‘Monolayer functionalization of silicon micro and nanowires: towards solar-to-fuel and sensing devices’
Silicon is an attractive semiconductor, especially when taking advantage of the larger surface area of silicon micro and nanowires. This thesis aims at the formation of molecular monolayers on H-terminated silicon micro and nanowires, for solar-to-fuel and sensing devices.
‘Surface functionalization with self-assembled monolayers can tune a substrate towards a desired application,’ Janneke Veerbeek explains. ‘Solar-to-fuel and sensing devices can highly benefit from oxide-free monolayers. (Silicon oxide layers function as an insulating layer, and thus retard electrical contact with the substrate.)’
The versatility of molecular monolayers on H-terminated silicon structures was described. ‘This can be used for the fabrication of solar-to-fuel devices,’ Janneke says. ‘Further, covalent and non-covalent immobilization of catalysts on surfaces was studied. Different catalysts can be coupled onto the same device via spatio-selective functionalization.’
For sensing devices new perspectives for stabilized silicon micro/nanosystems were opened this way. ‘More functionalities can be engineered now,’ according to Janneke. Oxide-free monolayers establish a higher stability of the sensor, owing to the direct Si-C bonds. Further a higher sensitivity is possible - due to the selective functionalization of the sensing area - and higher specificity, when using supramolecular chemistry to make an analyte-specific sensor.
The PhD work of Janneke Veerbeek fits very well within worldwide efforts to harvest hydrogen from sunlight in a one-step device. ‘Developing specialized monolayers and increasing reaction areas by using nanowires, can be viewed as intermediate stages towards this ultimate goal,’ Janneke says.
Janneke: ‘In my research, it took a while before promising results appeared. This is not a big problem since not-hoped for results are inevitable in dealing with novelties and innovative approaches. But finally observing that in solar-to-fuel cells efficiency benefits with several percentage points, are within reach, just because of one self-assembled monolayer, is fascinating. We used a theoretical model to fit in the experimental data and tried to explain the phenomena underlying these processes. This led to a publication in ACS Applied Materials and Interfaces.’
The PhD thesis chapters on functionalized monolayers in sensors came about as an extra topic, as her PhD work progressed.
‘Adding catalysts without disturbing the conductivity – so: without inadmissible insulating effects – is a promising and powerful tool,’ Janneke says. ‘It also reflects, I believe, me growing in creativity and self-confidence in the course of the PhD project. While working towards results one has to prove flexibility at some stages in research: carefully choosing your research directions and routes, but always being openminded towards intermediate results and unexpected outcomes. This can lead to new and promising views.’
Janneke collaborated with several MESA+ Groups. In producing the solar-to-fuel devices the input of the Mesoscale Chemical Systems Group, led by Professor Han Gardeniers, was very useful, as was the expertise on catalysts by the PhotoCatalytic Synthesis Group, led by Professor Guido Mul.
‘It is a great advantage that lots of interdisciplinary collaborations take place within one and the same institute,’ Janneke says. ‘My promotor, Professor Jurriaan Huskens of the Molecular NanoFabrication Group, is involved in quite some overlapping meetings at Mesa+, thus facilitating cross-group collaborations. For me as a researcher it is inspiring, and refreshing, to meet colleagues from different backgrounds. From time to time they come up with seemingly trivial questions, forcing you to clearly explain your field of expertise or, sometimes, to question in a critical way your own assumptions from which you proceed research. The open atmosphere within MESA+ is an important facilitator in this kind of collaborations.’
Following her PhD, Janneke will be working as an R&D scientist at Surfix, a spin-off company of Wageningen University in the Netherlands.
Janneke: ‘My work in the lab will be on surface chemistry as well. My expertise fits very well with the needs of the company. The timing was just perfect. I am looking forward to performing more application oriented research, turning the customer’s needs into promising and practical research projects.’
To observe that in solar-to-fuel cells efficiency benefits with several percentage points, are within reach, just because of one self-assembled monolayer, is fascinating.
Adding catalysts without disturbing the conductivity – so: without inadmissible insulating effects – is a promising and powerful tool.
Intermediate results and unexpected outcomes can lead to new and promising views.
From time to time colleagues come up with seemingly trivial questions, forcing you to clearly explain your field of expertise or, sometimes, to question in a critical way your own assumptions from which you proceed research.
In my future job, my expertise fits very well with the needs of the company. I am looking forward to performing application oriented research, turning the customer’s needs into promising and practical projects.