http://www.dspace.cam.ac.uk:80/handle/1810/227529 Tue, 21 May 2013 23:33:33 GMT 2013-05-21T23:33:33Z http://www.dspace.cam.ac.uk:80/handle/1810/244515 Title: Collagen fibre implant for tendon and ligament biological augmentation. In vivo study in an ovine model Authors: Enea, D; Gwynne, J; Kew, S; Arumugam, M; Shepherd, J; Brooks, R; Ghose, S; Best, S; Cameron, R; Rushton, N Abstract: Purpose Although most in vitro studies indicate that collagen is a suitable biomaterial for tendon and ligament tissue engineering, in vivo studies of implanted collagen for regeneration of these tissues are still lacking. The objectives of this study were the following: (1) to investigate the regeneration of the central third of the ovine patellar tendon using implants made of an open array of collagen fibres (reconstituted, extruded bovine collagen); and (2) to compare two collagen crosslinking chemistries: carbodiimide and carbodiimide associated with ethyleneglycoldiglycidylether. Methods Forty-eight Welsh Mountain sheep were operated on their right hind leg. The central third of patellar tendon was removed and substituted with carbodiimide (n = 16) and carbodiimide–ethyleneglycoldiglycidylether-crosslinked implants (n = 16). In the control group the defect was left empty (n = 16). The central third of contralateral unoperated tendons was used as positive controls. Half of the sheep in each group were killed at 3- and 6-month time points. After proper dissection, tendon sub-units (medial, central and lateral) were tested to failure (n = 6 for each group), whilst 2 non-dissected samples were used for histology. Results Both the implants had significantly lower stress to failure and modulus with respect to native tendon at both 3- and at 6-month time points. The implants did not statistically differ in stress to failure, whilst carbodiimide-crosslinked implants had significantly higher modulus than carbodiimide–ethyleneglycoldiglycidylether-crosslinked implants both at 3 and at 6 months. Histology showed carbodiimide-crosslinked implants to have a better integration with the native tendon than carbodiimide–ethyleneglycoldiglycidylether-crosslinked implants. Carbodiimide-crosslinked implants appeared partially resorbed and showed increased tissue ingrowth with respect to carbodiimide–ethyleneglycoldiglycidylether-crosslinked implants. Conclusions To deliver collagen implants as an open array of fibres allows optimal tendon–implant integration and good ingrowth of regenerated tissue. In the present study the resorption rate of both the examined implants was too low due to the high level of crosslinking. This led to only minor substitution of the implant with regenerated tissue, which in turn produced a low-strength implanted region. Further studies are needed to find the right balance between strength and resorption rate of collagen fibres. Tue, 19 Jun 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244515 2012-06-19T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/244509 Title: Exploring the application of stem cells in tendon repair and regeneration. Authors: Ahmad, Z; Wardale, J; Brooks, R; Henson, F; Noorani, A; Rushton, N Abstract: PURPOSE: To conduct a systematic review of the current evidence for the effects of stem cells on tendon healing in preclinical studies and human studies. METHODS: A systematic search of the PubMed, CINAHL (Cumulative Index to Nursing and Allied Health Literature), Cochrane, and Embase databases was performed for stem cells and tendons with their associated terminology. Data validity was assessed, and data were collected on the outcomes of trials. RESULTS: A total of 27 preclinical studies and 5 clinical studies met the inclusion criteria. Preclinical studies have shown that stem cells are able to survive and differentiate into tendon cells when placed into a new tendon environment, leading to regeneration and biomechanical benefit to the tendon. Studies have been reported showing that stem cell therapy can be enhanced by molecular signaling adjunct, mechanical stimulation of cells, and the use of augmentation delivery devices. Studies have also shown alternatives to the standard method of bone marrow-derived mesenchymal stem cell therapy. Of the 5 human studies, only 1 was a randomized controlled trial, which showed that skin-derived tendon cells had a greater clinical benefit than autologous plasma. One cohort study showed the benefit of stem cells in rotator cuff tears and another in lateral epicondylitis. Two of the human studies showed how stem cells were successfully extracted from the humerus and, when tagged with insulin, became tendon cells. CONCLUSIONS: The current evidence shows that stem cells can have a positive effect on tendon healing. This is most likely because stem cells have regeneration potential, producing tissue that is similar to the preinjury state, but the results can be variable. The use of adjuncts such as molecular signaling, mechanical stimulation, and augmentation devices can potentially enhance stem cell therapy. Initial clinical trials are promising, with adjuncts for stem cell therapy in development. Fri, 27 Jul 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244509 2012-07-27T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/244508 Title: A study of surface morphology and phase separation of polymer/cellulose liquid crystal composite membranes Authors: Tu, Mei; Han, Wanqing; Zeng, Rong; Best, Serena; Cameron, Ruth Abstract: This paper explores the effects of the incorporation of liquid crystalline phases into polyurethane (PU) matrix with the aim of creating composites with biomimetic surfaces. The surface morphology and phase separation structure of polyurethane/butyl hydroxypropyl cellulose ester (PU/BPC) composite membranes with different BPC contents and underwent different post-treatments were investigated by using polarized optical microscopy (POM), scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS). Well-dispersed liquid crystal (LC) domains occurred on the PU/BPC composite membranes surfaces. As the increment of BPC content, the LC domains tended to form enlarged quasispherical aggregates with poorly molecular orientation, and low degree of regular phase separation occurred between the LC domains and PU substrate. Membranes with different LC contents underwent heat treating and cooling at three different conditions exhibited distinct surface morphologies, meanwhile, a sharp peak emerged in the SAXS pattern, which indicated that the ordered arrangement of BPC molecular chains existed in the LC domains and the phase separation structure between substrate and LC domain had changed. Sharper and more intense SAXS peaks were found in the membranes that annealing in oven, indicating more regular arrangement of LC domains and more obvious phase separation presented than those cooling to 20 °C or −20 °C respectively. Results suggested that the surface morphology of polymer/LC membranes could be controlled through adjusting LC contents or post treatment conditions. Sat, 04 Aug 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244508 2012-08-04T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/244252 Title: Effect of fiber crosslinking on collagen-fiber reinforced collagen-chondroitin-6-sulfate materials for regenerating load-bearing soft tissues Authors: Shepherd, JH; Ghose, S; Kew, SJ; Moavenian, A; Best, SM; Cameron, RE Tue, 01 Jan 2013 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244252 2013-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/244229 Title: Synthetic Collagen Fascicles for the Regeneration of Tendon Tissue Authors: Kew, SJ; Gwynne, JH; Enea, D; Brooks, R; Rushton, N; Best, SM; Cameron, RE Abstract: The structure of an ideal scaffold for tendon regeneration must be designed to provide a mechanical, structural and chemotactic microenvironment for native cellular activity to synthesise functional (i.e. load bearing) tissue. Collagen fibre scaffolds for this application have shown some promise to date, although the microstructural control required to mimic the native tendon environment has yet to be achieved allowing for minimal control of critical in vivo properties such as degradation rate and mass transport. In this report we describe the fabrication of a novel multi-fibre collagen fascicle structure, based on type-I collagen with failure stress of 25 – 49 MPa, approximating the strength and structure of native tendon tissue. We demonstrate a microscopic fabrication process based on the automated assembly of type-I collagen fibres with the ability to produce a controllable fascicle-like, structural motif allowing variable numbers of fibres per fascicle. We have confirmed that the resulting post-fabrication type-I collagen structure retains the essential phase behaviour, alignment and spectral characteristics of aligned native type-I collagen. We have also shown that both ovine tendon fibroblasts and human white blood cells in whole blood readily infiltrate the matrix on a macroscopic scale and that these cells adhere to the fibre surface after seven days in culture. The study has indicated that the synthetic collagen fascicle (SCF) system may be a suitable biomaterial scaffold to provide a rationally-designed implantable matrix material to mediate tendon repair and regeneration. Sun, 01 Jan 2012 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244229 2012-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243440 Title: The interplay between physical and chemical properties of protein films affects their bioactivity Authors: Grover, CN; Farndale, RW; Best, SM; Cameron, RE Abstract: Although mechanical properties, roughness, and receptor molecule expression have all been shown to influence the cellular reactivity of collagen-based biomaterials, their relative contribution, in a given system remains unclear. Here, we study films containing combinations of collagen, gelatin, and soluble and insoluble elastin, crosslinking of which results in altered film stiffness and roughness. Collagen and gelatin have similar amino acid sequences but altered cell-binding sites. We studied cell response with both C2C12 myoblast cells (which possess RGD-recognizing integrins α(V) β(3) and α(5) β(1) ) and C2C12-α2+ cells (which, in addition, express the collagen-binding integrin α(2) β(1) ) to establish the effect of altering the available binding sites on cell adhesion and spreading on films. Systematically altering the composition, crosslinking and cell type, allows us to deconvolute the effects of physical parameters and available binding sites on the cell reactivity of films in this system. Collagen-based films were rougher and stiffer and supported lower cell surface coverage than gelatin-based films. Additionally, C2C12-α2+ cells showed preferential attachment to collagen-based films compared with C2C12 cells, but no significant difference was seen using gelatin-based films. The cell count and surface coverage were found to decrease significantly on all films after crosslinking (Coll XL coverage = 2-6%, Gel XL coverage = 20-32%), but cell area and aspect ratio on collagen films were affected to a greater extent than on gelatin films. The results show that, in this system, the composition, and more significantly, crosslinking, of films affects the cell reactivity to a greater extent than their stiffness or roughness. Sun, 08 Jul 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243440 2012-07-08T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243439 Title: Investigating the morphological, mechanical and degradation properties of scaffolds comprising collagen, gelatin and elastin for use in soft tissue engineering Authors: Grover, CN; Best, SM; Cameron, RE Abstract: Collagen-based scaffolds can be used to mimic the extracellular matrix (ECM) of soft tissues and provide support during tissue regeneration. To better match the native ECM composition and mechanical properties as well as tailor the degradation resistance and available cell binding motifs, other proteins or different collagen types may be added. The present study has explored the use of components such as gelatin or elastin and investigated their effect on the bulk physical properties of the resulting scaffolds compared to those made from pure collagen type I. The effect of altering the composition and crosslinking was evaluated in terms of the scaffold structure, mechanical properties, swelling, degradation and cell attachment. Results demonstrate that scaffolds based on gelatin had reduced tensile stiffness and degradation time compared with collagen. The addition of elastin reduced the overall strength and stiffness of the scaffolds, with electron microscopy results suggesting that insoluble elastin interacts best with collagen and soluble elastin interacts best with gelatin. Carbodiimide crosslinking was essential for structural stability, strength and degradation resistance for scaffolds of all compositions. In addition, preliminary cell adhesion studies showed these highly porous structures (pore size 130-160 μm) to be able to support HT1080 cell infiltration and growth. Therefore, this study suggests that the use of gelatin in place of collagen, with additions of elastin, can tailor the physical properties of scaffolds and could be a design strategy for reducing the overall material costs. Sun, 08 Jul 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243439 2012-07-08T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243438 Title: Crosslinking and composition influence the surface properties, mechanical stiffness and cell reactivity of collagen-based films. Authors: Grover, CN; Gwynne, JH; Pugh, N; Hamaia, S; Farndale, RW; Best, SM; Cameron, RE Abstract: This study focuses on determining the effect of varying the composition and crosslinking of collagen-based films on their physical properties and interaction with myoblasts. Films composed of collagen or gelatin and crosslinked with a carbodiimide were assessed for their surface roughness and stiffness. These samples are significant because they allow variation of physical properties as well as offering different recognition motifs for cell binding. Cell reactivity was determined by the ability of myoblastic C2C12 and C2C12-α2+ cell lines (with different integrin expression) to adhere to and spread on the films. Significantly, crosslinking reduced the cell reactivity of all films, irrespective of their initial composition, stiffness or roughness. Crosslinking resulted in a dramatic increase in the stiffness of the collagen film and also tended to reduce the roughness of the films (R(q)=0.417±0.035μm, E=31±4.4MPa). Gelatin films were generally smoother and more compliant than comparable collagen films (R(q)=7.9±1.5nm, E=15±3.1MPa). The adhesion of α2-positive cells was enhanced relative to the parental C2C12 cells on collagen compared with gelatin films. These results indicate that the detrimental effect of crosslinking on cell response may be due to the altered physical properties of the films as well as a reduction in the number of available cell binding sites. Hence, although crosslinking can be used to enhance the mechanical stiffness and reduce the roughness of films, it reduces their capacity to support cell activity and could potentially limit the effectiveness of the collagen-based films and scaffolds. Sun, 08 Jul 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243438 2012-07-08T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/243436 Title: Osteoinduction by combining bone morphogenetic protein (BMP)-2 with a bioactive novel nanocomposite Authors: Sharma, A; Meyer, F; Best, SM; Cameron, RE; Rushton, N Sun, 08 Jul 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/243436 2012-07-08T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/242431 Title: The consequences of high injected carrier densities on carrier localisation and efficiency droop in InGaN/GaN quantum well structures Authors: Hammersley, S; Watson-Parris, D; Dawson, P; Godfrey, M; Badcock, T; Kappers, M; McAleese, C; Oliver, R; Humphreys, C Abstract: There is a great deal of interest in the underlying causes of efficiency droop in InGaN/GaN quantum well light emitting diodes, with several physical mechanisms being put forward to explain the phenomenon. In this paper we report on the observation of a reduction in the localisation induced S-shape temperature dependence of the peak photoluminescence energy with increasing excitation power density. This S-shape dependence is a key fingerprint of carrier localisation. Over the range of excitation power density where the depth of the S shape is reduced we also observe a reduction in the integrated photoluminescence intensity per unit excitation power, i.e. efficiency droop. Hence the onset of efficiency droop occurs at the same carrier density as the onset of carrier delocalisation. We correlate these experimental results with the predictions of a theoretical model of the effects of carrier localisation due to local variations in the concentration of the randomly distributed In atoms on the optical properties of InGaN/GaN quantum wells. On the basis of this comparison of theory with experiment we attribute the reduction in the Sshape temperature dependence to the saturation of the available localised states. We propose that this saturation of the localised states is a contributory factor to efficiency droop whereby non localised carriers recombine non-radiatively. Tue, 17 Apr 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/242431 2012-04-17T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/242430 Title: Atom probe tomography characterisation of a laser diode structure grown by molecular beam epitaxy Authors: Bennett, Samantha; Smeeton, Tim; Saxey, David; Smith, George; Hooper, Stewart; Heffernan, Jonathan; Humphreys, Colin; Oliver, Rachel Abstract: Atom probe tomography (APT) has been used to achieve three-dimensional characterization of a III-nitride laser diode (LD) structure grown by molecular beam epitaxy (MBE). Four APT data sets have been obtained, with fields of view up to 400 nm in depth and 120 nm in diameter. These data sets contain material from the InGaN quantum well (QW) active region, as well as the surrounding p- and n-doped waveguide and cladding layers, enabling comprehensive study of the structure and composition of the LD structure. Two regions of the same sample, with different average indium contents (18% and 16%) in the QW region, were studied. The APT data are shown to provide easy access to the p-type dopant levels, and the composition of a thin AlGaN barrier layer. Next, the distribution of indium within the InGaN QW was analyzed, to assess any possible inhomogeneity of the distribution of indium (“indium clustering”). No evidence for a statistically significant deviation from a random distribution was found, indicating that these MBE-grown InGaN QWs do not require indium clusters for carrier localization. However, the APT data show steps in the QW interfaces, leading to well-width fluctuations, which may act to localize carriers. Additionally, the unexpected presence of a small amount (x = 0.005) of indium in a layer grown intentionally as GaN was revealed. Finally, the same statistical method applied to the QW was used to show that the indium distribution within a thick InGaN waveguide layer in the n-doped region did not show any deviation from randomness. Tue, 06 Mar 2012 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/242430 2012-03-06T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/242429 Title: Growth and optical characterization of multilayers of InGaN quantum dots Authors: Zhu, Tontong; El-Ella, Haitham; Reid, Benjamin; Holmes, Mark; Taylor, Robert; Kappers, Menno; Oliver, Rachel Abstract: We report on the growth (using metal-organic vapour phase epitaxy) and optical characterization of single and multiple layers of InGaN quantum dots (QDs), which were formed by annealing InGaN epilayers at the growth temperature in nitrogen. The size and density of the nanostructures have been found to be fairly similar for uncapped single and three layer QD samples if the GaN barriers between the dot layers are grown at the same temperature as the InGaN epilayer. The distribution of nanostructure heights of the final QD layer of three is wider and is centred around a larger size if the GaN barriers are grown at two temperatures (first a thin layer at the dot growth temperature, then a thicker layer at a higher temperature). Micro-photoluminescence studies at 4.2 K of capped samples have confirmed the QD nature of the capped nanostructures by the observation of sharp emission peaks with full width at half maximum limited by the resolution of the spectrometer. We have also observed much more QD emission per unit area in a sample with three QD layers, than in a sample with a single QD layer, as expected. Sun, 01 Jan 2012 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/242429 2012-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/242232 Title: Refining structures against reflection rank: An alternative metric for electron crystallography. Authors: Eggeman, Alexander; Migley, Paul Abstract: A new metric is proposed to improve the fidelity of structures refined against precession electron diffraction data. The inherent dynamical nature of electron diffraction ensures that direct refinement of recorded intensities against structure factor amplitudes can be prone to systematic errors. Here we show that the relative intensity of precessed reflections, their rank, can be used as an alternative metric for refinement. Experi- mental data from erbium pyrogermanate shows that applying precession reduces the dynamical transfer of intensity between reflections and hence stabilises their rank, enabling accurate and reliable structural refinements. This approach is then applied successfully to an unknown structure of an oxygen-deficient bismuth manganite result- ing in a refined structural model that is similar to a calcium analogue. Mon, 30 Apr 2012 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/242232 2012-04-30T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/242231 Title: Advances in Imaging and Electron Physics - Volume 170 Authors: Eggeman, Alexander; Midgley, Paul Sun, 01 Jan 2012 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/242231 2012-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/241105 Title: Collagen-Hyaluronic Acid Scaffolds for Adipose Tissue Engineering Authors: Davidenko, Natalia; Campbell, J. J.; Thian, E. S.; Watson, C. J,; Cameron, R. E. Abstract: Three-dimensional (3-D) in vitro models of the mammary gland require a scaffold matrix that supports the development of adipose stroma within a robust freely permeable matrix. 3-D porous collagen-hyaluronic acid (HA: 7.5% and 15%) scaffolds were produced by controlled freeze-drying technique and crosslinking with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride. All scaffolds displayed uniform, interconnected pore structure (total porosity approximately 85%). Physical and chemical analysis showed no signs of collagen denaturation during the formation process. The values of thermal characteristics indicated that crosslinking occurred and that its efficiency was enhanced by the presence of HA. Although the crosslinking reduced the swelling of the strut material in water, the collagen-HA matrix as a whole tended to swell more and show higher dissolution resistance than pure collagen samples. The compressive modulus and elastic collapse stress were higher for collagen-HA composites. All the scaffolds were shown to support the proliferation and differentiation 3T3-L1 preadipocytes while collagen-HA samples maintained a significantly increased proportion of cycling cells (Ki-67+). Furthermore, collagen-HA composites displayed significantly raised Adipsin gene expression with adipogenic culture supplementation for 8 days vs. control conditions. These results indicate that collagen-HA scaffolds may offer robust, freely permeable 3-D matrices that enhance mammary stromal tissue development in vitro. Fri, 01 Jan 2010 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/241105 2010-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/241027 Title: The Structure of Two New Non-Centrosymmetric Phases of Oxygen Deficient Bismuth Manganite Authors: Eggeman, Alexander, Sundaresan, A., Rao, C. N. R., Midgley, Paul A. Abstract: The structure of two new phases in the bismuth manganite system are reported. The phases were determined by electron diffraction studies of two oxygen-deficient bulk samples. The first phase, a minority component of bulk BiMnO2.94 forms a n=2 Ruddlesden-Popper phase with space group Cmc21 . The second phase, from bulk BiMnO2.99 , is an orthorhombic structure with spacegroup Pmn21 and a unit cell approximately equal to 4 × √ 2 × 2 √ 2 times the parent perovskite cell. Importantly both phases are non-centrosymmetric and offer further potential for multiferroic studies. Wed, 03 Aug 2011 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/241027 2011-08-03T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/239352 Title: Biomimetic Collagen Scaffolds with Anisotropic Pore Architecture Authors: Davidenko, Natalia; Gibb, T; Schuster, Carlos; Best, Serena Michelle; Campbell, JJ; Watson, CJ; Cameron, Ruth E Abstract: Sponge-like matrices with a specific 3D structural design resembling the actual extracellular matrix (ECM) of a particular tissue show significant potential for the regeneration and repair of a broad range of damaged anisotropic tissues. The manipulation of the structure of collagen scaffolds using a freeze-drying technique was explored in this work as an intrinsically biocompatible way of tailoring the inner architecture of the scaffold. The research was focused on the influence of temperature gradients, imposed during the phase of crystallisation of collagen suspensions, upon the degree of anisotropy in the microstructures of the scaffolds produced. Moulding technology was employed to achieve differences in heat transfer rates during the freezing processes. For this purpose various moulds with different configurations were developed with a view to producing uni-axial and multidirectional temperature gradients across the sample during this process. SEM analysis of different cross-sections (longitudinal and horizontal) of scaffolds revealed that highly aligned matrices with axially directed pore architecture were obtained where single unidirectional temperature gradient was induced. Alteration of freezing conditions by the introduction of multi-temperature gradients allowed collagen scaffolds to be produced with complex pore orientations, and anisotropy in pore size and alignment. Mon, 10 Jan 2011 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/239352 2011-01-10T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/237881 Title: Cavity Enhancement of Single Quantum Dot Emission in the Blue Abstract: Abstract Cavity-enhanced single-photon emission in the blue spectral region was measured from single InGaN/GaN quantum dots. The low-Q microcavities used were characterized using micro-reflectance spectroscopy where the source was the enhanced blue output from a photonic crystal fibre. Micro-photoluminescence was observed from several cavities and found to be ~10 times stronger than typical InGaN quantum dot emission without a cavity. The measurements were performed using non-linear excitation spectroscopy in order to suppress the background emission from the underlying wetting layer. Description: RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are. Sun, 27 Dec 2009 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/237881 2009-12-27T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/236787 Title: Young's modulus, Poisson's ratio, and residual stress and strain in (111)-oriented scandium nitride thin films on silicon Authors: Moram, M A; Barber, Z H; Humphreys, C J; Joyce, T B; Chalker, P R Abstract: Epitaxial scandium nitride films (225 nm thick) were grown on silicon by molecular beam epitaxy, using ammonia as a reactive nitrogen source. The main crystallographic orientation of ScN with respect to Si is (111)ScN || (111)Si and [1–10]ScN || [0–11]Si; however, some twinning is also present in the films. The films displayed a columnar morphology with rough surfaces, due to low adatom mobility during growth. The strain-free lattice parameter of ScN films grown under optimized conditions was found to be 4.5047±0.0005 Å, as determined using high-resolution x-ray diffraction (HRXRD). In-plane and out-of-plane strains were subsequently evaluated using HRXRD and were used to determine the Poisson ratio of ScN along the (111) direction, which is found to be 0.188±0.005. Wafer curvature measurements were made and combined with the strain information to determine the average Young’s modulus of the films, which is found to be 270±25 GPa. Residual film stresses ranged from −1 to 1 GPa (depending on film growth temperature and film thickness) due to competition between the tensile stress (induced by the differential thermal contraction between the ScN film and the Si substrate) and intrinsic compressive stresses generated during growth. Thu, 20 Jul 2006 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/236787 2006-07-20T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/236786 Title: High Curie temperatures in ferromagnetic Cr-doped AlN thin films Authors: Kumar, D; Antifakos, J; Blamire, Mark G; Barber, Z H Abstract: Al1-xCrxN thin films with 0.02≤x≤0.1 were deposited by reactive co-sputtering onto c-plane (001) sapphire. Room-temperature ferromagnetism with a coercive field of 85 Oe was observed in samples with chromium contents as low as x=0.027 (2.7%). With increasing Cr content the mean magnetic moment is strongly suppressed, with a maximum saturation moment of 0.62 and 0.71 μB per Cr atom at 300 and 50 K, respectively. We show that the Curie temperature of Al1-xCrxN for x=0.027 is greater than 900 K. Thu, 27 May 2004 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/236786 2004-05-27T23:00:00Z