arXiv subjects

Marija Drndić

Publications and source records attributed to Marija Drndić.

8 recordsLinked to original sources

arXiv2026

Evolution of Nonlinear Ion Transport in Nanopore Arrays: Ionic Conductance, Current Rectification, and Osmotic Power

Understanding the ionic transport and scaling behaviors in nanopore arrays is essential for bridging fundamental ion physics and blue energy applications. By fabricating sub-3 nm and sub-20 nm diameter nanopore arrays (NPAs) spanning from few pores to N ~ 10000, we systematically investigate ionic conductance, ion current rectification, and osmotic energy conversion. We report the ionic conductance scaling laws and nonlinearity with nanopore number, with stronger deviations from linearity at lower salt concentrations. Experimental evidence reveals that surface-charge-governed conductance and ion current rectification progressively weaken with increasing N and even vanish as the NPA scales up to N ~ 10000, resulting in an underestimation of surface charge density. In a sub-3 nm densely packed array (separation ~ 25 nm), the conductance exhibits an anomalous power-law dependence on concentration, deviating markedly from the single nanopore characteristics, attributed to the strong pore interactions. Furthermore, osmotic power harvesting measurements reveal a substantial reduction in power density upon scaling, with decreases of up to three orders of magnitude over the same range. To elucidate the underlying mechanism, we developed rigorous 3D modeling showing that the nonlinear behavior originates from concentration polarization at pore entrances and suppressed electric field across NPAs, collectively hindering ion transport. Our work provides insight into nonlinear ion-transport scaling and reveals fundamental differences between transport phenomena in single nanopores and nanopore arrays.

cond-mat.mtrl-sci↗

arXiv2025

Reversible nanopore sealing and in situ iron oxide nanoparticle synthesis on thin silicon nitride membranes

We report in-situ synthesis of iron oxide particles inside silicon nitride nanopores via a chemical reaction, monitored by current readout. Nanopores were formed by electroporation on glass chips (diameters from 1.7 to 11.3 nm), transmission electron microscopy (TEM) drilling (diameters from 6.5 to 64.6 nm), or hydrofluoric acid (HF) etching (diameters from 12.6 to 36.2 nm) in 5 to 20 nm thick membranes. Nanopores seal on timescales from ~1 ms to ~3.6 s, across a range of sizes and concentrations. We show single and ~5-pore arrays, as fabricated, after sealing, and after cleaning and pore recovery. These results are independent of fabrication method. Energy dispersive X-ray spectroscopy (EDS), aberration-corrected scanning TEM (AC-STEM), and powder X-ray diffraction (XRD) verify the synthesis of mixed magnetite and maghemite iron oxide. This work advances nanoparticle-nanopore chips for applications in biosensing, plasmonics and photonics when position and size control is required.

cond-mat.mtrl-sci↗

arXiv2025

Tungsten doping-induced phase transition in CVD-grown MoS2 bilayers

Controlling the crystal phase of two-dimensional (2D) transition metal dichalcogenides (TMDs) is essential for tailoring their optical and electronic properties. While phase transitions in monolayer TMDs and semiconductor-to-metal conversions have been widely studied, structural transitions between semiconducting polytypes - particularly in bilayer (2L) systems - remain underexplored. Here, we demonstrate a W doping-induced phase transition from non-centrosymmetric AA stacking to centrosymmetric AB' in 2L MoS2 synthesized by chemical vapor deposition (CVD). Using polarization-resolved second harmonic generation (SHG) and low-frequency Raman spectroscopy, we identify a phase transition correlated with increasing tungsten (W) concentration. The dilute W-doped 2L system exhibits a vanishing SHG signal and a stiffening of the layer-breathing (LB) vibrational mode, in contrast to undoped samples with strong SHG and a softer LB mode. Aberration corrected scanning transmission electron microscopy (AC-STEM) demonstrates the spatial distribution of W concentration and associated structural changes. These findings highlight W-doping as an effective strategy for inducing phase transitions in 2L TMDs, opening new possibilities for engineered heterostructures, phase-controlled device applications or as a source of single photon emitters.

cond-mat.mtrl-sci↗

arXiv2025

Observation of giant remnant polarization in ultrathin AlScN at cryogenic temperatures

The discovery of wurtzite ferroelectrics opens new frontiers in polar materials, yet their behavior at cryogenic temperatures remains unexplored. Here, we reveal unprecedented ferroelectric properties in ultrathin (10 nm) Al$_{0.68}$Sc$_{0.32}$N (AlScN) at cryogenic temperatures where the properties are fundamentally distinct from those of conventional oxide ferroelectrics. At 12 K, we demonstrate a giant remnant polarization exceeding 250 $μ$C/cm$^2$ -- more than twice that of any known ferroelectric -- driven by an enhanced c/a ratio in the wurtzite structure. Our devices sustain remarkably high electric fields (~13 MV/cm) while maintaining reliable switching, achieving over 104 polarization reversal cycles at 12 K. Critically, this breakdown field strength approaches that of passive dielectric materials while maintaining ferroelectric functionality. The extraordinary polarization enhancement and high-field stability at cryogenic temperatures contrasts sharply with oxide ferroelectrics, establishing wurtzite ferroelectrics as a distinct class of polar materials with implications spanning fundamental physics to cryogenic non-volatile memory and quantum technologies.

cond-mat.mtrl-sci↗

arXiv2024

Correlated Structural and Optical Characterization of Hexagonal Boron Nitride

Hexagonal boron nitride (hBN) plays a central role in nanoelectronics and nanophotonics. Moreover, hBN hosts room-temperature quantum emitters and optically addressable spins, making it promising for quantum sensing and quantum photonics. Despite many investigations of their optical properties, however, the emitters' chemical structure remains unclear, as does the role of contamination at surfaces and interfaces in forming the emitters or modifying their properties. We prepare hBN samples that are compatible with confocal photoluminescence (PL) microscopy, transmission electron microscopy (TEM), and atomic-force microscopy (AFM), and we use those techniques to quantitatively investigate correlations between fluorescent emission, flake morphology, and surface residue. We find that the microscopy techniques themselves induce changes in hBN's optical activity and residue morphology: PL measurements induce photobleaching, whereas TEM measurements alter surface residue and emission characteristics. We also study the effects of common treatments $\unicode{x2014}$ annealing and oxygen plasma cleaning $\unicode{x2014}$ on the structure and optical activity of hBN. The methods can be broadly applied to study two-dimensional materials, and the results illustrate the importance of correlative studies to elucidate structural factors that influence hBN's functionality as a host for quantum emitters and spin defects.

cond-mat.mtrl-sci↗

arXiv2024

High-Performance Ferroelectric Field-Effect Transistors with Ultra-High Current and Carrier Densities

Ferroelectric field-effect transistors (FeFET) with two-dimensional (2D) semiconductor channels are promising low-power, embedded non-volatile memory (NVM) candidates for next-generation in-memory computing. However, the performance of FeFETs can be limited by a charge imbalance between the ferroelectric layer and the channel, and for low-dimensional semiconductors, also by a high contact resistance between the metal electrodes and the channel. Here, we report a significant enhancement in performance of contact-engineered FeFETs with a 2D MoS2 channel and a ferroelectric Al0.68Sc0.32N (AlScN) gate dielectric. Replacing Ti with In contact electrodes results in a fivefold increase in on-state current (~120 uA/um at 1 V) and on-to-off ratio (~2*10^7) in the FeFETs. In addition, the high carrier concentration in the MoS2 channel during the on-state (> 10^14 cm^-2) facilitates the observation of a metal-to-insulator phase transition in monolayer MoS2 permitting observation of high field effect mobility (> 100 cm^2V^-1s^-1) at cryogenic temperatures. Our work and devices broaden the potential of FeFETs and provides a unique platform to implement high-carrier-density transport in a 2D channel.

physics.app-ph↗

arXiv2017

Materials analysis and focused ion beam nanofabrication of topological insulator Bi2Se3

Focused ion beam milling allows manipulation of the shape and size of nanostructures to create geometries potentially useful for opto-electronics, thermoelectrics, and quantum computing. We focus on using the ion beam to control the thickness of Bi2Se3 and to create nanowires from larger structures. Changes in the material structure of Bi2Se3 nanomaterials that have been milled using a focused ion beam are presented. In order to characterize the effects of ion beam processing on the samples, we use a variety of techniques including analytical transmission electron microscopy and atomic force microscopy. The results show that while part of the material remains intact after shaping, amorphous regions form where the beam has been used to thin the sample. For wires created by thinning the material down to the substrate, the sidewalls of the wires appear intact based on diffraction images from samples cut at an angle, but thin crystalline regions remain at the wire edges. Even with the resulting defects, focused ion beam milling shows promise for directly fabricating intricate nanodevices of Bi2Se3.

cond-mat.mtrl-sci↗

arXiv2011

In-situ electronic characterization of graphene nanoconstrictions fabricated in a transmission electron microscope

We report electronic measurements on high-quality graphene nanoconstrictions (GNCs) fabricated in a transmission electron microscope (TEM), and the first measurements on GNC conductance with an accurate measurement of constriction width down to 1 nm. To create the GNCs, freely-suspended graphene ribbons were fabricated using few-layer graphene grown by chemical vapor deposition. The ribbons were loaded into the TEM, and a current-annealing procedure was used to clean the material and improve its electronic characteristics. The TEM beam was then used to sculpt GNCs to a series of desired widths in the range 1 - 700 nm; after each sculpting step, the sample was imaged by TEM and its electronic properties measured in-situ. GNC conductance was found to be remarkably high, comparable to that of exfoliated graphene samples of similar size. The GNC conductance varied with width approximately as, where w is the constriction width in nanometers. GNCs support current densities greater than 120 \muA/nm2, two orders of magnitude higher than has been previously reported for graphene nanoribbons and 2000 times higher than copper.

cond-mat.mes-hall↗