Jinyong Choi

Length-dependent thermoelectric characteristics of silicon nanowires on plastics in a relatively low temperature regime in ambient air

We report on the thermoelectric characteristics of p-type silicon nanowires (NWs) on plastics in the relatively low temperature regime below 47 °C, and for temperature differences of less than 10 K in ambient air. Thermal profile images are utilized to directly determine the temperature difference in the NWs generated by Joule heating in air. The Seebeck coefficient of the NWs increases from 294 to 414 μV K(-1) as the NW length varies from 40 to 280 μm. For a temperature difference of 7 K, the maximal Seebeck voltage can be estimated to be 2.7 mV for NWs with a length of 280 μm. In contrast, the output power is maximized for NWs length of 240 μm. The maximized output power obtained experimentally in this study is 2.1 pW at a temperature difference of 6 K. The thermoelectric characteristics are analyzed and discussed.

Thermoelectric characteristics of nanocomposites made of HgSe and Ag nanoparticles for flexible thermoelectric devices

We synthesized thermoelectric nanocomposites by mixing HgSe nanoparticles (NPs) and Ag NPs in a solution and investigated the thermoelectric properties of the nanocomposite thin films on flexible plastic substrates. The X-ray diffraction patterns and the X-ray photoelectron spectra of the nanocomposites demonstrate that cation-exchange reactions occurred spontaneously in the mixed solution of HgSe and Ag NPs and that the HgSe NPs were completely converted to Ag2Se when the Ag NP content was 20 vol.%. The maximum power factor and the thermoelectric figure of merit were obtained as 75 μW/mK2 and 0.043 at 300 K, respectively, when the Ag NP content was 10 vol.%, which is 100 times higher than that of HgSe NP thin films. In addition, the mechanical stability of the thermoelectric nanocomposite film was confirmed through repeated bending tests.

Thermal conductivity of silicon nanowires embedded on thermoelectric platforms

In this study, we propose a simple method for obtaining the thermal conductivity of silicon nanowires (SiNWs) embedded on a thermoelectric platform. The approximation of the heat flux in SiNWs with temperature differences enables the determination of thermal conductivity. Using this method, the thermal conductivities of our n- and p-type SiNWs are found to be 18.06 ± 0.12 and 20.29 ± 0.77 W m−1 K−1, respectively. The atomic weight of arsenic ions in the n-type SiNWs is responsible for a lower thermal conductivity than that of boron ions in the p-type SiNWs. Our results demonstrate that this simple method is capable of measuring the thermal conductivity of thermoelectric nanomaterials embedded on thermoelectric devices.

Strain Effects on Optoelectronic Characteristics of Laterally Arrayed Silicon Nanowires on a Flexible Substrate

In this study, we array n-type silicon nanowires (SiNWs) on a flexible plastic substrate and investigate the effects of tensile strain on the optoelectronic characteristics of the laterally arrayed SiNWs under the illumination of 633-nm-wavelength light in air at room temperature. The unstrained SiNW array has an efficiency of approximately 5.3 µA/W at a bias voltage of 5 V. When the plastic substrate suffers from a tensile strain of up to 2.2% in parallel to the channels of SiNWs, dark current and photocurrent increase markedly owing to the change in their band structure caused by the tensile strain.

Field-effect modulation of the thermoelectric characteristics of silicon nanowires on plastic substrates

In this study, we demonstrate the substantial enhancement of the thermoelectric power factors of silicon nanowires (SiNWs) on plastic substrates achievable by field-effect modulation. The Seebeck coefficient and electrical conductivity are adjusted by varying the charge carrier concentration via electrical modulation with a gate voltage in the 0 to ±5 range, thus enhancing the power factors from 2.08 to 935 μW K-2 m-1) for n-type SiNWs, and from 453 to 944 μW K-2 m-1) for p-type SiNWs. The electrically modulated thermoelectric characteristics of SiNWs are analyzed and discussed.