Sheung Mei Ng

Magnetically assembled iron oxide nanoparticle coatings and their integration with pseudo-spin-valve thin films

The ability to prepare ordered crystalline structures by the assembly of magnetic nanoparticles is of great value for the design and fabrication of nanoparticle-based spintronics devices with novel structures and enhanced performances. In this work, nanoparticle coatings with both structural order and magnetic alignment were assembled onto flat substrates using monodisperse iron oxide nanoparticles by spin coating and heat treatment. The binary solvent mixture used as the carrier solvent for the nanoparticles enables solution-processed spin coating. The out-of-plane magnetic field applied during heat treatment promotes nanoparticle assembly. The magnetically assembled nanoparticle coating exhibits larger saturation magnetization and higher coercivity compared with its randomly aggregated counterpart, due to the easy-axis alignment and close packing of the nanoparticles. By tuning the experimental parameters, nanoparticle coatings with different morphologies were produced, in which locally ordered grains were formed due to anisotropic dipolar interactions. The potential of the nanoparticle coating for spintronic applications is demonstrated by integrating it with pseudo-spin-valve thin films, forming a nanoparticle-coated multilayer thin film structure. This composite system shows a magnetization switching behavior and spin-dependent magnetoresistance (MR) change. By decreasing the distance between the nanoparticle coating and the multilayer thin films, nanoparticle–thin film coupling and interlayer coupling were modulated, resulting in enhanced MR ratios. The presented results and proposed coupling mechanism provide insights into designing nanoparticle-based spintronic devices with enhanced performances and improved properties.

Peer volunteers in an integrative pain management program for frail older adults with chronic pain : study protocol for a randomized controlled trial

BackgroundChronic pain is common among the older population. A literature review on pain management program showed that exercise, yoga, massage therapy, Tai Chi, and music therapy could significantly reduce pain. In spite of the proven benefits of pain management programs, these intervention programs were effective only in the short term, and older adults would resume their old habits. It has been suggested that interventions comprising some type of social support have great potential to increase the participation of older adults. Therefore, we propose the inclusion of peer volunteers in an integrated pain management program to relieve pain among frail older adults. This study aims to explore the effectiveness of an integrated pain management program supplemented with peer volunteers in improving pain intensity, functional mobility, physical activity, loneliness levels, happiness levels, and the use of non-pharmacological pain-relieving methods among frail older adults with chronic pain.Methods/DesignWe intend to recruit 30 nursing home residents and 30 peer volunteers from the Institute of Active Ageing in Hong Kong in a group trial for an 8-week group-based integrated pain management program. There will be 16 sessions, with two 1-hour sessions each week.The primary outcome will be pain levels, while secondary outcomes will be assessed according to functional mobility, physical activity, loneliness levels, happiness levels, the use of non-pharmacological pain-relieving methods, and through a questionnaire for volunteers.DiscussionIn view of the high prevalence of chronic pain among older adults and its adverse impacts, it is important to provide older adults with tools to control their pain. We propose the use of peer volunteers to enhance the effects of an integrated pain management program. It is expected that pain can be reduced and improvements can be achieved among older adults in the areas of physical activity, functional mobility, loneliness levels, happiness levels, and the use of non-pharmacological pain relieving methods. Using these results, we will assess the need to conduct a larger study with a randomized controlled design.Trial registrationThis trial was registered on 24 February 2014 at the Australian New Zealand Clinical Trials Registry (ANZCTR) with the trial number: ACTRN12614000195651

Three-dimensional macroporous graphene monoliths with entrapped MoS2 nanoflakes from single-step synthesis for high-performance sodium-ion batteries

Layered metal sulfides (MoS2, WS2, SnS2, and SnS) offer high potential as advanced anode materials in sodium ion batteries upon integration with highly-conductive graphene materials. However, in addition to being costly and time-consuming, existing strategies for synthesizing sulfides/graphene composites often involve complicated procedures. It is therefore essential to develop a simple yet scalable pathway to construct sulfide/graphene composites for practical applications. Here, we highlight a one-step, template-free, high-throughput “self-bubbling” method for producing MoS2/graphene composites, which is suitable for large-scale production of sulfide/graphene composites. The final product featured MoS2 nanoflakes distributed in three-dimensional macroporous monolithic graphene. Moreover, this unique MoS2/graphene composite achieved remarkable electrochemical performance when being applied to Na-ion battery anodes; namely, excellent cycling stability (474 mA h g−1 at 0.1 A g−1 after 100 cycles) and high rate capability (406 mA h g−1 at 0.25 A g−1 and 359 mA h g−1 at 0.5 A g−1). This self-bubbling approach should be applicable to delivering other graphene-based composites for emerging applications such as energy storage, catalysis, and sensing.

Facile fabrication of highly ordered poly(vinylidene fluoride-trifluoroethylene) nanodot arrays for organic ferroelectric memory

Nano-patterned ferroelectric materials have attracted significant attention as the presence of two or more thermodynamically equivalent switchable polarization states can be employed in many applications such as non-volatile memory. In this work, a simple and effective approach for fabrication of highly ordered poly(vinylidene fluoride–trifluoroethylene) P(VDF-TrFE) nanodot arrays is demonstrated. By using a soft polydimethylsiloxane mold, we successfully transferred the 2D array pattern from the initial monolayer of colloidal polystyrene nanospheres to the imprinted P(VDF-TrFE) films via nanoimprinting. The existence of a preferred orientation of the copolymer chain after nanoimprinting was confirmed by Fourier transform infrared spectra. Local polarization switching behavior was measured by piezoresponse force microscopy, and each nanodot showed well-formed hysteresis curve and butterfly loop with a coercive field of ∼62.5 MV/m. To illustrate the potential application of these ordered P(VDF-TrFE) nanodot arrays, the writing and reading process as non-volatile memory was demonstrated at a relatively low voltage. As such, our results offer a facile and promising route to produce arrays of ferroelectric polymer nanodots with improved piezoelectric functionality.

The fabrication of large-area and uniform bilayer MoS2 thin films

Here, an approach for synthesizing large-area and high-quality MoS2 flakes was developed. In addition, we made up the MoS2 photoelectric detector and studied the photocurrent response of the detector. We firstly used the ceramic pieces to control MoO3 evaporation for obtaining large-area MoS2. Our CVD reaction is hydrogen free, very simple operation, high repetition rate and cost saving. The obtained MoS2 flakes exhibited large-area with lengths up to 400–500 micrometers. Through analyzing optical microscopy(OM), Raman and atomic force microscopy(AFM), we confirm the MoS2 thin film is bilayer. And the photoelectric characteristic experiment shows that the photoelectric detector has sensitive photoelectric response with the fine stability.

Elimination of hysteresis effect in superparamagnetic nanoparticle detection by GMR sensors for biosensing

The biosensing methods utilizing superparamagnetic nanoparticles as bio-tags and giant magneto-resistive (GMR) or tunneling magnetoresistive (TMR) sensors as signal detectors have attracted increasing interests in early disease diagnosis as well as in molecular biology research area. [1] To achieve the signal of targets, one commonly used method is to compare the sensor hysteresis loops before and after the introducing of superparamagnetic nanoparticles onto sensor surface, and the sensor response variation has been regarded as an indicator of target analytes amount. [2, 3] However, the hysteresis effect existing in ferromagnetic material may bring an error in the sensor output reading, which can be problematic in the superparamagnetic nanoparticle signal detection. Since the hysteresis behavior exists in all magnetoresistive sensors made of ferromagnetic material, it is necessary to investigate its effect on superparamagnetic nanoparticle detection and eliminate its negative influences.