Initial oxidation of H-terminated Si(111) surfaces studied by HREELS

Ikeda, Hiroya; Nakagawa, Yasuyuki; Toshima, M.; Furuta, Sadaaki; Zaima, Shigeaki; Yasuda, Yukio

doi:10.1016/s0169-4332(97)80061-x

Cited by 27 publications

(26 citation statements)

References 12 publications

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“…pnc-Si is expected to grow a negatively charged native oxide as silicon surfaces typically do in the presence of oxygen (28). This expectation is consistent with the negative zeta potential of untreated pnc-Si and the fact that electroosmostic flow is directed toward the negative electrode.…”

Section: Significancesupporting

confidence: 66%

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes

Snyder

Getpreecharsawas

Fang

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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We have developed electroosmotic pumps (EOPs) fabricated from 15-nm-thick porous nanocrystalline silicon (pnc-Si) membranes. Ultrathin pnc-Si membranes enable high electroosmotic flow per unit voltage. We demonstrate that electroosmosis theory compares well with the observed pnc-Si flow rates. We attribute the high flow rates to high electrical fields present across the 15-nm span of the membrane. Surface modifications, such as plasma oxidation or silanization, can influence the electroosmotic flow rates through pnc-Si membranes by alteration of the zeta potential of the material. A prototype EOP that uses pnc-Si membranes and Ag/ AgCl electrodes was shown to pump microliter per minute-range flow through a 0.5-mm-diameter capillary tubing with as low as 250 mV of applied voltage. This silicon-based platform enables straightforward integration of low-voltage, on-chip EOPs into portable microfluidic devices with low back pressures.lectroosmotic flow results from the interaction between an electric field and the diffuse layer of ions at a charged surface. In capillaries or pores, the migration of the diffuse layer toward the oppositely charged electrode causes the bulk fluid within the channel to flow through viscous drag. Electroosmotic pumps (EOPs) are designed to generate high flow rates in microchannels using these principles (1, 2). EOPs present a number of advantages over mechanical pumps, including the lack of mechanical parts, pulse-free flows, and ease of control through electrode actuation. EOPs have been suggested as pumps for cooling circuits (3) and microfluidic devices that aid in drug delivery (4, 5) or diagnostics (2, 6). Microfluidic devices enable the miniaturization of multistep laboratory processes into small, low-cost, disposable units (6, 7). The inclusion of multiple steps into a single device increases the need for the precision pumping of fluids on-chip.High voltages (>1 kV) are often required for direct current (dc) EOPs to achieve sufficient flow rates in microchannels (8, 9). However, devices with high-voltage EOPs require bulky external power supplies and a skilled technician to operate, which defeats the ease of use and portability aims of a microfluidic diagnostic tool. For these reasons, the development of a low-voltage EOP is a current focus in the literature. Several recent low-voltage EOPs have been fabricated from porous silicon (10), alumina (11-13), track-etched polymer (14), and carbon nanotube membranes (15). These low-voltage EOPs are much thinner than their highvoltage predecessors (60-350 μm compared with >10 mm). Yao et al. suggest that further thinning of EOPs will enable better voltage-specific characteristics (16). Here, we examine the electroosmotic pumping by nanoporous membranes that are more than two orders of magnitude thinner than any membrane material previously used in an EOP.We have recently developed an ultrathin (15-30 nm), nanoporous membrane material called porous nanocrystalline silicon (pnc-Si) (17). pnc-Si membranes are fabricated on silicon wafers usin...

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Section: Significancesupporting

confidence: 66%

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes

Snyder

Getpreecharsawas

Fang

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…The frequency of the loss peak due to the Si-O-Si mode is seen to shift up to~1050 cm − 1 at high coverage, likely due to coupling between adjacent molecules. Similar shifts to higher frequency upon increased coupling between Si-O-Si modes have been observed in the case of oxidation of H-terminated silicon surfaces [31].…”

Section: Resultssupporting

confidence: 74%

STM and HREELS investigation of gas phase silanization on hydroxylated Si(100)

Fan

Lopinski

2010

Surface Science

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“…For H/Si(111) surfaces with oxygen inserted into most of the available Si-Si back bonds, characteristic Si-O-Si modes are observed at ∼410, ∼830, and 1095 cm -1 with the last of these being the most prominent. 36 The spectral changes observed for the photochemically reacted surface can therefore be explained by the incorporation of oxygen into the Si-Si back bonds. The apparent upshift of the 800 and 1070 cm -1 features can be accounted for by the growth of the Si-O-Si modes on the high-frequency side of both of these peaks.…”

Section: Resultsmentioning

confidence: 99%

Formation of Organic Monolayers on Silicon via Gas-Phase Photochemical Reactions

Eves

Lopinski

2006

Langmuir

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A new method for the formation of molecular monolayers on silicon surfaces utilizing gas-phase photochemical reactions is reported. Hydrogen-terminated Si(111) surfaces were exposed to various gas-phase molecules (hexene, benzaldehyde, and allylamine) and irradiated with ultraviolet light from a mercury lamp. The surfaces were studied with in situ Fourier transform infrared spectroscopy, high-resolution electron energy loss spectroscopy, and scanning tunneling microscopy. The generation of gas-phase radicals was found to be the initiator for organic monolayer formation via the abstraction of hydrogen from the H/Si(111) surface. Monolayer growth can occur through either a radical chain reaction mechanism or through direct radical attachment to the silicon dangling bonds.

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Initial oxidation of H-terminated Si(111) surfaces studied by HREELS

Cited by 27 publications

References 12 publications

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes

STM and HREELS investigation of gas phase silanization on hydroxylated Si(100)

Formation of Organic Monolayers on Silicon via Gas-Phase Photochemical Reactions

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