Surface Of Semiconductor Materials Research Articles

Label-free photoelectric sensor for lactic acid determination in human sweat

A label-free lactic acid sensor has been successfully developed by using a Dysprosium single crystal-based photoelectric potential technique via Dy-SCN/FTO electrode. Interestingly, the proposed sensor demonstrated excellent performance for l-lactic acid analysis with a wide linear range of 0.0196∼16.31 mmol/L, the detection limit of as low as 3.20 µmol/L as well as an advisable stability. The feasibility of this strategy was also verified by practical application towards human sweat samples. The mechanism studies indicated that lactic acid molecules specifically bind to the surface of semiconductor materials, which alters the charge distribution of the electrode surface and subsequently results in band bending/photoelectric potential changes. The theoretical formula for this photoelectric chemistry (PEC) strategy was then derived according to charge balance theory. We believe that the proposed Dy-SCN/FTO sensor would open a new way for rapid, non-invasive l-lactic acid level evaluation during human physical condition monitoring.

Mn0.05Cd0.95S/Cu2SeI p-n heterojunction with high-conductivity for efficient photocatalytic hydrogen evolution

It is undoubtedly that constructing heterojunction on the surface of semiconductor materials is an effective way to improve the performance of photocatalysts. Here, Cu2SeI nanospheres were dispersed on the surface of Mn0.05Cd0.95S nanoparticles constructed a p-n heterojunction photocatalyst with high conductivity. Firstly, SEM and TEM showed that the load of Cu2SeI nanospheres successfully formed a close contact on the surface of MCS, which was conducive to the rapid charge transfer between the two. Under visible light irradiation, Na2S/Na2SO3 (0.35 M/0.25 M) was used as sacrifice reagent for hydrogen production. The results showed that the construction of p-n heterojunction was beneficial to charge transfer and the hydrogen evolution ability of the composite catalyst was greatly improve, the 3%MCS/Cu2SeI showed the best hydrogen production activity reaching 677.4 μmol after 5 h, it is 12.3 times higher than that of single catalyst MCS, In addition, the results of X-ray photoelectron spectroscopy (XPS) show that the binding energies of the elements in the composite catalysts are different compared with those in the catalysts alone, indicating that there is a interaction between the catalysts. Through the analysis of photoelectrochemical and fluorescence spectra, the charge transfer kinetics of the composite catalyst was explained and discussed in depth. On the basis of the above analysis results, the possible photocatalytic reaction mechanism of the composite catalyst was proposed, and the mechanism was analyzed and discussed. This work has undoubtedly made a further improvement for the activity of photocatalytic hydrogen production.

Impact of Loading of RuO2 Co-Catalyst on Photocatalytic Activity of PbTiO3 Nanorods for Hydrogen Production Under Visible Light

The split of charge carriers is an essential point that raises the rate of hydrogen evolution in the reaction of water splitting. The avoidance of charge carrier recombination can be attained by deposition of co-catalysts onto the surface of semiconductor materials. In this work, PbTiO3 nanorods were prepared using hydrothermal route in the presence of polyvinylpyrrolidone as a surfactant. Finally, PbTiO3 nanorods were decorated by RuO2 nanoparticles and the weight percent of RuO2 changed from 0.5 to 2.0 wt%. PbTiO3 nanorods and RuO2–PbTiO3 nanocomposites were investigated for their production of hydrogen under visible light illumination in the presence of glycerol as a scavenger. The outcomes recorded that the photocatalytic activity of PbTiO3 nanorods was improved by RuO2 nanoparticles decoration. The content of RuO2 nanoparticles had an important effect on the photocatalytic activity of PbTiO3 nanorods. The best weight percent of decorated RuO2 was 1.5 wt%, which improved photocatalytic activity of PbTiO3 nanorods by about 6 times. Moreover, the photocatalytic activity of 1.5 wt% RuO2–PbTiO3 nanocomposites was almost stable for five times. The enlargement of photocatalytic activity of PbTiO3 nanorods by RuO2 decoration was due to high surface area, small bandgap and avoidance of charge carrier recombination.

Effect of GaAs(100) substrate misorientation on structural, electronic, and optical properties of AlN nano-sized films obtained by reactive plasma-ion deposition

With the use of reactive plasma-ion deposition, thin nano-sized films of AlN were obtained on the substrates of GaAs(100) with a different degree of misorientation relative to the <100> direction.It was shown that the growth of the AlN films on GaAs substrates with a small degree of misorientation resulted in the formation of the AlN films in the nano-crystalline state. Hence, the film with a cubic crystal system was formed on a precisely oriented GaAs substrate, while on the substrate with 2° misorientation, the film consisted of a mixture of the AlN phases with cubic and hexagonal crystal symmetry. At the same time, the growth of the films on the substrates with a high degree of misorientation resulted in the disappearance of the long-range order in the crystalline structure of the AlN films; this implied the formation of the AlN phase in the amorphous state. The misorientation of the GaAs(100) substrate affected the sizes of the nano-islands formed on the surface of the AlN film. The lower the misorientation of the GaAs(100) substrate, the smaller were the lateral sizes of the nano-islands.Comparing our data for the optical band gap and the dispersion of the refractive index obtained by reactive ion-plasma deposition and the results for the AlN films grown by reactive sputtering, which is the closest method to the technology used in our work, we found that depending on the conditions of the reactive sputtering, nano-sized films of AlN with refractive index values within the range of 2.26–2.38 for the energy range of ∼4.7–4.9 eV and optical band gaps within 5.34–5.71 eV, were obtained. It was possible to obtain thin films with refractive index values within the range of 1.65–3.35 for energy values of ∼4.7–4.9 eV and optical band gaps of ∼5–6.2 eV by the application of the AlN deposition on the surface of semiconductor materials proposed in this study.An increase in the misorientation degree for the GaAs substrate was observed along with an improvement in the structural quality of nano-sized AlN films as well as in their electron structure, surface morphology, and optical properties. Thus, the morphology, surface composition, and optical functional characteristics of hetero-phase AlN/GaAs systems can be controlled by using GaAs substrates with a specified degree of misorientation relative to the <100> direction.

The iron oxyhydroxide role in the mediation of charge transfer for water splitting using bismuth vanadate photoanodes

The water photo-oxidation to oxygen on iron oxyhydroxide (FeOOH) deposited on a surface of semiconductor materials play a crucial role in the enhancement of different devices. In order to investigate how FeOOH works to produce O2 from water splitting, we have investigated the role of a deposited layer of FeOOH on the bismuth vanadate (BiVO4) films. The simple-modified method based on polyethylene glycol was applied to produce BiVO4 nanostructures and a FeOOH photoelectrodeposition methodology was used to cover the BiVO4 film surface. The photoelectrochemistry study for FeOOH modified BiVO4 revealed a 3.4 times increase in the photocurrent at 1.23 V vs. RHE. A possible explanation to the FeOOH mechanism is that it is actually a green rust containing a mixture of Fe (II) and Fe (III) that acts as center of charge transfer mediation and not as a catalyst itself. This hypothesis has been supported by a change absence in the onset potential, no photocurrent saturation, and no change in the charge carrier density. Moreover, the FeOOH also passivated the surface states of BiVO4 as the open circuit potential shifted 70 mV vs. RHE to more positive potentials.

X-ray topography of subsurface crystal layers.

New capabilities of the Berg-Barrett topographic method are demonstrated using a skew-asymmetric X-ray diffraction scheme for investigating structural changes near the surface of semiconductor materials. Specifying the X-ray extinction depth, the details of defects and strains are revealed with high resolution. Consequently, analysis of structural distortion of layers near the surface after various types of surface processing becomes more complete.

Stress vs sputtering effects in the propagation of surface ripples produced by ion-beam sputtering

Under low energy ion irradiation, periodic features (ripples) can develop on the surfaces of semiconductor materials, with typical sizes in the nanometric range. Recently, a theory of pattern formation has been able to account for the variability with the ion/target combination of the critical angle value separating conditions on ion incidence that induce the presence or the absence of ripples. Such a theory is based in the accumulation of stress in the damaged irradiated layer and its relaxation via surface-confined viscous flow. Here we explore the role of stress, and its competition with purely erosive mechanisms, to determine the sign of the velocity with which the ripple pattern moves across the target plane. Based on this theory, we discuss different situations and make specific testable predictions for the change of sign in that velocity.

Properties of Ion–Electron Emission from the Surface of Semiconductor Material During Reactive Ion–Beam Etching

The existing methods of diagnosis of solid surfaces in ion − plasma processes have been analyzed. We found that the most efficient method of estimating surface condition, determining the transition of the etching process from one layer to another and determining the end of the etching process is the registration of ion − electronic emission during ion − beam etching. Results on secondary electron current for ion beam etching of various semiconductors have been reported. We show the experimental setup and describe the electric circuit for the detection of secondary electrons. An experimental study has been carried out to determine the dependence of secondary electron current on the band gap E g and the height of the potential barrier (electron affinity) χ of Ge, Si, GaAs, GaP and SiC semiconductor materials. We found no clearly expressed dependence of integral signal of ion − electronic emission on E g and χ . We show that under the conditions of ion beam etching under the influence of the surface potential the electric field penetrates in the semiconductor volume, leading to a shift in the energy levels of electrons in the surface layer and a change in the secondary electron current due to the appearance of autoelectronic emission. We found that the signal of ion − electronic emission in n − type silicon is higher than in p − type silicon. A model of ion − electronic emission from the surface of semiconductors is presented for the conditions of ion − beam etching, consisting of: emission with the participation of conductivity band electrons, emission due to the direct transition of electrons in the ion – atom system, and autoelectronic emission under the influence of surface potential.

Particle density distribution in a pyramid-shaped quantum well

This paper is focused on analytical solution of the quantum–mechanical problem describing a particle confined into a pyramid-shaped quantum well. This type of micro- and nano-scale objects can be formed on the surface of semiconductor material as texturing elements for solar cells, Bragg reflectors, quantum dot lasers, etc. The problem was treated using specular reflections of plain wave functions of the particle from the sides of the pyramid. Defining a closed group of symmetry transformations for the system, we solve Schrödinger equation in the Cartesian coordinates. This wave function was used to calculate three-dimensional distributions of particle probability density within a square-based pyramid. Analysis of excited states energy reported in publications shown good correlation between our theoretical calculations and experimental data.

Silicate nanosized films prepared by the sol-gel method for use in planar technology for fabricating semiconductor gas sensors

This paper reports on the results of investigations into the specific features of the formation of silicate nanosized films from sols based on tetraethoxysilane (hydrolyzed in an acid medium in the presence of inorganic dopants) on the surface of semiconductor materials. The properties of the films thus prepared are analyzed as functions of the synthesis conditions of sols and the conditions of deposition and heat treatment of the films. It is demonstrated that these films can be used in technology for fabricating semiconductor gas sensors based on SnO2.

Scanning Probe Microscopy: Present Status and New Development. Basic Performance of Near-Field Optical Microscope and Its Applications.

The principles of aperture- and scattering (apertureless)-type near-field optical microscopies (NOM), their related techniques, and their applications are summarized. In terms of a key device of the aperture-type NOM, the functional performance of an optical fiber probe with a small metal aperture is demonstrated through measurement of the photoluminescence image of single quantum dots. In the range of 50-100nm spatial resolution, the aperture-type NOM is an established and reliable technique for the spectroscopy of highly localized structures: spatially resolved spectroscopy of the surface of semiconductor materials or spectroscopic analysis of single particles, such as single molecules, single quantum dots, single metal particles, and so on. The scattering-type NOM, on the other hand, is a promising device to be applied to the surface enhanced spectroscopy, nano-manufacturing, and high density optical memory with higher spatial accuracy and higher efficiency.

STM: Seeing is believing

In the last ten years the scanning tunnelling microscope (STM) has completely changed the way in which we look at the surfaces of semiconductor materials. However, due to the conflicting experimental geometries of the two techniques, it is only recently that it has been possible to combine high resolution STM imaging with a full scale MBE system. In this article we demonstrate the application of this technique in obtaining both morphological and atomic resolution images of MBE grown GaAs(001) surfaces and the same surfaces after deposition of Si.

Selective Electroless Gold Plating on the Surface of Semiconductor Materials for Fabrication of Device Heat Sink

A methodical experimentation for electroless deposition of Gold metal on semiconductor substrate like Silicon is presented. This method involves minimum loss of metal and thick layers can be easily deposited on the substrate using photoresist as a mask. The rate of coating is in the range of 7.0 micrometer to 10.0 micrometer per hour without any deterioration of the photoresist which makes the present method quite attractive for heatsink formation.

Proton backscattering investigation of deformed layers formed at treatment of surface of semiconductor materials: V P Alekhin et al,Struct Defects in Semicon, Coll, Novosibirsk 1973, 166–169 ( in Russian)

Proton backscattering investigation of deformed layers formed at treatment of surface of semiconductor materials: V P Alekhin et al,Struct Defects in Semicon, Coll, Novosibirsk 1973, 166–169 ( in Russian)

Silicon Slice Analyzer Using a He‐Ne Laser

Design criteria and performance characteristics are presented of an optical system capable of detecting imperfections (fractures, scratches, etc.) on the polished surfaces of semiconductor materials. This instrument is also capable of providing fast and accurate defect counting and distribution on polished, etched semiconductor surfaces. The principle involved is that of scanning a He‐Ne laser beam which is focused on the surface of the slice, and analyzing the reflected and scattered light via polarizers and photomultipliers.