ANU Research Publications

Permanent URI for this collectionhttps://hdl.handle.net/1885/26

The Australian National University's Research Publications collection is an online location for collecting, preserving and disseminating the scholarly output of the University. This service allows members of the University to share their research with the wider community. ANU Open Research accepts journal articles, conference papers, book chapters, working or technical papers and other forms of scholarly communication.

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On the maximal numerical range of some matrices
(2018-02-21) Hamed, Ali Nosherwan; Spitkovsky, Ilya Matveevich
The maximal numerical rangeW0(A) of a matrixAis the (regular) numerical rangeW(B) of its compressionBonto the eigenspaceLofA∗Acorresponding to its maximal eigenvalue. So, alwaysW0(A)⊆W(A). Conditions under whichW0(A) has a non-empty intersection with the boundary ofW(A) are established, in particular, whenW0(A) =W(A). ThesetW0(A) is also described explicitly for matrices unitarily similar to direct sums of 2-by-2 blocks, and some insight into thebehavior ofW0(A) is provided whenLhas codimension one.
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“It felt like walking in the dark”: A Collaborative Autoethnography on the Challenges of Conducting LGBTQ+ Research in Southeast Asia
(2026) Bin Ibrahim, Muhamad Alif; G. Pamoso, Aron Harold; Truong, Quynh; Liow, Jun Wei; Delos Santos, Junix Jerald; Ratanashevorn, Rattanakorn; Ojanen, Timo; Htike, Nay Lin; Hastut, Lita Widyo; Liem, Andrian; Tan, Kyle
The extant literature has shown that lesbian, gay, bisexual, transgender, and queer (LGBTQ+) communities face considerable barriers in pursuing higher education and achieving their academic aspirations. To date, a critical gap remains in scholarly understandings of the enablers and barriers faced by researchers conducting LGBTQ+ research in Southeast Asia (SEA). This study aims to illuminate the challenges of conducting LGBTQ+ research in Indonesia, Malaysia, Myanmar, the Philippines, Singapore, Thailand, and Vietnam. As researcher-participants in this study, we conducted a Collaborative Autoethnography, critically reflecting on our work and research with LGBTQ+ communities across these SEA countries. Data were analyzed using Reflexive Thematic Analysis. Through four themes, we illustrated the significant barriers encountered as we navigated the social, legal, and political contexts of SEA societies and academia. The neoliberal Western gaze in SEA academia further compounded these challenges. We grappled with how to garner trust from and represent our respective LGBTQ+ communities in our research. We also faced threats that negatively impacted our overall well-being. Our study underscores the urgency of creating safe spaces for LGBTQ+ researchers and their communities to collaborate on meaningful research agendas and interventions. Collaborative, multisectoral partnerships from various stakeholders can nurture an equity and social justice-based LGBTQ+ research agenda in the region.
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DNA functionalization of carbon nanotubes for ultrathin atomic layer deposition of high $ dielectrics for nanotube transistors with 60 mv/decade switching
(2006) Lu, Yuerui; Bangsaruntip, Sarunya; Wang, Xinran; Zhang, Li; Nishi, Yoshio; Dai, Hongjie
For single-walled carbon nanotube (SWNT) field effect transistors, vertical scaling of high κ dielectrics by atomic layer deposition (ALD) currently stands at ∼8 nm with a subthreshold swing S ≈ 70−90 mV/decade at room temperature. ALD on as-grown pristine SWNTs is incapable of producing a uniform and conformal dielectric layer due to the lack of functional groups on nanotubes and because nucleation of an oxide dielectric layer in the ALD process hinges upon covalent chemisorption on reactive groups on surfaces. Here, we show that by noncovalent functionalization of SWNTs with poly-T DNA molecules (dT40-DNA), one can impart functional groups of sufficient density and stability for uniform and conformal ALD of high κ dielectrics on SWNTs with thickness down to 2−3 nm. This enables approaching the ultimate vertical scaling limit of nanotube FETs and reliably achieving S ≈ 60 mV/decade at room temperature, and S ≈ 50 mV/decade in the band-to-band tunneling regime of ambipolar transport. We have also carried out microscopy investigations to understand ALD processes on SWNTs with and without DNA functionalization.
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Carbon Nanotube Transistors with 60mV/decade Switching and its Capacitance Measurement
(TechConnect, 2007) Lu, Yuerui; Dai, Hongjie; Nishi, Yoshio
Recently, we have been able to approach the ultimate vertical scaling limit of carbon nanotube field effect transistors (FETs) and reliably achieve S ~ 60 mV/decade at room temperature, by non-covalent functionalization of single walled carbon nonotubes (SWNTs) with ploy-T DNA molecules, which can impart functional groups of sufficient density and stability for uniform and conformal ALD of high-? dielectrics (HfO2) with thickness down to 2-3 nm on SWNTs. Moreover, the small top gate stack capacitance (~300aF/um) of the SWNT FET has been successfully measured directly, using a special technique. The mobility of the SWNT FETs at room temperature is also extracted by the capacitance measured directly.
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Taking Refuge: Buddhist Perspectives on Fear
(Australian Scholarly Publications, 2023) Finnigan, Bronwyn; Nellor, Daniel
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Negative Imaginary Systems Theory for Nonlinear Systems: A Dissipativity Approach
(2025) Ghallab, Ahmed G.; Mabrok, Mohammed A.; Petersen, Ian R.
Negative imaginary (NI) systems theory constitutes a well-established theoretical framework for analyzing and designing linear-time-invariant control systems. This article extends NI systems theory to the nonlinear domain using time-domain interpretations of the linear NI property. We formally define the nonlinear negative imaginary (NNI) property for general nonlinear systems using dissipativity notions with respect to a relevant work rate. An NNI system is shown to be dissipative/passive from the input to the time derivative of the output. Using Lyapunov stability theory, we derive a nonlinear generalization of the most general NI robust stability result. Specifically, we establish a robust stability result for the positive feedback interconnections of two NNI systems, serving as a counterpart to the passivity theorem for nonlinear systems. To demonstrate the applicability of this NNI stability result, we provide an example of a control design for a nonlinear mass-spring system, where the input is a force and the output is the mass displacement. In addition, we extend our framework to include NNI systems with free motion and present sufficient conditions under which a cascade connection of an affine-input and an integrator nonlinear system is guaranteed to be NNI.
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Sustainable Production of Activated Carbon from Waste Wood Using Goethite Iron Ore: Sustainability
(2025) Spencer, William; Ibana, Don; Singh, Pritam; Nikoloski, Aleksandar N.
The growing demand for eco-friendly activated carbon necessitates sustainable production methods. This study investigates the conversion of waste wood into activated carbon using goethite iron ore as an activating agent. A high-temperature rotary furnace was used to activate the carbon at 1373 K. The oxygen released from the iron oxide during the heat treatment reacted with the carbon in the wood, resulting in 49% of activated carbon with BET surface areas between 684 m2/g and 770 m2/g. The activated carbon and char showed type I isotherms with micropore areas between 600 m2/g and 668 m2/g, respectively. Additionally, 92% of the iron in the ore was reduced from ferric to ferrous. The findings demonstrate that goethite iron ore is an effective activating agent for producing wood-based activated carbon while also generating metallic iron as a byproduct. This alternative activation method enhances the sustainability and efficiency of activated carbon production.
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Effect of Borax-, KOH-, and NaOH-Treated Coal on Reducing Carbon Waste and Activated Carbon Production in Synthetic Rutile Production from Ilmenite
(2025) Spencer, William; Ibana, Don; Singh, Pritam; Nikoloski, Aleksandar N.
Coal is commonly used as both fuel and reducing agent in producing synthetic rutile from ilmenite (FeTiO3) via the Becher process, which upgrades ilmenite to high-purity TiO2 (>88%). However, coal-based reduction generates significant carbon waste. This study investigated the effect of adding 1–5% w/w potassium hydroxide (KOH), sodium hydroxide (NaOH), and sodium tetraborate (borax) to coal during ilmenite reduction to improve metallisation and reduce carbon burn-off. Results showed that 1% w/w additives significantly increased metallisation to 96% (KOH), 95% (NaOH), and 93% (borax), compared to 80% without additives, while higher concentrations (3–5% w/w) decreased metallisation. Scanning electron microscopy (SEM)analysis showed cleaner particle surfaces and optimal metallisation at 1% w/w, whereas higher additive levels caused agglomeration or sintering due to elevated silica and alumina activity. Additive type also influenced TiO2 quality, with KOH enhancing TiO2 at low concentrations but causing negative effects at higher levels, while NaOH and borax reduced TiO2 quality via sodium-based compound formation. All additives reduced carbon burn-off, with KOH producing the greatest reduction. The iodine number of the carbon residue increased with higher additive concentrations, with KOH achieving 710 mg/g at 1% w/w and 900 mg/g at 5% w/w, making the residue suitable for water treatment. Overall, KOH is the most effective additive for producing high-quality synthetic rutile while minimising carbon waste.
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Electrically driven light emission from hot single-walled carbon nanotubes at various temperatures and ambient pressures
(2007) Wang, Xinran; Zhang, Li; Lu, Yuerui; Dai, Hongjie; Kato, YK; Pop, Eric
Electroluminescence of individual single-walled carbon nanotubes down to ~ 15 K is measured. We observe electrically driven light emission from suspended quasimetallic nanotubes in vacuum down to ~ 15 K and under different gas pressures at room temperature. Light emission is found to originate from hot electrons in the presence of electrically driven nonequilibrium optical phonons. Reduced light emission is observed in exponential manner as electron and optical phonon temperatures in the nanotube are lowered by lower ambient temperature or higher gas pressure. The results reveal over wide ambient conditions, light emission in a suspended tube is from thermally excited electron-hole recombination.
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Radioisotope-powered ion gauge with super high stability, long life, and large sensitivity range from ultrahigh vacuum to high pressure
(2010) Lu, Yuerui; Lal, Amit
The authors report the radioisotope-powered ion gauge (RPIG) using the safe, low activity, planar radioactive 63Ni beta thin-film source as the cold cathode. RPIG has both high stability and long lifetime with 63Ni half-life of 100.1 years. The authors experimentally demonstrate an ultrahigh sensor dynamic range, from high vacuum (10−6 Torr) to high pressure (103 Torr), which is the largest sensitivity range among all the reported pressure sensors. With high source stability independent of temperature, and its self-powered nature, RPIG is a promising candidate for pressure measurement, which needs extreme low temperature or high temperature, in microsystems where power consumption and system complexity need to be minimized
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High-efficiency ordered silicon nano-conical-frustum array solar cells by self-powered parallel electron lithography
(2010) Lu, Yuerui; Lal, Amit
Nanostructured silicon thin film solar cells are promising, due to the strongly enhanced light trapping, high carrier collection efficiency, and potential low cost. Ordered nanostructure arrays, with large-area controllable spacing, orientation, and size, are critical for reliable light-trapping and high-efficiency solar cells. Available top-down lithography approaches to fabricate large-area ordered nanostructure arrays are challenging due to the requirement of both high lithography resolution and high throughput. Here, a novel ordered silicon nano-conical-frustum array structure, exhibiting an impressive absorbance of ∼99% (upper bound) over wavelengths 400−1100 nm by a thickness of only 5 μm, is realized by our recently reported technique self-powered parallel electron lithography that has high-throughput and sub-35-nm high resolution. Moreover, high-efficiency (up to 10.8%) solar cells are demonstrated, using these ordered ultrathin silicon nano-conical-frustum arrays. These related fabrication techniques can also be transferred to low-cost substrate solar energy harvesting device applications.
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Electrical transport properties and field effect transistors of carbon nanotubes
(2006) Dai, Hongjie; Javey, Ali; Pop, Eric; Mann, David; Kim, Woong; Lu, Yuerui
This paper presents a review on our recent work on carbon nanotube field effect transistors, including the development of ohmic contacts, high-κ gate dielectric integration, chemical functionalization for conformal dielectric deposition and pushing the performance limit of nanotube FETs by channel length scaling. Due to the importance of high current operations of electronic devices, we also review the high field electrical transport properties of nanotubes on substrates and in freely suspended forms. Owing to their unique properties originating from their crystalline 1D structure and the strong covalent carbon–carbon bonding configuration, carbon nanotubes are highly promising as building blocks for future electronics. They are found to perform favorably in terms of ON-state current density as compared to the existing silicon technology, owing to their superb electron transport properties and compatibility with high-κ gate dielectrics. Future directions and challenges for carbon nanotube-based electronics are also discussed.
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Vacuum-free self-powered parallel electron lithography with sub-35-nm resolution
(2010) Lu, Yuerui; Lal, Amit
The critical dimension, throughput, and cost of nanolithography are central to developing commercially viable high-performance nanodevices. Available top-down lithography approaches to fabricate large-area nanostructures at low cost, such as controllable nanowire (NW) array fabrication for solar cells applications, are challenging due to the requirement of both high lithography resolution and high throughput. Here, a minimum 35 nm resolution is experimentally demonstrated by using a new mask fabrication technique in our demonstrated vacuum-free high-throughput self-powered parallel electron lithography (SPEL) system, which uses large-area planar radioactive β-electron thin film emitters to parallel expose e-beam resist through a stencil mask. SPEL is the first-time demonstrated vacuum-free electron lithography, which overcomes the membrane mask distortion challenge that was shown to be the Achilles heel of previous attempts at electron projection lithography in vacuum. Monte Carlo simulations show that by using beryllium tritide thin film source in SPEL system, the exposure time can be reduced down to 2 min for each large-area (10000 cm2 or more) parallel exposure, with resolution not larger than 20 nm. Moreover, experimental demonstration of large-area diameter-and-density controllable vertical NW arrays fabricated by SPEL shows its promising utility for an application requiring large-area nanostructure definition.
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Self-powered near field electron lithography
(2009) Lu, Yuerui; Yoshimizu, Norimasa; Lal, Amit
Electron beam exposure is the tool of choice for highest resolution lithography but suffers from the low throughput during serial beam writing T. Ito and S. Okazaki, Nature (London) 406, 1027 (2000); R. F. Pease and S. Y. Chou, Proc. IEEE 96, 248 (2008). The authors designed and developed a low-cost self-powered near-field electron lithography (SPEL ) technique, which utilizes the spontaneously emitted energetic electrons from beta-emitting radioisotope thin films. This approach enables massively parallel e-beam lithography, with potentially arbitrarily large concurrently exposed surface area, controlled by the size of the radioactive source. This method potentially eliminates the need for vacuum systems and the electron focusing column as needed in the existing electron beam lithography systems. This will greatly simplify the overall lithographic system and reduce the cost of deep-subnanometer lithography. In SPEL system, emitted electrons are spatially blocked using a nanostenciled micromachined mask that is placed in proximity to an electron sensitive resist on the silicon substrate (Fig. 1). The electrons that are not blocked, impact and enter the e-beam resist, along with secondary electrons generated by primary electrons impacting the sidewalls of the stencil layer. Using three-dimensional 3D Monte Carlo (MC) simulations of electron paths, the authors show that the critical dimension (CD) in the system could be down to 20 nm with 14.9 keV electrons emitted from 63Ni. The 3D MC simulation considered both elastic scattering and inelastic scattering for the high energetic primary electrons as well as the cascade secondary electrons generated. The 20 nm limit is imposed by the secondary emission scattering. In order to prove the concept, experiments were conducted using the safe and low-activity (1 mCi/cm2) beta particle emitting 63Ni thin film source with electrons emitted at an average energy of 14.9 keV. They exposed negative tone resist NEB31A, and a minimum gap between ebeam resist posts or CD of 100 nm was achieved. The secondary electrons generated by the primary electron impact onto mask are also useful for exposure. Compared to traditional electron beam lithography, with serial raster scanning taking days to expose a wafer, the lithography system will enable parallel exposure of large patterns on arbitrarily large wafers in several minutes. SPEL may enable massively parallel top-down approach to realizing nanostructures in bulk quantities.
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Regulate the polarity of phosphorene’s mechanical properties by oxidation
(2017) Lü, Tie-Yu; Feng, Hai; Zhang, Yufeng; Lu, Yuerui; Zheng, Jin-Cheng
How to effectively manipulate the mechanical properties of atomically thin materials, is critical and can enable many new types of devices for various applications, such as sensing, actuation, energy harvesting, and so on. Here, we propose and demonstrate a new way to regulate the polarity of phosphorene’s mechanical properties by controlling the level of oxidation. Phosphorene and its low-level oxides are treated with ab initio methods in order to evaluate the influence of oxidation on the anisotropic mechanical properties of phosphorene. Our results show that the mechanical properties of phosphorene are anisotropic. For the stable configuration, the anisotropy is gradually reduced with the increase of the oxygen coverage. We have fitted the formulas of Young’s (shear) modulus and Poisson’s ratio of phosphorene oxide. We also investigated the mechanical properties of metastable configurations. The diagonal configuration increases the anisotropy. The horizontal configuration is very unstable and has no shear moduli. Our results demonstrate that the mechanical properties of phosphorene can be regulated by oxidation, which is useful in design of phosphorene-based mechanical and optoelectronic devices. Our general model for calculating the elastic modulus along arbitrary direction can be applied in any 2D materials
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Low-concentration mechanical biosensor based on a photonic crystal nanowire array
(2011) Lu, Yuerui; Peng, Songming; Luo, Dan; Lal, Amit
The challenge for new biosensors is to achieve detection of biomolecules at low concentrations, which is useful for early-stage disease detection. Nanomechanical biosensors are promising in medical diagnostic applications. For nanomechanical biosensing at low concentrations, a sufficient resonator device surface area is necessary for molecules to bind to. Here we present a low-concentration (500 aM sensitivity) DNA sensor, which uses a novel nanomechanical resonator with ordered vertical nanowire arrays on top of a Si/SiO2 bilayer thin membrane. The high sensitivity is achieved by the strongly enhanced total surface area-to-volume ratio of the resonator (108 m−1) and the state-of-the-art mass-per-area resolution (1.8×10−12 kg m−2). Moreover, the nanowire array forms a photonic crystal that shows strong light trapping and absorption over broad-band optical wavelengths, enabling high-efficiency broad-band opto-thermo-mechanical remote device actuation and biosensing on a chip. This method represents a mass-based platform technology that can sense molecules at low concentrations.
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Optical properties of ultrashort semiconducting single-walled carbon nanotube capsules down to sub-10 nm
(2008) Sun, Xiaoming; Zaric, Sasa; Daranciang, Dan; Welsher, Kevin; Lu, Yuerui; Li, Xiaolin; Dai, Hongjie
Single-walled carbon nanotubes (SWNTs) are typically long (≳100 nm) and have been well established as novel quasi one-dimensional systems with interesting electrical, mechanical, and optical properties. Here, quasi zero-dimensional SWNTs with finite lengths down to the molecular scale (7.5 nm in average) were obtained by length separation using a density gradient ultracentrifugation method. Different sedimentation rates of nanotubes with different lengths in a density gradient were taken advantage of to sort SWNTs according to length. Optical experiments on the SWNT fractions revealed that the UV−vis−NIR absorption and photoluminescence peaks of the ultrashort SWNTs blue-shift up to ∼30 meV compared to long nanotubes, owing to quantum confinement effects along the length of ultrashort SWNTs. These nanotube capsules essentially correspond to SWNT quantum dots.
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Hydrogenation and hydrocarbonation and etching of single-walled carbon nanotubes
(2006) Zhang, Guangyu; Qi, Pengfei; Wang, Xinran; Lu, Yuerui; Mann, David; Li, Xiaolin; Dai, Hongjie
We present a systematic experimental investigation of the reactions between hydrogen plasma and single-walled carbon nanotubes (SWNTs) at various temperatures. Microscopy, infrared (IR) and Raman spectroscopy, and electrical transport measurements are carried out to investigate the properties of SWNTs after hydrogenation. Structural deformations, drastically reduced electrical conductance, and an increased semiconducting nature of SWNTs upon sidewall hydrogenation are observed. These changes are reversible upon thermal annealing at 500 °C via dehydrogenation. Harsh plasma or high temperature reactions lead to etching of nanotubes likely via hydrocarbonation. Smaller SWNTs are markedly less stable against hydrocarbonation than larger tubes. The results are fundamental and may have implications to basic and practical applications including hydrogen storage, sensing, band gap engineering for novel electronics, and new methods of manipulation, functionalization, and etching of nanotubes.
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Effect of Surface Area, Particle Size and Acid Washing on the Quality of Activated Carbon Derived from Lower Rank Coal by KOH Activation
(2024) Spencer, William; Ibana, Don; Singh, Pritam; Nikoloski, Aleksandar N.
The use of coal-derived activated carbon (AC) for water treatment applications demands more sustainable production methods, with chemical activation emerging as a promising alternative to thermal activation due to its higher AC quality, lower carbon burn-off, and higher yield. The study explored the effect of surface area, particle size and acid washing on the quality of AC derived from three seams of lower-rank Collie coal under the same activation conditions with potassium hydroxide (KOH). The quality of AC was determined by surface area and iodine number. The study demonstrates that Collie coal, suitable for AC production via KOH activation, yielded iodine numbers of 640 and 900 mg/g, with yields of 53 and 57 wt.%. Particle size influenced AC yield, with finer particle sizes yielding AC at 57–59 wt.%, whereas coarser ones yielded around 58–65 wt.%. SEM analysis shows the well-developed porous structure in Collie coal-derived activated carbons, with cleaner particles after acid washing. A positive correlation exists between coal surface area and AC iodine numbers, with higher values in coal samples correlating to increased iodine numbers in resulting AC. The regression model’s predicted values yield a coefficient of determination (R²) of 0.99.
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Selective etching of metallic carbon nanotubes by gas-phase reaction
(2006) Zhang, Guangyu; Qi, Pengfei; Wang, Xinran; Lu, Yuerui; Li, Xiaolin; Tu, Ryan; Bangsaruntip, Sarunya; Mann, David; Zhang, Li; Dai, Hongjie
Metallic and semiconducting carbon nanotubes generally coexist in as-grown materials. We present a gas-phase plasma hydrocarbonation reaction to selectively etch and gasify metallic nanotubes, retaining the semiconducting nanotubes in near-pristine form. With this process, 100% of purely semiconducting nanotubes were obtained and connected in parallel for high-current transistors. The diameter- and metallicity-dependent “dry” chemical etching approach is scalable and compatible with existing semiconductor processing for future integrated circuits.

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