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Hysteresis response of epitaxially grown graphene nanoribbons devices on semi-insulating 4H-SiC in the armchair and zigzag directions is evaluated and studied. The influence of the orientation of fabrication and dimensions of graphene nanoribbons on the hysteresis effect reveals the metallic and semiconducting nature graphene nanoribbons. The hysteresis response of armchair based graphene nanoribbon side gate and top gated devices implies the influence of gate field electric strength and the contribution of surface traps, adsorbents, and initial defects on graphene as the primary sources of hysteresis. Additionally, passivation with AlOx and top gate modulation decreased the hysteresis and improved the current-voltage characteristics.

Reactive aluminum–nickel multilayer system shows exothermic energetic materials which act as a heat source for packaging and bonding of microsystems. The main challenge is controlling the self-propagation reaction velocity and temperature generated by thermal management through different thermal conductive substrate materials. The current work investigates the heat distribution of Al/Ni multilayer foils from different thermal conductive substrates which act as heat sink materials during the self-propagating reaction. A two-dimensional numerical model was developed to study thermal conductive heat loss and substrate thermal properties on the self-propagating reaction in Al/Ni multilayer foils. The self-propagating reaction was introduced on the surface of the foils by an electrical spark. Here we investigate the minimum critical thickness of Al/Ni multilayer foils which shows the self-propagation reaction on different substrates and verified from the two-dimensional numerical model. The outcomes of this investigation will facilitate the integration of Al/Ni multilayer foils on different substrates as intrinsic heat sources for different applications of micro/nanodevices. Graphical abstract

Silicon carbide layers were fabricated using self-propagating high-temperature synthesis of binary silicon-carbon based reactive multilayers. The silicon and carbon bilayers were fabricated with two different bilayer thicknesses. They are deposited by magnetron sputtering in an alternating layer system with a total thickness of 1 μm. The entire system is annealed by rapid thermal annealing at different temperatures ranging from 500 to 1100 °C. From XRD analysis we could find that the formation of the silicon carbide phase was initiated from 700 °C. With increasing bilayer thickness the silicon carbide phase formation was partially suppressed by the silicon recrystallization due to resulting lower carbon diffusion into silicon. The transformation process proceeds in a four-step process: densification/recrystallization, interdiffusion, nucleation and transformation. From this, it was noted that when compared to low bilayer thickness samples, the formation of the silicon carbide phase is delayed with increasing bilayer thickness and needs higher reaction initiation temperatures. Graphical abstract

In this work, we experimentally investigate the effects of electric bias on the degradation of few-layer MoS2 back-gated field-effect transistors in ambient air. The devices were fabricated using mechanically exfoliated MoS2 flakes, which were transferred to a Si/SiO2 substrate by a PDMS-based transfer. We report an accelerated electric bias-induced degradation of the devices under investigation and used optical and scanning electron microscopy (SEM) to monitor changes of the morphology of the MoS2 channel. In particular, we found a linear dependency of the degradation on the electric field between the Ti/Au source and drain contacts. In addition, we identify four regions in which morphological changes occur, of which the edges of the MoS2 channel are most affected.

A multitude gratings design consists of gratings with different pitches ranging from the micrometre down to sub 40 nm scale combined with sub 10 nm step heights modulating the surface morphology for length scale measurements is proposed. The surface morphology modulation was performed using electron beam lithography incorporating a standard semiconductor processing technology. The critical dimension, edge roughness, step heights and line morphology in dependence on the grating pitch is studied.

Efficient and green exfoliation of bulk MoS2 into few-layered nanosheets in the semiconducting hexagonal phase (2H-phase) remains a great challenge. Here, we developed a new method, water-assisted exfoliation (WAE), for the scalable synthesis of carboxylated chitosan (CC)/2H-MoS2 nanocomposites. With facile hand grinding of the CC powder, bulk MoS2 and water followed by conventional liquid-phase exfoliation in water, this method can not only efficiently exfoliate the 2H-MoS2 nanosheets, but also produce two-dimensional (2D) CC/2H-MoS2 nanocomposites. Interestingly, the intercalated CC in MoS2 nanosheets increases the interlayer spacing of 2H-MoS2 to serve as good candidates for the semiconductor devices. 2D CC/2H-MoS2 nanocomposites show superior electronic rectification effects in nonvolatile write-once-read-many-times memory (WORM) behavior with an ON/OFF ratio over 103, which can be rationally controlled by the weight ratios of CC and MoS2. These findings by the WAE method would open tremendous potential opportunities to prepare commercially available semiconducting 2D nanocomposites for promising high-performance device applications.

In this work a comprehensive study is presented for the analysis of epitaxial graphene layers using Raman spectroscopy. A wide range of graphene types is covered, from defective/polycrystalline single layer graphene to multilayer graphene with low defect density. On this basis the influence of strain type, Fermi level and number of layers on the Raman spectrum of graphene is investigated. A detailed view on the 2 D / G dispersion and the respective slopes of uniaxially and biaxially strained graphene is given and its implications on the asymmetry of the G peak analyzed. A linear dependency of the phonon mode asymmetry on uniaxial strain is presented in addition to the known Fermi level dependence. Additional impacts on the asymmetry are found to be arising from the defect density and transfer doping of adsorbates. The discovered transfer doping mechanism is contrary to pure phonon excitation through excitons and exhibits increasing asymmetry with increasing Fermi level. A new characteristic correlation between the 2 D mode line width and the inverse I(D)/I(G) ratio is introduced that allows the determination of the strain type and layer number and explains the difference between Raman line widths of monolayer graphene on different substrates.

Scandium aluminum nitride (ScxAl1-xN) is a promising material for sensor applications as it exhibits enhanced piezoelectric properties compared to pristine AlN while maintaining other advantageous properties like high thermal stability. Magnetoelectric sensors in particular are used to detect magnetic fields which leads to special requirements regarding the investigated ScAlN in order to achieve high sensor sensitivities. Co-sputtered ScAlN layers are investigated in this work using XRD, XPS, FTIR and Raman spectroscopy for scandium concentrations from 0 to 34 %. The impact of Sc incorporation regarding residual biaxial strain and bond softening is discussed on basis of the experimental results. The activity of the B1 and E2 modes found in the FTIR measurements is of special interest as the presumably oxygen related excitation is expected to influence the piezoelectric properties.

Gallium oxide was grown on silicon carbide substrates using a corona discharge assisted vapor phase epitaxy process and gold catalyst. It is shown that by implementing the corona discharge the morphology of the gallium oxide can be transformed. The excitation of the gas phase and the generation of excited species directly influence the growth morphology suppressing nanowire growth and supporting the transformation into heteroepitaxial growth.

Single side clamped 3C and 6H single crystal silicon carbide beams were elastic deformed using a special designed deformation stage in an electron microscope and subjected to high temperatures. The structural transitions occurring during the plastic relaxation process were recorded in situ in the electron microscope using reflection high energy electron diffraction in {110} azimuthal direction. For both polytypes, a polytype phase transition into the wurtzite silicon carbide polytype was observed independent on the surface polarity. The critical initial elastic deformation of the polytype phase transition into the wurtzite phase for the cubic silicon carbide polytype is larger compared to the 6H-SiC. This is due to the higher partial dislocation densities needed to transform the cubic modification into the wurtzite phase.

In this work a new approach of analyzing epitaxial graphene layers on semi-insulating SiC through the gray-scale entropy of SEM images as a measure for the graphene inhomogeneity is demonstrated. Raman spectroscopy as a versatile and the standard tool for graphene characterization allows additionally the determination of the layer properties such as layer count, Fermi level, defect concentration and strain. It is shown that the gray-scale entropy correlates with the defect density derived from Raman measurements and thus can be used as an additional characterization technique with much higher resolution than the conventional Raman spectroscopy allows. As a consequence, the results are used to reflect the two-stepped growth itself and to conclude for advantageous growth conditions.

The buffer layer samples grown on the Si-face of the 4H- and 6H-SiC substrates were heated in a hydrogen flow at different temperatures (600–900 °C) and heating times (40–60 min) in order t...

This article introduces a programmable gas phase nanoparticle electrodeposition concept which enables the fabrication of multi-modal conductometric gas sensor arrays. The sensor application requires the deposition of more than one nanoparticle type to achieve orthogonal sensing capabilities and multi gas sensitivity and selectivity. The demonstrated “electronic nose” like array contains 1080 freeform point-to-point gas sensitive nanobridges of platinum, nickel oxide and gold based electrical connections on a single chip. The introduced architecture is different from previous reports; instead of two-dimensional thin metallic films, each gas sensitive bridge is a three-dimensional (3D) structure, which in turn, is composed of a porous but electrically conducting nanoparticle network. It was found that this architecture is unique since it does not require external heating to function. A multimodal sensor array will be demonstrated to detect various levels of Ammonia (NH3), Carbon Monoxide (CO) and Hydrogen Sulfide (H2S). Gas phase nanoparticle electrodeposition method uses a spark discharge-based nanoparticle source in combination with biased surface electrodes and charged photoresist patterns to accomplish the required programmable site selective deposition. The nanobridges form through nearest neighbor coulombic interaction.

Pores are intrinsic defects of ceramic composites and influence their functional properties significantly. Their characterization is therefore a pivotal task in material and process optimization. It is demonstrated that polished section analysis allows for obtaining precise information on pore size, shape, area fraction, and homogeneous distribution. It is proven that laser scanning microscopy provides accurate height maps and is thus an appropriate technique for assessing surface features. Such data is used to compare areas with good and poor polishing results, and various surface parameters are evaluated in terms of their informative value and data processing effort. The material under investigation is a low temperature co-fired ceramic composite. Through statistical analysis of the data, the inclination angle was identified as an appropriate parameter to describe the polishing result. By using masked data, direct conclusions can be drawn about the leveling of load-bearing surface areas, which are crucial in photolithographic processing steps and bonding technology. A broad discussion of different defects based on the results contributes to a critical analysis of the potentials and obstacles of micromachining of low temperature cofired ceramic substrates.

To match the properties of a semiconductor to a desired application, it is crucial to control its crystal structure. Here, we show that, by implementing a corona discharge in a chemical vapor depos...

Parallel three-dimensional (3D) growth of different nanomaterials with submicrometer resolution is a promising approach to overcome some technological and economic limits encountered in planar integrated homogeneous films. The programmable multimaterial gas phase nanoparticle electrodeposition concept enables the fabrication of a 3D multimodal conductometric gas sensor array. The approach requires the deposition of more than one nanomaterial to achieve orthogonal sensing capabilities and multigas sensitivity and selectivity. The demonstrated "electronic nose"-like array contains 1080 self-aligning 3D nanobridge-based electrical connections of platinum, nickel oxide, and gold on a single chip. The nanobridges form through a nearest neighbor Coulombic interaction. Each gas sensitive bridge is a 3D structure composed of a porous but electrically conducting nanoparticle network. It was found that this architecture is unique, because it does not require external heating to operate. A trimodal sensor array will be demonstrated to detect various levels of ammonia (NH3), carbon monoxide (CO), and hydrogen sulfide (H2S). A 3 × 3 transfer matrix will be discussed to correlate the recorded signals with the gas composition.

Ternary (Si1-xCy)Gex+y solid solutions were grown on Si-face 4H-SiC applying atomic layer molecular beam epitaxy at low temperatures. The grown layers consist of twinned 3C-SiC revealed by cross section electron microscopy. The germanium was incorporated on silicon lattice sites as revealed by atomic location by channeling enhanced microanalysis transmission electron microscopy studies. The Ge concentration of the grown 3C-(Si1-xCy)Gex+y heteroepitaxial layers decreases with increasing growth temperatures, but exceeds the solid solubility limit.

This article reports on the use of corona discharge to assist the vapor liquid solid growth of gallium oxide nanowires on silicon carbide substrates. The corona discharge increases the nucleation efficiency of the gold catalysts from 60% to 98% for 3C-SiC(1 1 1)/Si(1 1 1) Si-face substrates and from 15% to 80% for 6H-SiC(0001) substrates. The growth mode and crystal structure are not affected by the corona discharge. The gallium oxide growth starts with the formation of [ −3 1 1] oriented laterally overgrown terrace like nucleation zones with the gold catalyst particles floating on top. With evolving process time, the growth proceeds in the faster [0 1 0] direction, resulting in nanowires with an inclination angle of 51° towards the substrate surface. On silicon and sapphire substrates, the nucleation and growth of gallium oxide nanowires are suppressed.

The fine structure of the exciton spectrum, containing optically allowed (bright) and forbidden (dark) exciton states, determines the radiation efficiency in nanostructures. We study time-resolved micro-photoluminescence in MoS$_2$ monolayers and bilayers, both unstrained and compressively strained, in a wide temperature range (10-300 K) to distinguish between exciton states optically allowed and forbidden, both in spin and momentum, as well as to estimate their characteristic decay times and contributions to the total radiation intensity. The decay times were found to either increase or decrease with increasing temperature, indicating the lowest bright or lowest dark state, respectively. Our results unambiguously show that, in an unstrained monolayer, the spin-allowed state is the lowest for a series of A excitons (1.9 eV) with the dark state being < 2 meV higher, and that the splitting energy can increase several times at compression. In contrast, in the indirect exciton series in bilayers (1.5 eV), the spin-forbidden state is the lowest, being about 3 meV below the bright one. The strong effect of strain on the exciton spectrum can explain the large scatter among the published data and must be taken into account to realize the desired optical properties of 2D MoS$_2$.

This contribution shows self-aligning ruthenium interconnects. The underlying process is gas phase electrodeposition, which allows metallic particles to be deposited locally. This is performed with an adjustable airgap between the insulator and the deposited metallic structure. The size of the enclosed airgap can be adjusted directly. The deposition power has a direct influence on the growth rate and the morphology of the structure. With increasing deposition power, the resulting self-aligning nano-bridge becomes more compact.

Chemical vapor deposition is a widely used material deposition technique. It commonly provides a uniform material flux to the substrate to cause uniform thin film growth. However, the ability to precisely adjust the local deposition rate would be highly preferable. This communication reports on a chemical vapor deposition method performed in a localized and programmable fashion by introducing an electrically charged and guided molecular flux. This allows for local adjustments of the deposition rate and three-dimensional shape by controlling the electric fields. Specifically, the precursor molecules are charged and then guided by arrays of electrodynamic funnels, which are created by a patterned dielectric layer, to predetermined deposition locations with a minimal spot size of 250 nm. Furthermore, nearest neighbor coupling is reported as a shaping method to cause the deposition of three-dimensional nanostructures. Additionally, the integration of individually addressable domain electrodes offers programmable charge dissipation to achieve an ON/OFF control. The described method is applicable to a wide variety of materials and precursors. Here, the localized and programmable deposition of three-dimensional copper oxide, chromium oxide, zinc oxide, and carbon nanowires is demonstrated.

The need to detect and identify trace amounts of airborne biological hazards with ever increasing sensitivity and selectivity is the main driver in sensor research. However, the low concentration of airborne hazardous entities requires the concentration of the analyte at the biosensor of choice. Here, we present a robust implementation of an effective “Airborne Analyte Transporter”, which (i) permits time-course sampling of airborne particles, (ii) precise localization and concentration of airborne particles at a designated location of a given biosensor (iii) and allows the biological downstream analysis of viable pathogens. The Airborne Analyte Transporter implements a corona discharge based analyte charging method in combination with an electrodynamic funnel concentration concept. The Airborne Analyte Transporter achieves a 1000-fold increase in particle concentration compared to diffusion and settling based transport and allows the precise and local collection of viable pollen, yeasts, spores, bacteria and virus particles with an additional lateral concentration. Potential biological hazards with concentrations down to 20 ppm can still be analyzed using different microscopy techniques and bacterial cultures. The Airborne Analyte Transporter provides a localized collection of airborne particles on a biosensor of choice to be utilized in monitoring air in the health care sector or in hygiene-sensitive areas.

A model based on the generation and recombination of defect was developed to describe the stability of stacking faults and basal plane dislocation loops in crystals with layered polytype structures. The stability of the defects configuration was analysed for stacking faults surrounded by Shockley and Frank partial dislocation as well as Shockley dislocation dipoles with long range elastic fields. This approach allows the qualitative prediction of defect subsystems in polytype structure in external fields.

The optical response of graphene on 6H-SiC was investigated by means of IR-reflectance measurements. Thereby, the anisotropy of the substrate is considered and its influence was studied by performing measurements with s- and p-polarized light. The anisotropy causes a splitting of the reststrahlen band in p-polarization, but does not affect spectra recorded with s-polarization. In both cases a thin film approximation was used to simulate the reflectance spectra. A model consisting of SiC, graphene and air enables the extraction of the graphene layer count.

Aluminium oxide was deposited on silicon, silicon carbide and epitaxial graphene grown on silicon carbide by atomic layer deposition using a standard MOCVD equipment. The morphology and the electrical properties of the aluminium oxide layers on both substrates were determined and compared to aluminium oxide layers deposited with a standard atomic layer deposition equipment. The high-k material fabricated with the developed MOCVD process show comparable or better properties compared to the standard atomic layer deposition process.

Secondary ion mass spectroscopy, Fourier transformed infrared spectroscopy, ellipsometry, reflection high energy diffraction and transmission electron microscopy are used to gain inside into the effect of Ge on the formation of ultrathin 3C-SiC layers on Si(111) substrates. Accompanying the experimental investigations with simulations it is found that the ultrathin single crystalline 3C-SiC layer is formed on top of a gradient Si1–x–yGexCy buffer layer due to a complex alloying and alloy decomposition processes promoted by carbon and germanium interdiffusion and SiC nucleation. This approach allows tuning residual stress at very early growth stages as well as the interface properties of the 3C-SiC/Si heterostructure. Useful yields of secondary ions of Ge in Si matrix and Si dimer are estimated.

Epitaxial graphene on semiinsulating silicon carbide was grown using a high temperature method at atmospheric pressure in argon atmosphere. The temperature dependence of the layer quality was analysed using Raman and infrared spectroscopy. It is demonstrated that infrared spectroscopy can be used as a versatile tool to access the layer count and the quality of the epitaxial grown graphene on silicon carbide. The results obtained by infrared spectroscopy correlate with the Raman measurements.

Epitaxial graphene nanoribbons were fabricated and geometrically measured via scanning electron microscope in the width range of 3...45nm in a new approach. The critical dimension measurement was improved using Monte Carlo simulations for analyzing back scattering effects of the semi-insulating substrate and gaussian convolutions. Different bias powers during oxygen plasma etching allowed the identification of under-etching depths.

Gallium oxide nanowires were grown on different substrates using a corona plasma assisted vapor phase epitaxy process and gold catalyst. It is shown that the silicon carbide pseudo substrate in combination with the plasma excitation of the gas phase supports the growth of the gallium oxide nanowires. Analyzing the orientation of the nanowires with respect to the growth surface, it is concluded that the nanowires growth proceed along the fast growth direction of gallium oxide.

Terbium-doped aluminum nitride thin films have been deposited by radio frequency magnetron sputtering. The influence of annealing treatments on structural, morphological and luminescence properties of the films is examined with the aim to optimize post-deposition annealing conditions. Temperatures starting from 500 up to 1000°C using two annealing techniques were investigated: rapid thermal processing and quartz tube furnace. X-ray diffraction analysis revealed the formation of aluminum oxide and aluminum oxynitride phases at temperatures higher than 750°C. The oxygen content in the surface layer was measured with energy dispersive X-ray. The terbium emission was obtained after excitation either by photons or electrons. The films treated with rapid thermal processing at 750°C resulted in the highest emission.

Gallium nitride (GaN) is commonly used in high-power and high-frequency devices but one limiting factor for its wide application is the availability of cost-effective substrates. The approach of “engineered substrates” is consequently followed up in this work. Low temperature cofired ceramics are used as carrier substrates in this work. The flexible material system allows the creation of a thermo-mechanically compatible base for GaN components. Sputtered aluminum nitride (AlN) layer form the buffer layer for the GaN deposition. The surface quality of these buffer layers reaches an arithmetic mean height R of 10 nm after chemical mechanical polishing and forms thus a surface quality which is adequate for thin film processing. GaN layers grown on these substrates can have both, tensile and compressive stress levels, while such grown on (100) silicon for comparison purpose show exclusively tensile stress. The growth of the GaN layer and resulting morphology is assumed to be mainly influenced by the process conditions during molecular beam epitaxy. The polycrystalline GaN layers show pronounced c-axis orientation at deposition temperatures of 700°C and 800°C. These first results encourage a further development of this new substrate architecture for integrated GaN systems.

Based on a Kronig-Penney model the electronic properties of heteropolytypic superlattices consisting of lamellas of 3C-and 4H-SiC polytypes with thicknesses below ten nanometers are analysed. Due to the large difference in the electron negativity and the resulting high barriers between the different polytypic lamellas an increased number of minizones compared to other materials are formed. The field strength for the appearance of the negative differential resistance in the heteropolytypic superlattice is lower than the critical fields in the silicon carbide polytypes.

Computer simulation of the concentration profiles evolution in SiC/Si heterostructures during growth and subsequent ion sputtering is presented. Simulation is based on a complex self-consistent approach combining kinetic and ballistic methods. Within the framework of the proposed method concentration depth profiles in SiC/Si heterostructure with pre-deposited Ge impurity are calculated and compared with experimental sputtering profiles obtained by secondary ion mass spectrometry.

A nanochannel array structure was applied to realize enhancement-mode high electron mobility transistors based on AlGaN/AlN/GaN-heterostructures grown on Si substrates using a SiC transition layer. The fabricated nanochannel array HEMT, consisting of 78 channels connected in parallel with a channel width of 100 nm defined by electron-beam lithography and dry etching, shows a threshold voltage of 0.35 V. The high electron mobility transistors with LG= 0.2 μm had a maximum drain current density of 445 mA/mm and a peak extrinsic tranconductance of 235 mS/mm. A unity current gain cut-off frequency of 30 GHz and maximum oscillation frequency of 40 GHz were measured on these devices.

All carbon three terminal junctions were fabricated from epitaxial graphene grown on semiinsulating Si-face 4H-SiC. It is demonstrated that self-contained gate devices exhibit current modulation characteristics. The obtained current gain depends on the device design and is controlled by the applied gate voltage.

The mechanical properties of Cr2AlC MAX phase structures were investigated by in-situ bending tests. Freestanding structures such as cantilevers and doubly clamped beams of Cr2AlC were produced. The structures exhibit a Young's modulus of 184 GPa which is close to the value obtained by vibrational measurements. The in-situ bending test allows the determination of the mechanical properties with a lower variance of the measurement results compared to the vibrational measurement. The results are a good starting point for the development of microelectromechanical structures based on MAX phases.

In this work, side gate transistors based on graphene and molybdenum disulfide in comparison to their respective top or back gated devices are presented. The graphene devices were fabricated based on an all carbon technology on silicon carbide substrates, whereas the molybdenum disulfide transistors were fabricated using the exfoliation technique. The output characteristics are analyzed in terms of transconductance in dependence on the geometrical device properties for each material. It is shown that side gate transistors are able to reach the transconductances of conventional top-gate MOSFETs and that this type of transistor can be used as a simple tool for material properties characterization.

A nanowire bonding process referred to as gas-phase electrodeposition is reported to form nanobridge-based interconnects. The process is able to grow free-standing point-to-point electrical connections using metallic wires. As a demonstration, programmable interconnects and an interdigitated electrode array are shown. The process is more material efficient when compared with conventional vapor deposition since the material is directed to the point of use.

A low-temperature scanning tunnelling microscope (STM) has been used to study the graphene-SiC(0001) interface before and after Li intercalation. For clean graphene, spectroscopy of the differential conductance corroborates previous theoretical findings for the interfacial electronic structure (M. Kajihara et al., Surf. Sci. 647, 39 (2016)). An unambiguous relation between the spectroscopic onset of the interface states with changes in STM images is presented. Li intercalation leads to the disappearance of the 6 × 6 superstructure of clean graphene on SiC(0001) and efficiently suppresses the interface states. The additional doping of graphene due to the presence of Li is reflected by the shift of the Dirac point further below the Fermi energy.