George C. K. Chen

Interfacing live cells with nanocarbon substrates.

Nanocarbon materials, including single-walled carbon nanotubes (SWCNTs) and graphene, promise various novel biomedical applications (e.g., nanoelectronic biosensing). In this Letter, we study the ability of SWCNT networks and reduced graphene oxide (rGO) films in interfacing several types of cells, such as neuroendocrine PC12 cells, oligodendroglia cells, and osteoblasts. It was found that rGO is biocompatible with all these cell types, whereas the SWCNT network is inhibitory to the proliferation, viability, and neuritegenesis of PC12 cells, and the proliferation of osteoblasts. These observations could be attributed to the distinct nanotopographic features of these two kinds of nanocarbon substrates.

Pulsed photothermal modeling of composite samples based on transmission-line theory of heat conduction

A transmission-line approach to obtain the thermal solutions for two- and three-layer samples at the front surface is described. These solutions are fitted to pulsed photothermal reflectance data for a Au/TAC/Si sample. The results indicate that the two- and three-layer models agree with each other and the embedded TAC film can be treated as a thermal resistance. The fitted thermal property of the TAC film is relatively close (κTAC ranging from 1.77 to 2.21 W/m per K) with different pulse shapes. This indicates that the pulse shape function does not play a significant role in the TAC film’s thermal property determination. However, the fitted thermal property of the Au layer is highly pulse shape function dependent (κAU ranging from 71 to 280 W/m per K). There one finds that the pulse shape function needs to match the excitation pulse in order to obtain the correct thermal property of the Au layer.

Multiplex spectral surface plasmon resonance imaging (SPRI) sensor based on the polarization control scheme

A two-dimensional (2D) spectral SPR sensor based on a polarization control scheme is reported in this paper. The polarization control configuration converts the phase difference between p- and s- polarization occurring at surface plasmon resonance (SPR) into corresponding color responses in spectral SPR images. A sensor resolution of 2.7 x 10(-6) RIU has been demonstrated, which corresponds to more than one order of magnitude resolution improvement (26 times) comparing to existing 2D spectral SPR sensors. Multiplex array detection has also been demonstrated with the spectral SPR imaging sensor. In a 8 x 4 sensor array, 32 samples with different refractive index values were monitored simultaneously. Detection on bovine serum albumin (BSA) antigen-antibody binding further demonstrated the multiplex detection capability of the 2D spectral SPR sensor for bio-molecular interactions. The detection limit is found to be 21 ng/ml, which is 36 times better than the detection limit previously reported by phase imaging SPR sensors. In light of the advantages of high sensitivity, 2D multiplex detection and real-time response, the spectral SPR imaging sensor can find promising applications in rapid, high throughput, non-labeling and multiplex detection of protein array for proteomics studies, biomarker screening, disease prognosis, and drug discovery.

Redistribution of the zero order by the use of a phase checkerboard pattern in computer generated holograms

A checkerboard phase plate is proposed to be used together with computer generated holograms to eliminate the zero order by working as a convolution function that shifts the zero order away from the center of a reconstructed pattern. By performing a preshift in the desired hologram pattern, it is possible to obtain a reconstructed pattern that is free of zero order. Simulation results have shown that the technique is tolerant of fabrication errors in the hologram. The technique is also shown to effectively reduce the zero order intensity by two orders in the presence of phase depth errors in the checkerboard. Experimental results using a spatial light modulator support the results shown in the simulation.

Optimization of spot pattern in indoor diffuse optical wireless local area networks

In this paper, a simulated annealing (SA) algorithm is proposed to be used in the optimization of the spot pattern for the indoor diffuse optical wireless network application. The channel response is analyzed using conventional grid-based patterns and a field of view (FOV) of 30 degrees is found to give a good performance balance in the uniformity of the received power distribution and multipath dispersion. Using the algorithm to determine the spot pattern for the minimum standard deviation of the received power, an improvement of more than 85% is realized. To optimize the spot pattern at 30 degrees FOV, a merit function is incorporated into the algorithm for two parameters, and the SA algorithm is run to obtain optimized spot patterns for both a 4.5m and 6m extent of the spot pattern. Various weights are used, and a performance improvement of 39% and 78% is observed for the 4.5m and 6m spot pattern sizes respectively which shows that the approach can be used to effectively optimize the spot pattern in the indoor optical wireless application.

Thermal conduction in metalized tetrahedral amorphous carbon (ta–C) films on silicon

Abstract Thermal conductivities of filtered cathodic vacuum arc (FCVA) deposited tetrahedral amorphous carbon films, ranging from 20 to 100 nm, are measured using pulsed photothermal reflectance technique. The internal thermal conductivity of the tetrahedral amorphous carbon film is 4.7 W/m K. No thermal conductivity size effect is observed. The thermal boundary resistance between tetrahedral amorphous carbon with gold and silicon is 1.9×10 −8 m 2 K/W, which suggest good contact between tetrahedral amorphous carbon film with gold and silicon are achieved. Our measurement technique is calibrated by measuring silicon-dioxide and gold films’ thermal conductivities. Internal thermal conductivity of tetrahedral amorphous carbon film is about four times higher than silicon-dioxides internal thermal conductivity.

Holographic diffuser for diffuse infrared wireless home networking

We present the design and fabrication of holographic diffus- ers for diffuse IR wireless home networking. Three optimization methods—error reduction, input-output, and simulated annealing—are studied and used to calculate the computer-generated holograms, which are employed to fabricate the holographic diffusers. To evaluate the per- formance of the computer-generated holograms generated using these techniques, a cost function is defined and calculated for each hologram. The computer-generated hologram generated from the simulated an- nealing is found to have the best output compared to the other two tech- niques. The diffusers are verified by displaying them onto a spatial light modulator. The fabrication of the computer-generated hologram onto a piece of quartz with a pixel size of 14314 mm using a laser writing sys- tem is achieved, and the diffraction pattern of the diffuser is demonstrated.

Thermal Conductivity of CrAlN and TiAlN Coatings Deposited by Lateral Rotating Cathode Arc

CrAlN and TiAlN coatings were deposited on stainless steel substrates by a lateral rotating cathode arc technique. The composition and structure of the as-deposited coatings were analyzed by energy dispersive analysis of X-rays (EDX) and X-ray diffraction (XRD). Thermal conductivity of these coatings is measured using pulsed photothermal reflectance (PPR) technique at room temperature. The measured thermal conductivity of pure TiN coating is around 11.9 W/mK. With increasing Al content, thermal conductivity of the TiAlN coatings decreased significantly and a minimum value of about 4.63 W/mK was obtained at the Al/Ti atomic ratio around 0.72. With the increase of Al content, thermal conductivity of CrAlN coatings decreased slightly but consistently. The variation of thermal conductivity in these coatings is explained in term of phonon scattering on grain boundaries and local strain centers caused by lattice distortion. In comparison with TiAlN, thermal conductivity of CrAlN coatings was evidently lower, which could be partially responsible for their better performance in high speed machining applications as observed in our previous work.

Holographic diffuser design using a modified genetic algorithm

A modified genetic algorithm is proposed for the optimization of holographic diffusers for diffuse IR wireless home networking. The novel algorithm combines the conventional genetic algorithm and the simulated annealing algorithm, in which the simulated annealing algorithm is used to maintain a better diversity of chromosomes for the genetic algorithm. A better performance in locating the global minimum is demonstrated.

Colorimetric surface plasmon resonance imaging (SPRI) biosensor array based on polarization orientation.

A colorimetric surface plasmon resonance (SPR) imaging biosensor array based on polarization orientation rotation is presented in this paper. It measures the spectral characteristic variations caused by the steep phase difference between the p- and s-polarization occurring at surface plasmon excitation. It provides one-order of magnitude sensor resolution improvement comparing to existing phase-sensitive SPR imaging sensors and the two-dimensional (2D) sensing capability of the imaging sensor enables multiplex, high throughput array based simultaneous detection for a range of different bio-molecular interactions. Experiments on the binding interactions detection between anti-bovine serum albumin (anti-BSA) and BSA antigen have been performed. All binding interactions occurred at 5×4 protein array were real-time monitored simultaneously. A sensor resolution of 8.26ng/ml (125pM) has been demonstrated, which is one-order of magnitude (12 times) better than the detection limit reported by existing phase-sensitive SPR imaging sensors in the literature, while no time-consuming phase modulation and phase extraction processes are required. Furthermore, the optical colorimetric image read-out of the sensor is easy to be identified by the end users comparing to conventional intensity or phase information. The colorimetric SPR imaging biosensor array can find promising potential applications in high throughput clinical disease diagnosis, protein biomarkers screening and drug screening.