Ion and Electron Emission from Liquid Metal Sources

In liquid metal ion sources, the emission is located at the apex of a liquid cone (the often so-called Taylor cone), formed by electrostatic forces and surface tension. Reversal of the extraction voltage polarity results in electron emission from the liquid metal surface. For small apex radii, ≤ 1 μm, steady field emission of electrons has been observed, whereas for apex radii ≥ 10 μm, explosive pulsed emission occurs. Since the onset voltage for electron emission has been found to be considerably lower than the critical voltage for the formation of the Taylor cone, it has been concluded that dc (direct current) electron emission from a field stabilized cone is not possible. In situ high-voltage transmission electron microscopy observations seem to confirm this conclusion, although in one case, a field-stabilized liquid micro-cone during electron emission has been observed for a liquid-gallium-indium-tin source. The literature on liquid metal ion and electron sources is reviewed. From in situ transmission electron microscopy observations of the cone formation, relations for cone angle and jet length dependent on ion emission current are derived. Growth and emission of microdroplets at liquid indium ion sources have been imaged. In the case of electron field emission from liquid indium sources, no liquid cone formation has been observed

Carbide Field Emitters

It has been reported that field emission current from a carbide single crystal is much more stable than a tungsten field emitter. Recent progress in the development of stable carbide field emitters is reviewed. Existence of an optimum flashing temperature is pointed out and a recently developed stabilizing technique of the carbide field emitter is introduced. It is also pointed out that the quality of the vacuum is still important for stable operation of a carbide field emitter

Ultrafast nonlocal control of spontaneous emission

Solid-state cavity quantum electrodynamics systems will form scalable nodes of future quantum networks, allowing the storage, processing and retrieval of quantum bits, where a real-time control of the radiative interaction in the cavity is required to achieve high efficiency. We demonstrate here the dynamic molding of the vacuum field in a coupled-cavity system to achieve the ultrafast nonlocal modulation of spontaneous emission of quantum dots in photonic crystal cavities, on a timescale of ~200 ps, much faster than their natural radiative lifetimes. This opens the way to the ultrafast control of semiconductor-based cavity quantum electrodynamics systems for application in quantum interfaces and to a new class of ultrafast lasers based on nano-photonic cavities.Comment: 15 pages, 4 figure

Nanoscale structuring of tungsten tip yields most coherent electron point-source

This report demonstrates the most spatially-coherent electron source ever reported. A coherence angle of 14.3 +/- 0.5 degrees was measured, indicating a virtual source size of 1.7 +/-0.6 Angstrom using an extraction voltage of 89.5 V. The nanotips under study were crafted using a spatially-confined, field-assisted nitrogen etch which removes material from the periphery of the tip apex resulting in a sharp, tungsten-nitride stabilized, high-aspect ratio source. The coherence properties are deduced from holographic measurements in a low-energy electron point source microscope with a carbon nanotube bundle as sample. Using the virtual source size and emission current the brightness normalized to 100 kV is found to be 7.9x10^8 A/sr cm^2

A 25 micron-thin microscope for imaging upconverting nanoparticles with NIR-I and NIR-II illumination.

Rationale: Intraoperative visualization in small surgical cavities and hard-to-access areas are essential requirements for modern, minimally invasive surgeries and demand significant miniaturization. However, current optical imagers require multiple hard-to-miniaturize components including lenses, filters and optical fibers. These components restrict both the form-factor and maneuverability of these imagers, and imagers largely remain stand-alone devices with centimeter-scale dimensions. Methods: We have engineered INSITE (Immunotargeted Nanoparticle Single-Chip Imaging Technology), which integrates the unique optical properties of lanthanide-based alloyed upconverting nanoparticles (aUCNPs) with the time-resolved imaging of a 25-micron thin CMOS-based (complementary metal oxide semiconductor) imager. We have synthesized core/shell aUCNPs of different compositions and imaged their visible emission with INSITE under either NIR-I and NIR-II photoexcitation. We characterized aUCNP imaging with INSITE across both varying aUCNP composition and 980 nm and 1550 nm excitation wavelengths. To demonstrate clinical experimental validity, we also conducted an intratumoral injection into LNCaP prostate tumors in a male nude mouse that was subsequently excised and imaged with INSITE. Results: Under the low illumination fluences compatible with live animal imaging, we measure aUCNP radiative lifetimes of 600 μs - 1.3 ms, which provides strong signal for time-resolved INSITE imaging. Core/shell NaEr0.6Yb0.4F4 aUCNPs show the highest INSITE signal when illuminated at either 980 nm or 1550 nm, with signal from NIR-I excitation about an order of magnitude brighter than from NIR-II excitation. The 55 μm spatial resolution achievable with this approach is demonstrated through imaging of aUCNPs in PDMS (polydimethylsiloxane) micro-wells, showing resolution of micrometer-scale targets with single-pixel precision. INSITE imaging of intratumoral NaEr0.8Yb0.2F4 aUCNPs shows a signal-to-background ratio of 9, limited only by photodiode dark current and electronic noise. Conclusion: This work demonstrates INSITE imaging of aUCNPs in tumors, achieving an imaging platform that is thinned to just a 25 μm-thin, planar form-factor, with both NIR-I and NIR-II excitation. Based on a highly paralleled array structure INSITE is scalable, enabling direct coupling with a wide array of surgical and robotic tools for seamless integration with tissue actuation, resection or ablation

Light emission, light detection and strain sensing with nanocrystalline graphene

Graphene is of increasing interest for optoelectronic applications exploiting light detection, light emission and light modulation. Intrinsically light matter interaction in graphene is of a broadband type. However by integrating graphene into optical micro cavities also narrow band light emitters and detectors have been demonstrated. The devices benefit from the transparency, conductivity and processability of the atomically thin material. To this end we explore in this work the feasibility of replacing graphene by nanocrystalline graphene, a material which can be grown on dielectric surfaces without catalyst by graphitization of polymeric films. We have studied the formation of nanocrystalline graphene on various substrates and under different graphitization conditions. The samples were characterized by resistance, optical transmission, Raman, X-ray photoelectron spectroscopy, atomic force microscopy and electron microscopy measurements. The conducting and transparent wafer-scale material with nanometer grain size was also patterned and integrated into devices for studying light-matter interaction. The measurements show that nanocrystalline graphene can be exploited as an incandescent emitter and bolometric detector similar to crystalline graphene. Moreover the material exhibits piezoresistive behavior which makes nanocrystalline graphene interesting for transparent strain sensors

Self-regenerating nanotips for low-power electric propulsion (EP) cathodes

Spindt-type field-emission cathodes for use in electric propulsion (EP) systems having self-assembling nanostructures that can repeatedly regenerate damaged cathode emitter nanotips. A nanotip is created by applying a negative potential near the surface of a liquefied base metal to create a Taylor cone converging to a nanotip, and solidifying the Taylor cone for use as a field-emission cathode. When the nanotip of the Taylor cone becomes sufficiently blunted or damaged to affect its utility, the base metal is re-liquefied by application of a heat source, a negative potential is reapplied to the surface of the base metal to recreate the Taylor cone, and a new nanotip is generated by solidifying the base metal.https://digitalcommons.mtu.edu/patents/1015/thumbnail.jp