Colloidal synthesis of ultrathin two-dimensional semiconductor nanocrystals

2D semiconductor quantum wells have been recognized as potential candidates for various quantum devices. In quantum wells, electrons and holes are spatially confined within a finite thickness and freely move in 2D space. Much effort has focused on shape control of colloidal semiconductor nanocrystals(NCs), and synthesis of 2D colloidal NCs has been achieved very recently. Here, recent advances in colloidal synthesis of uniform and ultrathin 2D CdSeNCs are highlighted. Structural and optical property characterization of these quantum-sized 2D CdSe NCs is discussed. Additionally, 2D CdSe NCs doped with Mn 2+ ions for dilute magnetic semiconductors (DMS) are presented.These 2D CdSe-based NCs can be used as model systems for studying quantum-well structures.     

Detecting oxidized contaminants in water using sulfur-oxidizing bacteria

For the rapid and reliable detection of oxidized contaminants (i.e., nitrite, nitrate, perchlorate, dichromate) in water, a novel toxicity detection methodology based on sulfur-oxidizing bacteria (SOB) has been developed. The methodology exploits the ability of SOB to oxidize elemental sulfur to sulfuric acid in the presence of oxygen. The reaction results in an increase in electrical conductivity (EC) and a decrease in pH. When oxidized contaminants were added to the system, the effluent EC decreased and the pH increased due to the inhibition of the SOB. We found that the system can detect these contaminants in the 5-50 ppb range (in the case of NO(3)(-), 10 ppm was detected), which is lower than many whole-cell biosensors to date. At low pH, the oxidized contaminants are mostly in their acid or nonpolar, protonated form which act as uncouplers and make the SOB biosensor more sensitive than other whole-cell biosensors which operate at higher pH values where the contaminants exist as dissociated anions. The SOB biosensor can detect toxicity on the order of minutes to hours which can serve as an early warning so as to not pollute the environment and affect public health.     

Synthesis of copper nanoparticles by solid-state plasma-induced dewetting

Copper nanoparticles were prepared by the plasma treatment of Cu thin films without extra heating. The Cu nanoparticles were formed through a solid-state dewetting process at temperatures of less than 450 K. The particle sizes, from 10 to 80 nm, were controlled by changing the thickness of the Cu film; the particle size increased linearly with the film thickness. The Cu nanoparticles produced by plasma treatment showed an excellent size uniformity compared to those prepared by heat treatment. In the early stage of the dewetting of the Cu film, uniformly distributed holes nucleated, and the holes grew and coalesced until the Cu nanoparticles were formed. The low operating temperatures used contributed to the production of uniform Cu nanoparticles.     

Realization of effective light trapping and omnidirectional antireflection in smooth surface silicon nanowire arrays

We have successfully fabricated well-ordered silicon nanowire (SiNW) arrays of smooth surface by using a low-cost and facile Ag-assisted chemical etching technique. We have experimentally found that the reflectance can be significantly suppressed (<1%) over a wide solar spectrum (300-1000 nm) in the as-grown samples. Also, based on our bundled model, we have used rigorous coupled-wave analysis to simulate the reflectance in SiNW arrays, and found that the calculated results are in good agreement with the experimental data. From a further simulation study on the light absorption in SiNW arrays, we have obtained a photocurrent enhancement of up to 425% per unit volume of material as compared to crystalline Si, implying that effective light trapping can be realized in the as-grown samples. In addition, we have demonstrated experimentally and theoretically that the as-grown samples have an omnidirectional high-efficiency antireflection property.     

A nanowire-based shift register for display scan drivers

The development of display scan drivers is an essential step in the effort to develop transparent and flexible display devices based on nanowire transistors. Here we report a transparent nanowire-based shift register that functions as the standard logic circuit of a display scan driver. To form the shift register circuits using only n-type nanowire transistors, a novel circuit structure was introduced to avoid the output voltage drop typical of purely n-type circuits. A circuit simulation based on the measured nanowire transistor characteristics was developed in the planning phase to verify the circuit operation of the shift register. The shift register successfully produced an output of 0-3 V without an output voltage drop while applying an input of 3 V peak to peak. In addition, the shift register was designed to have multiple channels with a randomly oriented nanowire placement method to enhance the operation yield.     

Light absorption mechanism in single c-Si (core)/a-Si (shell) coaxial nanowires

We have carried out detailed investigations on the light absorption mechanism in single crystalline silicon (c-Si) (core)/amorphous Si (a-Si) (shell) coaxial nanowires (NWs). Based on the Lorenz-Mie light scattering theory, we have found that the light absorption in the coaxial NWs relies on the leaky mode resonances and that the light absorption can be optimized towards photovoltaic applications when the a-Si shell thickness is about twice the c-Si core radius. The photocurrent has been found to be enhanced up to ～ 560% compared to c-Si NWs, and to be further enhanced up to ～ 60% by coating the nonabsorbing dielectric shells.     

Novel service protocol for supporting remote and mobile users in wireless sensor networks with multiple static sinks

A wireless sensor network typically consists of users, a sink, and a number of sensor nodes. The users may be remotely connected to a wireless sensor network and via legacy networks such as Internet or Satellite the remote users obtain data collected by the sink that is statically located at a border of the wireless sensor network. However, in practical sensor network applications, there might be two types of users: the traditional remote users and mobile users such as firefighters and soldiers. The mobile users may move around sensor fields and they communicate with the static sink only via the wireless sensor networks in order to obtain data like location information of victims in disaster areas. For supporting the mobile users, existing studies consider temporary structures. However, the temporary structures are constructed per each mobile user or each source nodes so that it causes large energy consumption of sensor nodes. Moreover, since some of them establish the source-based structure, sinks in them cannot gather collective information like mean temperature and object detection. In this paper, to effectively support both the remote users and the mobile users, we propose a novel service protocol relying on the typical wireless sensor network. In the protocol, multiple static sinks connect with legacy networks and divide a sensor field into the number of the multiple sinks. Through sharing queries and data via the legacy networks, the multiple static sinks provide high throughput through distributed data gathering and low latency through short-hops data delivery. Multiple static sinks deliver the aggregated data to the remote users via the legacy networks. In case of the mobile users, when a mobile user moves around, it receives the aggregated data from the nearest static sink. Simulation results show that the proposed protocol is more efficient in terms of energy consumption, data delivery ratio, and delay than the existing protocols.     

Highly Power‐Efficient Rack‐Level DC Power Architecture Combined with Node‐Level DC UPS

This letter presents a highly efficient rack‐level DC power architecture combined with a node‐level DC uninterruptible power supply (UPS). The proposed system can provide almost the equivalent power efficiency of a high‐voltage DC data center without any change in the existing power infrastructure. The node‐level DC UPS combined with a power distribution board provides high power efficiency as well as lower UPS installation costs. Implemented on a rack, the entire power system can be monitored through a network.