Towards smooth (010) ß-Ga2O3films homoepitaxially grown by plasma assisted molecular beam epitaxy: The impact of substrate offcut and metal-to-oxygen flux ratio

Smooth interfaces and surfaces are beneficial for most (opto)electronic devices that are based on thin films and their heterostructures. For example, smoother interfaces in (010) ß-Ga2O3/(AlxGa1-x)2O3 heterostructures, whose roughness is ruled by that of the ß-Ga2O3 layer, can enable higher mobility 2-dimensional electron gases by reducing interface roughness scattering. To this end we experimentally prove that a substrate offcut along the [001] direction allows to obtain smooth ß-Ga2O3 layers in (010)-homoepitaxy under metal-rich deposition conditions. Applying In-mediated metal-exchange catalysis (MEXCAT) in molecular beam epitaxy at high substrate temperatures (Tg = 900 °C) we compare the morphology of layers grown on (010)-oriented substrates having different unintentional offcuts. The layer roughness is generally ruled by (i) the presence of (110)-and bar 110-facets visible as elongated features along the [001] direction (rms < 0.5 nm), and (ii) the presence of trenches (5-10 nm deep) orthogonal to [001]. We show that an unintentional substrate offcut of only ˜ 0.1° almost oriented along the [001] direction suppresses these trenches resulting in a smooth morphology with a roughness exclusively determined by the facets, i.e. rms ˜ 0.2 nm. Since we found the facet-and-trench morphology in layer grown by MBE with and without MEXCAT, we propose that the general growth mechanism for (010)-homoepitaxy is ruled by island growth whose coalescence results in the formation of the trenches. The presence of a substrate offcut in the [001] direction can allow for step-flow growth or island nucleation at the step edges, which prevents the formation of trenches. Moreover, we give experimental evidence for a decreasing surface diffusion length or increasing nucleation density on the substrate surface with decreasing metal-to-oxygen flux ratio. Based on our experimental results we can rule-out step bunching as cause of the trench formation as well as a surfactant-effect of indium during MEXCAT. © 2020 The Author(s). Published by IOP Publishing Ltd

Australian Transnational Educational Leadership Roles: Challenges, Opportunities and Experiences

The establishment of higher educational hubs in Malaysia and Singapore has spurred the growth of transnational education (TNE) offerings in Asia, and attracted several Australian higher education providers to set up branch campuses in these countries. In Malaysia, TNE is seen as contributing to economic targets by helping to decrease the outflow of students and currency, and by attracting international students to Malaysian shores (British Council 2012). The provision of higher education through TNE raises issues somewhat distinct from those arising with local provision of higher education. These include the balance of local and foreign educational decision making and its implications for academic staff and for the learning experiences of students. This paper is informed by ‘Learning without Borders: Leadership in transnational education and internationalization of curriculum’, an Australian Office of Learning and Teaching (OLT) funded project undertaken at Curtin University and Swinburne University of Technology, involving Australian campuses and branch campuses. The project investigated staff experiences, expectations and preferences on TNE issues including career path opportunities, teaching and learning implications. The project focused particularly on the development of recognition and support for leadership roles in transnational education and on internationalization of curriculum. The paper highlights some of the TNE and internationalization measures that might enhance staff experiences and student learning

Ga2O3 polymorphs: Tailoring the epitaxial growth conditions

Gallium oxide is a wide bandgap n-type semiconductor highly interesting for optoelectronic applications (e.g., power electronics and solar blind UV photodetectors). Besides its most thermodynamically stable monoclinic β phase, Ga2O3 can crystallize in different polymorphs; among them the corundum α and the orthorhombic ϵ phases are the most promising ones. In this review we focus on the main aspects that promote the nucleation and stable growth of these Ga2O3 polymorphs. Particular emphasis is given to the ϵ phase since it is recently gaining increasing attention in the scientific community because of: (i) its higher lattice symmetry with respect to β-Ga2O3, which could favour the realization of heterostructures, (ii) the possibility to be grown on cheap sapphire substrates and (iii) its peculiar piezoelectric properties. While the growth of β-Ga2O3 is widely studied and understood, a thorough and comprehensive analysis of the chemical and physical aspects that allow for the stabilization of the metastable Ga2O3 phases with different synthesis methods is still missing. Therefore, the present review aims at filling this gap, by analysing the relevant growth parameters for several growth techniques (MOVPE, HVPE, mist-CVD, MBE, and PLD), highlighting similarities and differences, looking for a unified framework to understand the growth and nucleation of different Ga2O3 polymorphs. As a conclusion, we highlight practical guidelines for the deposition of the different Ga2O3 polymorphs with all the discussed thin film growth techniques

Faceting and metal-exchange catalysis in (010) β-Ga2O3 thin films homoepitaxially grown by plasma-assisted molecular beam epitaxy

We here present an experimental study on (010)-oriented -Ga2O3 thin films homoepitaxially grown by plasma assisted molecular beam epitaxy. We study the effect of substrate treatments (i.e., O-plasma and Ga-etching) and several deposition parameters (i.e., growth temperature and metal-to-oxygen flux ratio) on the resulting Ga2O3 surface morphology and growth rate. In situ and ex-situ characterizations identified the formation of (110) and (¯110)-facets on the nominally oriented (010) surface induced by the Ga-etching of the substrate and by several growth conditions, suggesting (110) to be a stable (yet unexplored) substrate orientation. Moreover, we demonstrate how metal-exchange catalysis enabled by an additional In-flux significantly increases the growth rate (>threefold increment) of monoclinic Ga2O3 at high growth temperatures, while maintaining a low surface roughness (rms < 0.5 nm) and preventing the incorporation of In into the deposited layer. This study gives important indications for obtaining device-quality thin films and opens up the possibility to enhance the growth rate in -Ga2O3 homoepitaxy on different surfaces [e.g., (100) and (001)] via molecular beam epitaxy

Your place or mine: transnational education and the locus of control

In transnational education the place – in both an organisational and a geographic sense – in which educational decisions are made impacts on the academics involved and on student learning. The subject of this paper is learning and accreditation that takes place outside a home university through offshore branch campuses. A case study of two Australian Universities with offshore campuses in Sarawak, Malaysia was undertaken. Policies and procedures were reviewed and an empirical study of the experiences of academics involved was conducted. The study focused on who makes decisions about curriculum content, learning and teaching activities, design and provision of educational resources, and the assessment of student work. Consequences of the organisational relationships for academics involved and for student learning are examined in this paper. On the basis of the study a high degree of local control is recommended, at least for units of study that have operated transnationally several times

Morphology-driven electrical and optical properties in graded hierarchical transparent conducting Al:ZnO

Graded Al-doped ZnO layers, constituted by a mesoporous forest like system evolving into a compact transparent conductor, were synthesized by Pulsed Laser Deposition with different morphology to study the correlation with functional properties. Morphology was monitored by measuring the resulting surface roughness and its effects on electrical conductivity (especially carrier mobility, which significantly decreases with increasing roughness) allow to discuss the limitations in conduction mechanisms. Significant changes in light scattering capability due to variations in morphology are also investigated and discussed to study the correlation between morphology and functional properties.Comment: 11 pages, 4 figure

Vibrational - Electrical Properties Relationship in Donor Doped TiO2 by Raman Spectroscopy

Transparent conducting TiO2, obtained by Nb or Ta doping of the anatase structure, is gaining increasing attention for the development of transparent electrodes. Usually, regardless the deposition technique, a crystallization process in reducing atmosphere is necessary to achieve large mobility; in addition, electrical and optical properties are also strongly sensitive to the oxygen deposition pressure. These facts reveal that the defect chemistry of donor doped TiO2 is not trivial and involves a strict interplay among extrinsic dopant atoms, oxygen vacancies and ‘electron killer’ defects such as Ti vacancies and O interstitials. We here present a Raman characterization of donor-doped TiO2 films synthesized under several deposition and post-annealing conditions, employing different doping levels and dopant elements (i.e. Ta and Nb). Correlations between structure, crystallinity, shift and width of Raman peaks and electrical properties are shown and discussed. In particular, a clear relationship between the shift of the Eg(1) anatase Raman mode and the charge carrier density is found, while the B1g(1) mode connected to Ti-Ti vibrations is significantly affected by the extrinsic doping level. In this complex framework Raman spectroscopy can provide an invaluable contribution towards understanding the material structure and its influence on the functional properties

Upregulation of natural killer cells functions underlies the efficacy of intratumorally injected dendritic cells engineered to produce interleukin-12

OBJECTIVE: Injection of dendritic cells (DC) engineered with recombinant adenoviral vectors to produce interleukin-12 (IL-12) inside experimental murine tumors frequently achieves complete regressions. In such a system the function of CD8(+) T cells has been shown to be an absolute requirement, in contrast to observations made upon depletion of CD4(+) T cells, which minimally affected the outcome. The aim of this work was to study the possible involvement of natural killer (NK) cells in this setting. MATERIALS, METHODS, AND RESULTS: Depletions with anti-AsialoGM1 antiserum showed only a small decrease in the proportion of complete regressions obtained that correlated with induction of NK activities in lymphatic tissues into which DC migrate, whereas combined depletions of CD4(+) and NK cells completely eliminated the antitumor effects. Likewise in vivo neutralization of interferon-gamma (IFN-gamma) also eliminated those therapeutic effects. Trying to define the cellular role played by NK cells in vivo, it was observed that injection of cultured DC inside the spleen of T- and B-cell-deficient (Rag1(-/-)) mice induced upregulation of NK activity only if DC had been adenovirally engineered to produce IL-12. In addition, identically transfected fibroblasts also activated NK cells, indicating that IL-12 transfection was the unique requirement. Equivalent human DC only activated in vitro the cytolytic and cytokine-secreting functions of autologous NK cells if transfected to express human IL-12. CONCLUSIONS: Overall, these results point out an important role played by NK cell activation in the potent immunotherapeutic effects elicited by intratumoral injection of IL-12--secreting DC and that NK activation under these conditions is mainly, if not only, dependent on IL-12

An anti-ICAM-2 (CD102) monoclonal antibody induces immune-mediated regressions of transplanted ICAM-2-negative colon carcinomas

Monoclonal antibodies (mAbs) can mediate antitumor effects by indirect mechanisms involving antiangiogenesis and up-regulation of the cellular immune response rather than by direct tumor cell destruction. From mAbs raised by immunization of rats with transformed murine endothelial cells, a mAb (EOL4G8) was selected for its ability to eradicate a fraction of established colon carcinomas that did not express the EOL4G8-recognized antigen. The antigen was found to be ICAM-2 (CD102). Antitumor effects of EOL4G8, which required a functional T-cell compartment, were abrogated by depletion of CD8(+) cells and correlated with antitumor CTL activity, whereas only a mild inhibition of angiogenesis was observed. Interestingly, we found that EOL4G8 acting on endothelial ICAM-2 markedly enhances leukotactic factor activity-1-independent adhesion of immature dendritic cells to endothelium-an effect that is at least in part mediated by DC-SIGN (CD209)