Few-atom silver clusters with rod-like geometries and high fluorescence quantum yields can be stabilized by DNA [1]. Now emerging in a number of sensing and photonic applications, much is still unknown about the mechanisms underlying the optical properties of these “AgN–DNA.” To better understand these mechanisms and to intelligently design applications, we investigate the effects of dielectric environment and cluster shape on electronic excitations of AgN–DNA. We first establish that the longitudinal plasmon wavelengths predicted by classical Mie-Gans (MG) theory agree with previous quantum calculations for excitation wavelengths of linear silver atom chains, even for clusters of just a few atoms. Application of MG theory to AgN–DNA with 400–850 nm cluster excitation wavelengths indicates that these clusters are characterized by a collective excitation process and suggests effective cluster thicknesses of ∼2 silver atoms and aspect ratios of 1.5 to 5. To investigate the sensitivity of these collective excitations to the surrounding medium, we measure the wavelength shifts produced by addition of glycerol. These are smaller than reported for much larger gold nanoparticles but easily detectable due to narrower line widths, suggesting that AgN–DNA may have potential for dielectric sensing in biomolecules at length scales of ∼1 nm

Strain engineering is a promising method for next-generation materials processing techniques. Here, we use mechanical milling and annealing followed by compression in diamond anvil cell to tailor both the intrinsic and extrinsic strain experienced by technologically important pyrochlore oxides, Dy2Ti2O7 and Dy2Zr2O7. Raman spectroscopy, X-ray pair distribution function analysis, and X-ray diffraction were utilized to characterize atomic order over a wide range of spatial scales at ambient conditions, providing a comprehensive picture for understanding the high-pressure structural response. Raman spectroscopy and X-ray diffraction were further used to interrogate the material in situ at high pressure. The high-pressure structural behavior is found to be dependent on the sample’s initial atomic order, defined by its crystal structure, concentration of cation anti-site and anion Frenkel defects, and internal strain. Overall, it is shown that properly tuning a material’s initial defect profile can lower the critical pressure of the phase transformation, and enhance the transformation’s kinetics, without sacrificing significant mechanical integrity.

Scanning Tunneling Microscopy (STM) and other forms of Scanning Probe Microscopy (SPM), are traditionally applied mainly to static structures that are investigated mainly under relatively artificial conditions, such as ultrahigh vacuum (UHV). This is surprising in light of the relative insensitivity of the operation mechanism of STM and that of most other types of SPM to such aspects as temperature or gas pressure or even the presence of liquids.

In this talk, I will demonstrate that it is possible to apply SPM techniques without compromising their atomic resolution even under harsh conditions. Extra attention is required to construct the SPM instrumentation such that it avoids the complications that are introduced by these conditions, such as excessive thermal drift or damage to delicate components. This is, in principle, a straightforward engineering task, which leads typically to dedicated designs for specific classes of imaging conditions.

The examples provided in this talk are all live STM observations of relevant dynamic surface phenomena. They range from model catalysts under the conditions of high temperatures and high pressures at which they are being used in the chemical industry, to the chemical vapor deposition of graphene on metal substrates6 and the atom-by-atom deposition or erosion of surfaces under the influence of atom and ion beams.

An interview with Dr. Frenken about his work and this talk is available here.

Microfluidic devices can be used to produce highly uniform, exquisitely structured materials based on the production of drops of one fluid in a second. This talk will describe the applications of this technology to create new materials and for very high-throughput screening, which is of great value in biotechnology.

Two-dimensional transition metal dichalcogenides (TMD) such as MoS2 are promising for applications in novel electronic and optical devices. One major drawback in the device applications of 2D materials, however, is related to their intrinsically anisotropic thermal conductivity in which cross-plane thermal conductivity is more than 10 times smaller than in-plane thermal conductivity. Consequently, cross-plane heat dissipation is not efficient, which has hindered the performance of the 2D devices. Strain has been found to be effective in tuning the band gap of the TMDs, but has yet been investigated in optimizing their thermal transport properties. With about 9% cross-plane compressive strain created by hydrostatic pressure in a diamond anvil cell, we observed about 12 times increase in the cross-plane thermal conductivity of multilayer MoS2. This drastic change arises from the greatly strengthened inter-layer interaction and heavily modified phonon dispersions along the cross-plane direction. The change in electronic thermal conductivity due to semiconductor to metal transition plays a minimal role. Our experimental and theoretical studies show that longitudinal acoustic phonons dominate the increase in cross-plane thermal conductivity under compressive strain; the saturation above 9% strain is associated with the combined effects from enhanced group velocity via the phonon hardening and reduced phonon lifetimes due to phonon unbundling. As a result, the anisotropic thermal conductivity in the multilayer MoS2 at ambient environment becomes almost isotropic under highly compressive strain, effectively transitioning from 2D to 3D heat dissipation. Our observation for the phonon-dominant change of thermal conductivity across the semiconductor-metal transition raises the prospective for designing electronic devices possessing both high electrical conductivity and high cross-plane thermal conductivity for effective heat dissipation, as well as heat modulators with controllable and directional heat flux. The concept for strain tuned 2D to 3D transition in the thermal transport property can be potentially extended to a larger ever increasing family of 2D van der Waals solids.

In Pixar’s Inside Out, Joy proclaims, “Do you ever look at someone and wonder, what’s going on inside?” My group asks the same question about nanomaterials whose function plays a critical role in energy and biologically-relevant processes. This presentation will describe new techniques that enable in situ visualization of chemical transformations and light-matter interactions with nanometer-scale resolution. We focus in particular on i) ion-induced phase transitions; ii) optical forces on enantiomers; and iii) nanomechanical forces using unique electron, atomic, and optical microscopies. First, we explore nanomaterial phase transitions induced by solute intercalation, to understand and improve materials for energy storage applications.  As a model system, we investigate hydrogen intercalation in palladium nanocrystals. Using environmental electron microscopy and spectroscopy, we monitor this reaction with sub-2-nm spatial resolution and millisecond time resolution. Particles of different sizes, shapes, and crystallinities exhibit distinct thermodynamic and kinetic properties, highlighting several important design principles for next-generation energy storage devices. Then, we investigate optical tweezers that enable selective optical trapping of nanoscale enantiomers, with the ultimate goal of improving pharmaceutical and agrochemical efficacy. These tweezers are based on plasmonic apertures that, when illuminated with circularly polarized light, result in distinct forces on enantiomers. In particular, one enantiomer is repelled from the tweezer while the other is attracted. Using atomic force microcopy, we map such chiral optical forces with pico-Newton force sensitivity and 2 nm lateral spatial resolution, showing distinct force distributions in all three dimensions for each enantiomer. Finally, we present new nanomaterials for efficient and force-sensitive upconversion. These optical force probes exhibit reversible changes in their emitted color with applied nano- to micro-Newton forces. We show how these nanoparticles provide a platform for understanding intra-cellular mechanical signaling in vivo, using C. elegans as a model organism.

An interview with Dr. Dionne about her work and this talk is available here.

Two-dimensional (2D) materials are solid crystals consisting of layered planes of atoms that results in anisotropic properties with strong contrast in in-plane and cross-plane physics. Under very high strain or pressure, the van der Waals gap reduces and the anisotropic differences diminishes leading to interesting physics including phase transition, electronic transition, structure transition, and thermal transitions. All in all, the behaviour of electrons, phonons and photons obey different symmetric rules under vertical pressure. In this talk, we will discuss our research on high-pressure effects on monolayer and multilayer TMDs, black phosphorus and heterostructures and the subsequent dramatic consequences. We find the underlying physics is distinct when comparing monolayer to multilayer counterparts. In addition, performance can be tuned far beyond what is observed in conventional bulk solids. These performance parameters include bandgap, mobility, carrier concentration, etc. Layered nanomaterials represent a new frontier where strain can play an effective role as a degree of freedom in controlling and tuning material structure and properties.

Single cell measurements, including transcriptomics and proteomics, are transforming the study of biology. Single cell techniques leverage a multitude of materials technologies including microfluidics and DNA-functionalized microbeads, enabling studies of the true heterogeneity of complex tissues and therefore potential disease treatments. However, it is still difficult to gather multiple types of biological measurements from single cells, which is necessary to determine how the myriad of biomolecules communicate and interact with each other. Here we present a strategy that enables the measurement of the whole transcriptome and selected proteins from a single cell using a microfluidic chip device. The challenge lies in how single cell resolution is obtained for each technique. Single cell proteomic resolution is obtained either temporally through flow cytometry and mass spectrometry, or spatially on antibody array chips. On the other hand, transcriptomic single cell resolution requires DNA-based barcodes to be placed on capture beads, which are extracted after the final sequencing step. By modifying the single cell barcode chip platform used for single cell proteomics, we have developed a DNA labeling strategy that bridges spatial single cell proteomic resolution with DNA-barcoded single cell transcriptomic resolution. Our method, called Spatially Correlated Sequencing (SpaCeSeq), allows RNA capture beads positioned in microfluidic chamber arrays to be tagged with location-encoding DNA strands. Therefore, after the RNA of a single cell is sequenced, it can be traced back to a microwell containing protein measurements taken by an antibody array, thus correlating sequenced transcripts and measured proteins from a single cell. SpaCeSeq can also be applied to label single cell transcriptomes with DNA corresponding to information such as treatments or culture conditions, and the proteomics chip can be further modified to capture metabolomic measurements. Ultimately, this technology can contribute to answers for a range of biological questions, from fundamental studies of the relationship between transcription and translation in single cells, to a better understanding of tumor biology and targeted treatments.

In high pressure (HP) research, an achievable static pressure limit is imposed by available strong materials and design of HP devices. Achieving higher and higher pressures will open new horizons for a deeper understanding of matter and the discovery of new physical and chemical phenomena at extreme conditions. Recently we developed a new technique of ultra-high static pressure generation in a double-stage diamond anvil cell. Nanocrystalline diamond (NCD) balls synthesized from glassy carbon were used as secondary anvils. Due to unique properties of NCD, this technique allowed us to reach pressures beyond 1 TPa and to study the behavior of a number of materials at such extreme conditions. In this contribution we will report on unique properties of the NCD material and its applications.

Laser heating techniques in diamond anvil cells (DACs) cover a wide pressure-temperature range – above 300 GPa and up to 5000 K. Recent advantages in on-line laser heating techniques resulted in a significant improvement of reliability of in situ X-ray powder diffraction studies in laser-heated DACs, which have become routine at a number of synchrotron facilities including specialized beam-lines at the 3rd generation synchrotrons. However, until recently, existing DAC laser-heating systems could not be used for structural X-ray diffraction studies aimed at structural refinements, i.e. measuring of the diffraction intensities, and not only at determining of lattice parameters. The reason is that in existing DAC laser-heating facilities the laser beam enters the cell at a fixed angle, and a partial rotation of the DAC, as required in monochromatic structural X-ray diffraction experiments, results in a loss of the target crystal and may be even dangerous if the powerful laser light starts to scatter in arbitrary directions by the diamond anvils. In order to overcome this problem we have develop a portable laser heating system and implement it at diffraction beam lines (ID9 and ID27 at ESRF, and P02 at PETRA III). We demonstrate the application of this system for simultaneous high-pressure and high-temperature powder and single crystal diffraction studies using examples of studies of chemical and phase relations in the Fe-O system, transition metals carbonates, and silicate perovskites.