NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
Christoph Metzke, Werner Frammelsberger, Jonas Weber, Fabian Kühnel, K. Zhu, M. Lanza, Günther Benstetter
On the Limits of Scanning Thermal Microscopy of Ultrathin Films
Materials, vol. 13, no. 3
2020
DOI: 10.3390/ma13030518
Abstract anzeigen
Heat transfer processes in micro- and nanoscale devices have become more and more important during the last decades. Scanning thermal microscopy (SThM) is an atomic force microscopy (AFM) based method for analyzing local thermal conductivities of layers with thicknesses in the range of several nm to µm. In this work, we investigate ultrathin films of hexagonal boron nitride (h-BN), copper iodide in zincblende structure (γ-CuI) and some test sample structures fabricated of silicon (Si) and silicon dioxide (SiO2) using SThM. Specifically, we analyze and discuss the influence of the sample topography, the touching angle between probe tip and sample, and the probe tip temperature on the acquired results. In essence, our findings indicate that SThM measurements include artefacts that are not associated with the thermal properties of the film under investigation. We discuss possible ways of influence, as well as the magnitudes involved. Furthermore, we suggest necessary measuring conditions that make qualitative SThM measurements of ultrathin films of h-BN with thicknesses at or below 23 nm possible.
NachhaltigF: Elektrotechnik und MedientechnikF: Maschinenbau und MechatronikI: IQMAZeitschriftenartikel
L. Jiang, Jonas Weber, F. Puglisi, P. Pavan, L. Larcher, Werner Frammelsberger, Günther Benstetter, M. Lanza
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.
NachhaltigF: Elektrotechnik und MedientechnikF: Maschinenbau und MechatronikI: IQMAZeitschriftenartikel
Tobias Berthold, Günther Benstetter, Werner Frammelsberger, R. Rodríguez, M. Nafría
Numerical Study of Hydrodynamic Forces for AFM Operations in Liquid Scanning (Article ID 6286595, 12 pages)
Scanning, no. Article ID 6286595, 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.
NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
Y. Ji, H. Fei, Y. Shi, V. Iglesias, D. Lewis, N. Jiebin, S. Long, M. Liu, Alexander Hofer, Werner Frammelsberger, Günther Benstetter, A. Scheuermann, P. McIntyre, M. Lanza
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.
NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
Tobias Berthold, Günther Benstetter, Werner Frammelsberger, R. Rodríguez, M. Nafría
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.
NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
Tobias Berthold, Günther Benstetter, Werner Frammelsberger, R. Rodríguez, M. Nafría
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.
F: Elektrotechnik und MedientechnikF: Maschinenbau und MechatronikI: IQMAZeitschriftenartikel
Werner Frammelsberger, Günther Benstetter, J. Kiely, R. Stamp
C-AFM-based thickness determination of thin and ultra-thin SiO2 films by use of different conductive-coated probe tips
Applied Surface Science, vol. 253, no. 7, pp. 3615-3626
2007
Abstract anzeigen
The influence of the probe tip type on the electrical oxide thickness result was researched for four differently coated conductive tip types using SiO2 (oxide) films with optical thickness of 1.7–8.3 nm. For this purpose, conductive atomic force microscopy (C-AFM) was used to measure more than 7200 current–voltage (IV) curves. The electrical oxide thickness was determined on a statistical basis from the IV-curves using a recently published tunnelling model for C-AFM application. The model includes parameters associated with the probe tip types used. The evolution of the tip parameters is described in detail. For the theoretical tip parameters, measured and calculated IV-curves showed excellent agreement and the electrical oxide thickness versus the optical oxide thickness showed congruent behaviour, independent of the tip type. However, differences in the electrical oxide thickness were observed for the different tip types. The theoretical parameters were modified experimentally in order to reduce these differences. Theoretical and experimental tip parameters were compared and their effect on the differences in the electrical oxide thickness is discussed for the different tip types. Overall, it is shown that the proposed model provides a comprehensive framework for determining the electrical oxide thickness using C-AFM, for a wide range of oxide thicknesses and for differently coated conductive tips.
F: Elektrotechnik und MedientechnikF: Maschinenbau und MechatronikI: IQMAVortrag
M. Lanza, M. Porti, M. Nafría, Günther Benstetter, Werner Frammelsberger, Heiko Ranzinger, Edgar Lodermeier, G. Jaschke
Influence of the manufacturing process on the electrical properties of thin (< 4 nm) Hafnium based high-k stacks observed with CAFM
18th European Symposium on Reliability of Electronic Devices, Failure Physics and Analysis (ESREF), Arcachon, Frankreich
2007
F: Elektrotechnik und MedientechnikF: Maschinenbau und MechatronikI: IQMAZeitschriftenartikel
M. Lanza, M. Porti, M. Nafría, Günther Benstetter, Werner Frammelsberger, Heiko Ranzinger, Edgar Lodermeier, G. Jaschke
Influence of the manufacturing process on the electrical properties of thin (< 4 nm) Hafnium based high-k stacks observed with CAFM
Microelectronics Reliability, vol. 47, no. 9, pp. 1424-1428
2007
Abstract anzeigen
In this work, the dependence of the electrical characteristics of some thin (<4 nm) HfO2, HfSiO and HfO2/SiO2 stacks on their manufacturing process is studied at the nanoscale. Topography, current maps and current–voltage (I–V) characteristics have been collected by conductive atomic force microscope (CAFM), which show that their conductivity depends on some manufacturing parameters. Increasing the annealing temperature, physical thickness or Hafnium content makes the structure less conductive.
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