Enhanced terahertz conductivity in ultra-thin gold film deposited onto (3-mercaptopropyl) trimethoxysilane (MPTMS)-coated Si substrates

Various material properties change considerably when material is thinned down to nanometer thicknesses. Accordingly, researchers have been trying to obtain homogeneous thin films with nanometer thickness but depositing homogeneous few nanometers thick gold film is challenging as it tends to form islands rather than homogenous film. Recently, studies have revealed that treating the substrate with an organic buffer, (3-mercaptopropyl) trimethoxysilane (MPTMS) enables deposition of ultra-thin gold film having thickness as low as 5 nm. Different aspects of MPTMS treatment for ultrathin gold films like its effect on the structure and optical properties at visible wavelengths have been investigated. However, the effect of the MPTMS treatment on electrical conductivity of ultra-thin gold film at terahertz frequency remains unexplored. Here, we measure the complex conductivity of nanometer-thick gold films deposited onto an MPTMS-coated silicon substrate using terahertz time-domain spectroscopy. Following the MPTMS treatment of the substrate, the conductivity of the films was found to increase compared to those deposited onto uncoated substrate for gold films having the thickness less than 11 nm. We observed 5-fold enhancement in the conductivity for a 7 nm-thick gold film. We also demonstrate the fabrication of nanoslot-antenna arrays in 8.2-nm-thick gold films. The nanoslot-antenna with MPTMS coating has resonance at around 0.5 THz with an electric field enhancement of 44, whereas the nanoslot-antenna without MPTMS coating does not show resonant properties. Our results demonstrate that gold films deposited onto MPTMS-coated silicon substrates are promising advanced materials for fabricating ultra-thin terahertz plasmonic devices

Ultrasonic Processing of Si and SiGe for Photovoltaic Applications

The usage of power ultrasound for sonochemical processing of Si wafers and thin layers of amorphous Si and SiGe alloys is described. Over the last decade different industries have become increasingly drawn to sonochemistry because it provides a green and clean alternative to conventional technologies, particular in the areas of processing of silicon-based materials for photovoltaic applications. Two techniques related to ultrasonic cleaning of Si wafers and sonochemical modification of Si, SiGe and a-Si/SiGe surfaces in hydrocarbon solutions of chloroform (CHCl3) and dichloromethane (CH2Cl2) are discussed. The occurrence of cavitation and bubble implosion is an indispensable prerequisite for ultrasonic cleaning and surface processing as it is known today. The use of higher ultrasonic frequencies to expand the range of ultrasonic cleaning and processing capabilities is emphasized. Although exact mechanisms of an improved photoelectric behavior of Si-based structures subjected to power ultrasound are not yet clarified in many cases, the likely scenarios behind the observed photovoltaic performances of Si, SiGe and a-Si/SiGe surfaces are proposed to involve the surface chemistry of oxygen and hydrogen molecules as well hydrocarbon chains

Revealing CdSe Quantum Dots Plasmonics Confined in Au Nanotrenches by Thermoacoustic Spectroscopy

In this work, the influence of Au plasmonics on the thermoacoustic (TA) response of integrated thiol-linked CdSe quantum dot-Au nanotrench structures is demonstrated. The TA measurement technique uses a modulated light beam illuminating the sample placed into the air-filled cell and measures the temperature oscillation in the sample resulting from the light absorption. The intermittent heat generates an acoustic signal in the cell that is detected by a microphone. We observed an enhanced acoustic signal with increased light absorption. The enhancement is correlated with the plasmonic absorption by the Au grating layers. The signal is even more enhanced in two well-defined spectral bands peaking at about 400 and 490 nm due to CdSe QDs. The approach presented here can be extended in various fields employing light-to-heat conversion processes in hybrid metal???semiconductor nanomaterials and nanoplasmonic systems

Photoelectric Response of Ge Nanocones Formed on Si1−xGex by Laser Radiation

Irradiation of SiGe-on-Si structures by pulsed Nd:YAG laser with intensities 1.0 MW/cm2 leads to the formation of Ge nanocones. As a result increases the surface photovoltage (SPV) signal up to 10 times. The SPV decays do not speed up with the radiation, thus indicating that the laser treatments do not cause an increase in the concentration of recombination centers at interfaces. Therefore the fabrication technique proposes here may be considered to be an effective approach of producing cost-competitive photosensors based on SiGe/Si

Thermoelectric energy conversion in layered structures with strained Ge quantum dots grown on Si surfaces

The efficiency of the energy conversion devices depends in many ways on the materials used and various emerging cost-effective nanomaterials have promised huge potentials in highly efficient energy conversion. Here we show that thermoelectric voltage can be enhanced by a factor of 3 using layer-cake growth of Ge quantum dots through thermal oxidation of SiGe layers stacked in SiO2/Si3N4 multilayer structure. The key to achieving this behavior has been to strain the Ge/Si interface by Ge dots migrating to Si substrate. Calculations taking into account the carrier trapping in the dot with a quantum transmission into the neighboring dot show satisfactory agreement with experiments above ≈200 K. The results may be of interest for improving the functionality of thermoelectric devices based on Ge/Si

PHOTOELECTRIC PROPERTIES OF HETEROSTRUCTURES BASED ON PEPC AND MEH-PPV FILMS DOPED WITH ZINC OCTABUTYLPHTHALOCYANINE

Planar organic heterostructures were prepared using poly-N- epoxypropylcarbazole films and poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene] by the method of successive deposition adding 2,3,9,10,16,17,23,24-zinc octabutylphthalocyanine. Photoelectric, photodielectric and photovoltaic properties of the heterostructures were studied