Preparing future STEM faculty through flexible teaching professional development.

We have prepared thousands of future STEM faculty around the world to adopt evidence-based instructional practices through their participation in two massive open online courses (MOOCs) and facilitated in-person learning communities. Our novel combination of asynchronous online and coordinated, structured face-to-face learning community experiences provides flexible options for STEM graduate students and postdoctoral fellows to pursue teaching professional development. A total of 14,977 participants enrolled in seven offerings of the introductory course held 2014-2018, with 1,725 participants (11.

A national professional development program fills mentoring gaps for postdoctoral researchers.

The Postdoc Academy: Succeeding as a Postdoc was designed to build postdocs' skills in career transition, career planning, collaborative research, resilience, and self-reflection. This study examined self-reported changes in five skills as learners progressed through the course. Data were collected from participants who responded to both pre- and post-surveys and engaged with the course learning activities.

Training in the art and science of facilitation to scale research mentor training in low and middle income countries.

Advancing biomedical research in low and middle income countries (LMICs) to expand the capacity for LMICs to integrate biomedical research into their health care systems and education has been the focus of many programs in global health over the past two decades. Central to the success of these programs is effective research mentoring, characterized by academic, career and psychosocial support through culturally appropriate practices. Research mentoring is a learned skill, developed through training, mutual discussions, practice and feedback.

Theory of change models deepen online learning evaluation.

Massive Open Online Courses (MOOCs) have gained traction as resources for professional development. This article presents the method that we used to evaluate a professional development MOOC for postdoctoral trainees that was created by a university consortium in the US. Most approaches to evaluating MOOCs focus on analysis of participation, outcomes from course assignments, self-reported learning outcomes, course completion and user pathways through the online content or clickstream data.

Long tailed trions in monolayer MoS: Temperature dependent asymmetry and resulting red-shift of trion photoluminescence spectra.

Monolayer molybdenum disulfide (MoS) has emerged as a model system for studying many-body physics because the low dimensionality reduces screening leading to tightly bound states stable at room temperature. Further, the many-body states possess a pseudo-spin degree of freedom that corresponds with the two direct-gap valleys of the band structure, which can be optically manipulated. Here we focus on one bound state, the negatively charged trion.

Extended depth-of-field microscopy with a high-speed deformable mirror.

We present a wide-field fluorescence microscopy add-on that provides a fast, light-efficient extended depth-of-field (EDOF) using a deformable mirror with an update rate of 20 kHz. Out-of-focus contributions in the raw EDOF images are suppressed with a deconvolution algorithm derived directly from the microscope 3D optical transfer function. Demonstrations of the benefits of EDOF microscopy are shown with GCaMP-labeled mouse brain tissue.

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2.

We demonstrate the continuous and reversible tuning of the optical band gap of suspended monolayer MoS2 membranes by as much as 500 meV by applying very large biaxial strains. By using chemical vapor deposition (CVD) to grow crystals that are highly impermeable to gas, we are able to apply a pressure difference across suspended membranes to induce biaxial strains. We observe the effect of strain on the energy and intensity of the peaks in the photoluminescence (PL) spectrum and find a linear tuning rate of the optical band gap of 99 meV/%.

Dictionary-based image reconstruction for superresolution in integrated circuit imaging.

Resolution improvement through signal processing techniques for integrated circuit imaging is becoming more crucial as the rapid decrease in integrated circuit dimensions continues. Although there is a significant effort to push the limits of optical resolution for backside fault analysis through the use of solid immersion lenses, higher order laser beams, and beam apodization, signal processing techniques are required for additional improvement. In this work, we propose a sparse image reconstruction framework which couples overcomplete dictionary-based representation with a physics-based forward model to improve resolution and localization accuracy in high numerical aperture confocal microscopy systems for backside optical integrated circuit analysis.

Digital sensing and sizing of vesicular stomatitis virus pseudotypes in complex media: a model for Ebola and Marburg detection.

Rapid, sensitive, and direct label-free capture and characterization of nanoparticles from complex media such as blood or serum will broadly impact medicine and the life sciences. We demonstrate identification of virus particles in complex samples for replication-competent wild-type vesicular stomatitis virus (VSV), defective VSV, and Ebola- and Marburg-pseudotyped VSV with high sensitivity and specificity. Size discrimination of the imaged nanoparticles (virions) allows differentiation between modified viruses having different genome lengths and facilitates a reduction in the counting of nonspecifically bound particles to achieve a limit-of-detection (LOD) of 5 × 10(3) pfu/mL for the Ebola and Marburg VSV pseudotypes.

Evanescent waves in high numerical aperture aplanatic solid immersion microscopy: effects of forbidden light on subsurface imaging.

The collection of light at very high numerical aperture allows detection of evanescent waves above the critical angle of total internal reflection in solid immersion lens microscopy. We investigate the effect of such evanescent modes, so-called forbidden light, on the far-field imaging properties of an aplanatic solid immersion microscope by developing a dyadic Green's function formalism in the context of subsurface semiconductor integrated circuit imaging. We demonstrate that the collection of forbidden light allows for sub-diffraction spatial resolution and substantial enhancement of photon collection efficiency albeit inducing wave-front discontinuities and aberrations.

Effect of vector asymmetry of radially polarized beams in solid immersion microscopy.

We theoretically and experimentally investigate the effect of imperfect vector symmetry on radially polarized beams focused by an aplanatic solid immersion lens at a numerical aperture of 3.3. We experimentally achieve circularly symmetric focused spot with a full-width-half-maximum of ~λ0/5.

Charge tuning of nonresonant magnetoexciton phonon interactions in graphene.

Far from resonance, the coupling of the G-band phonon to magnetoexcitons in single layer graphene displays kinks and splittings versus filling factor that are well described by Pauli blocking and unblocking of inter- and intra-Landau level transitions. We explore the nonresonant electron-phonon coupling by high-magnetic field Raman scattering while electrostatic tuning of the carrier density controls the filling factor. We show qualitative and quantitative agreement between spectra and a linearized model of electron-phonon interactions in magnetic fields.

How graphene slides: measurement and theory of strain-dependent frictional forces between graphene and SiO2.

Strain, bending rigidity, and adhesion are interwoven in determining how graphene responds when pulled across a substrate. Using Raman spectroscopy of circular, graphene-sealed microchambers under variable external pressure, we demonstrate that graphene is not firmly anchored to the substrate when pulled. Instead, as the suspended graphene is pushed into the chamber under pressure, the supported graphene outside the microchamber is stretched and slides, pulling in an annulus.

Single nanoparticle detectors for biological applications.

Nanoparticle research has become increasingly important in the context of bioscience and biotechnology. Practical use of nanoparticles in biology has significantly advanced our understanding about biological processes in the nanoscale as well as led to many novel diagnostic and therapeutic applications. Besides, synthetic and natural nanoparticles are of concern for their potential adverse effect on human health.

Transfer of CVD-grown monolayer graphene onto arbitrary substrates.

Reproducible dry and wet transfer techniques were developed to improve the transfer of large-area monolayer graphene grown on copper foils by chemical vapor deposition (CVD). The techniques reported here allow transfer onto three different classes of substrates: substrates covered with shallow depressions, perforated substrates, and flat substrates. A novel dry transfer technique was used to make graphene-sealed microchambers without trapping liquid inside.

Biomolecular detection employing the Interferometric Reflectance Imaging Sensor (IRIS).

The sensitive measurement of biomolecular interactions has use in many fields and industries such as basic biology and microbiology, environmental/agricultural/biodefense monitoring, nanobiotechnology, and more. For diagnostic applications, monitoring (detecting) the presence, absence, or abnormal expression of targeted proteomic or genomic biomarkers found in patient samples can be used to determine treatment approaches or therapy efficacy. In the research arena, information on molecular affinities and specificities are useful for fully characterizing the systems under investigation.

Label-free multiplexed virus detection using spectral reflectance imaging.

We demonstrate detection of whole viruses and viral proteins with a new label-free platform based on spectral reflectance imaging. The Interferometric Reflectance Imaging Sensor (IRIS) has been shown to be capable of sensitive protein and DNA detection in a real time and high-throughput format. Vesicular stomatitis virus (VSV) was used as the target for detection as it is well-characterized for protein composition and can be modified to express viral coat proteins from other dangerous, highly pathogenic agents for surrogate detection while remaining a biosafety level 2 agent.

Biaxial strain in graphene adhered to shallow depressions.

Measurements on graphene exfoliated over a substrate prepatterned with shallow depressions demonstrate that graphene does not remain free-standing but instead adheres to the substrate despite the induced biaxial strain. The strain is homogeneous over the depression bottom as determined by Raman measurements. We find higher Raman shifts and Gruneisen parameters of the phonons underlying the G and 2D bands under biaxial strain than previously reported.

Quantification of DNA and protein adsorption by optical phase shift.

A primary advantage of label-free detection methods over fluorescent measurements is its quantitative detection capability, since an absolute measure of adsorbed material facilitates kinetic characterization of biomolecular interactions. Interferometric techniques relate the optical phase to biomolecular layer density on the surface, but the conversion factor has not previously been accurately determined. We present a calibration method for phase shift measurements and apply it to surface-bound bovine serum albumin, immunoglobulin G, and single-stranded DNA.

Closed-form representations of field components of fluorescent emitters in layered media.

Dipole radiation in and near planar stratified dielectric media is studied theoretically within the context of fluorescence microscopy, as fluorescent emitters are generally modeled by electric dipoles. Although the main emphasis of this study is placed on the closed-form representations of the field components of fluorescent emitters in layered environments in near- and far-field regions, the underlying motive is to understand the limits of spectral self-interference fluorescence microscopy in studying the dipole orientation of fluorophores. Since accurate calculations of the field components of arbitrarily polarized electric dipoles in layered environments are computationally very time-consuming, a method for finding their closed-form representations is proposed using the closed-form potential Green's functions previously developed for microwave applications.

Direct observation of conformation of a polymeric coating with implications in microarray applications.

The conformation of a three-dimensional polymeric coating (copoly(DMA-NAS-MAPS)) and immobilization and hybridization of DNA strands on the polymer coated surface are investigated. A conformational change, specifically the swelling of the surface adsorbed polymer upon hydration, is quantified in conjunction with the application of this polymer coating for DNA microarray applications. Fluorescently labeled short DNA strands (23mers) covalently linked to the functional groups on the adsorbed polymer are used as probes to measure the swelling of the polymer.

Hyperspectral Fourier transform spectrometer for reflection spectroscopy and spectral self-interference fluorescence microscopy.

A hyperspectral Fourier transform spectrometer has been developed for studying biological material bound to optically reflecting surfaces. This instrument has two modes of operation: a white-light reflection mode and a spectral self-interference fluorescence mode. With the combined capability, information about the conformation of an ensemble of biomolecules may be determined.

Widefield subsurface microscopy of integrated circuits.

We apply the numerical aperture increasing lens technique to widefield subsurface imaging of silicon integrated circuits. We demonstrate lateral and longitudinal resolutions well beyond the limits of conventional backside imaging. With a simple infrared widefield microscope (lambda(0) = 1.

Label-free and dynamic detection of biomolecular interactions for high-throughput microarray applications.

Direct monitoring of primary molecular-binding interactions without the need for secondary reactants would markedly simplify and expand applications of high-throughput label-free detection methods. A simple interferometric technique is presented that monitors the optical phase difference resulting from accumulated biomolecular mass. As an example, 50 spots for each of four proteins consisting of BSA, human serum albumin, rabbit IgG, and protein G were dynamically monitored as they captured corresponding antibodies.