Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2610.15196

Nucleation at the GST--oxide interface and beam-driven ordering in amorphous Ge--Sb--Te: HAADF, EDS and electron pair distribution functions across a 4D-STEM dose series

Mridul Kumar·Kirill Sobolev·Alexander Upcher·Yevgeny Rakita
View original source ↗Read source document ↗Export metadata ↓

Abstract

Where crystal nuclei form in amorphous phase-change materials decides how they switch. We study six successive 4D-STEM scans, with simultaneous HAADF and EDS data, of a magnetron-sputtered Ge-Sb-Te (GST) film, restricted to the GST layer and its interface with the oxide beneath it. Nucleation sites do not differ in composition or number density: the nuclei lie on the same robust HAADF-EDS relation as the matrix, and at fixed HAADF the spread of the summed EDS signal equals its Poisson counting noise (ratio 1.03 +- 0.05). The nuclei are nevertheless crystalline and stand out in the 4D-STEM max-intensity virtual image (median z = 11.0) but not in HAADF (z = 1.3) or EDS (z = 0.3). We classify the film in four ways (HAADF intensity, I(q) phase mapping, PCA of the whole diffraction patterns and a self-supervised SimCLR encoder) and compare the electron pair distribution functions (PDFs) of all classes after calibrating reciprocal space on the Au cap. All bulk classes share one short-range structure (first shell 2.70-2.74 Å); towards the interface the first sharp diffraction peak (FSDP) moves to lower q, and every method isolates a thin interface-edge environment with a shorter or missing first shell. The I(q) classification isolates, in every scan, an interface environment that holds 62-100% of the nucleus pixels (1.2-2.5-fold above depth) and persists when the nucleus pixels are removed before classification. The interface, rather than a distinct composition or density of the nucleating volume, therefore marks where nuclei form. Over 4.7e3 e/Å^2 the HAADF signal falls by 17%, the first shell shortens by 0.03 Å and the FSDP narrows by 9%, apparently ordering the film as it damages it. All analyses used PySTEMLab, an interactive 4D-STEM analysis environment developed for this work.

Explore related subjects

cond-mat.mtrl-sci

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Mridul Kumar, Kirill Sobolev, Alexander Upcher, Yevgeny Rakita. 2026-10-10. Nucleation at the GST--oxide interface and beam-driven ordering in amorphous Ge--Sb--Te: HAADF, EDS and electron pair distribution functions across a 4D-STEM dose series. https://arxiv.org/abs/2610.15196

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Extreme Suppression of Thermal Conductivity in Monolayer Beryllene

We demonstrate an extreme suppression of thermal conductivity in monolayer beryllene through first-principles solutions of the phonon Boltzmann transport equation. While the fully converged three-phonon calculation predicts a room-temperature lattice thermal conductivity of 154.3 W/(m$\cdot$K), inclusion of four-phonon interactions suppresses it to 10.7 W/(m$\cdot$K), a reduction of more than 90\%. This exceptionally large reduction of the thermal conductivity is amongst the highest reported in two-dimensional materials. The microscopic origin of this breakdown is traced to the strong sensitivity of the low-frequency flexural ZA phonons to four-phonon scattering: mode-resolved scattering rates reveal a pronounced enhancement of ZA scattering, which substantially shortens their lifetimes and suppresses their dominant contribution to heat conduction. Moreover, the temperature dependence of the thermal conductivity changes from $κ\propto T^{-0.86}$ to $κ\propto T^{-1.38}$ upon inclusion of four-phonon processes. Our results establish $α$-beryllene as an unusually strong case of four-phonon-controlled thermal transport amongst two-dimensional materials. These findings identify selective higher-order scattering of flexural phonons as a key mechanism for controlling thermal transport in strongly anharmonic low-dimensional systems.

cond-mat.mtrl-sci↗
arXiv2026

Electric Edelstein Effect in Two Dimensions

We propose the electric Edelstein effect (EEE) in two-dimensional (2D) systems, where crossed out-of-plane and in-plane electric fields generate a spin polarization. The gate field converts the Edelstein response from a material-fixed spin polarization into a gate-tunable one. A symmetry analysis over all magnetic layer point groups shows that the EEE is allowed in a wide range of magnetic and nonmagnetic systems, including ferromagnets, antiferromagnets, and altermagnets. The EEE plays two distinct roles: it generates spin polarization where the linear Edelstein effect (EE) is symmetry-forbidden, as in centrosymmetric materials; and it adds a new gate-tunable component, generally non-collinear with the conventional one, where the EE is already present. The two fields then act as independent knobs and raise the control dimension of the spin polarization from one to two. Our microscopic theory traces the EEE to band-geometric quantities, which are strongly enhanced near small band gaps. First-principles calculations predict pronounced effects in the centrosymmetric ferromagnet MnSe2, where the linear EE is symmetry-forbidden. In the nonmagnet SnSe where the EE and EEE coexist, the two knobs cover an extended region of the spin sphere. Our findings establish the EEE as a symmetry-guided, gate-tunable route to electrical spin manipulation and open avenues for multistate spintronics in 2D quantum materials.

cond-mat.mtrl-sci↗
arXiv2026

A grand potential for molten-salt electrochemical phase diagrams from first principles

The clean-energy transition is driving unprecedented demand for metals, whose extraction is among the largest industrial sources of carbon emissions. Molten-salt electrolysis offers a path toward carbon-free production of aluminum, iron, titanium, and critical metals. However, corrosive operating conditions and complex, multicomponent feedstocks make experimental development costly and challenging. Here, we introduce a first-principles framework for constructing electrochemical phase diagrams of multicomponent systems to accelerate electrode and electrolyte design and guide the selection of compatible materials and operating conditions for electrochemical cells. We derive a grand potential that generates these diagrams at scale, and supply free energies using first-principles data obtained through a fine-tuned foundation machine-learned interatomic potential. For silicon in molten CaCl$_2$, the construction not only recovers the experimental diagram when using the first-principles framework on a limited set of structures, but also predicts further domains when extended to a larger set of crystal structures. Finally, we demonstrate the predictive power of the approach by screening ten alkali and alkaline-earth halide electrolytes for aluminum electrowinning. Three thermodynamic criteria identify NaF, where cryolite emerges as the stable aluminum-bearing phase, recovering the chemistry that Hall and Héroult established empirically in 1886. The framework provides a first-principles basis for selecting compatible electrodes, electrolytes, and operating conditions toward low-carbon metal production from complex source materials.

cond-mat.mtrl-sci↗