Publikationsliste FG Nanotechnologie

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Erstellt: Thu, 01 Jun 2023 23:02:04 +0200 in 0.0669 sec

Mathew, Sobin; Reiprich, Johannes; Narasimha, Shilpashree; Abedin, Saadman; Kurtash, Vladislav; Thiele, Sebastian; Hähnlein, Bernd; Scheler, Theresa; Flock, Dominik; Jacobs, Heiko O.; Pezoldt, Jörg
Three-dimensional MoS2 nanosheet structures: CVD synthesis, characterization, and electrical properties. - In: Crystals, ISSN 2073-4352, Bd. 13 (2023), 3, 448, S. 1-14

The proposed study demonstrates a single-step CVD method for synthesizing three-dimensional vertical MoS2 nanosheets. The postulated synthesizing approach employs a temperature ramp with a continuous N2 gas flow during the deposition process. The distinctive signals of MoS2 were revealed via Raman spectroscopy study, and the substantial frequency difference in the characteristic signals supported the bulk nature of the synthesized material. Additionally, XRD measurements sustained the material’s crystallinity and its 2H-MoS2 nature. The FIB cross-sectional analysis provided information on the origin and evolution of the vertical MoS2 structures and their growth mechanisms. The strain energy produced by the compression between MoS2 islands is assumed to primarily drive the formation of vertical MoS2 nanosheets. In addition, vertical MoS2 structures that emerge from micro fissures (cracks) on individual MoS2 islands were observed and examined. For the evaluation of electrical properties, field-effect transistor structures were fabricated on the synthesized material employing standard semiconductor technology. The lateral back-gated field-effect transistors fabricated on the synthesized material showed an n-type behavior with field-effect mobility of 1.46 cm2 V^-1 s^-1 and an estimated carrier concentration of 4.5 × 10^12 cm^-2. Furthermore, the effects of a back-gate voltage bias and channel dimensions on the hysteresis effect of FET devices were investigated and quantified.
Schlag, Leslie; Isaac, Nishchay Angel; Hossain, Mohammad M.; Hess, Anna-Lena; Wolz, Benedikt C.; Reiprich, Johannes; Ziegler, Mario; Pezoldt, Jörg; Jacobs, Heiko O.
Self-aligning metallic vertical interconnect access formation through microlensing gas phase electrodeposition controlling airgap and morphology. - In: Advanced electronic materials, ISSN 2199-160X, Bd. 9 (2023), 1, 2200838, S. 1-8

This publication reports self-aligning metallic via microlensing gas phase electrodeposition formation. Key operational parameters to fabricate vertical ruthenium and rhodium interconnects (via) with a diameter of 100 nm are discussed. Moreover, airgaps are implemented during the deposition process, which utilizes spark discharge to generate a flux of charged nanoparticles. An inert gas flow transports the nanoparticles through a reactor chamber close to the target substrate. The substrate uses a pre-patterned resist with openings to a silicon/silicon dioxide/metal stack to direct the deposition of the nanoparticles to form localized self-aligning vertical interconnects. Five process parameters were identified, which impact the morphology and conductance of the resulting interconnects: spark discharge power, gas flow rate, microlens via dimensions, substrate surface potential, and in situ flash lamp power. This parameter set enables a controlled adjustment of the via interconnect morphology and its minimum feature size. Gas flow rate in combination with spark discharge power contribute significantly to the morphology of the interconnect. Spark power and microlens via dimensions have the largest influence on the surface potential of the insulating resist cover, which enables a localized microlensing gas phase electrodeposition of a via with a controlled ratio between conducting diameter and airgap.
Zahn, Diana; Landers, Joachim; Buchwald, Juliana; Diegel, Marco; Salamon, Soma; Müller, Robert; Köhler, Moritz; Ecke, Gernot; Wende, Heiko; Dutz, Silvio
Large single domain iron oxide nanoparticles as thermal markers for lateral flow assays. - In: Biomedical engineering, ISSN 1862-278X, Bd. 67 (2022), S. 63
Kurtash, Vladislav; Mathew, Sobin; Thiele, Sebastian; Scheler, Theresa; Reiprich, Johannes; Hähnlein, Bernd; Stauffenberg, Jaqueline; Manske, Eberhard; Narasimha, Shilpashree; Abedin, Saadman; Jacobs, Heiko O.; Pezoldt, Jörg
Hysteresis associated with intrinsic-oxide traps in gate-tunable tetrahedral CVD-MoS2 memristor. - In: IEEE 22nd International Conference on Nanotechnology (NANO), (2022), S. 527-530

We introduce back gated memristor based on CVD-grown 30-40 nm thick MoS2 channel. The device demonstrates bipolar behaviour and the measurements are consistent with the simulations performed within the intrinsic-oxide traps model. This confirms the theory that the source of hysteresis in thin-film MoS2 memristors is charge trapping on MoS2/SiO2 interface and the grain boundaries. The impact of back gate voltage bias, voltage sweep range and channel area on memristive effect was studied and quantified using hysteresis area. Hysteresis in bipolar memristors can be tuned by back gate voltage, which makes these devices promising for neuromorphic computing.
Mathew, Sobin; Narasimha, Shilpashree; Reiprich, Johannes; Scheler, Theresa; Hähnlein, Bernd; Thiele, Sebastian; Stauffenberg, Jaqueline; Kurtash, Vladislav; Abedin, Saadman; Manske, Eberhard; Jacobs, Heiko O.; Pezoldt, Jörg
Formation and characterization of three-dimensional tetrahedral MoS2 thin films by chemical vapor deposition. - In: Crystal growth & design, ISSN 1528-7505, Bd. 22 (2022), 9, S. 5229-5238

A method to synthesize the three-dimensional arrangement of bulk tetrahedral MoS2 thin films by solid source chemical vapor deposition of MoO3 and S is presented. The developed synthesizing recipe uses a temperature ramping with a constant N2 gas flow in the deposition process to grow tetrahedral MoS2 thin film layers. The study analyses the time-dependent growth morphologies, and the results are combined and presented in a growth model. A combination of optical, electron, atomic force microscopy, Raman spectroscopy, and X-ray diffraction are used to study the morphological and structural features of the tetrahedral MoS2 thin layers. The grown MoS2 is c-axis oriented 2H-MoS2. Additionally, the synthesized material is further used to fabricate back-gated field-effect transistors (FETs). The fabricated FET devices on the tetrahedral MoS2 show on/off current ratios of 10^6 and mobility up to ∼56 cm^2 V^-1 s^-1 with an estimated carrier concentration of 4 × 10^16 cm-3 for VGS = 0 V.
Hähnlein, Bernd; Kellner, Maria; Krey, Maximilian; Nikpourian, Alireza; Pezoldt, Jörg; Michael, Steffen; Töpfer, Hannes; Krischok, Stefan; Tonisch, Katja
The angle dependent ΔE effect in TiN/AlN/Ni micro cantilevers. - In: Sensors and actuators, ISSN 1873-3069, Bd. 345 (2022), 113784

In this work, magnetoelectric MEMS sensors based on a TiN/AlN/Ni laminate are investigated for the first time in regards of the anisotropic elastic properties when using hard magnetic Nickel as magnetostrictive layer. The implications of crystalline, uniaxial and shape anisotropy are analysed arising from the anisotropic ΔE effect in differently oriented cantilevers with 25 µm length and 15˚ spacing. The ΔE effect is derived analytically to consider the angular dependency of the different anisotropies within the sensors. In the measured frequency spectra complex profiles are observable consisting of contributions from neighbouring structures which are connected by a common electrode. The crosstalk effect is strongly depending on the cantilever orientation and reflects the anisotropic mechanical properties of the material stack. The intensity of the crosstalk effect is increasing for shortened cantilevers and narrowing distance between structures. The ΔE effect is investigated based on cantilevers of different angular spacing and of a single cantilever that is rotated in the magnetic field. The derived peak sensitivities are reaching values of 1.15 and 1.31T-1. The angular dependency of the sensitivity is found to be approximately constant for differently oriented cantilevers. In contrast, for a singly rotated cantilever an angular dependency of the 4th order is observed.
Grieseler, Rolf; Gallino, Isabella; Duboiskaya, Natallia; Döll, Joachim; Shekhawat, Deepshikha; Reiprich, Johannes; Guerra, Jorge A.; Hopfeld, Marcus; Honig, Hauke; Schaaf, Peter; Pezoldt, Jörg
Silicon carbide formation in reactive silicon-carbon multilayers. - In: Materials science forum, ISSN 1662-9752, Bd. 1062 (2022), S. 44-48

An alternative low thermal budget silicon carbide syntheses route is presented. The method is based on self-propagating high-temperature synthesis of binary silicon-carbon-based reactive mul­tilayers. With this technique, it is possible to obtain cubic polycrystalline silicon carbide at relatively low annealing temperatures by a solid state reaction. The reaction starts above 600 ˚C. The transformation process proceeds in a four-step process. The reaction enthalpy was determined to be (-70 ± 4) kJ/mol.
Mathew, Sobin; Lebedev, Sergey P.; Lebedev, Alexander A.; Hähnlein, Bernd; Stauffenberg, Jaqueline; Manske, Eberhard; Pezoldt, Jörg
Silicon carbide - graphene nano-gratings on 4H and 6H semi-insulating SiC. - In: Materials science forum, ISSN 1662-9752, Bd. 1062 (2022), S. 170-174

A technical methodology of fabrication of hierarchically scaled multitude graphene nanogratings with varying pitches ranging from the micrometer down to sub 40 nm scale combined with sub 10 nm step heights on 4H and 6H semi-insulating SiC for length scale measurements is proposed. The nanogratings were fabricated using electron-beam lithography combined with dry etching of graphene, incorporating a standard semiconductor processing technology. A scientific evaluation of critical dimension, etching step heights, and surface characterization of graphene nanograting on both polytypes were compared and evaluated.
Kurtash, Vladislav; Thiele, Sebastian; Mathew, Sobin; Jacobs, Heiko O.; Pezoldt, Jörg
Designing MoS2 channel properties for analog memory in neuromorphic applications. - In: Journal of vacuum science & technology, ISSN 2166-2754, Bd. 40 (2022), 3, S. 030602-1-030602-5

In this paper, we introduce analog nonvolatile random access memory cells for neuromorphic computing. The analog memory cell MoS2 channel is designed based on the simulation model including Fowler-Nordheim tunneling through a charge-trapping stack, trapping process, and transfer characteristics to describe a full write/read circle. 2D channel materials provide scaling to higher densities as well as preeminent modulation of the conductance by the accumulated space charge from the oxide trapping layer. In this paper, the main parameters affecting the distribution of memory states and their total number are considered. The dependence of memory state distribution on channel doping concentration and the number of layers is given. In addition, how the nonlinearity of memory state distribution can be overcome by variation of operating conditions and by applying pulse width modulation to the bottom gate voltage is also shown.
Shekhawat, Deepshikha; Vauth, Maximilian; Pezoldt, Jörg
Size dependent properties of reactive materials. - In: Inorganics, ISSN 2304-6740, Bd. 10 (2022), 4, 56, S. 1-19

The nature of the self-sustained reaction of reactive materials is dependent on the physical, thermal, and mechanical properties of the reacting materials. These properties behave differently at the nano scale. Low-dimensional nanomaterials have various unusual size dependent transport properties. In this review, we summarize the theoretical and experimental reports on the size effect on melting temperature, heat capacity, reaction enthalpy, and surface energy of the materials at nano scale because nanomaterials possess a significant change in large specific surface area and surface effect than the bulk materials. According to the theoretical analysis of size dependent thermodynamic properties, such as melting temperature, cohesive energy, thermal conductivity and specific heat capacity of metallic nanoparticles and ultra-thin layers varies linearly with the reciprocal of the critical dimension. The result of this scaling relation on the material properties can affect the self-sustained reaction behavior in reactive materials. Resultant, powder compacts show lower reaction propagation velocities than bilayer system, if the particle size of the reactants and the void density is decreased an increase of the reaction propagation velocity due to an enhanced heat transfer in reactive materials can be achieved. Standard theories describing the properties of reactive material systems do not include size effects.