Tymoteusz Ciuk

Sensitivity and Offset Voltage Testing in the Hall-Effect Sensors Made of Graphene

Paper presents the results of the hall effect testing in the graphene structures. Special hall effect structures were designed and build, using large graphene sheets. Laboratory testing stand was developed to test sensitivity and offset voltage in hall effect structures under external magnetic field. Characteristics of investigated structures were measured, including such impacting factors as structure size, external magnetic field strength, temperature and time.

Step-edge-induced resistance anisotropy in quasi-free-standing bilayer chemical vapor deposition graphene on SiC

which results in macro steps � 10 nm in height. In this report, we study the qualitative and quantitative effects of SiC steps edges on the resistance of epitaxial graphene grown by chemical vapor deposition. We experimentally determine the value of step edge resistivity in hydrogen-intercalated QFS-bilayer graphene to be � 190Xlm for step height hS ¼ 10 nm and provide proof that it cannot originate from mechanical deformation of graphene but is likely to arise from lowered carrier concentration in the step area. Our results are confronted with the previously reported values of the step edge resistivity in monolayer graphene over SiC atomic steps. In our analysis, we focus on large-scale, statistical properties to foster the scalable technology of industrial graphene for electronics and sensor applications. V C 2014 AIP Publishing LLC .[ http://dx.doi.org/10.1063/1.4896581]

Fabrication and applications of multi-layer graphene stack on transparent polymer

In this report, we demonstrate the preparation method of a multi-layer stack with a pre-defined number of graphene layers, which was obtained using chemical vapor deposition graphene deposited on a copper substrate and subsequently transferred onto a poly(methyl methacrylate) (PMMA) substrate. The prepared multi-layer stack can also be transferred onto an arbitrary substrate and in the end, the polymer can be removed, which in consequence significantly increases the range of possible graphene applications. The multi-layer character was confirmed by optical transmittance measurements and Raman spectroscopy, whereas the microstructure of the multi-layer graphene stack was investigated using Scanning Electron Microscopy. The electrical properties in the function of the number of graphene layers were assessed with standard Hall Effect measurements. Finally, we showed the practical application of the multi-layer graphene stack as a saturable absorber of a mode-locked Er-doped fiber laser.

Laser ablation- and plasma etching-based patterning of graphene on silicon-on-insulator waveguides.

We present a new approach to remove monolayer graphene transferred on top of a silicon-on-insulator (SOI) photonic integrated chip. Femtosecond laser ablation is used for the first time to remove graphene from SOI waveguides, whereas oxygen plasma etching through a metal mask is employed to peel off graphene from the grating couplers attached to the waveguides. We show by means of Raman spectroscopy and atomic force microscopy that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method.

Graphene FET Gigabit ON–OFF Keying Demodulator at 96 GHz

We demonstrate the demodulation of a multi-Gb/s ON-OFF keying (OOK) signal on a 96 GHz carrier by utilizing a 250-nm graphene field-effect transistor as a zero bias power detector. From the eye diagram, we can conclude that the devices can demodulate the OOK signals up to 4 Gb/s.

Low-noise epitaxial graphene on SiC Hall effect element for commercial applications

In this report, we demonstrate a complete Hall effect element that is based on quasi-free-standing monolayer graphene synthesized on a semi-insulating on-axis Si-terminated 6H-SiC substrate in an epitaxial Chemical Vapor Deposition process. The device offers the current-mode sensitivity of 87 V/AT and low excess noise (Hooges parameter αH < 2 × 10−3) enabling room-temperature magnetic resolution of 650 nT/Hz0.5 at 10 Hz, 95 nT/Hz0.5 at 1 kHz, and 14 nT/Hz0.5 at 100 kHz at the total active area of 0.1275 mm2. The element is passivated with a silicone encapsulant to ensure its electrical stability and environmental resistance. Its processing cycle is suitable for large-scale commercial production and it is available in large quantities through a single growth run on an up to 4-in SiC wafer.

Graphene’s nonlinear-optical physics revealed through exponentially growing self-phase modulation

Graphene is considered a record-performance nonlinear-optical material on the basis of numerous experiments. The observed strong nonlinear response ascribed to the refractive part of graphene’s electronic third-order susceptibility χ(3) cannot, however, be explained using the relatively modest χ(3) value theoretically predicted for the 2D material. Here we solve this long-standing paradox and demonstrate that, rather than χ(3)-based refraction, a complex phenomenon which we call saturable photoexcited-carrier refraction is at the heart of nonlinear-optical interactions in graphene such as self-phase modulation. Saturable photoexcited-carrier refraction is found to enable self-phase modulation of picosecond optical pulses with exponential-like bandwidth growth along graphene-covered waveguides. Our theory allows explanation of these extraordinary experimental results both qualitatively and quantitatively. It also supports the graphene nonlinearities measured in previous self-phase modulation and self-(de)focusing (Z-scan) experiments. This work signifies a paradigm shift in the understanding of 2D-material nonlinearities and finally enables their full exploitation in next-generation nonlinear-optical devices.Graphene enables extraordinary nonlinear-optical refraction, far exceeding predictions based on conventional nonlinear-susceptibility theory. Here, Vermeulen et al. show that rather than the nonlinear susceptibility, a complex saturable refraction process is central to graphene’s unusual behavior.

Optical-quality controllable wet-chemical doping of graphene through a uniform, transparent and low-roughness F4-TCNQ/MEK layer

Controllable chemical doping of graphene has already proven very useful for electronic applications, but when turning to optical and photonic applications, the additional requirement of having both a high transparency and a low surface roughness has, to our knowledge, not yet been fulfilled by any chemical dopant system reported so far. In this work, a new method that meets for the first time this optical-quality requirement while also providing efficient, controllable doping is presented. The method relies on F4-TCNQ dissolved in methyl ethyl ketone (MEK) yielding a uniform deposition after spin coating because of an extraordinary charge transfer interaction between the F4-TCNQ and MEK molecules. The formed F4-TCNQ/MEK layer exhibits a very high surface quality and optical transparency over the visible-infrared wavelength range between 550 and 1900 nm. By varying the dopant concentration of F4-TCNQ from 2.5 to 40 mg ml−1 MEK, the doping effect can be controlled between Δn = +5.73 × 1012 cm−2 and +1.09 × 1013 cm−2 for initially strongly p-type hydrogen-intercalated graphene grown on 6H-silicon-carbide substrates, and between Δn = +5.56 × 1012 cm−2 and +1.04 × 1013 cm−2 for initially weakly p-type graphene transferred on silicon samples. This is the first time that truly optical-quality chemical doping of graphene is demonstrated, and the obtained doping values exceed those reported before for F4-TCNQ-based graphene doping by as much as 50%.

Temperature Dependence of Functional Properties of Graphene Hall-Effect Sensors Grown on Si Face and C Face of 4H-SiC Substrate

Paper presents the results of investigation of the temperature influence on the basic functional properties of graphene Hall-effect sensors. The measurement system utilizing Helmholtz coils as a source of external magnetic field and environmental chamber for setting temperature was developed. Two types of monolayer graphene structures grown on both Si and C face of SiC substrate were investigated in the room temperature (about 20 oC) and their functional properties were compared. Next, the temperature influence on functional properties of both types of graphene structures was investigated using environmental chamber. The results of measurements are presented as charts and analyzed in the paper. On the basis of the results, conclusions were formulated, which are included in the last section of the paper.

Localized optical-quality doping of graphene on silicon waveguides through a TFSA-containing polymer matrix

The use of graphene in optical and photonic applications has gained much attention in recent years. To maximize the exploitation of graphenes extraordinary optical properties, precise control over its Fermi level (e.g. by means of chemical doping) will be of vital importance. In this work, we show the usage of a versatile p-doping strategy based on the incorporation of bis(trifluoromethanesulfonyl)amide (TFSA), functioning as an active p-dopant molecule, into a poly(2,2,3,3,4,4,5,5-octafluoropentyl methacrylate) (POFPMA) polymer matrix. The TFSA/POFPMA dopant can be utilized both onto large size graphene regions via spin coating and on small predefined spatial zones of micrometer dimension by localized inkjet printing. Whereas pure TFSA suffers from a clustered layer deposition combined with environmental instability, the application of the POFPMA polymer matrix yields doping layers revealing superior properties counteracting the existing shortcomings of pure TFSA. A first key finding relates to the optical quality of the dopant layer. We obtain a layer with an extremely low surface roughness (0.4–0.8 nm/25 μm2) while exhibiting very high transparency (absorbance <0.05%) over the 500–1900 nm wavelength range, with strongly enhanced doping stability as a function of time up to several weeks (for inkjet-printed deposition) and months (for spin coated deposition). Finally, the doping efficiency is very high, reaching a carrier density around +4 × 1013 cm−2 whereas the optical transmission of a graphene-covered Si waveguide revealed a strong improvement (4.22 dB transmission increase per 100 μm graphene length at the wavelength of 1550 nm) after deposition of the dopant via inkjet printing.