Tibor Izak

Sensitivity of Diamond-Capped Impedance Transducer to Tröger’s Base Derivative

Sensitivity of an intrinsic nanocrystalline diamond (NCD) layer to naphthalene Trögers base derivative decorated with pyrrole groups (TBPyr) was characterized by impedance spectroscopy. The transducer was made of Au interdigitated electrodes (IDE) with 50 μm spacing on alumina substrate which were capped with the NCD layer. The NCD-capped transducer with H-termination was able to electrically distinguish TBPyr molecules (the change of surface resistance within 30-60 kΩ) adsorbed from methanol in concentrations of 0.04 mg/mL to 40 mg/mL. An exponential decay of the surface resistance with time was observed and attributed to the readsorption of air moisture after methanol evaporation. After surface oxidation the NCD cap layer did not show any leakage due to NCD grain boundaries. We analyzed electronic transport in the transducer and propose a model for the sensing mechanism based on surface ion replacement.

Influence of Diamond CVD Growth Conditions and Interlayer Material on Diamond/GaN Interface

In this study we present the diamond deposition on AlGaN/GaN substrates focusing on the quality of the diamond/GaN interface. The growth of diamond films was performed using microwave chemical vapour deposition system in different gas mixtures: standard CH4/H2 (at low and high ratio of CH4 to H2) and addition of CO2 to CH4/H2 gas chemistry. The diamond films were grown directly on GaN films either without or with thin interlayer. As interlayer, 100 nm thick Si3N4 was used. Surprisingly, in the case of standard CH4/H2 gas mixture, no diamond film was observed on the GaN with SiN interlayer, while adding of CO2 resulted in diamond film formation of both samples with and without SiN interlayer. Moreover, adding of CO2 led to higher growth rate. The morphology of diamond films and the quality of the diamond/GaN interface was investigated from the cross-section images by scanning electron microscopy and the chemical character (i.e. sp3 versus sp2 carbon bonds) was measured by Raman spectroscopy.

Osteoblastic cells trigger gate currents on nanocrystalline diamond transistor.

We show the influence of osteoblastic SAOS-2 cells on the transfer characteristics of nanocrystalline diamond solution-gated field-effect transistors (SGFET) prepared on glass substrates. Channels of these fully transparent SGFETs are realized by hydrogen termination of undoped diamond film. After cell cultivation, the transistors exhibit about 100× increased leakage currents (up to 10nA). During and after the cell delamination, the transistors return to original gate currents. We propose a mechanism where this triggering effect is attributed to ions released from adhered cells, which depends on the cell adhesion morphology, and could be used for cell culture monitoring.

Hydrogen-Terminated Diamond Sensors for Electrical Monitoring of Cells

In this paper we introduce fully optically transparent impedance biosensors based on intrinsic nanocrystalline diamond (NCD) films deposited on glass substrate. Prepared sensors have an interdigital electrode (IDE) structures realized by local hydrogen and oxygen termination of diamond surface, which mean in-plane configuration of active sensor area. Sensors were tested by real time monitoring of human osteoblast-like MG 63 cells in wide frequency range from 10 Hz to 100 kHz for several days. Two different measurement setups were used and compared regarding to their advantages and disadvantages. Proof of concept of diamond-based impedance sensor is showed, i.e. time dependence and frequency dependence (Nyquist plots) of absolute impedance.

CHAPTER 13:Low Temperature Diamond Growth

Diamond thin films represent a class of multi-functional materials whose morphological, chemical, optical and electronic properties can be tailored on demand for specific applications. Nevertheless, this materials versatility inherently requires a high degree of control and understanding of the diamond growth technology. Here, especially, processes at low temperatures become important because of physical limitations regarding the intrinsic properties of typical target substrates (i.e., low melting temperature, high expansion coefficient, high thermal diffusion and chemical reactivity) and compatibility with standard semiconductor industrial technologies. However, low temperature diamond growth (LTDG) is still highly challenging, where novel phenomena are encountered that still remain to be understood. The present chapter focuses on low temperature diamond growth from technological and practical points of view. The LTDG process is divided in two strategies, which are based on i) the modification of the deposition systems and ii) the change of gas chemistry. The state of the art of each strategy and the fundamental growth processes that are involved are reviewed. Among the discussed diamond growth processes, microwave surface wave plasma in linear antenna configuration with oxygen-containing gas mixtures is shown as the most promising process for LTDG over large areas with high optical and electronic grade materials. The growth phenomena observed in linear antenna microwave plasma provide a simple way to control nano- and poly-crystalline diamond character. A practical comparison between focused and linear antenna microwave plasma is presented on several key studies, which utilize LTDG on amorphous silicon, glass, germanium and optical elements used for IR spectroscopy.

AlGaN/GaN micromembranes with diamond coating for high electron mobility transistors operated at high temperatures

In this work, we present an application of NCD layers as backside cooling for AlGaN/GaN heterostructures grown on Si substrates. In this case, diamond nucleation is the most limiting technological step due to low mechanical stability of GaN membranes. We observed that standard nucleation techniques (ultrasonic seeding or bias enhanced nucleation) caused cracking of the membranes or not appropriate nucleation efficiency in the Z-depth of structures. Therefore we implemented PVA polymer consisting of diamond powder as seeding composite which resulted in a successful growth of diamond thin film.

Growth of carbon allotropes and plasma characterization in linear antenna microwave plasma CVD system

Growth of diamond coatings with tunable morphology and concurrent substrate catalyst pretreatment and further growth of carbon nanotubes were studied. The dependence of plasma parameters on gas composition was studied by Langmuir probe measurement. Grown diamond coatings and carbon nanotubes were characterized by scanning electron microscopy and Raman spectroscopy and correlated with process parameters. Well-defined nanocrystalline, polycrystalline, and porous diamond films were prepared. Concurrent substrate catalyst pretreatment and further growth of carbon nanotubes were shown.

Study of Ni-Catalyzed Graphitization Process of Diamond by in Situ X-ray Photoelectron Spectroscopy

Graphene on diamond has been attracting considerable attention due to the unique and highly beneficial features of this heterostructure for a range of electronic applications. Here, ultrahigh-vacuum X-ray photoelectron spectroscopy is used for in situ analysis of the temperature dependence of the Ni-assisted thermally induced graphitization process of intrinsic nanocrystalline diamond thin films (65 nm thickness, 50–80 nm grain size) on silicon wafer substrates. Three major stages of diamond film transformation are determined from XPS during the thermal annealing in the temperature range from 300 °C to 800 °C. Heating from 300 °C causes removal of oxygen; formation of the disordered carbon phase is observed at 400 °C; the disordered carbon progressively transforms to graphitic phase whereas the diamond phase disappears from the surface from 500 °C. In the well-controllable temperature regime between 600 °C and 700 °C, the nanocrystalline diamond thin film is mainly preserved, while graphitic layers form on the surface as the predominant carbon phase. Moreover, the graphitization is facilitated by a disordered carbon interlayer that inherently forms between diamond and graphitic layers by Ni catalyst. Thus, the process results in formation of a multilayer heterostructure on silicon substrate.

Schottky contact metallization stability on AlGaN/GaN heterostructure during the diamond deposition process

The issue of gate metallization stability on AlGaN/GaN heterostructure during the diamond deposition process has been studied. Among tested Ni, Ir, NiO and IrO2 materials the iridium-based has the most promising characteristic to be used. The diamond growth in focused microwave plasma system on transistors with Ir and IrO2 Schottky contact metallization has been demonstrated and discussed.

Nanocrystalline diamond films for electronic monitoring of gas and organic molecules

Nowadays, implementation of specific materials for (bio) sensors is one of the most rapidly developing micro-electronic field. Synthetic diamond thin films exhibit an extraordinary combination of intrinsic properties which make it an attractive material for investigation of solid state interaction with (bio) molecules or complex biological systems. Hydrogen terminated intrinsic diamond films reveal a phenomenological property — induced p-type surface conductivity which has been found as suitable for fabrication of various electronic devices, mainly impedance elements and field effect transistors. This study draws on research conducted by employing hydrogen terminated nanocrystalline diamond as the functional layer for (bio) sensoric uses and point out recent models for the detection principles.