The main research activity comprises the exploration of microwave and terahertz properties of dielectrics, ferroelectrics and semiconductors and superconductors with emphasis on thin films and nanostructures, but also of liquids and biomaterials. One of the most challenging materials for future investigation are graphene thin films. Norbert´s group invented several microwave and terahertz characterization methods based on resonator methods and evanescent probe techniques. Beyond material investigation, his group has developed microwave and terahertz devices for microwave communications applications such as low phase noise oscillator and microwave tunable filters, but also sensor devices and systems for homeland security, bio medical and industrial applications. In addition, micro- and nanomechanical structures have been fabricated and explored for sensor applications.
Norbert Klein joined Imperial College in Oct. 2009, is co-heading the thin film team http://www3.imperial.ac.uk/thinfilms together with Neil Alford and is currently establishing a Centre for Electromagnetic Material Characterization with strong emphasis on the terahertz frequency range. This work is in collaboration with the Centre for Plasmonics and Metamaterials http://www3.imperial.ac.uk/plasmonmeta . The team works in close collaboration with the materials division at the National Physical Laboratory http://www.npl.co.uk , where Norbert holds a part time research fellow position. Norbert´s spin out company EMISENS in Germany http://www.emisens.com/ , which is represented in the UK by Link Microtek http://www.linkmicrotek.com/ , is developing and commercializing new sensor concepts for homeland security and industrial applications.
Recent Research Publications
1. “High-sensitive microwave characterization of organic molecule solutions of nanolitre volume”, Shaforost, EN; Klein, N; Vitusevich, SA; Barannik, A.A; Cherpak, NT,
APPLIED PHYSICS LETTER Volume: 94 Article Number: 112901 Published: 2009
2. “Nanoliter liquid characterization by open whispering-gallery mode dielectric resonators at millimeter wave frequencies“,Shaforost, EN; Klein, N; Vitusevich, SA, et al. JOURNAL OF APPLIED PHYSICS Volume: 104 Issue: 7 Article Number: 074111 Published: 2008
3. “Design and fabrication of in-plane resonant microcantilevers“
Wu, YH; Panaitov, G; Zhang, Y, et al.
MICROELECTRONICS JOURNAL Volume: 39 Issue: 1 Pages: 44-48 Published: 2008
4. “Arrays of high-T-c Josephson junctions in open millimeter wave resonators“, Klushin, AM; He, M; Yan, SL, et al., APPLIED PHYSICS LETTERS Volume: 89 Issue: 23 Article Number: 232505 Published: DEC 4 2006
5. “Dielectric tunability of SrTiO3 thin films in the terahertz range“,Kuzel, P; Kadlec, F; Nemec, H, et al.
APPLIED PHYSICS LETTERS Volume: 88 Issue: 10 Article Number: 102901
Published: MAR 6 2006
Fig.1 : Electromagnetic characterization Lab, Department of Materials: Evanescent field scanning microscope, Terahertz time domain spectrometer, and resonator based liquid screening device (from left to right)
Fig. 2 : Electromagnetic characterization Lab, Department of Materials: Coplanar probe wafer station for frequencies up to 40 GHz
Facilities in your research group. We have several thin film deposition techniques available, including a Neocera pulsed laser ablation system (PLD), which can be used to manufacture a range of different oxide materials, including novel materials using targets made in-house. Prototype and proof-of-principle device manufacture is also possible with the new facilities at Imperial College for nanolithography. We have recently acquired a third chamber that can perform spread composition deposition, useful for combinatorial methods.
For measurement of microwave properties we have three Agilent parameter network analysers (PNA), which are used with microwave probe-stations and resonant cavities for characterising thin films and dielectrics at frequencies up to 40GHz. The microwave cavities have been designed which are tuneable, and which are used to perform measurements of loss (Q), permittivity and temperature coefficient of resonant frequency (TCf) down to cryogenic temperatures as low as 15 K. The equipment is also used to measure the surface resistance and the distribution of critical currents in high temperature superconductors. An impedance/gain-phase analyser with dielectric test fixtures is used for determining the low frequency properties of dielectrics, ferroelectrics, the Q of MRI receive coils and the impedance of piezoelectrics. We also have two probe stations providing on-wafer measurements of thin films and devices under external electrical bias and magnetic field (up to 0.15T) applied in horizontal and vertical directions, in a wide temperature (10K – 600K) and frequency (d.c. – 40 GHz) ranges. We have an Agilent RF-LCR meter capable of performing a range of measurements on ferroelectrics and semiconductors in the frequency range 1 Hz to 3GHz and an Agilent B1500 Semiconductor Analyser with high resolution module (HRSMU) that allows d.c. current measurements with 1 fA resolution.
We can perform a full range of P-E loop analysis over a range of temperatures using a ferroelectric tester on both thick film and bulk materials. A Radiant Technologies Precision LC unit is used to measure polarisation or current against voltage or electric field using voltages up to ±10KV with a high voltage power amplifier. Polarisation-Field loops obtained using the standard triangular wave or a user customised voltage profile show the ferroelectric behaviour of bulk samples while the memory effect and values of effective capacitance and dielectric constant can be measured using customised pulse measurements or the standard PUND (positive up, negative down) measurement. Using the thermal chamber attached to a liquid nitrogen cylinder ferroelectric measurements in the range of -184.4°C to 315.5°C can be obtained which can be used to find the Curie temperature and examine pyroelectric behaviour. In addition the unit can be used to measure current-voltage or capacitance-voltage characteristics, resistance measurements, leakage current and by subjecting the sample to a series of pulses, fatigue, imprint and loss of remnant polarisation.
We have recently purchased a Teraview THz spectrometer for performing terahertz time domain spectroscopy in the frequency range from 100 GHz up to 4 THz. Beyond transmission spectroscopy, which allows the determination of the complex valued permittivity of transparent thin film and bulk samples, the system is equipped with a fibre optic extension which allows to place the terahertz transmitter and receiver at arbitrary positions. We are going to construct a scanning terahertz reflectometer for spatially resolved material investigation, and will develop novel terahertz evanescent field probes emphasizing (sub)micrometer spatial resolution.