arXiv subjects

Thushari Jayasekera

Publications and source records attributed to Thushari Jayasekera.

5 recordsLinked to original sources

arXiv2026

Stabilization of Stone-Wales Defects in Metal-supported Graphene

The characteristics of graphene-metal interfaces play a decisive role in their electronic, optoelectronic, and mechanical applications. Properties such as charge transfer across the interface become particularly significant in the presence of topological defects. The stability of Stone Wales (SW) defects in graphene is governed by the balance between three energy descriptors, the activation energy, formation energy, and restoration energy. By comparing the energy parameters obtained from first-principles density functional theory calculations, we show that SW defect formation is energetically more favorable on metal-supported graphene. Our calculations for SW defects in graphene/Cu(111) and graphene/Al(111) systems indicate only a little dependence of energy profile on the type of metal. The presence of the metal substrate leads to a $\sim$ 12\% increase in the formation energy and a $\sim$ 20\% reduction in the activation energy, which together favor the formation of Stone Wales defects. Although the restoration energy decreases by about $\sim$ 35\% in metal-supported graphene, it remains significantly higher to prevent self-healing. As a result, once formed, the Stone Wales defects are likely to remain stable, suggesting the possibility of terminal SW defect formation in metal-supported graphene.

cond-mat.mtrl-sci↗

arXiv2017

Tunable Indirect-Direct Transition of Few-Layer SnSe via Interface Engineering

Tin Selenide (SnSe) is one of the best thermoelectric materials reported to date. The possibility of growing few-layer SnSe helped boost the interest in this long-known, earth abundant material. Pristine SnSe in bulk, mono- and few-layer forms are reported to have indirect electronic bandgaps. Possible indirect-direct transition in SnSe is attractive for its optoelectronic-related applications. Based on the results from first principles Density Functional Theory (DFT) calculations, we carefully analyzed electronic band structures of bulk, and bilayer SnSe with various interlayer stackings. We report the possible stacking-dependent indirect-direct transition of bilayer SnSe. By further analysis, our results reveal that it is the directionality of interlayer interactions that determine the critical features of their electronic band structures. In fact, by engineering the interface stacking between layers, it is possible to achieve few-layer SnSe with direct electronic band gap. This study provides fundamental insights to design few-layer SnSe and SnSe heterostructures for electronic/optoelectronic applications, where the interface geometry plays a fundamental role in device performance.

cond-mat.mtrl-sci↗

arXiv2016

Viable route towards large-area two dimensional MoS2 using magnetron sputtering

Structural, interfacial, optical, and transport properties of large-area MoS2 ultra-thin films on BN-buffered silicon substrates fabricated using magnetron sputtering are investigated. A relatively simple growth strategy is demonstrated here that simultaneously promotes superior interfacial and bulk MoS2 properties. Few layers of MoS2 are established using X-ray reflectivity, diffraction, ellipsometry, and Raman spectroscopy measurements. Layer-specific modeling of optical constants shows very good agreement with first-principles calculations. Conductivity measurements reveal that few-layer MoS2 films are more conducting than many-layer films. Photo-conductivity measurements reveal that the sputter deposited MoS2 films compare favorably with other large-area methods. Our work illustrates that sputtering is a viable route for large-area device applications using transition metal dichalcogenides.

cond-mat.mtrl-sci↗

arXiv2011

Unexpected Structures for Intercalation of Sodium in Epitaxial Graphene-SiC Interfaces

We show using scanning tunneling microscopy, spectroscopy, and ab initio calculations that several intercalation structures exist for Na in epitaxial graphene on SiC(0001). Intercalation takes place at room temperature and Na electron-dopes the graphene. It intercalates in-between single-layer graphene and the carbon-rich interfacial layer. It also penetrates beneath the interfacial layer and decouples it to form a second graphene layer. This decoupling is accelerated by annealing and is verified by direct Na deposition onto the interface layer. Our observations show that intercalation in graphene is fundamentally different than in graphite and is a versatile means of electronic control.

cond-mat.mes-hall↗

arXiv2006

Evaporative Cooling in Semiconductor Devices

We discuss the theory of cooling electrons in solid-state devices via ``evaporative emission.'' Our model is based on filtering electron subbands in a quantum-wire device. When incident electrons in a higher-energy subband scatter out of the initial electron distribution, the system equilibrates to a different chemical potential and temperature than those of the incident electron distribution. We show that this re-equilibration can cause considerable cooling of the system. We discuss how the device geometry affects the final electron temperatures, and consider factors relevant to possible experiments. We demonstrate that one can therefore substantial electron cooling due to quantum effects in a room-temperature device. The resulting cooled electron population could be used for photo-detection of optical frequencies corresponding to thermal energies near room temperature.

cond-mat.mes-hall↗