Malcolm A. Lawn

Two-way satellite time and frequency transfer networks in Pacific Rim region

A two-way satellite time and frequency transfer (TWSTFT) network in the Pacific Rim region is under construction to contribute to the calculation of the international atomic time (TAI). Four major time and frequency institutes in this region have been conducting long-term TWSTFT experiments. In addition to these institutes, several others in the region are planning to join the network. A new type of time transfer modem for TWSTFT is also described.

Long-term operation and performance of cryogenic sapphire oscillators

Cryogenic sapphire oscillators (CSO) developed at the University of Western Australia (UWA) have now been in operation around the world continuously for many years. Such oscillators, due to their excellent spectral purity are essential for interrogating atomic frequency standards at the limit of quantum projection noise; otherwise aliasing effects will dominate the frequency stability due to the periodic sampling between successive interrogations of the atomic transition. Other applications, which have attracted attention in recent years, include tests on fundamental principles of physics, such as tests of Lorentz invariance. This paper reports on the long-term operation and performance of such oscillators. We compare the long-term drift of some different CSOs. The drift rates turn out to be linear over many years and in the same direction. However, the magnitude seems to vary by more than one order of magnitude between the oscillators, ranging from 1014 per day to a few parts in 1013 per day

Metrological scanning probe microscope based on a quartz tuning fork detector

We give an overview of the design of a metrological scanning probe microscope (mSPM) currently under development at the National Measurement Institute Australia (NMIA) and report on preliminary results on the implementation of key components. The mSPM is being developed as part of the nanometrology program at NMIA and will provide the link in the traceability chain between dimensional measurements made at the nanometer scale and the realization of the International System of Units (SI) meter at NMIA. The instrument is based on a quartz tuning fork (QTF) detector and will provide a measurement volume of 100  μm×100  μm×25  μm with a target uncertainty of 1 nm for the position measurement. Characterization results of the nanopositioning stage and the QTF detector are presented along with an outline of the method for tip mounting on the QTFs. Initial imaging results are also presented.

Multifunctional graphene micro-islands: Rapid, low-temperature plasma-enabled synthesis and facile integration for bioengineering and genosensing applications.

Here, we present a rapid, low-temperature (200°C) plasma-enabled synthesis of graphene micro-islands (GMs). Morphological analyses of GMs by scanning electron microscopy (SEM) and atomic force microscopy (AFM) feature a uniform and open-networked array of aggregated graphene sheets. Structural and surface chemical characterizations by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) support the presence of thin graphitic edges and reactive oxygen functional groups. We demonstrate that these inherent properties of GMs enable its multifunctional capabilities as a bioactive interface. GMs exhibit a biocompatibility of 80% cell viability with primary fibroblast lung cells after 5 days. Further, GMs were assembled into an impedimetric genosensor, and its performance was characterized by electrochemical impedance spectroscopy (EIS). A dynamic sensing range of 1pM to 1nM is reported, and a limit of quantification (LOQ) of 2.03×10-13M is deduced, with selectivity to single-RNA-base mismatched sequences. The versatile nature of GMs may be explored to enable multi-faceted bioactive platforms for next-generation personalized healthcare technologies.

Anti-fouling graphene-based membranes for effective water desalination

The inability of membranes to handle a wide spectrum of pollutants is an important unsolved problem for water treatment. Here we demonstrate water desalination via a membrane distillation process using a graphene membrane where water permeation is enabled by nanochannels of multilayer, mismatched, partially overlapping graphene grains. Graphene films derived from renewable oil exhibit significantly superior retention of water vapour flux and salt rejection rates, and a superior antifouling capability under a mixture of saline water containing contaminants such as oils and surfactants, compared to commercial distillation membranes. Moreover, real-world applicability of our membrane is demonstrated by processing sea water from Sydney Harbour over 72 h with macroscale membrane size of 4 cm2, processing ~0.5 L per day. Numerical simulations show that the channels between the mismatched grains serve as an effective water permeation route. Our research will pave the way for large-scale graphene-based antifouling membranes for diverse water treatment applications.Intrinsic limitations of nanoporous graphene limit its applications in water treatment. Here the authors produce post-treatment-free, low-cost graphene-based membranes from renewable biomass and demonstrate their high water permeance and antifouling properties using real seawater.

Two-way satellite time transfer network in Pacific Rim region

A Two Way Satellite Time Transfer (TWSTT) network in the Pacific rim region is under construction to contribute to the International Atomic Time (TAI). Four major Time and Frequency Institutes in this region have been conducting long term TWSTT experiments. In addition to these institutes, several ones in this region are planning to join this TWSTT network.

Minimising the effect of nanoparticle deformation in intermittent contact amplitude modulation atomic force microscopy measurements

The results of systematic height measurements of polystyrene (PS) nanoparticles using intermittent contact amplitude modulation atomic force microscopy (IC-AM-AFM) are presented. The experimental findings demonstrate that PS nanoparticles deform during AFM imaging, as indicated by a reduction in the measured particle height. This deformation depends on the IC-AM-AFM imaging parameters, material composition, and dimensional properties of the nanoparticles. A model for nanoparticle deformation occurring during IC-AM-AFM imaging is developed as a function of the peak force which can be calculated for a particular set of experimental conditions. The undeformed nanoparticle height can be estimated from the model by extrapolation to zero peak force. A procedure is proposed to quantify and minimise nanoparticle deformation during IC-AM-AFM imaging, based on appropriate adjustments of the experimental control parameters.

Particle number density gradient samples for nanoparticle metrology with atomic force microscopy

Atomic force microscopy (AFM) can provide a link in the traceability chain between dimensional measurement techniques for nanoparticles, such as dynamic light scattering and differential centrifugal sedimentation, and the realization of the definition of the SI metre. Despite the size of nanoparticles being well within the resolution range of typical AFMs, the accurate measurement of nanoparticles with AFM presents a number of challenges. One of these challenges is the number density of particles deposited on substrates for AFM imaging and measurement. If the number density is too low, it is difficult to obtain adequate measurement statistics, whereas a number density that is too high can result in particle agglomeration on the substrate and make it difficult to image sufficient substrate area to obtain a reliable reference for height measurements. We present imaging and measurement results of 16 nm gold nanoparticles deposited on a substrate functionalized to produce a surface with a number density gradient across the sample. This substrate functionalization shows great potential for achieving reliable and efficient nanoparticle metrology with AFM.

Traceable nanoscale length metrology using a metrological Scanning Probe Microscope

We give an overview of the design and planned operation of the metrological Scanning Probe Microscope (mSPM) currently under development at the National Measurement Institute Australia (NMIA) and highlight the metrological principles guiding the design of the instrument. The mSPM facility is being established as part of the nanometrology program at NMIA and will provide the link in the traceability chain between dimensional measurements made at the nanometer scale and the realization of the SI meter at NMIA. The instrument will provide a measurement volume of 100 μm × 100 μm × 25 μm with a target uncertainty of 1 nm for the position measurement.

Reference micropotentiometer resistors for Ac-dc transfer and phase error measurements

The paper presents a range of radial thin-film resistors for use as references in micropotentiometer-type low-voltage ac-dc transfer standards and for the measurement of phase errors in precision resistors and current shunts. The measured ac-dc difference of new resistors with values above 3 Ω was within 10 μΩ/Ω at frequencies up to 1 MHz.