Revised Fowler-Dubridge model for photoelectron emission from two-dimensional materials

We revise the Fowler-Dubridge (FB) model for photoelectron emission from two-dimensional (2D) materials to include the effects of reduced dimensionality, non-parabolic and anisotropic energy dispersion of 2D materials. Two different directions of electron emission are studied, namely vertical emission from the surface and lateral emission from the edge. Our analytical model reveals a universal temperature scaling of T\b{eta} with \b{eta} = 1 and \b{eta} = 3/2, respectively, for the surface and edge emission over a wide class of 2D materials, which are distinct from the traditional scaling of \b{eta} = 2 originally derived for the traditional bulk materials. Our comparison shows good agreement to two experiments of photo-electron emitted from graphene for both surface and edge emission. Our calculations also show the photoelectron emission is more pronounced than the coexisting thermionic emission for materials with low temperature and Fermi energy. This model provides helpful guidance in choosing proper combinations of light intensity, temperature range and type of 2D materials for the design of photoemitters, photodetectors and other optoelectronicsComment: 6 pages, 4 figure

A holistic approach to the evaluation of sustainable housing

Residential housing is often evaluated against single or at best a limited number of similar criteria. These include quantifiable indicators such as energy use and its associated greenhouse gas emissions. It might also include material consumption from an embodied energy or resource use perspective. Social factors or qualitative indicators may be evaluated but are rarely placed or juxtaposed alongside these quantifiable indicators. A one-dimensional approach will be limiting because sustainable development includes both environmental and social factors. This paper describes the methodologies that have been developed to assess housing developments against five quite different criteria. These are: energy use, resource use, neighbourhood character, neighbourhood connectedness and diversity. In each case, high and low sustainability practice has been identified so that ranking is possible. These methodologies have then been tested by evaluating a typical precinct (approximately 400 m by 400 m) of a 1970-80s housing development in a suburb of Geelong. The rankings of the particular precinct have then been combined in a visual way to assist in the evaluation of the housing in a more holistic way. The results of this evaluation method are presented, along with a discussion of the strengths and weaknesses of the methodologies. The research is the outcome of collaboration by a cross-disciplinary group of academics within Deakin’s School of Architecture and Building

Control of atom-photon interactions with shaped quantum electron wavepackets

Photon emission from atoms and free electrons underlie a wealth of fundamental science and technological innovations. We present a regime where atom-photon and electron-photon interactions interfere with each other, resulting in substantial changes in the spontaneous emission rate compared to the sum of each interaction considered in isolation. We highlight the critical role played by quantum electron wavepackets, and how the emission can be tailored via the electron waveshape, as well as the atomic population and coherence. Our findings reveal that atom-photon and electron-photon interactions cannot be considered in isolation even when higher-order contributions involving all three bodies (atom, photon and free electron) are negligible. Our findings pave the way to more precise control over photon emission processes and related diagnostics.Comment: 9 pages, 4 figure

Electron beam ablation of materials

The channelspark, a low accelerating voltage, high current electron beam accelerator, has been used for ablation of materials applied to thin film deposition. The channelspark operates at accelerating voltages of 10 to 20 kV with ∼1500 A beam currents. The electron beam ionizes a low-pressure gas fill (10–20 mTorr Ar or N2)N2) to compensate its own space charge, allowing ion focused transport. Ablation of TiN, Si, and fused silica has been studied through several plasma diagnostics. In addition, thin films of SiO2SiO2 have been deposited and analyzed. Strong optical emission from ionized species, persisting for several microseconds, was observed in the electron beam ablated plumes. Free electron temperatures were inferred from relative emission intensities to be between 1.1 and 1.2 eV. Dye-laser-resonance-absorption photography showed Si atom plume expansion velocities from 0.38 to 1.4 cm/μs for several pressures of Ar or N2N2 background gas. A complex, multilobed plume structure was also observed, yielding strong indications that an electron beam instability is occurring, which is dependent upon the conductivity of the target. Nonresonant interferometry yielded line-averaged electron densities from 1.6 to 3.7×1023 m−33.7×1023m−3 near the target surface. Resonant UV interferometry performed on Si neutral atoms generated in the ablation plumes of fused silica targets measured line integrated densities of up to 1.6×1016 cm−2,1.6×1016cm−2, with the total number of ablated silicon neutrals calculated to be in the range 2.0×10152.0×1015 to 5.0×1013.5.0×1013. Electron beam deposited films of fused silica were microscopically rough, with a thickness variation of 7%. The average SiO2SiO2 deposition rate was found to be about 0.66 nm/shot. The electron beam-deposited fused silica films had accurately maintained stoichiometry. Ablated particulate had an average diameter near 60 nm, with a most probable diameter between 40 and 60 nm. For SiO2SiO2 targets, the mass of material ablated in the form of particulate made up only a few percent of the deposited film mass, the remainder being composed of atomized and ionized material. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70186/2/JAPIAU-86-12-7129-1.pd

Dynamics of electron beam ablation of silicon dioxide measured by dye laser resonance absorption photography

The dynamics of electron beam ablation plumes have been characterized through the application of dye laser resonance absorption photography. The ablation of fused silica by a channelspark electron beam was studied by probing the near-ground state, 3p2 1D−4s 1P03p21D−4s1P0 neutral Si transition at 288.158 nm. Necessary background gases (Ar or N2)N2) were tested at pressures of 15 or 30 mTorr. A two-lobed, Si atom plume shape was discovered that is hydrodynamically more complex than laser ablation plumes. These plumes merge into a single-lobed plume at about 400 ns after the e-beam current pulse rise. Plume front expansion velocities of Si atoms were measured at nearly 1 cm/μs, and are comparable to the expansion of laser ablated metal atom plumes with laser fluences of a few J/cm2. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70034/2/APPLAB-73-18-2576-1.pd

Space-charge-limited flows in the quantum regime

This paper reviews the recent developments of space-charge-limited (SCL) flow or Child-Langmuir (CL) law in the quantum regime. According to the classical CL law for planar diodes, the current density scales as 3/23∕2’s power of gap voltage and to the inverse squared power of gap spacing. When the electron de Broglie wavelength is comparable or larger than the gap spacing, the classical SCL current density is enhanced by a large factor due to electron tunneling and exchange-correlation effects, and there is a new quantum scaling for the current density, which is proportional to the 1/21∕2’s power of gap voltage, and to the inverse fourth-power of gap spacing. It is also found that the classical concepts of the SCL flow such as bipolar flow, transit time, beam-loaded capacitance, emitted charge density, and magnetic insulation are no longer valid in quantum regime. In the quantum regime, there exists a minimum transit time of the SCL flows, in contrast to the classical solution. By including the surface properties of the emitting surface, there is a threshold voltage that is required to obtain the quantum CL law. The implications of the Fowler-Nordheim-like field emission in the presence of intense space charge over the nanometer scale is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87757/2/056701_1.pd

Evaluation of housing developments for sustainability using a multi-criteria approach

New housing developments in Australia, particularly on Greenfield sites on the edge of existing urban centres, need to be sustainable in environmental and social terms if long term problems are to be avoided. Sustainability is multi-dimensional and existing analyses have been found to be inadequate in assessing housing developments holistically. This paper describes research which has used five criteria (energy use, resource use, neighbourhood character, neighbourhood connectivity and diversity), representing 31 indicators, to assess three housing precincts of a regional city in southern Australia. The method has been found to produce useful assessments of sustainability. The method has the potential to inform future housing developments and to be used to improve existing suburbs