Krzysztof Gajewski

Scanning probe microscopy investigations of the electrical properties of chemical vapor deposited graphene grown on a 6H-SiC substrate

Sublimated graphene grown on SiC is an attractive material for scientific investigations. Nevertheless the self limiting process on the Si face and its sensitivity to the surface quality of the SiC substrates may be unfavourable for later microelectronic processes. On the other hand, chemical vapor deposited (CVD) graphene does not posses such disadvantages, so further experimental investigation is needed. In this paper CVD grown graphene on 6H-SiC (0001) substrate was investigated using scanning probe microscopy (SPM). Electrical properties of graphene were characterized with the use of: scanning tunnelling microscopy, conductive atomic force microscopy (C-AFM) with locally performed C-AFM current-voltage measurements and Kelvin probe force microscopy (KPFM). Based on the contact potential difference data from the KPFM measurements, the work function of graphene was estimated. We observed conductance variations not only on structural edges, existing surface corrugations or accidental bilayers, but also on a flat graphene surface.

Microfabricated support structures for investigations of mechanical and electrical graphene properties

In this work we present the grid of microstructures which is used for the graphene mechanical and electrical properties investigations. The design of the mask used for the grid production was presented. Afterwards the technological process steps for the grid production were described. In result the support structures – trenches – in shape of lines, squares and circles are obtained with the detail dimensions varied from 1 micrometer up to 30 micrometers. Examples of graphite and graphene deposited on the support structures are also presented.

Self-supporting graphene films and their applications

UK NMS Programme, the EU EMRP (European Metrology Research Programme) projects MetNEMS and GraphOhm

Development of the tunneling junction simulation environment for scanning tunneling microscope evaluation

Proper configuration of scanning tunneling microscope electronics plays an important role in the atomic scale resolution surface imaging. Device evaluation in the tunneling contact between scanning tip and sample may be prone to the surface quality or mechanical disturbances. Thus the use of tunneling junction simulator makes electronics testing more reliable and increases its repeatability. Here, we present the theoretical background enabling the proper selection of electronic components circuitry used as a tunneling junction simulator. We also show how to simulate mechanics related to the piezoelectric scanner, which is applied in real experiments. Practical use of the proposed simulator and its application in metrological characterization of the developed scanning tunneling microscope is also shown.

Spatial variability in large area single and few-layer CVD graphene

Variability in graphene can result from the material synthesis or post-processing steps as well as the surrounding environment. This is a critical issue for the performance of large area devices as well as for the large-scale production of micro- and nano-scale graphene devices, leading to low yield and reliability. The aim of this study is to investigate variability of single and few-layer graphene structures, on different substrates, and the effects it has on its electronic properties. We demonstrate a combination of Kelvin probe force microscopy (KPFM) and non-contact Fourier transform infrared spectroscopy (FTIR) measurements for centimeter-scale quantitative mapping of the electrical variability of large-area chemical vapor deposited graphene films. KPFM provides statistical insight into the influence of micro-scale defects on the surface potential, while FTIR gives the spatially averaged chemical potential of the graphene structures. Test structures consisting of single-, bi- and few-layer graphene on SiO2 and Al2O3 were fabricated and analyzed.

Characterization of Diamond-like Carbon (DLC) films deposited by RF ICP PECVD method

The work presents the results of a research carried out with Plasmalab Plus 100 system, manufactured by Oxford Instruments Company. The system was configured for deposition of diamond-like carbon films by ICP PECVD method. The deposition processes were carried out in CH4 or CH4/H2 atmosphere and the state of the plasma was investigated by the OES method. The RF plasma was capacitively coupled by 13.56 MHz generator with supporting ICP generator (13.56 Mhz). The deposition processes were conducted in constant value of RF generator’s power and resultant value of the DC Bias. The power values of RF generator was set at 70 W and the power values of ICP generator was set at 300 W. In this work we focus on the influence of DLC film’s thickness on optical, electrical and structural properties of the deposited DLC films. The quality of deposited DLC layers was examined by the Raman spectroscopy, AFM microscopy and spectroscopic ellipsometry. In the investigated DLC films the calculated sp3 content was ranging from 60 % to 70 %. The films were characterized by the refractive index ranging from 2.03 to 2.1 and extinction coefficient ranging from 0.09 to 0.12.

Methods of investigation of the properties of the optoelectronic devices with use of atomic force microscopy

In the modern world, the influence the optoelectronic devices on the communications methods are still increasing. Therefore it is very important to find appropriate techniques for design, building, testing, measuring and packaging.