Properties characterisation

Physical Properties Measurement System.

PPMS - Physical Properties Measurement System

CMC has the use of a PPMS from Quantum design, which is relied heavily upon to characterize materials. The instrument measures in the temperature range 2-400 K (-271 to +127 ºC) and enables characterization of the following physical properties:

  • Resistivity
  • Hall coefficient
  • Heat capacity
  • Thermal transport
  • Susceptibility

ATL-160

As the PPMS operates at extremely low temperatures, it is cooled with liquid helium. Normally that helium would be lost as gas ("boil off") and replenishing it would incur a considerable running expense. This is avoided with the ATL-160 which continuously recovers and liquefies the helium gas from boil off. The helium is recovered in an energy efficient manner and with an average liquefaction rate of 22 liters/day. With the fully automated operation and self-cleaning properties, ATL-160 is both a time and cost effective device.

The second, considerable advantage of the ATL-160 is the enablement to produce (excess) liquid helium from bottled Helium gas. Liquid helium is a priced commodity for sample cooling in crystallography, as the ultralow temperatures it bestows (routinely <10 K) significantly dampen thermal motion in atoms and therefore enable acquisition of highly accurate structural data. 

Vibrating sample magnetometer

As add-on to the PPMS, CMC has access to a vibrating sample magnetometer which allow ultra-fast measurements of magnetization vs. temperature in the range 2-900 K (-271 to +627 ºC) or magnetization vs. field strength up to 9 Tesla.

Laser Flash

The Netsch Laser flash is capable of measuring heat diffusivity from room temperature to 1200 ºC. The diffusivity combined with the heat capacity allows us to obtain the thermal conductivity.

Seebeck microprobe

The instrument is capable of measuring spatially resolved Seebeck coefficients. The microprobe has a resolution of about 25 µm and was developed by PANCO. Maps of the Seebeck coefficient allows to check for sample purity and investigate functionally graded materials where an intended gradient in the Seebeck coeffients has been obtained, in order to determine the optimum composition for thermoelectric performance.

High temperature Seebeck

The high temperature Seebeck setup is designed for measurement of the Seebeck coefficient of non-insulators between room temperature and 1000 °C. The Seebeck coefficient plays a key role in thermoelectrics since it is the thermodynamic property responsible for generation of electrical voltage in the materials. The setup is designed according the state of the art principles and has very limited requirements for sample geometry. While it is built with hot pressed solids in mind, other inserts adapted for other sample types, such as thin films, can be easily constructed and implemented.

Resistivity and Hall-effekt analyzer

The resistivity is a key property of any electronic material while the Hall coefficient is important for characterizing conduction in especially semiconductors. This state-of-the-art setup can measure the resistivity of many kinds of materials, from near-insulators to metals, provided they can be prepared as thin slabs (~1 mm thickness). The Hall effect measurement is optimized for heavily doped semiconductors, such as thermoelectric materials, but any electrical conductor with a reasonably high electronic mobility can be measured.

SEM/TEM

CMC has access to state-of-the-art scanning and transmission electron microscopes at the Department of Physics at the Aarhus University. TEM and HR-TEM is done with a Phillips CM20 usually operating at 200 keV. SEM is done with a NovaSEM featuring a variety of detectors plus equipment for EDX, which also allow elemental mapping.

Talos F200X

Spearheaded by CMC, iNANO and Aarhus University acquired funding for an FEI "Talos" F200X analytical (S)TEM-microscope which was installed in 2014. The "Talos" is a very user-friendly instrument, has exceptionally high resolution and provides a number of advanced characterization facilities in addition to conventional TEM-micrography (bright-field and dark-field imaging, HR-TEM, etc.).

The "Talos" is equipped with a new advanced energy dispersive X-ray spectroscopy (EDS) system allowing for 3D chemical characterization with compositional mapping. The EDS is complimented by an Electron Energy Loss Spectroscopy (EELS) system with 0.7 eV energy resolution for image filtering (EFTEM) and quantitative analysis of the sample elements with high surface sensitivity. It is furthermore possible to acquire pictures with a High Annular Angle Dark Field (HAADF) detector.

Within CMC, one of the major activities which depend strongly on TEM is the studies of nanoparticles and nanomaterials in general. The size distribution, morphology and crystallinity of nanocrystals are key to their performance in various applications.

 

TGA/DSC

The Netsch Jupiter setup is capable of simultaneous measuring TGA and DSC. The setup is equipped with an interchangeable furnace covering a large temperature range. The low temperature setup goes from -180 to 600 ºC, whereas the high temperature setup gives access to temperatures from room temperature to 1500 ºC. The primary use of the instrument is to determine

  • Phase transitions
  • Melting temperature
  • Mass loss

 

 

TGA-MS

In addition to the Netzsch TGA/DSC, CMC has the use of a Perkin-Elmer STA6000 thermogravimetric analyzer which is coupled to a mass-spectrometer from Hiden, measuring in the 1-200 amu range. This enables very accurate detection of the gasses or species which are desorbed or evolved from the sample at different temperatures. This is highly useful e.g. for quantifying hydrogen storage properties.

BET

The phenomenon of all solid surfaces attracting surrounding gas molecules, is called gas (ad/de)- sorption. Monitoring the gas adsorption of porous materials provides useful information about characteristics of the mesoporous materials such as surface area (SBET), average pore size (Dmax), microporous pore volume (Vmicro), mesoporous pore volume (Vmeso) and total pore volume (Vtot).

If the sample has micropores (0 where micropore filling takes place. The adsorbate gas used is nitrogen N2, which has a known dimension and therefore a known monolayer thickness can be calculated. In the pressure range of about (0.05 - 0.3 p/p0), the monolayer of gas covers the surface of the sample. This makes calculation of the surface area (SBET) possible by using the Brunner Emmet Teller (BET) method. In the pressure range 0.35 - 1 p/p0, capillary condensation takes place for mesoporous materials. In this area it is possible to determine the maximum pore size distribution Dmax by the Barett Joyner Halenda (BJH) method. The total pore volume, Vtot is calculated by tagging the single highest sorption point 0.9 < p/p0 < 0.95 with the assumption of all pores being filled with condensate

SAXS

CMC has access to a powerful Small Angel X-ray Scattering (SAXS) instrument. SAXS probes electron density differences on the nanometer scale, making the technique ideal for examining particles or macromolecules. Within the CMC, SAXS is mainly used for the characterisation of inorganic nanoparticles in suspension, where measurements may provide valuable information on size, morphology and size distributions.

The instrument is a modified version of commercially available small-angle x-ray equipment (Bruker NanoStar), fitted with a rotating anode x-ray source (Cu Ka , 0.3 x 0.3 mm2 source point, 6 kW power) and a pinhole camera with two Göbel mirrors for monochromatizing and focusing the beam. The data is collected by a two-dimensional position-sensitive gas detector (HiSTAR).

More information about the instrument can be found at the webpage for the Soft Matter Group

Digital optical microscope

For visual inspection of samples which require only moderate magnifications, the CMC has an Olympus SZX16 stereo zoom microscope with attached camera  for the digital recording of micrographs. The microscope allow magnifications of up to 230x with a max. resolution of 900 LP/mm.

Streaming-potentiometer

Through the Inorganic Chemistry division, CMC commands a MicroTrac "Stabino" streaming-potentiometer, which measures the equivalent to zeta-potential, i.e. the static-electrical environment among nanoparticles in liquid dispersions. The streaming-potential (or zeta) identifies regions of repulsion or attraction between the particles and consequently their tendencies to precipitate or remain in a stable dispersion.