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The integration of photonics and electronics on a converged silicon CMOS platform is a long pursuit goal for both academe and industry. We have been developing technologies that can integrate III-V compound semiconductors and CMOS circuits on 200 mm silicon wafers. As an example we present our work on the integration of InGaP light-emitting diodes (LEDs) with CMOS. The InGaP LEDs were epitaxially grown on high-quality GaAs and Ge buffers on 200 mm (100) silicon wafers in a MOCVD reactor. Strain engineering was applied to control the wafer bow that is induced by the mismatch of coefficients of thermal expansion between III-V films and silicon substrate. Wafer bonding was used to transfer the foundry-made silicon CMOS wafers to the InGaP LED wafers. Process trenches were opened on the CMOS layer to expose the underneath III-V device layers for LED processing. We show the issues encountered in the 200 mm processing and the methods we have been developing to overcome the problems. Published version

Electronics with multifunctionalities such as transparency, portability, and flexibility are anticipated for future circuitry development. Flexible memory is one of the indispensable elements in a hybrid electronic integrated circuit as the information storage device. Herein, we demonstrate a transparent, flexible, and transferable hexagonal boron nitride (hBN)-based resistive switching memory with indium tin oxide (ITO) and graphene electrodes on soft polydimethylsiloxane (PDMS) substrate. The ITO/hBN/graphene/PDMS memory device not only exhibits excellent performance in terms of optical transmittance (∼85% in the visible wavelength), ON/OFF ratio (∼480), retention time (∼5 × 104 s) but also shows robust flexibility under bending conditions and stable operation on arbitrary substrates. More importantly, direct observation of indium filaments in an ITO/hBN/graphene device is found via ex situ transmission electron microscopy, which provides critical insight on the complex resistive switching mechanisms.

This study reports a novel strategy to obtain a layered metastable phase of molybdenum trioxide (MoO3). The metastable phase in the layered framework, i.e., MoO3-II, was a result of the topotactic phase transformation of hexagonal-MoO3 (h-MoO3) into MoO3-II. This transformation was realized through the removal of the water and ammonium molecules from the framework of h-MoO3. Next, a facile exfoliation strategy was adopted to prepare MoO3-II nanosheets, consisting of double-layers of MoO6 octahedra. The as-exfoliated MoO3-II nanosheets had measured thicknesses of 1.4, 2.4, and 11.2 nm, as quantified using atomic force microscopy (AFM), equivalent to 2, 3, and 16 double-layers of the MoO6 octahedra in MoO3-II, respectively, after taking into account their respective van der Waals gaps (thickness of a MoO3-II double-layer ∼0.709 nm). This work is the first attempt to synthesize MoO3-II nanosheets and shed light on their formation mechanism.

The Curie temperature (T C) of RT binary compounds consisting of 3d transition-metal (T ) and 4f rare-earth elements (R) is analyzed systematically by a developed machine learning technique called kernel regression-based model evaluation. Twenty-one descriptive variables were designed assuming completely obtained information of the T C. Multiple kernel regression analyses with different kernel types: cosine, linear, Gaussian, polynomial, and Laplacian kernels were implemented and examined. All possible descriptive variable combinations were generated to construct the corresponding prediction models. As a result, by appropriate combinations between descriptive variable sets and kernel formulations, we demonstrate that a number of kernel regression models can accurately reproduce the T C of the RT compounds. The relevance of descriptive variables for predicting T C are systematically investigated. The results indicate that the rare-earth concentration is the most relevant variable in the T C phenomenon. We demonstrate that the regression-based model selection technique can be applied to learn the relationship between the descriptive variables and the actuation mechanism of the corresponding physical phenomenon, i.e., T C in the present case.

We propose a data-driven method to extract dissimilarity between materials, with respect to a given target physical property. The technique is based on an ensemble method with Kernel ridge regression as the predicting model; multiple random subset sampling of the materials is done to generate prediction models and the corresponding contributions of the reference training materials in detail. The distribution of the predicted values for each material can be approximated by a Gaussian mixture models. The reference training materials contributed to the prediction model that accurately predicts the physical property value of a specific material, are considered to be similar to that material, or vice versa. Evaluations using synthesized data demonstrate that the proposed method can effectively measure the dissimilarity between data instances. An application of the analysis method on the data of Curie temperature ( T C ) of binary 3d transition metal- 4f rare-earth binary alloys also reveals meaningful results on the relations between the materials. The proposed method can be considered as a potential tool for obtaining a deeper understanding of the structure of data, with respect to a target property, in particular.

In this work, the coexistence of Write Once Read Many Memory (WORM) and memristor can be achieved in a single device of Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) and Polyvinyl Alcohol (PVA) blend organic memory system. In memristor mode, the bistable resistance states of the device can be cycled for more than 1000 times. Once a large negative bias of −8V was applied to the device, it was switched to permanent high resistance state that cannot be restored back to lower resistance states. The mechanism of the memristor effect can be attributed to the charge trapping behaviour in PVA while the WORM effect can be explained as the electrochemical characteristic of PEDOT: PSS which harnesses the percolative conduction pathways. The results may facilitate multipurpose memory device with active tunability. NRF (Natl Research Foundation, S’pore) ASTAR (Agency for Sci., Tech. and Research, S’pore) Published version

We study resistive switching memory phenomena in conducting polymer PEDOT PSS. In the same film, there are two types of memory behavior coexisting; namely, the switchable diode effect and write once read many memory. This is the first report on switchable diode phenomenon based on conducting organic materials. The effect was explained as charge trapping of PEDOT PSS film and movement of proton. The same PEDOT PSS device also exhibits write once read many memory (WORM) phenomenon which arises due to redox reaction that reduces PEDOT PSS and renders it non-conducting. The revelation of these two types of memory phenomena in PEDOT PSS highlights the remarkable versatility of this conducting conjugated polymer. ASTAR (Agency for Sci., Tech. and Research, S’pore) Published version

An optically readable write once read many memory (WORM) in Ag/Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH PPV)/ITO is demonstrated in this work. Utilising characteristics of the organic light emitting diode structure of Ag/MEH PPV/ITO and electrochemical metallization of Ag, a WORM with light emitting capability can be realised. The simple fabrication process and multifunction capability of the device can be useful for future wearable optoelectronics and photomemory applications, where fast and parallel readout can be achieved by photons. ASTAR (Agency for Sci., Tech. and Research, S’pore) Published version

The Poisson's ratio of perovskites with a high degree of anisotropy can change from negative to positive and become much larger than the normally observed range of 0.2–0.4 and even greater than the isotropic upper limit 0.5 along certain crystallographic orientations. These results pave the way for a better understanding of elastic-mediated physical properties of perovskites by engineering the orientation-dependent Poisson's ratios.

Gel-derived TiO2–SiO2 and N–TiO2–SiO2 mixed oxides with the TiO2 : SiO2 weight ratio of 95 : 5 are synthesised and employed for phenol removal under UVA light and natural sunlight in this study. Both SiO2 and N are interestingly found to improve the specific surface area of resulting catalysts up to 169 m2 g−1. Meanwhile, only N is observed to shift significantly the light absorption of derived catalyst to visible range. Optimisation between specific surface area and crystallinity in TiO2–SiO2 mixed oxide is found to give rise to the superior photoactivity of TiO2–SiO2 catalyst in comparison with TiO2 counterpart. Under natural sunlight in Hochiminh City on October 2007, N–TiO2–SiO2 presents the outstanding photoactivity towards decomposition of 10 ppm phenol aqueous solution with the efficiency up to 100% as compared to those of 65 and 48% for bare TiO2–SiO2 and bare TiO2, respectively.

We develop a method that combines data mining and first principles calculation to guide the designing of distorted cubane Mn^Mn^_3 single molecule magnets. The essential idea of the method is a process consisting of sparse regressions and cross-validation for analyzing calculated data of the materials. The method allows us to demonstrate that the exchange coupling between Mn^ and Mn^ ions can be predicted from the electronegativities of constituent ligands and the structural features of the molecule by a linear regression model with high accuracy. The relations between the structural features and magnetic properties of the materials are quantitatively and consistently evaluated and presented by a graph. We also discuss the properties of the materials and guide the material design basing on the obtained resutls.

Polyaniline (PANI), a promising conducting polymer for supercapacitor, exhibits high specific capacitance and good rate capability. However, it suffers from low cycling stability due to the breakage or scission of polymer chains and loss of contact caused by the volume change during the charge–discharge, as well as the irreversible oxidation and reduction. Here, a strategy for using aniline tetramers loaded on graphene oxide (AT-GO) is developed to prevent chain breaking and increase the tolerance of volume change. The potential window is also controlled to reduce the irreversible reactions. In a three electrode test, AT-GO exhibits a good cycling stability with specific capacitance remaining more than 93 to 96% after 2000 cycles. In a two electrode test, the specific capacitance remains 97.7% of its initial specific capacitance after 2000 cycles by suppressing the side reactions. AT-GO also shows a high specific capacitance of more than 769 F g−1 at 1 A g−1 and it remains 581 F g−1 at 60 A g−1, suggesting a good rate capability. These results suggest that AT-GO is a promising electrode material for practical applications.

Amorphous Si (a-Si) based memory devices that offer significant improvement in switching performance are fabricated by inserting a gold nanoparticles (Au NPs) monolayer between the amorphous Si and inert bottom electrodes. It is demonstrated that the Au NPs-interlayer amorphous Si memory devices deliver great improvements in lowering the electroforming voltage as well as enhancing the ON/OFF ratio, as compared to a pure amorphous Si memory structure. The switching mechanism is due to the modified electric field distribution with the insertion of Au NPs, which can directly affect the dynamic transport of ions and lead to the change of filament growth. Transmission electron microscopy (TEM) is used to directly capture the filaments growth process in these two types of memory devices to verify the evolution of conductive filament (CF). In addition, it is also demonstrated that the Au NPs-interlay amorphous Si memory fabricated on a flexible substrate can maintain low electroforming voltage and high ON/OFF ratio. This fabrication approach offers a versatile structural platform for next-generation memory applications with enhancement of the switching properties.

We investigate the emission of electromagnetic waves from biaxial subwavelength metamaterials. For anisotropic structures that exhibit a vanishing dielectric response along the longitudinal axis and possess a tunable transverse dielectric response, we find remarkable variation in the launch angles of energy associated with the emission of leaky wave radiation. We write closed-form expressions for the energy transport velocity and corresponding radiation angle $\ensuremath{\phi}$, defining the cone of radiation emission, as functions both of frequency and of material and geometrical parameters. Full wave simulations exemplify the broad range of directivity that can be achieved in these structures.

This paper measures impacts of production of crops, forestry, livestock and aquaculture on household welfare, poverty and inequality in rural Vietnam using fixed-effects regressions. Data used in this paper are from Vietnam Household Living Standard Surveys 2002 and 2004. It is found that impact estimates of the production of crops and forestry on per capita income and consumption expenditure are not statistically significant. Impact estimates of the livestock production are positive and statistically significant for per capita income, but not statistically significant for per capita expenditure. However, the aquacultural production has positive and statistically significant impacts on both income and expenditure. As a result, the aquacultural production helps the producing households reduce the poverty incidence by 4.3 percentage points. It also decreases the poverty gap and poverty severity indexes of the producing households by around 13 percent and 15 percent, respectively. The aquacultural production also reduces the rural expenditure inequality, albeit at an extremely small magnitude.

Text segmentation is a fundamental problem in natural language processing, which has application in information retrieval, question answering, and text summarization. Almost previous works on unsupervised text segmentation are based on the assumption of lexical cohesion, which is indicated by relations between words in the two units of text. However, they only take into account the reiteration, which is a category of lexical cohesion, such as word repetition, synonym or superordinate. In this research, we investigate the non-systematic semantic relation, which is classified as collocation in lexical cohesion. This relation holds between two words or phrases in a discourse when they pertain to a particular theme or topic. This relation has been recognized via a topic model, which is, in turn, acquired from a large collection of texts. The experimental results on the public dataset show the advantages of our approach in comparison to the available unsupervised approaches.

In this Letter, we theoretically investigate microwave transmission through a zero-index metamaterial loaded with dielectric defects. The metamaterial is impedance matched to free space, with the permittivity and permeability tending towards zero over a given frequency range. By simply varying the radii and permittivities of the defects, total transmission or reflection of the impinging electromagnetic wave can be achieved. The proposed defect structure can offer advances in shielding or cloaking technologies without restricting the object’s viewpoint. Active control of the observed exotic transmission and reflection signatures can occur by incorporating tunable refractive index materials such as liquid crystals and BaSr TiO3. Accepted version

Along with the growing software market in recent years, business requirements are changing more rapidly and the complexity of enterprise applications is growing continuously. An ideal goal is to encapsulate these requirements into a high-level abstraction, which can be used to drive large-scale adaptation of the underlying software implementation. Model Driven Engineering (MDE) is one of the enabling techniques that support this objective. One of the important parts in this process is the creation of Platform Independent Model (PIM). There are several approaches on this matter. However there is still the absence of clear documentation on the methods especially when the purpose is aimed for generic PIMs in a specific domain. This article introduces an approach to developing PIMs by using UML, OCL and promotes agility by applying agile modeling for this purpose. A practical example will be demonstrated.

Adapting a software system to the changing requirements and demands of the users is a big challenge in the area of software evolution. Representing these requirements in a high-level abstraction seems to be an optimal target. Model Driven Engineering (MDE) is one of the techniques that support this objective. Model transformation (automated and semi-automated), being the core mechanism in Model Driven Architecture (MDA), is considered to be the key factor in producing various software artifacts from all levels of modeling. Recently, the application of MDA to Web services has received considerable attention. This article introduces an approach of developing Web services by using model driven techniques, combined with the tools available on the market. We also present a view from a higher level of abstraction, describing particularly meta-model transformation using Kermeta.

This paper measures impacts of production of crops, forestry, livestock and aquaculture on household welfare, poverty and inequality in rural Vietnam using fixed-effects regressions. Data used in this paper are from Vietnam Household Living Standard Surveys 2002 and 2004. It is found that impact estimates of the production of crops and forestry on per capita income and consumption expenditure are not statistically significant. Impact estimates of the livestock production are positive and statistically significant for per capita income, but not statistically significant for per capita expenditure. However, the aquacultural production has positive and statistically significant impacts on both income and expenditure. As a result, the aquacultural production helps the producing households reduce the poverty incidence by 4.3 percentage points. It also decreases the poverty gap and poverty severity indexes of the producing households by around 13 percent and 15 percent, respectively. The aquacultural production also reduces the rural expenditure inequality, albeit at an extremely small magnitude.

Meta material has been demonstrated and applied in fabricating novel structures such as super lens, invisible cloaking and perfect absorber. The existence of a meta material layer in a stack consists of positive index material can result in a zero refractive index stack, which is also interesting in both physics and technology points of view. The stacking of negative index material and positive index material, where the impedances of negative index slab and positive index slab are matched, was manipulated so that the favorable outcome will be a zero equivalent index material with equivalent impedance different from zero. The reflection coefficient was zero at 90 degree incident angle, hence no reflection, and the calculated transmission is unity. Simulation demonstrates that there is no phase change and the wave propagates smoothly through the stack and the interfaces between slabs. Another kind of perfect absorber is also proposed by composing the 3-slab structure into the diffraction multi slits. Simulations show there are no back-scattering wave and transmitted wave.

Difference-in-differences with matching is a popular method to measure the impact of an intervention in health as well as social sciences. This method requires baseline data, i.e., data before interventions, which are not always available in reality. Instead, panel data with two time periods are often collected after interventions begin. In this paper, a simple matching method is proposed to measure the impact of an intervention using two-period panel data after the intervention. The method is illustrated by the measurement of the effect of health insurance in Vietnam using household panel data.

A development of new energetic materials are critical for the success propellants, micro-actuation, and power sources for next generation microsystems. If silicon (Si) can be utilized in the nanoenergetic field, a host of applications will soon arise because the standard silicon CMOS technology is well developed and widely used in the production of modern integrated circuits. Moreover, it is inexpensive, well characterized, and best adopted for microelectromechanical systems (MEMS). Porous silicon impregnated with solid state oxidants have demonstrated the combustion and explosion processes [1-4]. These processes can be used for various microactuators such as ignition for airbag systems [5] and self-destructed Si-chips [4]. Other applications may be in the field of MEMS, where nano-explosive devices can be used to propel miniature mechanical devices, for example, mini rockets [6]. In this paper we present mechanical impulse measurements for nanostructured porous silicon impregnated with solid state oxidants which can be utilized for jet-propulsion microsystem.

Farm workers are exposed to high risk of heat-related illness, especially when their jobs require working outside at a fast pace during hot days. Climate change has increased the number of days with high temperatures, and thereby the amount of time that farm workers are likely exposed to extreme heat. To better understand how high heat exposure affects farm workers, this study investigates how crop workers respond to heat exposure and estimates the effects of different pay and work arrangements on workers’ responses to heat exposure. We explore, specifically, whether piece-rate arrangements increase workers’ effort during periods with high heat exposure compared to workers paid by hourly wages. We use observational data from detailed measurements of localized heat exposure and individual workers’ effort in the field. First, these results show workers adjust their effort in response to heat exposure when the heat exposure level changes. Second, piece-rate arrangements increase workers’ effort during work shifts. Third, piece-rate arrangements allow workers to modify their effort more easily during different heat exposure levels. When facing low levels of heat exposure, workers who were paid by piece-rate arrangements exert a higher effort than workers paid by hourly wages, up until WBGT is 26.6˚C. When facing high levels of heat exposure (with WBGT exceeding 29.6˚C), workers paid by piece-rate arrangements lower their effort compared to workers paid by hourly wage arrangements.