arXiv subjects

Andrei Kolmakov

Publications and source records attributed to Andrei Kolmakov.

15 recordsLinked to original sources

arXiv2026

Understanding microfabricated nanocalorimeter performance and responses to the energy fluxes from low-temperature plasma discharges

Plasma diagnostics have a shortage of fast and sensitive calorimetric sensors that can track substrate temperature during plasma-assisted microfabrication. In this work, energy fluxes from argon and oxygen radiofrequency (RF) glow discharges have been probed using a novel nanocalorimeter sensor. The probe consists of an ultrathin SiNx membrane (100 nm) with a lithographically defined Pt micro-strip (100 nm) that serves as a calibrated resistance thermometer. The sensor temperature can increase from room temperature to several hundred degrees within a second upon exposure to RF plasma, depending on the experiment's geometry and plasma parameters. Such sensitivity and response time are due to the pre-designed reduced heat capacity of the sensor and significantly reduced thermal conductance of the cooling channels. These features enable the sensitive detection of low-energy plasma fluxes on surfaces and their rapid discrimination, as in the case of ion and electron fluxes, by biasing the sensor at negative or positive potentials. These biased nanocalorimeter energy readings have been compared with ion and electron kinetic energy dissipations assessed using a Langmuir probe and retarding field energy analyzer (RFEA). Finally, the robustness of the plasma nanocalorimeter is discussed in terms of its baseline drifts, degradation, and longevity.

physics.plasm-ph↗

arXiv2025

Toward the Origins of Binding Energy Shifts and Satellites Formation During Plasma-XPS Measurements

In plasma X ray photoelectron spectroscopy emerges as a powerful platform for real time, in situ chemical analysis under conditions relevant to semiconductor processing and other plasma enabled technologies. This study investigates the origins of binding energy shifts and satellite peaks formation observed during plasma XPS measurements across conductive, dielectric, and gas phase systems. Using a standard laboratory based ambient pressure XPS apparatus coupled with an alternating current driven capacitively coupled plasma source, we show that metastable surface species, such as transient Au oxides, can be detected during plasma exposure, revealing chemical states hardly accessible using conventional ultrahigh vacuum XPS. In dielectric samples, we observe pressure- and plasma type dependent BE shifts up to 50 eV, attributed to X ray induced and plasma mediated surface charging. These shifts are mitigated at higher pressures plasmas or in electronegative plasmas, the latter due to enhanced charge compensation mechanisms involving slow negative ions. For gas phase species, AC plasma excitation leads to spectral broadening and the emergence of satellite peaks with a few eV energy separations, linked to oscillating local plasma potentials in the probing volume. These findings highlight the important and complex interplay of plasma parameters, surface charging, and local electric fields in shaping XPS spectra. Overall, plasma XPS emerges as a critical metrological tool for probing transient surface chemistry, with implications for semiconductor processing, material synthesis, and plasma diagnostics.

physics.plasm-ph↗

arXiv2025

Automated Prediction of Thermodynamic Properties via Bayesian Free-Energy Reconstruction from Molecular Dynamics

Accurate free-energy calculations are essential for predicting thermodynamic properties and phase stability, but existing methods are limited: phonon-based approaches neglect anharmonicity and liquids, while molecular dynamics (MD) is computationally demanding, neglects low-temperature quantum effects, and often requires manual planning and post-processing of simulations. We present a unified workflow that reconstructs the Helmholtz free-energy surface from MD data using Gaussian Process Regression (GPR), augmented with zero-point energy corrections from harmonic/quasi-harmonic theory. The framework propagates statistical uncertainties, mitigates finite-size effects, and employs active learning to optimize sampling in the volume-temperature space. It applies seamlessly to both crystalline and liquid phases. We demonstrate the methodology by computing heat capacities, thermal expansion, isothermal and adiabatic bulk moduli, and melting properties for nine elemental FCC and BCC metals using 20 classical and machine-learned interatomic potentials, with all predictions accompanied by quantified confidence intervals. Automated, general, and uncertainty-aware, the workflow advances high-throughput thermodynamics and provides a systematic benchmark for interatomic potentials.

cond-mat.mtrl-sci↗

arXiv2025

Operando XPS in Reactive Plasmas: The Importance of The Wall Reactions

Advancements in differential pumping and electron optics over the past few decades have enabled x-ray photoelectron spectroscopy (XPS) measurements at (near-)ambient pressures, bridging the pressure gap for characterizing realistic sample chemistries. Recently, we demonstrated the capabilities of an ambient pressure XPS (APXPS) setup for in-situ plasma environment measurements, allowing plasma-surface interactions to be studied in operando rather than using the traditional before-and-after analysis approach. This new plasma-XPS technique facilitates the identification of reaction intermediates critical for understanding plasma-assisted surface processes relevant to semiconductor nanomanufacturing, such as physical vapor deposition, etching, atomic layer deposition, etc. In this report, we apply the plasma-XPS approach to monitor real-time surface chemical changes on a model Ag(111) single crystal exposed to oxidizing and reducing plasmas. We correlate surface-sensitive data with concurrent gas-phase XPS measurements and residual gas mass-spectra analysis of species generated during plasma exposure, highlighting the significant role of plasma-induced chamber wall reactions. Ultimately, we demonstrate that plasma-XPS provides comprehensive insights into both surface and gas-phase chemistry, establishing it as a versatile and dynamic characterization tool with broad applications in microelectronics research.

physics.plasm-ph↗

arXiv2024

Operando Plasma-XPS for Process Monitoring: Hydrogenation of Copper Oxide Confined Under h-BN Case Study

We demonstrate that ambient pressure x-ray photoelectron spectroscopy (APXPS) can be used for in situ studies of dynamic changes in surface chemistry in a plasma environment. Hexagonal boron nitride (h-BN) was used in this study as a model system since it exhibits a wide array of unique chemical, optical, and electrical properties that make it a prospective material for advanced electronics. To better understand the stability and surface chemistry of h-BN during plasma-assisted processing, we used polycrystalline Cu foils with single-layer h-BN, grown via chemical vapor deposition (CVD), and tracked in real-time the plasma-induced reduction of the underlying Cu oxide using APXPS equipped with 22 kHz 75 W discharge plasma source operating at 13 Pa. Residual gas analysis (RGA) mass-spectra were concurrently collected during plasma-XPS to track reaction products formed during plasma exposure. A clear reduction of CuxO is seen, while an h-BN layer remains intact, suggesting H radical species can attack the exposed and h-BN-covered Cu oxide patches and partially reduce the underlying substrate. In addition to the demonstration and discussion of plasma-XPS capabilities, our results indicate the h-BN encapsulated metallic Cu interface might be repaired without significantly damaging the overlaying h-BN, which is of practical importance for the development of h-BN encapsulated devices and interfaces

cond-mat.mtrl-sci↗

arXiv2021

Addressable Graphene Encapsulation of Wet Specimens on a Chip for Combinatorial Optical, Electron, Infrared and X-ray based Spectromicroscopy Studies

Label-free spectromicroscopy methods offer the capability to examine complex cellular phenomena. Electron and X-ray-based spectromicroscopy methods, though powerful, have been hard to implement with hydrated objects due to the vacuum incompatibility of the samples and due to the parasitic signals from (or drastic attenuation by) the liquid matrix surrounding the biological object of interest. Similarly, for many techniques that operate at ambient pressure, such as Fourier Transform Infrared spectromicroscopy (FTIRM), the aqueous environment imposes severe limitations due to the strong absorption by liquid water in the infrared regime. Here we propose a microfabricated multi-compartmental and reusable hydrated sample platform suitable for use with several analytical techniques, which employs the conformal encapsulation of biological specimens by atomically thin graphene. Such an electron, X-ray, and infrared transparent, molecularly impermeable as well as mechanically robust enclosure preserve the hydrated environment around the object for a sufficient time to allow in-situ examination of hydrated bio-objects with techniques operating both in ambient or high vacuum conditions. An additional hydration source, made by hydrogel pads patterned near/around the specimen and co-encapsulated, has been added to further extend the hydration lifetime. Scanning electron and optical fluorescence microscopies, as well as synchrotron radiation-based FTIR and X-ray fluorescence microscopies, have been used to test the applicability of the platform and for its validation with yeast, A549 human carcinoma lung cells and micropatterned gels as biological object phantoms.

physics.ins-det↗

arXiv2020

Probing Electrified Liquid-Solid Interfaces with Scanning Electron Microscopy

Electrical double layers play a key role in a variety of electrochemical systems. The mean free path of secondary electrons in aqueous solutions is on the order of a nanometer, making them suitable for probing of ultrathin electrical double layers at solid-liquid electrolyte interfaces. Employing graphene as an electron-transparent electrode in a two-electrode electrochemical system, we show that the secondary electron yield of the graphene-liquid interface depends on the ionic strength and concentration of electrolyte and applied bias at the remote counter electrode. These observations have been related to polarization-induced changes in the potential distribution within the electrical double layer and demonstrate the feasibility of using scanning electron microscopy to examine and map electrified liquid-solid interfaces

physics.app-ph↗

arXiv2019

Focused Electron and X-ray Beam Crosslinking in Liquids for Nanoscale Hydrogels 3D Printing and Encapsulation

Additive fabrication of biocompatible 3D structures out of liquid hydrogel solutions has become pivotal technology for tissue engineering, soft robotics, biosensing, drug delivery, etc. Electron and X-ray lithography are well suited to pattern nanoscopic features out of dry polymers, however, the direct additive manufacturing in hydrogel solutions with these powerful tools is hard to implement due to vacuum incompatibility of hydrated samples. In this work, we resolve this principal impediment and demonstrate a technique for in-liquid hydrogel 3D-sculpturing separating high vacuum instrumentation and volatile sample with ultrathin molecularly impermeable membranes transparent to low-energy electrons and soft X-rays. Using either scanning focused electron or synchrotron soft X-ray beams, the principle of the technique, particularities of the in-liquid crosslinking mechanism and factors affecting the ultimate gel feature size are described and validated through the comparison of experiments and simulations. The potential of this technique is demonstrated on a few practical examples such as encapsulation of nanoparticles and live-cell as well as fabrication of mesoscopic 3D-hydrogel structures via modulation of the beam energy

physics.app-ph↗

arXiv2018

In aqua electrochemistry probed by XPEEM: experimental setup, examples, and challenges

Recent developments in environmental and liquid cells equipped with electron transparent graphene windows have enabled traditional surface science spectromicroscopy tools, such as X-ray photoelectron spectroscopy (XPS), photoemission electron microscopy (PEEM), and scanning electron microscopy (SEM) to be applied to study solid-liquid and liquid-gas interfaces. Here, we focus on the experimental implementation of PEEM to probe electrified graphene-liquid interfaces using electrolyte-filled microchannel arrays as a new sample platform. We demonstrate the important methodological advantage of these multi-sample arrays: they enable the combination of the wide field of view hyperspectral imaging capabilities from PEEM with the use of powerful data mining algorithms to reveal spectroscopic and temporal behaviors at the level of the individual microsample or the entire array ensemble

cond-mat.mtrl-sci↗

arXiv2017

Stateful characterization of resistive switching TiO2 with electron beam induced currents

Metal oxide resistive switches are increasingly important as possible artificial synapses in next generation neuromorphic networks. Nevertheless, there is still no codified set of tools for studying properties of the devices. To this end, we demonstrate electron beam induced current measurements as a powerful method to monitor the development of local resistive switching in TiO2 based devices. By comparing beam-energy dependent electron beam induced currents with Monte Carlo simulations of the energy absorption in different device layers, it is possible to deconstruct the origins of filament image formation and relate this to both morphological changes and the state of the switch. By clarifying the contrast mechanisms in electron beam induced current microscopy it is possible to gain new insights into the scaling of the resistive switching phenomenon and observe the formation of a current leakage region around the switching filament. Additionally, analysis of symmetric device structures reveals propagating polarization domains.

cond-mat.mtrl-sci↗

arXiv2016

Enabling photoemission electron microscopy in liquids via graphene-capped microchannel arrays

Photoelectron emission microscopy PEEM is a powerful tool to spectroscopically image dynamic surface processes at the nanoscale but is traditionally limited to ultra high or moderate vacuum conditions. Here, we develop a novel grapheme capped multichannel array sample platform that extends the capabilities of photoelectron spectromicroscopy to routine liquid and atmospheric pressure studies with standard PEEM setups. Using this platform, we show that graphene has only a minor influence on the electronic structure of water in the first few layers and thus will allow for the examination of minimally perturbed aqueous phase interfacial dynamics. Analogous to microarray screening technology in biomedical research, our platform is highly suitable for applications in tandem with large-scale data mining, pattern recognition, and combinatorial methods for spectro temporal and spatiotemporal analyses at solid liquid interfaces. Using Bayesian linear unmixing algorithm, we were able to discriminate between different X-ray induced water radiolysis scenarios and observe a metastable wetting intermediate water layer during the late stages of bubble formationformation

cond-mat.mtrl-sci↗

arXiv2015

Visible Light Assisted Gas Sensing with TiO2 Nanowires

Sensing response of individual single-crystal titania nanowires configured as chemiresistors for detecting reducing (CO, H2) and oxidizing (O2) gases is shown to be sensitive to visible light illumination. It is assumed that doping of the TiO2 nanowires with C and/or N during carbon assisted vapor-solid growth creates extrinsic states in the band gap close to the valence band maximum, which enables photoactivity at the photon energies of visible light. The inherently large surface-to-volume ratio of nanowires, along with facile transport of the photo-generated carriers to/from the nanowires surface promote the adsorption/desorption of donor/acceptor molecules, and therefore open the possibility for visible light assisted gas sensing. The photo-catalytic performance of TiO2 nanowire chemiresistors demonstrates the prospect of combining light harvesting and sensing action in a single nanostructure.

cond-mat.mes-hall↗

arXiv2015

Design and Application of Variable Temperature Environmental Capsule for Scanning Electron Microscopy in Gases and Liquids at Ambient Conditions

Scanning electron microscopy (SEM) of nanoscale objects in their native conditions and at different temperatures are of critical importance in revealing details of their interactions with ambient environments. Currently available environmental capsules are equipped with thin electron transparent membranes and allow imaging the samples at atmospheric pressure. However these capsules do not provide the temperature control over the sample. Here we developed and tested a thermoelectric cooling / heating setup for available environmental capsules to allow ambient pressure in situ SEM studies over the -15 °C to 100 °C temperature range in gaseous, liquid, and frozen environments. The design of the setup also allows correlation of the SEM with optical microscopy and spectroscopy. As a demonstration of the possibilities of the developed approach, we performed real-time in situ microscopy studies of water condensation on a surface of wing scales of Morpho sulkowskyi butterfly. We have found that the initial water nucleation takes place on the top of the scale ridges. These results confirmed earlier discovery of a polarity gradient of the ridges of Morpho butterflies. Our developed thermoelectric cooling / heating setup for available SEM environmental capsules promises to impact diverse needs for in-situ nano-characterization including materials science and catalysis, micro-instrumentation and device reliability, chemistry and biology.

cond-mat.mtrl-sci↗

arXiv2014

Ambient-Pressure X-ray Photoelectron Spectroscopy through Electron Transparent Graphene Membranes

Photoelectron spectroscopy (PES) and microscopy are highly demanded for exploring morphologically complex solid-gas and solid-liquid interfaces under realistic conditions, but the very small electron mean free path inside the dense media imposes serious experimental challenges. Currently, near ambient pressure PES is conducted using sophisticated and expensive electron energy analyzers coupled with differentially pumped electron lenses. An alternative economical approach proposed in this report uses ultrathin graphene membranes to isolate the ambient sample environment from the PES detection system. We demonstrate that the graphene membrane separating windows are both mechanically robust and sufficiently transparent for electrons in a wide energy range to allow PES of liquid and gaseous water. The reported proof-of-principle experiments also open a principal possibility to probe vacuum-incompatible toxic or reactive samples enclosed inside the hermetic environmental cells.

physics.ins-det↗

arXiv2012

Electron transparent graphene windows for environmental scanning electron microscopy in liquids and dense gases

Due to its ultrahigh electron transmissivity in a wide electron energy range, molecular impermeability, high electrical conductivity and excellent mechanical stiffness the suspended graphene membranes appear to be a nearly ideal window material for in situ (in vivo) environmental electron microscopy of nano- and mesoscopic objects (including bio-medical samples) immersed in liquids and/or in dense gaseous media. In this communication, taking advantage of little modification of the graphene transfer protocol on to metallic and SiN supporting orifices, the reusable environmental cells with exchangeable graphene windows have been designed. Using colloidal gold nanoparticles (50 nm) dispersed in water as model objects for scanning electron microscopy in liquids, the different imaging conditions through graphene membrane have been tested. The limiting factors for electron microscopy in liquids such as electron beam induced water radiolysis and damage of graphene membrane at high electron doses were discussed.

cond-mat.mtrl-sci↗