Despite the huge progress achieved recently by means of the corrector for aberrations, allowing now a true atomic resolution of 0.1 nm, hence making it an unrivalled tool for nanoscience, transmission electron microscopy (TEM) suffers from a severe drawback: in a conventional electron micrograph only a poor phase contrast can be achieved, i.e. phase structures are virtually invisible. Therefore, conventional TEM is nearly blind for electric and magnetic fields, which are pure phase objects. Since such fields provoked by the atomic structure, e.g. of semiconductors and ferroelectrics, largely determine the solid state properties, hence the importance for high technology applications, substantial object information is missing. Electron holography in TEM offers the solution: by superposition with a coherent reference wave, a hologram is recorded, from which the image wave can be completely reconstructed by amplitude and phase. Now the object is displayed quantitatively in two separate images: one representing the amplitude, the other the phase. From the phase image, electric and magnetic fields can be determined quantitatively in the range from micrometre down to atomic dimensions by all wave optical methods that one can think of, both in real space and in Fourier space. Electron holography is pure wave optics. Therefore, we discuss the basics of coherence and interference, the implementation into a TEM, the path of rays for recording holograms as well as the limits in lateral and signal resolution. We outline the methods of reconstructing the wave by numerical image processing and procedures for extracting the object properties of interest. Furthermore, we present a broad spectrum of applications both at mesoscopic and atomic dimensions. This paper gives an overview of the state of the art pointing at the needs for further development. It is also meant as encouragement for those who refrain from holography, thinking that it can only be performed by specialists in highly specialized laboratories. In fact, a modern TEM built for atomic resolution and equipped with a field emitter or a Schottky emitter, well aligned by a skilled operator, can deliver good holograms. Running commercially available image processing software and mathematics programs on a laptop-computer is sufficient for reconstruction of the amplitude and phase images and extracting desirable object information.

The seeder of the pack: The electrical potential distribution (see phase image of an electron hologram) around the basal plane close to the prism faces of a hexagonal fluorapatite–gelatine nanocomposite seed influences the growth of the nanocomposite. The seed consists of elementary dipoles on the nanometer scale, which all have the same orientation along the c axis of the composite seed. Further form development of the seed leads to fractal patterns.

Impressive progress has been made in the processing and exploration of new material on an atomic scale (nanomaterials). However, the characterization of such materials by the usual transmission electron microscopy (TEM) techniques suffers from the drawback that the phase of the object-modulated electron wave is virtually lost in the recorded intensity images. Electron holography has opened possibilities for analyzing both the amplitude and phase of the electron wave, hence giving access to the object information encoded in the phase. Examples include intrinsic electric and magnetic fields, e.g. in ferroelectrics or ferromagnetics, which substantially determine the object properties and therefore are indispensable for a complete understanding of structure-properties relations.

Make it connected! 2D close-packed layers of inorganic nanoparticles are interconnected by organic fibrils of oleic acid as clearly visualized by electron holography. These fibrils can be mineralised by PbS to transform an organic-inorganic framework to a completely interconnected inorganic semiconducting 2D array.

Multiphoton laser scanning microscopy offers advantages in depth of penetration into intact samples over other optical sectioning techniques. To achieve these advantages it is necessary to detect the emitted light without spatial filtering. In this nondescanned (nonconfocal) approach, ambient room light can easily contaminate the signal, forcing experiments to be performed in absolute darkness. For multiphoton microscope systems employing mode-locked lasers, signal processing can be used to reduce such problems by taking advantage of the pulsed characteristics of such lasers. Specifically, by recovering fluorescence generated at the mode-locked frequency, interference from stray light and other ambient noise sources can be significantly reduced. This technology can be adapted to existing microscopes by inserting demodulation circuitry between the detector and data collection system. The improvement in signal-to-noise ratio afforded by this approach yields a more robust microscope system and opens the possibility of moving multiphoton microscopy from the research lab to more demanding settings, such as the clinic.

The investigation of three-dimensional (3D) ferromagnetic nanoscale materials constitutes one of the key research areas of the current magnetism roadmap and carries great potential to impact areas such as data storage, sensing, and biomagnetism. The properties of such nanostructures are closely connected with their 3D magnetic nanostructure, making their determination highly valuable. Up to now, quantitative 3D maps providing both the internal magnetic and electric configuration of the same specimen with high spatial resolution are missing. Here, we demonstrate the quantitative 3D reconstruction of the dominant axial component of the magnetic induction and electrostatic potential within a cobalt nanowire (NW) of 100 nm in diameter with spatial resolution below 10 nm by applying electron holographic tomography. The tomogram was obtained using a dedicated TEM sample holder for acquisition, in combination with advanced alignment and tomographic reconstruction routines. The powerful approach presented here is widely applicable to a broad range of 3D magnetic nanostructures and may trigger the progress of novel spintronic nonplanar nanodevices.

Nanoscale rotation moiré patterns are observed in double-layer nanoporous thin films produced with use of block-copolymer self-assembly. Periodic hexagonal moiré superstructures appear when the films possessing long-range order are superimposed at small misorientation angles. Overlapping films misoriented by angles close to 30°generate aperiodic quasi-crystal-like superstructures with 5-fold symmetries. The stacking of the disordered nanoporous films produces labyrinth-like patterns. Block-copolymer moiré superstructures are promising as nanolithography masks with controllable morphology and periodicity.Moiré patterns are common in everyday life and often occur when two lattices overlap one another (e.g., in folds of sheer curtains). They were used in technique 1 and even inspired artists. 2 Before the invention of holographic interferometry, moiré patterns constituted a popular tool to study deformations, which can be calculated from the moiré fringes formed by two interfering line screens, one is printed on the loaded solid model and the other is used as the reference. 1 The moiré phenomenon is omnipresent also at the nanoscale. Rotation moiré superlattices were observed in graphite layers since early days of scanning tunneling microscopy (STM). The origin of these superlattices is actively debated because of importance of pyrolytic graphite as a standard substrate for STM measurements. It is believed that moiré fringes in this system can appear due to interference of tunneling currents to multiple tips of the STM probe scanning adjacent crystalline grains, which are rotated with respect to each other. 3 Hexagonal moiré superstructures can arise also in folded-back graphite monolayers as the result of the interaction of the top and the bottom layers. 4 Regular hexagonal arrays of morphological units, identified as rotation moiré patterns, were observed by transmission electron microscopy (TEM) of stained folded biological membranes. 5 These patterns prove indirectly the high degree of crystalline order of the cell's membranes formed by lipid molecules. Recently, moiré fringes were shown to be a powerful tool for the generation of micro-and nanoscale patterns and twodimensional (2D) superlattices. Regular arrays of dislocation lines were obtained by twisting two identical silicon wafers one against the other at a precisely controlled angle and bonding them together to make a bicrystal. 6 Selective etching of the screw dislocations generated in this way permits controlled fabrication of nanodot arrays with 2-100 nm spacing. Moiré fringes characterized by a few micrometer spacing were synthesized by the two-step nanoindentation lithography on aluminum substrates with a master stamp consisting of regular arrays of Si 3 N 4 micropyramids. 7 The fringes obtained after amplification of the indentations by anodization realize novel kinds of micropatterns, which are hard to achieve with current state-of-the-art conventional lithography.In this paper, we report the first observation of rotation moiré patterns produced by...

In high resolution electron off-axis holography, the complete information about amplitude and phase of the complex electron image wave is captured in a single hologram, fed to a computer, numerically reconstructed, and analyzed using methods of wave optical image processing. Specifically, the blurring effect due to the aberration of the objective lens of the electron microscope is corrected under reconstruction.The presented first results, achieved with a Philips CM30FEG electron microscope specially developed for the needs of high resolution electron holography, reveal that the point resolution of modern electron microscopes is significantly improved.PACS numbers: 42.30.Rx, In contrast to the light optical case, in electron microscopy the lateral resolution is not limited by the diffraction error, i.e. , by the wavelength of the electrons, but instead is governed by the spherical aberration of the objective lens. As shown by Scherzer [1] already in 1936, this error cannot be avoided as long as common rotational symmetric lens designs are used. For example, in the case of the Philips CM30FEG high resolution electron microscope applied in this work, the best point resolution is 0.198 nm, about 2 orders of magnitude worse than the diffraction limit of the A = 1.98 pm wavelength, 300 keV electrons.In electron microscopy we deal with a complex electron wave o(r) = a(r) exp[i'(r)] modulated in both amplitude and phase due to the interaction with the object. During the imaging process from this object wave to the recordable image wave, the aberrations of the objective lens lead to a blurring of the available information.The backpropagation from the aberration-corrupted image wave b(r) = A(r) exp[i@(r)] to the level of the object is possible following the wave laws given by the Kirchhoff diffraction integral. Prerequisites are the registration of the image wave amplitude and phase as well as a sufhcient knowledge of the lens aberrations. This approachcalled holography -was proposed by Gabor already in 1948 [2] but it took nearly 50 years until electron holography finally achieved this goal. From the various forms of electron holography [3] under investigation, the off-axis technique has proven to be most promising [4]. Using a Moellenstedt biprism, the image wave is coherently superimposed with a plane reference wave, and the resulting interference pattern -the hologram -reveals a cosinusoidal intensity distribution, I(r) = 1 + A(r) + 2A(r) cos(2rrq, . r + &b(r)). (1)