A Silicon‐Based Room Temperature Spin Source without Magnetic Layers

Abstract

for self-assembled helical molecules attached to metals, mostly on gold substrates, [ 9 ] and for chiral molecules evaporated onto a magnetic substrate. [ 10 ] Recently, it was further shown that helical poly-alanine can be used to magnetize ferromagnetic nickel at low temperatures. [ 11 ] In this Communication we present a silicon-based spin source at room temperature without magnetic layers, based only on the spin fi lter effect in dsDNA covalently bound to Si(100).The fi rst step in developing the spin source requires the immobilization of dsDNA on Si(100). A good control of the selfassembly is possible via nucleophilic-electrophilic chemistry or by thiol-ene/yne click chemistry. Both approaches enable the binding of DNA to semiconductor surfaces. [ 12 ] In the present experiment we used the nucleophilic-electrophilic amine-isothiocyanate reaction. A schematic of the preparation steps involved in this reaction is shown in Figure 1 . For this purpose 2.5% HF acid solution was used to etch-off the natural oxide layer on silicon and to form a hydrogen terminated silicon surface. Subsequent treatment with acid peroxide (piranha solution) leads to the formation of a hydroxylated surface. Water contact angles of less than 20° indicate a highly hydrophilic nature of the surface, as expected. Functionalization of the surface with a solution of 3-isothiocyanatopropyl triethoxy silane (ICPTES) linker molecules in dry toluene increases the hydrophobicity, causing an increase of the contact angle to nearly 70°. [ 13 ] This confi rms the successful formation of linker molecules on the substrate, because the decrease of hydrophilicity is a result of the aliphatic chains of the linker molecules. Afterward, dsDNA was immobilized by wetting of the surface with 10 × 10 −6 M solution of 50 base pair dsDNA dissolved in phosphate buffer at pH 8 for 72 h. The water contact angle decreases to 35° due to the hydrophilicity of the DNA's backbone.The functionalization of the silicon surface was also investigated by X-ray photoelectron spectroscopy (XPS) for binding energies in the E B = 0-650 eV range, as shown in Figure 2 . On the hydroxylated silicon surface the Si 2p and 2s features are detected at E B = 100.7 eV and E B = 152.1 eV binding energies, respectively. Additionally, the O 1s signal is clearly visible at E B = 532.1 eV binding energy. After attaching the linker molecules to the surface additional signals appear from C 1s and N 1s at about 285 and 400 eV binding energies, respectively. Further, a small contribution from S 2s at E B = 226.3 eV can be discerned. These signals are contributions from the carbon chains and the N  C  S moiety of the linker molecules. In case of the dsDNA functionalized surface the intensity of nitrogen and carbon features increase and a P 2s signal appears at 191.8 eV binding energy. These changes are contributed from the dsDNA backbone. For a better insight into the preparation high resolution XPS allows to confi rm the binding of single Controlling the electron spin orientation and spin inj...

Theory of Chirality Induced Spin Selectivity: Progress and Challenges

“…[ 66 ] Experimentally, CISS has been observed using substrates with negligible SOC. [ 17,22,67 ] Therefore substrate SOC may indeed be an important contribution where it exists, but cannot explain the whole effect.…”

Chiro‐Spintronics: Spin‐Dependent Electrochemistry and Water Splitting Using Chiral Molecular Films

“…In this field, seminal research articles based on experimental and theoretical research work developed by Ron Naaman's group, since 1999, unequivocally confirms the spin‐selective electron transport phenomenon occurring through chiral molecular films . Several complimentary experimental methods have been successfully used in a number of different experiments to support the CISS effect, which include photoelectron spectroscopy, spin‐dependent electrochemical measurements, conductive‐atomic force microscopy techniques, photoluminescence, and solid‐state devices fabricated using chiral molecules . Thus, the main focus of the present review is to summarize recent exciting findings obtained in the development of suitable ferromagnetic/chiral electrodes to be used in the measurement of spin‐polarized currents in electrochemical experiments.…”

Structure dependent spin selectivity in electron transport through oligopeptides

“…The CISS effect relates to the ability of chiral molecules to transmit electrons in a spin-selective manner, hence the molecules act as spin filters. 6,7 Several chiral molecular species including DNA, [8][9][10][11][12] oligopeptides, [13][14][15] bacteriorhodopsin (bR), 16,17 a chiral conductive polymer, 18 1, 2-diphenyl-1,2-ethanediol (DPED), 19 helicenes, 20 and recently chiral CdSe quantum dots 21 have demonstrated efficient spin filtering. The spin filtering ability can be tuned by various means, for example, by varying the length of the chiral molecule, 8,9,13 by exposure to light, 22 or by varying the temperature.…”