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- Jafri, Syed Hassan Mujtaba, et al.
(författare)
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Conductivity engineering of graphene by defect formation
- 2010
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 43:4, s. 045404-
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Tidskriftsartikel (refereegranskat)abstract
- Transport measurements have revealed several exotic electronic properties of graphene. The possibility to influence the electronic structure and hence control the conductivity by adsorption or doping with adatoms is crucial in view of electronics applications. Here, we show that in contrast to expectation, the conductivity of graphene increases with increasing concentration of vacancy defects, by more than one order of magnitude. We obtain a pronounced enhancement of the conductivity after insertion of defects by both quantum mechanical transport calculations as well as experimental studies of carbon nano-sheets. Our finding is attributed to the defect induced mid-gap states, which create a region exhibiting metallic behaviour around the vacancy defects. The modification of the conductivity of graphene by the implementation of stable defects is crucial for the creation of electronic junctions in graphene-based electronics devices.
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| 5. |
- Blom, Tobias, et al.
(författare)
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An In-Situ Prepared Nano-Manipulator Tip for Electrical Characterization of Free Standing Graphene Like Sheets Inside a Focused Ion Beam/Scanning Electron Microscope
- 2011
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Ingår i: Journal of Nanoelectronics and Optoelectronics. - : American Scientific. - 1555-130X .- 1555-1318. ; 6:2, s. 162-168
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Tidskriftsartikel (refereegranskat)abstract
- Although contacting and moving atoms has been demonstrated using probe techniques, for many nano-objects, a fast and reproducible nano-probe technique is needed to acquire a large number of electrical measurements on nano-objects that are often similar but not the identical. Nano-manipulators have become a common tool in many scanning electron microscopes (SEM) and focussed ion beam devices (FIB). They can be rapidly and reproducibly moved from one nano-object to another. In this work we present a procedure to obtain reproducible electrical measurements of nano- to micron-sized objects by using a sharp, tungsten tip with well defined surface properties. The tip is a part of a manipulator and is sharpened in-situ by using the gallium ion beam inside a focused ion beam/scanning electron microscope (FIB/SEM). The contact resistance between a Au surface and the tip is 70 kΩ before the sharpening procedure and 10 Ω after sharpening. The leakage current of the total set-up of 10pA makes it possible to measure currents through a variety of nano-objects. This measurement technique is applied to measure the resistance of as grown, water treated and two HCl treated carbon nanosheets (CNS). These CNS vary in size and morphology. Using this nano-contacting set-up, we could obtain measurements of more than 400 different CNS. The obtained histograms allow us to observe a clear decrease of the resistance between original and 3 hour acid treated CNSs. We observe that longer periods of exposure of the CNS to the HCl do not further modify the resistance.
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| 8. |
- Giraldo, Sergio, et al.
(författare)
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Cu2ZnSnSe4 solar cells with 10.6% efficiency through innovative absorber engineering with Ge superficial nanolayer
- 2016
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Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 24:10, s. 1359-1367
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Tidskriftsartikel (refereegranskat)abstract
- In our recently published work, the positive effect of a Ge nanolayer introduced into the processing of Cu2ZnSnSe4 absorbers (CZTSe) was demonstrated. In this contribution, the complete optimization of this new approach is presented for the first time. Hence, the optimum Ge nanolayer thickness range is defined in order to achieve an improved performance of the devices, obtaining a record efficiency of 10.6%. By employing this optimized approach, the open-circuit voltage (V-OC) is boosted for our pure selenide CZTSe up to 489 mV, leading to V-OC deficit among the lowest reported so far in kesterite technology. Additionally, two important effects related to the Ge are unambiguously demonstrated that might be the origin of the V-OC boost: the improvement of the grain size and the corresponding crystalline quality, and the interaction between Ge and Na that allows for dynamic control over the CZTSe doping. Finally, evidences pointing to the origin of the deterioration of devices properties for large Ge concentrations are presented.
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| 9. |
- Giraldo, Sergio, et al.
(författare)
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Large Efficiency Improvement in Cu2ZnSnSe4 Solar Cells by Introducing a Superficial Ge Nanolayer
- 2015
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Ingår i: Advanced Energy Materials. - : Wiley. - 1614-6832 .- 1614-6840. ; 5:21
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Tidskriftsartikel (refereegranskat)abstract
- A large improvement of Cu2ZnSnSe4 solar cell efficiency is presented based on the introduction of a Ge superficial nanolayer. This improvement is explained by three complementary effects: the formation of a liquid Ge-related phase, the possible reduction of Sn multicharge states, and the formation of GeOx nanoinclusions, which lead to an impressive solar cell (VOC) increase.
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