Ilana Jessica Porter Molesky

All Publications

• High-resolution in situ characterization of laser powder bed fusion via transmission X-ray microscopy at X-ray free-electron lasers. Journal of synchrotron radiation Taylor, Z., Reddy, T., Fang, L., Oppermann, P., Kramer, P. L., Decker, F. J., Seaberg, M., Chollet, M., van Driel, T., Halavanau, A., Hart, P., Dayton, M., Seiboth, F., Wang, W., Gee, C., Wilson, A., Margraf-O'Neal, R., Chatterjee, G., Chen, Y., Molesky, I. J., Wang, Y., Irvine, S., Stanton, J., Melendrez, C., Banta, K., Nelson, S., Thampy, V., Katagiri, K., Haubro, M., Liu, S., Pal, D., Moghimi, L., Tassone, C., Dresselhaus-Marais, L. 2025

  Abstract

  In this work, we describe the instrumentation used to perform the first operando transmission X-ray microscopy (TXM) and simultaneous X-ray diffraction of laser melting simulating laser powder bed fusion on the XCS instrument at the Linac Coherent Light Source (LCLS) X-ray free-electron laser (XFEL). Our TXM with 40× magnification in the X-ray regime at 11 keV gave spatial resolutions down to 940 nm per line pair, with effective pixel sizes down to 206 nm, image integration times of <100 fs, and frame rates tunable between 2.1 and 119 ns for two probe frames (0.48 GHz to 8.4 MHz). Images were recorded on Zyla and Icarus (UXI) detectors to trade off between spatial resolution and time dynamics. A 1 kW CW IR laser was coupled into the interaction point to conduct pump-probe studies of laser melting and solidification dynamics. Our temporal and spatial resolution with attenuation-based contrast exceeds that currently possible with synchrotron-based high-speed radiography. This system was sensitive to feature velocities of 10-12000 m s-1 but we did not observe any motion in this range in the laser melting of Al6061 alloy. Shockwaves were not observed and hot cracking proceeded at velocities below the detection limits. Pore accumulation was observed between successive shots, indicating that bubble escape mechanisms were not active. With proper experimental design, the spatial resolution, contrast and field of view could be further improved or modified. The increased brightness and narrower bandwidth of the XFEL allowed for this imaging technique and it lays the groundwork for a wide range of operando techniques to study additive manufacturing.

  View details for DOI 10.1107/S1600577525001675

  View details for PubMedID 40167485

• Coherent Phonons in Antimony: An Undergraduate Physical Chemistry Solid-State Ultrafast Laser Spectroscopy Experiment JOURNAL OF CHEMICAL EDUCATION Porter, I. J., Zuerch, M. W., Baranger, A. M., Leone, S. R. 2022

  View details for DOI 10.1021/acs.jchemed.2c00816

  View details for Web of Science ID 000888146000001

• Characterization of Carrier Cooling Bottleneck in Silicon Nanoparticles by Extreme Ultraviolet (XUV) Transient Absorption Spectroscopy JOURNAL OF PHYSICAL CHEMISTRY C Porter, I. J., Lee, A., Cushing, S. K., Chang, H., Ondry, J. C., Alivisatos, A., Leone, S. R. 2021; 125 (17): 9319-9329

  View details for DOI 10.1021/acs.jpcc.1c02101

  View details for Web of Science ID 000648873500042

• Electron thermalization and relaxation in laser-heated nickel by few-femtosecond core-level transient absorption spectroscopy PHYSICAL REVIEW B Chang, H., Guggenmos, A., Cushing, S. K., Cui, Y., Din, N., Acharya, S., Porter, I. J., Kleineberg, U., Turkowski, V., Rahman, T. S., Neumark, D. M., Leone, S. R. 2021; 103 (6)

  View details for DOI 10.1103/PhysRevB.103.064305

  View details for Web of Science ID 000617038600001

• Layer-resolved ultrafast extreme ultraviolet measurement of hole transport in a Ni-TiO₂-Si photoanode SCIENCE ADVANCES Cushing, S. K., Porter, I. J., de Roulet, B. R., Lee, A., Marsh, B. M., Szoke, S., Vaida, M. E., Leone, S. R. 2020; 6 (14): eaay6650

  Abstract

  Metal oxide semiconductor junctions are central to most electronic and optoelectronic devices, but ultrafast measurements of carrier transport have been limited to device-average measurements. Here, charge transport and recombination kinetics in each layer of a Ni-TiO2-Si junction is measured using the element specificity of broadband extreme ultraviolet (XUV) ultrafast pulses. After silicon photoexcitation, holes are inferred to transport from Si to Ni ballistically in ~100 fs, resulting in characteristic spectral shifts in the XUV edges. Meanwhile, the electrons remain on Si. After picoseconds, the transient hole population on Ni is observed to back-diffuse through the TiO2, shifting the Ti spectrum to a higher oxidation state, followed by electron-hole recombination at the Si-TiO2 interface and in the Si bulk. Electrical properties, such as the hole diffusion constant in TiO2 and the initial hole mobility in Si, are fit from these transient spectra and match well with values reported previously.

  View details for DOI 10.1126/sciadv.aay6650

  View details for Web of Science ID 000523302400013

  View details for PubMedID 32284972

  View details for PubMedCentralID PMC7124930

• Differentiating Photoexcited Carrier and Phonon Dynamics in the Δ, <i>L</i>, and Γ Valleys of Si(100) with Transient Extreme Ultraviolet Spectroscopy JOURNAL OF PHYSICAL CHEMISTRY C Cushing, S. K., Lee, A., Porter, I. J., Carneiro, L. M., Chang, H., Zurich, M., Leone, S. R. 2019; 123 (6): 3343-3352

  View details for DOI 10.1021/acs.jpcc.8b10887

  View details for Web of Science ID 000459223200011

• Real-Time Observation of a Coherent Lattice Transformation into a High-Symmetry Phase PHYSICAL REVIEW X Teitelbaum, S. W., Shin, T., Wolfson, J. W., Cheng, Y., Porter, I. J., Kandyla, M., Nelson, K. A. 2018; 8 (3)

  View details for DOI 10.1103/PhysRevX.8.031081

  View details for Web of Science ID 000445601800003

• Photoexcited Small Polaron Formation in Goethite (α-FeOOH) Nanorods Probed by Transient Extreme Ultraviolet Spectroscopy JOURNAL OF PHYSICAL CHEMISTRY LETTERS Porter, I. J., Cushing, S. K., Carneiro, L. M., Lee, A., Ondry, J. C., Dahl, J. C., Chang, H., Alivisatos, A., Leone, S. R. 2018; 9 (14): 4120-4124

  Abstract

  Small polaron formation limits the mobility and lifetimes of photoexcited carriers in metal oxides. As the ligand field strength increases, the carrier mobility decreases, but the effect on the photoexcited small polaron formation is still unknown. Extreme ultraviolet transient absorption spectroscopy is employed to measure small polaron formation rates and probabilities in goethite (α-FeOOH) crystalline nanorods at pump photon energies from 2.2 to 3.1 eV. The measured polaron formation time increases with excitation photon energy from 70 ± 10 fs at 2.2 eV to 350 ± 30 fs at 2.6 eV, whereas the polaron formation probability (85 ± 10%) remains constant. By comparison to hematite (α-Fe2O3), an oxide analogue, the role of ligand composition and metal center density in small polaron formation time is discussed. This work suggests that incorporating small changes in ligands and crystal structure could enable the control of photoexcited small polaron formation in metal oxides.

  View details for DOI 10.1021/acs.jpclett.8b01525

  View details for Web of Science ID 000448083300047

  View details for PubMedID 29985006