Research Highlights

Multimodal X-ray and Electron Microscopy of the Allende Meteorite

September 20, 2019

A STROBE team from UCLA, Berkeley and Boulder developed a nanoscale multimodal X-ray and electron microscopy framework that is applicable to a wide range of inhomogeneous samples with complex structural and chemical properties. Using an Allende meteorite as an example, we performed structural and chemical mapping to infer the mineral composition and its potential processes. This work opens a route to future microscopies of complex materials.

Y.Hung Lo et al., “Multimodal x-ray and electron microscopy of the Allende meteorite”, Science Advances 5, eaax3009 (2019).

Atomic Motion Captured, for the First Time, in 4D

June 26, 2019

Everyday transformations from one state of matter to another – such as freezing, melting or evaporation – start with a process called “nucleation”, in which tiny particles containing just a few atoms or molecules begin to coalesce. Nucleation plays a critical role in events as diverse as the formation of clouds and the onset of neurodegenerative disease. STROBE Deputy Director Jianwei (John) Miao, led an interdisciplinary team from Lawrence Berkeley Lab, University of Colorado Boulder, University of Buffalo and the University of Nevada Reno, to gain a never-before-seen view of nucleation –– capturing how the atoms rearrange in the tiny seed particles at atomic resolution. Their findings, published in the journal Nature, differ from predictions based on the classical theory of nucleation that has long appeared in textbooks.

J. Zhou et al., "Observing crystal nucleation in four dimensions using atomic electron tomography," Nature 570, 500-503 (2019).


Stroboscopic Imaging of Nanoscale Transport

June 14, 2019

The functional properties of photovoltaics and nano-devices for electronics, thermoelectrics and data storage can be enhanced by tuning their structure at the nanoscale. However, at dimensions <100nm, bulk models can no longer accurately predict heat, charge or spin transport, or the mechanical properties of doped or nano-structured materials. A STROBE team from CU Boulder, UC Berkeley, and LBNL developed a real-time microscope to capture, map and understand nanoscale heat transport in nanostructures. This microscope was then used to validate a very surprising prediction - that an array of closely-spaced nanoscale heat sources can cool more quickly than when spaced far apart.

Frazer et al., “Engineering nanoscale thermal transport: Size- and spacing-dependent cooling of nanostructures,” Physical Review Applied 11, 024042 (2019);  Karl et al., “Full-Field Functional Imaging of Nanoscale Dynamics Using Tabletop High Harmonics”, Science Advances 4, eaau4295 (2018).

Deep Learning for Single-Shot Autofocus Microscopy

June 05, 2019

A STROBE team led by Prof. Waller, created a novel computational imaging autofocusing system for microscopes utilizing an of-the-shelf LED and a machine learning algorithm with optical physics knowledge incorporated into its design.

H. Pinkard et al., “Deep learning for single-shot autofocus microscopy”, Optica 6, 794 (2019). 

Information-rich Localization Microscopy Through Machine Learning

April 30, 2019

Artificial neural networks enable the extraction of multiple parameters, including spectral and depth information, from unmodified experimental single-molecule images for multidimensional super-resolution microscopy. Good color separation is thus achieved in fixed cells using two dyes ~80 nm apart in emission wavelength.

T. Kim et al., “Information-rich localization microscopy through machine learning”, Nature Communications 10, (2019).

Real Time Near-field Imaging of Biological and Nano-systems

April 03, 2019

Label-free chemical nano-imaging in dense molecular environments has remained a long-standing challenge. STROBE Thrust lead Markus Raschke led a team of academic and national laboratory scientists from LBNL, Boulder and Berkeley to speed-up scanning near-field optical microscopy (s-SNOM) by a factor of 10! This remarkable achievement allowed the team to image the surface shape and chemistry of biological samples, including mollusk shells, with nanometer spatial resolution.

MS. C. Johnson et al., "Infrared nanospectroscopic imaging in the rotating frame," Optica 4, 424 (2019).

Temporal magnification for streaked ultrafast electron diffraction and microscopy

January 29, 2019

UCLA STROBE researchers show how a radiofrequency cavity can be used as an electron longitudinal lens in order to produce a highly magnified temporal replica of an ultrafast process, and, in combination with a deflecting cavity, enable streaked electron images of optical-frequency phenomena, taking advantage of the time-stretch concept.

D. Cesar et al., “Temporal magnification for streaked ultrafast electron diffraction and microscopy” , Ultramicroscopy 199, 1 - 6 (2019).

De-blurring Images of Living Biological Samples

December 10, 2018

Imaging fast moving samples such as living biological samples is challenging because the images can appear blurred if the strobe light is not fast enough. This is an issue for high-quality quantitative phase imaging, which was too slow for many samples (image on right). STROBE faculty Laura Waller from Berkeley led a team to develop a new approach to reduce this blur, that enhances the speed to match the frame rate of the detector, to enable much clearer imaging of many biological systems (image on left).

M. Chen et al., "Quantitative differential phase contrast (DPC) microscopy with computational aberration correction," Optics Express 26, 32888-32899 (2018).

Correlative 3D X-ray Fluorescence and Ptychographic Tomography of Frozen-hydrated Green Algae

November 02, 2018

A STROBE team led by Prof. Miao, in collaboration with Argonne National Laboratory, implemented hybrid 3D X-ray microscopy by combining cryogenic hard X-ray ptychography and X-ray fluorescence microscopy. Here, STROBE's advanced GENFIRE tomography algorithm was used to correlate high resolution ultrastructure mapping and elemental distributions in an unlabeled, frozen-hydrated green algae.

J. Deng et al., “Correlative 3D x-ray fluorescence and ptychographic tomography of frozen-hydrated green algae”, Science Advances 4, eaau4548 (2018).

Electron Imaging Reveals the Conductance Watershed Between Two Electrodes

October 29, 2018

Traditional transmission electron microscopy (TEM) excels at determining the physical structure of a sample, but reveals little about the electronic structure. STROBE faculty Chris Regan at UCLA developed a new technique based on secondary electron emission (SE) and electron beam induced current (EBIC) to image the electronic structure of functioning devices with a TEM-like spatial resolution. He used this new SEEBIC technique to map the conductance of a nanodevice containing a thin silicon membrane (brown and green) separating two electrodes (blue).

Hubbard et al, "STEM Imaging with Beam-Induced Hole and Secondary Electron Currents," Physical Review Applied. 10, 044066 (2018).

Demonstration of Electron Ghost Imaging

September 11, 2018

The first demonstration of computational ghost imaging with electrons has been carried out at UCLA. A digital micromirror device is used to directly modulate the photocathode drive laser to control the transverse distribution of a relativistic electron beam incident on a sample. Correlating the structured illumination pattern to the total sample transmission then retrieves the target image, avoiding need for a pixelated detector. In our example, we use a compressed sensing framework to improve the reconstruction quality and reduce the number of shots compared to raster scanning a small beam across the target. Compressed electron ghost imaging can reduce both acquisition time and sample damage in experiments for which spatially resolved detectors are unavailable (e.g. spectroscopy) or in which the experimental architecture precludes full frame direct imaging.

S. Li et al., "Electron Ghost Imaging," Phys. Rev. Lett. 121, 114801 (2018).

Super-Resolution Imaging of Clickable Graphene Nanoribbons Decorated with Fluorescent Dyes

July 05, 2018

A STROBE team led by Ke Xu at Berkeley adapted advanced super-resolution microscopy techniques developed by the Weiss group at UCLA, to rapidly image graphene nanoribbons (GNRs) and carbon nanotubes (CNTs). These are important functional materials with great promise in nano-electronics and other applications. However, it has been a challenge to visualize and characterize them in a high-throughput manner due to their small physical dimensions. Temporal fluorescence intensity fluctuations in these samples enabled the reconstruction of SRM images through superresolution optical fluctuation imaging (SOFI) and the related superresolution radial fluctuation (SRRF) analysis methods.

D. Joshi et al., “Super-Resolution Imaging of Clickable Graphene Nanoribbons Decorated with Fluorescent Dyes,” Journal of the American Chemical Society 140, 9574 - 9580 (2018).

In Situ Coherent Diffractive Imaging

May 08, 2018

The Miao group at UCLA developed a new coherent diffractive imaging technique for capturing fast nanoscale dynamics. The concept leveraged time-invariant spatial redundancy in the field of view as a powerful constraint in the phase retrieval process. In addition, the introduction of high scattering features in the spatially redundant region also suggests the potential for dose-reduced imaging. Boulder and UCLA are collaborating to apply this in-situ imaging to materials undergoing phase transitions.

Y.Hung Lo et al., “In situ coherent diffractive imaging”, Nature Communications 9, (2018).

Wave-front Shaping Controls Nonlinearity in Complex Media

May 07, 2018

Wavefront shaping can enhance imaging through turbid media such as fog, or endoscopes. A CU Boulder STROBE team led by Rafael Piestun implemented a new kind of control that enables optimization of highly non-linear interactions through fibers. Tailoring the wave-front shape at the input, the system controls the generation of nonlinear phenomena known as stimulated-Raman-scattering cascades and four-wave-mixing, generating and shaping the different colors of the light pulses at the output of the fiber. This research has implications for the understanding of so-called adaptive systems, optical communications, fiber lasers, and imaging.

O. Tzang et al., “Adaptive wavefront shaping for controlling nonlinear multimode interactions in optical fibres” Nature Photonics 12, 368–374 (2018).

Sub-ångström Cryo-EM Structure of a Prion Protofibril Reveals a Polar Clasp

January 15, 2018

Brain dysfunction can be caused by aggregated proteins such as prions. In humans, the prion protein causes an infection by changing its shape and transforming into rope like aggregates. In this way, stable prion aggregates are immune to normal processes of destruction in an organism and bring about neuronal death and ultimately disease. There is no molecular explanation for the variable efficiency of prion spread between species. To investigate this phenomenon, STROBE scientists Rodriguez and Maio used cryo electron microscopy to reveal the atomic structures of regions within prion that have a high propensity to form structured aggregates. This made it possible to take an atomic look at structural motifs that may represent the molecular basis for a prion species barrier.

M. Gallagher-Jones et al., “Sub-ångström cryo-EM structure of a prion protofibril reveals a polar clasp,” Nature Structural & Molecular Biology 25, 131 - 134 (2018).

Semiconductor Voltage Sensors for Neuron Imaging

January 12, 2018

A STROBE team led by Simon Weiss implemented semiconductor-based voltage sensors as neuronal activity imaging probes. Unlike conventional voltage sensors, these nanosensors operating via the quantum confined Stark effect are highly sensitive, bright, and fast-responding. With further optimization, these nanosensors may enable single-particle detection and facilitate monitoring of neuronal signals at the nanoscale.

Kyoungwon Park et al., “Membrane insertion of—and membrane potential sensing by—semiconductor voltage nanosensors: Feasibility demonstration”, Science Advances 12 (2018).

Multiple Beam Illumination for Large Field-of-view, High Throughput, Imaging

January 01, 2018

The ability to record large field of view images without a loss in spatial resolution is critical for many applications of imaging science. However, for most imaging techniques, an increase in field-of-view comes at the cost of decreased resolution. STROBE scientists at CU Boulder implemented a novel extension to ptychographic coherent diffractive imaging that permits simultaneous full-field imaging of multiple simultaneous locations on a sample, by illuminating it with spatially separated, interfering beams. This technique allows for large field-of-view imaging in amplitude and phase while maintaining diffraction-limited resolution, without an increase in collected data i.e. diffraction patterns acquired. 

C. Bevis, “Multiple beam ptychography for large field of view, high throughput, quantitative phase contrast imaging,” Ultramicroscopy 184, 164–171 (2018).

GENFIRE: A Generalized Fourier Iterative Reconstruction Algorithm for High-resolution 3D Imaging

September 05, 2017

A STROBE team from the Miao group at UCLA implementated a powerful new tomographic algorithm, termed GENeralized Fourier Iterative REconstruction (GENFIRE), for high-resolution 3D reconstruction from a limited number of 2D projections. GENFIRE assembles a 3D Fourier grid with oversampling and then iterates between real and reciprocal space to search for a solution that is consistent with the measured data and physical constraints. This new algorithms has enabled many new imaging advances.

A. Pryor et al., “GENFIRE: A generalized Fourier iterative reconstruction algorithm for high-resolution 3D imaging”, Scientific Reports 7, 23: S1, (2017). 

Sub-wavelength Coherent Diffractive Imaging Using a Tabletop High Harmonic Light Source

March 20, 2017

Visible microscopes can produce crisp images with a spatial resolution on order of the illuminating wavelength, because of the availability of near-perfect lenses in this region of the spectrum. Extreme ultraviolet (EUV) and soft X-ray (SXR) light has wavelengths 10-100 times shorter than visible light: thus, it should be possible to design a powerful microscope that can image structures that are too small or too opaque to be seen with visible light. However, EUV/SXR lenses are very lossy and imperfect, limiting the advantage of using shorter wavelengths, and blurring the resulting images to >8 times the theoretical limit. Fortunately, new techniques pioneered by STROBE scientists Kapteyn, Murnane and Miao make it possible to build lensless microscopes illuminated by coherent laser-like beams — a capability that is revolutionizing X-ray imaging worldwide. Very recently, the Kapteyn-Murnane group at CU Boulder used tabletop EUV beams at a wavelength of 13nm to achieve sub-wavelength spatial resolution imaging at short wavelengths for the first time – essentially demonstrating the first near-perfect X-ray microscope. Moreover, because the EUV source produces exceedingly short, femtosecond (~10-15 sec), bursts of light, it can now be used to make stroboscopic movies to observe how the nanoworld functions. STROBE graduate student Dennis Gardner received the American Physical Society Division of Laser Science Thesis Award for this work.   

Gardner et al., Nature Photonics 11, 259 (2017).