• Journal of Biomedical Engineering Research
• /
• v.18 no.4
• /
• pp.421-428
• /
• 1997

Magnetic field sensors made from superconducting quantum interference device (SQUID) are the most sensitive low-frequency sensors available, enabling measurements of extremely weak magnetic fields from the brain. Neuromagnetic measurements allow superior spatial resolution, compared with the present electric measurements, and superior temporal resolution, compared with the fMRl and PET, providing useful informations for the functional diagnoses of the brain. We developed a 4-channel SQUID system for neuromagnetic applications. The main features of the system are its simple readout electronics and compact pickup coil structure. A magnetically shielded room has been constructed for the reduction of environmental magnetic noises. The developed SQUID system has noise level lower than the magnetic noise from the brain. Magnetic field signals of the spontaneous r-rhythm activity and auditory evoked magnetic fields have been measured.

• Journal of Radiation Industry
• /
• v.9 no.3
• /
• pp.143-151
• /
• 2015

A PET-MR system is particularly useful in diagnosing brain diseases. We have developed a prototype positron emission tomography (PET) system which can be inserted into the bore of a whole-body magnetic resonance imaging (MRI) system that enables us to obtain PET and MRI images simultaneously with a reduced cost. Silicon photomultipliers (SiPM) are appropriated as a PET detector at PET/MR system because detectors have a high gain and are insensitive to magnetic fields. Despite of its improved performance compared to that of PMT-based detectors, there is a problem of the photo-peak channel shift which is due to the increase of the temperature inside the ring detector. This problem will occur decreasing sensitivity of the PET and image distortion. In this paper, I quantitative analyze parameters of the KAIST SiPM depending on temperature by experiments. And I designed cooling methods in consideration of the degradation of sensors for correction of the temperature in the PET gantry. According to this research, we expect that distortive images and degradation of the sensitivity will not be occurred with using the above idea to reduce heat even if the PET system operates for a long time.

• Journal of Sensor Science and Technology
• /
• v.29 no.6
• /
• pp.388-393
• /
• 2020

In this study, a PbS quantum dots (QDs)-based H₂ gas sensor with a Pd electrode was proposed. QDs have a size of several nanometers, and they can exhibit a high surface area when forming a thin film. In particular, the NH₂ present in the ligand of PbS QDs and H₂ gas are combined to form NH₃⁺, subsequently the electrical characteristics of the QDs change. In addition to the resistance change owing to the reaction between Pd and H₂ gas, the resistance change owing to the reaction between the NH₂ of PbS QDs and H₂ gas increases the current signal at the sensor output, which can produce a high output signal for the same concentration of H₂ gas. Using the XRD and absorbance properties, the synthesis and particle size of the synthesized PbS QDs were analyzed. Using PbS QDs, the sensitivity was significantly improved by 44%. In addition, the proposed H₂ gas sensor has high selectivity because it has low reactivity with heterogeneous gases such as C₂H₂, CO₂, and CH₄.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.07b
• /
• pp.902-905
• /
• 2004

A heart diagnosis system adopts Superconducting Quantum Interface Device(SQUID) sensors for precision MCG signal acquisitions. Such system is composed of hundreds of sensors, requiring fast signal sampling and precise analog-digital conversions(ADC). Our development of hardware board, processing 64-channel 12-bit 1ks/s, is built by using 8-channel ADC chips, 8-bit microprocessors, SPI interfaces, and parallel data transfers between microprocessors to meet the 1ks/s, i.e. 1 ms speed. The test result shows that the signal acquisition is done in 168 usuc which is much shorter than the required 1 ms period. This hardware will be extended to 256 channel data acquisition to be used for the diagnosis system.

• Journal of the Korean Society of Radiology
• /
• v.8 no.7
• /
• pp.429-433
• /
• 2014

In this study, the morphology and the x-ray quantum efficient of mercury oxide (HgO) and lead oxide (PbO) sensors derived by particle sedimentation method were discussed. In the pursuit of this purpose, we investigated the electrical characteristics and the x-ray quantum efficiency of various thicknesses of HgO and PbO films in mammographic x-ray energy. We have therefore developed a particle-in-binder sedimentation method of fabricating large area polycrystalline films onto transparent glass substrates coated with indium tin oxide. We are currently optimizing the growth method to improve the quantum efficiency with the ultimate goal of obtaining as quantum efficiency close to that of single crystal performance. Our future efforts will concentrate on optimization of large area film growth techniques specifically for deposition on a-Si:H flat panel readout arrays.

• Journal of Sensor Science and Technology
• /
• v.33 no.4
• /
• pp.224-229
• /
• 2024

Quantum dot light-emitting diodes (QD-LEDs) are emerging as next-generation displays owing to their high color purity, wide color gamut, and solution processability. Enhancing the efficiency of QD-LEDs involves preventing non-radiative recombination mechanisms, such as Auger and interfacial recombination. Generally, ZnO serves as the electron transport layer, which is known for its higher mobility compared to that of organic semiconductors and can lead to excessive electron injection. Some of the injected electrons pass through the quantum dot emissive layer and undergo non-radiative recombination near or within the organic hole transport layer (HTL), resulting in HTL degradation. Therefore, the implementation of electron blocking layers (EBLs) is essential; however, studies on all-solution-processed inverted InP QD-LEDs are limited. In this study, poly(9-vinylcarbazole) (PVK) is introduced as an EBL to mitigate HTL degradation and enhance the emission efficiency of inverted InP QD-LEDs. Using a single-carrier device, PVK was confirmed to effectively inhibit electron overflow into the HTL, even at extremely low thicknesses. The optimization of the PVK thickness also ensured minimal disruption of the hole-injection properties. Consequently, a 1.5-fold increase in the maximum luminance was achieved in the all-solution-processed inverted InP QD-LEDs with the EBL.

• Applied Science and Convergence Technology
• /
• v.26 no.3
• /
• pp.47-49
• /
• 2017

Photocurrent enhancement has been investigated in monolayer (1L) $MoS_2$ with PbS quantum dots (QDs). A metal-semiconductor-metal (Au-1L $MoS_2$-Au) junction device is fabricated using a standard photolithography method. Considerably improved photo-electrical properties are obtained by coating PbS QDs on the Au-1L $MoS_2$-Au device. Time dependent photoconductivity and current-voltage characteristics are investigated. For the QDs-coated $MoS_2$ device, it is observed that the photocurrent is considerably enhanced and the decay life time becomes longer. We propose that carriers in QDs are excited and transferred to the $MoS_2$ channel under light illumination, improving the photocurrent of the 1L $MoS_2$ channel. Our experimental findings suggest that two-dimensional layered semiconductor materials combined with QDs could be used as building blocks for highly-sensitive optoelectronic detectors including radiation sensors.

• Journal of Sensor Science and Technology
• /
• v.19 no.2
• /
• pp.160-167
• /
• 2010

In this paper, we fabricated the optoelectronic device based on Cadmium selenide(CdSe) nanocrystal quantum dots (NQDs)/single-walled carbon nanotubes(SWNTs) heterostructure using dieletrophoretic force. The efficient charge transfer phenomena from CdSe to SWNT make CdSe-Pyridine(py)-SWNT unique heterostructures for novel optoelectronic device. The conductivity of CdSe-py-SWNT was increased when it was exposed at ultra violet(UV) lamp, and varied as a function of wavelength of incident light.

• Korean Journal of Materials Research
• /
• v.19 no.1
• /
• pp.44-49
• /
• 2009

Conjugated nanocrystals using CdSe/ZnS core/shell nanocrystal quantum dots modified by organic linkers and glucose oxidase (GOx) were prepared for use as biosensors. The trioctylphophine oxide (TOPO)-capped QDs were first modified to give them water-solubility by terminal carboxyl groups that were bonded to the amino groups of GOx through an EDC/NHS coupling reaction. As the glucose concentration increased, the photoluminescence intensity was enhanced linearly due to the electron transfer during the enzymatic reaction. The UV-visible spectra of the as-prepared QDs are identical to that of QDs-MAA. This shows that these QDs do not become agglomerated during ligand exchanges. A photoluminescence (PL) spectroscopic study showed that the PL intensity of the QDs-GOx bioconjugates was increased in the presence of glucose. These glucose sensors showed linearity up to approximately 15 mM and became gradually saturated above 15 mM because the excess glucose did not affect the enzymatic oxidation reaction past that amount. These biosensors show highly sensitive variation in terms of their photoluminescence depending on the glucose concentration.

• Journal of Sensor Science and Technology
• /
• v.31 no.4
• /
• pp.238-243
• /
• 2022

In this study, a pyrene-core single molecule with amino (-NH₂) functional group material was hybridized using ZnO quantum dots (QDs). The suppressed performance of the 1-aminopyrene (1-PyNH₂) single molecule as an emissive layer (EML) in light-emitting diodes (LEDs) was exploited by adopting the ZnO@1-PyNH₂ core-shell structure. Unlike pristine 1-PyNH₂ molecules, the ZnO@1-PyNH₂ hybrid QDs formed energy proximity levels that enabled charge transfer. This result can be interpreted as an improvement in surface roughness. The uniform and homogeneous EML alleviates dark-spot degradation. Moreover, LEDs with the ITO/PEDOT:PSS/TFB/EML/TPBi/LiF/Al configuration were fabricated to evaluate the performance of two emissive materials, where pristine-1-PyNH₂ molecules and ZnO@1-PyNH₂ QDs were used as the EML materials to verify the improvement in electrical characteristics. The ZnO@1-PyNH₂ LEDs exhibited blue luminescence at 443 nm (FWHM = 49 nm), with a turn-on voltage of 4 V, maximum luminance of 1500 cd/m², maximum luminous efficiency of 0.66 cd/A, and power efficiency of 0.41 lm/W.