| 1. |
- Ahlberg, Patrik, et al.
(författare)
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A two-in-one process for reliable graphene transistors processed with photolithography
- 2015
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 107:20
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Tidskriftsartikel (refereegranskat)abstract
- Research on graphene field-effect transistors (GFETs) has mainly relied on devices fabricated using electron-beam lithography for pattern generation, a method that has known problems with polymer contaminants. GFETs fabricated via photo-lithography suffer even worse from other chemical contaminations, which may lead to strong unintentional doping of the graphene. In this letter, we report on a scalable fabrication process for reliable GFETs based on ordinary photo-lithography by eliminating the aforementioned issues. The key to making this GFET processing compatible with silicon technology lies in a two-in-one process where a gate dielectric is deposited by means of atomic layer deposition. During this deposition step, contaminants, likely unintentionally introduced during the graphene transfer and patterning, are effectively removed. The resulting GFETs exhibit current-voltage characteristics representative to that of intrinsic non-doped graphene. Fundamental aspects pertaining to the surface engineering employed in this work are investigated in the light of chemical analysis in combination with electrical characterization.
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| 2. |
- Chen, Si, et al.
(författare)
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A graphene field-effect capacitor sensor in electrolyte
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:15, s. 154106-
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Tidskriftsartikel (refereegranskat)abstract
- The unique electronic properties of graphene are exploited for field-effect sensing in both capacitor and transistor modes when operating the sensor device in electrolyte. The device is fabricated using large-area graphene thin films prepared by means of layer-by-layer stacking. Although essentially the same device, its operation in the capacitor mode is found to yield more information than in the transistor mode. The capacitor sensor can simultaneously detect the variations of surface potential and electrical-double-layer capacitance at the graphene/electrolyte interface when altering the ion concentration. The capacitor-mode operation further facilitates studies of the molecular binding-adsorption kinetics by monitoring the capacitance transient
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| 3. |
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| 4. |
- Gao, Xindong, et al.
(författare)
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Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness
- 2011
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Ingår i: Electrochemical and solid-state letters. - : The Electrochemical Society. - 1099-0062 .- 1944-8775. ; 14:7, s. H268-H270
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Tidskriftsartikel (refereegranskat)abstract
- This letter presents a proof-of-concept process for tunable, self-limiting growth of ultrathin epitaxial NiSi2 films on Si (100). The process starts with metal sputter-deposition, followed by wet etching and then silicidation. By ionizing a fraction of the sputtered Ni atoms and biasing the Si substrate, the amount of Ni atoms incorporated in the substrate after wet etching can be controlled. As a result, the thickness of the NiSi2 films is increased from 4.7 to 7.2 nm by changing the nominal substrate bias from 0 to 600 V. The NiSi2 films are characterized by a specific resistivity around 50 mu Omega cm.
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| 5. |
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| 6. |
- Hu, Cheng, et al.
(författare)
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Characterization of Ni(Si,Ge) films on epitaxial SiGe(100) formed by microwave annealing
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:9, s. 092101-
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Tidskriftsartikel (refereegranskat)abstract
- Microwave annealing (MWA) is investigated as an alternative technique to rapid thermal processing with halogen lamp heating (RTP) for low-temperature silicide formation on epitaxially grown Si0.81Ge0.19 layers. Phase formation, resistivity mapping, morphology analysis, and composition evaluation indicate that the formation of low-resistivity NiSi1-xGex by means of MWA occurs at temperatures about 100 degrees C lower than by RTP. Under similar annealing conditions, more severe strain relaxation and defect generation are therefore found in the remaining Si0.81Ge0.19 layers treated by MWA. Although silicidation by microwave heating is in essence also due to thermal effects, details in heating mechanisms differ from RTP.
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| 7. |
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| 8. |
- Li, Jiantong, et al.
(författare)
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Ink-jet printed thin-film transistors with carbon nanotube channels shaped in long strips
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:8, s. 084915-
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Tidskriftsartikel (refereegranskat)abstract
- The present work reports on the development of a class of sophisticated thin-film transistors (TFTs) based on ink-jet printing of pristine single-walled carbon nanotubes (SWCNTs) for the channel formation. The transistors are manufactured on oxidized silicon wafers and flexible plastic substrates at ambient conditions. For this purpose, ink-jet printing techniques are developed with the aim of high-throughput production of SWCNT thin-film channels shaped in long strips. Stable SWCNT inks with proper fluidic characteristics are formulated by polymer addition. The present work unveils, through Monte Carlo simulations and in light of heterogeneous percolation, the underlying physics of the superiority of long-strip channels for SWCNT TFTs. It further predicts the compatibility of such a channel structure with ink-jet printing, taking into account the minimum dimensions achievable by commercially available printers. The printed devices exhibit improved electrical performance and scalability as compared to previously reported ink-jet printed SWCNT TFTs. The present work demonstrates that ink-jet printed SWCNT TFTs of long-strip channels are promising building blocks for flexible electronics.
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| 9. |
- Lu, Jun, et al.
(författare)
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Crystallization of NiSix in a Body-Centered Cubic Structure during Solid-State Reaction between an Ultrathin Ni Film and Si(001) Substrate at 150-350 degrees C
- 2013
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Ingår i: Crystal Growth & Design. - : American Chemical Society. - 1528-7483 .- 1528-7505. ; 13:5, s. 1801-1806
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Tidskriftsartikel (refereegranskat)abstract
- We investigate ultrathin silicide formation during a solid-state reaction between Ni layers and Si(001) substrates by aberration-corrected electron microscopy. Interdiffusion of two nm thick (equivalent) Ni layers with Si during magnetron-sputter deposition results in an amorphous Ni-Si solid solution. Upon annealing at 150-350 degrees C, a novel body-centered cubic (bcc) NiSix phase is found to grow epitaxially with a crystallographic relationship {100}andlt; 001 andgt; bcc-NiSix//{100}andlt; 001 andgt; Si. bcc-NiSix belongs to the space group I (4) over bar 3m (217) with random Ni and Si distribution. The cell parameter is 0.272 nm, which is approximately half that of NiSi2. Further annealing transforms bcc-NiSi to NiSi2 with an activation energy of 0.6 +/- 0.1 eV.
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| 10. |
- Luo, Jun, et al.
(författare)
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Thermal Stability and Dopant Segregation for Schottky Diodes With Ultrathin Epitaxial NiSi(2-y)
- 2011
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Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 32:8, s. 1029-1031
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Tidskriftsartikel (refereegranskat)abstract
- The Schottky barrier height (SBH) of an ultrathin epitaxial NiSi(2-y) film grown on Si(100) is modified significantly by means of dopant segregation (DS). The DS process begins with the NiSi(2-y) formation and is followed by dopant implantation and drive-in annealing. The rapid lattice restoration and superior morphological stability upon heat treatment up to 800 degrees C allow the epitaxial NiSi(2-y) film to take full advantage of the DS process. For drive-in annealing below 750 degrees C, the effective SBH is altered to similar to 0.9-1 eV for both electrons and holes by B-DS and As-DS, respectively, without deteriorating the integrity of the NiSi(2-y) film.
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| 11. |
- Piao, Yinghua, et al.
(författare)
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An extensive Raman spectroscopic investigation of ultrathin Co1-xNixSi2 films grown on Si(100)
- 2012
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 30:4, s. 041511-041518
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Tidskriftsartikel (refereegranskat)abstract
- Ultrathin silicide films were formed by starting from 1-8 nm thick Co1-xNix (x = 0, 0.25, 0.5, 0.75, and 1) at 350 degrees C-900 degrees C. For each composition x, there exists a critical thickness above which the transition temperature from monosilicides CoSi and NiSi to a disilicide-like phase increases with increasing film thickness. Below this thickness, the disilicide phase seems to form without exhibiting the monosilicides within the detection resolution limits of transmission electron microscopy and Raman spectroscopy. Raman spectroscopic analysis seems to indicate that Ni could be dissolved in the CoSi lattice to a certain fraction despite the fact that CoSi and NiSi are distinct with different crystallographic structures. Moreover, the disorder-induced Raman scattering in NiSi2 is found to be enhanced by Co incorporation. The observed annealing behaviors are attributed to variations in free energy change for phase transition caused by differences in metal thickness.
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| 12. |
- Sun, Zhengyi, 1982-, et al.
(författare)
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Buffer-enhanced electron injection in organic light-emitting devices with copper cathode
- 2013
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Ingår i: Organic electronics. - Amsterdam : Elsevier. - 1566-1199 .- 1878-5530. ; 14:2, s. 511-515
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Tidskriftsartikel (refereegranskat)abstract
- We explore in this work the use of Cu as a cathode material in organic light-emitting devices (OLEDs) and find a dual electron–injection enhancement mechanism derived from the LiF layer. Different from what observed previously in Ag- and Au-cathode devices, the LiF buffer layer in the Cu-cathode OLEDs starts to play its role in performance improvement when it is much thinner than 3 nm, the optimal value of buffer thickness, and in the case of optimal thickness, the device exhibits excellent performance comparable to conventional Al-cathode device. The phenomenon observed is ascribed to enhanced electron injection as a result of combined effect of interfacial reaction and tunneling barrier reduction mechanism: while chemical reaction plays a key role at the very beginning of interface formation, tunneling dominates in the subsequent stage leading to the tremendous improvement of the characteristics.
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| 13. |
- Vermang, Bart, 1981-, et al.
(författare)
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Improved Rear Surface Passivation of Cu(In,Ga)Se2 Solar Cells : A Combination of an Al2O3 Rear Surface Passivation Layer and Nano-Sized Local Rear Point Contacts
- 2014
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Ingår i: IEEE Journal of Photovoltaics. - 2156-3381 .- 2156-3403. ; 4:1, s. 486-492
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Tidskriftsartikel (refereegranskat)abstract
- An innovative rear contacting structure for copper indium gallium (di) selenide (CIGS) thin-film solar cells is developed in an industrially viable way and demonstrated in tangible devices. The idea stems from the silicon (Si) industry, where rear surface passivation layers are combined with micron-sized local point contacts to boost the open-circuit voltage (VOC) and, hence, cell efficiency. However, compared with Si solar cells, CIGS solar cell minority carrier diffusion lengths are several orders lower in magnitude. Therefore, the proposed CIGS cell design reduces rear surface recombination by combining a rear surface passivation layer and nanosized local point contacts. Atomic layer deposition of Al2O3 is used to passivate the CIGS surface and the formation of nanosphere-shaped precipitates in chemical bath deposition of CdS to generate nanosized point contact openings. The manufactured Al2O3 rear surface passivated CIGS solar cells with nanosized local rear point contacts show a significant improvement in VOC compared with unpassivated reference cells.
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| 14. |
- Xu, Peng, et al.
(författare)
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Phase formation and morphological stability of ultrathin Ni-Co-Pt silicide films formed onSi(100)
- 2014
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 32:3, s. 031503-
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Tidskriftsartikel (refereegranskat)abstract
- Ultrathin Ni, Co, and Pt films, each no more than 4 nm in thickness, as well as their various combinations are employed to investigate the competing growth of epitaxial Co1-y Ni ySi2 films against polycrystalline Pt1-z Ni zSi. The phase formation critically affects the morphological stability of the resulting silicide films, with the epitaxial films being superior to the polycrystalline ones. Any combination of those metals improves the morphological stability with reference to their parent individual metal silicide films. When Ni, Co, and Pt are all included, the precise initial location of Pt does little to affect the final phase formation in the silicide films and the epitaxial growth of Co1-x Ni xSi2 films is always perturbed, in accordance to thermodynamics that shows a preferential formation of Pt1-z Ni zSi over that of Co1-y Ni ySi2.
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| 15. |
- Zhang, Da, et al.
(författare)
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An ion-gated bipolar amplifier for ion sensing with enhanced signal and improvednoise performance
- 2014
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 105:8, s. 0821021-0821024
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a proof-of-concept ion-sensitive device operating in electrolytes. The device,i.e., an ion-gated bipolar amplifier (IGBA), consists of a modified ion-sensitive field-effect transistor(ISFET) intimately integrated with a vertical bipolar junction transistor for immediate currentamplification without introducing additional noise. With the current non-optimized design, theIGBA is already characterized by a 70-fold internal amplification of the ISFET output signal. Thissignal amplification is retained when the IGBA is used for monitoring pH variations. The tight integrationsignificantly suppresses the interference of the IGBA signal by external noise, which leadsto an improvement in signal-to-noise performance compared to its ISFET reference. The IGBAconcept is especially suitable for biochips with millions of electric sensors that are connected to peripheralreadout circuitry via extensive metallization which may in turn invite external interferencesleading to contamination of the signal before it reaches the first external amplification stage.
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| 16. |
- Zhu, Zhiwei, et al.
(författare)
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Conformal Ni-silicide formation over three-dimensional device structures
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:5, s. 053508-
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Tidskriftsartikel (refereegranskat)abstract
- This letter reports on conformal formation of ultrathin Ni-silicide films over a three-dimension structure relevant to the most advanced tri-gate transistor architecture. This is achieved by combining ionization of the sputtered Ni atoms with application of an appropriate bias to the Si substrate during the sputter-deposition of Ni films. In comparison, use of ordinary DC sputtering for Ni deposition results in thinner or less uniform silicide films on the vertical sidewalls than on the top surface of the three-dimensional structure. The roughened Si sidewall surface is ascribed to be responsible for a deteriorated thermal stability of the resultant silicide films.
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| 17. |
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| 18. |
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