arXiv subjects

Talip Serkan Kasırga

Publications and source records attributed to Talip Serkan Kasırga.

5 recordsLinked to original sources

arXiv2026

Non-monotonic hydration dependence of ionic transport in atomically-thin MnO2 sheets

The interlamellar space in van der Waals materials has served as a test bed for studies of strongly confined fluid and ion transport. Despite theoretical and experimental progress, it remains unclear how electrostatic correlations arising from interactions between the confined, hydrated ions and the substrate layer can be reconciled with non-equilibrium ionic transport and the substrate's morphological response. Here, we investigate field-driven ionic conduction in sodium- and water-intercalated layered manganese oxides ($\mathrm{MnO_2}$), a self-intercalated metal oxide nanofluidic system, as a model intrinsically-intercalated van der Waals solid, using nonequilibrium all-atom molecular dynamics simulations that explicitly capture ion-water correlations and layer morphology. We demonstrate that electric-field bias induces spontaneous nanoscale segregation of water within the interlayer space, producing coexisting hydrated and weakly hydrated ionic domains coupled to local lattice distortions. This feedback between hydration and morphology gives rise to heterogeneous transport pathways and leads to a non-monotonic dependence of ionic conductivity on water content. Suppressed conduction arises either from layer collapse at low water levels or from ionic hop blockage by excess water at high water levels. Concurrently, ionic transport exhibits a maximum at intermediate levels of intercalated water, where less hydrated ions can move at the boundaries of strongly hydrated ion clusters. While such non-monotonicity could explain the experimentally observed memristive response of $\mathrm{MnO_2}$ single crystals, these findings also provide a molecular-level mechanism linking intercalated water levels to ionic metal oxide nanofluidic systems, suggesting general design principles for robust, water-assisted ionic conductors.

cond-mat.mtrl-sci↗

arXiv2026

A review on scanning photocurrent microscopy and its application to one- and two-dimensional materials

The electrical response of a material when illuminated with light is a key to many optoelectronic device applications. This so-called photoresponse typically has a non-uniform spatial distribution through the active device area, and the ability to spatially resolve the photoresponse enables an in-depth understanding of the underlying physical mechanisms. Scanning photocurrent microscopy (SPCM) is a method that allows the spatial mapping of the photoresponse by raster scanning a focused laser beam over the sample. SPCM is becoming more popular due to its simplicity and power in unraveling fundamental optoelectronic processes. In this review, first, we provide the fundamentals of SPCM to lay the basics for the subsequent discussions. Then, we focus on the literature that employs SPCM to identify the photoresponse of one- and two-dimensional materials. We discuss SPCM measurement results of common materials in detail and introduce a systematic approach to interpreting the SPCM measurements. We have given particular emphasis on the photothermal mechanisms that are excited by the focused laser beam and critically reviewed studies in the literature from the perspective of laser-induced heating of the electronic and the lattice degrees of freedom. Finally, we discuss the shortcomings of SPCM in determining the mechanisms leading to the photoresponse.

cond-mat.mtrl-sci↗

arXiv2025

Synthesis of Ultra-thin Potassium Tungsten Bronze Single Crystals with Optically Contrasting Domains and Resistive Switching

Potassium tungsten bronzes (K$_x$WO$_3$) are nonstoichiometric oxides in which alkali ions, i.e., K+, occupy one-dimensional tunnels of the hexagonal WO6 framework, enabling coupled ionic-lectronic transport. While their bulk and nanostructured forms have been studied extensively, controlled synthesis of single-crystalline mesoscale samples suitable for device fabrication has remained limited. Here, we report a solid-liquid-solid (SLS) growth strategy that yields high-quality K$_x$WO$_3$ nanobelts with thicknesses down to ~36 nm and lateral sizes exceeding 100 um. The crystals display sharp optical domains arising from local variations in potassium occupancy, as confirmed by spatially resolved Raman spectroscopy and electron diffraction. Under applied bias, these domains vanish irreversibly, consistent with lateral redistribution of K+ ions along the tunnels. Two-terminal devices fabricated from individual nanobelts exhibit reproducible bipolar switching with resistance ratios of 10-30, characteristic short-term and long-term plasticity under pulsed excitation, and switching energies of ~25 nJ. These results establish K$_x$WO$_3$ as a model tunnel-structured oxide for studying electric-field-driven alkali-ion migration, while also highlighting its potential for stable, analog resistive switching and iontronic memory applications.

cond-mat.mtrl-sci↗

arXiv2024

Photoluminescence enhancement at the vertical van der Waals semiconductor-metal heterostructures

Excitons in monolayer transition metal dichalcogenides (TMDCs) offer intriguing new possibilities for optoelectronics with no analogues in bulk semiconductors. Yet, intrinsic defects in TMDCs limit the radiative exciton recombination pathways. As a result, the photoluminescence (PL) quantum yield (QY) is limited. Methods like superacid treatment, electrical doping, and plasmonic engineering can inhibit nonradiative decay channels and enhance PL. Here, we show a more straightforward approach that allows PL enhancement. An engineered vertical van der Waals (vdW) metal-monolayer semiconductor junction (MSJ) results in PL enhancement of more than an order of magnitude at technologically relevant excitation powers. Such MSJ can be constructed by vertically stacking metals with suitable work function either above or below a monolayer semiconducting TMDC. Our experiments reveal that the underlying PL enhancement mechanism is to be the suppressed exciton quenching due to the absence of metal-induced gap states and weak Fermi level pinning, thanks to the vdW gapped interface between the metal and the TMDC. Our time-resolved PL measurements further indicate that reduced exciton-exciton annihilation, even at high generation rates, contributes to the observed PL enhancement. The PL intensity is further increased by the proximity of surface plasmons in the metal with the TMDC layer. Our findings shed light on the interaction at vdW metal-semiconductor interfaces and offer a path to improving the optoelectronic performance of semiconducting TMDCs.

cond-mat.mes-hall↗

arXiv2023

Second Harmonic Generation in Chemical Vapor Deposition Synthesized CuS Crystals

Copper sulfide (CuS) has garnered significant attention in various fields of application due to its unique electronic, optical, and catalytic features. In this study, we present the chemical vapor deposition (CVD)-based synthesis of ultrathin CuS crystals as thin as 14 nm with lateral sizes up to 60 um. The structure, morphology, and composition of the as-synthesized CuS crystals were thoroughly characterized. Among our results, we measured the first-order temperature coefficients of Raman shifts of CuS. Moreover, we showed that CuS crystals exhibited an unexpected second harmonic generation (SHG), which is attributed to the presence of defects in the CuS lattice. Our results suggest that single crystalline CuS possesses a considerable potential for nonlinear optical applications in conjunction with its current applications in electronics and catalysis.

cond-mat.mtrl-sci↗