arXiv subjects

Marcos Penedo

Publications and source records attributed to Marcos Penedo.

6 recordsLinked to original sources

arXiv2026

Agentic AI for operating scientific instruments for nanoscale characterization

Operating a scientific instrument such as an atomic force microscope (AFM) requires continuous expert decision-making. A trained user defines the experimental intent, translates it into instrument commands, assesses incoming data, adjusts imaging parameters, and post-processes the final image. Existing automation usually addresses only parts of this workflow through hard-coded routines, task-specific controllers, or trained machine-learning models. Here we present an agentic-AI framework that operates the executable part of the AFM workflow using a general-purpose, tool-augmented large language model connected to instrument functions through the Model Context Protocol (MCP). The framework consists of 3 MCP-based agents: AFM Messenger converts natural-language instructions into checked instrument commands; AFM Pilot assesses image quality through a large language model (LLM) and, if necessary, adapts imaging parameters; and AFM Doctor diagnoses image artifacts and applies transparent post-processing from a pre-approved tool set. Because the language model performs image assessment rather than a fixed scalar objective or external optimizer, the same strategy can be applied across sample types and imaging modes without specific retraining. Safe hardware operation is enforced through an ambiguity check layer before execution. Benchmarking against fine-tuned and off-the-shelf tool-using models shows that this guarded execution layer, rather than model capability alone, reduces wrong-command execution to zero. In live experiments on different samples, AFM Pilot matched expert operators in image quality, iteration count, and tuning time, with no significant difference. These results demonstrate a safe route to agentic operation of scientific instruments, where experimental intent remains human-defined while command execution, image-based tuning, and post-processing are delegated to AI agents.

cs.AI↗

arXiv2026

In-situ correlative SEM/KPFM for semiconductor devices and 2D heterostructures

Correlative nanoscale surface characterization benefits from simultaneously measuring electronic and structural properties in the same environment, a capability that is essential for modern-day materials science and semiconductor failure analysis. In-situ AFM-SEM measurements facilitated by self-sensing cantilevers offer great potential here; however, they are limited due to their inherent capacitive crosstalk. Here, we demonstrate for the first time the in-situ implementation of single-pass heterodyne Kelvin probe force microscopy inside a scanning electron microscope, using piezo-resistive cantilevers. We overcome the capacitive crosstalk prevalent in piezo-resistive cantilevers by demodulating excitation and detection to simultaneously map surface topography and contact potential difference for correlation with compositional analysis. We systematically compare different operational modes of this heterodyne technique, elucidating their spatial resolution, signal sensitivity, and signal-to-noise ratio. The integrated approach yields exceptional signal quality and reveals how electron beam scan parameters can directly influence surface potential contrast. We demonstrate this correlative analysis workflow on two-dimensional heterostructures and semiconductor circuits. This work establishes a robust and versatile correlative imaging mode for in-situ Kelvin force and topography imaging inside a scanning electron microscope for next-generation semiconductor device analysis and materials science.

cond-mat.mes-hall↗

arXiv2023

Enhanced feedback performance in off-resonance AFM modes through pulse train sampling

Dynamic atomic force microscopy (AFM) modes that operate at frequencies far away from the resonance frequency of the cantilever (off-resonance tapping (ORT) modes) can provide high-resolution imaging of a wide range of sample types, including biological samples, soft polymers, and hard materials. These modes offer precise and stable control of vertical force, as well as reduced lateral force. Simultaneously, they enable mechanical property mapping of the sample. However, ORT modes have an intrinsic drawback: a low scan speed due to the limited ORT rate, generally in the low kHz range. Here, we analyze how the conventional ORT control method limits the topography tracking quality and hence the imaging speed. The closed-loop controller in conventional ORT restricts the sampling rate to the ORT rate and introduces a large closed-loop delay. We present an alternative ORT control method in which the closed-loop controller samples and tracks the vertical force changes during a defined time window of the tip-sample interaction. Through this, we use multiple samples in the proximity of the maximum force for the feedback loop, rather than only one sample at the maximum force instant. This method leads to improved topography tracking at a given ORT rate and therefore enables higher scan rates while refining the mechanical property mapping. Keywords: atomic force microscopy (AFM); off-resonance tapping (ORT); pulsed-force mode; feedback control

physics.ins-det↗

arXiv2020

Coexistence of distinct skyrmion phases observed in hybrid ferromagnetic/ferrimagnetic multilayers

Materials hosting magnetic skyrmions at room temperature could enable new computing architectures as well as compact and energetically efficient magnetic storage such as racetrack memories. In a racetrack device, information is coded by the presence/absence of magnetic skyrmions forming a chain that is moved through the device. The skyrmion Hall effect that would eventually lead to an annihilation of the skyrmions at the edges of the racetrack can be suppressed for example by anti-ferromagnetically-coupled skyrmions. However, avoiding modifications of the inter-skyrmion distances in the racetrack remains challenging. As a solution to this issue, a chain of bits could also be encoded by two different solitons such as a skyrmion and a chiral bobber. The major limitation of this approach is that it has solely been realized in B20-type single crystalline material systems that support skyrmions only at low temperatures, thus hindering the efficacy for future applications. Here we demonstrate that a hybrid ferro/ferri/ferromagnetic multilayer system can host two distinct skyrmion phases at room temperature. By matching quantitative magnetic force microscopy data with micromagnetic simulations, we reveal that the two phases represent tubular skyrmions and partial skyrmions (similar to skyrmion bobbers). Furthermore, the tubular skyrmion can be converted into a partial skyrmion. Such multilayer systems may thus serve as a platform for designing skyrmion memory applications using distinct types of skyrmions and potentially for storing information using the vertical dimension in a thin film device.

cond-mat.mtrl-sci↗

arXiv2017

Halbach arrays at the nanoscale from chiral spin textures

Mallinson's idea that some spin textures in planar magnetic structures could produce an enhancement of the magnetic flux on one side of the plane at the expense of the other gave rise to permanent magnet configurations known as Halbach magnet arrays. Applications range from wiggler magnets in particle accelerators and free electron lasers, to motors, to magnetic levitation trains, but exploiting Halbach arrays in micro- or nanoscale spintronics devices requires solving the problem of fabrication and field metrology below 100 μm size. In this work we show that a Halbach configuration of moments can be obtained over areas as small as 1 x 1 μm^2 in sputtered thin films with Néel-type domain walls of unique domain wall chirality, and we measure their stray field at a controlled probe-sample distance of 12.0 x 0.5 nm. Because here chirality is determined by the interfacial Dyzaloshinkii-Moriya interaction the field attenuation and amplification is an intrinsic property of this film, allowing for flexibility of design based on an appropriate definition of magnetic domains. 100 nm-wide skyrmions illustrate the smallest kind of such structures, for which our measurement of stray magnetic fields and mapping of the spin structure shows they funnel the field toward one specific side of the film given by the sign of the Dyzaloshinkii-Moriya interaction parameter D.

cond-mat.mtrl-sci↗

arXiv2016

Surface single-molecule dynamics controlled by entropy at low temperatures

Configuration transitions of individual molecules and atoms on surfaces are traditionally described with energy barriers and attempt rates using an Arrhenius law. This approach yields consistent energy barrier values, but also attempt rates orders of magnitude below expected oscillation frequencies of particles in the meta-stable state. Moreover, even for identical systems, the measurements can yield values differing from each other by orders of magnitude. Using low temperature scanning tunnelling microscopy (STM) to measure an individual dibutyl-sulfide molecule (DBS) on Au(111), we show that we can avoid these apparent inconsistencies if we account for the relative position of tip apex and molecule with accuracy of a fraction of the molecule size. Altering the tip position on that scale modifies the transition's barrier and attempt rate in a highly correlated fashion, which on account of the relation between the latter and entropy results in a single-molecular enthalpy-entropy compensation. By appropriately positioning the tip apex the STM tip can be used to select the operating point on the compensation line and modify the transition rates. The results highlight the need to consider entropy in transition rates of a single molecule, even at temperatures where entropy effects are usually neglected.

cond-mat.mes-hall↗