Energy Relaxation Research Articles

High-temperature non-equilibrium atom-diatom collisional energy transfer.

The change of the vibrational energy within a molecule after collisions with another molecule plays an essential role in the evolution of molecular internal energy distributions, which is also the limiting process in the relaxation of gases toward equilibrium. Here, we investigate the energy transfer between the translational motion and the vibrational motion of the diatom during the atom-diatom collision, the simplest case involving the transfer between inter-molecular and intra-molecular energies. We are interested in the situation when the translational temperature of the gas is high, in which case, there are significant probabilities for the vibrational energy to change over widely separated energy levels after a collision. Data from quasi-classical trajectory simulations of the N + N2 system with abinitio potential energies suggest that the transition probability dependence on the collisional energy possesses an "activation-saturation" behavior and can be described by a simple model. The model allows for explicit evaluation of the vibrational state-to-state transition rate coefficients, from which the evolution of the vibrational energy distribution from any initial conditions can be solved by using the master equation approach. An example of the vibrational energy relaxation in the N + N2 system mimicking the gas behind strong shocks in a hypersonic flow is shown and the results are in good agreement with the available data.

Enhanced energy storage properties and relaxation behavior of BNT-based ceramics via A-sites substitution

Enhanced energy storage properties and relaxation behavior of BNT-based ceramics via A-sites substitution

Computational Study on Flow Characteristics of Shocked Light Backward-Triangular Bubbles in Polyatomic Gas

This study computationally examined the Richtmyer–Meshkov instability (RMI) evolution in a helium backward-triangular bubble immersed in monatomic argon, diatomic nitrogen, and polyatomic methane under planar shock wave interactions. Using high-fidelity numerical simulations based on the compressible Navier–Fourier equations based on the Boltzmann–Curtiss kinetic framework and simulated via a modal discontinuous Galerkin scheme, we analyze the complex interplay of shock-bubble dynamics. Key findings reveal distinct thermal non-equilibrium effects, vorticity generation, enstrophy evolution, kinetic energy dissipation, and interface deformation across gases. Methane, with its molecular complexity and higher viscosity, exhibits the highest levels of vorticity production, enstrophy, and kinetic energy, leading to pronounced Kelvin–Helmholtz instabilities and enhanced mixing. Conversely, argon, due to its simpler atomic structure, shows weaker deformation and mixing. Thermal non-equilibrium effects, quantified by the Rayleigh–Onsager dissipation function, are most significant in methane, indicating delayed energy relaxation and intense turbulence. This study highlights the pivotal role of molecular properties, specific heat ratio, and bulk viscosity in shaping RMI dynamics in polyatomic gases, offering insights on uses such as high-speed aerodynamics, inertial confinement fusion, and supersonic mixing.

Vibrational Energy Relaxation in Solid Carbon Monoxide

Vibrational Energy Relaxation in Solid Carbon Monoxide

Wetting of a Dynamically Patterned Surface Is a Time-Dependent Matter.

In nature and many technological applications, aqueous solutions are in contact with patterned surfaces, which are dynamic over time scales spanning from ps to μs. For instance, in biology, exposed polar and apolar residues of biomolecules form a pattern, which fluctuates in time due to side chain and conformational motions. At metal/and oxide/water interfaces, the pattern is formed by surface topmost atoms, and fluctuations are due to, e.g., local surface polarization and rearrangements in the adsorbed water layer. All these dynamics have the potential to influence key processes such as wetting, energy relaxation, and biological function. Yet, their impact on the water H-bond network remains often elusive. Here, we leverage molecular dynamics to address this fundamental question at a self-assembled monolayer (SAM)/water interface, where ns dynamics is induced by frustrating SAM-water interactions via methylation of the terminal -OH groups of poly(ethylene glycol) (PEG) chains. We find that surface dynamics couples to the water H-bond network, inducing a response on the same ns time scale. This leads to time fluctuations of local wetting, oscillating from hydrophobic to hydrophilic environments. Our results suggest that rather than average properties, it is the local─ both in time and space─ solvation that determines the chemical-physical properties of dynamically patterned surfaces in water.

Unexpected XPS Binding Energy Observations Further Highlighted by DFT Calculations of Ruthenocene-Containing [IrIII(ppy)2(RCOCHCORc)] Complexes: Cytotoxicity and Crystal Structure of [Ir(ppy)2(FcCOCHCORc)

The series of iridium(III) complexes, [Ir(ppy)2(RCOCHCOR')], with R = CH3 and R' = CH3 (1), Rc (2), and Fc (3), as well as R = Rc and R' = Rc (4) or Fc (5), and R = R' = Fc (6), ppy = 2-phenylpyridinyl, Fc = FeII(η5-C5H4)(η5-C5H5), and Rc = RuII(η5-C5H4)(η5-C5H5), has been investigated by single-crystal X-ray crystallography and X-ray photoelectron spectroscopy (XPS) supplemented by DFT calculations. Here, in the range of 3.74 ≤ ΣχR ≤ 4.68, for Ir 4f, Ru 3d and 3p and N 1s orbitals, binding energies unexpectedly decreased with increasing ΣχR (ΣχR = the sum of Gordy group electronegativities of the R groups on β-diketonato ligands = a measure of electron density on atoms), while in Fe 2p orbitals, XPS binding energy, as expected, increased with increasing ΣχR. Which trend direction prevails is a function of main quantum level, n = 1, 2, 3…, sub-quantum level (s, p, d, and f), initial state energies, and final state relaxation energies, and it may differ from compound series to compound series. Relations between DFT-calculated orbital energies and ΣχR followed opposite trend directions than binding energy/ΣχR trends. X-ray-induced decomposition of compounds was observed. The results confirmed good communication between molecular fragments. Lower binding energies of both the Ir 4f7/2 and N 1s photoelectron lines are associated with shorter Ir-N bond lengths. Cytotoxic tests showed that 1 (IC50 = 25.1 μM) and 3 (IC50 = 37.8 μM) are less cytotoxic against HeLa cells than cisplatin (IC50 = 1.1 μM), but more cytotoxic than the free β-diketone FcCOCH2COCH3 (IC50 = 66.6 μM).

Theoretical analysis and predictions for the two-neutrino double electron capture of 124Xe

Abstract We provide a complete theoretical description of the two-neutrino electron capture in 124Xe, improving both the nuclear and the atomic structure calculations. We improve the general formalism through the use of the Taylor expansion method, leading to higher-order terms in the decay rate of the process. The nuclear part is treated with pn-QRPA and interacting shell model (ISM) methods. The nuclear matrix elements (NMEs) are calculated with the pn-QRPA method with isospin restoration by fixing the input parameters so that the experimental decay rate is reproduced, resulting in values significantly lower than in previous calculations. The validity of the pn-QRPA NMEs is tested by showing their values to be comparable with the ones for double-beta decay with the emission of two antineutrinos of 128,130Te, which have similar pairing features. Within the ISM, we reproduce the total experimental half-life within a factor of two and predict the capture fraction to the KK channel of about 74%. We also predict the capture fractions to other decay channels and show that for the cumulative decay to the KL1–KO1 channels, a capture fraction of about 24% could be observed experimentally. On the atomic side, calculations are improved by accounting for the Pauli blocking of the decay of innermost nucleon states and by considering all s-wave electrons available for capture, expanding beyond the K and L1 orbitals considered in previous studies. We also provide improved atomic relaxation energies of the final atomic states of 124Te, which may be used as input for background modeling in liquid Xenon experiments.

Nonadiabatic Excited-State Molecular Dynamics with an Explicit Solvent: NEXMD-SANDER Implementation.

In this article, the nonadiabatic excited-state Molecular dynamics (NEXMD) package is linked with the SANDER package, provided by AMBERTOOLS. The combination of these software packages enables the simulation of photoinduced dynamics of large multichromophoric conjugated molecules involving several coupled electronic excited states embedded in an explicit solvent by using the quantum/mechanics/molecular mechanics (QM/MM) methodology. The fewest switches surface hopping algorithm, as implemented in NEXMD, is used to account for quantum transitions among the adiabatic excited-state simulations of the photoexcitation and subsequent nonadiabatic electronic transitions, and vibrational energy relaxation of a substituted polyphenylenevinylene oligomer (PPV3-NO2) in vacuum and methanol as an explicit solvent has been used as a test case. The impact of including specific solvent molecules in the QM region is also analyzed. Our NEXMD-SANDER QM/MM implementation provides a useful computational tool to simulate qualitatively solvent-dependent effects, like electron transfer, stabilization of charge-separated excited states, and the role of solvent reorganization in the molecular optical properties, observed in solution-based spectroscopic experiments.

Energy relaxation of N2O in gaseous, supercritical, and liquid xenon and SF6.

Rotational and vibrational energy relaxation (RER and VER) of N2O embedded in xenon and SF6 environments ranging from the gas phase to the liquid, including the supercritical regime, is studied at a molecular level. Calibrated intermolecular interactions from high-level electronic structure calculations, validated against experiments for the pure solvents, were used to carry out classical molecular dynamics simulations corresponding to experimental state points for near-critical isotherms. The computed RER rates in low-density solvents of krotXe=(3.67±0.25)×1010 s-1 M-1 and krotSF6=(1.25±0.12)×1011 s-1 M-1 compare well with the rates determined by the analysis of two-dimensional infrared experiments. Simulations find that an isolated binary collision description is successful up to solvent concentrations of ∼4 M. For higher densities, including the supercritical regime, the simulations do not correctly describe RER, probably due to the neglect of solvent-solute coupling in the analysis of the rotational motion. For VER, the near-quantitative agreement between simulations and pump-probe experiments captures the solvent density-dependent trends.

Temperature-dependent vibrational energy relaxation of hydrogen-bonded and free OD groups at the air-water interface.

Water interfaces play a crucial role in regulating interactions and energy flow. Vibrational sum-frequency generation (vSFG) spectroscopy provides structural and dynamic information on water molecules at interfaces. It has revealed, for instance, the presence of the hydrogen-bonded and free OH groups at the air-water interface. Here, using temperature-dependent, time-resolved vSFG, we focus on the vibrational energy relaxation dynamics of interfacial heavy water (D2O). We reveal that while the relaxation timescale for hydrogen-bonded OD stretch modes is temperature-independent, the lifetime of the free OD stretch mode decreases with increasing temperature. Our data, supported by simulations, suggest that both intramolecular energy transfer and rotational reorientation mechanisms jointly contribute to the energy relaxation process of the free OD, with temperature influencing these mechanisms differently.

Integer Fluxonium Qubit

We describe a superconducting qubit derived from operating a properly designed fluxonium circuit in a zero magnetic field. The qubit has a frequency of about 4 GHz and an energy relaxation quality factor Q≈0.7×107, even though the dielectric loss quality factor of the circuit components is in the low-105 range. The Ramsey coherence time exceeds 100μs, and the average fidelity of Clifford gates is benchmarked to F>0.999. These figures are expected to improve with optimized fabrication and measurement procedures. Our work establishes a ready-to-use “partially protected” superconducting qubit functioning in the frequency range of conventional transmons. Published by the American Physical Society 2024

Time-resolved photoelectron spectroscopy at surfaces

Light is still an important spectroscopic tool for investigating the electronic structure of surfaces. Time-resolved photoelectron spectroscopy has mainly been developed in the last 30 years. It is therefore not surprising that the topic was hardly mentioned in the last issue on “The first thirty years” of surface science. In the second thirty years, however, we have seen tremendous progress in the development of time-resolved photoelectron spectroscopy on surfaces. Femtosecond light pulses and advanced photoelectron detection schemes are increasingly being used to study the electronic structure and dynamics of occupied and unoccupied electronic states and dynamic processes such as the energy and momentum relaxation of electrons, charge transfer at interfaces and collective processes such as plasmonic excitation and optical field screening. Using spin- and time-resolved photoelectron spectroscopy, we were able to study ultrafast spin dynamics, electron-magnon scattering and spin structures in magnetic and topological materials. Light also provides photon energy as well as electric and magnetic fields that can influence molecular surface processes to steer surface photochemistry and hot-electron-driven catalysis. In addition, we can consider light as a chemical reagent that can alter the properties of matter by creating non-equilibrium states and ultrafast phase transitions in correlated materials through the coupling of electrons, phonons and spins. Electric fields have also been used to temporarily change the electronic structure. This opened up new methods and areas such as high harmonic generation, light wave electronics and attosecond physics. This overview certainly cannot cover all these interesting topics. But also as a testimony to the cohesion and constructive exchange in our ultrafast community, a number of colleagues have come together to share their expertise and views on the very vital field of dynamics at surfaces. Following the introduction, the interested reader will find a list of contributions and a brief summary in Section 1.3.

A Hybrid Strategy to Enhance Small-Sized Upconversion Nanocrystals

Upconversion nanoparticles (UCNPs) are characterized by high photostability, narrow spectral bands, excellent tuneability, and low biotoxicity, facilitating a broad range of biomedical applications. However, the small size required in many biological applications implies a lower luminescent brightness, as large surface-to-volume ratio is always accompanied with severe surface quenching. Herein, we introduce a strategy to overcome the surface quenching by incorporating an acceptor dye, sulforhodamine B (SRB) to surpass energy relaxation on long-lived lanthanide excited states. The surface modification of SRB led to up to 98.8% energy transfer efficiency, accompanied with the emergence of an intense SRB emission, with four orders of magnitude of change in the SRB/UCNPs emission ratio. The further structural optimisation led to an 8-fold upconversion emission enhancement. Moreover, the system exhibits excellent photostability, with only a 25% reduction over two hours under intense irradiation. By incorporating a pH responsive 5-carboxytetramethylrhodamine (5-TAMRA) to the UCNPs, we achieved a self-referencing protochromic sensor that are specific to protons and resistant to interference from various metal ions. This work provides a facile method for enhancing small-sized nanocrystals for biomedical sensing and imaging applications.

Novel reddish-orange emitting BaBPO5:Eu3+ phosphor for n-UV warm white-LEDs: Synthesis and study of structural and spectroscopic investigations

A novel reddish-orange emitting 2Ba2-xO-B2O3-P2O5:xEu3+ (x= 0.04, 0.06, 0.08, 0.10, 0.12 and 0.14 mol%) phosphor with different concentrations of Eu3+ ions were synthesized through high temperature solid-state reaction technique. The crystal structure has been studied by X-ray diffraction technique for all the concentrations of Eu3+ ions. The morphology and elemental analysis of the optimal ∼0.1 mol% concentration was examined by the SEM-EDS images. The functional groups were analysed by the FTIR characterization technique. The thermal properties were studied by the TGA-DSC analysis. The energy band gap of all the samples were analysed by using UV–VIS DRS technique. The photoluminescence properties of BaBPO5:Eu3+ phosphor with different concentrations of Eu3+ ions were investigated at λem = 611 nm and λex = 394 nm. Variation in emission intensity with Eu3+ ion concentrations, phonon side bands, multi-phonon relaxation rate and energy transfer mechanisms were studied. The BaBPO5:Eu3+ phosphors exhibit characteristic emission peaks corresponding to 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+ ions under n-UV excitation. Among all the transitions, 5D0 → 7F1 (593 nm) transition shows higher intensity and asymmetric ratio (R21) for all concentrations of Eu3+ ions were calculated. The lifetimes of 5D0 level of Eu3+ ions in BaBPO5: Eu3+ phosphor were calculated by using fluorescent decay curve analysis. The CIE color coordinates reveal, reddish-orange emission in the low CCT range. These findings imply that BaBPO5: 0.1Eu3+ phosphor is a promising candidate for solid-state lighting applications as well as phosphor-converted warm w-LEDs.

Visible Light-Sensitized CO2 Methanation along a Relaxed Heat Available Route.

In photocatalysis, the resulted heat by the relaxation of most of incident light no longer acts as the industrially favorite driving force back to the target photo-reaction due to more or less the negative relation between photocatalytic efficiency and temperature. Here, we reported a visible light-sensitized protocol that completely reversed the negatively temperature-dependent efficiency in photo-driven CO2 methanation with saturated water vapor. Uniform Pt/N-TiO2/PDI self-assembly material decisively injects the excited electron of PDI sensitizer into N-TiO2 forming Ti-H hydride which is crucially temperature-dependent nucleophilic species to dominate CO2 methanation, rather than conventionally separated and trapped electrons on the conductor band. Meanwhile, the ternary composite lifts itself temperature from room temperature to 305.2 °C within 400 s only by the failure excitation upon simulated sunlight of 2.5 W/cm2, and smoothly achieves CO2 methanation with a record number of 4.98 mmol g-1 h-1 rate, compared to less than 0.02 mol g-1 h-1 at classic Pt/N-TiO2/UV photocatalysis without PDI sensitization. This approach can reuse ~53.9 % of the relaxed heat energy from the incident light thereby allow high-intensity incident light as strong as possible within a flowing photo-reactor, opening the most likely gateways to industrialization.

Structural, optical, and thermal traits of Sm³⁺-doped SrB₂O₄ phosphors for solid-state lighting applications

We synthesized Sm³⁺-doped SrB₂O₄ phosphors through a solid-state reaction method, varying the Sm³⁺ doping concentrations. Structural and morphological characteristics of material were investigated using Fourier-transform infrared spectroscopy (FTIR), X-Ray Diffraction (XRD) and scanning electron microscopy (SEM). Optical transitions were analyzed by recording the diffuse reflectance spectroscopy, while photoluminescent (PL) spectra were used to evaluate luminescence properties. The PL spectra revealed a strong orange emission at 598 nm under 402 nm excitation. The optimal Sm³⁺ doping concentration was determined to be 0.02 mol, beyond which concentration quenching occurred. This quenching is attributed to exchange-type interactions, which facilitate non-radiative energy relaxation. The CIE color chromaticity coordinates of all the synthesized phosphors fell within the orange region of the chromaticity diagram. Temperature dependent photoluminescence revealed lower activation energy and phonon energy. Thermal quenching temperature was calculated which is inline with commercially available LEDs. All of these results indicate the candidature of SrB2O4 phosphor doped with Sm3+ ions for solid state lighting and optical thermal sensing applications.

Using Bifluxon Tunneling to Protect the Fluxonium Qubit

Encoding quantum information in quantum states with disjoint wave-function support and noise-insensitive energies is the key behind the idea of qubit protection. While fully protected qubits are expected to offer exponential protection against both energy relaxation and pure dephasing, simpler circuits may grant partial protection with currently achievable parameters. Here, we study a fluxonium circuit in which the wave functions are engineered to minimize their overlap while benefiting from a first-order-insensitive flux sweet spot. Taking advantage of a large superinductance (L∼1 μH), our circuit incorporates a resonant tunneling mechanism at zero external flux that couples states with the same fluxon parity, thus enabling bifluxon tunneling. The states |0⟩ and |1⟩ are encoded in wave functions with parities 0 and 1, respectively, ensuring a minimal form of protection against relaxation. Two-tone spectroscopy reveals the energy-level structure of the circuit and the presence of 4π quantum-phase slips between different potential wells corresponding to m=±1 fluxons, which can be precisely described by a simple fluxonium Hamiltonian or by an effective bifluxon Hamiltonian. Despite suboptimal fabrication, the measured relaxation (T1=177±3 μs) and dephasing (T2E=75±5 μs) times not only demonstrate the relevance of our approach but also open an alternative direction toward quantum computing using partially protected fluxonium qubits. Published by the American Physical Society 2024

Flame retardant epoxy vitrimers employing a Meldrum's acid-functionalized and phosphorus-containing bisphenol compound as the cross-linking agent for conventional epoxy

In addition to recycling and reprocessing features, designs of vitrimers possessing critical properties required for conventional cross-linked polymers are of interest. In this work, a newly designed Meldrum's acid (MA)-functionalized and phosphorus-containing bisphenol compound (P-MADV) compound is synthesized. Employing P-MADV as a curing agent, simultaneous formation of permanent and dynamic covalent linkages through one-pot reaction has been achieved in formation of flame retardant epoxy resin vitrimers. The newly synthesized P-MADV compound is an effective cross-linking agent for commercially-available epoxy resins for synthesis of flame-retardant epoxy vitrimers through the conventional cross-linking conditions and processes. The cross-linked epoxy vitrimer passes the flame test under UL 94V-0 specification contributed from the phosphorus-containing groups. The flame retardant vitrimer also exhibits a storage modulus of 1.2 GPa at 50 °C and a Tg (tanδ peak) of 185 °C, which are comparable to the values found with conventional phenolic novolac-cross-linked epoxy resin (storage modulus: 1.6 GPa; Tg: 155 °C). Without addition of catalysts for dynamic bond exchanging reaction, the cross-linked epoxy vitrimer shows stress relaxation time of 397 s at 230 °C and an activation energy of stress relaxation of 97.8 kJ mol−1. The dynamic features warrant the epoxy vitrimer being recyclable under thermally pressing at 230 °C and 16 MPa for 1 h. The recycled samples exhibit thermal and mechanical properties being comparable to the pristine resin. This work has demonstrated an attractive approach for preparation of flame retardant epoxy resin vitrimers in viewpoints of both manufacturing processes and resins properties.

Hierarchical Equations of Motion for Quantum Chemical Dynamics: Recent Methodology Developments and Applications.

ConspectusQuantum effects are critical to understanding many chemical dynamical processes in condensed phases, where interactions between molecules and their environment are usually strong and non-Markovian. In this Account, we review recent progress from our group in development and application of the hierarchical equations of motion (HEOM) method, highlighting its ability to address some challenging problems in quantum chemical dynamics.In the HEOM method, the bath degrees of freedom are represented using effective modes from exponential decomposition of the bath correlation function. Complex spectral densities and low temperature simulations often require a larger number of modes, making the simulations very expensive. Recent advances, such as the barycentric spectral decomposition (BSD) technique, can significantly reduce the number of effective modes, allowing to handle complex spectral densities and enabling simulations at very low temperatures, including near-zero temperature dynamics.Another key improvement in the computational efficiency is the use of tensor network methods like matrix product states and hierarchical tensor networks. These techniques allow for efficient HEOM propagation with thousands of effective modes, crucial for simulating large molecular systems interacting with multiple baths. This combination enables simulations of excitation energy transfer (EET) in systems like the Fenna-Matthews-Olson (FMO) complex and even larger systems with experimentally determined spectral densities.The versatility of the HEOM method is demonstrated through applications to a wide range of chemical dynamics problems. Simulations of EET and related ultrafast spectroscopy are first briefly covered. Applications of the HEOM to quantum tunneling effects in proton transfer reactions are then presented. Early works have studied the non-Kramers dependence of the rate constant as a function of bath friction due to deep tunneling and revealed vibrationally nonadiabatic dynamics within the so-called nontraditional view of proton transfer reactions. A recent work on the large kinetic isotope effects in soybean lipoxygenase also indicated that many quantum correction approximations to classical transition-state theory may fall short in describing deep tunneling effects.Charge transport and separation dynamics in organic semiconductors are another area where the HEOM method has been instrumental. We first demonstrate that the HEOM provides a unified description of both band-like and thermally assisted charge carrier transport in organic materials. The effect of non-nearest neighbor transitions is then investigated by combining generalized master equations with exact memory kernels. The HEOM method also enables simulation of charge separation in organic photovoltaics (OPVs) and reveals how factors such as external electric fields, entropy, and charge delocalization influence the charge separation barrier and dynamics.Moreover, HEOM has been applied to investigate hydrogen atom scattering on the Au(111) surface and vibrational energy relaxation at molecule-metal interfaces. These studies provide deeper insights into how electron-hole pair excitations and temporary charge transfer states influence the nuclear motion, offering a new framework for simulating nonadiabatic dynamics on metal surfaces.In summary, the HEOM method has developed into a robust tool for simulating quantum effects in condensed phases. Future developments in algorithm efficiency and computational power will likely expand its applicability to even more complex systems.

Electron trapping in HfO2 layer deposited over a HF last treated silicon substrate

Electron trapping in HfO2-based MOS structures was studied through pulsed capacitance-voltage (C-V) technique. 10 nm HfO2 layer was deposited by atomic layer deposition over a HF last treated Si substrate. The C-V curves were observed to shift to positive voltages driven by the positive applied voltage along the pulses, consistent with electron trapping due to tunneling transitions between the substrate and pre-existing defects within the oxide and the subsequent lattice relaxation through electron-phonon interaction. The dependences of the voltage shift for a given capacitance value (ΔVC) with stress bias and time, allowed to distinguish two mechanisms. An initial trapping process occurs for times shorter than the microsecond, probably associated with a thin non-stoichiometric SiOx interfacial layer, which is followed by a trapping process that starts after tens of μs and progressively slowed down, associated with traps within the HfO2 layer. Numerical simulations yield for the HfO2 traps an energy of 1.3 eV below the conduction band edge, decreasing exponentially with the distance from the Si interface with a characteristic length of 1.7 nm; and phonon and relaxation energies of 50 meV and 1 eV, respectively. These physical parameters are consistent with previous reports of electron trapping in HfO2 layers deposited on a controlled interfacial layer, suggesting that trapping properties of defects inside the HfO2 layer are insensitive to the treatment of the Si surface before HfO2 deposition. On the other hand, the observed large initial trapping suggests that the non-controlled SiOx interfacial region is more defective than a controlled one.