Investigations into the electrical properties of hybrid memristor devices containing surface modified zinc oxide nanorods

This thesis focusses on improving the fabrication and electronic switching properties of hybrid memristor devices that have been developed in the nanophysics group at the University of Hull. The devices consist of vertically aligned semiconducting ZnO nanorods embedded within an organic polymer (Polymethyl-methacrylate) matrix. They are made using a novel ultra-fast microwave fabrication technique, which provides a simple and cost effective route to the fabrication of devices in large numbers and on lightweight and flexible substrates.The primary aim of this work was to improve the resistance on/off ratio in the memristors by modifying the ZnO surface stoichiometry. The nanorods high surface area to volume ratio is expected to be important in the switching since it has been shown that the mobility of defects at surfaces of transition metal oxides is much higher than in the bulk. Thus it is possible that either oxygen vacancies and/or zinc interstitials confined on the surface of the ZnO shuttle up and down along the lengths of the nanorods to mediate the switching. Investigations are focussed on the modification of the nanorod surface through oxygen plasma treatment as well as studying changes in the electrical performance of the nanorods by changing the nanorod diameter.Investigations into the effects of exposing the nanorods to an oxygen plasma showed increased resistance of both the high and low resistive states (HRS/LRS) of devices. Energy Dispersive X-Ray spectroscopy results indicated that a likely cause of the increased resistance is increased oxygen in the nanorod surface, producing a more stoichiometric (ZnO2) and resistive material.Attempts at manipulating the overall surface stoichiometry through changes in the surface area to volume ratio, implemented by changing the nanorods diameter, was not successful with the approach used in this work. This was because the nanorod diameter could not be significantly modified through the technique of changing the annealing temperature of the nanocrystal seed layer. This was unexpected as it has been previously reported that the nanorod diameter can be varied between 40nm and 350nm by annealing the seed layer at temperatures between 150°C and 500°C respectively.It is worth noting throughout the investigations that the use of low incidence X-ray diffraction measurements on the thin-films proved to be a quick and reliable way to confirm nanorod alignment and growth along the C axis

Bingham Lands in Alexander and Cooper

Property map with no scale, showing numbered lots in the Alexander and the town of Cooper. The map indicates eastern boundaries with Township No. 19 and Crawford, Plantation No. 14, and Princeton, Maine. The property was once part of the lands first surveyed Rufus Putnam. From Gardner Family Papers, 1830-1939. John Gardner (1801-1888), was the principal surveyor in Calais, Maine. His son, Benjamin E. Gardner (1869-1939), a civil engineer and land surveyor took over for his father and worked most frequently with local attorneys doing land title research.https://digitalcommons.library.umaine.edu/mainebicentennial/1030/thumbnail.jp

Undated property map, Washington County

Undated property map, with no scale, drawn in black ink on yellow vellum. A white sticker with a red border is labeled, “Tshp 13.” Labeled bodies of water include Tomah Stream and Beaver Brook. A handwritten map key includes the following information: p—pine d—hardwood g—good land h—heath m—meadow l—low land S—sedan b—burnt land A—camp x—local attraction r—rocky From Gardner Family Papers, 1830-1939. John Gardner (1801-1888), was the principal surveyor in Calais, Maine. His son, Benjamin E. Gardner (1869-1939), a civil engineer and land surveyor took over for his father and worked most frequently with local attorneys doing land title research.https://digitalcommons.library.umaine.edu/mainebicentennial/1036/thumbnail.jp

Undated property map with Porter lots [Washington County]

Undated property map, with no scale, drawn in black ink on yellow vellum. The map location is not clearly identified though features include a body of water identified as “Cheputnecticook River” and a bend in Tomah Stream. Five lots, numbers 1, 2, 15, 29 and 30, are labeled with the name “Porter.” The map includes faint pencil notations suggesting names for streams. From Gardner Family Papers, 1830-1939. John Gardner (1801-1888), was the principal surveyor in Calais, Maine. His son, Benjamin E. Gardner (1869-1939), a civil engineer and land surveyor took over for his father and worked most frequently with local attorneys doing land title research.https://digitalcommons.library.umaine.edu/mainebicentennial/1034/thumbnail.jp

Some combinatorial theorems with an application to a problem in number theory

The main object of this thesis is to study the following extremal problem in number theory: Let n and k be integers satisfying n ≥ k ≥ 3. Denote by f(n,k) the largest positive integer for which there exists a set S of f(n,k) integers satisfying -- (i) S ⊑ { 1,2...,n } and -- (ii) no k numbers in S have pairwise the same greatest common divisor. -- We investigate the behaviour of f(n,k) in the case where k → ∞ with n. In particular we obtain estimates for f(n, [logαn]) for fixed α > 0 and f(n,[nα]) for fixed α, 0 < α < 1. -- In the course of our investigations we make use of certain intersection theorems for systems of finite sets. We also include a number of new results concerning these theorems

Plan of the Hinkley Township & Gore

Pen and ink map of Hinkley Township & Gore in Washington County, Maine, and includes Grand Lake featuring Dyer Cove and Grand Lake Stream. Scale: 160 Rods to an Inch.https://digitalcommons.library.umaine.edu/mainebicentennial/1041/thumbnail.jp

Plan of the Hinkley Township & Gore

Pen and ink map of Hinkley Township & Gore in Washington County, Maine, and includes Grand Lake featuring Dyer Cove and Grand Lake Stream. Scale: 160 Rods to an Inch.https://digitalcommons.library.umaine.edu/mainebicentennial/1041/thumbnail.jp

Monson Lot near Lewies Lake

Pen and ink rendering of Monson lots and details drawings of properties near the County Road bridge spanning the outlet of Lewy Lake and the intersection of 20th Century roads, U.S. Highway 1 and Rolfe Street. Lots are labeled P. Rolfe Land, P. Carl Lot, and Tavern Lot.https://digitalcommons.library.umaine.edu/mainebicentennial/1056/thumbnail.jp

Plan of Alexander, No. 16

Blue print copy of properties of Plan of Alexander (previously Township No. 16). The map includes no scale. Handwritten caption reads: “The black dotted lines were run by B. R. Jones in 1807 & 8. The principal line were then run ten degrees to the left of the cardinal points. At present (1842) the same lines range eight degrees to the left of said points by the magnet. Dennysville, March 15, 1842 (signed) Benj. R. Jones. Copied by R. V. H. Sept. 16, 1843. B.E.G. May 31, 1901. From Gardner Family Papers, 1830-1939. John Gardner (1801-1888), was the principal surveyor in Calais, Maine. His son, Benjamin E. Gardner (1869-1939), a civil engineer and land surveyor took over for his father and worked most frequently with local attorneys doing land title research.https://digitalcommons.library.umaine.edu/mainebicentennial/1031/thumbnail.jp

Kinematic Evolution of Simulated Star-Forming Galaxies

Recent observations have shown that star-forming galaxies like our own Milky Way evolve kinematically into ordered thin disks over the last ~8 billion years since z=1.2, undergoing a process of "disk settling." For the first time, we study the kinematic evolution of a suite of four state of the art "zoom in" hydrodynamic simulations of galaxy formation and evolution in a fully cosmological context and compare with these observations. Until now, robust measurements of the internal kinematics of simulated galaxies were lacking as the simulations suffered from low resolution, overproduction of stars, and overly massive bulges. The current generation of simulations has made great progress in overcoming these difficulties and is ready for a kinematic analysis. We show that simulated galaxies follow the same kinematic trends as real galaxies: they progressively decrease in disordered motions (sigma_g) and increase in ordered rotation (Vrot) with time. The slopes of the relations between both sigma_g and Vrot with redshift are consistent between the simulations and the observations. In addition, the morphologies of the simulated galaxies become less disturbed with time, also consistent with observations, and they both have similarly large scatter. This match between the simulated and observed trends is a significant success for the current generation of simulations, and a first step in determining the physical processes behind disk settling.Comment: ApJ accepted; 6 pages; A pdf with full resolution figures can be found at https://db.tt/8y4Vzaff (2.8M