Dr Nianhua Peng

Transparent conductors are a vital component of smartphones, touch-enabled displays, low emissivity windows and thin film photovoltaics. Tin-doped In2O3 (ITO) dominates the transparent conductive films market, accounting for the majority of the current multi-billion dollar annual global sales. Due to the high cost of indium, however, alternatives to ITO have been sought but have inferior properties. Here we demonstrate that molybdenum-doped In2O3 (IMO) has higher mobility and therefore higher conductivity than ITO with the same carrier density. This also results in IMO having increased infrared transparency compared to ITO of the same conductivity. These properties enable current performance to be achieved using thinner films, reducing the amount of indium required and raw material costs by half. The enhanced doping behavior arises from Mo 4d donor states being resonant high in the conduction band and negligibly perturbing the host conduction band minimum, in contrast to the adverse perturbation caused by Sn 5s dopant states. This new understanding will enable better and cheaper TCOs based on both In2O3 and other metal oxides.

There are many technical challenges in the fabrication of devices from novel materials. The characterization of these materials is critical in the development of efficient photovoltaic systems. We show how the application of recent advances in MeV IBA, providing the self-consistent treatment of RBS (Rutherford backscattering) and PIXE (particle induced X-ray emission) spectra, makes a new set of powerful complementary depth profiling techniques available for all thin film technologies, including the chalcopyrite compound semiconductors. We will give and discuss a detailed analysis of a CuInAl metallic precursor film, showing how similar methods are also applicable to other films of interest.

The calcium iron oxide Ca 2 Fe 2 O 5 which contains alternate layers of iron-oxygen octahedra and tetrahedra has been found to take up additional oxygen under high pressure and elevated temperature. The Mössbauer spectra in the range 4.2-290 K establish that all the original material has been transformed into a new phase which is still structurally related to the original lattice, but features a disordered introduction of oxygen into the tetrahedral layers and oxidation of some of the iron to the +4 oxidation state. At least six distinct iron sites can be identified, and the coordination numbers established. The structural relationship of these sites and the magnetic characteristics are discussed.

Penetration of a nanochannel mask by 190keV Co ions is tested for the purpose of achieving laterally modulated ion implantation into a SiO thin film on a Si substrate. A 2D-nanoporous membrane of anodic aluminum oxide (AAO) is chosen as the mask. Criteria and challenges for designing the mask are presented. Implantation experiments through a mask with pore diameter of 125 nm and inter-pore distance of 260 nm are carried out. Cross-sectional TEM (XTEM) is shown as an ideal tool to assess depth distribution and lateral distribution of implanted ions at the same time, complemented by Rutherford backscattering spectroscopy. Using energy dispersive x-ray spectroscopy linescans, a Co distribution with lateral modulation is found at 120 nm below the oxide surface. First experiments in converting the atomic distribution of Co to discrete nanoparticles by in-situ TEM annealing are presented. © 2012 Materials Research Society.

Progress in ion implantation of metal ions into substrates of amorphous silica or Si-nitride with respect to lateral periodic patterning is presented. We use a 2D-nanoporous membrane of anodic aluminium oxide (AAO) as mask to conduct the Co ion implantations. The criteria for successful masked implantation and main problems are presented, including testing of the masks in a focused ion beam (FIB) system. It is proposed that electron transparent thin windows are the most suitable substrate for methods development, as TEM observation can be followed without any further sample milling. Co clusters are found to exhibit the same lateral order as the pores, and first annealing tests to achieve Co nanoparticles are shown using an in-situ heating TEM holder. © 2012 IEEE.

In combination with oxygen depletion, the different decrease behaviours of superconductivity in Fe, Ni and Zn doped YBa 2Cu 3O 7- δ compounds have been investigated in this report. The oxygen depletion induced superconductivity decrease rates are very close in the YBa 2Cu 2.9Fe 0.1O 7- δ , YBa 2Cu 2.9Ni 0.1O 7- δ and YBa 2Cu 3O 7- δ compounds, but this parameter is doubled in the YBa 2Cu 2.9Zn 0.1O 7- δ sample. This implies that 3d transition metals not only suppress superconductivity in YBa 2Cu 3O 7- δ as a magnetic impurity centre but also reduce the mobility of the mobile holes. The different decrease rates observed in Fe, Ni and Zn doped compounds suggest that the destruction of complete CuO 2 plane long-range magnetic ordering is rather crucial for the superconductivity.

The electrical characteristics of gallium-doped zinc oxide (ZnO:Ga) thin films prepared by rf diode sputtering were altered via nitrogen implantation by performing two implants at 40 keV and 80 keV with doses of 1×1015 and 1×1016 cm−2 to achieve a p-type semiconductor. An implantation of 1×1015 cm−2 N+-ions yielded a p-type with hole concentrations 1017–1018 cm−3 in some as-implanted samples. The films annealed at temperatures above 200°C in O2 and above 400°C in N2 were n-type with electron concentrations 1017–1020 cm−3. The higher nitrogen concentration (confirmed by SRIM and SIMS), in the films implanted with a 1×1016 cm−2 dose, resulted in lower electron concentrations, respectively, higher resistivity, due to compensation of donors by nitrogen acceptors. The electron concentrations ratio n(1×1015)/n(1×1016) decreases with increasing annealing temperature. Hall measurements showed that 1×1016 cm−2 N-implanted films became p-type after low temperature annealing in O2 at 200°C and in N2 at 400°C with hole concentrations of 3.2×1017 cm−3 and 1.6×1019 cm−3, respectively. Nitrogen-implanted ZnO:Ga films showed a c-axes preferred orientation of the crystallites. Annealing is shown to increase the average transmittance (>80%) of the films and to cause bandgap widening (3.19–3.3 eV).

We have studied the magnetization of vertically aligned graphene nanoflakes irradiated with nitrogen ions of 100 KeV energy and doses in the range 10¹¹–10¹⁷ ions/cm². The non-irradiated graphene nanoflakes show a paramagnetic contribution, which is increased progressively by ion irradiation at low doses up to 10¹⁵/cm². However, further increase on implantation dose reduces the magnetic moment which coincides with the onset of amorphization as verified by both Raman and x-ray photoelectron spectroscopic data. Overall, our results demonstrate the absence of ferromagnetism on either implanted or unimplanted samples from room temperature down to a temperature of 5 K.

Understanding the effect of radiation damage and noble gas accommodation in potential ceramic hosts for plutonium disposition is necessary to evaluate their long-term behaviour during geological disposal. Polycrystalline samples of Nd-doped zirconolite and Nd-doped perovskite were irradiated ex situ with 2 MeV Kr+ at a dose of 5 1015 ions cm2 to simulate recoil of Pu nuclei during alpha decay. The feasibility of thin section preparation of both pristine and irradiated samples by Focused Ion Beam sectioning was demonstrated. After irradiation, the Nd-doped zirconolite revealed a well defined amorphous region separated from the pristine material by a thin (40–60 nm) damaged interface. The zirconolite lattice was lost in the damaged interface, but the fluorite sublattice was retained. The Nd-doped perovskite contained a defined irradiated layer composed of an amorphous region surrounded by damaged but still crystalline layers. The structural evolution of the damaged regions is consistent with a change from orthorhombic to cubic symmetry. In addition in Nd-doped perovskite, the amorphisation dose depended on crystallographic orientation and possibly sample configuration (thin section or bulk). Electron Energy Loss Spectroscopy revealed Ti remained in the 4+ oxidation state but there was a change in Ti coordination in both Nd-doped perovskite and Nd-doped zirconolite associated with the crystalline to amorphous transition.

Lateral ordered Co, Pt and Co/Pt nanostructures were fabricated in SiO2 and Si3N4 substrates by high fluence metal ion implantation through periodic nanochannel membrane masks based on anodic aluminium oxides (AAO). The quality of nanopatterning transfer defined by various AAO masks in different substrates was examined by transmission electron microscopy (TEM) in both imaging and spectroscopy modes.

carbide (SiC), having various intrinsic color centers, is a highly promising optical material for making monolithic quantum integrated photonic circuits, by combining the single-photon sources with the integrated photonic components in SiC integrated platforms. Based on this quantum-material platform, we propose polarization-independent 1 x 2 and 2 x 2 multimode interference based beam splitters and Mach-Zehnder interferometers (MZI) for single-photon manipulation with unknown polarization states. We experimentally demonstrate that these devices exhibit excellent performances with incident light at both high power (>-10 dBm) and ultra-low power ( 100 nm and > 70 nm, respectively. The MZI exhibits high transmittance, with a visibility of 98.3% and 97.6% for the high-power measurement and an even higher visibility of 99.0 +/- 0.4% and 98.7 +/- 0.6% for the ultra-low power measurement, for the TE and TM polarizations, respectively.

The cubic perovskite solid solution Sr 2 FeSnO 5.71 , which contains both Fe 3+ and Fe 4+ cations, has been shown to be a spin-glass by a combination of magnetic susceptibility with 57 Fe and 119Sn Mössbauer spectroscopic measurements. The zero-field-cooled and field-cooled magnetic susceptibility diverge below a temperature of 15 ± 2 K, and a relaxational collapse of the Mössbauer magnetic hyperfine splitting with rise in temperature is complete by 26 ± 2 K. The transferred hyperfine nteractions in the 119 Sn resonance at 4.2 K give evidence to support the existence of randomly oriented spin moments. The composition Sr 2 FeSnO 5.50 which can be obtained by heating in vacuo contains only Fe 3+ cations and shows magnetic relaxation in a similar temperature region. However, electron diffraction measurements give evidence for short-range cation ordering to produce a supercell of √2a p ×√2a p × 2a p , where a p is the cubic perovskite lattice parameter, and the 119 Sn spectrum at 4.2 K shows that there is a substantial but unidentified ordering of the tin and iron cations.

1 MeV ion implantations of 4H SiC have been performed to various doses with ion probes of 5 µm diameter. Defect introduction has been studied by microscopic photoluminescence.

The perovskite-related oxide Ca 2 Fe 2 O 5 takes up additional oxygen under high pressure and elevated temperature. The Mössbauer spectra from a number of preparations establish the existence of new phases which are structurally related to the original lattice. The latter features an ordered arrangement of oxygen vacancies so as to form alternate layers of octahedral and tetrahedral Fe polyhedra. The introduction of oxygen to give CaFeO 2.60 initially increases the number of octahedral layers to give a sequence [ootot], and some of the iron in the double-octahedral layers undergoes oxidation to the 5+ oxidation state (by a nominal charge disproportionation of Fe 4+ at low temperature). At least six distinct iron sites can be identified, and their coordination numbers established. It is believed that the charge disproportionation is reversed with increasing temperature. Further uptake of oxygen to give CaFeO 2.69 produces some layers with five-coordination. The Mössbauer spectra reveal the existence of unusually complicated and subtle magnetic interactions, which include spin-reorientation effects and may be triggered by a change in oxidation state of some cations. Oxidation can extend to at least CaFeO 2.80 before any substantial intergrowth of CaFeO 3 becomes apparent. It is clear that a wide range of non-stoichiometry can be achieved by the intergrowth of layers of Fe in different coordination, and the extra oxygen is counterbalanced by the generation of Fe 5+ cations in octahedral coordination. The charge disproportionation appears to be established within two-dimensional layers of corner-sharing octahedra.

Superconductivity with T sub(c(onset)) = 100 K, T sub(c(midpoint)) = 84 K and T sub(c(zero)) = 72 K in the Tb-Tl-Ba-Cu-O system has been observed. X-ray diffraction as well as energy dispersive spectrometric studies were carried out to determine the probable composition and crystal structure of the superconducting phase. We propose that Tb-substituted Tl sub(2)Ba sub(2)CuO sub(6) is responsible for superconductivity at 84 K. Tb super(4+) and Ba super(2+) sites is proposed; these substitutions would effectively reduce the hole concentration, or overdoping, of the parent Tl sub(2)Ba sub(2)CuO sub(6) compound, leading to enhanced superconducting properties.

A new perovskite related Sr 0.97 NbO 3 phase has been synthesized. Although both powder X-ray diffraction and selected area electron diffraction studies suggest a primitive cubic perovskite structure with a p 4.023 Å, high resolution powder neutron diffraction reveals a subtle lattice distortion from cubic symmetry. The detailed crystal structure has been refined with the orthorhombic space group P 2 1 2 1 2 with a =5.6881 Å, b =5.6821 Å and c =8.0566 Å. The structure is built up from two types of NbO 6 octahedra, one elongated, the other compressed along c . The lattice distortion from cubic symmetry has been found to mainly originate from tilting of NbO 6 octahedra, whereas the √2 a p ×√2 a p ×2 a p superstructure arises from ordering of alternate elongated and compressed octahedra.

The effect of 600 keV He+ ion irradiation on the temperature and magnetic field dependence of the critical current density JC in high quality BaFe1.84Co0.16As2 (Co-doped Ba122 type) thin films is investigated. The films are prepared by pulsed-laser-deposition (PLD) on CaF2 (00 $l$) substrates. The irradiation dosages are varied between 1 × 1013 and 1 × 1016 cm−2. Upon irradiation, the superconducting transition temperature TC drops slightly from 25 K for the unirradiated sample to about 20 K for the sample with the highest irradiation level. The JC values of the thin film samples are calculated by using the Bean critical state model. The results showed that JC could be enhanced substantially. The maximum JC value at 4.5 K temperature is enhanced up to 2.4 MA cm−2 under 1 T field. The analysis of pinning force dependence on magnetic field shows that the pinning behavior is not changed in the irradiated samples, suggesting more pinning centers of similar nature to those of presented in the unirradiated samples are introduced by the irradiation process. The results indicate that the irradiation of light element ions He+ with relatively low energy could increase the critical current density in iron based superconductors.

An apparatus has been built to perform irradiation and electrical testing of REBCO coated conductors (CC) held below their critical temperature (Tc). Patterned tracks of Fujikura GdBCO CC were irradiated with 2 MeV He+ ions in steps up to 4 mdpa whilst held at 40 K, and the critical current density (Jc) determined from I–V characteristics. These 'in-situ' samples then underwent annealing experiments at room temperature. The superconducting performance, both before and after room temperature annealing, has been compared to equivalent samples irradiated at room temperature and then cooled for testing at 40 K to understand how the damage tolerance of these materials is affected by sample temperature. Details of the apparatus and experimental results from preliminary work are presented and discussed. These preliminary results show that both Tc and Jc values of patterned tracks degrade with irradiation dose, with most samples showing similar behaviour. The room temperature annealing of 'in-situ' irradiated samples resulted in a significant recovery of properties. We conclude that irradiation temperature does alter how the superconducting properties of GdBCO CC are affected by ion irradiation, and that this observation has implications for the design of high temperature superconducting magnets for future fusion reactors.

Transmission electron microscopy (TEM) of ex-situ He ion irradiated bulk W has been performed to quantitatively compare the damage microstructure to that observed in regions of comparable thicknesses during in-situ ion irradiation with TEM experiments. Samples were irradiated to achieve He-appm/DPA ratios of 2000 and 500 at temperatures of 500 and 800 °C to 1.5 and 3.0 DPA. For irradiations at 500 °C, bubble diameters (∼2 nm) were larger and areal bubble densities (∼1012 bubbles/cm2) were lower than those in the in-situ experiments. This is attributed to greater amounts of He being retained in the ex-situ bulk experiments whereas in the in-situ experiments some may escape due to the proximity of surfaces. Dislocation loops were observed in all samples and were characterised as b = ±½ type with no b = type loops. Dislocation loop populations were dominated by interstitial type (∼60%) agreeing with in-situ experiments. However, dislocation loops in this work were larger, ranging in size from 7 to 100 nm and large concentrations of entangled dislocation lines were observed in the bulk of the grain as compared to in the in-situ experiments.

Films of ZnO have been implanted with fluxes of Co and Eu ions so as to give a layer of Zn0.96Co0.04O or Zn0.96Eu0.04O or Zn0.92Co0.04Eu0.04O that is approximately 15 nm thick. The ZnO films were deposited by pulsed laser deposition and had an O-polar surface. The properties of the as-implanted films were compared with those obtained after annealing in air and vacuum. The amount of radiation damage was measured using Raman scattering. Measurements of the lattice constants and EXAFS demonstrated that after annealing in air the Co2+ were on Zn sites in the lattice and Eu3+ ions were surrounded by oxygen ions. The air-annealed films were ferromagnetic and the magnetic moment of the ZnCoEuO was close to the sum of that from ZnCoO and ZnEuO. This method of producing ferromagnetic ZnCoO and ZnEuO films was competitive with other methods including pulsed laser deposition.

The nature of the electronic state of a metal depends strongly on its dimensionality. In a system of isolated conducting chains, the Fermi-liquid (quasiparticle) description appropriate for higher dimensions is replaced by the so-called Tomonaga-Luttinger liquid picture characterized by collective excitations of spin and charge. Temperature is often regarded as a viable tuning parameter between states of different dimensionality, but what happens once thermal broadening becomes comparable to the interchain hopping energy remains an unresolved issue, one that is central to many organic and inorganic conductors. Here we use the ratio of the thermal to electrical conductivities to probe the nature of the electronic state in PrBa2Cu4O8 as a function of temperature. We find that despite the interchain transport becoming non-metallic, the charge carriers within the CuO chains appear to retain their quasiparticle nature. This implies that temperature alone cannot induce a crossover from Fermi-liquid to Tomonaga-Luttinger-liquid behaviour in quasi-one-dimensional metals.

The polarization beam splitter is a key component for polarization manipulation in photonic integrated circuits, but it is challenging to design for low-refractive-index optical materials, due to the low birefringence of the waveguides. We propose what we believe is a novel compact vertical-dual-slot waveguide-based coupling scheme for silicon carbide, enabling efficient low-birefringence polarization splitting by extensively modulating the transverse-magnetic mode distribution. We numerically and experimentally demonstrate the device in the 4H-silicon-carbide-on-insulator integrated platform, with a small footprint of 2.2 μm×15 μm. The device, easy to fabricate via a single lithography process as other components on the chip, exhibits low insertion loss of

Materials research for advances in fusion technologies will depend an analytical sensitivity to Li, but appropriate nuclear reaction cross-sections are very poorly known. Here we determined the differential cross-sections for 7Li(3He,p0~4)9Be, 7Li(3He,d0)8Be and 6Li(3He,p0)8Be from 1.2 to 3 MeV at a lab angle of 146°. All sources to the total combined standard uncertainty in the measurement were discussed in detail.

An understanding of the effect of cumulative radiation damage on the integrity of ceramic wasteforms for plutonium and minor actinide disposition is key to the scientific case for safe disposal. Alpha recoil due to the decay of actinide species leads to the amorphisation of the initially crystalline host matrix, with potentially deleterious consequences such as macroscopic volume swelling and reduced resistance to aqueous dissolution. For the purpose of laboratory studies the effect of radiation damage can be simulated by various accelerated methodologies. The incorporation of short-lived actinide isotopes accurately reproduces damage arising from both alpha-particle and the heavy recoil nucleus, but requires access to specialist facilities. In contrast, fast ion implantation of inactive model ceramics effectively simulates the heavy recoil nucleus, leading to amorphisation of the host crystal lattice over very short time-scales. Although the resulting materials are easily handled, quantitative analysis of the resulting damaged surface layer has proved challenging. In this investigation, we have developed an experimental methodology for characterisation of radiation damaged structures in candidate ceramics for actinide disposition. Our approach involves implantation of bulk ceramic samples with 2 MeV Kr+ ions, to simulate heavy atom recoil; combined with grazing incidence X-ray absorption spectroscopy (GI-XAS) to characterise only the damaged surface layer. Here we present experimental GI-XAS data acquired at the Ti and Zr K-edges of ion implanted zirconolite, as a function of grazing angle, demonstrating that this technique can be successfully applied to characterise only the amorphised surface layer. Comparison of our findings with data from metamict natural analogues provide evidence that heavy ion implantation reproduces the amorphous structure arising from naturally accumulated radiation damage.

Both Rutherford backscatterings of He-4(+) beams and non-Rutherford backscatterings of He-4(+) and H+ beams have been used in this study to investigate the depth profiles of B dopant in Mg target upon B implantation and post annealing. Primitive data analysis suggests an enhanced diffusion of surface C contaminant during the B implantation process, together with enhanced surface oxidation upon implantation and thermal annealing in flowing N-2 atmosphere. Published by Elsevier B.V.