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So far Lauren Mason has created 270 blog entries.

Exploring the 3D Nano and Atomic World: Coherent Diffractive Imaging and Atomic Electron Tomography

The discovery and analysis of X-ray diffraction from crystals by Max von Laue, William Henry Bragg and William Lawrence Bragg in 1912 marked the birth of crystallography. Over the last century, crystallography has been fundamental to the development of many fields of science. However, many samples in physics, chemistry, materials science, nanoscience, geology, and biology are non-crystalline, and thus their 3D structures are not accessible by traditional crystallography. Overcoming this hurdle has required the development of new structure determination methods. In this talk, I will present two methods that can go beyond crystallography: coherent diffractive imaging (CDI) and atomic electron tomography (AET). In CDI, the diffraction pattern of a non-crystalline sample or a nanocrystal is first measured and then directly phased to obtain an image. The well-known phase problem is solved by combining the oversampling method with iterative algorithms. In the first part of the talk, I will briefly discuss the principle of CDI and highlight its capability of direct observation of 3D topological spin textures and their interactions in a ferromagnetic superlattice. In the second part of the talk, I will present a general tomographic method, termed AET, for 3D structure determination of crystal defects and disordered materials at the single atomic level. By combining advanced electron microscopes with powerful computational algorithms, AET has been used to reveal the 3D atomic structure of crystal defects and chemical order/disorder and to precisely localize the 3D coordinates of individual atoms in materials without assuming crystallinity. The experimentally measured coordinates can then be used as direct input for quantum mechanical calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy. As coherent X-ray sources and powerful electron microscopes are under rapid development around the world, we expect that CDI and AET will find broad applications in both the physical and biological sciences.

The Prime Suspect: Hot Band Absorption

In a new paper published in the Journal of Physical Chemistry Letters, Jimenez and his team report a new experimental setup to search for the cause of a mysterious fluorescent signal that appears to be from entangled photon excitation. According to Jimenez: “We built a setup where you could use either a classical laser or entangled photons to look for fluorescence. And the reason we built it is to ask: ‘What is it that other people were seeing when they were claiming to see entangled photon-excited fluorescence?’ We saw no signal in our previous work published a year ago, headed by Kristen Parzuchowski. So now, we’re wondering, people are seeing something, what could it possibly be? That was the detective work here.” The results of their new experiments suggested that hot-band absorption (HBA) by the subject molecules, could be the potential culprit for this mysterious fluorescent signal, making it the prime suspect.

New twists on chemistry and physics in atomically layered materials

Atomically thin or two-dimensional (2D) materials can be assembled into bespoke heterostructures to produce some extraordinary physical phenomena. Likewise, these highly tunable materials are useful platforms for exploring fundamental questions of interfacial chemical/electrochemical reactivity. One exciting and relatively recent example is the formation of moiré superlattices from azimuthally misoriented (twisted) layers. These moiré superlattices result in flat bands that lead to an array of correlated electronic phases. However, in these systems, complex strain relaxation can also strongly influence the fragile electronic states of the material. Precise characterization of these materials and their properties is therefore critical to the understanding of the behavior of these novel moiré materials (and 2D heterostructures in general). In this talk, I will discuss how spontaneous mechanical deformations (atomic reconstruction) and resultant intralayer strain fields at moiré superlattices of twisted bilayer graphene have been quantitatively imaged using 4D-STEM Bragg interferometry. I will also discuss the impact of these mechanical deformations to the electronic band structure of these moiré superlattices and the correlated electronic phases they host. The talk will then explore how various degrees of freedom that are unique to 2D materials may be used to tailor interfacial chemistry at well-defined mesoscopic electrodes and the outlook for new paradigms of functional materials for energy conversion and low-power electronic devices.

Congratulations to Charlie Bevis for Receiving a Marie Skłodowska-Curie Individual Fellowship (MSCA-IF)

The European Commission will support a total of 1156 experienced post-doctoral researchers with €242 million to work at top universities, research centres, private organisations and small and medium-sized enterprises in Europe and the rest of the world. The European Research Executive Agency (REA) received 8356 applications for this call. The Commission will award €206 million to 1025 researchers through European Postdoctoral Fellowships, allowing them to carry out their projects in the EU or countries associated to Horizon Europe. The action provides support to excellent individual researchers to implement an original and personalized research project, while developing their skills through advanced training, international, interdisciplinary and inter-sectoral mobility.

Multimodal and Dynamic Microscopy on Perovskite Semiconductors

Uncovering structure/function relationships in condensed phase electronic materials is increasingly important for applications from solar energy to quantum optoelectronics. In this talk, we will explore multimodal microscopy to the role of microscopic heterogeneity and defects in emerging semiconductors, focusing on halide perovskites as a system that is not only technologically important, but also scientifically challenging. Halide perovskites are soft, and easily damaged by low doses of electrons. They are also complicated mixed conductors, exhibiting electronic and ionic relaxation dynamics that vary across many orders of magnitude in time and space. To probe these systems, we combine hyperspectral optical spectroscopy, electron microscopy, scanning probe microscopy, and data science tools to understand and control defects for applications in photovoltaics, showing how surface and grain boundary passivation enables the growth of films that approach thermodynamic efficiency limits for performance, while also problem the role of processing additives on microstructure and performance.

Congratulations to Heather Lewandowski for Being Designated as a CU President’s Teaching Scholar

The University of Colorado President’s Teaching Scholars Program recognizes CU faculty who skillfully integrate teaching and research at an exceptional level. The title of President’s Teaching Scholar recognizes excellence in and commitment to learning and teaching, as well as active, substantial contributions to scholarly work. President Saliman solicits annual nominations of faculty across the four campuses for the designation, which is a lifetime appointment.

Vibrational exciton nanoscopy: a quantum molecular ruler to probe functional materials on their elementary scales

Properties and functions of molecular materials often emerge from intermolecular interactions and associated nanoscale structure and morphology. However, defects and disorder disturb the performance of, e.g., molecular electronic or photonic materials. We address these outstanding problems in several novel combinations of spatio-spectral and spatio-temporal infrared nano-imaging. In this talk I will give an overview of these new developments with a focus on intermolecular coupling induced molecular wavefunction delocalization and its disturbance through structural disorder. This provides for a molecular ruler to imagine structure, coupling, and dynamics of elementary processes on their elementary nanometer-femtosecond scales. I will further demonstrate how Purcell-enhanced and strongly coupled vibrational light matter interactions provide for new modalities in molecular nano-metrology and -sensing. I will conclude with a perspective how these novel quantum-enhanced modalities provide for qualitatively novel functional imaging as new tools to guide molecular device fabrication with improved performance.

Postdoc Positions in Deep Tissue Imaging with cumulative coherent nonlinear scattering at Colorado State University

Postdoc positions available at the school of biomedical engineering at Colorado state University. Salary is $70K annually.

We are seeking two postdoctoral applicants to work on a CZI-funded project for ultra deep nonlinear imaging inside of biological tissues. This work builds on a recently demonstrated second harmonic generation (SHG) holographic tomography (https://doi.org/10.1038/s41566-020-0638-5) that will be combined with coherent reflection matrices to enable SHG imaging at unprecedented depths. Postdocs will also be actively involved in the CZI deep tissue imaging team.

About CSU and Fort Collins
Applicant requirements

Application process
Successful candidates must have a Ph.D. in Optics, Physics, Engineering, or related field. Candidates with or motivated to learn the following skills are strongly encouraged to apply:
— Experience or a strong interest in light propagation in highly scattering media, with a particular focus on transmission and reflection matrices
— Experience or a strong interest in construction of multiphoton microscopes, nonlinear optics, and ultrafast lasers
— Experience or a strong interest in imaging deep inside of biological tissues Colorado State University is an Equal Opportunity Employer

CSU is a leading research institution. CSU is located in the city of Fort Collins, near the Rocky Mountains. Fort Collins is often named America’s “Best Place to Live,” including in 2020 by livability.com. Fort Collins enjoys an average of 300 days of sunshine per year, moderate winters, and a mild climate year-round.

Review of applications starts immediately and the positions will remain open until successful candidates have been found. To apply, interested applicants should forward their CV including a
publication list, contact details of three reference writers and a one-page description of their experience and research interests related to this position. For more information and for applying, please contact Randy Bartels directly (randy.bartels@colostate.edu).

Postdoctoral positions in Molecular Quantum Optics at Max Planck Institute for the Science of Light in Erlangen, Germany

Postdoctoral positions are now available in the Nano-Optics division of the Max Planck Institute for the Science of Light (MPL) in Erlangen, Germany. You will be embedded in a dynamic interdisciplinary group at a world-leading research institute with excellent resources such as state-of-the-art mechanical and electronic workshops and a high-end nanofabrication cleanroom.

The overarching goal in a number of exciting projects is to understand and control the interaction of quantum emitters, in particular organic molecules, with their nanoscopic environment and with each other. To do this, we explore and employ a wide range of phenomena, involving the optical near field, phononic couplings as well as long-range photonic interactions in integrated nanocircuits. For more information about the activities of MPL and the Nano-Optics group please consult a sample of our publications [1-6] and website at: https://www.mpl.mpg.de

We seek highly motivated candidates with a strong scientific background and hands-on experience in physics or physical chemistry. Mastery of at least one of the following research areas is highly desirable:
• Laser spectroscopy
• Atomic and molecular physics
• Quantum optics
• Condensed matter physics
• Optomechanics
• Quantum information science
• Optical microscopy

In addition, candidates should enjoy team work. Programing skills (e.g., Matlab, Python, LabView), advanced knowledge of electronics, cryogenic experience, and excellent organizational and communication skills are also advantageous. The position will be funded for two years with an option for extension up to five years. Application material should include 1) curriculum vitae, 2) motivation letter, 3) university grades, 4) list of publications, and 5) names of three individuals who could send a letter of recommendation. Applications should be sent to sandoghdar-office@mpl.mpg.de.

The Max Planck Society strives for gender and diversity equality. We welcome applications from all backgrounds. Furthermore, the Max Planck Society is committed to increasing the number of individuals with disabilities in its workforce and therefore encourages applications from such qualified individuals.

[1] A. Pscherer, et al, Phys. Rev. Lett., 127, 133603 (2021); [2] C. Toninelli, et al, Nature Materials 20, 1615
(2021); [3] V. Sandoghdar, Nano Lett. 20, 4721 (2020); [4] D. Wang, et al, Nature Physics 15, 483-489 (2019); [5]
A. Maser, et al, Nature Photonics 10, 450 (2016); [6] R. Lettow, et al, Phys. Rev. Lett. 104, 123605 (2010).

New forms of computational tomographic and super-resolution imaging

Conventional optical microscopy focuses on designing optical systems to faithly replicate an image of a magnified object to reveal very small spatial features. Image quality, and thus the ability to observe small spatial features, is limited by the ability to form high quality images for widefield microscopy, or for focusing to the smallest possible spot for laser scanning microscopy. Computational imaging can sidestep such limitations by taking into account a model of the image process, and this way computational imaging is able to produce high resolution imaging with a greater flexibility for optical systems. I will provide an overview of several recent results on computational imaging from my group: 1) three dimensional widefield second harmonic generation tomographic imaging based in defocused illumination, 2) tomographic fluorescent imaging by mimicking coherent light propagation, and 3) saturated super deconvolution microscopy.

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