Browsing by Author "Izquierdo, N."

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Growth of Very Large MoS2Single Crystals Using Out-Diffusion Transport and Their Use in Field Effect Transistors
(Institute of Electrical and Electronics Engineers Inc., 2021) Pandey, S.K.; Izquierdo, N.; Campbell, S.
Monolayer molybdenum disulfide (MoS2) is an attractive 2D material with a wide range of potential applications in the field of electronics and optoelectronics. To obtain the best performance, it is very necessary to grow large area single crystals of MoS2 (single domain) to avoid the effects of grain boundaries, but is exceptionally challenging to do this. Here, we report a novel method which we call out-diffusion vapor transport to grow large area single crystal monolayer MoS2 using an otherwise conventional chemical vapor deposition system. In this method, microchannels were created on the boat to significantly limit the region where MoOx vapor can react with S vapor to form crystals. This growth method resulted in triangular monolayer MoS2 single crystals up to ?640 ?m on a side grown on an oxidized silicon substrate, the largest crystals reported to date. Most of these crystals were multilayer at the center. This common feature has been identified in the literature as partially reduced transition metal oxide nucleates a second layer. We also achieved fully monolayer MoS2 single crystals up to ?450 ?m on a side, the largest demonstrated without the MoOx. Fabricated field effect transistors (FET) using MoS2 monolayer crystal as the active layer demonstrate a conventional n-type behavior, room-temperature mobility up to 45.5 cm2 V-1 s-1 and a maximum ON-Current (ION)/OFF-current (IOFF) ratio of 1.8 × 107. Raman and Photoluminescence results indicate that the as-grown large area monolayer crystals have high crystalline quality and uniformity with minimal defects, a finding that is consistent with the high electron mobility. This research work provides a superior technique to grow large-area high-quality single-crystal monolayer MoS2 without resorting to exotic equipment or techniques. © 2002-2012 IEEE.
Recent advancements in growth and stability of phosphorene: Prospects for high-performance devices
(CRC Press, 2022) Pandey, S.K.; Garg, V.; Izquierdo, N.; Kumar, A.
Atomically thin two-dimensional (2D) materials like graphene and the transition metal dichalcogenides have made a significant impact in the field of electronics and optoelectronics devices. Graphene, however, has no bandgap, which creates hurdles for many device applications. Similarly, the modest carrier mobility of transition metal dichalcogenides makes them less suitable for high-performance electronic and optoelectronic device applications. Phosphorene, a monolayer or few-layer form of black phosphorus (BP), has attracted considerable interest owing to its unique anisotropic manner, layer-dependent direct bandgaps, high carrier mobility, and quasi-one-dimensional excitonic nature, which are not present in other abovementioned 2D materials. Phosphorene has a bandgap of ˜0.3 eV in the bulk form and can be increased with reducing layer thicknesses, approaching ˜2 eV for the monolayer. As a result, there have been stimulating reports on field-effect transistors and inverters fabricated in the material system. Phosphorene is also becoming an interesting material for solar cells and photodetectors. Despite novel properties, the development of this material itself remains in an embryonic state. One of the reasons for the slow progress is that phosphorene-based devices use either mechanical or liquid exfoliation method to deposit phosphorene from crystalline black phosphorus (c-BP). In these processes, one peels a thin layer of material from a bulk BP crystal using adhesive tape or by liquid intercalation. The exfoliation process for this material is possible due to its intralayer strong covalent bonds and interlayer weak van der Waals forces. The exfoliation method does not have the thickness, uniformity, position, orientation, and surface control needed to get repeatable experimental results. In this chapter, detailed information will be provided about phosphorene deposition using the abovementioned and other methods. Phosphorene demonstrates instability under ambient conditions, which is the main obstacle for its practical applications. Various studies have been conducted in the past to investigate the mechanism of the degradation of phosphorene and passivation techniques to resolve its problem of instability under ambient conditions. To know the various fundamental properties correctly, the stability of this 2D material is very important, which can be achieved by novel passivation strategies. Detailed passivation strategies of phosphorene are elaborated in this chapter. The effects of the passivation layers composition on the thermal stability of phosphorene are also provided. Different growth techniques are described to deposit the passivation layers without altering the properties of phosphorene. To understand the different properties of passivated phosphorene, different measurement techniques such as X-ray diffraction (XRD), Raman spectroscopy, optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM) are discussed in this chapter. The effects of annealing temperatures on the properties of passivated phosphorene are discussed in detail. Finally, an overview on the utilization of phosphorene for a variety of applications is also given. A detailed study about 2D phosphorene/3D materials-based next-generation devices are presented in this chapter. The roadmaps to address present challenges for phosphorene are investigated as the properties of this material are very appropriate for next-generation devices. The information presented in this chapter will accelerate the further development of high-performance phosphorene-based electronics and optoelectronics devices. © 2022 selection and editorial matter, Ashish Raman, Deep Shekhar and Naveen Kumar; individual chapters, the contributors.