Engineering topics

Apte, Amey

Publications and source records attributed to Apte, Amey.

3 records

DOE OSTI2022

Low temperature CVD growth of WSe 2 enabled by moisture-assisted defects in the precursor powder

Two-dimensional transition metal dichalcogenides (TMDs) have been proposed for a wide variety of applications, such as neuromorphic computing, flexible field effect transistors, photonics, and solar cells, among others. However, for most of these applications to be feasible, it is necessary to integrate these materials with the current existing silicon technology. Although chemical vapor deposition is a promising method for the growth of high-quality and large-area TMD crystals, the high temperatures necessary for the growth make this technique incompatible with the processes used in the semiconductor industry. Herein, we demonstrate the possibility of low-temperature growth of TMDs, using tungsten selenide (WSe 2 ) as a model, by simply using moisture-assisted defective tungsten oxide (WO 3 ) precursor powders during the growth of these materials. Density functional theory calculations reveal the mechanism by which moisture promotes the defect formation on the precursor crystal structure and how it dictates the reduction of the temperature of the growth. The results were compared with the standard growth at high temperatures and with a precursor mixture with alkali salts to show the high quality of the WSe 2 grown at temperatures as low as 550 °C. To conclude, the work improves the understanding of nucleation and growth mechanisms of WSe 2 at low temperatures and provides a useful strategy for the growth of TMDs at temperatures required for the back-end-of-line compatibility with current silicon technology.

2D materials↗

DOE OSTI2020

Scale-Enhanced Magnetism in Exfoliated Atomically Thin Magnetite Sheets

The discovery of ferromagnetism in atomically thin layers at room temperature widens the prospects of 2D materials for device applications. Recently, two independent experiments demonstrated magnetic ordering in two dissimilar 2D systems, CrI 3 and Cr 2 Ge 2 Te 6 , at low temperatures and in VSe 2 at room temperature, but observation of intrinsic room-temperature magnetism in 2D materials is still a challenge. Here a transition at room temperature that increases the magnetization in magnetite while thinning down the bulk material to a few atom-thick sheets is reported. DC magnetization measurements prove ferrimagnetic ordering with increased magnetization and density functional theory calculations ascribe their origin to the low dimensionality of the magnetite layers. Additionally, surface energy calculations for different cleavage planes in passivated magnetite crystal agree with the experimental observations of obtaining 2D sheets from non-van der Waals crystals.

2D Magnetism↗

DOE OSTI2020

2D Electrets of Ultrathin MoO 2 with Apparent Piezoelectricity

Since graphene, a variety of 2D materials have been fabricated in a quest for a tantalizing combination of properties and desired physiochemical behavior. 2D materials that are piezoelectric, i.e., that allow for a facile conversion of electrical energy into mechanical and vice versa, offer applications for sensors, actuators, energy harvesting, stretchable and flexible electronics, and energy storage, among others. Unfortunately, materials must satisfy stringent symmetry requirements to be classified as piezoelectric. Here, 2D ultrathin single-crystal molybdenum oxide (MoO 2 ) flakes that exhibit unexpected piezoelectric-like response are fabricated, as MoO 2 is centrosymmetric and should not exhibit intrinsic piezoelectricity. However, it is demonstrated that the apparent piezoelectricity in 2D MoO 2 emerges from an electret-like behavior induced by the trapping and stabilization of charges around defects in the material. Arguably, the material represents the first 2D electret material and suggests a route to artificially engineer piezoelectricity in 2D crystals. Specifically, it is found that the maximum out-of-plane piezoresponse is 0.56 pm V -1 , which is as strong as that observed in conventional 2D piezoelectric materials. The charges are found to be highly stable at room temperature with a trapping energy barrier of ≈2 eV.

36 MATERIALS SCIENCE↗