arXiv subjects

Doruk Pehlivanoğlu

Publications and source records attributed to Doruk Pehlivanoğlu.

5 recordsLinked to original sources

arXiv2026

Pt-wedge squeegee cleaning of two-dimensional materials and heterostructures

The surface of ultra-thin materials plays a crucial role in determining the properties. This is particularly important in two-dimensional (2D) materials where the surface-bulk distinction is no longer present. While mechanical cleaning of two-dimensional materials to remove interfacial and surface contaminants is used to achieve better sample quality, low throughput and the challenging optimization of cleaning procedures hinder their widespread adoption. Here, we report on atomic force microscope (AFM)-based mechanical cleaning with modified AFM cantilevers for high-throughput and easy-to-implement cleaning of 2D materials and their heterostructures. A Pt-wedge is deposited via focused ion beam on the cantilever to improve the mechanical cleaning of samples and streamline the cleaning procedures. We demonstrate that a cleaning rate of 3 μ^2/s can be achieved with our modified cantilevers, compared to the 0.01 μ^2/s effective cleaning rate in pointy-tip cleaning. As showcases, we demonstrate that monolayer WS2 on h-BN exhibits much sharper photoluminescence (PL) emission at room temperature after AFM cleaning, and WS2 monolayers exhibit a higher quality contacts to cleaned Au electrodes as compared to uncleaned electrodes. We also showed that h-BN encapsulated heterostructures can be cleaned rapidly using the improved method. Overall, our results exhibit a feasible and facile path for the large-scale application of AFM-based cleaning of integrated 2D materials.

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↗

arXiv2025

In-Situ Growth and Ionic Switching Behavior of Single-Crystalline Silver Iodide Nanoflakes

Silver iodide (AgI) is a prototypical superionic conductor, undergoing a first-order phase transition at 147 Celsius that enables rapid ionic transport through its lattice, making it attractive for solid-state ionic devices. However, due to the presence of mobile Ag ions, controlled chemical vapor deposition (CVD) synthesis of high-quality AgI single crystals has remained largely unexplored. Here, we present the controllable synthesis of thin, single-crystalline β-AgI nanoflakes using a home-built CVD setup with real-time optical observation capability, offering insights into their nucleation and growth dynamics. We evaluate the material's environmental stability through temperature-dependent photodegradation and Ag nanoparticle formation induced by electron beam irradiation. Electrical measurements on two-terminal devices with silver contacts demonstrate a remarkable six-order-of-magnitude resistance drop in lateral configurations at elevated temperatures, indicative of switchable ionic conductivity. Additionally, vertical device architectures exhibit clear memristive (resistive switching) characteristics, likely due to the formation of conductive filaments. Our work addresses the key synthesis challenges and highlights the unique electrical properties of thin AgI single crystals, suggesting its potential for innovative devices in unconventional computing, data storage, and advanced neuromorphic systems.

cond-mat.mtrl-sci↗

arXiv2023

Synthesis of Ultra-Thin Superionic Cu2Se and New Aspects of the Low-Temperature Crystal Configurations

Superionic conductors offer unique advantages for novel technological devices in various fields, such as energy storage and neuromorphic computing. Above 414 K, Cu2Se turns into a well-known superionic conductor via a phase transition, and it is demonstrated to exhibit peculiar electrical and thermoelectric properties in bulk. Here, we report a large-area synthesis of ultra-thin single crystalline Cu2Se using the chemical vapor deposition method. We demonstrate that Cu2Se crystals exhibit optically and electrically controllable robust phase reconfiguration below 414 K. Moreover, our results show that the mobility of the liquid-like Cu ion vacancies in Cu2Se causes macroscopic fluctuations in the Cu ordering. Consequently, phase variations are not dictated by the diffusive motion of the ions but by the local energy minima formed due to the interplay between the extrinsic and the intrinsic material parameters. As a result, long-range ordering of the crystal below 414 K is optically observable at a micrometer scale. Our results show that Cu2Se could find applications beyond thermoelectric such as smart optical coatings, optoelectronic switching, and ionic transistors.

cond-mat.mtrl-sci↗

arXiv2023

Single-material MoS$_{2}$ thermoelectric junction enabled by substrate engineering

To realize a thermoelectric power generator, typically a junction between two materials with different Seebeck coefficient needs to be fabricated. Such difference in Seebeck coefficients can be induced by doping, which renders difficult when working with two-dimensional (2d) materials. Here, we employ substrate effects to form a thermoelectric junction in ultra-thin few-layer MoS2 films. We investigated the junctions with a combination of scanning photocurrent microscopy and scanning thermal microscopy. This allows us to reveal that thermoelectric junctions form across the substrate-engineered parts. We attribute this to a gating effect induced by interfacial charges in combination with alterations in the electron-phonon scattering mechanisms. This work demonstrates that substrate engineering is a promising strategy to develop future compact thin-film thermoelectric power generators.

cond-mat.mtrl-sci↗