| 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. |
- Ahlberg, Patrik, 1985-, et al.
(författare)
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Interface Dependent Effective Mobility in Graphene Field Effect Transistors
- 2018
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Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 47:3, s. 1757-1761
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Tidskriftsartikel (refereegranskat)abstract
- By pretreating the substrate of a graphene field-effect transistor (G-FET), a stable unipolar transfer characteristic, instead of the typical V-shape ambipolar behavior, has been demonstrated. This behavior is achieved through functionalization of the SiO2/Si substrate that changes the SiO2 surface from hydrophilic to hydrophobic, in combination with postdeposition of an Al2O3 film by atomic layer deposition (ALD). Consequently, the back-gated G-FET is found to have increased apparent hole mobility and suppressed apparent electron mobility. Furthermore, with addition of a top-gate electrode, the G-FET is in a double-gate configuration with independent top- or back-gate control. The observed difference in mobility is shown to also be dependent on the top-gate bias, with more pronounced effect at higher electric field. Thus, the combination of top and bottom gates allows control of the G-FET's electron and hole mobilities, i.e., of the transfer behavior. Based on these observations, it is proposed that polar ligands are introduced during the ALD step and, depending on their polarization, result in an apparent increase of the effective hole mobility and an apparent suppressed effective electron mobility.
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| 3. |
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| 4. |
- Grudén, Mathias, et al.
(författare)
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Field Operational Testing for Safety Improvement of Freight Trains using Wireless Monitoring by Sensor Network
- 2013
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Ingår i: IET Wireless Sensor Systems. - : Institution of Engineering and Technology (IET). - 2043-6386 .- 2043-6394.
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Tidskriftsartikel (refereegranskat)abstract
- Today, the majority of wagon failures on railroad systems are because of the poor maintenance of ball bearings, which causes emergent stops and delays. The existing stationary detectors, lack in predicting failures which cause troubles in scheduling maintenance. During the fall of 2011, a trial was performed by applying a wireless sensor network (WSN) aboard a train wagon with the objective to demonstrate a proof of concept for monitoring the temperature of ball bearings aboard the train wagon. This trial investigates several key aspects when applying sensor networks such as radio wave propagation, energy scavenging and performance of the WSN aboard the wagon. Two wireless links were used in the WSN. The aboard network communicates at 2.45 GHz, and the external communication is an 868 MHz radio frequency identification radio link. Since the energy in the WSN node is limited, appropriate energy scavenging devices are also presented and evaluated in a lab environment. Effort has been made to overcome these problems. The energy consumption in the network is still a problem; the most promising energy scavenging technique is piezoelectric harvesting by vibrations, which in the experiments scavenged 2.32 mW.
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| 7. |
- Hinnemo, Malkolm, et al.
(författare)
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Design of a miniaturized patch antenna for easy deployment on metal surfaces
- 2013
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Ingår i: Microwave and optical technology letters (Print). - : Wiley. - 0895-2477 .- 1098-2760. ; 55:4, s. 723-727
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Tidskriftsartikel (refereegranskat)abstract
- A small dual-layer patch antenna designed for placement on a large conducting surface is presented. It uses the surrounding metal as a ground plane in order to reduce its size. The result is a small patch antenna with good radiation qualities in metallic surroundings. It can also be used in applications where shielding sensitive equipment from radiated fields is necessary, by using the shielding as the metal surface. It is constructed for use with the IEEE 802.15.4 standard at the 2.45 GHz ISM band. The lower layer is made in Fr-4 with standard height and width. This makes eventual serial production cheaper. The antenna has a measured total efficiency between 1.5 dB and 3.6 dB in the frequency range it is designed for. The longest side is 18.35 mm, equaling 14.9% of the wavelength.
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| 8. |
- Hinnemo, Malkolm, 1986-, et al.
(författare)
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On Monolayer Formation of Pyrenebutyric Acid on Graphene
- 2017
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 33:15, s. 3588-3593
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Tidskriftsartikel (refereegranskat)abstract
- As a two-dimensional material with high charge carrier mobility, graphene may offer ultrahigh sensitivity in biosensing. To realize this, the first step is to functionalize the graphene. This is commonly done by using 1-pyrenebutyric acid (PBA) as a linker for biornolecules. However, the adsorption of PBA on graphene remains poorly understood despite reports of successful biosensors functionalized via this route. Here, the PBA adsorption on graphene is characterized through a combination of Raman spectroscopy, ab initio calculations, and spectroscopic ellipsometry. The PBA molecules are found to form a self-assembled monolayer on graphene, the formation of which is self-limiting and Langmuirian. Intriguingly, in concentrated solutions, the PBA molecules are found to stand up and stack horizontally with their edges contacting the graphene surface. This morphology could facilitate a surface densely populated with carboxylic functional groups. Spectroscopic analyses show that the monolayer saturates at 5.3 PBA molecules per nm(2) and measures similar to 0.7 nm in thickness. The morphology study of this PBA monolayer sheds light on the pi-pi stacking of small-molecule systems on graphene and provides an excellent base for optimizing functionalization procedures.
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| 9. |
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| 10. |
- Hinnemo, Malkolm, 1986-
(författare)
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On the Road to Graphene Biosensors
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biosensors are devices that detect biological elements and then transmit a readable signal. Biosensors can automatize diagnostics that would otherwise have to be performed by a physician or perhaps not be possible to perform at all. Current biosensors are however either limited to particular diseases or prohibitively expensive. In order to further the field, sensors capable of many parallel measurements at a lower cost need to be developed. Field effect transistor (FET) based sensors are possible candidates for delivering this, mainly by allowing miniaturization. Smaller sensors could be cheaper, and enable parallel measurements.Graphene is an interesting material to use as the channel of FET-sensors. The low electrochemical reactivity of its plane makes it possible to have graphene in direct contact with the sample liquid, which enhances the signal from impedance changes. Graphene-FET based impedance sensors should be able to sense almost all possible analytes and allow for scaling without losing sensitivity.In this work the steps needed to make graphene based biosensors are presented. An improved graphene transfer is described which by using low pressure to dry the graphene removes most contamination. A method to measure the contamination of graphene by surface enhanced Raman scattering is presented. Methods to produce double gated and electrolyte gated graphene transistors on a large scale in an entirely photolithographic process are detailed. The deposition of 1-pyrenebutyric acid (PBA) on graphene is studied. It is shown that at high surface concentrations the PBA stands up on graphene and forms a dense self-assembled monolayer. A new process of using Raman spectroscopy data to quantify adsorbents was developed in order to quantify the molecule adsorption. Biosensing has been performed in two different ways. Graphene FETs have been used to read the signal generated by a streaming potential setup. Using FETs in this context enables a more sensitive readout than what would be possible without them. Graphene FETs have been used to directly sense antibodies in high ionic strength. This sensing was done by measuring the impedance of the interface between the FET and the electrolyte.
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