Periodic Report Summary 2 - FUNPROB (Functional semiconductor nanowire probes)
Project Summary
Scanning probe microscopy (SPM) is an established technique for the characterisation of materials and structures at the nanoscale and is increasingly bridging traditional disciplines including the biosciences. As such, it is of fundamental and practical interest across the sciences and industry. The geometry of the tip is the critical factor which determines the resolution of an SPM sensor. In an attempt to achieve ultra-high spatial resolution, carbon nanotubes have been widely investigated and shown some promise. However, it is extremely difficult to control the properties of these tubes, especially the electrical behaviour and growth geometry. Equally, their manipulation is a daunting task. We propose to use III-V semiconductor nanowires as functioning sensors at the apex of scanning probes. These structures can be directly grown on the substrates or SPM cantilevers with controllable properties at the nanometre scale. Using these nanowires offers excellent new avenues for the integration of established semiconducting devices onto the tip of a scanning probe. This will improve the sensitivity and functionality of scanning probe methods. An example of potential applications for such a novel probe is the detection of viruses based on their electrical response which can be coupled to that of nanowires under appropriate conditions. Within the framework of this project, we will combine the complementary expertise of various internationally leading institutions for the creation of integrated individual semiconductor nanowire SPM probes exhibiting enhanced functionalities.
Objectives
The research objectives listed be were successfully implemented, leading to more than 80 journal publications.
- To controllably grow III-V NW and to characterise individual III-V NWs including their electrical, mechanical, optical and thermal properties. This should include the characterisation of NWs with dielectric barriers which could form the basis of future nano memory arrays.
- To undertake fundamental investigation of the growth of III-V NWs on complex substrates. This will include amorphous, patterned, oxidised and etched substrates. In particular, the growth of wires on micro pillars and from recessed holes. The investigation will include the morphological, crystallographic, chemical, electrical and optical properties of the NWs.
- To model the growth mechanism with the view to identifying and implementing the optimal growth conditions which will enable the international team to fine tune the properties of the NW so produced.
- To develop theoretical models that will not only facilitate the interpretation of the data but also optimise both the growth and the fabrication of the SPM probe.
- To fabricate a versatile ultra-high resolution thermal probe capable of simultaneously recording optical and electrical properties. This takes advantage of the very small size of NWs (a few nanometres in diameter) and their well-defined structure (i.e. high aspect ratio).
- To address their integration into a scanning probe using purposely designed substrates. Although nanowires have already demonstrated exceptional sensitivity, they have not yet been successfully integrated in a SPM probe configuration because of the on-going difficulty to manipulate them.
- Integration in a scanning probe will reduce mechanical stress exerted on the nanowires, therefore rendering the sensors more robust and expanding the range of applications.
- To enable the electrical detection individual viruses based on the known phenomena of the variation their conductivity with adsorption. This will investigate the chemical and biological environment likely to facilitate immobilisation of antibodies onto the nanowire probe, to enhance the electrical response of a virus under thermal and optical excitation.
Scanning probe microscopy (SPM) is an established technique for the characterisation of materials and structures at the nanoscale and is increasingly bridging traditional disciplines including the biosciences. As such, it is of fundamental and practical interest across the sciences and industry. The geometry of the tip is the critical factor which determines the resolution of an SPM sensor. In an attempt to achieve ultra-high spatial resolution, carbon nanotubes have been widely investigated and shown some promise. However, it is extremely difficult to control the properties of these tubes, especially the electrical behaviour and growth geometry. Equally, their manipulation is a daunting task. We propose to use III-V semiconductor nanowires as functioning sensors at the apex of scanning probes. These structures can be directly grown on the substrates or SPM cantilevers with controllable properties at the nanometre scale. Using these nanowires offers excellent new avenues for the integration of established semiconducting devices onto the tip of a scanning probe. This will improve the sensitivity and functionality of scanning probe methods. An example of potential applications for such a novel probe is the detection of viruses based on their electrical response which can be coupled to that of nanowires under appropriate conditions. Within the framework of this project, we will combine the complementary expertise of various internationally leading institutions for the creation of integrated individual semiconductor nanowire SPM probes exhibiting enhanced functionalities.
Objectives
The research objectives listed be were successfully implemented, leading to more than 80 journal publications.
- To controllably grow III-V NW and to characterise individual III-V NWs including their electrical, mechanical, optical and thermal properties. This should include the characterisation of NWs with dielectric barriers which could form the basis of future nano memory arrays.
- To undertake fundamental investigation of the growth of III-V NWs on complex substrates. This will include amorphous, patterned, oxidised and etched substrates. In particular, the growth of wires on micro pillars and from recessed holes. The investigation will include the morphological, crystallographic, chemical, electrical and optical properties of the NWs.
- To model the growth mechanism with the view to identifying and implementing the optimal growth conditions which will enable the international team to fine tune the properties of the NW so produced.
- To develop theoretical models that will not only facilitate the interpretation of the data but also optimise both the growth and the fabrication of the SPM probe.
- To fabricate a versatile ultra-high resolution thermal probe capable of simultaneously recording optical and electrical properties. This takes advantage of the very small size of NWs (a few nanometres in diameter) and their well-defined structure (i.e. high aspect ratio).
- To address their integration into a scanning probe using purposely designed substrates. Although nanowires have already demonstrated exceptional sensitivity, they have not yet been successfully integrated in a SPM probe configuration because of the on-going difficulty to manipulate them.
- Integration in a scanning probe will reduce mechanical stress exerted on the nanowires, therefore rendering the sensors more robust and expanding the range of applications.
- To enable the electrical detection individual viruses based on the known phenomena of the variation their conductivity with adsorption. This will investigate the chemical and biological environment likely to facilitate immobilisation of antibodies onto the nanowire probe, to enhance the electrical response of a virus under thermal and optical excitation.