Investigation of the Effect of Spin Crossover on the Static and Dynamic Properties of MEMS Microcantilevers Coated with Nanocomposite Films of [Fe(Htrz)₂(trz)](BF₄)@P(VDF-TrFE)

Round 1

Reviewer 1 Report

Authors describe mechanical/actuator properties of a microelectromechanical cantilever system spray coated with the (presumed) 1D Fe(II) triazole/triazolate spin crossover material dispersed in a polymer. The work is well written and joins related "device" papers on similar topics.

Some small matters:

p.2 line 70  'spay' should be spray; p. 2 line 81 reference to reverse micelle method  should cite the work of Letard who first used this teachnique; p. 7 line 241 - integrable ??   Introduction general reference to spin crossover should include the book edited by Halcrow.

I was intrigued to see papers in 1909 and 1925 (refs 26,27) are still cited in this kind of study.

Overall- the paper is worthy of acceptance in Magnetochemistry.

Author Response

REFEREE 1: p.2 line 70  'spay' should be spray :

AUTHORS: Corrected.

REFEREE 1: p. 2 line 81 reference to reverse micelle method should cite the work of Letard who first used this teachnique;

AUTHORS: Completed.

REFEREE 1: p. 7 line 241 - integrable ?? 

AUTHORS: Corrected.

REFEREE 1: Introduction general reference to spin crossover should include the book edited by Halcrow.

AUTHORS: Completed.

Reviewer 2 Report

Authors report on the influence of the deposition of nanocomposite films of [Fe(Htrz)2(trz)](BF4)@P(VDF-TrFE) on microcantilevers. Homogeneous films of high quality are obtained upon spray coating, albeit the irregularities of the underlying microelectromechanical systems. This result alone is of interest for the community aiming at developing devices using spin-crossover films. The authors evidence the reversible modulation of the dynamics and static properties of the cantilevers by thermal transition of the spin-crossover complexes in the films. It is worth mentioning that the authors took care in disentangling the contributions from the cantilever, P(VDF-TrFE) and spin-crossover nanoparticles. The manuscript is well written, and I believe that these results are interesting for the community. I, therefore, strongly recommend the publication of the present manuscript in magnetochemistry.

Minor comments:

• Figure 2c shows the MEMS resonance frequency upon 105 successive thermal cycles. The frequency change is significantly larger than the one shown in Figure 2b. I am, therefore, wondering if the frequency change is primarily driven by temperature-dependent properties of the P(VDF-TrFE) matrix? These data would therefore not be very informative on the resilience of the spin-crossover properties upon many heating/cooling cycles. This point is not critical for the claims of the manuscript but could be clarified by the authors.
• Line 70, there is a typo “spay”=>spray.
• Figure 3: the labels of the x axes do not appear correctly in panels a—c.

Author Response

REFEREE 2: Figure 2c shows the MEMS resonance frequency upon 105 successive thermal cycles. The frequency change is significantly larger than the one shown in Figure 2b. I am, therefore, wondering if the frequency change is primarily driven by temperature-dependent properties of the P(VDF-TrFE) matrix? These data would therefore not be very informative on the resilience of the spin-crossover properties upon many heating/cooling cycles. This point is not critical for the claims of the manuscript but could be clarified by the authors.

AUTHORS: The referee is right, the MEMS dynamical properties are primarily determined by the thermomechanical properties of the matrix – this is indeed the reason for the considerable difference of frequency shifts between Fig. 2b and 2c. Yet, we feel the cycling reproducibility is an important result as any irreversible change in the composite properties (fatigue/damage of matrix or SCO) should appear in these data – and it is not the case. More specifically, the resilience of spin crossover properties were proven by the good reproducibility of the static MEMS properties (Fig 3c) through 10 cycles. We have added a comment to the paper on page 4 along these lines.

REFEREE 2: Line 70, there is a typo “spay”=>spray.

AUTHORS: Corrected.

REFEREE 2: Figure 3: the labels of the x axes do not appear correctly in panels a—c.

AUTHORS: Corrected.

Reviewer 3 Report

Authors report an investigation of static and dynamic properties of MEMS microcantilevers coated with composite thin films incorporating spin-crossover microparticles and piezo-/ferroelectric polymers. From the data, the authors extract typical parameters characterizing the actuation generated by the spin transition in the composite. This work is interesting and can be published in Magnetochemistry after providing some additional details.

How is the size distribution of the spin transition particles? The particles cannot be observed in the SEM image (Fig 1b). What is the scale of this image and the significance of 1500nm? Is there a preferential orientation of the particles within the film deposited on the device?. In this case, is it important for the data analysis?

It appears that on heating and on cooling the Curie temperatures of the polymer are just below the spin transition temperatures. It’s not clear to me whether the thermal cycling of the spin-transition particles only occur in presence of a polymer in the paraelectric phase. What is the consequence of this point on the observed effects?

Author Response

REFEREE 3: How is the size distribution of the spin transition particles?

AUTHORS: As noted on page 2, TEM analysis of the particles revealed ca. 1000 nm long and 200 nm large rod-shaped particles. We have not conducted extensive analysis of their size distribution, but the morphology of the particles appears fairly similar.

REFEREE 3: The particles cannot be observed in the SEM image (Fig 1b). What is the scale of this image and the significance of 1500nm?

AUTHORS: The scale is 200 micrometers – we have added a better quality image to see the scalebar properly. The significance of 1500 nm was only for internal use (it indicated the film thickness) we have removed it from the revised MS.

REFEREE 3: Is there a preferential orientation of the particles within the film deposited on the device?. In this case, is it important for the data analysis?

AUTHORS: We have not investigated particle orientation, but indeed it can be expected that the rod-shaped particles are oriented with their long axis parallel to the substrate plane. For the basic analysis presented in the paper this has no importance, but for a deeper analysis it will need to be taken into account. We have added a note to the revised MS on page 6 regarding this issue.

REFEREE 3: It appears that on heating and on cooling the Curie temperatures of the polymer are just below the spin transition temperatures. It’s not clear to me whether the thermal cycling of the spin-transition particles only occur in presence of a polymer in the paraelectric phase. What is the consequence of this point on the observed effects?

AUTHORS: The spin transition in the particles and the Curie transition in the matrix occurs in nearly the same temperature range (TCurie = 110 °C and 70 °C on heating and cooling, respectively, TSCO = 118 °C and 72 °C on heating and cooling, respectively). As a consequence, in the MEMS dynamical behavior, which is governed chiefly by the matrix properties, we cannot discriminate the SCO phenomenon properly. Luckily, the Curie transition affects much less the static MEMS properties, which allow for a clear assessment of the SCO events. We have made this point clear on page 6 of the revised MS.