Periodic Nano Research Articles

Polycrystalline silicon thin-film solar cells: Status and perspectives

The present article gives a summary of recent technological and scientific developments in the field of polycrystalline silicon (poly-Si) thin-film solar cells on foreign substrates. Cost-effective fabrication methods and cheap substrate materials make poly-Si thin-film solar cells promising candidates for photovoltaics. However, it is still the challenge for research and development to achieve the necessary high electrical material quality known from crystalline Si wafers on glass as a prerequisite to harvest the advantages of thin-film technologies. A wide variety of poly-Si thin-film solar cell approaches has been investigated in the past years, such as thermal solid phase crystallization – the only technology that had already been matured to industrial production so far – the seed layer concept where a large-grained seed layer is epitaxially thickened, direct growth of fine grained material, and liquid phase crystallization methods by laser or electron beam. In the first part of this paper, the status of these four different poly-Si thin-film solar cell concepts is summarized, by comparing the technological fabrication methods, as well as the structural and electrical properties and solar cell performances of the respective materials. In the second part, three promising technologies are described in more detail due to their highly auspicious properties regarding material quality and throughput aspects during fabrication: (1) High-rate electron–beam evaporation of silicon for the low-cost deposition of high-quality material, (2) large-area periodic nano- and micro-structuring of poly-Si by the use of imprinted substrates providing a large absorption enhancement by a factor of six at a wavelength of 900nm, (3) liquid-phase crystallization of silicon thin-film solar cells by electron–beam, yielding an excellent poly-Si material quality reflected by an open-circuit voltage of 582mV which has been achieved only very recently. A successful combination of these three complementary technologies is envisaged to be the basis for a prospective low-cost and highly efficient poly-Si solar cell device.

Nano Slit And Dot Array Pattern Of Au On SiO2 substrates Using Laser Beam Lithography

Highly monochromatic coherent light intensity of lasers provides the possibility of fabricating periodic nano-patterns which are needed in many applications. Here, we report 2D grating structure and periodic nano hole and dot arrays fabricated using two laser beam interference lithography. Using this method periodic grating as well as dot patterns have been fabricated with structure size of 50 -100 nm and pitch of 200-300 nm on SiO2 substrate. The nano-patterns are formed by inverting an array of photoresist posts by a lift-off process and subsequent reactive-ion etching using chromium as an etch mask. The depth of patterns can be tuned simple by laser dose to obtain high aspect ratio gratings. Transmission spectra measured in Au slits shows strong resonance features at 520 and 640 nm. Finite difference time domain simulations are used to estimate the near-field enhancement at the center of the slit pattern. Copyright © 2013 VBRI press.

Development of Multi Scale Structured Al/Al<SUB>2</SUB>O<SUB>3</SUB> Nanowires for Controlled Cell Guidance

Cell responses to surface and contact cell guidance are of great interest in bio-applications especially on nano- and micro scale features. Recently we showed selective cell responses on Al/Al2O3, bi-phasic nanowires (NWs). In this context, Al/Al2O3 NWs were synthesized by the chemical vapor deposition of (tBuOAIH2)2. Afterwards, linear periodic nano- and micro structured NWs were formed using laser interference lithography (LIL) technique to study the contact guidance of neurons from rat dorsal root ganglion (DRG), human umbilical vein smooth muscle cells (HUVSMC), human umbilical vein endothelial cells (HUVEC) and human osteoblast (HOB). LIL treatment did not alter surface chemistry of NWs. From our preliminary research LIL patterned NWs lead to alignment of axons contrary to non-patterned NWs. Morphology of HUVSMC changed from poly- to linear shapes and strong alignment was observed while HUVEC and HOB were not affected.

나노패턴된 기판 위에서의 그래핀의 비등방성 전자 수송 특성

주기적인 나노트랜치 패턴이 있는 기판 위에 놓인 CVD 그래핀의 전도특성을 측정하였다. 나노트랜치에 대해 평행한 방향과 수직한 방향 사이에 전도특성의 큰 비등방성을 발견하였다. 전기 전도의 방향이 나노트랜치에 수직한 경우, 약한 한곳모임의 특성에 있어서도 큰 차이점이 발견되었는데, 이는 퍼텐셜 변조에 의해 생겨나는 전하밀도의 비균일성에 의해 생겨나는 것으로 해석된다. We report on the measurements of electronic transport properties of CVD graphene placed on a pre-patterned substrate with periodic nano trenches. A strong anisotropy has been observed between the transport parallel and perpendicular to the trenches. Characteristically different weak localization corrections have been also observed when the transport was perpendicular to the trench, which is interpreted as due to a density inhomogeneity generated by the potential modulations.

Controlling absorption enhancement in organic photovoltaic cells by patterning Au nano disks within the active layer

We show experimentally and theoretically enhancement of external quantum efficiency in the green-NIR spectrum for organic photovoltaic device, by the incorporation of patterned Au nano-disk arrays that extend from the front electrode into the active layer. Enhancement mechanisms and design rules are extracted by comprehensive simulations which match the experimental findings. The enhanced efficiency is shown to stem from field enhancement originating from both localized plasmonic resonances and periodic nano patch antennas configuration.

Ultra-fast photoacoustic flow cytometry with a 05 MHz pulse repetition rate nanosecond laser

In vivo photoacoustic (PA) flow cytometry (PAFC) has great potential for detecting disease-associated biomarkers in blood and lymph flow, as well as real-time control of the efficacy of photothermal (PT) and other therapies through the counting of circulating abnormal objects. We report on a high speed PAFC with a Yb-doped fiber laser having a 0.5-MHz pulse repetition rate at a wavelength of 1064 nm, pulse width of 10 ns, and energy up to 100 µJ. This is the first biomedical application of PA and PT techniques operating at the highest pulse repetition rate of nanosecond lasers that provide 100-fold enhancement in detection speed of carbon nanotube clusters, as well as real-time monitoring of the flow velocity of individual targets through the width of PA signals. The laser pulse rate limits for PT and PA techniques depending on the sizes of laser beam and targets and flow velocity are discussed. We propose time-overlapping mode and generation of periodic nano- and microbubbles as PA-signal and PT-therapy amplifiers, including discrimination of small absorbing targets among large ones. Taking into account the relatively low level of background signals from most biotissues at 1064 nm, our data suggest that a nanosecond Yb-doped fiber laser operating at high pulse repetition rate could be a promising optical source for time-resolved PA and PT cytometry, imaging, microscopy, and therapy, including detection of nanoparticles and cells flowing at velocities up to 2.5 m/s.

Glassy alloy composites for information technology applications

With the aim of developing a novel preparation process for bit-patterned-media, nano-patterned glassy alloy composite composed of zero-magneto-striction Co–Fe–B amorphous alloy thin film, Pd–Cu–Ni–P glassy alloy and Co/Pd multi-layer with perpendicular magnetization was prepared. Using the commercial imprinting mold, periodic nano hole array with a hole diameter of 90 nm and a pitch of 180 nm was successfully prepared on the surface of Pd-based glassy alloy thin film. By overlaying the Co/Pd multi-layer with perpendicular magnetization and surface polishing, isolated Co/Pd magnetic dots embedded into nano hole array can be obtained. These magnetic dots act as single magnetic domains. In addition, the change in magnetization direction was confirmed under magnetic fields of ±20 kOe. These results suggest that the glassy alloy nano-composite is suitable for BPM of high data density HDD. It is therefore concluded that the preparation method is candidate process for the preparation of BPM of high data density HDD.

Fabrication of SnO2 Nano Patterns Using Surface Relief Grating

ABSTRACTNano- and micro-structured SnO2 has been widely utilized as gas sensors. These SnO2 based gas sensors are often made by chemical etching, vapor deposition or lithography. Here we report a facile and vacuum-free technique to fabricate large area one-dimensional periodic SnO2 nano arrays using surface relief grating created on azobenzene functionalized polymer thin films as template. Atomic force microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy characterizations confirmed the successful fabrication of SnO2 nano arrays. The fabricated SnO2 structure exhibited the same periodicity as the template with a width of a few hundred nanometers.