- Electroanalytical Techniques
- Renishaw InVia Reflex Raman Spectroscopy System
- Polarization Modulated Infrared Reflection Absorption Spectroscopy (PM-IRRAS and IRRAS)
- Gas Chromatography – Mass Spectroscopy (GC-MS)
- Contact Angle Measurements
- Chemical Vapour Deposition
- Clean Room
- Organic Synthesis Labs
- High-Shear Mixer
- Optical Microscopy
- Electron Microscopy
- X-ray Photoelectron Spectroscopy (XPS)
- Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)
Using electrochemical techniques we have the tools to both modify and analyse surfaces. In general, electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy can be used to study the reactivity of surfaces and species in solution. Furthermore, modification of surfaces (metal, glassy carbon, graphene etc.) can be performed by applying an electrical potential in the presence of reactive species (e.g., aryl diazonium salts), which gives the surface new properties. Modification and analysis of localized regions on surfaces are possible by means of Scanning Electrochemical Microscopy (SECM), hence making electrochemical imaging or patterning of surfaces feasible.
We have a number of electrochemistry workstations are available in the group.
- For general electrochemical measurements, voltametric methods, galvonostatic methods, chronoamperometry, chronovoltammetry, and elektrochemical impedance spectroscopy CHI 601C, 2 x CHI 601D, and CHI 660 B, are employed. In addition, we also have access to an Autolab potentiostat/galvanostat.
- For Scanning electrochemical microscopy (SECM) a CHI900 B bipotentiostat is used.
- For electrochemical quartz crystal microbalance (EQCM) measurements we have access to equipment from Q-sense.
Renishaw InVia Reflex Raman Spectroscopy System
In 2014 the group acquired an InVia Raman Microscope/Spectrometer. The instrument is placed in iNANO building 1590, room 063, and is equipped with an optical microscope (Leica) with 5 objectives (working distance): x5 ( mm), x20 (1.15 mm), x50 (0.37 mm), x100 (0.33 mm), and x150 (0.20 mm). This part is connected to an eyepiece, video camera or Raman spectrograph. The stage is fully xyz-motorized and controlled via joystick or software. This allows Raman mapping on surfaces ranging from 11.2 cm × 7.6 cm to 100 μm × 100 μm with a minimum step size of 0.1 μm (xy) and 16 nm on the z-axis. The moving velocity on the 3 axes of the stage is automatically correlated with the magnification of the objective. Two lasers are currently mounted: An Ar-ion laser provides Raman signals at 457 nm (20 mW) and 514 nm (100 mW) and a HeNe laser at 785 nm (100 mW). Rejection filters for each laser wavelength provide a minimum wavenumber of 100—130 cm-1. The spectrograph has two gratings: 2400 lines/mm and 1200 lines/mm. The usual combinations of laser wavelength/grating are 457 nm and 514 nm/2400 lines/mm and 785 nm/1200 lines/mm which allow a scan range of ~600 cm-1 with a spectral resolution of ~1 cm-1. However, in the fast (2500 spectra in 153 sec) static mode the particular combination 514nm/1200 lines/mm provides a scan range of ~1200 cm-1 with a spectral resolution of ~2 cm-1. The gratings can be tilted in extended scanning in order to allow wider spectral range (100 – 4200 cm-1) in high resolution (~1 cm-1) but at a much slower rate. A Peltier cooled (-70 oC) CCD-detector (1024×256 pixels) records the Raman signal.
The instrument is suitable for recording single point Raman spectra of solids or liquids, xy surface mapping (lateral resolution ~1 μm), and for depth profiling of layered materials (i.e., multi-layered polymer films) with a confocal depth resolution of 1—2 mm depending on the laser wavelength.
Polarization Modulated Infrared Reflection Absorption Spectroscopy (PM-IRRAS and IRRAS)
The equipment consists of two parts: A Thermo FTIR 6700 spectrometer and a Varian external Experiment Module. The intensity modulated IR-beam exits from the side of the spectrometer and enters the experiment module where it can be focussed on the sample at different angels (50o – 90o) and be reflected to the narrow band mercury-cadmium-telluride (MCT/A) detector cooled in liquid nitrogen. Before hitting the sample the infrared beam is p- or s-polarized by a gold wire polarizer and in PM-IRRAS polarization-modulated (74 kHz) with a photoelastic modulator (Hinds PEM-90/II/ZS37).
In IRRAS the p-polarized reflectivity of the film, Rp(d), is divided with the reflectivity of the bare substrate, Rp(0), to provide IRRAS absorbance, ‒log [Rp(d)/Rp(0)]. Subsequent baseline correction and spectrum manipulations are made using the facilities of the OMNIC 8.2 program.
In PM-IRRAS the two signals, Rp – Rs and, Rp + Rs, were extracted with a high-pass filter (40 kHz; EG&G model 189) and a lock-in amplifier (SR 810 DSP) and digitized simultaneously in two channels by the spectrometer.
The techniques are best suited for highly reflective metallic surfaces (Au, Pt, stainless steel) where a near-grazing angle (75o -85o) is used. On carbon materials (GC) an incident angle of 60o is generally used, and in some cases the insertion of an extra polarizer before the detector is required. With IRRAS organic films thicker than 10 nm can be measured providing good quality and full range spectra. Thinner organic film (<10 nm), with good IR chromophores, can be characterized by PM-IRRAS but only in limited spectral ranges, i.e. 1000—2000 cm-1 and 3500—2500 cm-1 determined by the lopes of the Bessel function. Hence additional experiments are required to cover the full spectral range.
Gas Chromatography – Mass Spectroscopy (GC-MS)
The group uses a GC-MS system (G-1530A) from Agilent to analyze product mixtures of compounds, weighing 50-600 Da and with low to medium polarity. The system is usually equipped with a HP-5MS column (length: 25 m, diameter: 0.2 mm, film: 0.33 mm) suitable for all-round analysis. The GC (GC 6890) is equipped with a HP 6890 autosampler with room for 100 samples. The mass analyzer (MSD 5973) uses electron impact ionization (EI at 70 eV) for ionization and fragmentation, a low resolution quadrupole for mass measurement and finally an Electron Multiplier for ion-current detection. The autosampler, GC and MS are all completely controlled by a PC via the Program Enhanced Chemstation ver D.2.0. Standard analytical methods can be developed and are used for most purposes. New samples can always be added to the sample tray and included in the log file.
The standard output from the GC-MS includes a chromatogram showing the total ion current (TIC) versus time, a small integration report and an automatic library identification report. The mass-spectrum library is from NIST and contains spectra of more than. 60.000 compounds. Single or averaged mass spectrum can be extracted from the chromatogram or from the NIST library.
Ellipsometry is an optical technique, which we use to determine film thicknesses ranging from 1—100 nm on reflective substrates. A Dre Ellipsometer (EL X-02C) is used for general measurements. For more advanced analysis we also have access to a Sentech Spectroscopic Ellipsometer in the cleanroom facilities at iNANO, Aarhus University.
For polymer films with thickness >50 nm, the thickness is usually measured using profilometry, which we have access to at the Department of Physics and Astronomy, Aarhus University.
Contact Angle Measurements
Contact angle measurements are used to quantify the wettability of solid substrates. A small drop of water or a buffer solution is placed on the sample, and the contact angle between the drop and the substrate is measured using a camera. Through this the hydrophilic/hydrophobic properties of the surface can be tested. It can also be used to investigate responsive properties of for example polymer brush systems.
Chemical Vapour Deposition
Chemical vapour deposition (CVD) is a versatile synthesis technique and is widely used in, e.g., the semiconductor industry for growing thin films. The basic concept is to deposit/grow specific compounds from gas-phase precursors, usually by exploiting a surface-assisted chemical reaction or breakdown. To overcome the activation barrier, heat is usually employed as process initiator.
The CVD setup in our group is a low-pressure system (working in the range of 0.1 – 20 mbar), mostly used for growing graphene films on various transition metal substrates. Graphene is grown at temperatures near 1000⁰C using, e.g., methane as precursor. Pre-annealing of the metal substrate in a reducing atmosphere is often necessary to ensure proper cleanliness and optimal growth conditions.
MoS2 (a 2D material similar to graphene) has also been succesfully synthesised with this setup, but from solid precursors. Under normal conditions mass flow controllers finely control the gas/reactant feed, but solids need to be evaporated inside the reaction chamber and therefore the partial pressures become more difficult to handle.
At the Interdisciplinary Nanoscience Centre, clean room facilities are available with state of the art instrumentation for micro/nano-fabrication and characterisation (Class 100, ISO class 5). Nanoscale patterns are defined through various lithographic approaches, and advanced deposition and processing equipment allow these patterns to be translated into functional structures (electronics, microfluidics etc.).
More information is found at: http://inano.au.dk/research/research-platforms/cleanroom/
Organic Synthesis Labs
Organic synthesis is extremely important for essentially all our projects. We use organic chemistry as a tool for synthesiszing the organic compounds and fascinating new materials we need in our studies and not with an aim of developing new reaction protocols. Our laboratory facilities for performing organic synthesis are complete, including rotary evaporators, vacuum lines etc. We also have full access to all the necessary analytical tools such as NMR, infrared spectroscopy, UV spectroscopy and mass spectroscopy.
Processing of some materials requires high shear forces in order to obtain good dispersions, breakdown of material etc. Our Silverson L5M High-shear mixer is used for production of graphene from graphite in organic solvents. Using the different workheads available we can process solutions from 20 mL to 12 L.
A Nikon Eclipse CI instrument is used for optical microscopy. As a quick and versatile tool, optical microscopy allows easy imaging of surfaces at magnifications of 10x, 50x and 100x. The setup allows for both Bright-Field and Dark-Field imaging of surface structures.
Working with materials on the nanoscale level, we need methods for imaging very small structures. Through collaboration with iNANO and the Department of Physics, Aarhus University, we have access to both Scanning Electron Microscopy (SEM) and Transmission Electron Miscroscopy (TEM). This allows imaging of modified surfaces or polymer materials at sub-nanometer resolution.
X-ray Photoelectron Spectroscopy (XPS)
The Kratos Axis Ultra DLD (Kratos Analytical Ltd) is equipped with two X-ray sources; a monochromated Al source for high energy resolution, and non-monochromated Mg and Al sources. The instrument integrates a hemispherical and a spherical mirror energy analyzers and a delay line detector (DLD) which allows for operation in both a spectroscopic and an imaging mode. The hemispherical analyzer provides both high-energy resolution and high-sensitivity spectroscopic performance with spatial resolution down to 15 μm. In parallel imaging mode photoelectrons are transferred to the spherical mirror analyzer to produce real time chemical state images down to 3 μm spatial resolution. Insulating samples can be analyzed by using the integral charge neutralizer. The instrument is also equipped with a monoatomic Ar and a polyatomic coronene (C24H12) ion guns for depth profiling. The sample stage has temperature control from -150 °C to +600 °C.
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)
A high spatial and mass resolution TOF-SIMS 5 (ION-TOF GmbH) incorporating a Bi, Cs and C60 ion sources as analysis and/or depth profiling etch sources. The instrument is equipped with a reflectron TOF analyser giving high secondary ion transmission with high mass resolution, a sample chamber with 5-axis manipulator (x, y, z, rotation and tilt) for flexible navigation, a fast entry load-lock, charge compensation for the analysis of insulators, a secondary electron detector for SEM imaging. The instrument also processes heating and cooling stages in the entry lock and analysis chamber. The instrument is also able to provide detailed elemental and molecular information about surfaces, thin layers, and interfaces, and it gives a full three-dimensional analysis of the sample.