We have fabricated and operated two cantilevers in parallel in a new mode for imaging with the atomic force microscope (AFM). The cantilevers contain both an integrated piezoresistive silicon sensor and an integrated piezoelectric zinc oxide (ZnO) actuator. The integration of sensor and actuator on a single cantilever allows us to simultaneously record two independent AFM images in the constant force mode. The ZnO actuator provides over 4 μm of deflection at low frequencies (dc) and over 30 μm deflection at the first resonant frequency. The piezoresistive element is used to detect the strain and provide the feedback signal for the ZnO actuator.
Precise in situ atomic force microscopy (AFM) is used to monitor the formation of the solid electrolyte interphase (SEI) on Si electrodes. The stability of these passivation films on negative electrodes is critically important in rechargeable Li-ion batteries, and high capacity materials such as Si present substantial challenges because of the large volume changes that occur with Li insertion and removal. The results reported here show that the initial rapid SEI formation can be stabilized before significant Li insertion into the Si begins and that the rate at which this occurs varies significantly with the nature of the surface. The initial cycling conditions also have a substantial impact on the SEI that forms, with faster rates leading to a smoother, thinner SEI film. To quantitatively interpret the SEI measurements, irreversible expansion of the Si during the first cycle was also monitored in situ with specifically designed specimen configurations. On the basis of the experimental results, relatively simple models were also used to describe the initial formation and stabilization of the SEI and to describe the relationship between the SEI thickness and expected SEI degradation mechanisms.
Bias controlled capacitive driven cantilever oscillation for high resolution dynamic force microscopy Appl. Phys. Lett. 102, 073110 (2013) Friction measurement on free standing plates using atomic force microscopy Rev. Sci. Instrum. 84, 013702 (2013) A correlation force spectrometer for single molecule measurements under tensile load J. Appl. Phys. 113, 013503 (2013) Compact metal probes: A solution for atomic force microscopy based tip-enhanced Raman spectroscopy Rev. Sci. Instrum. 83, 123708 (2012) Note: Radiofrequency scanning probe microscopy using vertically oriented cantilevers Rev. Sci. Instrum. 83, 126103 (2012) Additional information on Appl. Phys. Lett.
Articles you may be interested inReal time reduction of probe-loss using switching gain controller for high speed atomic force microscopy Rev. Sci. Instrum.Increasing the imaging speed of tapping mode atomic force microscopy ͑AFM͒ has important practical and scientific applications. The scan speed of tapping-mode AFMs is limited by the speed of the feedback loop that maintains a constant tapping amplitude. This article seeks to illuminate these limits to scanning speed. The limits to the feedback loop are: ͑1͒ slow transient response of probe; ͑2͒ instability limitations of high-quality factor ͑Q͒ systems; ͑3͒ feedback actuator bandwidth; ͑4͒ error signal saturation; and the ͑5͒ rms-to-dc converter. The article will also suggest solutions to mitigate these limitations. These limitations can be addressed through integrating a faster feedback actuator as well as active control of the dynamics of the cantilever.
here signifi cant research is focused on higher voltage electrolytes). [ 2,3 ] The thicker anode SEI fi lms make a much larger contribution to irreversible Li consumption. However, there is very little understanding of how the chemomechanical degradation of SEI leads to capacity loss.Full battery models have employed descriptions of long-term Li capacity loss due to SEI, [ 4,5 ] some of which include specifi c models for the growth of the SEI layer. [ 6,7 ] SEI stability is particularly important with newer anode materials such as silicon and tin, which have much higher capacity than the intercalation materials which are currently used commercially. For example, the capacity increase of silicon is almost ten times that of graphite. However, this is accompanied by a large volume change (>300%), which leads to mechanical degradation of the SEI layer during repeated expansion and contraction of the electrode. Mechanical degradation of silicon electrodes has been addressed in recent research, [ 8,9 ] including work on damage mechanisms such as critical fracture size, [ 10 ] impact of the surface oxide, [ 11 ] other mechanical properties, [ 12 ] and some scalable mitigation techniques. [ 13 ] Experimental investigations of SEI degradation are signifi cantly more challenging, because the layers are very thin and they typically consist of multiple phases. Some of the relevant issues have been addressed in recent experiments, [14][15][16][17][18] but there is still only very limited information about SEI formation and its mechanical degradation on silicon.The research reported here employs several different techniques to probe critical SEI properties, with a focus on in situ electrochemical atomic force microscopy (AFM). Other studies have also employed in situ AFM on battery electrodes. [19][20][21][22] This includes several that look at SEI formation on anodes. [23][24][25][26] PeakForce tapping AFM was also recently used to examine near surface mechanical properties. [ 27 ] Our investigations are primarily based on comparisons between "slow cycling" and faster "pulse cycling." This includes detailed analysis of in situ AFM data, supported with electrochemical impedance spectroscopy (EIS). A structural model that explains the observed mechanical and electrochemical properties is proposed. Based on this description, a simple mathematical model is then developed The formation of the solid electrolyte interphase (SEI) on Si is examined in detail using several in situ techniques. The results show that employing different conditions during the fi rst lithiation cycle produces SEI fi lms with substantially different properties. Longer time at higher potentials produces softer SEI, whereas inorganic phases produced at lower potentials have higher elastic moduli. The SEI thickness stabilizes during the fi rst cycle; however, the SEI resistance decreases during the fi rst 20 cycles (in sharp contrast to typical surface passivation processes, where resistance is expected to increase with time). This behavior is consistent with t...
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