Nanofabrication laboratory.
Microwave laboratory.
Alex Patterson (summer student) and the 3D-systems rapid prototyping facility.
Dr Tom Isaac in the ultra-fast laser lab.
Vector MOKE probe station.
Sputtering system.
Multiphoton laboratory.
X-ray photo-emission electron microscopy measurements.
Soft x-ray beamline STG52 at the synchrotron radiation source BESSY (Berlin).

Research facilities:

Fabrication - Experimental - Computational

Fabrication

Focussed Ion Beam (FIB) and e-beam Nano-fabrication

The group has a dedicated Nova 600 system from FEI.  This system is a dual-beam unit that provides the capability to undertake ion-beam milling and electron-beam lithography, as well as standard scanning electron microscopy.

Etched Nanosphere lithography (ENSL)

We have developed a fabrication methodology for producing large area patterned thin-film structures using the e-beam facility described above. The fabrication technique is based on polystyrene nanosphere self-assembly which is performed on water interface and then transferred onto thin film surfaces. The fabrication steps include reactive ion etching and thin film milling which are performed by a PlasmaPod system (JLS  Design) . The system is fully automated and can operate using a combination of etching gases.

Rapid Prototyping

A Projet 3000 HD 3D-printing system that provides production of cm- and mm- sized photonic crystal and metamaterial designs for microwave experimentation with feature sizes down to 200 microns.  We also have use of further college facilities in X-AT.

Deposition

Several vacuum evaporators are available for the deposition of thin metal layers which are used in the study of surface plasmons and microstructured metamaterial surfaces. We have an automated ophthalmics coater (sputterer), and associated design software, enabling optical multilayers of arbitrary design to be fabricated. Typically Si, SiO2, Zr and ZrO2 are deposited, though other materials can be used.

Fabrication of nanostructured magnetic materials

Ultrathin magnetic films are deposited within a four source magnetron sputtering system with DC and RF power supplies.  The system has a base pressure on the 10-10 mbar scale when sealed completely with metal gaskets while base pressures are typically on the low 10-10 mbar scale when sealed with a viton gasket for rapid changeover of substrates.  An in-situ motorized mask carousel is available for fabrication of cross-strip magnetic tunnel junctions.  The deposited films may be further patterned either by a nanosphere lithography technique capable of yielding mm sized domains, or by the electron beam lithography and focused ion beam facilities available within the Physics department.

UV grating fabrication interferometer

An optical interferographic system based around a 325 nm laser source is available to make optical gratings with pitches down to 160 nm

Experimental

Ultrafast Laser Lab

We use an amplified Ti:Sapphire Legend laser system to probe the electronic and phononic properties of semiconductors and graphene based systems. With a time averaged power of 3 W, produced in over one thousand ultrafast (100 fs) pulses per second, a range of time-resolved experiments are possible.  THz time domain spectroscopy is used in both collimating and focusing configurations to probe materials at low energies (approximately 4meV). Temperature controlled samples can be used within these time resolved measurements and the THz generation dynamics of different materials can also be measured. Time resolved (pump-probe) measurements are performed at visible and near-infrared frequencies, with bespoke chambers for in-situ measurements in ambient, vacuum or inert gas environments.

Multiphoton Lab

Within this ultrafast lab we can align up to five different laser sources, ranging from 700-1600 nm in wavelength, through two inverted microscopes to provide spatial resolution of approximately 1 micron at the sample. With picosecond and femtosecond operation, a wide range of optical measurements can be taken. Multiphoton fluorescence, Second- and Third-Harmonic Generation (SHG & THG), Stimulated Raman Scattering (SRS),Coherent Anti-stokes Raman Scattering (CARS) and time-resolved pump-probe measurements are all taken within this single facility. With such a broad range of available wavelengths, coupled with the high spatial resolution of the microscope (with raster scanning capability), this lab offers researchers the ability to probe a variety of different biological and solid-state systems.

Microwave Lab

Capability from 70kHz - 70GHz using three Vector Network Analysers (VNAs).  Scalar ability up to 110 GHz.  Horn antennas that can be utilised from 800-1000 MHz and 5 to 110 GHz.  Microwave benches with rotating stages that provide a collimated (distance source) beam to determine the response of test samples as a function of angle of incidence. A computer controlled 3D scanner provides the ability to measure the intensity and phase of the electromagnetic fields scattered from objects under test. 

High frequency electrical measurements

In addition to the VNAs described above, we also perform high frequency electrical and electro-optical measurements on both contacted devices and at the wafer level using high frequency probe stations.  These experiments also utilise a 50 GHz spectrum analyzer, a 50 GHz sampling oscilloscope, a 40 GHz microwave synthesizer, and an assortment of smaller microwave frequency components.  We have made measurements upon both spin transfer oscillators and phase change random access memory devices at the wafer level.

Monochromator system

A collimated monochromatic beam system for studies of samples from 400 to 900 nm equipped with rotating sample stage and fully computerized data acquisition system.

Optical conoscope

A convergent beam polarizing optical conoscope system is available for the study of liquid crystal cells. This uses 632.8 nm radiation and has flow cell capability for exploring the director profiles in liquid crystal cells under pressure driven flow.

Angle scanned optical systems

Three computer controlled angle-scan optical systems are available for the study of the angle dependent reflectivity and transmissivity of thin film systems using single wavelength well-collimated sources.

Polarising microscope

Several polarizing microscopes are available for the optical study of liquid crystal cells as well as for the exploration of other microstructured photonic surfaces.

Acoustic experimentation

A collimated beam acoustic apparatus for measuring the air-borne far-field response of test samples to high frequencies, in the frequency and time domain.  A SONAR facility to similarly characterise the repsonse of samples underwater in the time-domain. A computer controlled 3D scanner provides the ability for mapping local pressure fields.

Micro-spectroscopy

Spectroscopy in the visible in reflection, transmission and by dark-field is available using a system based on a CCD coupled to a grating spectrometer and a Nikon inverted microscope

Time-resolved scanning magneto-optical microscopes

We operate several time-resolved (pump-probe) imaging systems offering a range of measurement modes. The systems are used for studies of electron, spin, and lattice dynamics in the time and space domains, with time resolution down to 50 fs and spatial resolution down to 300 nm. We image ultrafast dynamics excited in samples either optically or by pulsed or cw microwave magnetic fields. The measurements are performed at bias magnetic fields up to 1 Tesla (soon, up to 5 Tesla) and temperatures down to 6 K.  The areas of investigations range from magnonics and ultrafast magnetic switching in magnetic nano-structures to phase change materials. 

Scatterometer system

An optical system for imaging the angle-dependent and polarisation-dependent reflection or transmission scattering from the entire hemisphere above or behind a sample, and in this way measuring it reflection distribution function. 

300 kHz ultrafast regenerative amplifier system

A 300 kHz regenerative amplifier system is used for pump-probe and other non-linear optical measurements.  Micro-Joule pulses of less than 80 fs duration are generated  at 800 nm wavelength.  Visible and near-infrared optical parameteric amplifiers, a difference frequency generator, and various doubling units allow pulses to be generated with wavelength ranging from the ultraviolet to the infrared.  Spectrometers, beam profilers, autocorrelators, and a Spectral Phase Interferometry for Direct Electric-field Reconstruction (SPIDER) instrument are available for beam characterization.  The seed oscillator is equipped with a synchrolock unit to facilitate phase locking to other instruments.

Time resolved X-ray measurements

Synchrotron radiation sources are inherently pulsed and can be used to perform time resolved measurements that complement our in-house optical pump-probe capability.  We have developed a phase resolved x-ray Ferromagnetic Resonance (XFMR) measurement technique at the Diamond Light Source (DLS) near Oxford and at the Advanced Light Source in Berkeley, California.  We are also working on the development of time resolved x-ray photoemission electron microscopy (XPEEM) measurements at DLS that offer wide field imaging with sub-100 nm spatial resolution.

Magneto-optical Kerr effect magnetometer

An optical magnetometer for the acquisition of magnetic hysteresis loops.  Continuous film samples can be characterized using the polar, longitudinal, and transverse magneto-optical Kerr effects and the magneto-optical Faraday effect (transparent samples only).  The samples are probed using a continuous wave laser (wavelength = 633 nm), while the magneto-optical effects are detected using a balanced photodiode polarizing bridge detector.  Hysteresis loops may also be acquired from microscale samples (including arrays of nanoscale samples) using a scanning Kerr microscope equipped with a high numerical aperture objective lens and a quadrant photodiode polarizing bridge detector.  The microscope allows three components of the magnetization vector to be detected simultaneously yielding hysteresis loops for the component of magnetization parallel and perpendicular to the applied external field.

Small- Angle Neutron Scattering (SANS) and Polarised Neutron Reflectivity (PNR)

We use neutron scattering techniques to probe the magnetic structure of magnetic thin films and superconductors. The experiments are performed at neutron radiation sources such as ISIS (beamline ‘CRISP’, Rutherford Laboratory, UK), ILL (beamlines D17, D11 and D22, Grenoble, France). The measurements can be performed with variable temperatures and magnetic field.

Soft X-ray Magnetic Resonance Scattering (SXRMS)

We are regular users of synchrotron radiation facilities.  X-ray spectroscopy and scattering techniques are used to investigate magnetic correlations in thin films and interfaces. The techniques are based on the effect of x-ray circular magnetic dichroism (XMCD) probing the magnitude and the orientation of the local magnetic moment. An element specific analysis is possible by tuning to the corresponding absorption edge of the material. Experiments are carried out at beam-lines I10 (Diamond Light Source, UK) and ID08 (ESRF, Grenoble, France). Measurements can be performed in reflective geometry with either a point detector (‘theta-two theta’  dependence) or a CCD (off-specular, 2D  scattering). Variable temperature and field environments are available to suit specific magnetic configurations.

X-ray Magnetic Holography

Soft X-ray highly coherent light at the 3rd generation synchrotron sources is used to perform holographic imaging of magnetic domains in magnetic thin films and multilayers.  In collaboration with I06 instrument support group (DLS) we have developed an experimental set-up for holographic measurements in transmission and grazing incidence geometry. Element specific measurements can be performed as function of magnetic field (currently up to 2 kG) imaging the perpendicular (to the surface) component of magnetisation within 1-2 micron field of view with the resolution of 40nm. Our experiments  are also carried out at other synchrotron sources:  beamline STG52 (BESSY, Berlin, Germany), BL13-3 (SSRL, Stanford, USA).  An optical holography set-up is also availbale to investigate different regimes of structural holography and sample geometry to inform measurements on X-ray sources. The optical set-up uses  a visible light laser source, and can be performed in both transmission and reflection geometry.

Torque magnetometry

A cantilever torque magnetometer is used to investigate magnetic anisotropy and demagnetising fields of thin films and nanostructures. The system is based on a 7 Tesla superconducting magnet cryostat (‘MagLab - 8’, Oxford Instruments) with a variable temperature insert ( 1.4-300K).  The temperature is maintained through a PID regulated needle valve maintaining minimum mechanical vibrations. The measurements are automated via a LabView interface and can be programmed to combine temperature-field-angle regimes. The cryostat has a capability to work with other experiments, including  magneto-resistive measurements, using separate inserts and the corresponding electronic equipment.

Computational

Numerical and analatical modelling

We are advanced users of Ansoft HFSS and Comsol Multiphysics for finite element method (FEM) modelling of electromagnetic and acoustic systems.  Differential methods for predicting the response of multilayered corrugated surfaces (diffraction gratings) have been developed, together with modal matching analytical techniques for predicting the response of well-defined photonic structures. Our team have expertise in the development of finite difference time domain (FDTD) methods for predicting the response of advanced photonic materials, including the incorporation of the Landau-Lifshitz-Gilbert equation for the study of magnetic materials.

Micromagnetic modelling of magnonic phenomena

The ability to accurately predict properties of magnetic nano-structures and devices theoretically would generate huge savings of resources, but remains elusive at present. Hence, micromagnetic modelling has become a growing area of research in Exeter. Dynamical phenomena, such as spin waves in magnetic nanostructures (magnonics) and Bose-Einstein condensation and generally kinetics of magnons, are in the focus, set by the related experimental activity. 

FPGA programming suite

Modern field-programmable gate arrays (FGPAs) halp to simplify and accelerate the process of development and upgrade of complex electronic boards. The schematics can be changed with software only, no actual PCB/network retracing needed. We are able to develop Xilinx(TM) FPGA functionality, program it to an FPGA chip, and test/debug the device behaviour.  This suit can be used in all fields of experiment control and data acquisition, from photon counters to fast image sensors.

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