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Hsinchu, Taiwan

Protasov D.Y.,RAS Semiconductor Physics Institute | Jian W.-B.,NCTU | Svit K.A.,RAS Semiconductor Physics Institute | Duda T.A.,RAS Semiconductor Physics Institute | And 4 more authors.
Journal of Physical Chemistry C

Aggregation clusters of CdS quantum dots (QDs) on the highly ordered pyrolytic graphite substrate were investigated by atomic force microscopy and scanning tunneling microscopy. QDs were initially formed within Y-type Langmuir-Blodgett (LB) films of cadmium behenate. The LB matrix was then removed by annealing. To study the process of QD assembly, the density of QDs in the initial film was varied systematically by increasing the number of monolayers (MLs) from 1 to 20 ML. It was found that, at a small LB ML number, only a small part of CdS molecules form into QDs by diffusion along the plane of LB layers. With an increase of the LB ML number, the interlayer diffusion arises that leads to almost full binding of CdS molecules into QDs. The individually standing QDs were formed on the substrate for 1 and 2 ML samples. The QD size distributions of the samples with a small ML number are broader than that predicted by the two-dimensional Lifshitz-Slezov diffusion model. With an increase of the LB matrix thickness, QDs begin to assemble into clusters, revealing a ribbon structure due to diffusion-limited aggregation, and for the 20 ML LB matrix, a submonolayer QD film arises. By analyzing the occurrence of QDs as a function of aggregation number, pair bondings were estimated to be about 34 and 62 meV for the 4 and 8 ML samples, respectively. © 2011 American Chemical Society. Source

Milekhin A.G.,Novosibirsk State University | Yeryukov N.A.,RAS Semiconductor Physics Institute | Sveshnikova L.L.,RAS Semiconductor Physics Institute | Duda T.A.,RAS Semiconductor Physics Institute | And 8 more authors.
Journal of Physical Chemistry C

We present a study of resonant and surface enhanced Raman scattering by arrays of nanocrystals (cadmium sulfide CdS, lead selenide PbSe, and zinc oxide ZnO) with various areal density fabricated by using the Langmuir-Blodgett technique and colloidal chemistry. Resonant Raman scattering by transverse, longitudinal, and surface optical (TO, LO, and SO) phonons and their overtones up to ninth order was achieved for nanocrystal (NC) arrays by adjusting the laser energy to that of the interband transitions. The resonance enhancement allowed a Raman response from arrays of NCs with a low areal density (down to 10 PbSe NCs per 1 μm 2) to be measured. An enhancement of Raman scattering by LO and SO modes in CdS NC arrays with a low areal density by a factor of about 730 was achieved due to the resonant surface enhanced Raman scattering effect. © 2012 American Chemical Society. Source

Chang W.-T.,Asia University, Taiwan | Din Y.-T.,NCTU
Proceedings - 2015 International Conference on Network and Information Systems for Computers, ICNISC 2015

IEEE 802.11e is an extension for media access control in wireless network. It is used for different Quality of Service requirement for different transmission application. But it assumes that all terminals operate in the same transmission speed. But when terminals use different transmission speeds, the access mechanism, EDCA, can not perform to its design purposes. Because the parameters designed for the four different categories can not be adapted according to the transmission speed. For high priority application, it is given a fixed transmission time, this will make the terminal with low speed difficult to achieve the required QoS due to insufficient time to transmit large packet. However, for low priority application, the system will be occupied by terminal with slow transmission speed when transmitting a long packet. This will affect the real time requirement of the QoS service and eventually reduce the total system performance. This paper will address the above two issues and try to purpose methods to improve it. First, a method is used to reduce the time that a low speed terminal will take when transmitting low priority data. Secondly, another method is used to enhance the QoS for all terminals with different transmission speed. With those two methods, we can obtain better throughput and better QoS for the WiFi system. © 2015 IEEE. Source

Cheng T.-C.,National Chung Cheng University | Liao Y.-T.,NCTU | Tsai T.-H.,National Chung Cheng University
2015 Transducers - 2015 18th International Conference on Solid-State Sensors, Actuators and Microsystems, TRANSDUCERS 2015

This paper presents an integration of the capacitive micromachined ultrasonic transducers (CMUTs) and the transimpedance amplifier in medical ultrasound systems. The proposed CMUT and the sensing circuits are both fabricated on the same chip in a 0.18μm CMOS MEMS technology. Two interlayer metal structures are proposed to improve the sensitivity. The CMUTs are designed with 2MHz cells for medical diagnosis. The conversion efficiency of the CMUTs is 4 times and 1.8 times higher than that in the published structures. © 2015 IEEE. Source

Ou Y.-C.,Institute of Physics | Zhuravlev K.S.,RAS Semiconductor Physics Institute | Fang J.,Binghamton University State University of New York | Jian W.-B.,NCTU
Journal of Physical Chemistry C

Although self-organization of semiconductor nanocrystals (or quantum dots) into 3D superlattices and exploration of their collective optical, magnetic, and transport properties have been demonstrated, little is known about the underlying physics of self-assembly, growth mechanisms, and interdot-coupling- induced collective properties. Here we report a facile way of preparing nanocrystal-assembled 2D islands by drop-casting nanocrystal suspension on a hot substrate. Growth mechanisms such as scaling function, spinodal decomposition phase separation, and diffusion-limited aggregation are investigated based on the observation of quasi-monolayer coverage. After a curve fitting to several theoretical growth models, the pair bond (interaction) energy, critical nucleus size, and the phase of growth patterns were determined. Moreover, by heating the substrate and controlling the concentration of nanocrystal suspension, the spinodal decomposition and diffusion-limited aggregation can be tuned to modulate growth patterns of 2D nanocrystal islands. The interplay of these two mechanisms results in a variation of wavelength in spinodal growth patterns and of fractal pattern dimensions. By using this experimental approach, various sizes and shapes of nanocrystal-assembled 2D islands can be deposited on a flat surface of either graphite or gold. © 2010 American Chemical Society. Source

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