Ahmed Kursumovic
University of Cambridge
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Publication
Featured researches published by Ahmed Kursumovic.
Applied Physics Letters | 2008
L. Dunlop; Ahmed Kursumovic; Judith L. MacManus-Driscoll
Nitrogen doped ZnO (ZnO:N) films were deposited by atmospheric atomic layer deposition (ALD) between 100 and 300°C. Postannealing was required to remove compensating defects. After a low temperature dark annealing, originally n-type films became p-type. Films deposited at low temperatures (⩽150°C) have low hole mobilities (μ) of 0.2–0.4cm2V−1s−1 and moderate hole concentrations (np) of around 1×1015cm−3. Higher temperature deposited films (⩾200°C) have higher μ values (6cm2V−1s−1) but np values <1×1013cm−3. This crossover in transport properties can be explained by the opposing effects of deposition temperature on nitrogen doping level and distribution, and film crystallinity.
Nano Letters | 2012
OonJew Lee; Sophie A. Harrington; Ahmed Kursumovic; Emmanuel Defay; Haiyan Wang; Zhenxing Bi; Chen-Fong Tsai; Li Yan; Quanxi Jia; Judith L. MacManus-Driscoll
There are numerous radio frequency and microwave device applications which require materials with high electrical tunability and low dielectric loss. For phased array antenna applications there is also a need for materials which can operate above room temperature and which have a low temperature coefficient of capacitance. We have created a nanoscaffold composite ferroelectric material containing Ba(0.6)Sr(0.4)TiO(3) and Sm(2)O(3) which has a very high tunability which scales inversely with loss. This behavior is opposite to what has been demonstrated in any previous report. Furthermore, the materials operate from room temperature to above 150 °C, while maintaining high tunability and low temperature coefficient of tunability. This new paradigm in dielectric property control comes about because of a vertical strain control mechanism which leads to high tetragonality (c/a ratio of 1.0126) in the BSTO. Tunability values of 75% (200 kV/cm field) were achieved at room temperature in micrometer thick films, the value remaining to >50% at 160 °C. Low dielectric loss values of <0.01 were also achieved, significantly lower than reference pure films.
AIP Advances | 2012
D. Muñoz-Rojas; M. Jordan; C. Yeoh; A. T. Marin; Ahmed Kursumovic; L. A. Dunlop; D. C. Iza; Aiping Chen; Haiyan Wang; J. L. MacManus Driscoll
Phase pure, dense Cu2O thin films were grown on glass and polymer substrates at 225°C by rapid atmospheric atomic layer deposition (AALD). Carrier mobilities of 5 cm2V−1s−1 and carrier concentrations of ∼1016 cm−3 were achieved in films of thickness 50 - 120 nm, over a >10 cm2 area. Growth rates were ∼1 nm·min−1 which is two orders of magnitude faster than conventional ALD.. The high mobilities achieved using the atmospheric, low temperature method represent a significant advance for flextronics and flexible solar cells which require growth on plastic substrates.
Applied Physics Letters | 2013
Eun-Mi Choi; E. Weal; Zhenxing Bi; Haiyan Wang; Ahmed Kursumovic; Thomas Fix; M. G. Blamire; Judith L. MacManus-Driscoll
Self-assembled, nanocomposite heteroepitaxial films of BiFeO3 + Fe3O4 (x BiFeO3 + (1 − x) Fe3O4), where x = 0.5 or 0.9, were grown on (011) SrTiO3. Depending on the value of x and on the film thickness, either exchange bias or exchange enhancement of coercivity was demonstrated. In epitaxially and highly strained (7%) films of 250 nm thickness, and for x = 0.9, exchange bias (HEB) values of 40 Oe and HEB/HC ratios of 0.5 were achieved. Most crucially, these effects were measured at room temperature, showing the high potential of chemically compatible BiFeO3 + Fe3O4 for achieving room temperature magnetoelectricity.
Nature Communications | 2016
Seungho Cho; Chao Yun; Stefan Tappertzhofen; Ahmed Kursumovic; Shinbuhm Lee; Ping Lu; Quanxi Jia; Meng Fan; Jie Jian; Haiyan Wang; Stephan Hofmann; Judith L. MacManus-Driscoll
Resistive switches are non-volatile memory cells based on nano-ionic redox processes that offer energy efficient device architectures and open pathways to neuromorphics and cognitive computing. However, channel formation typically requires an irreversible, not well controlled electroforming process, giving difficulty to independently control ionic and electronic properties. The device performance is also limited by the incomplete understanding of the underlying mechanisms. Here, we report a novel memristive model material system based on self-assembled Sm-doped CeO2 and SrTiO3 films that allow the separate tailoring of nanoscale ionic and electronic channels at high density (∼1012 inch−2). We systematically show that these devices allow precise engineering of the resistance states, thus enabling large on–off ratios and high reproducibility. The tunable structure presents an ideal platform to explore ionic and electronic mechanisms and we expect a wide potential impact also on other nascent technologies, ranging from ionic gating to micro-solid oxide fuel cells and neuromorphics.
Physica C-superconductivity and Its Applications | 2003
R.I. Tomov; Ahmed Kursumovic; M Majoros; B.A. Glowacki; J.E. Evetts; A. Tuissi; E. Villa; M. Zamboni; Y.F. Sun; S. Tönies; H.W. Weber
Abstract Pulsed laser deposition of YBa 2 Cu 3 O 7− δ (YBCO)/buffer (Y 2 O 3 , YSZ, CeO 2 ) heterostructures have been performed in situ onto recently developed non-magnetic oxygenation resistant NiCrW tape. The influence of the critical processing parameters on texture development are investigated and the issues involved in NiO formation and relation to the substrate surface quality are discussed. The roles of Ni poisoning YBCO as well as local cation disorder are considered as possible current limiting factors. X-ray diffraction has been used for macro-texture evaluation. Both buffers and YBCO layers show good biaxial alignment with ω and ϕ scans having best YBCO FWHM values of 4.0° and 6.5° respectively. A comparison is made with results achieved on industrial Ni 50 Fe 50 tape. The film morphology has been characterized using atomic force microscopy and scanning electron microscopy. The cation disorder has been studied by Raman spectroscopy. Critical temperatures of 90 K (Δ T c =5 K) have been measured. Direct transport as well as magnetic measurements shows the critical current density J c is 0.2 MA/cm 2 in self-field at liquid nitrogen temperatures.
Applied Physics Letters | 2010
E. Weal; S. Patnaik; Zhenxing Bi; Haiyan Wang; Thomas Fix; Ahmed Kursumovic; J. L. MacManus Driscoll
10% Fe3O4–90% BiFeO3 nanocomposite thin films of 180 nm thickness were grown by pulsed laser deposition on SrTiO3 (011) single crystals. A 3–4 nm nanolamella structure of Fe3O4 and BiFeO3 was formed. While BiFeO3 has the expected epitaxial relationship with the substrate, Fe3O4 grew epitaxially and highly strained (7%). Compared to pure Fe3O4 films of similar thickness, the nanolamella structure of Fe3O4 gives rise to a greatly enhanced saturation magnetization of 900 emu/cc, and, after field cooling, an enhanced coercivity of 450 Oe. Piezoresponse force microscopy measurements show similar polar switching properties between the nanocomposite and pure BiFeO3 films.
Advanced Functional Materials | 2014
Eun-Mi Choi; Thomas Fix; Ahmed Kursumovic; C. J. Kinane; D. A. Arena; Suman Lata Sahonta; Zhenxing Bi; Jie Xiong; Li Yan; Jun-Sik Lee; Haiyan Wang; S. Langridge; Yong-Min Kim; Albina Y. Borisevich; Ian MacLaren; Quentin M. Ramasse; M. G. Blamire; Quanxi Jia; Judith L. MacManus-Driscoll
Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ∼ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (∼ 0.58 μB/f.u) on high quality (001) SrTiO3. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above.
Applied Physics Letters | 2005
Karen A. Yates; Z. Lockman; Ahmed Kursumovic; Gavin Burnell; N. A. Stelmashenko; J. L. MacManus Driscoll; M. G. Blamire
The effects of oxygen on the superconducting properties of thin films of MgB2 have been studied. It is found that after annealing for short times in flowing O2 at 400°C, complex oxides of Mgx(ByO)z are formed that cause a “two-step” behavior in the resistively determined superconducting transition. These oxides are not stable at room temperature and decay into MgO and B2O3 precipitates. As the complex oxides decay so the original Tc behavior of the films is restored to its preoxygenation level.
APL Materials | 2015
Judith L. MacManus-Driscoll; Ady Suwardi; Ahmed Kursumovic; Zhenxing Bi; Chen Fong Tsai; Haiyan Wang; Quanxi Jia; Oon Jew Lee
Auxetic-like strain states were generated in self-assembled nanocomposite thin films of (Ba0.6Sr0.4TiO3)1−x − (Sm2O3)x(BSTO − SmO). A switch from auxetic-like to elastic-like strain behavior was observed for x > 0.50, when the SmO switched from being nanopillars in the BSTO matrix to being the matrix with BSTO nanopillars embedded in it. A simple model was adopted to explain how in-plane strain varies with x. At high x (0.75), strongly enhanced ferroelectric properties were obtained compared to pure BSTO films. The nanocomposite method represents a powerful new way to tune the properties of a wide range of strongly correlated metal oxides whose properties are very sensitive to strain.