We utilized in situ laser-heating within a TEM to reveal how nanomaterials transform from amorphous precursors, and used electron spectroscopy to characterize the optical properties of these nanostructures in situ and in real time. The recrystallization, grain growth, phase separation, and solid state dewetting of AgNi films were investigated using stepwise laser heating. The experiments reveal a wealth of in situ information, including changes of composition and lattice constants during phase separation. To establish the true and dynamic structure–property relationship of nanostructures, we also characterized the photonic properties of the synthesized materials in situ. For example, the plasmon modes of metallic particles were mapped using electron energy gain induced by photon-plasmon-electron coupling. These in situ TEM studies of laser-induced heating are a valuable discovery tool for the rapid exploration of synthesis pathways and functional properties of nanostructures.
KEYWORDS: Nanophotonics, Microscopy, Plasmonics, Single photon, Nonlinear optics, Color centers, Structural design, Scanning electron microscopy, Quantum optics, Quantum information processing
Non-linear manipulation of light at the nanoscale is increasingly important for quantum optics and photonics. Plasmonic media provide one important workbench for the manipulation of these nonlinearities.1 The design of plasmonic structures typically involves time-consuming, iterative, computer simulations, nanofabrication and characterization with large suites of independent tools. Hence, in-situ fabrication and characterization along with real time design optimization is an appealing option for the development of hybrid quantum nanophotonic devices. Here, we will describe emerging capabilities for in situ electron beam induced deposition (EBID) and cathodoluminescence (CL) microscopy in an environmental SEM. We outline our work writing and characterizing nanoplasmonic structures that exhibit well-defined field localization and multiple tunable resonances over a broad spectrum as part of the development of new high-efficiency nanophotonic nonlinear media. Developing deter- ministic high-quality single photon emitters is an equally important direction for photonic quantum information processing. Due to the sub-nanometer footprint of such emitters, optical methods are often insufficient for local characterization. We describe our efforts to create, manipulate and characterize color centers in 2D and bulk materials such as hBN. We discuss e-beam induced effects for localized defect creation and EBID based control of color centers to allow emission tuning. Cathodoluminescence lifetime and autocorrelation measurements are utilized for sub-diffraction-limited in-situ assessment of the single photon emission properties.
Incorporating dopants in monolayer transition metal dichalcogenides (TMD) can enable manipulations of their electrical and optical properties. Previous attempts in amphoteric doping in monolayer TMDs have proven to be challenging. Here we report the incorporation of molybdenum (Mo) atoms in monolayer WS2 during growth by chemical vapor deposition, and correlate the distribution of Mo atoms with the optical properties including photoluminescence and ultrafast transient absorption dynamics. Dark field scanning transmission electron microscopy imaging quantified the isoelectronic doping of Mo in WS2 and revealed its gradual distribution along a triangular WS2 monolayer crystal, increasing from 0% at the edge to 2% in the center of the triangular WS2 triangular crystals. This agrees well with the Raman spectra data that showed two obvious modes between 360 cm-1 and 400 cm-1 that corresponded to MoS2 in the center. This in-plane gradual distribution of Mo in WS2 was found to account for the spatial variations in photoluminescence intensity and emission energy. Transition absorption spectroscopy further indicated that the incorporation of Mo in WS2 regulate the amplitude ratio of XA and XB of WS2. The effect of Mo incorporation on the electronic structure of WS2 was further elucidated by density functional theory. Finally, we compared the electrical properties of Mo incorporated and pristine WS2 monolayers by fabricating field-effect transistors. The isoelectronic doping of Mo in WS2 provides an alternative approach to engineer the bandgap and also enriches our understanding the influence of the doping on the excitonic dynamics.
One critical area for EUV lithography is the development of appropriate mask repair strategies. To this end, we have explored etching repair strategies for nickel absorber layers and focused electron beam induced deposition of ruthenium capping layers. Nickel has higher EUV absorption than the standard TaN absorber layer and thus thinner films and improved optical quality can be realized. A thin (2.5 nm) ruthenium film is commonly used as a protective capping layer on the Mo-Si EUV multi-layer mirror which mechanically and chemically protects the multi-layers during standard mask-making procedures. The gas field ion (GFIS) microscope was used to investigate helium and neon ion beam induced etching (IBIE) of nickel as a candidate technique for EUV lithography mask editing. No discernable nickel etching was observed for helium, however transmission electron microscopy (TEM) revealed subsurface damage to the underlying Mo-Si multilayers. Subsequently, neon beam induced etching at 30 keV was investigated and successfully removed the 50 nm nickel absorber film. TEM imaging also revealed subsurface damage in the underlying Mo-Si multilayer. Two damage regimes were apparent, namely: 1) beam induced mixing of the Mo-Si layers and 2) nanobubble formation. Monte Carlo simulations were performed and the observed damage regimes were correlated to: 1) the nuclear energy loss and 2) a critical implant concentration. Electron beam induced deposition (EBID) was explored to deposit ruthenium capping/protective layers. Several ruthenium precursors were screened and so far liquid bis(ethylcyclopentyldienyl)ruthenium(II) was successful. The purity of the as-deposited nanodeposits was estimated to be 10% Ru and 90% C. We demonstrate a new chemically assisted electron beam purification process to remove carbon by-products and show that high-fidelity nanoscale ruthenium repairs can be realized.
This paper presents an evaluation of e-beam assisted deposition and welding of conductive
carbon nanotube (c-CNT) tips for electrical scanning probe microscope measurements.
Variations in CNT tip conductivity and contact resistance during fabrication were determined as
a function of tip geometry using tunneling AFM (TUNA). Conductive CNT tips were used to
measure 2D dopant concentration as a function of annealing conditions in BF2-implanted
samples.
Progress in the application of vertically-aligned carbon nanofibers (VACNF) as parallel subcellular and molecular-scale probes for biological manipulation and monitoring is reported. VACNFs possess many attributes that make them very attractive for implementation as functional, nanoscale features of microfabricated devices. For example, they can be synthesized at precise locations upon a substrate, can be grown many microns long, and feature sharp, nano-dimensioned tips. This, and their needlelike, vertical orientation upon a substrate, makes them particularly attractive as multielement cellular scale probes or as a parallel embodiment of traditional single-point microinjection or microelectrophysiological systems. We will overview our progress with fabricating and characterizing several embodiments of VACNF cell probing systems, which all feature arrays of nanoscale electrochemically-active probing regions at the tips of individually electrically-addressed nanofiber elements. We also overview our techniques of integrating these probing structures with intact cells and how these structures may be used on a massively parallel basis for measurement and control around and within viable cells.
KEYWORDS: Etching, Electron beams, Silicon, Transmission electron microscopy, Monte Carlo methods, Ion beams, Photomicroscopy, Ionization, Tungsten, Metrology
Electron-beam-stimulated etching has been investigated as a clean, alternative method for nanoscale selective processing. Primarily fluorine-based precursors have been used to etch a variety of technologically relevant materials. Empirical data reveals that with decreasing the electron beam energy increases the material removal rate, however the effective beam width increases. Both of these observations are consistent with the fact that cross-sections for electron-gas scattering increases with decresaing beam energy. Monte Carlo models of the electron-gas and electron-solid interactions have been performed to better udnerstand the fundamentals of the process. Finally, specific application to soft transmission electron microscopy sample preparation is made.
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