Low-energy electron transmission imaging of clusters on free-standing graphene

Longchamp, Jean-Nicolas; Latychevskaia, Tatiana; Escher, Conrad; Fink, Hans‐Werner

doi:10.1063/1.4752717

Cited by 47 publications

(48 citation statements)

References 28 publications

(46 reference statements)

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“…Furthermore, the oversampling condition in the detector plane corresponds to zero-padding in the object plane which requires the sample to be surrounded by a support with known transmission properties. For instance, when imaging a biological molecule, it must ideally be either levitating or resting on a homogeneous transparent film such as graphene [39][40] . Another problem is the missing signal in the central overexposed region of the diffraction pattern.…”

Section: Experimental Issues In CDImentioning

confidence: 99%

When holography meets coherent diffraction imaging

Latychevskaia¹,

Longchamp²,

Fink³

2012

Opt. Express

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The phase problem is inherent to crystallographic, astronomical and optical imaging where only the intensity of the scattered signal is detected and the phase information is lost and must somehow be recovered to reconstruct the object's structure. Modern imaging techniques at the molecular scale rely on utilizing novel coherent light sources like X-ray free electron lasers for the ultimate goal of visualizing such objects as individual biomolecules rather than crystals. Here, unlike in the case of crystals where structures can be solved by model building and phase refinement, the phase distribution of the wave scattered by an individual molecule must directly be recovered. There are two well-known solutions to the phase problem: holography and coherent diffraction imaging (CDI). Both techniques have their pros and cons. In holography, the reconstruction of the scattered complex-valued object wave is directly provided by a well-defined reference wave that must cover the entire detector area which often is an experimental challenge. CDI provides the highest possible, only wavelength limited, resolution, but the phase recovery is an iterative process which requires some pre-defined information about the object and whose outcome is not always uniquely-defined. Moreover, the diffraction patterns must be recorded under oversampling conditions, a pre-requisite to be able to solve the phase problem. Here, we report how holography and CDI can be merged into one superior technique: holographic coherent diffraction imaging (HCDI). An inline hologram can be recorded by employing a modified CDI experimental scheme. We demonstrate that the amplitude of the Fourier transform of an inline hologram is related to the complex-valued visibility, thus providing information on both, the amplitude and the phase of the scattered wave in the plane of the diffraction pattern. With the phase information available, the condition of oversampling the diffraction patterns can be relaxed, and the phase problem can be solved in a fast and unambiguous manner. We demonstrate the reconstruction of various diffraction patterns of objects recorded with visible light as well as with low-energy electrons. Although we have demonstrated our HCDI method using laser light and low-energy electrons, it can also be applied to any other coherent radiation such as X-rays or high-energy electrons. ABSTRACTThe phase problem is inherent to crystallographic, astronomical and optical imaging where only the intensity of the scattered signal is detected and the phase information is lost and must somehow be recovered to reconstruct the object's structure. Modern imaging techniques at the molecular scale rely on utilizing novel coherent light sources like X-ray free electron lasers for the ultimate goal of visualizing such objects as individual biomolecules rather than crystals. Here, unlike in the case of crystals where structures can be solved by model building and phase refinement, the phase distribution of the wave scattered by an individual molecule mus...

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Section: Experimental Issues In CDImentioning

confidence: 99%

When holography meets coherent diffraction imaging

Latychevskaia¹,

Longchamp²,

Fink³

2012

Opt. Express

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“…The transmission was also experimentally investigated. Longchamp et al 12 measured the transparency in a setup in which electrons emitted by a tungsten tip used as the point source were passed through a graphene sheet before reaching a microchannel detector plate. They determined the transmission of graphene for 66 eV electrons to be 0.73.…”

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confidence: 99%

Transparency of graphene for low-energy electrons measured in a vacuum-triode setup

et al. 2015

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Graphene, being an atomically thin conducting sheet, is a candidate material for gate electrodes in vacuum electronic devices, as it may be traversed by low-energy electrons. The transparency of graphene to electrons with energies between 2 and 40 eV has been measured by using an optimized vacuum-triode setup. The measured graphene transparency equals ∼60% in most of this energy range. Based on these results, nano-patterned sheets of graphene or of related two-dimensional materials are proposed as gate electrodes for ambipolar vacuum devices.

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“…Apparently, freestanding clean graphene is almost transparent even for low-energy electrons. 19,30 The presence of graphene can only be confirmed by observing individual adsorbates, possibly from the gas phase, sticking to the monolayer. For comparison, Fig.…”

Section: Methodsmentioning

confidence: 99%

Ultraclean freestanding graphene by platinum-metal catalysis

Longchamp

Escher²,

Fink³

2013

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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Articles you may be interested in N-doped graphene-supported Pt and Pt-Ru nanoparticles with high electrocatalytic activity for methanol oxidation J. Renewable Sustainable Energy 5, 021405 (2013) While freestanding clean graphene is essential for various applications, existing technologies for removing the polymer layer after transfer of graphene to the desired substrate still leave significant contaminations behind. The authors discovered a method for preparing ultraclean freestanding graphene utilizing the catalytic properties of platinum metals. Complete catalytic removal of polymer residues requires annealing in air at a temperature between 175 and 350 C. Low-energy electron holography investigations prove that this method results in ultraclean freestanding graphene.

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Low-energy electron transmission imaging of clusters on free-standing graphene

Cited by 47 publications

References 28 publications

When holography meets coherent diffraction imaging

When holography meets coherent diffraction imaging

Transparency of graphene for low-energy electrons measured in a vacuum-triode setup

Ultraclean freestanding graphene by platinum-metal catalysis

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