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ABSTRACT: Three types of a-C:Co/Si samples were fabricated using the pulsed laser deposition: Co2-C98/Si with Co dispersed in the a-C film, Co2-C98/Si with Co segregated at the interface, and a-C/Co/Si with Co continuously distributed at the a-C/Si interface. Both types
of Co2-C98/Si samples had the positive bias-voltage-dependent magnetoresistance (MR) at 300 K, and all MRs had saturated behavior. The
study on the electrotransport properties indicated that the MR appeared in the diffusion current region, and the mechanism
of MR was proposed to be that the applied magnetic field and local random magnetic field caused by the superparamagnetic Co
particles modulate the ratio of singlet and triplet spin states, resulting in the MR effect. In addition, the very different
physical and structural properties of all samples revealed that Co played a crucial role in the room-temperature positive
MR of a-C:Co/Si system.
Keywordsmagnetoresistance–carbon film–pulsed laser deposition
Science China: Physics, Mechanics and Astronomy 04/2012; 54(7):1213-1217. · 0.78 Impact Factor
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ABSTRACT: Various carbon based spintronic materials or devices have been made by pulsed laser deposition. It is found that amorphous carbon (a-C) film shows a very large magnetoresistance (MR) of 27% at B=7T and 2 K. It is also found that the a-C/Si heterojunction shows a memory effect at 80 K. A solar cell with structure of Fe<sub>x</sub>-C<sub>1-x</sub>/Al<sub>2</sub>O<sub>3</sub>/Si has been made which shows a power conversion efficiency of 2.01% with AM1.5 illumination. Our work show that carbon and silicon can be used to make a hybrid material/device which shows many novel structural dependent physical properties, such as MR, memory effect and photovoltaic effect.
IEEE Transactions on Magnetics 11/2011; · 1.36 Impact Factor
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ABSTRACT: Iron doped amorphous carbon films were deposited by pulse laser deposition on n-type silicon substrates. The as-fabricated structure shows a positive magnetoresistance (MR) of 34% at 5 T. Hall measurements show that the carbon film is hole-conducting and therefore a p-n heterojunction forms near the interface so that the current transport channel is transferred from the above carbon films at low temperatures to the Si substrates at high temperatures. The MR measured at high temperatures is attributed to the silicon substrates rather than to an inversion layer in the substrates as reported for many Metal/Insulating Barrier/Si structures.
IEEE Transactions on Magnetics 11/2011; · 1.36 Impact Factor
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ABSTRACT: Inhomogeneity-induced magnetoresistance (IMR) reported in some non-magnetic semiconductors, particularly silicon, has generated considerable interest owing to the large magnitude of the effect and its linear field dependence (albeit at high magnetic fields). Various theories implicate spatial variation of the carrier mobility as being responsible for IMR. Here we show that IMR in lightly doped silicon can be significantly enhanced through hole injection, and then tuned by an applied current to arise at low magnetic fields. In our devices, the 'inhomogeneity' is provided by the p-n boundary formed between regions where conduction is dominated by the minority and majority charge carriers (holes and electrons) respectively; application of a magnetic field distorts the current in the boundary region, resulting in large magnetoresistance. Because this is an intrinsically spatial effect, the geometry of the device can be used to enhance IMR further: we designed an IMR device whose room-temperature field sensitivity at low fields was greatly improved, with magnetoresistance reaching 10% at 0.07 T and 100% at 0.2 T, approaching the performance of commercial giant-magnetoresistance devices. The combination of high sensitivity to low magnetic fields and large high-field response should make this device concept attractive to the magnetic-field sensing industry. Moreover, because our device is based on a conventional silicon platform, it should be possible to integrate it with existing silicon devices and so aid the development of silicon-based magnetoelectronics.
Nature 09/2011; 477(7364):304-7. · 36.28 Impact Factor
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ABSTRACT: Iron doped amorphous carbon (a-C: Fe) films on n-Si substrates were fabricated by pulse laser deposition technique. Barrier heights of the heterojunctions, measured in the electrical methods, were found to decrease gently below 300 °C and then increase anomalously thereafter. An interface energy band model was proposed to interpret the band structure of the heterojunctions as well as to calculate bandgaps of the a-C: Fe films. The abnormal increase in the barrier heights above 300 °C was attributed to the narrowing of π and π* bands due to the increased ordering degree of the sp2 clusters in a-C films, which was verified in Raman spectra and electron energy loss spectroscopy.
Journal of Applied Physics 05/2011; 109(10):103706-103706-7. · 2.17 Impact Factor
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ABSTRACT: The decay of spin polarization poses serious problems for spintronic devices. It will be greatly helped by the availability of spintronic materials with a long spin diffusion length. Carbon has small spin-orbital interaction and longer coherent length. This makes carbon suitable material for exploitation in the spintronic materials and devices. A great deal of magnetoresistance (MR) research has been carried out in carbon nanotubes, grapheme and small carbon molecules. However, the MRs of these materials are normally observed at low temperature, making these carbon materials difficult used in information industry. In this paper, we introduce a novel class of carbon based hybrid materials Fe(x)-C(1-x)/Si structure which show larger MR at room temperature. These materials have also some other novel physical properties, such as electromagnetoresistance, switch effect, pressure sensitivity, gas sensitivity and photoconductivity. This kind of carbon based materials has shown early sign of being excellent candidates for spintronic materials operating at room temperature.
Journal of Nanoscience and Nanotechnology 03/2011; 11(3):2583-7. · 1.56 Impact Factor
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ABSTRACT: Amorphous carbon (a-C) film/n-Si heterojunctions have been fabricated by pulse laser deposition, and their current-voltage characteristics have been investigated. The results show that the atmosphere relative humidity (RH) has a significant effect on the reverse bias I-V characteristics of the heterojunctions. For the low bias voltages, the resistance of the a-C/Si heterojunction decreases with the increase of the RH. However, when the applied voltage is greater than a threshold, the resistance of the a-C/Si heterojunctions increases with the increase of the RH. This humidity-dependent phenomenon is attributed to the charge transfer from the absorbed H2O molecular to a-C film.
Applied Physics Letters 11/2010; 97(21):212101-212101-3. · 3.84 Impact Factor
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ABSTRACT: CoxC1−x granular films and pure carbon films were deposited on n-type Si substrates using the pulsed laser deposition method. Three types of samples were obtained: pure C/Si, CoxC1−x granular film/Si with Co dispersed in the C film, and CoxC1−x/Si with Co segregated at the interface. After comparing the physical properties and structures of these three types of samples, we found that the segregation of Co at the interface not only increased the maximum value of magnetoresistance but also improved the magnetoresistance sensitivity in the CoxC1−x/Si system.
Journal of Applied Physics 09/2010; 108(6):063712-063712-5. · 2.17 Impact Factor
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ABSTRACT: Co <sub>x</sub>– C <sub>1-x</sub> granular films were deposited on n -type Si substrates by pulsed laser deposition method. The heterostructure, investigated in current-perpendicular-to-plane geometry, has a bias voltage dependent positive magnetoresistance (MR), and at room temperature, the MR value reaches 16% at magnetic field H=2.5 kOe and bias voltage of 6 V. All MRs have saturated behavior when H≫2.5 kOe . The mechanism of this MR is attributed to that the applied magnetic field and local random magnetic field modulate the ratio of singlet and triplet spin states leading to the MR.
Applied Physics Letters 08/2009; · 3.84 Impact Factor
