Research equipment and facilities

With the FLS1000 from Edinburgh Instruments, the Department of Functional Nanostructures has a state-of-the-art photoluminescence spectrometer for measuring emission and excitation spectra with high resolution and a measuring range of 200–1600 nm at hand. Time-resolved measurements using pulsed lasers for excitation are also possible in the subnanosecond range. Various sample holders are available for the measurement of solutions, solids and coatings, as well as an integrating sphere for the measurement of quantum yields and reflectivities.

The optical cryostat OptistatCF of Oxford Instruments can be combined with both high-end spectrometers (FLS1000 and CARY 5000) of the Department of Functional Nanostructures, so that spectroscopic investigations in the range of 200–2500 nm at different temperatures are possible. The measuring range is from 500 to 3.4 K (in operation with liquid helium) and 77 K (in operation with liquid nitrogen).

The DUAL-FL from Horiba is a combination of a Bench-Top-Spectrofluorometer and a UV/Vis Spectrophotometer. Emission, extinction and excitation spectra can be detected in the range of 200–1000 nm. By installation of the integrating sphere "Quanta-Phi" an absolute determination of quantum yields of fluorescent systems is possible. Furthermore, this instrument is connected to one of our gloveboxes, which makes it possible to also measure water- and air-sensitive samples under inert gas atmosphere.

With the help of this spectrometer setup, slow optically excited charge carrier states can be investigated over time. The temporal resolution is in the microsecond range. A neodymium YAG laser is used for excitation, which can excite the wavelengths 1064, 532, 355, 266 nm and the range from 420 to 950 nm by means of different modules. The probe pulse is generated by a xenon lamp. Due to an exchangeable central module in the sample chamber, it is possible to measure not only flat samples in reflection but also in cuvettes in transmisson. In this case, temperature control by means of a thermostat is possible.

Three potentiostats (Solartron ModuLab XM ECS, Princeton Applied Research PARSTAT 3000A-DX bipotentiostat, Zahner Zennium), different light sources (xenon lamp with monochromator and chopper, different LEDs), a function generator (to control the LEDs), and a 7270 DSP lock-in amplifier from Signal Recovery are available for the photoelectrochemical characterization of nanoparticles and nanoparticle assemblies. The combination of Lock-In Amplifier and Potentiostat allows the detection of very low (photo-)currents in the pA range, e.g. the charge carrier dynamics in single particles and assemblies. In addition, both potentiostats are impedance-capable (frequencies up to 7 MHz).

A Metrohm Autolab PGSTAT204 and a rotating disk electrode (RRDE-3A from ALS) are also available for measuring catalytic properties.

The laser microscope consists of an upright Zeiss Axio Imager.A2m with objectives between 2.5x and 50x magnification. A Gryphax Prokyon microscope camera from Jenoptik is used to capture the images. This allows color images with up to 5760 x 3600 pixels to be captured. Furthermore, panoramic images, focus stacks, videos, time-lapse or slow-motion videos can be recorded.

For the examination of visibly emitting samples, a 470 nm LED with adjustable intensity is available as top light. If required, a Rapp OptoElectronic DL-Series laser source (wavelength 405 nm) can be connected. Together with the UGA-42 Firefly control module, fast, dynamic illumination of points or user-defined areas in the microscope's field of view can be realized. Individual points are thereby in the submicrometer range.

The Department of Functional Nanostructures owns a TGA/DSC 3+ from Mettler Toledo for thermogravimetric analysis. This allows mass changes between room temperature and 1100 °C to be measured both under nitrogen and air flow, e.g. for the determination of organic sample proportions. Thanks to SDTA technology, it is also possible to measure the heat flow.

The Quantachrome Nova 3200e is used for the determination of specific surfaces and pore sizes/volumes of nanoparticle assemblies and other porous materials. Sample preparation of up to four samples simultaneously can be performed under vacuum or in a gas stream at temperatures of up to 350 °C. The sample preparation can be performed under vacuum or in a nitrogen stream. During the subsequent measurement (up to three samples simultaneously), micro- and mesopores from a diameter of about 0.5 nm can be detected. Argon is used as a standard adsorptive gas, but other gases (N₂, CO₂, etc.) can also be used.

The Zetasizer Nano ZSP from Malvern Panalytical allows the analysis of particle behavior in solution. With this device, both particle sizes and the zeta potential of the particles can be determined via dynamic light scattering. The instrument is equipped with a 633 nm laser. Automated pH-dependent measurements are also possible with the available autotitrator (Malvern MPT-2).

This ESA/Zeta potential measuring instrument enables the measurement of highly concentrated (up to 74 vol%), turbid or viscous dispersions. The instrument has an electro-acoustic amplifier as well as a temperature, conductivity and pH probe (measuring range: 2–14). The integrated titration module (two-way piston pumps with 1.0 µL resolution) enables potentio & volumetric determination of the effect of additives on suspensions as well as automatic determination of the isoelectric point. For more accurate determination of the particle size guide value (1 to 50 µm), the measurement is performed at three different frequencies.

There are two single and two double glove boxes available from MBraun (models Labstar, 2x UNIlab Plus and MB-200B). All glove boxes are equipped with solvent filters (activated carbon or molecular sieve), three of them are also equipped with a freezer. The glove boxes are primarily used for the storage and safe handling of air- and moisture-sensitive as well as toxic chemicals. In addition, extinction and emission spectra of solutions can be measured with the Dual-FL via fiber optics. It is also possible to perform photoelectrochemical measurements under inert conditions.

The Quorum E3100 Critical Point Dryer is a versatile device for gentle drying of macroscopic structures and enables the production of aerogels with extremely large specific surfaces. First the alcohol in the samples is displaced by liquid CO₂, which then passes into the supercritical phase by increasing the temperature (1100 psi & 31.5 °C). After the CO₂ has been released, the dry sample is obtained. The instrument itself has a robust design with a horizontal cylindrical chamber (63.5 x 82 mm) and various sample holder sizes. The CO₂ content is visible through the window during the drying process and the decisive parameters (pressure and temperature) can be monitored on site. The instrument is connected to a temperature-controlled water bath with exact heating and cooling capability.

The freeze dryer is used for lyophilization of aqueous, frozen samples. This device has 3 unheated platforms as well as additional connections for 8 round-bottom flasks, wide-neck filter cap bottles or distributor pieces for ampoules. At a condenser temperature of -58 °C and a maximum negative pressure of 0.036 mbar, up to 2.5 kg of water can be frozen per drying process. This device is essential for the production of nanoparticle-based cryoaerogels.

An Atlas Suntest CPS+ is available for further experiments under simulated sunlight. It can vary the light intensity between 1 and 100 mW/cm² and control the temperature between 30 °C and 100 °C.

Agilent's gas chromatography (GC 8860) is used to separate and analyze volatile mixtures and gases into individual chemical compounds. The instrument has two inlet valves, each driving two separate separation columns and two different detectors (Flame Ionization Detector (FID) or Thermal Conductivity Detector (TCD)).

With the acetylene-air flame used, the flame absorption spectrometer (Varian AA140) allows the quantitative analysis of metals and semimetals in aqueous solution by measuring element-specific absorption bands. With the aid of calibration series prepared in each case, the concentration of individual analytes can be determined in the range of linear correlation. The following elements can be analyzed: Ag, Au, Cd, Cu, Fe, In, Mn, Ni, Pb, Pd, Pt, Se, Si, Sn, Te, Ti and Zn.

The Fluoromax-4 is a bench-top spectrofluorometer which, in addition to recording emission and excitation spectra up to 850 nm, allows time-correlated single-photon counting lifetime measurements (TCSPC with 200 ps lower limit). The device is equipped with a dual monochromator system and allows measurements of liquid and solid samples in special holders. To determine the lifetime of the samples, various NanoLED picosecond laser sources with wavelengths from UV to visible are used.

The research section Functional Nanostructures has a CARY 5000 spectrophotometer manufactured by Agilent Technologies at hand. This high-end spectrometer is capable of transmission and extinction measurements of liquids, coated transparent materials and powders in a spectral range of 175–3300 nm in high resolution. In addition, if required, the instrument can be equipped with expanding accessories such as a DRA-2500 integrating sphere for the measurement of absorption and reflection spectra or a thermostat-controlled 1x1 Peltier cell holder for temperature-dependent transmission and extinction spectroscopy.

The Dorfs group works with a setup which has is a pulsed neodymium-YAG laser manufactured by Continuum as core element. This device is capable of emitting high-energy light pulses of 5 ns length with a wavelength of 1064 nm and a maximum energy of 475 mJ per pulse through nanoparticle solutions. With the help of several exchangeable harmonic crystals, further wavelengths (532 nm, 355nm and 266nm) can be generated. The energy hitting the samples can be gradually attenuated in the existing setup using OD filters and detected by a Coherent pyroelectric energy sensor. The irradiated solutions can be stirred with a stirrer enclosed in the cuvette holder of the setup.

The PHI 5000 VersaProbe III X-ray photoelectron spectrometer offers a wide range of surface-sensitive measurement methods that allow conclusions to be drawn about the bonding situations, surface compositions and electronic states of the samples. In addition to classical X-ray photoelectron spectroscopy (XPS), the instrument offers the following techniques:

•     Depth profiling by sample ablation (using argon ions or clusters).
•     Auger electron spectroscopy (AES) to analyze the chemical composition of the sample surface
•     UV photoelectron spectroscopy (UPS) for determination of molecular orbital energies in the valence band
•     Reflection electron energy loss spectroscopy (REELS) to obtain information about band gaps and defects on surfaces
•     (Low Energy) Inverse Photoemission Spectroscopy (LEIPS) for characterization of unoccupied electronic states on surfaces
•     Heated sample chamber

These techniques can be used to comprehensively characterize sample surfaces of various textures. The instrument also features imaging techniques such as scanning electron microscopy so that material distributions on sample surfaces can be graphically displayed. The instrument has a spectral resolution of 0.1 eV and a beam diameter of 9 to 200 µm (15 kV) for XPS measurements.

The instrument is operated in collaboration with the Behrens group of the Institute of Inorganic Chemistry.

The research section Functional Nanostructures has at its disposal a HELIOS FIRE Transient Absorption Spectrometer from Ultrafast Systems. The instrument enables a comprehensive investigation of the type, origin and temporal course of photo-excited charge carrier states of optically interfering systems. The samples to be investigated are excited from the ground state with an ultrashort excitation laser pulse (~100 fs), while a time-shifted interrogation laser pulse images the sample response at different times after excitation. The HELIOS FIRE covers an optical broadband range of 350–1600 nm. Samples can be characterized in solution or as films. The optical excitation is covered over a wide spectral range by an OPA (~260–2100 nm).