Impact of pressure and temperature on the broadband dielectric response of the HKUST-1 metal-organic framework
Arun S. Babal, Lorenzo Donà, Matthew R. Ryder, Kirill Titov, Abhijeet K. Chaudhari, Zhixin Zeng, Chris S. Kelley, Mark D. Frogley, Gianfelice Cinque, Bartolomeo… 展开作者
Arun S. Babal, Lorenzo Donà, Matthew R. Ryder, Kirill Titov, Abhijeet K. Chaudhari, Zhixin Zeng, Chris S. Kelley, Mark D. Frogley, Gianfelice Cinque, Bartolomeo Civalleri, Jin-Chong Tan
Herein we employed high-resolution spectroscopic techniques in combination with periodic ab initio density functional theory (DFT) calculations to establish the different polarization processes for a porous copper-based MOF, termed HKUST-1. We used alternating current measurements to determine its dielectric response between 4 Hz and 1.5 MHz where orientational polarization is predominant, while synchrotron infrared (IR) reflectance was used to probe the far-IR, mid-IR, and near-IR dielectric response across the 1.2 THz to 150 THz range (ca. 40 - 5000 cm^-1) where vibrational and optical polarizations are principal contributors to its dielectric permittivity. We demonstrate the role of pressure on the evolution of broadband dielectric response, where THz vibrations reveal distinct blue and red shifts of phonon modes from structural deformation of the copper paddle-wheel and the organic linker, respectively. We also investigated the effect of temperature on dielectric constants in the MHz region pertinent to microelectronics, to study temperature-dependent dielectric losses via dissipation in an alternating electric field. The DFT calculations offer insights into the physical mechanisms responsible for dielectric transitions observed in the experiments and enable us to explain the frequency shifts phenomenon detected under pressure. Together, the experiments and theory have enabled us to glimpse into the complex dielectric response and mechanisms underpinning a prototypical MOF subject to pressure, temperature, and vast frequencies.
There is rising interest on low-k dielectric materials based on porous metal-organic frameworks (MOFs) for improved electrical insulation in microelectronics. Herein, we demonstrate the concept of MOF dielectric sensor built from a single crystal of HKUST-1. We study guest encapsulation effects of polar and non-polar molecules, by monitoring the transient dielectric response and AC conductivity of the crystal exposed to different vapors (water, I2, methanol, ethanol). The dielectric properties were measured along the <100> crystal direction in the frequency range of 100 Hz to 2 MHz. The dielec…
Metal-organic framework (MOF) thin-films show unmatched promise as smart membranes and photo-catalytic coatings. However, their nucleation and growth resulting from intricate molecular assembly processes are not well understood, yet crucial to control the thin-film properties. Here, we directly observe the nucleation and growth behaviour of HKUST-1 thin-films by real-time in-situ AFM at different temperatures in the Cu-BTC solution. In combination with ex-situ infrared (nano-)spectroscopy, synthesis at 25°C reveals initial nucleation of rapidly growing HKUST-1 islands surrounded by a continuou…
Introducing hierarchical pore structure to microporous materials such as metal-organic frameworks (MOFs) can be beneficial for reactions where the rate of reaction is limited by low rates of diffusion or high pressure drop. This advantageous pore structure can be obtained by defect formation, mostly via post-synthetic acid etching, which has been studied extensively on water-stable MOFs. Here we show that a water-unstable HKUST-1 MOF can also be modified in a corresponding manner by using phosphoric acid as a size-selective etching agent and a mixture of dimethyl sulfoxide and methanol as a di…
Understanding of the complex mechanical behavior of metal-organic frameworks (MOF) beyond their elastic limit will allow the design of real-world applications in chemical engineering, optoelectronics, energy conversion apparatus, and sensing devices. Through in situ compression of micropillars, the uniaxial stress-strain curves of a copper paddlewheel MOF (HKUST-1) were determined along two unique crystallographic directions, namely the (100) and (111) facets. We show strongly anisotropic elastic response where the ratio of the Young's moduli are E(111) ~ 3.6 x E(100), followed by extensive pl…
In this work, we demonstrate BNAs high potential for efficient generation of high power THz using ytterbium laser wavelengths. We study the generation theoretically and experimentally using laser wavelength of 960-1150 nm. Broadband pulses of 0-7 THz and high efficiency of 0.6% are demonstrated.
We are reporting on terahertz generation from organic crystal BNA using a 1.15 to 1.55 um near infrared pump. We observed a very large emission spectrum extending up to 7 THz, compared to 2.5 THz from Ti:Sa pump in previous reports. The maximum optical-to-THz conversion efficiency in our experiment was 0.8% at 1 kHz repetition rate and without saturation leading to a peak electric field of 1 GV/m. Our results show pronounced phase matching privilege for intense terahertz generation using a pump in the 1.15 to 1.25 um range where high energy near infrared pump sources operate.
Materials based on the cubic perovskite unit cell continue to provide the basis for technologically important materials with two notable recent examples being lead-based relaxor piezoelectrics and lead-based organic-inorganic halide photovoltaics. These materials carry considerable disorder, arising from site substitution in relaxors and molecular vibrations in the organic-inorganics, yet much of our understanding of these systems derives from the initial classic work of Prof. Roger A. Cowley, who applied both theory and neutron scattering methods while at Chalk River Laboratories to the study…
We characterize the terahertz (THz) generation of N-benzyl-2-methyl-4-nitroaniline (BNA), with crystals ranging in thickness from 123-700 μm. We compare excitation using 800-nm and 1250 to 1500-nm wavelengths. Pumping BNA with 800-nm wavelengths and longer near-infrared wavelengths results in a broad spectrum, producing out to 6 THz using a 100-fs pump, provided the BNA crystal is thin enough. ~200 μm or thinner crystals are required to produce a broad spectrum with an 800-nm pump, whereas ~300 μm thick crystals are optimal for broadband THz generation using the longer wavelengths. We report t…
We present the frequency-dependant (dynamic) dielectric response of a group of topical polycrystalline zeolitic imidazolate-based metal-organic framework (MOF) materials in the extended infrared spectral region. Using synchrotron-based FTIR spectroscopy in specular reflectance, in conjunction with density functional theory (DFT) calculations, we have revealed detailed structure-property trends linking the THz region dielectric response to framework porosity and structural density. The work demonstrates that MOFs are promising candidate materials not only for low-\k{appa} electronics applicatio…
The zero-dimensional (0D) metal halides comprise periodically distributed and isolated metal-halide polyhedra, which act as the smallest inorganic quantum systems and can accommodate quasi-localized Frenkel excitons. These excitons exhibit unique photophysics including broadband photon emission, huge Stokes shift, and long decay lifetime. The polyhedra can have different symmetries due to the coordination degree of the metal ions. Little is known about how the polyhedron type affects the characteristics of the 0D metal halide crystals. We synthesize and comparatively study three novel kinds of…
Polycrystalline samples of Z-type hexaferrites, having nominal compositions $\mathrm{Ba_3Co_{2+x}Fe_{24-2x}M_xO_{41}}$ where M = $\mathrm{Ir^{4+}, Hf^{4+}, Mo^{4+}}$ and x=0 and 0.05, were processed via ceramic processing protocols in pursuit of low magnetic and dielectric losses as well as equivalent permittivity and permeability. Fine process control was conducted to ensure optimal magnetic properties. Organic dispersants (i.e., isobutylene and maleic anhydride) were employed to achieve maximum densities. Crystallographic structure, characterized by X-ray diffraction, revealed that doping wi…
The ultrafast polarization response to incident light and ensuing exciton/carrier generation are essential to outstanding optoelectronic properties of lead halide perovskites (LHPs). A large number of mechanistic studies in the LHP field to date have focused on contributions to polarizability from organic cations and the highly polarizable inorganic lattice. For a comprehensive understanding of the ultrafast polarization response, we must additionally account for the nearly instantaneous hyperpolarizability response to the propagating light field itself. While light propagation is pivotal to o…
