This study uses clusters formed in a UHV-compatible cluster apparatus, which was built and commissioned during this thesis. The design and operation of the cluster deposition system is described. This system is optimised for high clus- ter fluxes and for the production of cluster assembled nanoscale devices. One key feature of the system is a high degree of flexibility, including interchangeable sputtering and inert gas aggregation sources, and two kinds of mass spectrome- ter, which allow both characterisation of the cluster size distribution and deposi- tion of mass-selected clusters. Another key feature is that clusters are deposited onto electrically contacted lithographically defined devices mounted on an UHV- compatible cryostat cold finger, allowing deposition at room temperature as well as at cryogenic and at elevated temperatures. The electrically contacted nanoscale cluster devices were fabricated using a novel template technique. Hereby, clusters are placed between two electrodes separated only by ∼100 nm. The width of the cluster ensemble is in the order of a few cluster diameters, which means that the assembled clusters form a cluster wire bridging the electrode separation. During this thesis, the design and layout has been optimised to be able to measure electrical properties of the cluster devices and in particular to investigate the interaction between the cluster ensemble and the contact electrodes. In-situ electrical characterisation of cluster assembled nanoscale devices are performed in the temperature range 4.2 K to 375 K. The samples are provided with a backgate, which in principle allows modification of the conduction through the cluster ensemble by applying a gate voltage. However, no change in conduc- tion with changes in gate voltages was seen. The main focus of the electrical measurements is on the current voltage char- acteristics. It was noticed that the nanoscale bismuth (and antimony) cluster devices exhibited non-linear current voltage characteristics, which were in stark contrast to the linear current voltage characteristics measured for cluster films previously. Investigations into the causes of this non-linearity suggests that tun- nelling conduction occurs between the cluster ensemble (wire) and the contact electrodes. The non-linear current voltage characteristics were fitted using three models of tunnelling conduction and appear to be best fitted using a model in- volving fluctuation-assisted tunnelling through barriers of different heights. Further, measurements of the temperature dependent resistance are performed showing an increase of resistance with decreasing temperature for bismuth and antimony assembled cluster devices. The temperature dependence of bismuth as- sembled cluster wires can be explained by the decrease of the carrier concentration in bismuth for decreasing temperature. Annealing of the cluster ensemble and the cluster contact connection resulted in an increase in conduction. This increase of conduction can be explained due to the current flow through the cluster wire. Locally, at the bottlenecks, the current flow causes resistive heating and subsequently coalescence of two (or more) clusters.

No description available.

This study uses clusters formed in a UHV-compatible cluster apparatus, which was built and commissioned during this thesis. The design and operation of the cluster deposition system is described. This system is optimised for high clus- ter fluxes and for the production of cluster assembled nanoscale devices. One key feature of the system is a high degree of flexibility, including interchangeable sputtering and inert gas aggregation sources, and two kinds of mass spectrome- ter, which allow both characterisation of the cluster size distribution and deposi- tion of mass-selected clusters. Another key feature is that clusters are deposited onto electrically contacted lithographically defined devices mounted on an UHV- compatible cryostat cold finger, allowing deposition at room temperature as well as at cryogenic and at elevated temperatures. The electrically contacted nanoscale cluster devices were fabricated using a novel template technique. Hereby, clusters are placed between two electrodes separated only by ∼100 nm. The width of the cluster ensemble is in the order of a few cluster diameters, which means that the assembled clusters form a cluster wire bridging the electrode separation. During this thesis, the design and layout has been optimised to be able to measure electrical properties of the cluster devices and in particular to investigate the interaction between the cluster ensemble and the contact electrodes. In-situ electrical characterisation of cluster assembled nanoscale devices are performed in the temperature range 4.2 K to 375 K. The samples are provided with a backgate, which in principle allows modification of the conduction through the cluster ensemble by applying a gate voltage. However, no change in conduc- tion with changes in gate voltages was seen. The main focus of the electrical measurements is on the current voltage char- acteristics. It was noticed that the nanoscale bismuth (and antimony) cluster devices exhibited non-linear current voltage characteristics, which were in stark contrast to the linear current voltage characteristics measured for cluster films previously. Investigations into the causes of this non-linearity suggests that tun- nelling conduction occurs between the cluster ensemble (wire) and the contact electrodes. The non-linear current voltage characteristics were fitted using three models of tunnelling conduction and appear to be best fitted using a model in- volving fluctuation-assisted tunnelling through barriers of different heights. Further, measurements of the temperature dependent resistance are performed showing an increase of resistance with decreasing temperature for bismuth and antimony assembled cluster devices. The temperature dependence of bismuth as- sembled cluster wires can be explained by the decrease of the carrier concentration in bismuth for decreasing temperature. Annealing of the cluster ensemble and the cluster contact connection resulted in an increase in conduction. This increase of conduction can be explained due to the current flow through the cluster wire. Locally, at the bottlenecks, the current flow causes resistive heating and subsequently coalescence of two (or more) clusters.

No description available.

No description available.

No description available.

No description available.

The objective of this thesis is to successfully design, fabricate, and characterize an optimum metal-insulator-metal diode that can be used as a fast switching diode in various applications such as solar energy conversion. The improvements of this type of diode will result in rectification of a wider spectrum of AC signals to usable electricity. In this project, several proposed designs of MIM diodes were successfully fabricated and characterized. Pt-Al2O3-Al metal-insulator-metal diode was fabricated to have high asymmetry in I-V curve. Additionally, in an attempt to study the effect of material properties on MIM diode???s performance, four different combinations of MIIIIM diode were compared and discussed. Many processes were involved in the fabrication of these diodes such as E-beam evaporation, photolithography, reactive ion etching RIE, and Atomic Layer Deposition (ALD) technique. The fabricated tunneling diodes are intended to operate in the GHz regime and can also operate at higher frequencies (THz) by changing and scaling the dimensions. In addition to MIM diode work, this project attempted to engineer the contrast curve of polystyrene as a negative resist used for E-beam lithography using multi layer resist stack. If the resist stack has a very high contrast and its sensitivity differs between the various layers, it can be ideal for the fabrication of multi-level zone-plate/Fresnel lens.

abstract: Single molecules in a tunnel junction can now be interrogated reliably using chemically-functionalized electrodes. Monitoring stochastic bonding fluctuations between a ligand bound to one electrode and its target bound to a second electrode ("tethered molecule-pair" configuration) gives insight into the nature of the intermolecular bonding at a single molecule-pair level, and defines the requirements for reproducible tunneling data. Importantly, at large tunnel gaps, there exists a regime for many molecules in which the tunneling is influenced more by the chemical identity of the molecules than by variability in the molecule-metal contact. Functionalizing a pair of electrodes with recognition reagents (the "free analyte" configuration) can generate a distinct tunneling signal when an analyte molecule is trapped in the gap. This opens up a new interface between chemistry and electronics with immediate implications for rapid sequencing of single DNA molecules. / Dissertation/Thesis / Ph.D. Physics 2012

Driven by exciting new research and applications, top-down and bottom-up fabrication techniques are producing ever more intricate, reproducible, plasmonic nano-architectures with gaps and junctions approaching the single nanometre and atomic scales. Such atomic-sized features promote the intersection of physics, chemistry and biology in plasmonics. Consequently, understanding light-matter interactions in such closely spaced, electromagnetically coupled, metallic nanosystems is of vital importance to a tremendous variety of current and future nanophotonic technologies. This thesis describes the first dynamically controlled, optically broadband, experimental investigations of light-driven plasmonic coupling between two metal nanostructures with sub-nanometre separation. A new experimental apparatus and nanosystem alignment technique was developed to enable the required sub-nanometre inter-nanoparticle geometry to be created and probed. Two conducting atomic force microscopy tips with nanoparticle functionalised apices are brought into nanoscale `tip-to-tip' axial alignment with dynamically-controlled spacing and ultra-wide optical access. Resonant electrical parametric mixing, created by oscillating the electromechanically coupled tips, is utilised to extract an electronic signal due to nanoscale changes in inter-tip position. Experimental results match theory confirming the viability of the technique. By functionalising the tip apices, this unique multi-functional observation platform allows the plasmonic response of nanoparticle dimers with sub-nanometre separations to be characterised. By simultaneously capturing both the electrical and optical properties of tip-mounted gold nanoparticles with controllable sub-nanometre separation, the first evidence for the quantum regime of optically driven tunnelling plasmonics is revealed in unprecedented detail. It is demonstrated that quantum mechanical effects are critically important at approximately the 0.3 nm scale where spatially non-local tunnelling plasmonics controls the optical response. All observed phenomena are in good agreement with a recently developed quantum-corrected model of plasmonic systems. The findings imply that tunnelling establishes a quantum limit for plasmonic field enhancement and confinement. Additionally, the work suggests the highly enhanced local density of photonic states in nanoscale cavities could enable coherent plasmon-exciton coupling. This thesis prompts new experimental and theoretical investigations into quantum-domain plasmonic systems, and impacts the future of nanoplasmonic device engineering, nanoscale photochemistry and plasmon-mediated electron tunnelling.