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We demonstrate new liquid cell architectures utilizing graphene-sealed Si or SiN cavities for in situ electron microscopy. While previous graphene liquid cell techniques have shown graphene to be an ideal sealing layer and electron-transparent viewing window, they trap irregular geometries of liquid with unknown sample volumes. Our new technique allows for a leak-proof confinement of liquids of precise volume in the tens of attoliter range while maintaining the benefits of graphene as a viewing window. The utility of this new cell architecture is demonstrated by imaging the dynamics of gold nanoparticles in three dimensions with atomic resolution under a transmission electron microscope.

4 5The best voltage for milk pasteurization by using ohmic heating was 80 V compared with 110, 220 V, both of which were inadequate for pasteurization. Heating at 80 V was safer and inexpensive as it required less power (80 V) in contrast with higher voltages (110-220 V) and less dangerous. Voltage of 80 V does not change milk color to brownish as it was noticed at 110- 220 V and undesirable smells were not present. Heating at 80 V did not cause fouling or precipitation of deposits on electrodes compared to 110-220 V. The best electrical conductivity was at 80 V as there were no deposits on the electrodes. The practical temperature of milk was stable because of the thermal valve, which controls the temperature at 72°C. The electric conductivity and current were increased with increasing temperature in ohmic heating at 220, 110, and 80 V while these were decreased with the increase of temperature at 220 V. The thermal conductivity and thermal diffusivity were increased with the increase of temperature at all voltages in the ohmic heating and high time short temperature (HTST).The introductory part of this chapter includes importance of thermal processing of milk, existing heating methods used and their effects on different quality characteristics. Authors explored alternative methods for thermal processing of milk and milk products, and briefly discussed microwave-assisted processing with recent research findings. Further, they discussed the influence of microwave heating on physicochemical properties, microbial destruction, enzyme inactivation, and volatile components of milk. Finally, they concluded that microwave heating has potential to meet industrial needs as an alternative technology for thermal processing of milk. The viscosity of milk and its density were decreased with the increase of temperature at all voltages in the ohmic heating and HTST. The period of keeping milk in the device was decreased with the increase of voltage in the ohmic heating, which was less than HTST. At 80 V of treatment, the highest coefficient of performance was 0.80, compared with 220, 110 V, with performance coefficient of 0.49 and 0.76, respectively. The percentages of protein, lipid, lactose, ash, and humidity in raw milk were 3.6, 3.7, 5.02, 0.68, and 87.0%, respectively. These values at 80 V were 3.5, 3.6, 6.2, 0.69, and 85.9%, respectively; and at 110 V were 3.54, 3.6, 6.9, 0.69, and 85.2%, respectively; and at 220 V were 3.5, 3.6, 7.1, 0.73, and 85.0%, respectively, and in HTST were 3.57, 3.7, 6.0, 0.71, and 87.0%, respectively. The percentage of acidity in raw milk was 0.15% and was 0.14, 0.14, 0.13, and 0.15%, respectively, for ohmic heating at 220, 110, 80 V, and HTST. The pH prior the pasteurization was 6.6 compared to 6.7, 6.8, 6.8, and 6.8 after the pasteurization by ohmic heating at 220, 110, 80 V, and HTST treatment, respectively. The phosphatase enzyme test gave positive results in raw milk and negative one in pasteurized milk treated either by ohmic heating on all voltages and HTST. The clot on boiling test and turbidity test gave negative results for raw milk. The microbiological results of pasteurized milk by ohmic heating showed no colonies in total 6count bacteria, coli form, Staph-110, yeasts, and molds. Milk treated by HTST pasteurization had bacteria while bacteria were absent. The shelf- life study of pasteurized milk by ohmic heating at 4°C for 15 days showed no change in pH and acidity. The results also showed no colonies in bacterial total count bacteria, coli form, staph-110, yeasts, and molds. However, pasteurized milk by both methods (ohmic and HTST) could only be stored for 72 h at room temperature. The HTST treated milk could be stored for 8 days at 4°C for 8 days.

Atomic defects in crystalline structures have pronounced affects on their bulk properties. Aberration-corrected transmission electron microscopy has proved to be a powerful characterization tool for understanding the bonding structure of defects in materials. In this article, recent results on the characterization of defect structures in two dimensional materials are discussed. The dynamic behavior of defects in graphene shows the stability of zigzag edges of the material and gives insights into the dislocation motion. Polycrystalline graphene is characterized using advanced electron microscopy techniques, revealing the global crystal structure of the material, as well as atomic-resolution observation of the carbon atom positions between neighboring crystal grains. Studies of hexagonal boron nitride (hBN) are also visited, highlighting the interlayer bonding, which occurs upon defect formation, and characterization of grain boundary structures. Lastly, defect structures in monolayer polycrystalline transition metal dichalcogenides grown by CVD are discussed.

The application of strain to semiconductors allows for controlled modification of their band structure. This principle is employed for the manufacturing of devices ranging from high-performance transistors to solid-state lasers. Traditionally, strain is typically achieved via growth on lattice-mismatched substrates. For two-dimensional (2D) semiconductors, this is not feasible as they typically do not interact epitaxially with the substrate. Here, we demonstrate controlled strain engineering of 2D semiconductors during synthesis by utilizing the thermal coefficient of expansion mismatch between the substrate and semiconductor. Using WSe2 as a model system, we demonstrate stable built-in strains ranging from 1% tensile to 0.2% compressive on substrates with different thermal coefficient of expansion. Consequently, we observe a dramatic modulation of the band structure, manifested by a strain-driven indirect-to-direct bandgap transition and brightening of the dark exciton in bilayer and monolayer WSe2, respectively. The growth method developed here should enable flexibility in design of more sophisticated devices based on 2D materials., Strain engineering is an essential tool for modifying local electronic properties in silicon-based electronics. Here, Ahn et al. demonstrate control of biaxial strain in two-dimensional materials based on the growth substrate, enabling more complex low-dimensional electronics.

Charge transfer at the interface between dissimilar materials is at the heart of electronics and photovoltaics. Here we study the molecular orientation, electronic structure, and local charge transfer at the interface region of C60 deposited on graphene, with and without supporting substrates such as hexagonal boron nitride. We employ ab initio density functional theory with van der Waals (vdW) interactions, and experimentally characterize interface devices using high-resolution transmission electron microscopy and electronic transport. Charge transfer between C60 and the graphene is found to be sensitive to the nature of the underlying supporting substrate and to the crystallinity and local orientation of the C60. Even at room temperature, C60 molecules interfaced to graphene are orientationally locked into position. High electron and hole mobilities are preserved in graphene with crystalline C60 overlayers, which has ramifications for organic high-mobility field-effect devices.

We develop an automatic and objective method to measure and correct residual aberrations in atomic-resolution HRTEM complex exit waves for crystalline samples aligned along a low-index zone axis. Our method uses the approximate rotational point symmetry of a column of atoms or single atom to iteratively calculate a best-fit numerical phase plate for this symmetry condition, and does not require information about the sample thickness or precise structure. We apply our method to two experimental focal series reconstructions, imaging a β-Si3N4 wedge with O and N doping, and a single-layer graphene grain boundary. We use peak and lattice fitting to evaluate the precision of the corrected exit waves. We also apply our method to the exit wave of a Si wedge retrieved by off-axis electron holography. In all cases, the software correction of the residual aberration function improves the accuracy of the measured exit waves.

The bulk properties of polycrystalline materials are directly influenced by the atomic structure at the grain boundaries that join neighboring crystallites. In this work, we show that graphene grain boundaries are comprised of structural building blocks of conserved atomic bonding sequences using aberration corrected high-resolution transmission electron microscopy. These sequences appear as stretches of identically arranged periodic or aperiodic regions of dislocations. Atomic scale strain and lattice rotation of these interfaces is derived by mapping the exact positions of every carbon atom at the boundary with ultrahigh precision. Strain fields are organized into local tensile and compressive dipoles in both periodic and aperiodic dislocation regions. Using molecular dynamics tension simulations, we find that experimental grain boundary structures maintain strengths that are comparable to idealized periodic boundaries despite the presence of local aperiodic dislocation sequences.

The recent development of graphene liquid cells, a nanoscale version of liquid bubble wrap, is a breakthrough for in situ liquid phase electron microscopy (EM). Using ultrathin graphene sheets as the liquid sample container, graphene liquid cells have allowed the unprecedented atomic resolution observation of solution phase growth and dynamics of nanocrystals. Here we explore the potential of this technique to probe nanoscale structure and dynamics of biomolecules in situ, using artificial Au nanoparticle–DNA artificial molecules as model systems. The interactions of electrons with both the artificial molecules and the liquid environment have been demonstrated and discussed, revealing both the opportunities and challenges of using graphene liquid cell EM as a new method of bio-imaging.

Liquid-phase transmission electron microscopy (TEM) can probe and visualize dynamic events with structural or functional details at the nanoscale in a liquid medium. Earlier efforts have focused on the growth and transformation kinetics of hard material systems, relying on their stability under electron beam. Our recently developed graphene liquid cell technique pushed the spatial resolution of such imaging to the atomic scale but still focused on growth trajectories of metallic nanocrystals. Here, we adopt this technique to imaging three-dimensional (3D) dynamics of soft materials instead, double strand (dsDNA) connecting Au nanocrystals as one example, at nanometer resolution. We demonstrate first that a graphene liquid cell can seal an aqueous sample solution of a lower vapor pressure than previously investigated well against the high vacuum in TEM. Then, from quantitative analysis of real time nanocrystal trajectories, we show that the status and configuration of dsDNA dictate the motions of linked nanocrystals throughout the imaging time of minutes. This sustained connecting ability of dsDNA enables this unprecedented continuous imaging of its dynamics via TEM. Furthermore, the inert graphene surface minimizes sample-substrate interaction and allows the whole nanostructure to rotate freely in the liquid environment; we thus develop and implement the reconstruction of 3D configuration and motions of the nanostructure from the series of 2D projected TEM images captured while it rotates. In addition to further proving the nanoconjugate structural stability, this reconstruction demonstrates 3D dynamic imaging by TEM beyond its conventional use in seeing a flattened and dry sample. Altogether, we foresee the new and exciting use of graphene liquid cell TEM in imaging 3D biomolecular transformations or interaction dynamics at nanometer resolution.

The atomic structure of graphene on polycrystalline copper substrates has been studied using scanning tunneling microscopy. The graphene overlayer maintains a continuous pristine atomic structure over atomically flat planes, monatomic steps, edges, and vertices of the copper surface. We find that facets of different identities are overgrown with graphene's perfect carbon honeycomb lattice. Our observations suggest that growth models including a stagnant catalytic surface do not apply to graphene growth on copper. Contrary to current expectations, these results reveal that the growth of macroscopic pristine graphene is not limited by the underlying copper structure.

Interest in new ultraincompressible hard materials has prompted studies of transition metal diboride solid solutions. We have synthesized pure RuB2 and solid solutions of Os1−xRuxB2. The mechanical properties of these materials are investigated using in situ high-pressure X-ray diffraction and Vickers hardness testing techniques. Both bulk moduli and hardness vary linearly with composition in accordance with Vegard’s law, whereas the differing behavior among end-members can be explained by relativistic effects, core electron density, and differences in the cohesive energy of the parent metals. The results provide a refinement of the rules previously reported for the design of new superhard materials.

We have characterized the structure of 176 different single-layer graphene grain boundaries using $>$1000 experimental HRTEM images using a semi-automated structure processing routine. We introduce a new algorithm for generating grain boundary structures for a class of hexagonal 2D materials and use this algorithm and molecular dynamics to simulate the structure of $>$79000 graphene grain boundaries covering 4122 unique orientations distributed over the entire parameter space. The dislocation content and structural properties are extracted from all experimental and simulated boundaries, and various trends are explored. We find excellent agreement between the simulated and experimentally observed grain boundaries. Our analysis demonstrates the power of a statistically significant number of measurements as opposed to a small number of observations in atomic science. All experimental and simulated boundary structures are available online., 12 pages, 10 figures, submitted to Physical Review B

Twisted bilayer graphene (tBLG) forms a quasicrystal whose structural and electronic properties depend on the angle of rotation between its layers. Here we present a scanning tunneling microscopy study of gate-tunable tBLG devices supported by atomically-smooth and chemically inert hexagonal boron nitride (BN). The high quality of these tBLG devices allows identification of coexisting moir\'e patterns and moir\'e super-superlattices produced by graphene-graphene and graphene-BN interlayer interactions. Furthermore, we examine additional tBLG spectroscopic features in the local density of states beyond the first van Hove singularity. Our experimental data is explained by a theory of moir\'e bands that incorporates ab initio calculations and confirms the strongly non-perturbative character of tBLG interlayer coupling in the small twist-angle regime., Comment: 4 figures

The optical transparency and high electron mobility of graphene make it an attractive material for photovoltaics. We present a field-effect solar cell using graphene to form a tunable junction barrier with an Earth-abundant and low cost zinc phosphide (Zn_3P_2) thin-film light absorber. Adding a semitransparent top electrostatic gate allows for tuning of the graphene Fermi level and hence the energy barrier at the graphene-Zn_3P_2 junction, going from an ohmic contact at negative gate voltages to a rectifying barrier at positive gate voltages. We perform current and capacitance measurements at different gate voltages in order to demonstrate the control of the energy barrier and depletion width in the zinc phosphide. Our photovoltaic measurements show that the efficiency conversion is increased 2-fold when we increase the gate voltage and the junction barrier to maximize the photovoltaic response. At an optimal gate voltage of +2 V, we obtain an open-circuit voltage of V_(oc) = 0.53 V and an efficiency of 1.9% under AM 1.5 1-sun solar illumination. This work demonstrates that the field effect can be used to modulate and optimize the response of photovoltaic devices incorporating grapheme.

The two-dimensional structure of graphene is known to impart high strength, but can be hard to synthesize without grain boundaries. Here, the authors find that strength increases with grain boundary mismatch, which results from low atomic-scale strain in the carbon–carbon bonds at the boundary.

We explore the feasibility of growing a continuous layer of graphene in prepatterned substrates, like an engineered silicon wafer, and we apply this as a mold for the fabrication of AFM probes. This fabrication method proves the fabrication of SU-8 devices coated with graphene in a full-wafer parallel technology and with high yield. It also demonstrates that graphene coating enhances the functionality of SU-8 probes, turning them conductive and more resistant to wear. Furthermore, it opens new experimental possibilities such as studying graphene–graphene interaction at the nanoscale with the precision of an AFM or the exploration of properties in nonplanar graphene layers.

All living systems contain naturally occurring nanoparticles with unique structural, biochemical and mechanical characteristics. Specifically, human saliva exosomes secreted by normal cells into saliva via exocytosis, are novel biomarkers showing tumor-antigen enrichment during oral cancer. Here we show the substructure of single human saliva exosomes, using a new ultra sensitive low force Atomic Force Microscopy (AFM) exhibiting sub-structural organization unresolvable in Electron Microscopy. We correlate the data with Field Emission Scanning Electron Microscopy (FESEM) and AFM images to interpret the nanoscale structures of exosomes under varying forces. Single exosomes reveal reversible mechanical deformation displaying distinct elastic, 70-100nm tri-lobed membrane with sub-structures carrying specific trans-membrane receptors. Further, we imaged and investigated, using force spectroscopy with antiCD63 IgG functionalized AFM tips, highly specific and sensitive detection of antigenCD63, potentially useful cancer markers on individual exosomes. The quantitative nanoscale morphological, biomechanical and surface biomolecular properties of single saliva exosomes, are critical for the applications of exosomes for cancer diagnosis and as a model for developing new cell delivery systems.

With the motivation of realizing an all graphene-based circuit for low power, we present a reliable nonvolatile graphene memory device, single-layer graphene (SLG) ferroelectric field-effect transistor (FFET). We demonstrate that exfoliated single-layer graphene can be optically visible on a ferroelectric lead-zirconate-titanate (PZT) substrate and observe a large memory window that is nearly equivalent to the hysteresis of the PZT at low operating voltages in a graphene FFET. In comparison to exfoliated graphene, FFETs fabricated with chemical vapor deposited (CVD) graphene exhibit enhanced stability through a bi-stable current state operation with long retention time. In addition, we suggest that the trapping/de-trapping of charge carriers in the interface states is responsible for the anti-hysteresis behavior in graphene FFET on PZT. V C 2011 American Institute of Physics. [doi:10.1063/1.3619816] Graphene is considered to be an exceptional material with high potential for future electronics, owing to its excellent electronic properties; 1 linear electron energy dispersion, and high room temperature mobility. If feasible, an all graphene-based circuit, including logic, analog, and memory devices, would be of great interest to further extend the performance of current Si-based electronics. Among various device applications, graphene based memory structures are still in their infancy in comparison to its logic and analog applications. To date, graphene memory has been demonstrated through chemical modification, 2 filament-type memristor, 3 nanomechanical switch, 4 and graphene FFETs. 5‐7 In graphene FFETs, however, the ambipolar conduction leads to undesirable on/off states for memory applications. Moreover, the absence of an electronic bandgap and controlled doping makes it difficult to resolve such issues. Therefore, a systematic study of graphene FFET is beneficial to realize graphene-based memory structures. In this Letter, we investigate graphene/PZT FFET structures using exfoliated- and CVD-SLG and their mechanism of operation. We show that exfoliated SLG can be optically identified on a PZT substrate and exhibit a hysteresis of the Vshaped conductance with a large memory window at low operating gate voltages. We compare exfoliated- with CVDSLG FFETs and show that devices made of CVD-SLG exhibit a robust bi-stable current state with a long retention time. In order to construct the SLG FFET, we first engineered a ferroelectric substrate to identify SLG. Previously, we have demonstrated that SLG is invisible under the optical micro

We have developed a low noise all-fiber interferometer for use as the deflection sensor in liquid environment frequency modulated atomic force microscopy (FM-AFM). A detailed description and rationale for the choice of the critical components are provided along with the design of a simple alignment assembly. The optimization of the deflection sensor toward achieving the highest possible sensitivity and lowest deflection noise density is discussed in the context of an ideal interference cavity. Based on the provided analysis we have achieved deflection noise densities of 2 fm/square root(Hz) on commercially available cantilevers in both ambient and liquid environments. The low noise interferometer works without the need for differential detection, special focusing lenses, or polarization sensitive optics, dramatically simplifying measurements. True atomic resolution imaging of muscovite mica by FM-AFM in water is demonstrated using the developed deflection sensor.