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Introduction
Publications
Publications (87)
Tungsten diselenide (WSe2) is a transition metal dichalcogenide (TMDC) that belongs to a class of nanomaterials with potential in optoelectronic device applications.
Several characteristics that define the electronic, optical, and thermal
properties of these two-dimensional (2D) crystals are thickness, crystal symmetry changes, and growth defects....
High-Resolution Multimodal Confocal Raman-Imaging in SEM by Means of RISE Microscopy - Jan Englert, Ute Schmidt, Olaf Hollricher, Harald Fischer
Confocal R aman imaging is uniquely capable of characterizing semiconducting materials. It can reveal a sample's chemical composition , identify possible contaminants and visualize strain fields in a crystal, all without damaging the sample. Additional information on, for example, topography or grain boundaries can be acquired from complementary im...
High-resolution measurements of particles are of great interest in many fields of application. Combining confocal Raman microscopy with particle analysis tools makes it possible to find, classify and identify particles almost entirely automatically.
In recent years, confocal Raman imaging and related techniques have become more and more popular in many fields of application such as materials science, pharmaceutics, life sciences, geoscience, food technology, and many others. The available Raman microscopes are focused on user-friendly and intuitive operation. Additionally, several key qualitat...
Microscopy techniques are widely used in life sciences to study cells and tissues. Fluorescence microscopy, for example, is a very common method in many laboratories. While reliable and strong fluorescence signals are a clear advantage of this method, the labelling procedure with fluorescent dyes, the availability of required antibodies or the pote...
RISE Characterization of 2D materials
Raman spectroscopy is a weak scattering technique in which typically less than one in a million excitation photons give rise to a single Raman photon. The situation is even more difficult in confocal Raman microscopy, as the detection volume is reduced by the small pinhole and thousands of spectra must be collected in a short period of time. Theref...
RISE, the combination of Raman Imaging and Scanning Electron microscopy is a promising technique that adds chemical information to the high resolution imaging capability of electron microscopy. By automatically transferring the sample from the electron beam to a separate Raman position inside the vacuum chamber, Raman molecular imaging can be perfo...
In this chapter, the theory of optical image formation in an optical microscope is described and the difference between conventional and confocal microscopy is explained. The selection of the appropriate pinhole diameter is discussed in detail, as the pinhole diameter is crucial in obtaining the highest depth resolution as well as optimizing collec...
Confocal Raman imaging is a well-established technique for investigating the chemical and molecular compositions of solid and liquid samples. Its varied fields of application in academia and industry range from materials and surface sciences to environmental and geo sciences to life sciences and pharmaceutics. The array of measured sample character...
This second edition provides a cutting-edge overview of physical, technical and scientific aspects related to the widely used analytical method of confocal Raman microscopy. The book includes expanded background information and adds insights into how confocal Raman microscopy, especially 3D Raman imaging, can be integrated with other methods to pro...
RISE Microscopy is a novel correlative microscopy technique that combines confocal Raman Imaging and Scanning Electron (RISE) microscopy within one microscope system (Fig. 1a). This unique combination provides distinct advantages with regard to comprehensive sample characterization: electron microscopy is an excellent technique for visualizing surf...
The characterization of low‐dimensional materials such as graphene or transition metal dichalogenides (TMDCs) often requires more than one technique to obtain a thorough understanding of their attributes for specific applications. Graphene and TMDCs both have layered structures and properties that vary significantly with thickness as compared to si...
div class="title">New Developments in RISE Microscopy: Correlative Raman and SEM Imaging
- Volume 22 Issue S3 - Ute Schmidt, Philippe Ayasse, Olaf Hollricher
div class="title">Multimodal Low-Dimensional Materials Characterization with Correlative Microscopy: Raman-PL-FLIM-AFM-SNOM-SEM
- Volume 22 Issue S3 - Ute Schmidt, Wei Liu, David Steinmetz, Thomas Dieing, Olaf Hollricher
The development and production of drug delivery systems requires efficient and reliable control mechanisms to ensure the quality of the final products. These products can vary widely in composition and application. Therefore analyzing methods that provide both comprehensive chemical characterization and the flexibility to adjust the method to the i...
The implementation of correlative microscopy techniques for materials and surface analysis has grown steadily in recent years. This trend is being driven by the increasing demands placed on analytical methods for detailed and comprehensive sample investigations. WITec's Raman Imaging and Scanning Electron (RISE) microscope is the latest advance in...
The authors have developed a new method to integrate a scanning electron microscope (SEM) with a confocal Raman microscope (CRM) that uses full optical microscopy inside the vacuum chamber of the SEM, and thus bring the capabilities of a stand-alone CRM instrument into the combined tool. A focused ion beam is also integrated into the system, thereb...
Confocal Raman Microscope (CRM) is integrated with Scanning Electron Microscope (SEM) and its standard analyzers such as Energy Dispersive X-ray spectroscope (EDX), that can be further equipped with Focused Ion Beam (FIB). This yields valuable chemical information about molecular composition and chemical bonds in the sample on top of the high resol...
The discovery by Novoselov and Geim of a simple method to transfer a single atomic layer of carbon from the c-face of graphite to a substrate suitable for measurements of its electrical and optical properties has led to an increased interest in studying and employing two-dimensional model systems. An overview of electron and phonon properties of gr...
WITec GmbH, Germany, has extended Raman imaging to large-scale samples without extensive tilt alignment or sample preparation, and without comprising the advantages of confocal imaging by launching True Surface Microscopy. By integrating a Raman spectrometer with a confocal microscope setup, Raman imaging with a spatial resolution down to 200 nm la...
A scanning near-field optical microscope (SNOM), where the tip is scanned rather than the sample, is presented. The advantage
of this ‘stand-alone’ type SNOM besides its compact setup is its ability to scan on arbitrarily extended samples. Furthermore,
the sample can be manipulated during scanning (e.g. heated or extended), which may be of special...
In this chapter, the theory of optical image formation in an optical microscope is described, and the difference between conventional
and confocal microscopy is explained. The selection of the appropriate pinhole diameter is discussed in detail, as the pinhole
diameter is crucial in obtaining the highest depth resolution as well as optimizing colle...
Raman spectroscopy is a weak scattering technique in which typically less than one in a million excitation photons give rise
to a single Raman photon. The situation is even more difficult in confocal Raman microscopy, as the detection volume is reduced
by the small pinhole and thousands of spectra must be collected in a short period of time. Theref...
Part I: Theory.- Confocal Microscopy.- Introduction into the Fundamentals of Raman Spectroscopy.- Raman Equipment.- Software Requirements and Data Analysis in Confocal Raman Microscopy.- Part II: Applications.- Identification of Pathogens.- Imaging of Individual Carbon Nanotubes and Isolated Graphene Sheets.- Raman Microscopy in Geosciences.- Raman...
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of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.
Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009
A thorough knowledge of structural and chemical properties is essential in the fields of nanotechnology, materials research, and life science, leading to a growing demand for characterization methods for heterogeneous systems on the nanometer scale. However, certain properties are difficult to study with conventional characterization techniques due...
Typical confocal Raman images consist of thousands of individual spectra from which various pieces of information can be extracted in order to display certain chemical information as an image. In order to acquire these images in a reasonable amount of time, the time required for a single spectrum must be minimized. This can be achieved through the...
of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008
The combination of a confocal Raman microscope and an atomic force microscope (AFM) in an automated microscope system is used to study large samples in terms of chemical composition and morphological conformation on the nanometer scale. Recent developments in CCD detectors and ultra-high throughput spectrometer enable the acquisition of Raman spect...
The investigation of living cells at physiological conditions requires very sensitive, sophisticated and non-invasive methods. In this study, Raman spectroscopy, a chemically and structurally sensitive measuring technique is combined with high-resolution confocal microscopy to investigate different biomolecules inside of cells. In Raman spectral im...
The use of an EM-CCD camera can greatly increase detection efficiency and speed, especially for the short integration times necessary with a confocal Raman microscope. The distribution of a 7.1 nm PMMA as well as a 4.2 nm alkane layer on a glass substrate could be easily detected and identified with an integration time of only 7 ms per spectrum, wh...
Interdigital heterobarrier metal—semiconductor—metal (MSM) structures are proposed as ultrafast photodetectors of visible radiation. Vertical photocarrier drift in MSM diode structures provides the simplest way of reducing the active region of a detector to a submicron size and of considerably shortening the response time without a significant loss...
of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007
The investigation of living cells at physiological conditions requires very sensitive, sophisticated, non invasive methods. In this study, Raman spectral imaging is used to identify different biomolecules inside of cells. Raman spectroscopy, a chemically and structurally sensitive measuring technique, is combined with high resolution confocal micro...
The combination of an atomic force microscope (AFM) and a Confocal Raman Microscope (CRM) has been used to study various surface coatings. The high spatial resolution of the AFM enables the morphological characterization of the top layer of the coating with molecular resolution. Raman spectroscopy provides additional information on the chemical com...
In this study, Raman spectral imaging is used to investigate the stress fields around Vickers indents produced with various load forces on a silicon sample. Raman spectroscopy, a chemically and structurally sensitive measuring technique, is combined with high resolution confocal microscopy, thus enabling the identification of different chemical com...
The combination of an atomic force microscope (AFM) and a Confocal Raman Microscope (CRM) has been used to study an emulsion consisting of alkyd and acrylic latexes. Alkyds and acrylics are used as binders in paints and coatings. These materials produce a shiny, hard finish that is highly water-resistant. The high spatial resolution of the AFM enab...
The combination of an atomic force microscope (AFM) with a Confocal Raman Microscope (CRM) has been used to study the composition of various thin films of polymer blends. The high spatial resolution of the AFM enables the morphological characterization of the polymer blends on the nanometer scale. Furthermore, when operating the AFM in Digital Puls...
Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005.
Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005.
Materials research, biomedical research, and semiconductor manufacturing can all benefit from nondestructive, high-resolu- tion methods of analysis. As most materials are heterogeneous, it is important to not only acquire high resolution topographic informa- tion, but also to identify the chemical composition of samples. A combination of high resol...
Due to their outstanding dielectric and ferroelectric properties, barium titanate (BaTiO(3))-based ceramics have found many applications in electronic devices. To optimise the final quality of such ceramics, a detailed knowledge of the complex processes involved in the formation of BaTiO(3) is required. The phase formation process in ordered struct...
Patterned carbon nanotube assemblies with bent nanotube bundles were investigated with combined atomic force microscopy and confocal Raman imaging spectroscopy to identify conditions of carbon nanotubes in the bent state. We showed that the tangential G mode on Raman spectra systematically shifts downward upon nanotube bending as was predicted earl...
of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.
Confocal Raman Microscopy - Volume 9 Issue S02 - J. Müller, W. Ibach, K. Weishaupt, O. Hollricher
Scanning Near-field Optical Microscopy (SNOM) allows optical microscopy with highest spatial resolution beyond the diffraction limit. We present a new microscope set-up which uses micro-machined cantilever SNOM sensors and combines in a unique way the advantages of Scanning Near-field Optical Microscopy, Confocal Scanning Microscopy (CSM) and Atomi...
Transitions of fluorescent Rhodamine 6G dye molecules into metastable dark states with lifetimes of several seconds were observed by single-molecule detection (SMD) using far-field confocal microscopy. The samples were protected with different organic thin films and were characterized using atomic force microscopy. The data are compared to publishe...
We show that the use of fiber overtone resonance modes up to 3 MHz for shear-force distance control has two advantages for near-field microscopy. The higher dither frequency allows a shorter feedback loop time delay, which in turn allows scanning speeds of 100 mu m/s on a sample with, for example, a 150 nm height variation over a 1 mu m distance. E...
A multicolor scanning near-field optical microscope (color-SNOM) has been developed to provide real color images of nanoscopic samples for biological and spectroscopical purposes. The sample illumination consists either of a single or a combined beam of different laser wavelengths. A common SNOM setup has been modified in a way that three photomult...
Dry-etching of laser facets is commonly used for (InAl)GaN/sapphire-based structures since the epitaxial planes of the nitride layers are rotated with respect to the substrate planes making cleaving impractical. To achieve steep and smooth facets by chemically assisted ion beam etching, a 3-layer resist system is developed for patterning. Character...
A series of three perylene tetracarboxylic acid bisimide dyes 3a-c bearing phenoxy substituents at the four bay positions of the perylene core were synthesized and their complexation behavior to complementary ditopic dialkyl melamines 8a-c was investigated. Binding constants and Gibbs binding energies for the hydrogen bonds between the imide and th...
The cover picture shows mesoscopic strands of highly fluorenscent perylene bisimide–melamine assemblies as visualized by confocal fluorenscence microscopy. This technique does not only provide topological information such as related AFM or STM images, but truly shows the functionality of fluorescent optical networks of the present supramolecular sy...
A new two-step method to fabricate scanning near-field optical microscope (SNOM) probes with an aperture size clearly below 100 nm has been developed. For the first step, a chemical etching process is used in which an optical fiber is dipped with its acrylate jacket into hydrofluoric acid to get a suitable tapered shape of the fiber. The second ste...
In our experiments we show, that a contaminating water film is very important for the shear-force distance control in near-field optical microscopy. This is demonstrated at the transition between a hydrophilic glass surface and a hydrophobic Langmuir-Blodgett film of arachidic acid at different relative humidities. This contaminating water film is...
We present a piezoelectrical shear-force distance control setup for scanning near-field optical microscopy. The setup is compact and tip exchange is easy. The topographical sensitivity is comparable to optical feedback systems. With an acceptable vibration amplitude of 5-10 nm we obtained a topographical resolution of 5 pm/square root of Hz. Becaus...
Spatially resolved near-field luminescence spectroscopy was carried out on locally grown InP ridges, overgrown by a GaInAsP layer in metal organic molecular beam epitaxy. For free access to the quaternary layer the cleaved surface was investigated. Two different reflection scanning near-field microscopy setups were used. In the illumination mode we...
We present investigations of band-gap variations on selective grown GaxIn1−xAsyP1−y multiple quantum wells (MQW, Q1.05) using near-field optical microscopy. The MQW is excited with the near-field probe and the luminescence is collected through the same tip. By this mode, we are able to detect variation of the band gap with a lateral resolution of a...
We present investigations of band-gap variations on selective grown GaxIn1-xAsyP1-y multiple quantum wells (MQW, Q1.05) using near-field optical microscopy. The MQW is excited with the near-field probe and the luminescence is collected through the same tip. By this mode, we are able to detect variation of the band gap with a lateral resolution of a...
Experiments using photons as a probe provide an excellent energy resolution. The wavelength of the light, however, sets a lower limit to the probed area perpendicular to the di¬rection of propagation. This limit is of the order of the wavelength of the light. Scanning probe microscopes, on the other hand, have a superb spatial resolution. The energ...
In order to apply scanning near-field optical microscopy to life science, it is essential to have an accurate distance feedback that also works on soft biological samples in liquids. In this letter, the authors report measurements of neuron cells in aqueous solution using an advanced piezoelectrical shear-force detection setup. Simultaneously obtai...
Scanning near-field optical microscopy (SNOM) was used to investigate the fluorescence energy transfer between a monomolecular film of monomethin oxacyanine and a layer of monomethin thiacyanine in arachidic acid. The donor and acceptor chromophores are fixed in Langmuir–Blodgett (LB) films, spaced by the identical chains of the arachidic acid and...
We introduce an improved piezoelectric shear-force feedback system for tip-sample distance control in a scanning near-field optical microscope. A tapered glass fiber is glued into a metal tube and both are integrated in a mounting, sandwiched between two piezosegments. One of the piezoelements excites the fiber tip at mechanical resonance while the...
A novel micromachined aperture tip has been developed for near-field scanning optical microscopy. The advantages of the new probe over commonly used fiber probes are illustrated. The aperture tip is fabricated in a reliable batch process which has the potential for implementation in micromachining processes of scanning probe microscopy sensors and...
It is often difficult to characterize and distinguish heterogeneous materials with domain sizes below 1 micrometer. The range between 1 nm and 1 µm lies in the crossover region where light scattering is applicable to the upper wavelength range and where x-ray and neutron scattering is strongest for the lower wavelength end. In addition the scatteri...
We present an easy‐to‐use non‐optical shear‐force detection system for tip–sample distance control in scanning near‐field optical microscopes. The fibre tip is fixed in a four‐segmented piezo‐tube by a polymer, Polyisobutylene, which couples the tip stiffly to the piezo at frequencies of 10 kHz or more at room temperature. One segment of the piezo‐...
Superconducting microstriplines of YBa 2 Cu 3 O 7-x have been deposited and patterned on substrates of silicon on sapphire and GaAs. In both substrates fast semiconducting photoswitches were fabricated and integrated into the microstriplines. Short lightpulses of 100 fs length generated electrical pulses in the semiconducting photoswitches. The ele...
We report on design, fabrication, and characterization of an ultrafast vertical metal–semiconductor–metal photodetector. A CoSi2 layer in silicon acts both as a bottom Schottky contact and a buried light reflector. A semi‐transparent metallization on top of a photosensitive silicon mesa serves as top Schottky contact. Time‐domain studies of the pul...
LiTaO3 is a widely used material for electro-optic sampling of electrical pulses. Many group now use thin sensor crystals of 20 micrometer thickness, which is an optimum thickness for best measurement accuracy and minimum invasiveness of the probe. We demonstrate that by using these crystals of 20 micrometer thickness, a severe distortion of the me...
We report on the first investigation of the optoelectronic behaviour of an MSM diode above a two dimensional electron gas. The photodetector was fabricated in the InP/InGaAs material system on a HEMT layer structure. Optoelectronic measurements on a device with a finger spacing of 4 μm show a FWHM of the pulse response of 1 ps, at a temperature of...
High quality YBa 2 Cu 3 O 7-x films on silicon‐on‐sapphire were grown using a multiple buffer layer, consisting of YSZ and CeO 2 . Ion channeling reveals the high crystalline perfection of the YBa 2 Cu 3 O 7-x films. A channeling minimum yield for the Ba signal as low as 3% was measured. The normal state resistivity of 200 μΩ cm at 300 K, critical...
We describe a heterostructure metal-semiconductor-metal photodetector with subpicosecond response time. In this diode, the intrinsic speed is enhanced by ultrafast real- space transfer of the photogenerated charge carriers from the light-absorbing layer to a reservoir layer underneath.
