Steven E Kooi

Massachusetts Institute of Technology (MIT), Institute for Solider Nanotechnologies, Principal Research Scientist

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Papers by Steven E Kooi

Spectrally and Spatially Resolved Smith-Purcell Radiation in Plasmonic Crystals with Short-Range Disorder

Physical Review X, 2017

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Novel environmentally-safe, non-toxic, and supply-chain-resilient biomaterials for optical detection of molecules

Alignment and Reordering of a Block Copolymer by Solvent-Enhanced Laser Thermal Direct Write

Bulletin of the American Physical Society, Mar 5, 2014

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Observation of enhanced free-electron radiation from photonic flatband resonances

arXiv (Cornell University), Oct 7, 2021

Flatbands emerge from a myriad of structures such as Landau levels [1], Lieb and Kagome lattices ... more Flatbands emerge from a myriad of structures such as Landau levels [1], Lieb and Kagome lattices [2-5], line graphs [6], and more recently moiré superlattices [7, 8]. They enable unique properties including slow light [9] in photonics, correlated phases [7] in electronics, and supercollimation [10, 11] in both systems. Despite these intense parallel efforts, flatbands have never been shown to affect the core light-matter interaction between electrons and photons, which is limited by a dimensionality mismatch. Here, we reveal that a photonic flatband can overcome this mismatch between localized electrons and extended photons and thus remarkably boost their light-matter interaction. We design flatband resonances in a silicon-oninsulator photonic crystal slab to control and enhance the radiation emission from free electrons by tuning their trajectory and velocity. In particular, we record a 100-fold radiation enhancement from the conventional diffractionenabled Smith-Purcell radiation [12], and show the potential of our approach to achieve 10 6-fold enhancements and beyond. The enhancement also enables us to perform polarization shaping of free electron radiation from multiple flatbands and demonstrate an approach to measure photonic bands via angle-resolved electron-beam measurements. Our results suggest flatbands as ideal test beds for strong light-electron interaction in various systems, with particular relevance for efficient and compact freeelectron light sources and accelerators.

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3D Micro- and Nanostructures via Interference Lithography

Advanced Functional Materials, Oct 5, 2007

Small size scale Fast Large areas Limited volume fraction range Unintentional defects Difficult t... more Small size scale Fast Large areas Limited volume fraction range Unintentional defects Difficult to control geometrical parameters Colloidal self-assembly [3,4] Large areas Wide range of size scale Low cost Construction-based approach Layer by layer conventional semiconductor manufacturing [7,12] Large area fabrication Low defect density Expensive Time intensive Structures are built by layers to approximate a 3D structure Limited material platforms Two-photon lithography [13,14] Arbitrary structure Slow Small area coverage problem 3D printing / Direct writing [11] Arbitrary structure Resolution issue at smaller length scale Slow Small area coverage problem Micromanipulation [15,16] Low defect density Very slow Interference lithography Multibeam interference lithography [17-21] Large area Defect free Control over geometry Can not make arbitrary structure Complex optical setup Phase mask lithography [22,23] Large area Defect free Simple setup Can not make arbitrary structure Correlation between mask element and desired structure not fully established

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Additive Laser Excitation of Giant Nonlinear Surface Acoustic Wave Pulses

arXiv (Cornell University), Sep 28, 2022

The laser ultrasonics technique perfectly fits the needs for non-contact, non-invasive, non-destr... more The laser ultrasonics technique perfectly fits the needs for non-contact, non-invasive, non-destructive mechanical probing of samples of mm to nm sizes. This technique is however limited to the excitation of low-amplitude strains, below the threshold for optical damage of the sample. In the context of strain engineering of materials, alternative optical techniques enabling the excitation of high amplitude strains in a non-destructive optical regime are seeking. We introduce here a non-destructive method for laser-shock wave generation based on additive superposition of multiple laser-excited strain waves. This technique enables strain generation up to mechanical failure of a sample at pump laser fluences below optical ablation or melting thresholds. We demonstrate the ability to generate nonlinear surface acoustic waves (SAWs) in Nb:SrTiO3 substrates, at typically 1 kHz repetition rate, with associated strains in the percent range and pressures close to 100 kbars. This study paves the way for the investigation of a host of high-strength SAW-induced phenomena, including phase transitions in conventional and quantum materials, plasticity and a myriad of material failure modes, chemistry and other effects in bulk samples, thin layers, or two-dimensional materials.

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3D-Printed Topology-Optimized Metaoptics

Conference on Lasers and Electro-Optics, 2020

Extreme Plastic Deformation of Glassy Polymer Thin Films at Ballistic Strain Rates

Bulletin of the American Physical Society, Mar 7, 2018

The Parametric Study of Focused Laser-Induced Marangoni Dewetting for Patterning Polymer Thin Films

Bulletin of the American Physical Society, Mar 14, 2016

localized focused laser spike (FLaSk) heating of polymer thin films is a resist-and developer-fre... more localized focused laser spike (FLaSk) heating of polymer thin films is a resist-and developer-free alternative to 2D laser direct write for creating patterns on the single micron or, by exploiting overlap effects, submicron scale. The massive temporal and spatial thermal gradients and resulting thermal Marangoni stresses generated by FLaSk are an effective means for the directed dewetting and patterning of such films. Here, the general applicability of this technique to glassy amorphous polymer thin film systems is investigated through systematic investigation of film thickness, glass transition temperature, and polymer mobility. The results reveal that the important parameters are the film thickness (coupled to the optical heating effects through anti-reflection coating effects) and the high-temperature polymer melt mobility, allowing for generation of single features with linewidths of down to 1 µm. Further, the introduction of spatial mobility variations by using polymer brushes, bilayers, and microphase separated block copolymers leads to additional profile manipulation effects (i.e.spontaneous 2D pattern generation and flattened top profiles).

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Ionization Dynamics of Transition Metal - Carbon Clusters

Plasmonic Ag nanostructures on thin substrates for enhanced energy harvesting

Proceedings of SPIE, Sep 18, 2013

ABSTRACT Nanoparticles and nanostructures with plasmonic resonances are currently being employed ... more ABSTRACT Nanoparticles and nanostructures with plasmonic resonances are currently being employed to enhance the efficiency of solar cells. Ag stripe arrays have been shown theoretically to enhance the short-circuit current of thin silicon layers. Such Ag stripes are combined with 200 nm long and 60 nm wide &quot;teeth&quot;, which act as nanoantennas, and form vertical rectifying metal-insulator-metal (MIM) nanostructures on metallic substrates coated with thin oxides, such as Nb/NbOx films. We characterize experimentally and theoretically the visible and near-infrared spectra of these &quot;stripeteeth&quot; arrays, which act as microantenna arrays for energy harvesting and detection, on silicon substrates. Modeling the stripe-teeth arrays predicts a substantial net a.c. voltage across the MIM diode, even when the stripe-teeth microrectenna arrays are illuminated at normal incidence.

Elektrochemische Modifizierung einzelner Kohlenstoff-Nanoröhren Diese Arbeit wurde von der Europäischen Union (Projektnummer HPRN-CT-1999-00011) unterstützt. Die Autoren danken B. Siegle, Max-Planck-Institut für Metallforschung, Stuttgart, für die Unterstützung bei der Aufnahme der Auger-Spektren

Angewandte Chemie, Apr 15, 2002

Spectrally and Spatially Resolved Smith-Purcell Radiation in Plasmonic Crystals with Short-Range Disorder

Physical Review X, Jan 17, 2017

Electrons interacting with plasmonic structures can give rise to resonant excitations in localize... more Electrons interacting with plasmonic structures can give rise to resonant excitations in localized plasmonic cavities and to collective excitations in periodic structures. We investigate the presence of resonant features and disorder in the conventional Smith-Purcell effect (electrons interacting with periodic structures) and observe the simultaneous excitation of both the plasmonic resonances and the collective excitations. For this purpose, we introduce a new scanning-electron-microscope-based setup that allows us to probe and directly image new features of electron-photon interactions in nanophotonic structures like plasmonic crystals with strong disorder. Our work creates new possibilities for probing nanostructures with free electrons, with potential applications that include tunable sources of short-wavelength radiation and plasmonic-based particle accelerators.

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Emission Color Tuning with Polymer Molecular Weight for Difluoroboron Dibenzoylmethane-Polylactide

Advanced Materials, Jun 4, 2008

A series of novel polylactide (PLA) polymers were synthesized initiated by 4-dicyanomethylene-2-m... more

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Corrigendum: Focused laser-induced marangoni dewetting for patterning polymer thin films

Journal of Polymer Science Part B, Feb 6, 2017

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Solar metadevice with enhanced absorption, scattering, and spectral control

Lightweight, portable solar blankets, constructed from thin film photovoltaics, are of great inte... more Lightweight, portable solar blankets, constructed from thin film photovoltaics, are of great interest to hikers, the military, first responders, and third-world countries lacking infrastructure for transporting heavy, brittle solar cells. These solar blankets, as large as two square meters in area, come close to satisfying specifications for commercial and military use, but they still have limited absorption due to insufficient material efficiency, and therefore are large and too heavy in many cases. Metasurfaces, consisting of monolayers of periodic and semi-random plasmonic particles patterned in a scalable manner, are explored to enhance scattering into thin photovoltaic films (currently of significant commercial and military value), in order to enhance absorption and efficiency of solar blankets. Without nano-enhancement, absorption is limited by the thickness of the thin photovoltaic active layer in the long-wavelength region. In this study, lithographically patterned, periodic Al nanostructure arrays demonstrate experimentally a large absorption enhancement, resulting in a predicted increase in short-circuit current density of at least 35% and as much as 70% for optimized arrays atop 200-nm amorphous silicon thin films. Optimized arrays extend thin-film absorption to the near infrared region. This impressive absorption enhancement and predicted increase in short-circuit current density may significantly increase the efficiency and reduce the weight of solar blankets, enabling their use for commercial and military applications.

High-order Smith-Purcell radiation in Silicon Nanowires

Conference on Lasers and Electro-Optics, 2017

We present experimental results demonstrating multiple order Smith-Purcell radiation in high aspe... more

Energy Disposal in the Photodissociation of Co(CO)<sub>3</sub>NO near 225 nm

Journal of Physical Chemistry A, Dec 1, 1998

ABSTRACT The photodissociation of Co(CO)3NO was studied near 225 nm. Apparent two-photon dissocia... more ABSTRACT The photodissociation of Co(CO)3NO was studied near 225 nm. Apparent two-photon dissociation of the parent compound produces Co* in a number of excited states that emit in the range of 340−360 nm. Both quartet and doublet states of Co* are observed, implying the existence of spin-conserving and nonspin-conserving dissociation channels. Assignment of the Co* emission is used to calculate an upper limit for the average metal−ligand bond dissociation energy of 36.2−38.6 kcal/mol with no spin-conservation restrictions and 41.2−43.9 kcal/mol with spin-conservation restrictions. The Co* emission intensities are used to determine the relative populations of particular J and spin states and to demonstrate that J states within a particular LS configuration are statistically populated. The NO photoproduct was detected by fluorescence excitation spectroscopy. The NO appears to follow dual Boltzmann statistics with rotational temperatures of 580 ± 70 K for Erot &lt; 500 cm-1 and 2800 ± 300 K for Erot &gt; 500 cm-1.

Relaxation Dynamics of Electronically Excited Nanoscale Metal−Carbon Complexes: Vanadium−Carbon Clusters

Nano Letters, Feb 20, 2001

First measurements of the relaxation dynamics of electronically excited states in nanoscale trans... more First measurements of the relaxation dynamics of electronically excited states in nanoscale transition metal−carbon species are reported. In this communication, time-resolved measurements, made with the femtosecond laser pump−probe technique by employing 50 fs pulses at 620 and 400 nm, reveal the excited-state dynamics in vanadium−carbon clusters including the vanadium Met-Car, V 8 C 12. Size dependent trends are observed in the pump−probe transients, which suggest a more extensive free electron character in the larger clusters as compared to the smaller species.

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Maximal spontaneous photon emission and energy loss from free electrons

Nature Physics, Jul 16, 2018

Free electron radiation such as Cerenkov [1], Smith-Purcell [2], and transition radiation [3, 4] ... more Free electron radiation such as Cerenkov [1], Smith-Purcell [2], and transition radiation [3, 4] can be greatly affected by structured optical environments, as has been demonstrated in a variety of polaritonic [5, 6], photoniccrystal [7], and metamaterial [8-10] systems. However, the amount of radiation that can ultimately be extracted from free electrons near an arbitrary material structure has remained elusive. Here we derive a fundamental upper limit to the spontaneous photon emission and energy loss of free electrons, regardless of geometry, which illuminates the effects of material properties and electron velocities. We obtain experimental evidence for our theory with quantitative measurements of Smith-Purcell radiation. Our framework allows us to make two predictions. One is a new regime of radiation operation-at subwavelength separations, slower (nonrelativistic) electrons can achieve stronger radiation than fast (relativistic) electrons. The second is a divergence of the emission probability in the limit of lossless materials. We further reveal that such divergences can be approached by coupling free electrons to photonic bound states in the continuum (BICs) [11-13]. Our findings suggest that compact and efficient free-electron radiation sources from microwaves to the soft X-ray regime may be achievable without requiring ultrahigh accelerating voltages. The Smith-Purcell effect epitomizes the potential of freeelectron radiation. Consider an electron at velocity β = v/c traversing a structure with periodicity a; it generates far-field radiation at wavelength λ and polar angle θ, dictated by [2]

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Steven E Kooi

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