NachhaltigElektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
L. Larcher, F. Puglisi, L. Jiang, Jonas Weber, Günther Benstetter, P. Pavan, M. Lanza, Werner Frammelsberger
Understanding Current Instabilities in Conductive Atomic Force Microscopy
Materials, vol. 12, no. 3
2019
DOI: 10.3390/ma12030459
Abstract anzeigen
Conductive atomic force microscopy (CAFM) is one of the most powerful techniques in studying the electrical properties of various materials at the nanoscale. However, understanding current fluctuations within one study (due to degradation of the probe tips) and from one study to another (due to the use of probe tips with different characteristics), are still two major problems that may drive CAFM researchers to extract wrong conclusions. In this manuscript, these two issues are statistically analyzed by collecting experimental CAFM data and processing them using two different computational models. Our study indicates that: (i) before their complete degradation, CAFM tips show a stable state with degraded conductance, which is difficult to detect and it requires CAFM tip conductivity characterization before and after the CAFM experiments; and (ii) CAFM tips with low spring constants may unavoidably lead to the presence of a ~1.2 nm thick water film at the tip/sample junction, even if the maximum contact force allowed by the setup is applied. These two phenomena can easily drive CAFM users to overestimate the properties of the samples under test (e.g., oxide thickness). Our study can help researchers to better understand the current shifts that were observed during their CAFM experiments, as well as which probe tip to use and how it degrades. Ultimately, this work may contribute to enhancing the reliability of CAFM investigations.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
J. Michalicka, S. Li, Z. Bi, Y. Zhang, Ondrej Man, Y. Hong, Y. Wu, W. Ni, H. Fan, Günther Benstetter, L. Liu, Q. Yang, D. Liu
The effect of O2 impurity on surface morphology of polycrystalline W during low-energy and high-flux He+ irradiation
Fusion Engineering and Design, vol. 139, pp. 96-103
2019
DOI: 10.1016/j.fusengdes.2019.01.003
Abstract anzeigen
The interaction between the impurities (such as carbon, nitrogen, oxygen) and the plasma-facing materials (PFMs) can profoundly influence the performance and service of the PFMs. In this paper, we investigated the influence of oxygen (O2) impurity in the helium radio frequency (RF) plasma on the surface morphology of polycrystalline tungsten (W) irradiated at the surface temperature of 1450 ± 50 K and the ion energy of 100 eV. The pressure ratio of O2 to He (R) in RF source varied from 4.0 × 10−6 to 9.0 × 10-2. The total irradiation flux and fluence were ˜1.2 × 1022 ions·m-2·s-1 and ˜1.0 × 1026 ions·m-2, respectively. After He+ irradiation, the specimen surface morphology was observed by scanning electron microscopy. It was found that with increasing R from 4.0 × 10−6 to 9.0 × 10-2 the thickness of nano-fuzz layer at the W surface was thinner and thinner, accompanied by the formation of rod-like structures. The erosion yield increased from 5.2 × 10-4 to 2.3 × 10-2 W/ion when R varied from 4.0 × 10-6 to 9.0 × 10-2. The X-ray diffraction analysis shows that tungsten oxides were formed at the near surface of specimens when R exceeded 1.8 × 10-2. The erosion yield measurements revealed that in addition to surface physical sputtering process, the chemical erosion process could occur due to the interaction between oxygen-containing species and W at the surface. The results indicated that the presence of O2 impurity in He plasma can obviously affect the surface microstructure of W. The study suggested that O2 impurity can effectively reduce the growth of nano-fuzz structures.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
X. Jing, E. Grustan-Gutierrez, M. Buckwell, Y. Ji, A. Kenyon, M. Rommel, Y. Shi, A. Mehonic, L. Jiang, A. Paskaleva, F. Hui, Günther Benstetter, S. Chen, W. Ng, M. Lanza
On the Limits of Scalpel AFM for the 3D Electrical Characterization of Nanomaterials
Advanced Functional Materials, vol. 28, no. 52
2018
DOI: 10.1002/adfm.201802266
Abstract anzeigen
Conductive atomic force microscopy (CAFM) has been widely used for electrical characterization of thin dielectrics by applying a gentle contact force that ensures a good electrical contact without inducing additional high‐pressure related phenomena (e.g., flexoelectricity, local heat, scratching). Recently, the CAFM has been used to obtain 3D electrical images of thin dielectrics by etching their surface. However, the effect of the high contact forces/pressures applied during the etching on the electrical properties of the materials has never been considered. By collecting cross‐sectional transmission electron microscopy images at the etched regions, it is shown here that the etching process can modify the morphology of Al2O3 thin films (producing phase change, generation of defects, and metal penetration). It is also observed that this technique severely modifies the electrical properties of pSi and TiO2 wafers during the etching, and several behaviors ignored in previous studies, including i) observation of high currents in the absence of bias, ii) instabilities of etching rate, and iii) degradation of CAFM tips, are reported. Overall, this work should contribute to understand better the limitations of this technique and disseminate it among those applications in which it can be really useful.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
S. Li, Z. Bi, Y. Zhang, D. Liu, Y. Hong, Y. Wu, W. Ni, H. Fan, Günther Benstetter, L. Liu, Q. Yang
Surface damages of polycrystalline W and La2O3-doped W induced by high-flux He plasma irradiation
Journal of Nuclear Materials, vol. 501, no. April, pp. 275-281
2018
Abstract anzeigen
In this study, polycrystalline tungsten (W) and three oxide dispersed strengthened W with 0.1 vol %, 1.0 vol % and 5.0 vol % lanthanum trioxide (La2O3) were irradiated with low-energy (200 eV) and high-flux (5.8 × 1021 or 1.4 × 1022 ions/m2⋅s) He+ ions at elevated temperature. After He+ irradiation at a fluence of 3.0 × 1025/m2, their surface damages were observed by scanning electron microscopy, energy dispersive spectroscopy, scanning electron microscopy-electron backscatter diffraction, and conductive atomic force microscopy. Micron-sized holes were formed on the surface of W alloys after He+ irradiation at 1100 K. Analysis shows that the La2O3 grains doped in W were sputtered preferentially by the high-flux He+ ions when compared with the W grains. For irradiation at 1550 K, W nano-fuzz was formed at the surfaces of both polycrystalline W and La2O3-doped W. The thickness of the fuzz layers formed at the surface of La2O3-doped W is 40% lower than the one of polycrystalline W. The presence of La2O3 could suppress the diffusion and coalescence of He atoms inside W, which plays an important role in the growth of nanostructures fuzz.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
M. Lorenz, Manuel Bogner, M. Kneiß, O. Oeckler, M. Grundmann, Y. Fu, C. Yang, Günther Benstetter, D. Souchay, H. Wei
Transparent flexible thermoelectric material based on non-toxic earth-abundant p-type copper iodide thin film
nature COMMUNICATIONS, no. July
2017
DOI: 10.1038/ncomms1607
Abstract anzeigen
Thermoelectric devices that are flexible and optically transparent hold unique promise for future electronics. However, development of invisible thermoelectric elements is hindered by the lack of p-type transparent thermoelectric materials. Here we present the superior room-temperature thermoelectric performance of p-type transparent copper iodide (CuI) thin films. Large Seebeck coefficients and power factors of the obtained CuI thin films are analysed based on a single-band model. The low-thermal conductivity of the CuI films is attributed to a combined effect of the heavy element iodine and strong phonon scattering. Accordingly, we achieve a large thermoelectric figure of merit of ZT=0.21 at 300 K for the CuI films, which is three orders of magnitude higher compared with state-of-the-art p-type transparent materials. A transparent and flexible CuI-based thermoelectric element is demonstrated. Our findings open a path for multifunctional technologies combing transparent electronics, flexible electronics and thermoelectricity.
NachhaltigElektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
M. Nafría, Tobias Berthold, Günther Benstetter, R. Rodríguez, Werner Frammelsberger
Numerical Study of Hydrodynamic Forces for AFM Operations in Liquid Scanning (Article ID 6286595, 12 pages)
Scanning, pp. 1-12
2017
DOI: 10.1155/2017/6286595
Abstract anzeigen
For advanced atomic force microscopy (AFM) investigation of chemical surface modifications or very soft organic sample surfaces, the AFM probe tip needs to be operated in a liquid environment because any attractive or repulsive forces influenced by the measurement environment could obscure molecular forces. Due to fluid properties, the mechanical behavior of the AFM cantilever is influenced by the hydrodynamic drag force due to viscous friction with the liquid. This study provides a numerical model based on computational fluid dynamics (CFD) and investigates the hydrodynamic drag forces for different cantilever geometries and varying fluid conditions for Peakforce Tapping (PFT) in liquids. The developed model was verified by comparing the predicted values with published results of other researchers and the findings confirmed that drag force dependence on tip speed is essentially linear in nature. We observed that triangular cantilever geometry provides significant lower drag forces than rectangular geometry and that short cantilever offers reduced flow resistance. The influence of different liquids such as ultrapure water or an ethanol-water mixture as well as a temperature induced variation of the drag force could be demonstrated. The acting forces are lowest in ultrapure water, whereas with increasing ethanol concentrations the drag forces increase.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
X. Jing, E. Grustan-Gutierrez, Y. Illarionov, X. Song, Emanuel Panholzer, T. Grasser, Y. Shi, F. Hui, Günther Benstetter, M. Lanza
Fabrication of scalable and ultra low power photodetectors with high light/dark current ratios using polycrystalline monolayer MoS2 sheets
Nano Energy, vol. 30, no. December, pp. 494-502
2016
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
D. Liu, W. Ni, H. Fan, Günther Benstetter, L. Liu, Q. Yang, Y. You, C. Liu
Surface degeneration of W crystal irradiated with low-energy hydrogen ions
Scientific Reports (Nature Publishing Group), vol. 6, no. Article number: 23738
2016
DOI: 10.1038/srep23738
Abstract anzeigen
The damage layer of a W (100) crystal irradiated with 120 eV hydrogen ions at a fluence of up to 1.5 × 1025/m2 was investigated by scanning electron microscopy and conductive atomic force microscopy (CAFM). The periodic surface degeneration of the W crystal at a surface temperature of 373 K was formed at increasing hydrogen fluence. Observations by CCD camera and CAFM indicate the existence of ultrathin surface layers due to low-energy H irradiation. The W surface layer can contain a high density of nanometer-sized defects, resulting in the thermal instability of W atoms in the surface layer. Our findings suggest that the periodic surface degeneration of the W crystal can be ascribed to the lateral erosion of W surface layers falling off during the low-energy hydrogen irradiation. Our density functional theory calculations confirm the thermal instability of W atoms in the top layer, especially if H atoms are adsorbed on the surface.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
S. Li, Z. Bi, D. Liu, Y. Hong, W. Ni, H. Fan, Günther Benstetter, L. Liu, Q. Yang
High-flux He+ irradiation effects on surface damages of tungsten under ITER relevant conditions
Journal of Nuclear Materials, vol. 471, no. April, pp. 1-7
2016
DOI: 10.1016/j.jnucmat.2016.01.001
Abstract anzeigen
A large-power inductively coupled plasma source was designed to perform the continuous helium ions (He+) irradiations of polycrystalline tungsten (W) under International Thermonuclear Experimental Reactor (ITER) relevant conditions. He+ irradiations were performed at He+ fluxes of 2.3 × 1021–1.6 × 1022/m2 s and He+ energies of 12–220 eV. Surface damages and microstructures of irradiated W were observed by scanning electron microscopy. This study showed the growth of nano-fuzzes with their lengths of 1.3–2.0 μm at He+ energies of >70 eV or He+ fluxes of >1.3 × 1022/m2 s. Nanometer-sized defects or columnar microstructures were formed in W surface layer due to low-energy He+ irradiations at an elevated temperature (>1300 K). The diffusion and coalescence of He atoms in W surface layers led to the growth and structures of nano-fuzzes. This study indicated that a reduction of He+ energy below 12–30 eV may greatly decrease the surface damage of tungsten diverter in the fusion reactor.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
Y. Ji, V. Igelsias, Alexander Hofer, M. Liu, D. Lewis, Y. Shi, S. Long, N. Jiebin, P. McIntyre, Günther Benstetter, A. Scheuermann, H. Fei, M. Lanza, Werner Frammelsberger
Characterization of the photocurrents generated by the laser of atomic force microscopes
Review of Scientific Instruments, vol. 87, no. 8
2016
DOI: 10.1063/1.4960597
Abstract anzeigen
The conductive atomic force microscope (CAFM) has become an essential tool for the nanoscale electronic characterization of many materials and devices. When studying photoactive samples, the laser used by the CAFM to detect the deflection of the cantilever can generate photocurrents that perturb the current signals collected, leading to unreliable characterization. In metal-coated semiconductor samples, this problem is further aggravated, and large currents above the nanometer range can be observed even without the application of any bias. Here we present the first characterization of the photocurrents introduced by the laser of the CAFM, and we quantify the amount of light arriving to the surface of the sample. The mechanisms for current collection when placing the CAFM tip on metal-coated photoactive samples are also analyzed in-depth. Finally, we successfully avoided the laser-induced perturbations using a two pass technique: the first scan collects the topography (laser ON) and the second collects the current (laser OFF). We also demonstrate that CAFMs without a laser (using a tuning fork for detecting the deflection of the tip) do not have this problem.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
D. Liu, C. Liu, W. Ni, Y. Wang, H. Fan, Günther Benstetter, Y.-W. You, L. Liu, Q. Yang
Nanostructured fuzz growth on tungsten under low-energy and high-flux He irradiation
Scientific Reports (Nature Publishing Group), vol. 5, no. Article number: 10959, pp. 1-9
2015
DOI: 10.1038/srep10959
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
M. Nafría, Tobias Berthold, Günther Benstetter, R. Rodríguez, Werner Frammelsberger
Nanoscale characterization of CH3-terminated Self-Assembled Monolayer on copper by advanced scanning probe microscopy techniques
Applied Surface Science, vol. 356, pp. 921-926
2015
DOI: 10.1016/j.apsusc.2015.08.182
Abstract anzeigen
In this study, we used Self-Assembled Monolayer (SAM) with CH3 end-group molecules to protect copper surfaces from oxidation and investigated at nanometer scale the integrity and temperature stability of the protective film. The films were characterized by dynamic Chemical Force Microscopy (dCFM), Torsional Resonance Tunneling Atomic Force Microscopy (TR-TUNA) and Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR).
We observed that temperature stress degraded local properties of our SAM films significantly, when compared to unstressed films. After temperature stress at 100 °C, tunneling current increased and hydrophobicity decreased substantially. In combination with the ATR-FTIR results we assigned local high current spots and local hydrophobic variations to cuprous oxide (Cu2O). After temperature stress at 150 °C, the measurements indicate a decomposition of the SAM film and a further oxidation of the copper surface. In addition, the results show that dynamic dCFM and TR-TUNA are appropriate tools to characterize SAM films structurally, chemically and electrically. Most important, in contrast to conventional contact mode Atomic Force Microscopy techniques, we did not observe any damage to the SAM film by dCFM and TR-TUNA measurements.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
R.Y.Q. Fu, Alexander Hofer, Manuel Bogner, Günther Benstetter, H. Gruber
Differential 3ω method for measuring thermal conductivity of AIN and SI3N4 thin films
Thin Solid Films, vol. 591 Part B, pp. 267-270
2015
DOI: 10.1016/j.tsf.2015.03.031
Abstract anzeigen
The thermal conductivity λ of plasma enhanced chemical vapor deposited Si3N4 and sputtered AlN thin films deposited on silicon substrates were obtained utilizing the differential 3ω method. A thin electrically conductive strip was deposited onto the investigated thin film of interest, and used as both a heater and a temperature sensor. To study the thickness dependent thermal conductivity of AlN and Si3N4 films their thickness was varied from 300 to 1000 nm. Measurements were performed at room temperature at a chamber pressure of 3.1 Pa. The measured thermal conductivity values of AlN and Si3N4 thin films were between 5.4 and 17.6 Wm− 1 K− 1 and 0.8 up to 1.7 Wm− 1 K− 1, respectively. The data were significantly smaller than that of the bulk materials found in literature (i.e., λAlN = 250–285 Wm− 1 K− 1, λSi3N4 = 30 Wm− 1 K− 1), due to the scaling effects, and also strongly dependent on film thickness, but were comparable with literature for the corresponding thin films.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
Alexander Hofer, M. Mattheis, L. Hamann, M. Haas, Günther Benstetter, R. Zapf-Gottwick
Use of Coated-Metal Particles in Rear Busbar Pastes to Reduce Silver Consumption
IEEE Journal of Photovoltaics, vol. 5, no. 2, pp. 534-537
2015
DOI: 10.1109/JPHOTOV.2014.2388080
Abstract anzeigen
Reducing the amount of silver is one of the most important ways to reduce the cost of photovoltaic cells. The common way to reduce silver consumption on a cell is the reduction of the metal content in the paste. We present a new paste with silver-coated nickel particles, reducing the silver amount and still keeping the properties of silver related to oxidation and sintering. This paper shows the limits in conductivity due to porosity and oxidation of coated-metal particle pastes in comparison with silver pastes. Simulations and cell tests show that coated-metal particle pastes reduce silver consumption without decreasing the cell efficiency replacing busbar pastes. Coated-metal particle pastes are able to decrease silver consumption for rear-side busbars to c Ag <; 1.4 mg/cm 2 , leading to a conductivity σ BB = 1.110 5 S/cm, without decreasing cell or module efficiency. The conductivity of coated-metal particle pastes is too low using pastes with coated-metal particles as a replacement for the metallization paste for grid fingers but good enough to replace the silver paste for busbars with a cheap alternative.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
M. Nafría, Tobias Berthold, Günther Benstetter, R. Rodríguez, Werner Frammelsberger
Nanoscale characterization of copper oxide films by Kelvin Probe Force Microscopy
Thin Solid Films, vol. 584, no. June 2015, pp. 310-315
2015
DOI: 10.1016/j.tsf.2015.01.071
Abstract anzeigen
In this work Peakforce Kelvin Probe Force Microscopy (PF-KPFM) at ambient environment is used to characterize both oxidation states of copper (Cu) surfaces, cupric oxide CuO and cuprous oxide Cu2O, with high lateral resolution. Characteristic values of the contact potential difference were obtained for the copper oxide states. By this means, PF-KPFM measurements enabled to distinguish between the different types of Cu oxide with nanometer resolution and to correlate the oxidation states to local topography features. It was even possible to identify single oxide grains on top of the Cu surface. As a result, PF-KPFM is able to address the needs for nanoscale characterization methods in semiconductor manufacturing or other related technologies where the local oxidation behavior of copper is a critical issue.
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