Energy Electron Point Source Microscope Research Articles

Nanometer Resolution Holography with the Low Energy Electron Point Source Microscope

Holography with the low energy electron point source (LEEPS) microscope has been explored for imaging of unstained biomolecules. DNA ropes are prepared on microfabricated sample supports and imaged with coherent 40 eV electrons emitted from a W(111) point source. We reconstruct the electron wave front and show that the correct source-to-object distance can be determined by analyzing the focus of the reconstruction. Upon variation of the source position, the reconstruction shows reproducible object features with an object focus located at the correct tip-to-object distance with a depth of sharpness of ∼40 nm. It is argued that reconstruction artifacts can be identified by their focus behavior and that only features in the first focus – coming from the screen – truly relate to the object's structure.

Determination of the specific resistance of individual freestanding ZnO nanowires with the low energy electron point source microscope

A low energy electron point source microscope is used to determine the electrical conductivity of freestanding ZnO nanowires. The nanowires were contacted with a manipulation tip and I-V curves were taken at different wire lengths. From those, the specific resistance was calculated and separated from the contact resistance. By comparing the specific resistances of ZnO nanowires with diameters between 1100 and 48nm, a large surface contribution for the thin nanowires was found. A geometric model for separation between surface and bulk contributions is given.

Cryogenic low energy electron point source microscope

The design and performance of a cryogenic low energy electron point source microscope are described. The microscope can be immersed in liquid helium, thus allowing for investigations at cryogenic temperatures. The cryogenic environment is associated with a low fluctuation in the field emission electron beam current and, combined with a compact and rigid mechanical design, low mechanical drift characteristics.

Charge distribution mapping by low energy electrons

We demonstrate how low energy electron point source microscope can be used for quantitative mapping of linear charge distribution along one-dimensional wires. Imaging of electrically biased carbon nanotube ropes suspended across two electrodes showed different charge distributions for three different experimental situations: (1) ropes having good ohmic contacts to both electrodes, (2) ropes with one good and one poor ohmic contacts, and (3) ropes with one end contacted and the other end free standing. The technique gives a linear charge density resolution below 0.1e per nanometer with a spatial resolution better than 10nm. The resolution can be further improved by the proper modification of experimental setup.

Synthesis, Analysis, Transport and Field emission Measurements of Compound B-C-N Nanotubes

AbstractMultiwalled B-C-N nanotubes of various morphologies and chemical compositions were synthesized by reacting C-based nanotube templates with boron oxide and nitrogen at 1573 K- 2173 K. The nanotubes were thoroughly analysed using a high-resolution field-emission 300 kV transmission electron microscope (TEM), an energy-filtered field-emission 300 kV electron microscope (Omega filter), an electron energy loss spectrometer and an energy dispersion X-ray detector. Transport and field emission properties of the nanotubes were studied using a low energy electron point source microscope and via in-situ measurements in TEM equipped with a scanning tunnelling microscope (STM) unit.

Optimization of the low energy electron point source microscope: imaging of macromolecules

Optimal conditions for low energy electron point source microscopy are investigated by the simulation and numerical reconstruction of holograms of phthalocyaninato polysiloxane, PcPS, a rod-like macromolecule. The effects of the electron energy, width of the electron beam and the detector size on the spatial resolution in the reconstructed images are modeled. We find that for electron energies around 200 eV, with the specimen 0.1 μm from the source, a screen recording the image in a cone of at least 15° half angle (7 cm lateral dimension at 10 cm from the source) with at least 512×512 pixel and 8-bit resolution will result in near atomic resolution.

Holographic imaging of macromolecules

The low energy electron point source microscope (kendroscope) is used to acquire in-line holograms of rodlike macromolecules of phthalocyaninato polysiloxane (PcPS). The molecules were placed on a new class of substrates, thin microstructured silicon membranes that have slits about 100 nm wide which can be “bridged” by the molecular chains. The resulting in-line holograms of PcPS were recorded digitally and reconstructed numerically via a Kirchoff–Helmholtz transform. The mechanisms of image formation and uncertainties relating to the interpretation of the holograms are discussed.