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Films of conductive coordination network compounds are interesting as functional materials for charge storage, electrocatalysis, electrochromic switching, or conversion of light. The electrical con...

We experimentally and theoretically investigate the thermal conductivity and mechanical properties of polycrystalline HKUST-1 metal���organic frameworks (MOFs) infiltrated with three guest molecules: tetracyanoquinodimethane (TCNQ), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F$_{4}$-TCNQ), and (cyclohexane-1,4-diylidene)dimalononitrile (H$_{4}$-TCNQ). This allows for modification of the interaction strength between the guest and host, presenting an opportunity to study the fundamental atomic scale mechanisms of how guest molecules impact the thermal conductivity of large unit cell porous crystals. The thermal conductivities of the guest@MOF systems decrease significantly, by on average a factor of 4, for all infiltrated samples as compared to the uninfiltrated, pristine HKUST-1. This reduction in thermal conductivity goes in tandem with an increase in density of 38% and corresponding increase in heat capacity of ���48%, defying conventional effective medium scaling of thermal properties of porous materials. We explore the origin of this reduction by experimentally investigating the guest molecules��� effects on the mechanical properties of the MOF and performing atomistic simulations to elucidate the roles of the mass and bonding environments on thermal conductivity. The reduction in thermal conductivity can be ascribed to an increase in vibrational scattering introduced by extrinsic guest-MOF collisions as well as guest molecule-induced modifications to the intrinsic vibrational structure of the MOF in the form of hybridization of low frequency modes that is concomitant with an enhanced population of localized modes. The concentration of localized modes and resulting reduction in thermal conductivity do not seem to be significantly affected by the mass or bonding strength of the guest species.

For the first time, a procedure has been established for the growth of surface-anchored metal–organic framework (SURMOF) copper(II) benzene-1,4-dicarboxylate (Cu-BDC) thin films of thickness control with single molecule accuracy. For this, we exploit the novel method solution atomic layer deposition (sALD). The sALD growth rate has been determined at 4.5 Å per cycle. The compact and dense SURMOF films grown at room temperature by sALD possess a vastly superior film thickness uniformity than those deposited by conventional solution-based techniques, such as dipping and spraying while featuring clear crystallinity from 100 nm thickness. The highly controlled layer-by-layer growth mechanism of sALD proves crucial to prevent unwanted side reactions such as Ostwald ripening or detrimental island growth, ensuring continuous Cu-BDC film coverage. This successful demonstration of sALD-grown compact continuous Cu-BDC SURMOF films is a paradigm change and provides a key advancement enabling a multitude of applications that require continuous and ultrathin coatings while maintaining tight film thickness specifications, which were previously unattainable with conventional solution-based growth methods.

This investigation on metal-organic framework (MOF) HUKUST-1 films focuses on comparing the undoped pristine state and with the case of doping by TCNQ infiltration of the MOF pore structure. We have determined the temperature dependent charge transport and p-type conductivity for HKUST-1 films. Furthermore, the electrical conductivity and the current–voltage characteristics have been characterized in detail. Because the most common forms of MOFs, bulk MOF powders, do not lend themselves easily to electrical characterization investigations, here in this study the electrical measurements were performed on dense, compact surface-anchored metal-organic framework (SURMOF) films. These monolithic, well-defined, and (001) preferentially oriented MOF thin films are grown using quasi-liquid phase epitaxy (LPE) on specially functionalized silicon or borosilicate glass substrates. In addition to the pristine SURMOF films also the effect of loading these porous thin films with TCNQ has been investigated. Positive charge carrier conduction and a strong anisotropy in electrical conduction was observed for highly oriented SURMOF films and corroborated with Seebeck coefficient measurements. Van der Pauw four-point Hall sample measurements provide important insight into the electrical behavior of such porous and hybrid organic–inorganic crystalline materials, which renders them attractive for potential use in microelectronic and optoelectronic devices and thermoelectric applications.

High Entropy Alloys (HEAs) and Refractory High-Entropy Alloys (RHEAs) are novel potential materials for high-temperature applications [1]. NbMoTaW, a RHEAs, such as the one in Fig. 1, possess superior mechanical properties, combining high strength, outstanding thermal stability, and resistance to softening at high temperatures [2]. The influence of adding Vanadium [3], Tantalum [4], and Rhenium [5] to NbMoTaW alloys on the bulk mechanical behavior was investigated by the previous studies. In this research, the effect of adding Rhenium with different (Re0, Re0.5, Re1) on the microstructure and the mechanical properties of NbMoTaW thin films will be nvestigated. The larger the enthalpy of mixing in negative values, the higher the binding force between the elements, which has been enhanced with Rhenium addition. As for the entropy of mixing, it increased from 11.53 to 13.38 for Re0 and Re1, respectively. The higher the mixture entropy suggests a more stable solid solution. This is confirmed by calculating the thermodynamic parameters proposed by Yang et. Al [6] where they suggested that a mixture with δ < 6.6 and Ω > 1.1 correspond to solid solution formation. The anticipated crystal structure for the three samples is BCC structure according to the valence electron concentration (VEC) theory, where the VEC values were less than 6.87 as suggested by Gou et. Al [7]. The RexNbMoTaW HEAs thin films are fabricated using RF magnetron sputtering. The film thickness, deposition power, and temperature impact on the films’ characteristics are studied. Field emission (FE-SEM), X-ray diffraction (XRD), and nanoindentation are used to investigate the RexNbMoTaW thin films’ crystal structure, surface morphology, and mechanical properties. The mechanical properties of the thin films will be compared with their counterpart bulk materials. References Kim, H., et al., International Journal of Refractory Metals and Hard Materials, 2019. 80: p. 286-291. Feng, X., et al., Materials Letters, 2018. 210: p. 84-87. Senkov, O.N., et al., Intermetallics, 2011. 19(5): p. 698-706. Han, Z.D., et al., Materials Science and Engineering: A, 2018. 712: p. 380-385. Zhang, J., et al., Journal of Alloys and Compounds, 2020. 827. Yang, X. and Y. Zhang, Materials Chemistry and Physics, 2012. 132(2-3): p. 233-238. Guo, S., et al., Journal of Applied Physics, 2011. 109(10): p. 103505. Figure 1

Thermoelectric materials have attracted significant attention due to their potential application in power generation and refrigeration systems, because they can convert thermal energy into electric energy from waste heat recovery. Thin thermoelectric films can be used to create thermoelectric generators, where the power they create does not result in any additional emissions. PbTe, PbSe and Sb2Te3, Bi2Te3 present excellent choices for thermoelectric energy harvesting devices. Among these, Sb2Te3 and its derivatives have high Seebeck coefficient and good electrical conductivity, which make these the most promising p-type material for low temperature thermoelectric device. The high figure of merit ZT values at relatively low temperature make these exceptional thermoelectric materials. This study investigates Seebeck coefficient measurements of Sb2Te3 thin film synthesized by Atomic Layer Deposition (ALD) technology using a Veeco Nanotech thermal ALD reactor. For the ALD synthesis of Sb2Te3 we used SbCl3 as precursor1 and (Si(CH3)3)2Te Bis(trimethylsilyl)telluride as precursor 2. Antimony trichloride Sb2Te3 is a solid ALD precursor requiring preheating to the melting temperature around 73 ℃ to generate sufficient vapor pressure. A typical film morphology of ALD Sb2Te3 is shown in the SEM micrograph of Fig.1. The efficiency of thermoelectric materials is expressed by the dimensionless thermoelectric figure of merit, ZT = S2σT/ k, where S is the Seebeck coefficient, σ is the electrical conductivity, and k is the thermal conductivity. Because the crucial Seebeck coefficient factors directly into the equation by the power of two to determine ZT and the power factor, it is imperative to optimize the thermoelectric thin film material for maximum Seebeck coefficient. Maximizing the figure of merit ZT is challenging because in thermoelectric materials the quantities S, σ and κ are interrelated in such a way as to make independent control of these variables to increase ZT not straightforward. An increase in S typically results in a decrease of σ. Following the Wiedeman- Franz law a decrease in σ produces a decrease in the electronic contribution to κ complicating matters. Figure 1

Electronic packaging industries are in an ongoing transition to lead free soldering due to the adverse effect on environment and human health [1]. Sn-Ag-Cu (SAC) have been recognized as promising alternatives due to its low eutectic temperature, higher wettability and strength, superior resistance to creep and thermal fatigue. Surface roughness has a significant influence on mechanical parameters determined nanoindentation tests. Although research has been conducted to analyze the mechanical properties of bulk SAC material, there have been limited prior studies on SAC thin films and their mechanical properties since fabricating a smooth SAC thin film is a fundamental challenge. SAC thin films with four different Sn–Ag–Cu ternary eutectic composition: 96.5Sn-3.0Ag-0.5Cu, 95.5Sn-3.8Ag–0.7Cu, 95.5Sn-3.9Ag–0.6Cu & Sn-4.0Ag–0.5Cu will be deposited using RF magnetron sputtering with different deposition rates and annealed at various temperature to fabricate a smooth continuous film. Figures 1 and 2 depict SAC05 deposited using RF magnetron sputtering at Figure 1: SEM image of SAC-05 surface at 10,000X. 20W, 2.4 mTorr pressure, and argon flow flow rate of 20.5 sccm. Surface morphology will be examined using Field emission Scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Crystallinity of the deposited film will be examined using X-ray diffraction (XRD). Mechanical properties will be studied using nanoindentation [2]. Properties of the thin film will be compared with the bulk material with similar eutectic composition. References M. Abtew G. Selvaduray. (2000). Lead-free Solders in Microelectronics. Materials Science & Engineering. a Review Journal., 27(5-6), 95. Long, X., Wang, S., Feng, Y., Yao, Y., & Keer, L. M. (2017). Annealing Effect on Residual Stress of Sn-3.0Ag-0.5Cu Solder Measured by Nanoindentation and Constitutive Experiments. Materials Science and Engineering: A, 696, 90-95. Figure 1

The choice of a material and the engineering design that is intended to lead to a beam exit window capable of sustaining mechanical and thermal loads in a high-radiation environment, while minimizing the beam loss and maximizing the window lifetime is discussed. Thin titanium windows have been typically used in industrial accelerators in the tens of kW beam power [1]. The focus of this research is to conduct fundamental studies related to the choice of a material, from a material science point of view, for MW-class beam exit windows and an engineering design, including parameters such as the window size, thickness, and cooling scheme, suitable for industrial accelerators. CrMnV and CrMnTiV HEAs were selected for this study. According to Yang et al., [2], 1.1 and 6.6% should be expected as the criteria for forming high entropy stabilized solid solution phases. The two parameters of the CrMnV and CrMnTiV alloys are and respectively. Therefore, the two alloys are expected to be solid solution. The mechanical properties of CrMnV and CrMnTiV solid solution HEAs exit window prior to E-beam irradiation were measured using nanoindentation. The nanoindentation testing was carried out using XP Nanoindenter tester equipped with a three-sided diamond Berkovich indenter tip with maximum displacement of 2000 nm. The hardness is measured as 5.2 and 6.1 GPa for the bulk CrMnV and CrMnTiV solid solution HEAs at a depth of indentation of 900 nm respectively, Fig. 1. We also observe that both solid solution CrMnV and CrMnTiV HEAs depict indentation size effect. References Chmielewski A.G., Zimek, Z., Panta P., Drabik W., Radiat. Phys. Chem. 45 1029 (1995). Yang, X. and Y. Zhang, Prediction of high-entropy stabilized solid-solution in multi-component alloys. Materials Chemistry and Physics, 2012. 132(2-3): p. 233-238. Figure 1

Metal-oxide (MO) semiconductor-based gas sensors such as SnO2 and ZnO, have traditionally been the common materials of choice to be used for gas detection based on the mechanism of chemosensitivity. They are some of the most economic and efficient gas sensing materials, and they show a relatively quick response to several volatile organic compounds (VOCs). Doping of the MO nano surface lattices with noble and transition metals has been shown to further enhance their gas-sensing performance by improving the catalytic properties of the MO, ameliorating their response kinetics and selectivity toward a particular gas. However, the chemosensitivity method requires electrical contacts to the MO sensor material connecting the electrical circuits to detect electrical changes of the MO in response to volatile analytes. This approach introduces inherent errors into the measurements due to the need to make physical electrical contacts with the sensing MO semiconductor surface. In this talk, I will discuss the use of a microwaves-based detection technique known as Broadband dielectric spectroscopy (BDS) to rapidly interrogate a dynamic range of material characteristics such as polarizability, phase, electrical conductivity, etc. This technique eliminates the introduction of parasitic measurement errors which come about due to electrical contacts. Specifically, we show that the microwave signal propagation characteristics (i.e., S-parameters) induces chemical changes which allow us to characterize the detection of VOCs using ZnO doped with a selection of noble and transition metals as the sensing material, at temperatures under 100 °C.

In this work we report on a novel CaO ALD process development with a little used solid ALD precursor for Calcium. This forms part of a larger effort to synthesize 12CaO·7Al2O3 [C12A7], which is a new electronic oxide compound with very low work function and applications potentials in displays and Field-Emission (FE) Cathodes. Currently there are no existing thin film technologies for the conformal deposition of C12A7 electride films on complex device surfaces with nanoscale precision. Use of ALD to obtain precise nanoscale interleaving of CaO and Al2O3 layers over Micro-Hollow Cathode Discharge devices MHCD or FE devices allows conversion to correct alloying of C12A7 in the desired nano-layers. Success in reproducibly obtaining these layers will significantly benefit applications using cathodes, such as light sources, nano-sat thrusters, vacuum electronics and small-format microwave amplifiers. For the final C12A7 film, the challenge is to develop two ALD processes for two binary films in this case CaO and Al2O3 which must be synthesized as alternating nanolaminates in the correct stoichiometric ratio and are subsequently reacted under high temperature annealing. Since ALD of Al2O3 is already a well-known established ALD process, we had to focus on developing an ALD process for CaO. For this study we decided to utilize the relatively novel solid ALD precursor Bis(N,N-di-iso-propylformamidinato)calcium(II) dimer [Ca(famd)2], which is a low vapor pressure solid Ca amidinate precursor and which has to be reacted with ozone or DI H2O vapors. The chemical structure of the Calcium precursor is shown schematically in Fig. 1. The Al2O3 binary compound will be synthesized with trimethylaluminum (TMA) and DI water vapor. The low vapor pressure of Ca amidinate precursor Ca(famd)2 in solid form constitutes a major technical challenge and cannot be reacted by ALD in vapor draw mode but necessitated as new hardware a 150mL booster bubbler with dip tube for bubbling the molten precursor and the installation of a Low Vapor Pressure Delivery (LVPD) kit with bypass. For this presentation we will report the physical characterization of the ALD CaO film with FE-SEM surface morphology studies, SEM EDS elemental analysis of the final composition, X-ray diffraction XRD analysis and atomic force microscopy AFM. Fig. 1: Schematic of chemical structure of the novel solid ALD Ca amidinate precursor Bis(N,N-di-iso-propylformamidinato)calcium(II) dimer [Ca(famd)2] Figure 1

Traditional volatile organic compounds (VOC) detection with metal semiconductor oxide (MOS) sensing elements depends on chemical resistivity measurements which require electrical contact to the sensing materials [1]. These measurement contacts / probes are inadequate because they tend to introduce parasitic electrical errors which result in misleading reported resistivity values [2]. On the other hand, contactless broadband dielectric spectroscopy (BDS) is a potential alternative metrology [3]. In this paper, we will demonstrate that by using contactless broadband dielectric spectroscopy (BDS)-based metrology, in combination with a metal-organic framework (HKUST-1 SMOF) sensing element, we can avoid distortions in the reported resistivity values in gas monitoring, as well as develop new and unique mechanistic insights into the VOC detection. Specifically, we show that the experimental ambient influences the detection mechanism. The microwave insertion loss data (S21) shows that we lose resolution when N2 was used as the flushing agent, as compared to air, during the measurements. This suggests a possible competition between the ethanol and the N2 for the unsaturated copper centers inside the MOF. Therefore, we opted to use air as a flushing agent in the subsequent experiments. Additionally, the use of BDS enables stable VOC sensing in air at temperatures below 100 °C, which are well below the 200-300C normally used for VOC detection [1, 2]. 1) Huaping Wang et al 2021 J. Phys.: Condens. Matter 33 303001 2) Chem. Soc. Rev., 2020,49, 6364-6401, https://doi.org/10.1039/C9CS00778D 3) Papa K Amoah et al 2021 J. Phys. D: Appl. Phys. 54 135104

Metal-oxide (MO) semiconductor gas sensors based on chemical resistivity necessarily involve making electrical contacts to the sensing materials. These contacts are imperfect and introduce errors into the measurements. In this paper, we demonstrate the feasibility of using contactless broadband dielectric spectroscopy (BDS)-based metrology in gas monitoring that avoids distortions in the reported resistivity values due to probe use, and parasitic errors (i.e. tool-measurand interactions). Specifically, we show how radio frequency propagation characteristics can be applied to study discrete processes on MO sensing material, such as zinc oxide (i.e. ZnO) surfaces, when exposed to a redox-active gas. Specifically, we have used BDS to investigate the initial oxidization of ZnO gas sensing material in air at temperatures below 200 °C, and to show that the technique affords new mechanistic insights that are inaccessible with the traditional resistance-based measurements.

Whether the presence of adsorbates increases or decreases thermal conductivity in metal-organic frameworks (MOFs) has been an open question. Here we report observations of thermal transport in the metal-organic framework HKUST-1 in the presence of various liquid adsorbates: water, methanol, and ethanol. Experimental thermoreflectance measurements were performed on single crystals and thin films, and theoretical predictions were made using molecular dynamics simulations. We find that the thermal conductivity of HKUST-1 decreases by 40 – 80% depending on the adsorbate, a result that cannot be explained by effective medium approximations. Our findings demonstrate that adsorbates introduce additional phonon scattering in HKUST-1, which particularly shortens the lifetimes of low-frequency phonon modes. As a result, the system thermal conductivity is lowered to a greater extent than the increase expected by the creation of additional heat transfer channels. Finally, we show that thermal diffusivity is even more greatly reduced than thermal conductivity by adsorption., Metal-organic frameworks are attractive adsorbents for gas storage and separations, but appropriate heat dissipation is important for practical application. Here the authors use experiment and theory to show the impact of liquid adsorbates on thermal transport in metal-organic frameworks.

The inevitable current overshoot which follows forming in filamentary RRAM devices is often perceived as a source of variability that should be minimized. This sentiment has led to efforts to curtail the overshoot by decreasing the parasitic capacitance using highly integrated 1T-1R or 1R-1R device structures. While this is readily achievable in single device test structures, it poses an intricate design constraint for memory array designs. Several papers (Degraeve et al., 2010, 2014; Fantini et al., 2013; Raghavan et al., 2013; Padovani et al., 2015) suggest that there is insufficient current to form stable filaments for small parasitic capacitances and/or low current compliance levels. Thus, the relationship between minimizing overshoot current and improved filament stability is tenuous. In this study, we utilize the forming energy-based understanding of filamentary forming to reveal that the parasitic capacitance should be optimized, rather than minimized for better filament control.

The ability to transfer bulk quality III-N thin layers onto foreign platforms is a powerful strategy to enable high-efficiency and low-cost optoelectronic devices. Ion-cut using sub-surface defect engineering has been an effective process to split and transfer a variety of semiconductors. With this perspective, hydrogen-implanted AlN samples were annealed in air at temperatures ranging from 300°C to 600°C for 5 min to study the influence of pre-layer splitting treatments on the nanomechanical properties. There is a clear dependence of the hardness on implanted hydrogen implantation fluence. We observe that the as-implanted hardness increased from 18 GPa for the virgin reference sample to ∼25 GPa for the highest fluence of 3 × 1017 H cm-2 prior to annealing. In the case of reference single crystalline Si samples, a significant drop in the hardness and elastic modulus is observed in the H implantation-induced damage zone subsequent to thermal annealing , while for crystalline epitaxial AlN samples with 0.5 × 1017 and 2.0 × 1017 H implant fluences, the hardness increases and peaks until the thermal annealing temperature reaches 350°C and subsequently begins to drop thereafter for higher annealing temperatures. However, for the 1.0 × 1017 H implantation fluence the hardness continues to increase with increasing thermal annealing temperature.

To combat the large variability problem in resistive random access memory, current compliance elements are commonly used to limit the in-rush current during the forming operation. Regardless of the compliance element (1R-1R or 1T-1R), some degree of current overshoot is unavoidable. The peak value of the overshoot current is often used as a predictive metric of the filament characteristics and is linked to the parasitic capacitance of the test structure. The reported detrimental effects of higher parasitic capacitance seem to support this concept. However, this understanding is inconsistent with the recent successes of compliance-free ultrashort pulse forming which guarantees a maximum peak overshoot current. We use detailed circuit analysis and experimental measurements of 1R-1R and 1T-1R structures to show that the peak overshoot is independent of the parasitic capacitance while the overshoot duration is strongly dependent on the parasitic capacitance. Forming control can be achieved, in ultrashort pulse forming, since the overshoot duration is always less than the applied pulse duration. The demonstrated success of ultrashort pulse forming becomes easier to reconcile after identifying the importance of overshoot duration.

Resistive random access memory (RRAM) technology promises superior performance and scalability while employing well-developed fabrication processes. Conductance in insulating oxides employed in RRAM devices can be strongly affected by atomic-level changes that makes cell switching properties extremely sensitive to operation conditions inducing local structural modifications. This opens an opportunity to condition the memory cell stack by forming a conductive filament capable of high frequency, low energy switching. Certain materials with pre-existing conductive paths, in particular some polycrystalline oxides, like hafnia, are shown to respond well to this approach. For this class of materials, the concept of ultra-fast pulse technique as an ultimate method for assessing RRAM switching capabilities in circuitry operations is discussed. Hafnia-based cells demonstrate compliance-free (1R) forming with no current overshoot, low operation currents, and reduced variability.

We report on new fluctuation dynamics of the high resistance state of Hafnia-based RRAM devices after RESET. We observe that large amplitude fluctuations occur more frequently immediately after programming and their frequency of occurrence decays in the tens of microseconds. The fluctuation amplitude, on the other hand, does not decay noticeably over the entire millisecond read time. While post-programming instability and post-programming resistance dispersion have both been reported in the literature, the relaxation in the frequency of occurrence without a commensurate amplitude decay is new. Since picosecond pulses were used for our RESET operation, post-programming thermalization occurs on the nanosecond time scale. This clearly eliminates a thermally driven mechanism as the cause of the observed fluctuation behavior. Furthermore, reducing the READ voltage by tenfold does not have any effect and also eliminates read disturb as possible cause.

Thermoelectrics is a green renewable energy technology which can significantly contribute to power generation due to its potential in generating electricity out of waste heat. The main challenge for the development of thermoelectrics is its low conversion efficiency. One key strategy to improve conversion efficiency is reducing the thermal conductivity of thermoelectric materials. In this paper, the state-of-the-art progresses made in improving thermoelectric materials are reviewed and discussed, focusing on phononic engineering via applying porous templates and ALD deposited nanolaminates structure. The effect of nanolaminates structure and porous templates on Seebeck coefficient, electrical conductivity and thermal conductivity, and hence in figure of merit zT of different types of materials system, including PnCs, lead chalcogenide-based nanostructured films on planar and porous templates, ZnO-based superlattice, and hybrid organic-inorganic superlattices, will be reviewed and discussed.

This contribution describes the latest milestones of a multiyear program to build and operate a compact $\ensuremath{-}300\text{ }\text{ }\mathrm{kV}$ dc high voltage photogun with inverted insulator geometry and alkali-antimonide photocathodes. Photocathode thermal emittance measurements and quantum efficiency charge lifetime measurements at average current up to 4.5 mA are presented, as well as an innovative implementation of ion generation and tracking simulations to explain the benefits of a biased anode to repel beam line ions from the anode-cathode gap, to dramatically improve the operating lifetime of the photogun and eliminate the occurrence of micro-arc discharges.

Carbon is inherently abundant in nature and relatively inexpensive, which can potentially reduce the manufacturing cost of solar cells. In recent years, carbon has been used as a hole transport layer or counter electrode in perovskite solar cells. Herein, we demonstrate that carbon can also be used as a charge transport layer capable of enhancing the energy conversion efficiency of a CH3NH3PbI3-xClx solar cell when carbon is combined with PCBM. Particularly, we have been able to deposit an ultra-flat carbon layer using an e-beam irradiation method, which exhibited much better conductivity than the competitive PCBM/C60 layer. In addition, quantitative analysis of interfacial charge dynamics shows that the quenching efficiency of PCBM/carbon is comparable to that of PCBM/C60 but better interface defect passivation and improved series and shunt resistances were observed when PCBM/carbon was employed. For the photovoltaic performance, the reference perovskite solar cell fabricated from the widely used PCBM/C60 has a power conversion efficiency (PCE) of 14% while the perovskite solar cell with PCBM/carbon has an increased PCE of 16%. Our results demonstrate the potential of the use of cost-effective carbon for perovskite solar cells, which could reduce production costs.

Despite the overwhelming effort to improve the efficacy of resistive random access memory (RRAM), the underlying physics governing RRAM operation have proven elusive. A survey of the recent literature almost universally indicates that the remaining glaring issues center around variability as well as endurance. The initial filamentary “forming” process is often linked to these problems. This work details our recent efforts to bring the forming process under control and the resulting improvements in RRAM viability in hafnia-based devices. We track the forming process via a “forming energy” metric that allows for filament optimization. By removal of all current compliance elements, and their associated parasitics, a targeted forming energy is achieved using ultrashort voltage pulses. By tailoring the forming energy, we show remarkable endurance window control.

Surface Anchored Metal-organic-framework (SURMOF) films are designed quasi-crystalline compounds that consists of metal ions connected by organic ligands, forming highly ordered porous structures. The SURMOF films initially were considered to have limited applications in electronic devices because of their insulating character. Recently, several approaches were found to tune the electrical conductivity of MOFs [1]. One of the effective methods found is to infiltrate guest molecules inside the porous framework to transport ions, and hence to modulate the electrical properties of the host framework. MOF Cu3(BTC)2 (BTC: benzene tricarboxylate) is a typical MOF film known as HKUST-1 (Hong Kong University of Science and Technology 1). Its electrical conductivity could increase up to 7 orders of magnitude by introducing tetracyano-quinodimethane (TCNQ) guest molecules. Recently MOFs films received more attention in the fields of switching nanodevices [2], sensors, and thermoelectrics. reported MOF films loaded with TCNQ@Cu3(BTC)2 exhibiting high Seebeck coefficients and low thermal conductivity [3]. However, the low electrical conductivity reduces the figure of merit ZT of MOFs. In this work we present alternating MOF/PbTe and MOF/PbSe nanolaminate structure synthesized by alternately depositing SURMOF films and lead chalcogenide films. The SURMOFs were fabricated by liquid phase epitaxy (LPE) technique. Ethanoic solution of copper acetate hydrate (1mM) and organic linker solution (1, 3, 5-benzenetricarboxylic acid) (0.2mM) were used as precursors for HKUST-1 MOFs. TCNQ was loaded to modulate electrical conductivity of MOFs. PbTe and PbSe were synthesized on the top of MOFs by thermal ALD technology. Lead bis(2,2,6,6-tetramethyl-3,5-heptanedionato) (Pb(C11H19O2)2), (trimethylsilyl) telluride ((Me3Si)2Te) and (trimethylsilyl) selenide ((Me3Si)2Se) were employed as the chemical ALD precursors for lead, telluride and selenide, respectively. 20 sccm N2 was used as a carrier gas to transport the chemical precursors into the ALD reaction chamber. The ALD growth temperature was 150 ˚C. The solid lead precursor was volatilized at a temperature of 170 ˚C, the liquid Te precursor required heating to 40 ˚C, and the liquid Se precursor was kept at room temperature. The chamber base pressure was kept at 30 mTorr. Composite nanolaminate structure of MOF/PbTe and MOF/PbSe with film thickness of 10 nm/ 10 nm, 20 nm/ 20 nm, and 60 nm/ 60 nm were fabricated and investigated. Several physical characterization techniques have been employed to determine the surface characters of the sample. The samples were characterizated by X-ray diffraction (XRD) for film crystal structure, and by field emission scanning electron microscopy (FE-SEM) for film morphology and structure. For thermoelectrical properties of the sample, Seebeck coefficient both in vertical and horizontal directions were measured. Electrical conductivity and thermal conductivity of the films were investigated as well to envaluate ZT value of the samples. Figure 1 shows the IV characteristics of MOF films loaded with TCNQ. The linear IV curve indicates Ohmic conduction in TCNQ loaded MOFs. Figure 2 displays the Seebeck coefficient of TCNQ loaded MOF films over a temperature range of 290 K ~330 K. The maximum Seebeck coefficient of the film occurs at 290 K and the positive Seebeck coefficient reveals positive charge carriers in the MOF film. References: 1. Talin, A.A., et al., Tunable electrical conductivity in metal-organic framework thin-film devices. Science, 2014. 343(6166): p. 66-69. 2. Wang, Z., et al., Resistive Switching Nanodevices Based on Metal–Organic Frameworks. ChemNanoMat, 2016. 2(1): p. 67-73. 3. Erickson, K.J., et al., Thin Film Thermoelectric Metal–Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity. Advanced Materials, 2015. 27(22): p. 3453-3459. Figure 1

Temporary bonding has attracted renewed interest for the integration of dissimilar materials in device structures, which cannot be achieved by epitaxial growth techniques alone when the lattice mismatch between the dissimilar materials is too large. In this quest polydimethylglutarimide (PMGI) based lift-off (LOR) resist has been found suitable to serve as a temporary sacrificial adhesive for clean film exfoliation, layer transfer and temporary bonding applications [1]. Furthermore polydimethylglutarimide (PMGI) lends itself easily for temporary bonding purposes, because subsequent complete de-bonding can be readily achieved using an n-methyl-2-pyrrolidone (NMP)-based solvent. In this study we focus on the nanomechanical analysis of PMGI using the Nanoindenter XP by Agilent with continuous stiffness measurement (CSM) attachment. This investigation is aiming to elucidate the relationship between bonding parameters, bond strength and the nanomechanical properties of Young’s modulus and hardness of polydimethylglutarimide (PMGI) as a function of prebake temperature and PMGI resist film thickness. The influence of the spin-on process and the pre-bake treatment on the structure and properties of the PMGI adhesive layers is discussed and correlated to the resulting hardness, modulus and final bond strength and the corresponding Thermal Gravimetric Analysis (TGA) tracking the mass loss of the resist as a function of temperature. . For this experiment Si wafers were first cleaned with standard clean 1 (H2O:NH4OH:H2O2=5:1:1). Afterwards the wafers were spin coated at 2000 rpm with LOR 5A (from MicroChem), which is based on PMGI, and subsequently pre-baked in order to partially evaporate the solvent in the resist. The spin speeds were optimized to achieve 1.00 μm and 500 nm resist thickness for this investigation. Thicker lift-off resist thickness is not practical for a load-depth analysis with a Berkovich tip, because the nanoindenter is depth limited. The solvent, which is used with PMGI lift-off resist is cyclopentanone with a boiling point of 131ºC. With a glass transition point (Tg) of 180-190 ºC, we have chosen to conduct a series of prebakes at 50 °C, 70 °C, 90 °C, 110 °C and 130 °C, 150 °C & 160 °C each for 5 min and to benchmark the results against the hardness and bond strength achieved after thermal compression bonding of Silicon wafer pairs via adhesive PMGI layers at 250 C. This series of different thermal treatments influenced the resist mechanical properties, hardness and modulus. Our nanoindentation experimental results are indicated in Figure 1. As expected, the 500 nm films exhibited high hardness values as compared to the 1 µm thick films. Both PMGI lift-off resist films hardness approach the Si substrate hardness. References: [1] T. Matsumae, A. D. Koehler, D. Greenlee, T. J. Anderson, H. Baumgart, G. G. Jernigan, K. D. Hobart and F. J. Kub, ECS Journal of Solid State Science and Technology, 4 (7) P1-P5 (2015). Figure 1

Thin metallic films and coatings of Ag, Cu, and Ni for interconnect and contact in next generation nanoelectronic are expected to have high conductivity, high temperature stability, good ohmic contacts to both p- and n- type semiconductors, and also superb mechanical properties. These metallic thin film are used in a variety of electronic applications due to their low cost of production, non-toxicity and excellent electrical conductivity. However, their applications in nanoelectronics are still limited due to diffusion into the commonly used silicon substrates and the tendency of developing oxides under atmospheric conditions. Thin oxide layers form immediately on metallic films surfaces’ upon contact with air even at room temperature. Thin metallic oxide films `tend to exhibit brittle behavior with a sharp jump in the mechanical properties such as hardness and modulus and results in high resistivity. Although the formation of oxides is still perceived as the primary impediment in using thin metallic films in nanoelectronics, thin metallic films exhibit promising applications in large-area electronics such as memories, MEMS, and microprocerssors. Metallic films of Ag, Cu, and Ni each of 150, 300, 600 and 1000 nm thick were deposited on Si using E-beam evaporation and deposition technique. A shutter was used to successively cover increments of 1² of the wafer at a time, starting with the wafer fully uncovered. A thin titanium layer of 10 nm is first deposited over the entire Si wafers followed by 150, 300, 600, and 1000 nm of the 2² target. Vacuum conditions at the start were ~1x10-7 torr and reached as high as 2x10-6 torr during the copper deposition due to outgassing. Similar vacuum conditions were maintained for the other films. The Ag, Cu, and Ni films thickness were verified using field emission scanning electron microscopy. A sample cross sectional FE-SEM of the 150 nm thick Ag film is shown in Figure1. Nanocrstalline grain structure formation is observed to dominate the crystal film growth. The nanomechanical properties were measured using nanoindentation to determine the modulus and hardness of the Ag, Cu, and Ni films. Indentations of 1/3 and 2/3 of the film thickness in addition to 2 µm deep indents were performed on each film to study the film properties irrespective of the Si substrate influence as well as the substrate influence on the mechanical properties. Figures 2 and 3 depict hardness versus normalized depth of indentation to film thickness for Ag and Cu. The hardness increases as the film thickness decreases and remains nearly flat (no size effects) for the same film with depth of indentation except for the very thin films as they suffer what is known as tapping effect [1]. References: [1] David E. Stegal, Md. Abdullah Mamun, Bryan Crawford, and Abdelmageed Elmustafa, J. Mater. Res., Vol. 27, No. 12, Jun 28, 2012. Figure 1

Single-crystal, low-cost, low-temperature, hydrothermal synthesis ZnO nanorods were grown on ZnO fine grained random nanocrystalline seed layers prepared by atomic layer deposition (ALD) and benchmarked against spin coating techniques for seed layers. As the growth temperature increased to 90 °C, more nanorods were observed on the samples. Increasing the growth time from 16 h to 24 h resulted in higher nanorod density for the ALD seeded samples, but less nanorods for the spin-coated seeded samples. Our work demonstrates that the final density of ZnO nanorods and their shape and size are primarily influenced by the characteristics of the ZnO seed layer, such as composition, morphology, grain size, impurity content and thickness, as well as the time spent heated. At ∼10 nm the ALD generated random polycrystalline seed layer grains were one order of magnitude smaller compared to the spin coating generated seed layer grains which appear structurally different as ∼100 nm columnar grains. This morphological seed layer difference caused the ZnO nanorods grown on spin coated seed layers to reach only ∼34% of the average nanorod length achieved on ALD seeds with comparable rod diameter and can also account for the diminished nanorod density. The exact mechanism of how the seed layer affects nucleation and subsequent nanorod growth is unknown, but results suggest that there is a significant impact. Future research can be directed to investigating the ability of metal nanoparticles to self-assemble on these nanorods and to further nanoscale catalysis.

Metal organic frameworks (MOFs) are crystalline three-dimensional porous solids featuring a high surface area, which have attracted considerable attention in a wide range of applications e.g. in catalysis, hydrogen storage, gas separation, thermoelectric applications or as chemical sensors. Beyond solvothermal synthesis of bulk MOF crystals, growing MOFs thin films has been limited so far to rather conventional solution-based techniques. However, traditional growth methods from solution such as spin-coating, spray-coating or dip-coating generate MOFs thin films with a rather low film quality and an alarming lack of a precise film thickness control under 1 nm. This renders them unsuitable for most industrial applications and severely limits their future application potential. Atomic layer deposition (ALD) provides this capability, but is limited by the necessity to use gaseous precursors in vacuum conditions at temperatures typically above 100°C. This is incompatible with the typically high temperature sensitivity of many hybrid metal-organic compounds such as the MOFs. In this perspective, we have transferred the principles of ALD to precursors dissolved in liquid solvents. The ‘solution ALD’ (sALD) method can be implemented in a variety of microfluidic or slot-die processing devices. We have demonstrated that the principles of classical, gas-based ALD —self-limiting surface reactions— are reproduced in sALD. sALD shares the fundamental properties of standard ‘gas ALD’ (gALD), in particular the self-limiting surface chemistry and the ability to coat deep pores in a conformal manner Furthermore, sALD allows the experimentalist to design new, advantageous, reactions of known semiconductors (oxides, heavier chalcogenides), or to deposit materials otherwise inaccessible to ALD altogether, such as polymers, ionic solids, and metal-organic frameworks. They may be obtained in highly pure, crystalline form at room temperature, either as planar films or as conformal coatings of porous substrates. Based on these advances, we have been able to make the first sALD-derived films of a MOF, Cu-BDC. At any chosen thickness, sALD MOF films feature significantly lower roughness and better adhesion than those generated by the best spray-coating and dip-coating methods available currently.

Germanium-on-insulator (GeOI) films fabricated using the SMART CUT wafer bonding and film exfoliation technology were investigated for the mechanical properties and induced phase transformations by using nanoindentation and Raman spectroscopy experiments. The hardness and modulus results of the GeOI films are significantly different from the published SOI literature and bulk germanium results obtained by Liu et al., 2020 [1] and SOI films results obtained by Miller et al., 2007 [2]. From our measured hardness results of 8 to 10 GPa for very thin single crystal Ge(100) films compared to 13.1 GPa for Bulk Ge (100), one can conclude that the thinning of crystalline Ge films leads to a considerable softening of the crystalline Ge resulting in less brittle robust films. Similarly, our measured modulus of 130 to 140 GPa for thin Ge (100) films compared to the reported bulk Ge (100) value of 157 GPa corroborates these research findings. The GeOI films are softer and more flexible as compared to bulk Ge hardness and stiffness properties. The Raman spectroscopy of the spherical indents indicate bands of metastable Ge phases @ 220 cm-1, 195 cm-1 and 184 cm-1 wavenumbers. Our results demonstrate that a spherical indenter impacted a wider area of contact and produced GeOI indented surfaces free of cracks and fracture. The spherical indenter tip kept the Ge top layer intact when compared to the Berkovich indenter tip during penetration. In contrast, the Berkovich indenter tip developed excessive fracture that resulted in displacing the Ge top layer sideways and exposed the Si substrate underneath revealing Raman spectra bands of metastable Si phases @ 350 cm-1, 399 cm-1 and 430 cm-1. Apart from the well documented electrical advantages of GeOI, the reported research on the nanomechanical properties reveals considerable softening and flexibility of the very thin exfoliated single crystal Ge films that promise added benefits and further implications for enhancing potential device application of GeOI wafers for process integration. 1.] N. Liu, X-J Yang, Z. Yu, and L. Zhao, Trans. Nonferrous Met. Soc. China, 30, 181 (2020). 2.] N. Miller, K. Tapily, H. Baumgart, G.K. Celler, F. Brunier, and A.A. Elmustafa, Mater. Res. Soc. Symp. Proc. Vol. 1021 © 2007 Materials Research Society, 1021-HH05-24. Boston, Massachusetts. (2007).

Thermoelectric materials based on porous hybrid and MOFs constitute a very recent development, with many new and undiscovered phenomena for the research field. These porous Hybrid materials and MOF (Metal-Organic-Framework) films represent modern designer materials that exhibit many requirements of a near ideal and tunable future thermoelectric (TE) material. It is anticipated that especially the inherent porosity can be used advantageously in the design and simulation predictions of future thermoelectric materials. In principle, porous Hybrid and MOFs materials can comply with most of the requirements of an ideal and tunable future thermoelectric (TE) material. In contrast to traditional semiconducting bulk thermoelectric materials, porous hybrid MOF templates can be used to overcome some of the constraints of physics in bulk thermoelectric materials. These porous hybrid systems are amenable for simulation and modeling to design novel optimized electron-crystal phonon-glass materials with potentially very high Figure of Merit (ZT) numbers. Porous MOF and Hybrid materials possess an ultra-low thermal conductivity, which can be further modulated by phonon engineering within their complex porous and hierarchical architecture to advance the thermoelectric figure of merit ZT. This class of novel materials offers new approaches to the design of complex and hierarchical porous structures, possessing ultra-low thermal conductivity, which are able to trap, and localize phonons, thus resulting in a new generation of thermoelectric materials with a high ZT number. This work is demonstrating recent results of MOF thermoelectric Materials and provides a future outlook to the search for the next generation thermoelectric porous Hybrid and MOF materials, which could be part of a green renewable energy revolution with novel materials of sustainable high ZT values.

Metal-organic frameworks (MOFs) are porous and crystalline Coordination Network Compounds (CNCs), also referred to as porous coordination polymers (PCPs), which consist of inorganic metal (or metal/oxo) clusters connected by organic linkers. Surface Anchored Metal-organic-framework (SURMOF) films consist of quasi-liquid phase epitaxially grown highly ordered crystalline MOF films. For this study we used MOF Cu3(BTC)2 (BTC: benzene tricarboxylate) films, also known as HKUST-1 (Hong Kong University of Science and Technology-1), which were infiltrated with tetracyano-quinodimethane (TCNQ) guest molecules to modulate the charge transport characteristics. HKUST-1 MOF thin films have been grown using a liquid phase epitaxy (LPE) spray method in which the metal-containing solution [1 mmol Cu(OAc)2] and the linker solution [0.1 mmol BTC] are sprayed alternately on modified silicon substrates. Subsequently, the samples were immersed into an ethanoic TCNQ solution. We report on localized charge transfer processes at microwave frequencies of porous metal-organic framework (MOF) HKUST-1 Cu2(BTC)3 samples. As part of this study we will compare measurements done in the HKUST-1 pristine form of the material with open pores and HKUST-1, where the pores have been infiltrated with tetracyano-quinodimethane (TCNQ), resulting in a hybrid structure with enhanced electrical conductivity and a significant measurable effect in the microwave propagation characteristics [1]. We present data and analysis from an evaluation of pristine and loaded HKUST-1 SURMOF films using the contactless broadband microwave dielectric spectroscopy (BDS). The technique enables the accurate operando evaluation of the electrical and magnetic properties of materials without compromising the kinetic conditions of the experiment. The BDS method is uniquely suitable for investigating charge transfer reactions, regardless of the nature of the charge carriers, i.e., electrons and holes [2]. As such, these material state-sensitive parameters could be used to monitor charge transfer changes in the SURMOF and SURMOF-TCNQ hybrid analytes. [1] G. M. Espallargas and E. Coronado, “Magnetic functionalities in MOFs: from the framework to the pore”, Chem. Soc. Rev., 2018,47, 533, DOI: 10.1039/c7cs00653e [2] A. M. Wernbacher et al, Operando Electrical Conductivity and Complex Permittivity Study on Vanadia Oxidation Catalysts, J. Phys. Chem. C 2019, 123, 8005−8017, DOI: 10.1021/acs.jpcc.8b07417

Among the various Metal Oxide Semiconductor (MOS) gas sensor types, solid-state gas sensors based on ZnO nanostructures have been widely used due to their properties of large exciton binding energy, wide band gape of 3.37 eV, good electrical conductivity, low cost, and high mechanical stability. In this work, ZnO nanotube nanostructures were employed for gas sensing of ethanol vapor concentrations, which is aided by their high electrochemical stability, nontoxicity, and, especially, high surface-to-volume ratio. Multiple coaxial nested ZnO nanotubes were synthesized inside porous membranes and porous templates to further enhance the sensing response to ethanol vapors with vastly increased reaction surfaces. In this study, ZnO nanotubes were synthesized by Atomic Layer Deposition (ALD) on porous Anodic Aluminum Oxide (AAO) templates with sacrificial Al2O3 layers and on porous Si membranes. The Al2O3 sacrificial layers were synthesized on porous AAO and porous Si by ALD with TMA (Al2(CH3)6) and DI water as ALD precursors. Then ZnO thin films were deposited on the surface of the sacrificial layer with precisely controlled thickness by ALD. The entire ALD procedure is considered as one ALD super cycle. More super cycles were applied to synthesize additional coaxial ZnO nanotubes. For the final removal of the sacrificial layer, Precision Ion Polishing System (PIPS) was used to first remove the top ALD surface cover. In this way, the Al2O3 sacrificial layers were exposed for Sodium Hydroxide (NaOH) etching. The objective of the Al2O3 sacrificial layers was to expose additional reactive sensing surfaces to react with the target gas by subsequent removal of these sacrificial layers. Finally, after the sacrificial layers were completely removed by wet chemical NaOH dissolution, the nested coaxial ZnO nanotube gas sensor design was fabricated with multiple sensing surfaces. To investigate the sensing performance of ZnO nanotube gas sensors to ethanol vapor, a gas sensor testing system was developed with a sealed reaction chamber and control system with stable temperature control and accurate concentration control. The sensing performance of single ZnO nanotubes, two nested coaxial ZnO nanotubes, and three nested coaxial ZnO nanotubes to ethanol vapor were measured and analyzed under various ethanol vapor concentrations and at different operating temperatures. The ZnO nanostructures sensing results on ethanol vapor demonstrated the sensing performance was considerably enhanced due to the increased surface to volume ratio in the ZnO tube structures.

Historically, metal-oxide semiconductor-based gas sensors, such as SnO2 and ZnO, have been used to detect gases based on chemiresistivity [1]. In this approach, the electrical changes in response to analytes are measured with electrical circuits, that necessarily involve making electrical contacts to the sensing materials. These contacts are imperfect and introduce errors into the measurements. In this paper, we will demonstrate the feasibility of BDS-based metrology in addressing this gap in metrology to avoid these tool-measurand interactions / parasitic errors. Specifically, we will discuss how radio frequency (RF) propagation characteristics can be applied to probe and study charge transfer chemical changes in these metal-oxide VOC sensing materials. For this study, the solid-state gas sensor device under test consisted of hydrothermally synthesized ZnO nanorods grown on a fine grain seed layer of atomic layer deposition (ALD) ZnO on a silicon substrate. The sample was placed on a waveguide situated in a controlled environment to study the redox reactions of the ZnO sensor detecting ethanol target gas under thermal heating. In this configuration, the ZnO gas sensing element couples to the microwave through an evanescent mode. The temperature of the assembly was varied from room temperature to approximately 180 °C, in a variety of gaseous environments, while continuously monitoring the microwave signal going through the waveguide. Analysis of the BDS data (at specific frequencies) gave us electrical information that can be correlated to charge-transfer reactions involving the defects in the ZnO material and the molecules in the gaseous environment. For example, according to the S21 data, the sample became more resistive as temperature increased. This can be attributed to the redox reactions occurring on the ZnO nanorod gas sensor surface. Illustratively, Figure 1 shows time-lapse evolution on microwave signal loss in the experimental setup attributable to the discrete events occurring in the ZnO in response to various environmental conditions. The resistivity (as indicated by the S21) of the ZnO is stable below 120°C. At 120C, the system becomes increasing resistive with time, possibly as adsorbed water molecules on the ZnO rods desorb and to the healing of the ZnO surface defects, in a distinct two-step process [1]. Finally, the system became less lossy (i.e., electrical resistivity decreased) when ethanol target gas (technical grade C2H5OH, EtOH) was injected into the reactor. However, this decrease in resistivity might have been influenced by the decrease in temperature once the EtOH was introduced. From the S-parameters, we calculate a microwave attenuation constant (i.e. the real part of the microwave propagation constant) which quantified energy dissipation into the ZnO material. The attenuation constant data suggest the redox reaction induced changes in the semiconductor rods are reversible within the temperature range in this experiment. To the best of our knowledge, such detailed description of the discrete events that occur in the metal-oxide sensing material cannot be obtained with the traditional electrical DC resistivity measurements. In the future, we may be able to use this technique to discern differences, and distinguish between ZnO surface- and bulk reactions, as well as identify / characterize point defects. References H-J. Kim, and J.-H. Lee, “Highly sensitive and selective gas sensors using p-type oxide semiconductors: Overview”, Sensors and Actuators B 192 (2014) 607– 627 Heine, F. Girgsdies, A. Trunschke, R. Schlögl, and M. Eichelbaum, “The model oxidation catalyst α-V2O5: insights from contactless in situ microwave permittivity and conductivity measurements”, Applied Physics A, vol. 112, pp. 289–296, 2013 DOI 10.1007/s00339-013-7800-6 Figure 1

Germanium-on-insulator (GeOI) films fabricated using the Smart Cut™ wafer bonding and film exfoliation technology were investigated for the mechanical properties and induced phase transformations by using nanoindentation and Raman spectroscopy experiments. The hardness and modulus results of the GeOI films are significantly different from the literature published Silicon-on-Insulator and bulk germanium results. The GeOI films are softer and more flexible as compared to bulk Ge hardness and stiffness properties. The Raman spectroscopy of the spherical indents indicates bands of metastable Ge phases @ 220 cm−1, 195 cm−1, and 184 cm−1 wavenumbers. Our results demonstrate that a spherical indenter impacted a wider area of contact and produced GeOI indented surfaces free of cracks and fracture. The spherical indenter tip kept the Ge top layer intact when compared to the Berkovich indenter tip during penetration. In contrast, the Berkovich indenter tip developed excessive fracture that resulted in displacing the Ge top layer sideways and exposed the Si substrate underneath revealing Raman spectra bands of metastable Si phases @ 350 cm−1, 399 cm−1, and 430 cm−1.

Metal hexacyanometallates (MHCMs) form a large family of coordination network compounds [1]. They have variable and tunable physical and chemical properties due to the three-dimensional framework of alternating metal knots connected by a non-innocent small bridging ligand forming interconnected channels that can accommodate solvent molecules and counter ions. Therefore, these materials have been comprehensively studied in several different fields, including, functional materials for charge storage, electrocatalysis, electrochromic devices or light harvesting. For the mentioned applications, conductivity is critical, to which i) electronic conductivity by electrons or holes [2], ii) ionic conductivity by mobile alkali ions in the channels of the MHCMs [3], and iii) proton conductivity [4] may contribute. In larger scale for real application, the conductivity depends not only on intrinsic material properties but also on the morphology. Morphology (particularly grain boundaries) plays an important role in determining the pathway of charge carrier transport (electrons and holes) in the film. From first principles it is expected that continuous compact crystalline films will have better electrical conductivity. Here, we present results on copper hexacyanoferrate which demonstrate particularly well the variation of film morphology and its influence on conductivity as a key functional property. We succeeded in devising a simple method for preparation of metal hexacyanoferrates as a thin continuous film by a combination of sonication-assisted casting and vapor-assisted conversion, without the need for surface pre-treatment. This is especially helpful for coating substrates composed of different materials. Films obtained in this way show conductivities higher than that of powder pellets with equivalent crystal structure. Temperature-dependent and humidity-dependent measurements on powder pellets revealed the activation energies for charge transport as well as the role of zeolitic water in facilitating the charge transfer. 1. Paolella, A.; Faure, C.; Timoshevskii, V.; Marras, S.; Bertoni, G.; Guerfi, A.; Vijh, A.; Armand, M.; Zaghib, K. A Review on Hexacyanoferrate-based Materials for Energy Storage and Smart Windows: Challenges and Perspectives. Mater. Chem. A 2017, 5, 18919–18932. 2. Behera, J. N.; D’Alessandro, D. M.; Soheilnia, N.; Long, J. R. Synthesis and Characterization of Ruthenium and Iron−Ruthenium Prussian Blue Analogues. Mater. 2009, 21, 1922–1926. 3. Ishizaki, M.; Ando, H.; Yamada, N.; Tsumoto, K.; Ono, K.; Sutoh, H.; Nakamura, T.; Nakao, Y.; Kurihara, M. Redox-Coupled Alkali-Metal Ion Transport Mechanism in Binder-Free Films of Prussian Blue Nanoparticles. Mater. Chem. A 2019, 7, 4777–4787. 4. Ohkoshi, S.-I.; Nakagawa, K.; Tomono, K.; Imoto, K.; Tsunobuchi, Y.; Tokoro, H. High Proton Conductivity in Prussian Blue Analogues and the Interference Effect by Magnetic Ordering. Am. Chem. Soc. 2010, 132, 6620–6621.