The differences in energy between electronic bands due to valley splitting are of paramount importance in interpreting transport spectroscopy experiments on state-of-the-art quantum devices defined by scanning tunnelling microscope lithography. Using vasp, we develop a plane-wave density functional theory description of systems which is size limited due to computational tractability. Nonetheless, we provide valuable data for the benchmarking of empirical modelling techniques more capable of extending this discussion to confined disordered systems or actual devices. We then develop a less resource-intensive alternative via localised basis functions in siesta, retaining the physics of the plane-wave description, and extend this model beyond the capability of plane-wave methods to determine the ab initio valley splitting of well-isolated δ-layers. In obtaining an agreement between plane-wave and localised methods, we show that valley splitting has been overestimated in previous ab initio calculations by more than 50%.

Monolayer δ-doped structures in silicon have attracted renewed interest with their recent incorporation into atomic-scale device fabrication strategies as source and drain electrodes and in-plane gates. Modeling the physics of δ-doping at this scale proves challenging, however, due to the large computational overhead associated with ab initio and atomistic methods. Here, we develop an analytical theory based on an effective mass approximation. We specifically consider the Si:P materials system, and the limit of high donor density, which has been the subject of recent experiments. In this case, metallic behavior including screening tends to smooth out the local disorder potential associated with random dopant placement. While smooth potentials may be difficult to incorporate into microscopic, single-electron analyses, the problem is easily treated in the effective mass theory by means of a jellium approximation for the ionic charge. We then go beyond the analytic model, incorporating exchange and correlation effects within a simple numerical model. We argue that such an approach is appropriate for describing realistic, high-density, highly disordered devices, providing results comparable to density functional theory, but with greater intuitive appeal, and lower computational effort. We investigate valley coupling in these structures, finding that valley splitting in the low-lying Γ band grows much more quickly than the Γ-∆ band splitting at high densities. We also find that many-body exchange and correlation corrections affect the valley splitting more strongly than they affect the band splitting.

Objective Combined, nursing and allied health constitute most of the Australian health workforce; yet, little is known about graduate practice destinations. University Departments of Rural Health have collaborated on the Nursing and Allied Health Graduate Outcomes Tracking to investigate graduate entry into rural practice. Design Data linkage cohort study. Setting Monash University and the University of Newcastle. Participants Graduates who completed their degree in 2017 across seven disciplines. Main outcome measure(s) The outcome variable was Australian Health Practitioner Regulation Agency principal place of practice data. Explanatory variables included discipline, age, gender, location of origin, and number and duration of rural placements. Result Of 1130 graduates, 51% were nurses, 81% females, 62% under 21 years at enrolment, 23% of rural origin, 62% had at least one rural student placement, and 23% had over 40 cumulative rural placement days. At the time of their second Australian Health Practitioner Regulation Agency registration, 18% worked in a ‘Rural principal place of practice.’ Compared to urban, rural origin graduates had 4.45 times higher odds ratio of ‘Rural principal place of practice.’ For graduates who had <20 cumulative rural placement days, compared to zero the odds ratio of ‘Rural principal place of practice’ was the same (odds ratio = 1.10). For those who had 20‐40 rural placement days, the odds ratio was 1.93, and for >40 rural placement days, the odds ratio was 4.54). Conclusion Rural origin and more rural placement days positively influenced graduate rural practice destinations. Outcomes of cumulative placements days may compare to immersive placements.

Recent breakthroughs in single-atom fabrication in silicon have brought the exciting prospect of monolayerbased nanoelectronics and theoretical understanding of such systems into sharp focus. Of particular interest is the effect of such sharp two-dimensional Coulomb array confinement on electronic properties of these donor-based semiconducting systems such as valley splitting, which is critical to quantum electronic applications. In this paper we apply ab initio techniques to these high-density donor systems specifically in order to investigate the approach to monolayer confinement. An optimized basis set is developed for Si:P and validated against our previous work on single δ-doped layers. A systematic study is then conducted wherein the effect of multiple adjacent phosphorus δ layers on the electronic properties of the material is explored. We find nonmonotonic electronic behavior as we approach the monolayer confinement limit, with potentially far-reaching implications for large-scale fabrication techniques.

Epitaxial circuitry offers a revolution in silicon technology, with components that can be fabricated on atomic scales. We perform the first ab initio calculation of atomically thin epitaxial nanowires in silicon, investigating the fundamental electronic properties of wires two P atoms thick, similar to those produced this year by Weber et al. For the first time, we catch a glimpse of disorder-related effects in the wires--a prerequisite for understanding real fabricated systems. Interwire interactions are made negligible by including 40 ML of silicon in the vertical direction (and the equivalent horizontally). Accurate pictures of band splittings and the electronic density are presented, and for the first time the effective masses of electrons in such device components are calculated.

A mixture of cyclic gold(I) complexes [Au(2)(μ-cis-dppen)(2)]X(2) (X = OTf 1, PF(6)3) and [Au(cis-dppen)(2)]X (X = OTf 2, PF(6)4) is obtained from the reaction of [Au(tht)(2)]X (tht = tetrahydrothiophene) with one equivalent of cis-dppen [dppen = 1,2-bis(diphenylphosphino)ethylene]. The analogous reaction with trans-dppen or dppa [dppa = bis(diphenylphosphino)acetylene] affords the cyclic trinuclear [Au(3)(μ-trans-dppen)(3)]X(3) (X = OTf 11, PF(6)12) and tetranuclear [Au(4)(μ-dppa)(4)]X(4) (X = OTf 13, PF(6)14, ClO(4)15) gold complexes, respectively. Recrystallization of 15 from CH(2)Cl(2)/MeOH yielded a crystal of the octanuclear gold cluster [Au(8)Cl(2)(μ-dppa)(4)](ClO(4))(2)16. Attempts to prepare dicationic binuclear gold(II) species from the reaction of a mixture of 3 and 4 with halogens gave a mixture of products, the components of which confirmed to be acyclic binuclear gold(I) [Au(2)X(2)(cis-dppen)] (X = I 5, Br 7) and cyclic mononuclear gold(III) [AuX(2)(cis-dppen)]PF(6) (X = I 6, Br 8) complexes. Complexes 11-14 reveal weak emission in butyronitrile glass at 77 K, but they are non-emissive at room temperature. Ab initio modelling was performed to determine the charge state of the gold atoms involved. Extensive structural comparisons were made to experimental data to benchmark these calculations and rationalize the conformations.

Novel physical phenomena emerge in ultra-small sized nanomaterials. We study the limiting small-size-dependent properties of MoS2 monolayer rhombic nanoflakes using density-functional theory on structures of size up to Mo35S70 (1.74 nm). We investigate the structural and electronic properties as functions of the lateral size of the nanoflakes, finding zigzag is the most stable edge configuration, and that increasing size is accompanied by greater stability. We also investigate passivation of the structures to explore realistic settings, finding increased HOMO-LUMO gaps and energetic stability. Understanding the size-dependent properties will inform efforts to engineer electronic structures at the nano-scale.

The s manifold energy levels for phosphorus donors in silicon are important input parameters for the design and modeling of electronic devices on the nanoscale. In this paper we calculate these energy levels from first principles using density functional theory. The wavefunction of the donor electron’s ground state is found to have a form that is similar to an atomic s orbital, with an effective Bohr radius of 1.8 nm. The corresponding binding energy of this state is found to be 41 meV, which is in good agreement with the currently accepted value of 45.59 meV. We also calculate the energies of the excited 1s(T 2) and 1s(E) states, finding them to be 32 and 31 meV respectively.