Matthew Alexander

Dr Matt Alexander was awarded a PhD from the Corrosion and Protection Centre, University of Manchester in 2000, and after a position as research engineer at BP Amoco, he then joined the Physical Electrochemistry Group, University of Bristol to conduct research into novel diamond electrode devices.

In 2001 he joined the Electrospray Research Group, Queen Mary University of London as a post-doctoral research assistant before taking up a lectureship position in Energy Engineering at Queen Mary, with specialism in electrospray technology.

In his leading role within the electrospray group at Queen Mary, Dr Alexander’s work led directly to the exciting discovery of new electrospray pulsating spray modes which have been shown capable of the controlled ejecting minute volumes of fluid for use in material deposition and high accuracy dispensing applications and have resulted in several patent applications and the formation of the spin-out company Emdot Ltd in 2007, with Dr Alexander as academic founder. His senior role within the company has led to extensive links with major stakeholders throughout the printing sector and in-depth experience of inkjet technology, markets and future opportunities.

In 2008 he was winner of the Royal Academy of Engineering ERA foundation entrepreneur prize. This award was in recognition of the significant potential of the novel printing technology to bring future economic benefits to the UK.

Dr Alexander has more than 14 years of research experience in the field of electrospray technology and he returned to academia in 2013 to take a lectureship position in Energy Engineering at the University of East Anglia where he now looks to further develop his research strategy in electrospray and electrostatic atomisation technology

High-Resolution Electrostatic Inkjet Printing

While inkjet printing has proven suitable for many direct writing applications, the size of the generated features cannot easily be reduced below a few tens of micrometers. It is possible to obtain smaller feature sizes by scaling the size of the inkjet nozzle down to micrometer diameters but this leads to nozzle clogging. The accuracy of droplet placement is limited by the free trajectory of the ejected droplet which is vulnerable to disturbances. As a result, the best printing accuracy so far reported has been 5mm. Inkjet printing as a direct writing method for electronics is therefore limited by the problems of multi-layer accuracy and the difficulty of avoiding clogging if smaller drops are needed. Clearly then there exists a capability gap between the high resolution at high costs of photolithography and the low cost but low resolution of inkjet printing.

Electrospray occurs when the electrostatic force on the surface of a liquid overcomes the surface tension and is most commonly used today as a source of gas phase ions in mass spectrometry, where it has transformed the analysis of large biomolecules. The most studied and most stable form of the process is the cone-jet regime, wherein the balance between electrostatic stresses and surface tension creates a Taylor cone, from the apex of which a liquid jet is emitted. The use of standard electrospray as a direct printing technique would have to overcome severe technical obstacles. The foremost of these is flow control as in traditional electrospray operation the supply of fluid to the spray cone is controlled either by a pump or by using a pressure head and cannot be rapidly controlled to stop or start the spray.

Nanoelectrospray, in its simplest form, is when the electrospray flow rate is exclusively controlled by the applied voltage. One of the benefits of nanoelectrospray is that very low flowrates are easily achieved by selection of the correct nozzle and liquid combination. In previous work we identified new modes of electrospray called pulsating nanoelectrospray (Alexander MS et al, 2006) which allows the controlled ejection of minute volumes of liquid, as low as sub-femtoliter, which may be used to pattern surfaces with micron-sized features (Paine,  M. Alexander, MS. Stark, JPW. 2007)

This equates to a 10-fold advancement in print resolution over current inkjet technology and our research focus is on the further development of the nanoelectrospray printing technique as a key enabling tool for numerous applications

Figure 1 A) High speed images of jet formation and collapse on a 50um nozzle, B) Fluorescent microscopy image of patterned 2D albumin feature with line width of ~8µm

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