The Nanoanalysis Group is focussed on the development of spectroscopic and scanning probe techniques to characterise a material’s microstructure and properties.

Research themes

Degree of Molecular Order

order

Ordering of molecules in semiconducting materials can have significant effects on their optoelectronic properties. For example, thin films of regioregular poly(3-hexylthiophene) (RR-P3HT) can exhibit a high degree of molecular order (π–π stacking of molecules). This high degree of molecular order can lead to an increase in absorption at longer wavelength and a dramatic increase in charge carrier mobility as compared to its disordered form. Understanding of this molecular order is important to clarify the structure–property relationship in thin films and to make use of these thin films as active layers in various devices.

  • Exact determination of local molecular order
  • Advantages over X-ray based techniques

Please read more:

Faraday Discuss., 2014,174, 267-279

J. Am. Chem. Soc., 2011, 133 (25), pp 9834–9843

ACS Nano, 2012, 6 (11), pp 9646–9656

J. Mater. Chem. C, 2013,1, 6235-6243

Chemical Compositions

Chemical Composition

Micro-Raman mapping allows the relative composition to be inferred from the strength of characteristic Raman peaks in order to build up a two-dimensional spatial map of composition. The technique also reveals variations in polymer chain conformation through shifts in the position and changes in the relative intensity of the Raman peaks.

Please read more:

Macromolecules, 2010, 43 (3), pp 1169–1174

Electrical stability

electstab

Although much progress has been made in improving polymer light-emitting diode performance, there has been little work to address device intrinsic degradation mechanisms due to the challenge of tracking minute chemical reactions in the 100-nm-thick buried active layers during operation. Here we have elucidated a hole-mediated electrical degradation of triarylamine-based blue polymer diodes using in situ Raman microspectroscopy.

Please read more:

Chem. Phys. Lett. 386 (2004) 2-7

In-situ monitoring of phase changes

In sITU

In situ simultaneous monitoring of molecular vibrations of two components in organic photovoltaic blends can be acheived using resonant Raman spectroscopy. Changes in Raman spectra associated with crystallizationprocesses of each component of a blend and their impact on thin film morphology can be studied during thermal annealing and cooling processes.

Please read more:

Appl. Phys. Lett. 102, 173302 (2013)

Molecular Orientation

Molecular Orientation

In addition to being nondestructive, Raman spectroscopy uses a small excitation laser spot size (∼1 μm), allowing the localized, intragrain structural properties of the large (>10 μm) crystalline domains observed here to be investigated. Polarized Raman spectroscopy has previously been demonstrated as an effective local probe of molecular orientation and order for a range of organic semiconductor films, including strained graphene monolayers, TIPS-pentacene, and oligothiophenes. Polarized Raman plots for are generated by recording the Raman scattering intensities of selected modes at each polarization rotation angle.

Please read more:

http://pubs.acs.org/doi/full/10.1021/nn403073d

Natures of Electronic Transitions

Electronic Transitions

A strong resonant enhancement in the Raman scattering intensity occurs when the energy of the excitation photon matches the energy of a dipole-allowed electronic transition of the molecule. This enhancement is observed for those Raman-active vibrational normal modes which map onto the geometric distortion of the molecule accompanying the electronic transition. In order to elucidate the natures of the different electronic transitions we can use 457 and 785 nm excitations, which allow us to selectively probe the high and low energy absorption bands.

Please read more:

Energy Environ. Sci., 2015, Advance Article

Photostability

Photostability

We can probe the effect of photodegradation on the molecular structure of polymer chains in order to understand how different units react with with oxygen and light at molecular level. RBy comparing experimentally observed Raman spectra to theoretical spectra obtained from Density Functional Theory (DFT) simulations of likely degradation products, we identify the nature of photo-oxidised species. This information can assist the development of analogue polymers modified to hinder or avoid that degradation process, potentially allowing the fabrication of high-efficiency long-lifetime OPV devices.

Please read more:

J. Mater. Chem. A, 2014, 2, 20189-20195

Nanometrology Tools

Confocal Raman- AFM Spectroscopy

Raman spectroscopy is a vibrational spectroscopy based on a molecule's polarisability. Raman spectroscopy relies on the inelastic scatter of light via a virtual excited state, leaving a molecule in excited vibrational state. Using Raman spectroscopy we can detect the chemical composition of a sample, the molecular conformation and molecular orientation. We can also use it to probe the nature of different excited states.

R

5 laser excitation wavelengths (457 - 785 nm)
Steamlined 3D mapping
Angle dependent polarisation control
Confocal fluorescence
Surface Enhanced Raman Spectroscopy (SERS)
Tip Enhanced Raman Spectroscopy (TERS)
In Situ Pressure Dependent Raman Spectroscopy
In Situ Temperature Dependent Raman Spectroscopy (77 - 600 K)
In Situ Device Operation
In Situ Cyclic Voltammetry
In Situ Electrochemical Degradation

UV-Excitation Source

Summary of the table's contents

 Please Read More:

Raman Review, SERS application.

 

 

Scanning Probe Microscopy

Scanning Probe Microscopy lets us map the surface features of our thin film structures. We can generate images of our microstructures with nanometre resolution, which allows us to see the nature of different domains. Depending on the 'mode', we can image different magnetic domains, the response of a surface to charge injection or how conductive the samples are.

AFM

Non-Contact Atomic Force Microscopy
Tapping Mode Atomic Force Microscopy
Scanning Kelvin Probe Microscopy
Conductive Atomic Force Microscopy
Magnetic Force Microscopy
Piezo Force Microscopy
Summary of the table's contents

Ellipsometry

We have a range of other nanoanalysis techniques to let us look at the vibrational and electronic energy levels of materials. We can track the formation of excitons through our materials and blends.

E

Fourier Transform Infrared Spectroscopy
UV-Visible Absorption Spectroscopy
Polarized UV-Visible Absorption Spectroscopy
Photoluminescence
Transient Absorption Spectroscopy
 
Variable Angle Spectroscopic Ellipsometry
Illumination wavelengths (200nm-20um) 
Spectroscopic Ellipsometry
FT-IR Ellipsometry & Spectroscopy
Summary of the table's contents

KP, SPS and APS

The APS-04 allows us to perform three different measurement techniques. Firstly the Kelvin Probe accurately measures the workfunction of metals or semiconductors by applying a backing voltage to a vibrating gold tip that sits millimetres above the sample and interpolating when the workfunctions of the two materials are aligned. Air photoelectron spectroscopy (APS) allows direct measurement of workfunction (metals) or valence band/HOMO energy levels (semiconductors) by irradiating the sample with UV light. The photoelectrons then ionise air molecules which are detected by the gold tip. Surface photovoltage spectroscopy (SPS) allows the response of a photoactive material to be obtained by irradiating the sample with different wavelengths from a quartz-tungsten-halogen (QTH) source. The photogenerated charges produce a shift in workfunction that is measured by the Kelvin probe.

APS

QTH source has wavelength range from 400-1000 nm.
In-situ temperature stage (293-500K)
UHV cube for air sensitive samples
APS allows density of states (DoS) measurement.
APS energy range: 3.4 eV - 7.0 eV (360 nm - 176 nm)
50μm gold tip available for higher resolution scanning kelvin probe microscopy measurements