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Peng-Han Lu

Publications and source records attributed to Peng-Han Lu.

13 recordsLinked to original sources

Residual neural-field ptychography for dose-efficient electron, X-ray, and optical nanoscopy

Ptychography spans from sub-angstrom to meter scales yet suffers from convergence instability and excessive data redundancy. Here we introduce self-correcting residual neural fields as a dose-efficient framework for electron, X-ray, and optical ptychography. Unlike approaches that split complex fields, our complex-valued architecture employs holomorphic phasor activation e^i{\omega}z to preserve intrinsic phase-amplitude coupling. We reformulate reconstruction as residual learning, where the network learns only corrections to physical priors rather than complete wavefields. By embedding the physical model as a differentiable layer within the network, we enable end-to-end automatic differentiation where experimental parameters are jointly corrected alongside the neural fields. We validate our scheme across conventional, near-field, coded, and Fourier ptychography and achieve record-breaking lensless resolution of 244-nm linewidth with visible light. Extending to electron wavelengths, we reveal synaptic connectivity in brain sections with superior performance over conventional approaches. Our framework provides a solution for high-throughput, dose-efficient nanoscopy across the electromagnetic spectrum.

physics.optics

Towards reliable electrical measurements of superconducting devices inside a transmission electron microscope

Correlating structure with electronic functionality is central to the engineering of quantum materials and devices whose properties depend sensitively on disorder. Transmission electron microscopy (TEM) offers high spatial resolution together with access to structural, electronic, and magnetic degrees of freedom. However, operando electrical transport measurements on functional quantum devices remain rare, particularly at liquid helium temperature. Here, we demonstrate electrical transport measurements of niobium nitride (NbN) devices inside a TEM using a continuous-flow liquid-helium-cooled sample holder. By optimizing a thermal radiation shield to limit radiation from the nearby pole pieces of the objective lens, we achieve an estimated base sample temperature of 8-9 K, as inferred from the superconducting transition temperatures of our devices. We find that both electron beam illumination and objective lens excitation perturb the superconducting state. In addition, we evaluate the imaging capabilities and stability of the sample holder at low temperature by imaging the magnetic domain structure of the van der Waals ferromagnet CrBr$_3$. Finally, we perform calculations that underscore the importance of cryo-shielding for minimizing thermal radiation onto the device. This capability enables correlative low-temperature TEM studies, in which structural, spectroscopic, and electrical transport data can be obtained from the same device, thereby providing a platform for probing the microscopic origins of quantum phenomena.

cond-mat.supr-con

Electrostatic interference control of a high-energy coherent electron beam using a three-element Boersch phase shifter

In contrast to static holographic phase shifters, which are restricted to specific electron beam energies and microscope settings, Boersch phase shifters are promising for creating programmable arrays for generating two- and three-dimensional electron beam patterns. We recently demonstrated a three-element Boersch phase shifter device [Thakkar et al., J. Appl. Phys. 128 (2020), 134502], which was fabricated by electron beam lithography and is compatible with up-scaling. However, it suffers from parasitic beam deflection and resulting cross-talk. Here, we report a five-layer phase shifter device, which is based on a metal-insulator-metal-insulator-metal structure (as originally envisioned by Boersch) that reduces cross-talk. We demonstrate a three-element Boersch phase shifter that shows minimal beam deflection of voltage-controlled three-electron-beam interference patterns in a transmission electron microscope operated at 200 keV. The feasibility of using such multi-element phase shifter arrays is discussed.

physics.app-ph

Magnetic Phase Imaging using Lorentz Near-field Electron Ptychography

Over the past few years, the combination of diffuser and near-field electron ptychography has drawn more attention by its ability to recover large field of view with few diffraction patterns. In this paper, we purpose a novel design and implementation of amplitude diffuser. The amplitude diffuser introduces structures to the illumination while reducing the inelastic scattering. And the amplitude diffuser is implemented at the condenser lens aperture, allowing us to vary the illumination size under the same microscope setup. We demonstrate the reconstruction results under both conventional Transmission Electron Microscopy (TEM) mode as well as Lorentz mode.

cond-mat.mtrl-sci

A quantum logic gate for free electrons

The topological charge $m$ of vortex electrons spans an infinite-dimensional Hilbert space. Selecting a two-dimensional subspace spanned by $m=\pm 1$, a beam electron in a transmission electron microscope (TEM) can be considered as a quantum bit (qubit) freely propagating in the column. A combination of electron optical quadrupole lenses can serve as a universal device to manipulate such qubits at the experimenter's discretion. We set up a TEM probe forming lens system as a quantum gate and demonstrate its action numerically and experimentally. High-end TEMs with aberration correctors are a promising platform for such experiments, opening the way to study quantum logic gates in the electron microscope.

quant-ph

Experimental demonstration of an electrostatic orbital angular momentum sorter for electrons

We report the first experimental demonstration of an electrostatic electron orbital angular momentum (OAM) sorter, which can be used to analyze the OAM states of electrons in a transmission electron microscope. We verify the sorter functionality for several electron beams possessing different superpositions of OAM states, and use it to record the electron beams OAM spectra. Our current electrostatic OAM sorter has an OAM resolution of 2 in the units of h/bar - the reduced Planck constant. It is expected to increase the OAM resolution of the sorter to the optimal resolution of 1 in the future via fine control of the sorting phase elements.

physics.ins-det

Design of electrostatic phase elements for sorting the orbital angular momentum of electrons

The orbital angular momentum (OAM) sorter is a new electron optical device for measuring an electron s OAM. It is based on two phase elements, which are referred to as the unwrapper and corrector and are placed in Fourier conjugate planes in an electron microscope. The most convenient implementation of this concept is based on the use of electrostatic phase elements, such as a charged needle as the unwrapper and a set of electrodes with alternating charges as the corrector. Here, we use simulations to assess the role of imperfections in such a device, in comparison to an ideal sorter. We show that the finite length of the needle and the boundary conditions introduce astigmatism, which leads to detrimental cross-talk in the OAM spectrum. We demonstrate that an improved setup comprising three charged needles can be used to compensate for this aberration, allowing measurements with a level of cross-talk in the OAM spectrum that is comparable to the ideal case.

physics.ins-det

Generation of electron vortices using non-exact electric fields

Vortices in electron beams can manifest several types of topological phenomena, such as the formation of exotic structures or interactions with topologically structured electromagnetic fields. For instance, the wavefunction of an electron beam can acquire a phase vortex upon propagating through a magnetic monopole, which, in practice, provides a convenient method for generating electron vortex beams. Here, we show how an electric field must be structured in order to achieve a similar effect. We find that, much as in the case of magnetic fields, closed but not exact electric fields can produce electron vortex beams. We proceed by fabricating a versatile near-obstruction-free device that is designed to approximately produce such fields and we systematically study their influence on incoming electron beams. With such a single device, electron vortex beams that are defined by a wide range of topological charges can be produced by means of a slight variation of an applied voltage. For this reason, this device is expected to be important in applications that rely on the sequential generation and manipulation of different types of electron vortices.

quant-ph

Highly Deformable and Mobile Palladium Nanocrystals as Efficient Carbon Scavengers

Fouling of surfaces leads to performance degradation in many energy-intensive industrial processes, but the present solutions are either too complicated to be routinely used or incomplete for eradication. Here we propose and demonstrate that carbon-containing deposits can be catalytically wiped out in an efficient way by roaming palladium nanoparticles with extreme shape flexibility at relatively low temperatures. Surprisingly, during their dramatic liquid-like migrations, these particles could still maintain crystalline interior and conserve their initial crystal orientations through self-surface diffusion. Moreover, these catalytic particles were even able to become regenerated by other roaming particles after occasionally deactivated by surface coking or multiple-particle sintering. These findings shed light on metabolically driven, "living" nanocrystals, and also open a new avenue for efficient catalysis.

physics.app-ph

Towards a holographic approach to spherical aberration correction in scanning transmission electron microscopy

Recent progress in phase modulation using nanofabricated electron holograms has demonstrated how the phase of an electron beam can be controlled. In this paper, we apply this concept to the correction of spherical aberration in a scanning transmission electron microscope and demonstrate an improvement in spatial resolution. Such a holographic approach to spherical aberration correction is advantageous for its simplicity and cost-effectiveness.

physics.ins-det

Spherical aberration correction in a scanning transmission electron microscope using a sculpted foil

Nearly twenty years ago, following a sixty year struggle, scientists succeeded in correcting the bane of electron lenses, spherical aberration, using electromagnetic aberration correction. However, such correctors necessitate re-engineering of the electron column, additional space, a power supply, water cooling, and other requirements. Here, we show how modern nanofabrication techniques can be used to surpass the resolution of an uncorrected scanning transmission electron microscope more simply by sculpting a foil of material into a refractive corrector that negates spherical aberration. This corrector can be fabricated at low cost using a simple process and installed on existing electron microscopes without changing their hardware, thereby providing an immediate upgrade to spatial resolution. Using our corrector, we reveal features of Si and Cu samples that cannot be resolved in the uncorrected microscope.

physics.ins-det

Super-oscillating Electron Wave Functions with Sub-diffraction Spots

Almost one and a half centuries ago, Ernst Abbe [1] and shortly after Lord Rayleigh [2] showed that when an optical lens is illuminated by a plane wave, a diffraction-limited spot with a radius 0.61*lambda/sin(alpha) is obtained, where lambda is the wavelength and alpha is the semi-angle of the beam's convergence cone. However, spots with much smaller features can be obtained at the focal plane when the lens is illuminated by an appropriately structured beam. Whereas this concept is known for light beam, here, we show how to realize it for massive-particle wave function of a free electron. We experimentally demonstrate an electron central spot of radius 106 pm, which is more than two times smaller than the diffraction limit of the experimental setup used. In addition, we demonstrate that this central spot can be structured by adding orbital angular momentum to it. The resulting super-oscillating vortex beam has a smaller dark core with respect to the regular vortex beam. This new family of electron beams having hot-spots with arbitrarily small features and tailored structure can be useful for studying electron-matter interactions with sub-atomic resolution.

physics.optics

Measuring an electron beam's orbital angular momentum spectrum

Quantum complementarity states that particles, e.g. electrons, can exhibit wave-like properties such as diffraction and interference upon propagation. \textit{Electron waves} defined by a helical wavefront are referred to as twisted electrons~\cite{uchida:10,verbeeck:10,mcmorran:11}. These electrons are also characterised by a quantized and unbounded magnetic dipole moment parallel to their propagation direction, as they possess a net charge of $-|e|$~\cite{bliokh:07}. When interacting with magnetic materials, the wavefunctions of twisted electrons are inherently modified~\cite{lloyd:12b,schattschneider:14a,asenjo:14}. Such variations therefore motivate the need to analyze electron wavefunctions, especially their wavefronts, in order to obtain information regarding the material's structure~\cite{harris:15}. Here, we propose, design, and demonstrate the performance of a device for measuring an electron's azimuthal wavefunction, i.e. its orbital angular momentum (OAM) content. Our device consists of nanoscale holograms designed to introduce astigmatism onto the electron wavefunctions and spatially separate its phase components. We sort pure and superposition OAM states of electrons ranging within OAM values of $-10$ and $10$. We employ the device to analyze the OAM spectrum of electrons having been affected by a micron-scale magnetic dipole, thus establishing that, with a midfield optical configuration, our sorter can be an instrument for nano-scale magnetic spectroscopy.

quant-ph