Surface State Generation Research Articles

Designing Gallium-Containing Hydroxyapatite Coatings on Low Modulus Beta Ti-45Nb Alloy

Low-modulus β-type Ti-45Nb alloy is a promising implant material due to its good mechanical biocompatibility, non-toxicity, and outstanding corrosion resistance. Its excellent chemical stability brings new challenges to chemical surface modification treatments, which are indispensable for both osteogenesis and antibacterial performance. Coatings containing metal ions as anti-microbial agents can be an effective way to reduce implant-associated infections caused by bacterial biofilm. Gallium ion (Ga3+) has the potential to reduce bacterial viability and biofilm formation on implant surfaces. In this study, a novel two-step process has been proposed for Ga3+ incorporation in hydroxyapatite (HAP) to develop bioactive and antibacterial surfaces on Ti-45Nb alloy. For the generation of bioactive surface states, HAP electrodeposition was conducted, followed by wet chemical immersion treatments in gallium nitrate (1 mM). Different buffers such as phosphate, sodium bicarbonate, ammonium acetate, and citrate were added to the solution to maintain a pH value in the range of 6.5–6.9. Coating morphology and HAP phases were retained after treatment with gallium nitrate, and Ga3+ ion presence on the surface up to 1 wt.% was confirmed. Combining Ga and HAP shows great promise to enable the local delivery of Ga3+ ions and consequent antibacterial protection during bone regeneration, without using growth factors or antibiotics.

Rutile-TiO2: Post heat treatment and its influence on the photocatalytic degradation of MB dye

Photocatalytic degradation of hazardous Methylene blue (MB) attracts greater concern as it is the dominant effluent of textile industry that is mixing with the ground water resources. In this regard, we have explored the possibility for an efficient optimization of MB dye degradation using rutile TiO2. We have studied the post heat treatment of faceted Rutile TiO2 nano crystallites synthesized by sol-gel method, which was carried out towards understanding the generation of surface states and its role on the dye degradation. The phase purity and its morphological structures were confirmed by XRD, Raman analysis, FESEM and HRTEM. The XPS analysis reveals the passivation of Ti3+ defect upon high temperature treatment above 600 ᵒC and also found generating surface defect states which are evidenced from the photoluminescence study. An EPR investigation clearly reveals the distributed presence of electron and hole trap states in the faceted R–TiO2 nano crystallites. Corresponding EIS measurement of flat band potential of the electrochemical interface between R–TiO2/NaCl shows the upward band bending of R–TiO2 favourable for the improved charge transfer between R–TiO2 to Methylene blue (MB) dye. The consolidated results indicate that the high temperature treatment passivates the Ti3+ defects and promotes the generation of surface defects that favourably enhances the photocatalytic performance of MB dye from 63% to 90%. The details are discussed in this paper.

Use of MIS Sensors of Radiation in High-Field Electron Injection Modes

A model is proposed that describes the change in the charge state of metal-insulator-semiconductor (MIS) structures and sensors made from it under the conditions of the simultaneous effect of radiation ionization and high-field injection of electrons from a semiconductor. The proposed model takes into account the interaction of injected electrons with holes generated by radiation and high-field ionization and holes trapped at the interface of the SiO2 film with a semiconductor, as well as the generation of surface states during the annihilation of part of holes during their interaction with injected electrons. It is shown that the MIS sensor, where the high-field injection of electrons into the dielectric film takes place, can be used to control the intensity of radiation by determining the radiation ionization current from the time dependence of the voltage across the sensor using the proposed model. It has been established that in the high-field electron injection mode, a significant increase in the dose sensitivity of MIS sensors is possible, but at the same time, the operating time and dose range of the MIS sensor can be significantly reduced.

The high-speed ultraviolet photodetector of ZnO nanowire Schottky barrier based on the triboelectric-nanogenerator-powered surface-ionic-gate

Nanowires have a high specific surface area and high surface activity, and the surface states are key factors controlling the nanowire Schottky barrier. Therefore, adjusting the surface states is an important strategy for developing high-performance electronic and optoelectronic devices based on nanowire Schottky barriers. Here, a surface-ionic-gate modulation technique was developed to modulate the surface states and Schottky barrier of nanowires, based on the gas discharge induced by triboelectric nanogenerators (TENGs). It is demonstrated that the Schottky barrier height and electrical transport characteristics of the Ag/ZnO nanowires can be modulated by effectively controlling the surface states. The experimental results from different atmospheres show that O2− ions and electrons generated by gas discharge can form local ions on nanowires surface, which is the source for modulating surface states. Reversible modulation of the surface states and barrier height could be achieved by combining the surface-ionic-gate modulation with ultraviolet (UV) light. In addition, the recovery time of the ZnO nanowire Schottky barrier UV photodetector was reduced from 87 s to 0.3 s using the surface-ionic-gate modulation technique, the recovery speed increased 290 times, making it a universal method for achieving fast UV detection in different environments, such as in air, in oxygen, and in nitrogen. The TENG-based surface-ionic-gate modulation technique proposed here can modulate the surface states of nanowires in real time and in situ. This provides a novel method to study the dynamic generation and relaxation process of surface states and to develop high-performance electronic and optoelectronic nanodevices with broad application prospects.

Model for Charge Accumulation in n- and p-MOS Transistors during Tunneling Electron Injection from a Gate

A quantitative model for charge accumulation in an undergate dielectric during tunneling electron injection from a gate according to the Fowler–Nordheim mechanism is developed. The model takes into account electron and hole capture at hydrogen-free and hydrogen-related traps as well as the generation of surface states during the interaction of holes with hydrogen-related centers. The experimental dependences of the threshold voltage shift and gate voltage shift of n- and p-channel MOS (metal–oxide–semiconductor) transistors on the injected charge in the constant current mode are analyzed based on the model.

Role of defect states on nonlinear properties of 8 MeV electrons irradiated zinc oxide thin films under off-resonant regime

In the present work, ZnO thin films were synthesized by sol-gel with subsequent spin coating on corning glass substrates. To understand the variations in the structural, optical, and nonlinear optical properties of ZnO thin films, 8 MeV electron irradiation with different dose rates (0 kGy, 1 kGy, 5 kGy, and 10 kGy) was performed. The XRD spectra showed transition from polar crystal growth orientation to non-polar crystal growth orientation of the films when the irradiation dose rate was increased from 0 kGy to 10 kGy and this was attributed to the reduced thickness of the irradiated films. The generation of localized surface states below the conduction band upon electron irradiation was confirmed by the quantification of the Urbach energy. A large band gap shrinkage was observed in the irradiated films (3.31–3.10 eV) due to the enhanced surface states. The photoluminescence spectra showed reduction in the NBE emission due to the enhanced surface states in the irradiated films. Open aperture and closed aperture Z-scan measurements were performed to extract the nonlinear absorption coefficient (β) and nonlinear refractive index (n2) values using 532 nm Nd:YAG laser having pulse width of 7 ns. The open aperture Z-scan profiles of the films showed the presence of normalized transmittance valley, which was attributed to the two photon absorption (TPA) behaviour. The reduction in the depth of the normalized transmittance valley in irradiated films was ascribed to the bleaching of carriers in the ground states due to their trapping in the defect states. The closed aperture Z-scan curves showed the presence of normalized pre-focal peak, followed by a valley, which is characteristic of the self-defocusing nonlinear refraction behaviour. The electron irradiation with different dose rates provided an opportunity to understand the variations in the optoelectronic properties of the ZnO thin films considering the various defect states generated upon irradiation.

Модель накопления зарядов в n- и p-МОП-транзисторах при туннельной инжекции электронов из затвора

AbstractA quantitative model for charge accumulation in an undergate dielectric during tunneling electron injection from a gate according to the Fowler–Nordheim mechanism is developed. The model takes into account electron and hole capture at hydrogen-free and hydrogen-related traps as well as the generation of surface states during the interaction of holes with hydrogen-related centers. The experimental dependences of the threshold voltage shift and gate voltage shift of n - and p -channel MOS (metal–oxide–semiconductor) transistors on the injected charge in the constant current mode are analyzed based on the model.

Thickness-Dependent Binding Energy Shift in Few-Layer MoS2 Grown by Chemical Vapor Deposition

The thickness-dependent surface states of MoS2 thin films grown by the chemical vapor deposition process on the SiO2-Si substrates are investigated by X-ray photoelectron spectroscopy. Raman and high-resolution transmission electron microscopy suggest the thicknesses of MoS2 films to be ranging from 3 to 10 layers. Both the core levels and valence band edges of MoS2 shift downward ∼0.2 eV as the film thickness increases, which can be ascribed to the Fermi level variations resulting from the surface states and bulk defects. Grainy features observed from the atomic force microscopy topographies, and sulfur-vacancy-induced defect states illustrated at the valence band spectra imply the generation of surface states that causes the downward band bending at the n-type MoS2 surface. Bulk defects in thick MoS2 may also influence the Fermi level oppositely compared to the surface states. When Au contacts with our MoS2 thin films, the Fermi level downshifts and the binding energy reduces due to the hole-doping characteristics of Au and easy charge transfer from the surface defect sites of MoS2. The shift of the onset potentials in hydrogen evolution reaction and the evolution of charge-transfer resistances extracted from the impedance measurement also indicate the Fermi level varies with MoS2 film thickness. The tunable Fermi level and the high chemical stability make our MoS2 a potential catalyst. The observed thickness-dependent properties can also be applied to other transition-metal dichalcogenides (TMDs), and facilitates the development in the low-dimensional electronic devices and catalysts.

Positive bias temperature instability in p-type metal-oxide-semiconductor devices with HfSiON/SiO2 gate dielectrics

We present a detailed investigation on positive-bias temperature stress (PBTS) induced degradation of nitrided hafnium silicate (HfSiON)/SiO2 gate stack in n+-poly crystalline silicon (polySi) gate p-type metal-oxide-semiconductor (pMOS) devices. The measurement results indicate that gate dielectric degradation is a composite effect of electron trapping in as-fabricated as well as newly generated neutral traps, resulting a significant amount of stress-induced leakage current and generation of surface states at the Si/SiO2 interface. Although, a significant amount of interface states are created during PBTS, the threshold voltage (VT) instability of the HfSiON based pMOS devices is primarily caused by electron trapping and detrapping. It is also shown that PBTS creates both acceptor- and donor-like interface traps via different depassivation mechanisms of the Si3 ≡ SiH bonds at the Si/SiO2 interface in pMOS devices. However, the number of donor-like interface traps ΔNitD is significantly greater than that of acceptor-like interface traps ΔNAit, resulting the PBTS induced net interface traps as donor-like.

Comparison of electrical stress-induced charge carrier generation/trapping and related degradation of SiO 2 and HfO 2/SiO 2 gate dielectric stacks

We compare charge carrier generation/trapping related degradation in control oxide (SiO 2) and HfO 2/SiO 2 stack of an identical equivalent-oxide-thickness (EOT) during constant gate voltage stress of n-type metal-oxide-semiconductor (nMOS) capacitors. Irrespective of these two dielectrics, the kinetics of generation of both surface states and oxide-trapped positive charges are found to be similar. Our analysis shows that the positive oxide charge buildup during CVS is due to trapping of protons by the strained Si O Si bonds in either of the devices. We demonstrate that compared to SiO 2 devices, HfO 2 devices with an equal EOT better perform in CMOS logic applications. On the other hand, our results indicate that the control oxide is better in charge trapping memory devices. Furthermore, the lifetime of the control oxide devices is observed longer than that of HfO 2 devices at a given operating voltage.

Ultrahigh Responsivity Visible and Infrared Detection Using Silicon Nanowire Phototransistors

Nanowire photodetectors can perform exceptionally well due to their unique properties arising from the nanowire geometry. Here we report on the phenomenal responsivity and extended spectral range of scalable, vertically etched, silicon nanowire photodetector arrays defined by nanoimprint lithography. The high internal gain in these devices allows for detection at below room temperatures of subfemtowatt per micrometer visible illumination and picowatt infrared illumination resulting from band to surface state generation.

Charge Trapping Related Degradation of Thin HfAlO ∕ SiO2 Gate Dielectric Stack during Constant-Voltage Stress

Charge carrier generation/trapping and the related degradation of a thin stack in n-type metal-oxide-semiconductor capacitors have been investigated under constant gate voltage stress. The results show that dielectric degradation is a composite effect of neutral trap creation, surface state generation at the interface, and positive charge trapping in the bulk. The neutral traps created during stress are homogeneously distributed across the oxide following Poisson’s random statistics. A significant amount of border-trapped charges was observed in both as-deposited and poststressed devices. The kinetics of generation of both oxide-trapped positive charges and interface trapped charges are found to be similar. Both these defects are possibly created by the hydrogen-related species. We demonstrate that compared to devices, HfAlO devices with an equal equivalent oxide thickness (EOT) show better performances in memory and logic applications. On the contrary, at a given stress voltage, the threshold voltage degradation and stress-induced leakage current degradation in HfAlO samples are larger, indicating a shorter device lifetime compared to the samples of the same EOT.

Processing Factors Impacting the Leakage Current and Flicker Noise of Germanium p + -n Junctions on Silicon Substrates

The impact of several processing factors, such as the n-well doping, the use of nickel-germanidation, and the postmetallization anneal (PMA) temperature, on the reverse current and flicker noise of -n junctions fabricated in epitaxial germanium-on-silicon substrates is investigated. It is shown that a higher well doping leads to a lower leakage current, in the range studied here, both for the perimeter and bulk component. It is furthermore shown that there exists an optimal PMA temperature around , depending on the leakage current component and the process details. The use of NiGe contacts improves the series resistance (forward current) but may deteriorate the perimeter leakage associated with surface-state generation at the interface. This is confirmed by the low-frequency noise results, showing a dominance of the perimeter component. It is demonstrated that these effects are related to the occurrence of Ni-germanidation-induced voids along the edge of the -n junctions.

Direct real-time observation of catastrophic optical degradation in operating semiconductor lasers using scanning tunneling microscopy

Cross-sectional scanning tunneling microscopy is performed on operating semiconductor quantum well laser devices to reveal real time changes in device structure. Low and nominally doped capping regions adjacent to the quantum well active region are found to heat under normal operating conditions. The increase in anion-vacancy defect formation and the generation of surface states pins the Fermi level at the surface and begins the process of catastrophic optical degradation which eventually destroys the device. The technique has implications for the study of defect generation and in-operation changes in all nanostructures.

The Role of a “Schottky Barrier” at an Electron‐Collection Electrode in Solid‐State Dye‐Sensitized Solar Cells

Solid-state dye-sensitized solar cells perform in a strictly different manner when tested under monochromatic as opposed to white-light illumination. Without a UV component in the illumination source, a Schottky barrier is present at the anode interface. Data suggest (see figure) that the generation of surface states, under white-light illumination, results in a pinning of the Fermi level in the TiO2 at the anode interface. Improving this contact facilitates significant improvement in the device performance.

Trap generation in cycled hot-electron-injection-programed/hot-hole-erased silicon-oxide-nitride-oxide-silicon memories

Generation of surface states and bulk traps in the bottom oxide of the silicon-oxide-nitride-oxide-silicon memory cells with thick bottom oxide programed by hot electron injection and erased by hot hole injection is investigated by using charge-pumping technique. It is shown that the degradation of the bottom oxide under the hot hole stress is the responsible mechanism for the shift of the programed state threshold voltage in retention bake. A physical model of the memory cell degradation is proposed that supposes trap generation by breaking the Si–H bonds in the vicinity of Si-bottom oxide interface and explains the observed trap generation kinetics.

Study of human serum albumin-TiO 2 nanocrystalline electrodes interaction by impedance electrochemical spectroscopy

The adsorption of human serum albumin (HSA) onto nanocrystalline TiO 2 electrodes was studied by electrochemical impedance spectroscopy (EIS) in function of pH and electrode potential. The characterization and physico-chemical properties of the TiO 2 electrode were investigated by scanning electron microscopy (SEM), UV-photoelectron spectroscopy (UPS), cyclic voltammetry and capacitance measurements. The impedance response of the particulate TiO 2 electrode/protein interface was fitted using an equivalent circuit model to describe the adsorption process. The adsorbed protein layer, which is formed as soon as the protein is injected into the solution and becomes in contact with the electrode, was investigated as a function of electrode potential and solution pH. The measurements were performed under pseudo-steady-state and steady-state conditions, which gave information about the different states of the system. With the pseudo-steady state measurements, it was possible to determine two rate constants of the protein adsorption process, which correspond to two different states of the protein. The shortest one was associated with the first contact between the protein and the substrate and the second relaxation time, with the protein suffering an structural rearrangement due to the interaction with the TiO 2 electrode. It was detected that at sufficiently long times (approx. 1 h, where the system was under steady state conditions), a quasi-reversible protein adsorption mechanism was established. The measurements performed as a function of frequency under steady-state conditions, an equivalent circuit with a Warburg element gave the better fitting to data taken at −0.585 V closer to the oxide flat band potential and it was associated with protein diffusion. Experimental results obtained at only one frequency as a function of potential could be fitted to a model that takes into account non-specific and probable specific protein adsorption, which renders to be potential- and pH-dependent. Low capacity values were obtained in the whole potential range, which were measured in the presence and in the absence of the protein layer. The capacity dependence on potential and pH were associated with the generation of surface states on TiO 2. A surface state concentration of 4.1×10 18 cm −2 was obtained by relating the parallel capacitance with oxide surface states arising from the protein–oxide interaction.

Enhanced Generation of Interface States in MIS IC Elements under the Action of UV and X-ray Radiations

The effect of enhanced generation of states at the Si/SiO2 interface was first observed in polySi-gate MIS structures successively subjected to UV and X-ray radiations. It was studied on test MIS transistors of series-produced ICs by the methods of subthreshold currents, charge pumping currents, and internal photoemission. A possible reason for enhanced generation of the states is the presence of hydrogen at the interface with the polySi gate. Under UV irradiation, the hydrogen diffuses toward the substrate and causes surface state generation under subsequent irradiation by X-rays.

Generation of active surface states of gold and the role of such states in electrocatalysis

The cyclic voltammetry behaviour of gold in aqueous media is often regarded in very simple terms as a combination of two distinct processes, double layer charging/discharging and monolayer oxide formation/removal. This view is questioned here on the basis of both the present results and earlier independent data by other authors. It was demonstrated in the present case that both severe cathodization or thermal pretreatment of polycrystalline gold in acid solution resulted in the appearance of substantial Faradaic responses in the double layer region. Such anamolous behaviour, as outlined recently also for other metals, is rationalized in terms of the presence of active metal atoms (which undergo premonolayer oxidation) at the electrode surface. Such behaviour, which is also assumed to correspond to that of active sites on conventional gold surfaces, is assumed to be of vital importance in electrocatalysis; in many instances the latter process is also quite marked in the double layer region.

Investigation of the oxidation of glassy carbon by the method of electroreflectance—relevance to activation processes

Abstract The oxidation of the surface of glassy carbon (GC) in 0.5 M KOH was studied by the method of electroreflectance (ER). For a freshly-prepared mechanically polished GC surface, the ER spectra have relatively low intensity and exhibit inversion of sign at the electrode potential −0.4 V. The ER spectra of the GC electrode change substantially after the electrochemical oxidation at E=+0.6 V. Oxidation considerably increases the intensity of ER, and the band located at quantum energies from 1.8 to 2.4 eV (Band A) becomes much broader. The maximum of the band shifts towards higher energies. The ER spectra depend strongly on the electrode modulation frequency. It is concluded that anodic oxidation leads to the generation of surface states whose impact on the ER spectra of GC is especially important at potentials close to the pzc. Structurally, the surface states seem to be related to the generation of edge-type carbon atoms caused by oxidation. Broadening and the shift of Band A in the ER spectra of an oxidized surface are hypothesized to be a manifestation of optical transitions from the Fermi level to the surface states. The frequency dispersion shows that there are several surface states with distinct kinetic differences. These observations support the hypothesis that activation of the surface of carbon materials is accompanied by the generation of surface states.