3D Nanomaterials: Fabrication, Properties and Smart Applications
By Reza Abolhassani
Nanoscale materials with multifunctional properties have received increasing interest in scientific and industrial communities because of their versatile applications in advanced technologies. A new class of nanomaterials, so called smart materials, has been recently emerged as very potential candidates for various applications because of their capability to self-respond to any external stimuli (e.g. stress, temperature, light, electric or magnetic field, deformation, electrochemical, pH, etc.) by altering their one or more properties in form of a reliable read out signal. Their extensive applications in healthcare, aerospace, automotive, electronic, smart polymers, smart textile, sensors, medicine, and etc. makes it essential to study and research on this young novel technology. Nanomaterial fabrication in the desired compact form is the most important prerequisite for any scientific and technological development, and nowadays, the key challenge is to design the nanomaterial in 3D complex smart forms which are equipped with right functions and simultaneously are easy to utilise.
The aim of this PhD project is to synthesise 1D ZnO nanostructures based complex shaped nanostructures and selectively surface engineering of arm morphologies using state-of-the-art micro- and nanofabrication methods for enhancing their optical, electronic, chemical, and mechanical properties which will be carefully characterised, analysed, and understood. The structure-property relationships of these materials will be understood, and they will be explored for applications in various smart technologies in direction of optics, catalysis, energy, sensing, and smart textiles, and they will be utilised for various possible applications.
Supervisor: Yogendra Kumar Mishra
High-accuracy prediction of meat expiration dates by overcoming non-linearity barriers for microcantilever biosensors
By Lawrence Nsubuga
There is a yearly waste of 137,500 tons of meat and fish products in Denmark, of which about 43,000 tons are wasted due to overly careful expiration date estimations, resulting into high carbon emissions. Today households, restaurants, catering, and food stores rely on the printed expiration date, which is based on general prediction curves for meat degradation. For example, for pork cuts at 5°C under aerobic conditions the prediction curve says 8 days (+/-) 3 days. So, to be on the safe side, expiration dates are set to 5 days. The only means to control actual freshness of meat products are microbiological tests conducted at external laboratories requiring shipping of samples, growing, and counting bacteria. Such tests are seldomly carried out, since they are expensive (app. 335 € /sample), time consuming (48 hours) and do not predict the exact expiration date. There are other analysis methods available, but they all need to be carried out at external laboratories, e.g., measurement of cadaverine levels using gas chromatography mass spectrometry. Cadaverine is a volatile biogenic amine providing an exact measure for meat spoilage level. The amount of cadaverine gas increases in a predictable way over time depending on the type of meat. This PhD project proposes to realise great potential for CO2 reduction, by development of a biosensor for cadaverine in meat, enabling on-site highly accurate prediction of meat expiration dates. The main objective is to develop a biosensor enabling precise measurements of low levels of cadaverine and use this to predict meat expiration dates. Very small differences in cadaverine levels, at an early deterioration stage, translates into large differences with respect to expiration date. Therefore, it is a strict requirement that the biosensor enables high-accuracy measurements of +/- 10% at low levels of cadaverine, down to 10μg per kg of meat. To achieve this, we must overcome current state-of-the-art barriers; that microcantilevers provide nonlinear responses and that mathematical response processing models for nonlinearity compensation are lacking. The research hypothesis is that an array of microccntilever beams in different sizes or with different coatings, leading to different characteristic frequency modes, will enable dynamic real-time monitoring of an array of constants that can be fed into a mathematical model developed for non-linearity compensation.
Supervisor: Roana Melina de Oliveira Hansen
The stretchable OLED display
By Jes Linnet
Flexible optoelectronic devices such as light-emitting diodes (LEDs) typically consist
s of a multilayer structure deposited on a flexible substrate. The active layers are often based on organic semiconductors that can be made with excellent optoelectronic properties and have some mechanical flexibility. Several companies are developing flexible OLEDs for displays and lighting. However, such devices are only bendable, but they are not stretchable: they can be bent to a certain radius of curvature, but pure strain beyond a few percent will lead to immediate failure, and they can therefore not be mounted on a 3D-surface. The aim of this project is to develop stretchable organic light-emitting diodes and ultimately realize a business card-sized display. The approach in this project, to resolve the strain limitation, is based on a substrate with specially designed surface corrugations. Upon stretching the substrate, these corrugations flatten out, and locally the surface only bends. The outcome will be OLEDs that can conform 3-dimensional surfaces for lighting and display applications within a range of product areas. The specific objectives are to design and develop an elastomeric substrate with a surface corrugation pattern that allows substrate stretching without significant surface strain and to realize an OLED display layer stack on top consisting of a transparent bottom electrode, a sandwich structure of several organic semiconductor materials for hole/electron balancing and light emission, and a top electrode. Furthermore, an encapsulation solution will be developed and implemented to protect against degradation that results from exposure to ambient conditions. This project is an industrial PhD project; a collaboration between SDU and Polyteknik.
Supervisor: Jakob Kjelstrup-Hansen
Graphene-Organic Semiconductor Heterostructures for Photodetector Applications
By Cecilie Clausen Fynbo
Graphene-organic semiconductor heterostructures have been proposed as highly efficient organic phototransistors. These heterostructures exploit the high charge mobility in graphene and the optical-spectral-sensitivity of organic semiconductors to obtain high quantum efficiency and high bandwidth. Fabrication of such structures is typically a two-step procedure where the graphene layer is synthesised and transferred to a substrate followed by deposition of the organic semiconductor material. The growth of the organic semiconductor film and the quality of the graphene layer are the limiting factors of such a device as the microscopic morphology, crystal quality, and the interfacial properties of the organic semiconductor film greatly affect the performance of the organic phototransistor. Fortunately, epitaxially grown organic crystals on graphene show highly oriented molecular structures as well as defect-less surfaces. Most reported graphene-organic semiconductor phototransistors use organic semiconductors with absorption in the visible spectrum, only a few have developed devices with absorption in the near infrared regime. One of the materials used in such a device is the fullerene C60. However, C60 molecules have shown to be photochemically instable and responsible for degradation mechanisms in organic solar cells. Therefore, it is suggested to use different diketopyrrolopyrrole-based oligomers and polymer to fabricate graphene-organic semiconductor phototransistors able to detect near infrared light. This project investigates the possibilities of graphene-organic semiconductor heterostructures as these structures are expected to have promising photodetector applications. The aim is to create an organic phototransistor with a high response time and high photoresponsivity, however, these two performance parameters are often a trade-off. To obtain such a device it is critical to minimise the defects in graphene and maximise the absorption and exciton diffusion in the organic semiconductor film which can be done by optimising the molecular alignment. Additionally, the electrode design and organic semiconductor film thickness should also be optimised as they affect the transit time of the photocarriers and the performance criteria of the device, respectively.
Supervisor: Jakob Kjelstrup-Hansen
Applications of Hyperspectral Thermal Imaging
By Mads Nibe Larsen
Infrared thermography is an imaging technique that records long-wave infrared light (8 – 14 µm) and it is often used for remote temperature determination of objects by measuring the amount of thermal radiation they give off. However, different materials have different emission spectra, and the camera must be calibrated to the specific material being imaged. A hyperspectral thermal imaging system can record spectra of every element in the scene, making it possible to segregate multiple materials simultaneously and determine their temperature. This project utilizes a first-order scanning Fabry-Pérot Interferometer (FPI) combined with a thermal camera to capture hyperspectral thermal images. The objective of the project can be split in two: Firstly, an existing prototype of the imaging system must be improved enough that it can become the world’s first commercially available FPI based hyperspectral thermal camera. This includes integration of RGB data in order to incorporate parts of the visible spectrum for improved data analysis. Furthermore, since hyperspectral imaging in the thermal regime is a relatively new and untested technique, finding new applications and associated data analysis tools is a priority. Examples could be detecting and identifying different organic gasses or detect wear and defects in buildings. Secondly, a new thermal radiation sensor will be developed. The highest performing commercially available solutions are very expensive and require cryogenic cooling such as Mercury Cadmium Telluride (MCT) detectors. Microbolometers are a less expensive alternative which do not require additional cooling, but they are, however, much less sensitive. The aim is to fabricate an uncooled graphene field-effect transistor, which utilizes the excellent bolometric properties of graphene and combines it with a partially reflecting Bragg mirror. The graphene is suspended inside a reflecting cavity formed by the mirror and a gold coated substrate, which allow incoming radiation to pass through the graphene multiple times, hereby increasing the probability of absorption. The aim is to fabricate a single pixel detector which will indicate the feasibility of future development of an entire graphene-based focal plane array. This is an industrial PhD-project carried out as a collaboration between Newtec Engineering A/S and SDU.
Supervisor: Jakob Kjelstrup-Hansen