J. Nelayah

Direct imaging of surface plasmon resonances on single triangular silver nanoprisms at optical wavelength using low-loss EFTEM imaging.

Using low-loss energy-filtering transmission electron microscopy (EFTEM) imaging, we map surface plasmon resonances (SPRs) at optical wavelengths on single triangular silver nanoprisms. We show that EFTEM imaging combining high spatial sampling and high energy resolution enables the detection and for the first time, to the best of our knowledge, mapping at the nanoscale of an extra multipolar SPR on these nanoparticles. As illustrated on a 276.5 nm long nanoprism, this eigenmode is found to be enhanced on the three edges where it exhibits a two-lobe distribution.

Electron energy losses in Ag nanoholes—from localized surface plasmon resonances to rings of fire

Using valence-loss energy-filtering transmission electron microscopy, we measure the optical response of an arrangement of nanoholes in a Ag film over a wide range of wavelengths (0.5-2 microm). This technique allows us to detect the full transition from localized excitations to traveling guided modes with a spatial resolution of a few nanometers. By the well-defined arrangement of the nanoholes, we can clearly distinguish coupling effects from single-hole resonances. This type of experiment is ideally suited for the future design of biosensors and metamaterials.

Low-loss EFTEM Imaging of Surface Plasmon Resonances in Ag Nanostructures

Understanding how light interacts with matter at the nanometer scale is a fundamental issue in optoelectronics, nanophotonics and nanoplasmonics. The optical properties of metallic nanoparticles are entirely dependent on collective excitations of their valence electrons, known as surface plasmon resonances (SPR), under electromagnetic illumination. Measuring these properties locally at the level of the individual nanoobject in combination with spectral information over the entire visible range constitutes a challenging issue for linking of the global response of the nanoparticles and the underlying structure and morphology. The visualization of localized SPRs on the nanometer scale in combination with spectral information over the entire visible range is of prime importance in the field of biosensors, surface-enhanced Raman spectroscopy, and for the design of metamaterials. But also the explanation of abnormal transmission of light through sub-wavelength holes relies on such information.

Sub-0.5 eV EFTEM mapping using the Zeiss SESAM

Co-based alloys are used in numerous commercial applications because of their excellent performance under severe environments, which require high-temperature strength, corrosion resistance, wear resistance, etc. In general, these alloys belong to a multi-component system, and the composition and heat and/or mechanical treatments to achieve a desired property are often complex. In this respect, understanding the microstructural changes during the processing is indispensable for the optimal selection of various processing parameters. In particular, the identification of phases in the early stages of phase transformation, which necessitates atomic level observations, is critical to elucidate the origin of the mechanical properties of the alloys.

Study of surface plasmon resonances on assemblies of slits in thin Ag films by low-loss EFTEM imaging

With the ongoing developments in nanotechnology, surface plasmon resonances (SPRs) have started to play a crucial role in many different areas of science. Surface Plasmon resonances are described as collective oscillations in the valence electron density at the surface of a conductor. They have especially received attention in the areas of biosensing in cancer diagnostics [1], near-field Raman spectroscopy [2] and different applications in optoelectronics. In this study, the optical response of a specially perforated thin Ag film is investigated with EFTEM. The experiments were carried out in the 200 kV FEG-TEM Sub-Electron-VoltSub-Angstrom-Microscope (Zeiss SESAM) equipped with an electrostatic monochromator and the in-column MANDOLINE filter [3]. The superior properties of this instrument enable EFTEM imaging in the ultraviolet–near-infrared domain with very high energy resolution and spatial sampling [4]. The Ag specimen was prepared as follows: Using physical vapour deposition, a Ag film with about 100 nm thickness was deposited onto a C film on a standard TEM Cu grid (the dimensions of each mesh is 100 × 100 μm). Focused ion beam (FIB) technique was used to drill different slit structures into the Ag film. The EFTEM series were acquired in the energy loss range from 0.4 eV to 5 eV by using a 0.19 eV energy slit and a step size of 0.2 eV. The EFTEM images were recorded on a 2k × 2k CCD camera with 8 times binning and an acquisition time of 30 sec / image (at each energy loss 3 images were recorded with an exposure time of 10 s and then aligned and averaged). Figure 1(a) shows a zero loss bright-field image of a double-slit structure with dimensions of 200 nm × 1 μm and a separation of 100 nm. A sample image taken from the drift-corrected EFTEM series at an energy loss of 0.6 eV is shown in figure 1(b). The intensity distribution is attributed to a localized plasmon resonance. Such resonances will be discussed and compared with numerical simulations [5].

Surface plasmon resonance effects in a perforated Ag film studied by energy-filtering TEM

The visualization of localized surface plasmon resonances (LSPR) on the nanometer scale in combination with spectral information over the entire visible range is of prime importance in the field of biosensors, surface-enhanced Raman spectroscopy (SERS), aperture-less scanning near-field optical microscopy (SNOM), and for the design of metamaterials. But also the understanding of the abnormal transmission of light through sub- wavelength holes may gain by this technique. With the advent of monochromators and highly dispersive energy filters, energy- filtering TEM has now become available for the study of the optical response of materials. This technique was applied to the detection of band gaps (1) as well as to the study of surface plasmons on metal particles, like Ag nanoprisms (2-4) or Au nanorods (5). Here, the dielectric response of holes in a 100 nm thick Ag film, drilled by using a focused ion beam, is studied by acquiring EFTEM series in the energy range between 0.4 and 4 eV using the Zeiss SESAM microscope (Fig.1). The energy-slit width was 0.2 eV. Apart from multipolar ring-shaped resonances, visible particularly at the isolated holes in the upper row, a number of LSPRs are found which are due to the strong coupling effects between adjacent holes. They sensitively depend on the hole arrangement (6).

Low-loss-energy EFTEM imaging of triangular silver nanoparticles

Understanding how light interacts with matter at the nanometer scale is a fundamental issue in optoelectronics and nanophotonics. It is known that the optical properties of nanoparticles are entirely dependent on collective excitations of their valence electrons, known as “surface plasmon resonances” (SPR’s), under electromagnetic illumination. Measuring these properties locally at the level of the individual nano-object constitutes a challenging issue for linking of the global response of the nanoparticles and the underlying structure and morphology.

Band gap mapping using monochromated electrons

The recent development of monochromators for transmission electron microscopes has made valence electron energy-loss spectroscopy (VEELS) a powerful technique to study the semiconductor band structure with high spatial resolution. Albeit difficulties of the band structure measurements were encountered [1], solutions have been demonstrated for several material systems [2]. Taking advantage of the Zeiss SESAM microscope, an energy resolution below 100 meV is achieved routinely [3], which is highly appreciated for band structure measurements using low-loss EELS.