Thermal Field Treatment Research Articles

Application of Unconventional External-Field Treatments in Air Pollutants Removal over Zeolite-Based Adsorbents/Catalysts

Zeolite-based materials are widely used as adsorbents and catalysts for purifying air pollutants like NOx and VOCs due to abundant pore structure, regular pore distribution, and numerous ion exchange sites. Thermal treatment is a necessary procedure for both removing impurities in pores and promoting the metal active dispersed evenly before the zeolite-based adsorbents/catalysts were applied for purifying the NOx/VOCs. Nevertheless, the conventional thermal field treatment (i.e., high-temperature calcination, high-temperature purging, etc.) takes large energy consumption. In contrast, unconventional external-field treatments such as non-thermal plasma and microwave show significant advantages of high efficiency, low energy consumption as well and low pollution, which were used to substitute the traditional thermal treatment in many fields. In this paper, the roles of non-thermal plasma or microwave in the adsorption/catalysis of the NOx/VOCs are reviewed from three aspects assisting activation of materials, cooperative catalysis process, and assisting zeolites synthesis. The reasons for unconventional treatments in improving textural properties, active sites, performance, etc. of zeolite-based materials were illuminated in detail. Moreover, the influences of various parameters (i.e., power, time, temperature, etc.) on the above aspects are elaborated. It is hoped that this review could provide some advanced guidance for the researchers to develop highly efficient materials.

Влияние ловушек на накопление подвижного заряда в МОП-структурах при термополевых обработках

A quantitative model describing the influence of traps on the parameters of mobile charge migration in the gate dielectric of MOS structures is presented. The dependences of the effective diffusion coefficients and activation energy on trap accumulation, ion-trapping binding energy, impurity concentrations, and thermal field treatment temperatures are calculated. An increase in trap concentration was found to hamper mobile charge accumulation in the vicinity of the Si-SiO2 interface. The presented model can be used to explain the scattering of experimental data on sodium ion diffusion in silicon dioxide.

Prediction of the Magnitude of the Trapped Charge in the Buried Oxide of Silicon-on-Insulator Structures Using the Poole–Frenkel Effect

The possibility of predicting the magnitude of the trapped charge in the buried oxide of silicon-on-insulator structures using the Poole–Frenkel effect is investigated. The conditions for the Poole–Frenkel effect in this layer are determined by measuring and modeling the current–voltage characteristics of buried silicon oxide at various temperatures. Processes occurring in the buried oxide when measuring the current–voltage characteristics and during annealing are considered. The conditions of thermal-field treatment of the buried oxide for imitation of the radiation effect using injection are determined. The dependence of the magnitude of the accumulated positive charge in buried silicon oxide due to injection on the Poole–Frenkel current is evaluated. The possibility of applying the Poole–Frenkel effect for evaluating the imperfection of the buried oxide when fabricating microcircuits with increased radiation-dose resistance is shown.

Прогнозирование величины захваченного заряда в захороненном оксиде кремния структур кремний-на-изоляторе с применением эффекта Пула-Френкеля

The opportunity to predict trapped charge value in buried silicon oxide of silicon-on-insulator structures using Poole−Frenkel effect was investigated. Using measuring and modeling of current–voltage characteristics of buried silicon oxide at different temperatures conditions for Poole−Frenkel effect in this layer were determined. Processes taking place in buried oxide during measurement of current–voltage characteristics and annealing were considered. Conditions of thermal field treatment of buried oxide for radiation exposure imitation using injection were determined. Dependence of accumulated positive charge value in buried silicon oxide as a result of injection on Poole−Frenkel current value was estimated. The opportunity to use Poole−Frenkel effect for buried oxide defectiveness evaluation during manufacturing of microcircuits with enhanced dose radiation hardness is shown.

Electrochemical etching of metal wires in low-stress electric contact using a liquid metal electrode to fabricate tips for scanning tunneling microscopy

A liquid metal electrode of Ga was used to reproducibly fabricate a sharpened metal tip with an elongated shank by electrochemical etching for scanning tunneling microscopy (STM). The electrode was in contact with the wire for the tip in low stress; it was prevented that the tip end from being rugged owing to mechanical tear-off on splitting into two pieces by etching. The wire was vertically penetrated down through a film of an electrolyte solution held in meniscus onto a platinum (Pt) ring, and the lower part of the wire under the film was softly in contact with an electrode of the liquid metal having high wettability and viscosity, resulting in a good electric contact. A tip with a radius less than 20nm and an elongated tip length of order of 1μm was obtained, which was preferable for the build-up process in a thermal-field treatment. The tip was evaluated by scanning electron microscopy and field emission microscopy, and used in STM observation.

Self-correction of field-effect transistor characteristics in the mode of spontaneous space-charge ion polarization of gate oxide

Spontaneous space-charge ion polarization of gate oxide in the inversion n-channel silicon field-effect transistor was accomplished in the mode of its Joule heating by the drain current Id. The transistor characteristics measured at room temperature (Tr) before and after thermal-field treatment show that positive ion (Na+) localization near the SiO2/Si interface is accompanied by an increase in the effective electron mobility (by a factor of ∼ 2.3), steepness, Id, and by a small decrease in the threshold voltage (ΔVth = 0.58 V). At T = Tr, the modified transistor characteristics are retained for months; they can be easily and predictably varied by changing Id and heating duration.

Thermal-field treatment for creating single-crystal tungsten tips with ultimate sharpness

Thermal-field (TF) treatment conditions for ⟨111⟩ oriented single-crystal tungsten tips have been systematically studied using the remolding process, which employs a reversely polarized field in the treatment, in order to establish a treatment sequence for producing the nanotip that ends with a very sharp ⟨111⟩ apex at the end. As the remolding voltage is increased at a specific temperature, initially hemispherical tungsten tip evolves in shape due to the growth of low index facets such as (110), (211), and (110) crystal-planes. The tip finally takes a polyhedral shape. The treatment temperature has a significant effect in the shape evolution course. When the temperature is high enough, the (211) planes shrink as the treatment field is increased. Three (110) planes make the ⟨111⟩ apex in this case. At lower temperatures, the ⟨111⟩ apex remains formed by the (211) planes until the remolding voltage is increased to an extreme, which results in a number of microprotrusions on the tip surface. A scheme has been proposed for the creation of the nanotip with ultimate sharpness. Here, the TF treatment is first conducted at a relatively high temperature until the (211) plane collapse takes place. Then, the temperature is reduced and the increase of the remolding voltage resumed. It is possible, by periodically observing field-emission patterns, to terminate the TF treatment at the right stage where the ⟨111⟩ apex achieves the sharpest configuration. The field emission from the nanotip can provide electron beam with much better angular intensity and confinement than conventional field emitters.

Mechanism of surface-tension reduction by electric-field application: Shape changes in single-crystal field emitters under thermal-field treatment

The shape change of the ⟨100⟩-oriented tungsten single-crystal field emitter tip under thermal-field (TF) treatment was systematically studied with increasing remolding field (i.e., reversely polarized field opposite to field-emission polarity) at a constant temperature. The initially hemispherical emitter tip builds up to polyhedral shapes with increasing remolding voltage. These shapes are formed by certain low-index crystal planes. On further increase of the voltage, an overremolding state is reached in which the emitter takes a rugged surface structure. A thermodynamic model is proposed to explain the buildup mechanism utilizing the reduction of the surface tension under the influence of a strong electric field. The theory assumes the emitter-extractor system to comprise an electric capacitor and includes the electrostatic-field energy stored around the emitter into the system under consideration. It is shown that the electrostatic-field energy term in the Gibbs free energy could be interpreted as an effective reduction of the surface tension. The initially moderate anisotropy of the intrinsic surface tension is increasingly enhanced by the electrostatic-field energy through the reduction mechanism. The facets on the emitter surface consequently develop in accordance with the Wulff construction of the equilibrium crystal shape (ECS). By application of an electric field, the surface free-energy anisotropy can be made large enough to induce complete faceting of the crystal even at an elevated temperature where the crystal shape can immediately follow the ECS.

Field-Desorption Microscopy Study of the Deformation of a Tungsten Tip Subjected to Thermal Treatment in an Electric Field

Deformation of a tungsten tip 500 to 1000 nm in radius subjected to heating in an electric field is studied using field-emission microscopy and continuous-mode field-desorption microscopy. Measurements are performed immediately after the thermal field treatment without any smoothing of the tip by either heating or field evaporation. The edges of the tip (which is shaped into a polyhedron) are found to consist of monatomic steps about 1 nm wide and about 100 nm long. Microscopic protrusions about 10 nm in size are shaped like pyramids or wedges with single-atom apexes or monatomic edges and facets that are a continuation of the facets of the reconstructed tip or an outgrowth on which the protrusions are situated. The outgrowths are shaped like stepped truncated pyramids with monatomic edges. The observed phenomena are explained in terms of competing processes of surface diffusion, crystal growth in an electric field, and field evaporation.

Formation processes of fine structures induced by high electric fields

The buildup processes of a [100]-oriented tungsten surface in two steps have been studied by field-electron microscopy (FEM). An initial thermal field treatment is necessary to obtain an ideal tip profile around the [100] orientation. Based on this pretreated tip, some fine and unusual emission patterns result. Three types of buildup processes that cannot be obtained by conventional methods are observed. The experiment shows that the application of FEM can go one step further for the thermal-field case based on conventional methods.

Surface reconstruction induced electrically in two steps

Field electron microscopy (FEM) studies on the reconstruction in two steps are reported. The ordering of crystal plane terraces of the W(1 0 0) tip is observed under favorable conditions. An initial thermal field treatment is applied to obtain a relative ideal smaller tip around the [1 0 0] orientation. An unusual build-up process is induced electrically and ordered arrangement patterns of atoms and clusters of a W(1 0 0) surface covered with oxygen can be obtained at 1300 K by FEM. The migration process of terraces can be in situ observed. The formation of a nanometer size protrusion on tip apex with terrace structure is introduced to explain the ordered arrangement patterns.

Tunneling condition dependence of electron standing waves in vacuum gaps on Au(111) and Si(001) observed by scanning tunneling microscopy

Using a scanning tunneling microscope, the differential conductance (d I/d V) versus the applied bias voltage ( V) on Au(111) and n- and p-type Si(001) surfaces was measured under a constant tunneling current. STM tips were treated by a thermal-field treatment before measurements to improve the reproducibility of d I/d V– V curves. For both directions of electron tunneling from tip to sample and vice versa, oscillation phenomena in the d I/d V– V curves were found, owing to excitation of electron standing waves in a vacuum gap between a tip and a sample surface. For electron tunneling from sample to tip, oscillation peaks for n-type Si(001) were weakened near applied voltages corresponding to an averaged work function of sample and tip possibly due to electron emission from surface states. The features in the oscillation phenomena of the d I/d V– V curves are discussed on the basis of the energy band diagram.

Effect of thermal-field treatment and ionizing radiation on the energy spectrum of interfacial states at the Si-SiO2 interface of a MOS transistor

Effect of thermal-field treatment and ionizing radiation on the energy spectrum of interfacial states at the Si-SiO2 interface of a MOS transistor

Sharpening Processes of Scanning Tunneling Microscopy/Scanning Tunneling Spectroscopy Tips by Thermal Field Treatment

In order to prepare a scanning tip suitable for scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS) operated in ultrahigh vacuum (UHV) with a reproducible and ideal profile of the [111]-oriented W tip, sharpening and cleaning treatments were carried out by heating the tip while applying high voltage in UHV (thermal field (T-F) treatment). The treated tips were evaluated by field emission microscopy (FEM). The appropriate values to build up the W tip along the [111] axis for a treatment parameter, |VT-F/V base|, range from 2 to 2.6 under fixed conditions of tip heating temperature and time of about 1300 K and 60 s, respectively. It has been also realized that the formation of an ideal tip completely surrounded by three {112} facets at its apex requires a successive heat treatment: an initial T-F treatment, simple heating at about 1000 K to develop the {112} facets, and a final T-F treatment.