arXiv subjects

Kenneth R. Beyerlein

Publications and source records attributed to Kenneth R. Beyerlein.

5 recordsLinked to original sources

arXiv2026

Synergistic Role of Electron and Photon Dose in Stepwise Laser-Induced Complete Deoxygenation of Graphene Oxide Revealed by In-situ TEM

Laser-induced reduction of graphene oxide (GO) represents a highly promising route to graphene synthesis, offering spatially localized processing, elimination of hazardous chemical reagents, and compatibility with ambient conditions. Here, we introduce a stepwise laser reduction strategy employing a 532 nm pulsed laser, monitored in real-time by in situ dynamic transmission electron microscopy (DTEM). By systematically varying the pulse sequence and the cumulative photon and electron dose, complete deoxygenation of GO is achieved while preserving film integrity. Core-loss EELS confirms full removal of oxygen functional groups and restoration of the sp$^2$ graphitic network, evidenced by a ${\pi}^*-{\sigma}^*$ energy separation of 7.0 eV, in close agreement with graphite (7.1 eV). Crucially, the cumulative electron dose is identified as an active parameter governing the reduction mechanism: electron beam exposure accounts for approximately 5 at. % of the initial oxygen removal and synergistically lowers the energy barrier for subsequent laser-driven deoxygenation, while excessive electron exposure compromises film integrity through crack formation. The optimal configuration achieves complete deoxygenation at a cumulative photon dose of 2.5 x 10$^3$ mJ/cm$^2$ with superior in-plane crystallographic order and minimal beam-induced thinning. This work establishes a versatile multi-parameter strategy for controlled scalable graphene synthesis via combined electron beam and laser irradiation.

physics.app-ph↗

arXiv2026

Fast reduction of electron-beam-activated graphene oxide by an infrared laser pulse

Rapid and controllable reduction of graphene oxide (GO) remains a critical challenge for realizing its full technological potential. Here, we report efficient reduction of GO by a synergistic electron-beam-assisted single-pulse near-infrared (NIR) laser process. Time-resolved electron energy-loss spectroscopy measured with a dynamic transmission electron microscope (DTEM) is used to locally track the oxygen concentration evolution after NIR laser pulse irradiation. This finds an oxygen diffusivity of 1.6 +/- 0.4 x 10$^{-8}$ m$^2$/s, which corresponds to 90% reduction of a 46-nm thick film within 960 ns. Electron beam irradiation is found to change the optical absorptivity of GO in the NIR region and the thermal heating cycle resulting from the laser pulse is simulated. Structural characterization via selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) finds localized restoration of sp$^2$ bonding accompanied by turbostatic disorder in the reduced GO. Together, these results point to a mechanism involving the creation of defects and vacancies produced by electron beam irradiation, which increases the efficiency of NIR light absorption and oxygen diffusion normal to the layers. This study demonstrates the important role of such defects in controlling the photochemistry of GO and its response to NIR illumination.

physics.app-ph↗

arXiv2026

Tracking visible pulsed laser annealing of Hf$_{0.5}$Zr$_{0.5}$O$_2$ heterostructures with in situ transmission electron microscopy

Laser annealing offers a promising route to back end of the line fabrication of ferroelectric thin film transistors based on hafnium-zirconium oxide (HZO). Due to the wide band gap of this material, previous reports have studied the crystallization of HZO using ultraviolet or infrared light. In contrast, we monitor its crystallization in a Si$_3$N$_4$/TiN/Hf$_{0.5}$Zr$_{0.5}$O$_2$ thin film heterostructure upon irradiation with visible nanosecond laser pulses. This geometry mimics the structure of CMOS devices and harnesses the absorption of TiN in the visible regime to generate the heat necessary for the transformation. Through a series of local in situ measurements using a modified transmission electron microscope, we quantify the relationship between the HZO film thickness, critical laser energy density and the ferroelectric HZO phase fraction, finding a sharp threshold behavior in the laser pulse energy necessary to crystallize HZO. The optimal condition of irradiating an 8-nm HZO film with a single laser pulse with an energy density of 177 mJ/cm$^2$ is found to produce 86% of the ferroelectric orthorhombic phase. Heat transfer dynamics within the heterostructure during laser annealing are revealed by finite element simulations, where the partial melting of the silicon nitride substrate is found to play an important role limiting the temperature to 1900 {\deg}C. This finding as well as the observed laser pulse energy threshold behavior support a kinetic crystallization pathway involving the tetragonal phase. More generally, these findings show how laser-driven phase engineering can lead to scalable design and enhanced performance of ferroelectric materials in advanced electronic applications.

cond-mat.mtrl-sci↗

arXiv2018

Time-spliced X-ray Diffraction Imaging

Diffraction imaging of non-equilibrium dynamics at atomic resolution is becoming possible with X-ray free-electron lasers. However, there are unresolved problems with applying this method to objects that are confined in only one dimension. Here I show that one-dimensional coherent diffraction imaging is possible by splicing together images recovered from different delays in a time-resolved experiment. This is used to image the time and space evolution of antiferromagnetic order in a complex oxide heterostructure from measurements of a resonant soft X-ray diffraction peak. Mid-infrared excitation of the substrate is shown to lead to a magnetic front that propagates at a velocity exceeding the speed of sound, a critical observation for the understanding of driven phase transitions in complex condensed matter.

cond-mat.str-el↗

arXiv2018

Femtosecond x-ray diffraction from an aerosolized beam of protein nanocrystals

We demonstrate near-atomic-resolution Bragg diffraction from aerosolized single granulovirus crystals using an x-ray free-electron laser. The form of the aerosol injector is nearly identical to conventional liquid-microjet nozzles, but the x-ray-scattering background is reduced by several orders of magnitude by the use of helium carrier gas rather than liquid. This approach provides a route to study the weak diffuse or lattice-transform signal arising from small crystals. The high speed of the particles is particularly well suited to upcoming MHz-repetition-rate x-ray free-electron lasers.

physics.bio-ph↗