Reversible Trapping Research Articles

Reversible and irreversible trapping at room temperature in poly(thiophene) thin-film transistors

We measured the bias stress characteristics of poly(thiophene) semicrystalline thin-film transistors (TFTs) as a function stress times, gate voltages, and duty cycles. At room temperature, the bias stress has two components: a fast reversible component and a slow long-lived component. We hypothesize that the irreversible component is due to charge trapping in the disordered areas of the semiconductor film. At low duty cycle (<2%), the fast bias stress component is reversed during the off-part of the cycle therefore the observed threshold voltage (VT) shift is only caused by long-lived trapping. Long-lived trapping follows power-law kinetics with a time exponent approximately equal to 0.37. We use these findings to estimate the lifetime of TFTs used as switches in display backplanes.

Temperature-Sensitive Photoluminescence of CdSe Quantum Dot Clusters

The formation of narrow size dispersed and nanometer size aggregates (clusters) of cadmium selenide (CdSe) quantum dots (QDs) and their temperature-sensitive photoluminescence (PL) spectral properties close to room temperature (298 K) are discussed. CdSe QDs formed stable clusters with an average diameter of approximately 27 nm in the absence of coordinating solvents. Using transmission electron microscopy (TEM) imaging, we identified the association of individual QDs with 2-5 nm diameters into clusters of uniform size. A suspension of these clusters in different solvents exhibited reversible PL intensity changes and PL spectral shifts which were correlated with temperature. Although the PL intensity of CdSe QDs encapsulated in host matrixes and the solid state showed a response to temperature under cryogenic conditions, the current work identified for the first time QD clusters showing temperature-sensitive PL intensity variations and spectral shifts at moderate temperatures above room temperature. Temperature-sensitive reversible PL changes of clusters are discussed with respect to reversible thermal trapping of electrons at inter-QD interfaces and dipole-dipole interactions in clusters. Reversible luminescence intensity variations and spectral shifts of QD clusters show the potential for developing sensors based on QD nanoscale assemblies.

Trapping/De-Trapping Gate Bias Dependence of Hf-Silicate Dielectrics with Poly and TiN Gate Electrode

Constant voltage stress induced Vth shift and its detrapping characteristics under the negative gate bias has been extensively investigated with HF-silicate dielectrics with poly and TiN gate electrode. The threshold voltage shift in negative-channel metal-oxide semiconductor (NMOS) transistors under the positive gate bias stress is found to be associated mostly with the reversible electron trapping. A proper negative bias can be used to de-trap the electrons accumulated during the positive stress. However, an aggressive de-trapping can cause an additional Vth instability due to the excessive de-trapping of existing charge or additional hole trapping at the interface with poly gate. TiN metal gate is found to be more stable with de-trapping negative gate bias. To de-trap the electrons accumulated in the dielectric during the positive constant voltage stress (CVS), the negative bias and its duration should be chosen very carefully to avoid the additional charging associated with the hole trapping.

Molecule‐to‐Metal Bonds: Electrografting Polymers on Conducting Surfaces

Electrografting is a powerful and versatile technique for modifying and decorating conducting surfaces with organic matter. Mainly based on the electro-induced polymerization of dissolved electro-active monomers on metallic or semiconducting surfaces, it finds applications in various fields including biocompatibility, protection against corrosion, lubrication, soldering, functionalization, adhesion, and template chemistry. Starting from experimental observations, this Review highlights the mechanism of the formation of covalent metal-carbon bonds by electro-induced processes, together with major applications such as derivatization of conducting surfaces with biomolecules that can be used in biosensing, lubrication of low-level electrical contacts, reversible trapping of ionic waste on reactive electrografted surfaces as an alternative to ion-exchange resins, and localized modification of conducting surfaces, a one-step process providing submicrometer grafted areas and which is used in microelectronics.

Impact of reversible trapping of tracer and the presence of blood metabolites on measurements of myocardial glucose utilization performed by PET and 18F-fluorodeoxyglucose using the Patlak method

In this study we demonstrated that significant egress of FDG from myocardium occurs within the first hour after tracer injection leading to nonlinear Patlak plots. There are also significant amounts of acidic FDG metabolites present in the blood. However, the impact of these metabolites on the estimates of myocardial glucose utilization (MGU) is negligible. Although further studies will be required to elucidate the reason for the egress of tracer from myocardium, not accounting for it will result in erroneous estimates of MGU.

Photoinduced magnetic memory effect in an iron (II) spin-crossover complex

We report a bidirectional reversible light-induced excited spin state trapping (LIESST) effect featuring an associated memorey effect in an Fe(II) spin-crossover complex [FeL(CN)2]·H2O (where L is a Schiff-base macrocyclic ligand). Depending on the illumination history, bidirectional LIESST processes have been successfully observed that are induced by irradiation with the same two wavelengths. A large zero-point energy difference, strong overlapping spectra of the high-spin and low-spin bands and image internal pressure could account for this photomagnetic phenomenon.

Effect of Pre-Existing Defects on Reliability Assessment of High-K Gate Dielectrics

Response of the high-k gate dielectrics to low voltage stresses was studied by probing high-k transistors with various voltage/time measurements at different temperatures. The observed dependence of the transistor threshold voltage on stress time was attributed to electron trapping at pre-existing defects in the high-k dielectric rather than stress-induced trap generation. The dominance of the contribution from the reversible electron trapping on the pre-existing defects in the low voltage stress response raises the question on the applicability of the conventional reliability assessment methodology to the high-k dielectrics.

Microelectrochemical electronic effects in two-layer structures of distinct Prussian blue type metal hexacyanoferrates

The formation of a rigid bilayer structure from two metal hexacyanoferrates: Prussian blue (PB) and nickel hexacyanoferrate (NiHCNFe), as inner and outer films, respectively, has been demonstrated. To avoid intermingling of the granular cyanometallate microstructures, namely of the outer film (NiHCNFe) into the inner film (PB), the morphology of outer film material was changed by forming a polymeric hybrid (composite) of NiHCNFe with poly(N-methylpyrrole). The outer NiHCNFe film is physically separated from the electrode surface, and it undergoes redox reactions at potentials characteristic of the inner PB film. This arrangement leads to the reversible charge state trapping and bistable switching during voltammetric potential cycling. Under solid-state voltammetric conditions in the absence of contact with the liquid electrolyte phase, when the bilayer structure of PB and the oxidized NiHCNFe was formed between two sandwich-forming carbon electrodes, unidirectional rectifying current flow has been observed.

Probing Dynamic Equilibria between Platinum(II)−η2-Benzene Adducts and Unobserved Five-Coordinate Platinum(IV) C−H Oxidative Addition Intermediates

Low-temperature addition of nitrile ligands to platinum(II) η2-benzene reagents, [(κ2-HTp‘)Pt(η2-C6H6)(R)][BAr‘4] (R = H, Ph), results in reversible trapping of the postulated five-coordinate C−H oxidative addition product to give cationic platinum(IV) nitrile adducts, [(κ2-HTp‘)Pt(C6H5)(H)(R)(NCR‘)][BAr‘4] (R = Ph, H, R‘ = Me, CMe3, p-XC6H4). At higher temperatures, irreversible loss of benzene from the Pt(II) η2-benzene reagents occurs to form cationic Pt(II) nitrile products.

Pseudo-Prolines: Reversible Conformational Trap of Cyclosporin C as Novel Concept for Prodrug Design

The selective and reversible insertion of pseudo-proline (? Pro) systems in cyclosporin C (CsC) featuring different C(2) substituents at the oxazolidine ring and its impact on the conformational and biological properties is described. The presence of a 5-membered ring exerts drastic effects upon the backbone conformation of CsC as demonstrated by NMR analysis. For example, the number of conformations, in particular in DMSO-d6, is strongly reduced and a cis 1-2 amide bond is induced when dialkylated at the C(2) position, resulting in a complete loss of the binding capacity to its receptor CypA. The reversibility of ?Pro insertion allows the temporary introduction of conformational constraints representing a new strategy in pro-drug design.

Hydrogen trap states in ultrahigh-strength AERMET 100 steel

Hydrogen (H) trap states and binding energies were determined for AERMET 100 (Fe-13.4Co-11Ni-3Cr-1.2Mo-0.2C), an ultrahigh-strength steel using thermal desorption methods. Three major H desorption peaks were identified in the precipitation-hardened microstructure, associated with three distinct metallurgical trap states, and apparent activation energies for desorption were determined for each. The lattice diffusivity (D L ) associated with interstitial H was measured experimentally and verified through trapping theory to yield H-trap binding energies (E b ). Solid-solution elements in AERMET 100 reduce D L by decreasing the pre-exponential diffusion coefficient, while the activation energy for migration is similar to that of pure iron. M2C precipitates are the major reversible trap states, with E b of 11.4 to 11.6 kJ/mol and confirmed by heat treatment that eliminated these precipitates and the associated H-desorption peak. A strong trap state with E b of 61.3 to 62.2 kJ/mol is likely associated with martensite interfaces, austenite grain boundaries, and mixed dislocation cores. Undissolved metal carbides and highly misoriented grain boundaries trap H with a binding energy of 89.1 to 89.9 kJ/mol. Severe transgranular hydrogen embrittlement in peak-aged AERMET 100 at a low threshold-stress intensity is due to H repartitioning from a high density of homogeneously distributed and reversible M2C traps to the crack tip under the influence of high hydrostatic tensile stress.

A general strategy for target-promoted alkylation in biological systems.

Selective alkylation of a chosen sequence of DNA typically relies on ligand-directed delivery of a compound that expresses an intrinsic reactivity. A significant and biologically relevant enhancement in specificity is theoretically possible if such an intrinsic reactivity could be replaced by a latent activity induced solely by the target of interest, but examples of this are rare and not easily emulated. A simple strategy for target-promoted alkylation is now illustrated by an intramolecular adduct formed by an oligonucleotide-quinone methide conjugate. This adduct persists in the absence of a complementary sequence of DNA for at least 8 days, yet remarkably is able to alkylate target DNA upon duplex hybridization. Neither formation of the intramolecular self-adduct nor transfer of the quinone methide to its target is significantly quenched by 450-fold excess 2-mercaptoethanol. Similarly, noncomplementary DNA is neither subject to alkylation by the self-adduct nor able to effect its consumption. Reversible trapping of the nascent quinone methide through an intramolecular reaction thus appears efficient enough to inhibit competing intermolecular reaction. Only complementary base pairing induces a conformational change necessary to promote intermolecular transfer of the quinone methide. Generalization of this approach based on reversible intramolecular trapping of a reactive intermediate by a ligand with multiple recognition subdomains has the potential for wide-ranging applications in targeting nucleic acids and proteins.

The interaction of hydrogen with internally oxidized Pd alloys as illustrated by Pd–Fe alloys

Hydrogen interactions in internally oxidized Pd alloys have been illustrated using Pd–Fe alloys. Internal oxidation of Pd–Fe alloys results in composites consisting of fine dispersions of nano-sized Fe2O3 precipitates in a matrix of pure Pd. Hydrogen solubility measurements can be used as a probe to characterize the reversible and irreversible trapping at the metal–oxide interfacial regions. The effect of hydriding and dehydriding (cycling) on solubilities has been characterized. Hydrogen isotherms can be used to characterize the extent of internal oxidation, and understand the effect of the dispersed internal oxides on hysteresis and H capacity.

Internal hydrogen embrittlement of ultrahigh-strength AERMET 100 steel

Near-peak-aged AERMET 100 is susceptible to severe internal hydrogen embrittlement (IHE) at 23 °C, if a sufficient diffusible hydrogen content is present, compromising the high toughness of this ultrahigh-strength steel (UHSS). Evidence includes the threshold stress intensity for subcritical IHE (K TH ) as low as 10 pct of the plane-strain fracture toughness (K IC ) and a fracture-mode transition from microvoid coalescence to brittle transgranular (TG) cracking, apparently along martensite lath interfaces and cleavage planes. The K TH value decreases from a K IC value of 132 to 143 MPa√m to 12 MPa√m, and the amount of brittle TG fracture increases to nearly 100 pct as the concentration of diffusible H increases from essentially 0 to 8 wppm, with severe embrittlement in the 0 to 2 wppm H regime. The IHE is time dependent, as evidenced by increasing K TH values with increasing dK/dt and K-independent subcritical crack growth rates, and is attributed to diffusional H repartition from reversible trap sites to the stressed crack tip. The partition distance is ∼1 µm, consistent with the fine-scale microstructure of AERMET 100. The causes of the susceptibility of AERMET 100 to TG IHE are very high crack-tip stresses and a reservoir of mobile H trapped reversibly at (Fe,Cr,Mo)2C precipitates. These factors enable repartition of H to misoriented martensite lath interfaces and interstitial sites near cleavage planes, with each prone to decohesion along a connected path. Predissolved H also reduces the ductile fracture toughness of AERMET 100 at high loading rates, perhaps due to reduced void growth caused by H trapped strongly at undissolved metal carbides.

Simulation of Hydrogen Thermal Desorption under Reversible Trapping by Lattice Defects

The hydrogen thermal desorption of a martensitic steel has been simulated assuming lattice hydrogen diffusion under a local equilibrium with reversibly trapped hydrogen as the rate-determining process. The calculated desorption curves reproduced the observed shift of the peak temperature associated with the specimen thickness and the heating rate. The calculation method involves a combination of a defect density and a hydrogen/defect binding energy as parameters. The dependence of the peak temperature on the defect density and the binding energy has been quantitatively shown. Assignment of the lattice defect relevant to the desorption curves is discussed. A calculation that took into account the increase in the defect density yielded results consistent with the observed change in the desorption curves associated with plastic strain.

Visualization of hydrogen diffusion in steels by high sensitivity hydrogen microprint technique

Hydrogen diffusion in steels was examined by both a high sensitivity hydrogen microprint technique (HMT) and an electrochemical hydrogen permeation method. The main diffusion path in an extremely low carbon steel was lattice within grains; grain boundaries were not accelerated diffusion paths. In the case of a hypo-eutectoid steel, hydrogen diffused through proeutectoid ferrite and ferrite in pearlite under steady-state of hydrogen diffusion. The diffusion paths, however, were carbide/ferrite interfaces when hydrogen charging was interrupted before achievement of the steady state. This is probably ascribable to the reversible trapping effect of the interface. The detection efficiency of the high sensitivity HMT was 75% for the low carbon steel and 40% for the hypo-eutectoid steel.

Capacitance and conductance characterization of ferrocene-containing self-assembled monolayers on silicon surfaces for memory applications

Self-assembled monolayers of 4-ferrocenylbenzyl alcohol attached to silicon provided the basis for electrolyte-molecule-silicon capacitors. Characterization by conventional capacitance and conductance techniques showed very high capacitance and conductance peaks near ∼0.6 V associated with charging and discharging of electrons into and from discrete levels in the monolayer owing to the presence of the redox-active ferrocenes. The reversible charge trapping of these molecules suggest their potential application in memory devices. Due to the molecular scalability and low-power operation, molecular-silicon hybrid devices may be strong candidates for next-generation electronic devices.

Three-dimensional simulations of reversible bimolecular reactions: The simple target problem

We report three-dimensional simulations of the reversible reaction A+B↔C for a single static A molecule and a uniform initial concentration of noninteracting B-molecules. The results are compared with various analytic approximations for the time-dependence of the binding probability. They are in excellent agreement with a recent theory of Sung and Lee [J. Chem. Phys. 111, 796 (1999)] for all times and rate parameters. The second-order term in the long-time expansion of this theory is incorrect, yet it explains an apparent kinetic transition observed when the B-concentration increases. We also investigate the concentration profiles near the reversible trap.

Physical properties of the spin-crossover compound hexakis(1-methyltetrazole- N4)iron(II) triflate, steady state and relaxation studies, X-ray structure of the isomorphic Ni(II) compound

The synthesis and characterization of the spin transition compound hexakis(1-methyltetrazole- N 4)iron(II) trifluoromethanesulfonate obtained from the reaction of 1-methyltetrazole and iron(II) triflate are described. The spin transition of [Fe(mtz) 6](CF 3SO 3) 2 ( 1) presents a hysteresis loop in magnetism with T ↓=157.0 and T ↑=179.5 K. Only one-third of the Fe(II) ions undergo this transition, the other two-thirds of the ions remain in the high-spin state. Mössbauer spectroscopy and relaxation studies have shown that the actual width of the hysteresis is only 12 K, with T ↓=167.5 and T ↑=179.5 K. Thermal spin-state trapping appears to be possible. The trapped high-spin state is stable up to 103 K. The relaxation is not first-order. After irradiation with red light, reverse light-induced excited spin state trapping (LIESST) is observed. The new low-spin state is stable up to 42 K. Also, its relaxation to HS is non-first-order. A reverse light-induced thermal hysteresis loop of approximately 7 K width is present too. No LIESST effect could be observed. Finally, a ferromagnetic type of coupling has been recognized, which is temperature and field dependent.

Permeation of hydrogen through amorphous ferrum membrane

Hydrogen permeation through amorphous and recrystallized foils of Fe-based alloys was investigated. It was found that surface layers of both types of samples were enriched by metalloids. These layers prevented permeation of hydrogen from molecular and atomic phases. Only the ionization of the gas in glow discharge near the upstream side of foils resulted in big permeation fluxes. Kinetics of flux relaxation to the steady-state values revealed reversible trapping in amorphous alloy. Permeation flux demonstrated Arrhenius linear dependence for recrystallized samples and non-monotonous for amorphous ones. Values of steady-state flux through amorphous foils were several times higher than through ordered samples at temperatures below 200°C. The mechanism of hydrogen transport is proposed taking into account re-emission and diffusion processes. Activation energies for thermal desorption and diffusion are evaluated.