen (H2) affects the formation of Fe NPs from the as-deposited film as well as their composition during the forest growth. We find that the addition of H2 to a CNT forest growth process at 680 degrees C (C2H2/He [30/600 sccm]) increases the CNT alignment substantially. H2 can also reduce iron-oxides which otherwise would impede the formation of NPs. As a result, H2 has multiple roles: besides its chemical reactivity, H2 is important for catalyst reconstruction into NPs having a proper size distribution as well as surface density.

Liquid metal-based applications are limited by the wetting nature of polymers toward surface-oxidized gallium-based liquid metals. This work demonstrates that a 120 s CF4/O2 plasma treatment of polymer surfacessuch as poly­(dimethylsiloxane) (PDMS), SU8, S1813, and polyimideconverts these previously wetting surfaces to nonwetting surfaces for gallium-based liquid metals. Static and advancing contact angles of all plasma-treated surfaces are >150°, and receding contact angles are >140°, with contact angle hysteresis in the range of 8.2–10.7°, collectively indicating lyophobic behavior. This lyophobic behavior is attributed to the plasma simultaneously fluorinating the surface while creating sub-micron scale roughness. X-ray photoelectron spectroscopy (XPS) results show a large presence of fluorine at the surface, indicating fluorination of surface methyl groups, while atomic force microscopy (AFM) results show that plasma-treated surfaces have an order of magnitude greater surface roughness than pristine surfaces, indicating a Cassie–Baxter state, which suggests that surface roughness is the primary cause of the nonwetting property, with surface chemistry making a smaller contribution. Solid surface free energy values for all plasma-treated surfaces were found to be generally lower than the pristine surfaces, indicating that this process can be used to make similar classes of polymers nonwetting to gallium-based liquid metals.

Articles you may be interested inEffect of different carrier gases and their flow rates on the growth of carbon nanotubes Phys. Plasmas 22, 043501 (2015); 10.1063/1.4916057 Growth of high-density carbon nanotube forests on conductive TiSiN supports Appl. Phys. Lett. 106, 083108 (2015); 10.1063/1.4913762Effect of hydrogen pretreatment on the spin-capability of a multiwalled carbon nanotube forest Spin-capable multiwalled carbon nanotube (MWCNT) forests that can form webs, sheets, and yarns provide a promising means for advancing various technologies. It is necessary to understand the critical factors to grow spin-capable carbon nanotubes (CNTs) in a repeatable fashion. Here we show how both the spinning capability and morphology of MWCNT forests are significantly changed by controlling the C 2 H 2 concentration and ramp rate of temperature. The acetylene gas flow was varied in the range of 0.25-6.94% by volume. The MWCNTs grown at C 2 H 2 concentrations between 1.47-3.37% are well-aligned and become spin-capable. The well-aligned forests have higher areal density and shorter distance between CNTs. The thermal ramp rate was also changed from 30 C/min to 70 C/min. A specific range of thermal ramp rate is also required to have the suitably sized nanoparticles with sufficient density resulting in higher CNT areal density for spinnable MWCNTs. A ramp rate of 50 C/min forms suitable sized nanoparticles with sufficient density to produce CNT forests with a higher areal density and a shorter tube spacing.

Fluorinated amorphous carbon films that are thermally stable at 400 C have been deposited in a plasma enhanced chemical vapor deposition system using tetrafluorocarbon and disilane (5% by volume in helium) as precursors. The bulk dielectric constant (k) of the film has been optimized from 2.0/2.2 to 1.8/1.91 as-deposited and after heat treatment, by varying process parameters including power density, deposition temperature, and wall temperature. Films, failing shrinkage rate requirements, possessing promising k-values have been salvaged by utilizing a novel extended heat treatment scheme. Film properties including chemical bond structure, F/C ratio, refractive index, surface planarity, contact angle, dielectric constant, flatband voltage shift, breakdown field potential and optical energy gap have been evaluated by varying process pressure, power, substrate temperature, and flow rate ratio of processing gases. Both x-ray photoelectron spectroscopy and FTIR results confirm that the stoichiometry of the ultralow k film is close to that of CF 2 with no oxygen. C-V characteristics indicate the presence of negative charges that are either interface trapped charges or bulk charges. Average breakdown field strength was in the range of 2-8 MV/cm while optical energy gap varied between 2.2 and 3.4 eV.

Multiwalled carbon nanotube (MWCNT) sheets that can be spun directly from a spin-capable MWCNT forest promise novel applications that utilize the unique and outstanding characteristics of this material. The growth of spin-capable MWCNT forests will be achieved through the understanding of the important factors affecting the forest growth, since the precise conditions necessary for effective spin-capability are extremely sensitive. In this paper, we discuss the effect of carrier gas, the initial catalyst thickness, and the roles of the hydrogen. These factors were investigated in order to assess and understand these critical parameters and thereby develop a repeatable and reliable spin-capable MWCNT growth process.Index Terms-Carrier gas, catalyst, spin-capable multiwalled carbon nanotube (MWCNT).