Thickness Of SiO2 Layer Research Articles

The 30-band k ⋅ p theory of valley splitting in silicon thin layers

The valley splitting of the conduction-band states in a thin silicon-on-insulator layer is investigated using the 30-band k ⋅ p theory. The system composed of a few nm thick layer embedded within thick SiO2 layers is analyzed. The valley split states are found to cross periodically with increasing quantum well width, and therefore the energy splitting is an oscillatory function of the quantum well width, with period determined by the wave vector K0 of the conduction band minimum. Because the valley split states are classified by parity, the optical transition between the ground hole state and one of those valley split conduction band states is forbidden. The oscillations in the valley splitting energy decrease with electric field and with smoothing of the composition profile between the well and the barrier by diffusion of oxygen from the SiO2 layers to the Si quantum well. Such a smoothing also leads to a decrease of the interband transition matrix elements. The obtained results are well parametrized by the effective two-valley model, but are found to disagree from previous 30-band calculations. This discrepancy could be traced back to the fact that the basis for the numerical solution of the eigenproblem must be restricted to the first Brillouin zone in order to obtain quantitatively correct results for the valley splitting.

Influence of SiO2 Spacer Layer Thickness on Performance of Plasmonic Textured Silicon Solar Cell

We investigated the effect of SiO2 spacer layer thickness between the textured silicon surface and silver nanoparticles (Ag NPs) on solar cell performance using quantum efficiency analysis. Separation of Ag NPs from high index silicon with SiO2 layer led to modified absorption and scattering cross-sections due to graded refractive index medium. The forward scattering from Ag NPs is very sensitive to SiO2 layer thickness in plasmonic silicon cell performance due to the evanescent character of generated near-fields around the NPs. With the optimized ∼30–40 nm SiO2 spacer layer, we observed an enhancement of solar cell efficiency from ∼8.7 to ∼10 %, which is due to the photocurrent enhancement in the off-resonance surface plasmon region. We also estimated minority carrier diffusion lengths (Leff) from internal quantum efficiency data, which are also sensitive to SiO2 spacer layer thickness. We observed that the Leff values are enhanced from ∼356 to ∼420 μm after placing Ag NPs on ∼40 nm spacer layer due to improved forward (angular) scattering of light from the Ag NPs into silicon.

Adsorbate dynamics on a silica-coated gold surface measured by Rydberg Stark spectroscopy

Trapping a Rydberg atom close to a surface is an important step towards the realisation of many proposals for quantum information processing or hybrid quantum systems. One of the challenges in these experiments is posed by the electric field emanating from contaminations on the surface. Here we report on measurements of an electric field created by 87Rb atoms adsorbed on a 25 nm thick layer of SiO2, covering a 90 nm layer of Au. The electric field is measured using a two-photon transition to the and states. The electric field value that we measure is higher than typical values measured above metal surfaces, but is consistent with a recent measurement above a SiO2 surface. In addition, we measure the temporal behaviour of the field and observe that we can reduce it in a single experimental cycle, using ultraviolet light or by mildly locally heating the surface with one of the excitation lasers, whereas the buildup of the field takes thousands of cycles. We explain these results by a change in the adatom distribution on the surface. These results indicate that, while the stray electric field can be reduced, achieving field-free conditions above a silica-coated gold chip remains challenging.

Interference-enhanced Raman scattering of F16CuPc thin films

Interference-enhanced Raman scattering (IERS) was observed for thin films of copper(II) hexadecafluorophthalocyanine (F16CuPc) deposited on SiO2 layers on a Si substrate. The enhancement of the Raman scattering originates from the interference of the light in the transparent SiO2 layer. Stripes of SiO2/Si with gradually varying oxide layer thickness were used as IERS substrates for a systematic study of the enhancement parameters. Raman measurements were carried out using three laser lines (325, 514.7, and 632.8 nm) in order to probe the F16CuPc thin films at non-resonant and resonant Raman conditions. Spectroscopic ellipsometry was used to determine both the SiO2 layer and thin film thicknesses. The intensity enhancement of the F16CuPc Raman peaks occurs periodically, corresponding to the alternating interference conditions for the Raman scattered light with increasing SiO2 layer thickness. The enhancement factors were calculated using the optical constants of the layers involved and the geometric parameters. This allows a straightforward application of IERS for optical studies of thin films and interfaces by calculating the dielectric thickness where maximum Raman enhancement is expected.

Al doped ZnO based metal–semiconductor–metal and metal–insulator–semiconductor–insulator–metal UV sensors

The paper reports the fabrication and characterization of Al doped ZnO (Al:ZnO) based metal–semiconductor–metal (MSM) and metal–insulator–semiconductor–insulator–metal (MISIM) ultraviolet sensors (Ss). The Al:ZnO thin film was grown on a p-type Si substrates by RF-sputtering method and palladium (Pd) was used as interdigitated metal electrodes for the MSM and MISIM devices. Approximately 5nm thick layer of SiO2 were deposited above Al:ZnO thin film for MISIM devices. The I–V characteristics of MSM and MISIM devices with finger-spacing of 5μm were measured under dark and under ultraviolet (UV) light. It was found that Iphoto/Idark values were 0.893×102 and 1.735×103 also the measured responsivities were 0.0411 and 0.0155A/W for MSM and MISIM UV sensors (UVSs), respectively. These devices can find applications in various electronic and optoelectronic systems.

Effect of different oxide thickness on the bending Young's modulus of SiO2@SiC nanowires.

The surface or sheath effect on core-shell nanowires plays an important role in the nanomechanical test. In the past few years, SiC nanowires have been synthesized using various methods with an uneven and uncontrollable amorphous silicon dioxide sheath. The bending Young’s modulus of the SiC nanowires has scarcely been measured, and the effect of the oxide sheath has not been taken into account. In this paper, SiO2-coated SiC (SiO2@SiC) nanowires were synthesized using the chemical vapor deposition method, followed by thermal reduction. Scanning electron microscopy and transmission electron microscopy show that the SiO2@SiC nanowires in this paper have diameters ranging from 130 ~ 150 nm, with the average thickness of SiO2 layer approximately 14 nm. After different processing times with 1 mol/L NaOH, approximately 5 nm, 9 nm, 14 nm silicon dioxide layers were obtained. The results of the three-point-bending test show that the modulus of SiO2@SiC nanowires is found to clearly decrease with the increase in oxide thickness and the influence of the oxide sheath should not be ignored when the layer thickness is above 5 nm. Young’s modulus of the SiO2@SiC nanowires calculated in this study by the core-shell structure model is in good agreement with the theoretical value.

Periodic oscillation in the reflection and photoluminescence spectra of suspended two-dimensional crystal flakes

Suspended two-dimensional (2D) materials have been widely used to improve the device performances in comparison with the case of supported 2D materials. To realize such a purpose, 2D materials are mainly suspended on the holes of substrates, which are usually used to support 2D materials. The holes beneath the 2D materials are usually full of air. The air layer with the thickness identical to the hole depth will affect the spectral features of the reflection and photoluminescence spectra of suspended 2D materials because there exist multiple optical interferences in the air/2D-flakes/air/Si multilayer structures. However, it is not clear that how the spectral features depend on the hole depth. In this paper, the reflection spectra of suspended multilayer graphene and MoS2flakes as well as the photoluminescence spectra of suspended multilayer MoS2flakes are systematically studied. The reflection spectra of suspended multilayer graphene flakes exhibit obvious oscillations, showing the optical characteristic with periodic oscillations in wavenumber. The oscillation period decreases with increasing the hole depth (or the thickness of the air layer), but is independent of the thickness of suspended graphene flakes. This can be well explained by the model based on multiple optical interferences in the air/graphenes/air/Si multilayer structures, which have been successfully utilized to understand the Raman intensity of ultrathin 2D flakes and substrate beneath the ultrathin 2D flakes dependent on the thickness of 2D flakes, the thickness of SiO2 layer, the laser wavelength and the numerical aperture of objective. The theoretical simulation shows that the oscillation is obviously observable only when the hole depth reaches up to the value on the order of microns. For suspended multilayer MoS2flakes, the reflection and photoluminescence spectra show similar periodic oscillations in wavenumber and the oscillation period is also dependent on the hole depth. The hole depth is measured by the surface profiler. It is found that the calculated oscillation period based on the measured hole depth and multiple optical interference model is usually larger than the experimental one, which is attributed to the existence of the dielectric layer in the holes. The dielectric layer may be the residues after the hole etching process, which have much smaller refractive indexes than substrates and 2D flakes. This results in an increase of the effective hole depth, which becomes larger than the one measured by the surface profiler. The observation of oscillation period in the reflection and photoluminescence spectra of different flakes of 2D materials demonstrates that the periodic oscillation is a general optical characteristic for optical spectra of suspended 2D materials. In principle, the electroluminescence spectra of suspended 2D materials may also exhibit similar periodic oscillations in wavenumber. These findings may be helpful for understanding the optical spectra of various suspended 2D materials and monitoring the existence of the residues in the holes of substrate after the etching process.

Characterization of effective conductive layer of nano organic thin film using reflectance spectroscopy

We propose an optical approach for analyzing the formation of the conductive layer during organic thin film growth. The relationship between the properties of multi-layer film, such as thickness and optical coefficients, and the corresponding differential reflectance spectrum (DRS) is derived as math formula based on the effective medium approximation. With the deduced formula, the thickness of the deposited film, for example, electron transport layer in this paper, can be estimated according to the measured DRS data. But, in fact, the fitting error always exists. It is, on the other hand, a useful evidence to indicate the actual situation of the thin film. A concept of the normalized fitting error (NFE) is offered here to equivalently assess the fitting results of all DRS data in the growth process. The curve of NFE versus time is proposed to analyze the growth revolution of the thin film and reveal the inner physical mechanism. In order to demonstrate the performance of the proposed method, an organic field effect transistor (OFET) with a bottom-gate structure is fabricated and pentacene organic thin film is deposited by vacuum thermal evaporation, as an electron transport layer, on the top of the transistor, i. e., an insulator substrate of Si/SiO2. The reflected optical spectrum and the current between the drain and the source of the OFET device are investigated in real time in the growth process. It has been reported that pentacene has three kinds of crystal structures and their optical properties differ from each other. The actual phase of the pentacene film in our experiment is discussed at first. The fitting results show that the pentacene layer exists mainly in thin film phase here. Then, the thickness of SiO2 layer is determined to be 296 nm, which is close to the design value of 300 nm. With those parameters, a four-layer model is used to calculate the thickness of the organic film. The thickness data indicate that the film appears to be linearly growing and the growth rate is 0.2 nm/min. Next, the NFE is plot as a function of time. In this plot, the curve of the NFE increases quickly at the beginning of the growth and reaches to a positive peak at 70 min. After that, the NFE decreases and then keeps constant for a while. When the measured current-time curve is added into this plot, one finds that the increase of the current happens at the same time with the peak of the NFE. It implies that the NFE is related to the structure change of the organic film and thus linked indirectly to the electronic property. The peak of the NFE, to a certain extent, reveals the completeness of the organic conductive layer. As a result, the presented optical approach is valuable for analyzing the electronic status of the organic thin film, especially if the electronic test cannot be performed.

Optimization of a guided-mode resonance filter by varying the thickness of the buffer layer

In this Letter, we demonstrate that by adjusting the thickness of the buffer layer, the optical responses of a guided-mode resonance filter (GMRF) can be improved for sensor applications. The GMRF is fabricated using a replica molding with a plastic substrate and a UV-curable polymer. SiO2 buffer layers of different thicknesses are deposited before the waveguide-layer deposition. The sensitivity of the GMRFs decreases slightly with increasing SiO2 layer thickness. By contrast, the full width at half-maximum reduces substantially with increasing SiO2 layer thickness, resulting in the improvement of the overall figure of merit.

Structural and phonon properties of InN synthesized by ion implantation in SiO2

Ion-implantation is a powerful technique for the formation of compound semiconductor nanocrystal precipitates in a host medium. The aim is to elaborate quantum dots for device technology purposes. High dose (5.2×1016ions/cm2) implantations of Indium (In) and Nitrogen (N) ions have been performed in a 206nm thick SiO2 layer thermally grown on <111> silicon. The implantation energies have been chosen from 12 to 180keV to produce 5–10at.% profiles overlapping at a mean depth of about 100nm. Thermal treatments between 500°C and 900°C for different annealing times lead to the formation of InN nanometric precipitates and to cure the oxide defects. In addition, the In2O3 and metallic indium phases have been observed. Their sizes, crystalline structures and depth distributions have been studied as a function of annealing temperature using grazing incidence X-ray diffraction, transmission electron microscopy, Rutherford back scattering spectrometry and Raman spectroscopy.

BeZnCdSe quantum-well ridge-waveguide laser diodes under low threshold room-temperature continuous-wave operation

Low threshold current ridge-waveguide BeZnCdSe quantum-well laser diodes (LDs) have been developed by completely etching away the top p-type BeMgZnSe/ZnSe:N short-period superlattice cladding layer, which can suppress the leakage current that flows laterally outside of the electrode. The waveguide LDs are covered with a thick SiO2 layer and planarized with chemical-mechanical polishing and a reactive ion etching process. Room-temperature lasing under continuous-wave condition is achieved with the laser cavity formed by the cleaved waveguide facets coated with high-reflectivity dielectric films. For a 4 μm-wide green LD lasing around a wavelength of 535 nm, threshold current and voltage of 7.07 mA and 7.89 V are achieved for a cavity length of 300 μm, and the internal differential quantum efficiency, internal absorption loss, gain constant, and nominal transparency current density are estimated to be 27%, 4.09 cm−1, 29.92 (cm × μm)/kA and 6.35 kA/(cm2 × μm), respectively. This compact device can realize a significantly improved performance with much lower threshold power consumption, which would benefit the potential application for ZnSe-based green LDs as light sources in full-color display and projector devices installed in consumer products such as pocket projectors.

Embedded Ge nanocrystals in SiO2 synthesized by ion implantation

200 nm thick SiO2 layers grown on Si substrates were implanted with 150 keV Ge ions at three different fluences. As-implanted samples were characterized with time-of-flight secondary ion mass spectrometry and Rutherford backscattering spectrometry to obtain depth profiles and concentration of Ge ions. As-implanted samples were annealed at 950 °C for 30 min. Crystalline quality of pristine, as-implanted, and annealed samples was investigated using Raman scattering measurements and the results were compared. Crystalline structure of as-implanted and annealed samples of embedded Ge into SiO2 matrix was studied using x-ray diffraction. No secondary phase or alloy formation of Ge was detected with x-ray diffraction or Raman measurements. Scanning transmission electron microscope measurements were done to get the nanocrystal size and localized information. The results confirmed that fluence dependent Ge nanocrystals of different sizes are formed in the annealed samples. It is also observed that Ge is slowly diffusing deeper into the substrate with annealing.

Metal-catalyst-free and controllable growth of high-quality monolayer and AB-stacked bilayer graphene on silicon dioxide

A systematic study shows that continuous graphene with controllable number of layers and stacking structure can be directly grown on SiO2/Si without any metal catalysts by chemical vapor deposition. Raman spectroscopy and mapping confirm the monolayer, bilayer and few-layer nature of the graphene with a high coverage over ∼95%. Ultraviolet photoemission spectroscopy verifies that the monolayer graphene and AB-stacked bilayer graphene have a work function of 4.46 eV and 4.50 eV, respectively, which are close to that of the intrinsic graphene. This is in contrast to the much lower work function of 4.26 eV observed on Cu-catalyzed graphene probably due to contaminants produced during the transfer process. Field-effect transistors were directly fabricated on graphene/SiO2/Si for evaluating their electric properties. Importantly, we reveal a crucial role of SiO2 layer thickness in controlling the graphene structure: (1) monolayer graphene preferably grown on thick SiO2 layer (∼300 nm or higher) by a surface-catalyzed process, and (2) AB-stacked bilayer or few-layer graphene favorably formed on thin SiO2 layer by a surface-adsorption/precipitation process. This study sheds light on the graphene growth mechanism on SiO2/Si and this insightful understanding is important to large-scale, controllable CVD growth of graphene in absence of metal catalysts.

Sensitivity enhancement of surface plasmon resonance sensor based on graphene–MoS2 hybrid structure with TiO2–SiO2 composite layer

In this paper, surface plasmon resonance (SPR) sensor based on graphene–MoS2 hybrid structure with composite layer of TiO2–SiO2 is presented. The angular interrogation method is used for the analysis of reflected light from the sensor. For the calculation of the sensitivity, first of all the thicknesses of TiO2, SiO2 and gold layers are optimized for the monolayer graphene and MoS2. Thereafter, at these optimum thicknesses the reflectance curves are plotted for different sensor structure and comparison of change in resonance angle is made among these structures. It is observed that the sensitivity of the graphene–MoS2-based sensor is enhanced by 9.24 % with respect conventional SPR sensor. The sensitivity is further enhanced by including TiO2–SiO2 composite layer between prism base and metal layer and observed that the enhanced sensitivity for this sensor is 12.82 % with respect to conventional SPR sensor and 3.28 % with respect to graphene–MoS2-based SPR sensor. At the end of this paper, the variation of the sensitivity and minimum reflectance is plotted with respect to sensing layer refractive index at the optimum thickness of all the layers and optimum number of MoS2 and graphene layers. It is also observed that four layers of MoS2 and monolayer graphene are best selection for the maximum enhancement of the sensitivity.

Multilevel Resistive Switching with Oxygen Vacancy Filaments in Pt/TaOx/Cu and Pt/TaOx/Pt Devices

Paper demonstrates that multilevel switching of oxygen vacancy (VO) conductive filaments (CF) in Cu/TaOx/Pt devices is characterized by the relation Ron=A/Icc n between ON-state resistance (Ron) and compliance current (Icc). However, in contrast to metallic (Cu, Ag) CFs, where the exponent n for various devices is found universally to be n≈1, we find for VO CFs to be n=1.36 with A=0.022. This constitutes a significant departure from n=1 found for all metallic CFs. As a consequence of n>1, the constant A can no longer be interpreted as the universal minimum switching voltage. In fact, our experiments confirmed that no minimum Vset for Vo could be ascertained. Locally, for a small Icc intervals, one can still fit the data with n=1 and extract following values for the constant A: for Icc ≈ 10nA A=1.7V, for Icc ≈ 0.1mA A=0.52 V, and for Icc=10mA A=0.06V. One concludes that at low Icc currents the minimum set voltage is high and at high Icc currents very low. We have measured the Vset of Vo CF as a function of voltage sweep rate v. We find that, as in the case of metallic CFs, the SET voltage decreases linearly with the log(v). However, in contrast to metallic CFs, the Vset for Vo CF does not saturate at a minimum set voltage, even at such slow ramp rates as v=1x10-5 V/s. We argue that an exponent n>1 implies two distinct mechanisms responsible for the formation of VO CFs. 1st mechanism is similar to the formation mechanism for metallic CFs and accounts for the unity part of the exponent, while the 2nd mechanism is responsible for the remainder (n-1). There is a consensus that at the interface between the active electrode (Cu) and the metal oxide dielectric a redox reaction is taking place: Cu ←→ Cu++e-. When negative bias is applied to Cu electrode, the redox reaction provides an efficient surface injection mechanism of electrons into the oxide while Cu+ ions are returned to the Cu electrode. The electrons are injected and may charge and dislodge a negative oxygen ion from the metal oxide matrix leaving behind a neutral oxygen vacancy Vo according to the reaction: TaOx+2e-→TaOx-1+O2-=TaOxVo+O2-. Since the redox reaction takes place at the Cu/TaOx interface and produces a large number of electrons, the creation of Vo will take place predominantly at the interface. Since the oxygen vacancy is known to provide a local Fermi level close to the conduction band, the vacancy will extend the active electrode into the oxide and act as a conduit for more electrons. Thus it is likely that another Vo will be formed below the first one extending thus the partial Vo filament as an extension of the electrode deeper into the oxide. This leads to an increased electric field between the end of the partial Vo CF and the inert electrode Pt. The self-accelerating mechanism is similar to the formation of Cu CF at positive bias. The 2nd mechanism for creation of oxygen vacancies consists in electron migration into the oxide, at random, and at some point creating a (Vo,O2-) pair but now in the bulk rather than at the surface. Over the stress time, more and more of vacancies will be generated in the same way. The increased density of vacancies will reach a critical concentration of vacancies allowing for a conductive percolation path between the two electrodes. The 2nd mechanism is verified on Pt/TaOx/Pt devices where the 1st surface electron injection mechanism is eliminated. We measure Vset for Vo CF for Pt/TaOx/Pt devices to be significantly higher, Vset≈-8V than for Cu/TaOx/Pt with Vset≈-2V. Also for Pt/TaOx/Pt devices the relation Ron=A/Icc n cannot be fully constructed: Only for Icc>1mA stable non-volatile Vo CFs could be formed. At higher set currents the cell could be set and reset but less than 10-20 times before the device is permanently damaged. To investigate the two Vo mechanisms further, we fabricated and characterized Cu/SiO2/Pt and Pt/SiO2/Pt devices. The thickness of SiO2 layer is dSiO2=32,16, and 8nm. SiO2 is known to be very stable and not susceptible to oxide damage induced by Vo. For both kind of devices with dSiO2=32nm no Vo CF could be formed even at voltages as high as 15V. For dSiO2=16nm devices Vo CF could be formed but not reliably set and reset. For dSiO2=8nm the Vo CF could be readily formed, set and reset. This behavior is explained in terms of critical size of Vo cluster and compared for ALDTa2O5, TaOx, and SiO2 dielectrics, and complements the two mechanisms discussed above.

Voltage linearity modulation and polarity dependent conduction in metal-insulator-metal capacitors with atomic-layer-deposited Al2O3/ZrO2/SiO2 nano-stacks

Excellent voltage linearity of metal-insulator-metal (MIM) capacitors is highly required for next generation radio frequency integration circuits. In this work, employing atomic layer deposition technique, we demonstrated how the voltage linearity of MIM capacitors was modulated by adding different thickness of SiO2 layer to the nano-stack of Al2O3/ZrO2. It was found that the quadratic voltage coefficient of capacitance (α) can be effectively reduced from 1279 to −75 ppm/V2 with increasing the thickness of SiO2 from zero to 4 nm, which is more powerful than increasing the thickness of ZrO2 in the Al2O3/ZrO2 stack. This is attributed to counteraction between the positive α for Al2O3/ZrO2 and the negative one for SiO2 in the MIM capacitors with Al2O3/ZrO2/SiO2 stacks. Interestingly, voltage-polarity dependent conduction behaviors in the MIM capacitors were observed. For electron bottom-injection, the addition of SiO2 obviously suppressed the leakage current; however, it abnormally increased the leakage current for electron top-injection. These are ascribed to the co-existence of shallow and deep traps in ZrO2, and the former is in favor of the field-assisted tunnelling conduction and the latter contributes to the trap-assisted tunnelling process. The above findings will be beneficial to device design and process optimization for high performance MIM capacitors.

Laser ablation of monocrystalline silicon under pulsed-frequency fiber laser

Subject of research. The paper deals with research of the surface ablation for single-crystal silicon wafers and properties of materials obtained in response to silicon ablation while scanning beam radiation of pulse fiber ytterbium laser with a wavelenght λ = 1062 nm in view of variation of radiation power and scanning modes. Method. Wafers of commercial p-type conductivity silicon doped with boron (111), n-type conductivity silicon doped with phosphorus (100) have been under research with a layer of intrinsical silicon oxide having the thickness equal to several 10 s of nanometers and SiO2 layer thickness from 120 to 300 nm grown by thermal oxidation method. The learning system comprises pulse fiber ytterbium laser with a wavelenght λ = 1062 nm. The laser rated-power output is equal to 20 W, pulse length is 100 ns. Pulses frequency is in the range from 20 kHz to 100 kHz. Rated energy in the pulse is equal to 1.0 mJ. Scanning has been carried out by means of two axial scanning device driven by VM2500+ and controlled by personal computer with «SinMarkТМ» software package. Scanning velocity is in the range from 10 mm/s to 4000 mm/s, the covering varies from 100 lines per mm to 3000 lines per mm. Control of samples has been carried out by means of Axio Imager A1m optical microscope Carl Zeiss production with a high definition digital video camera. All experiments have been carried out in the mode of focused laser beam with a radiation spot diameter at the substrate equal to 50 μm. The change of temperature and its distribution along the surface have been evaluated by FLIR IR imager of SC7000 series. Main results. It is shown that ablation occurs without silicon melting and with plasma torch origination. The particles of ejected silicon take part in formation of silicon ions plasma and atmosphere gases supporting the plasmo-chemical growth of SiO2. The range of beam scanning modes is determined where the growth of SiO2 layer is observed. Beginning with scanning velocity equal to 2000 mm/s, the torch existence is not fixed visually; silicon oxide origination is stopped, and silicon particles with nanometer sizes are formed as a result of silicon destruction. The process of silicon destruction is followed by sounds of different frequency depending on scanning velocity. Practical significance. The surface ablation for single-crystal silicon has been shown for the first time ever to be influenced significally by such features of laser radiation as laser beam scanning velocity and the covering of scanning lines. Laser beam scanning modes of pulse fiber ytterbium laser with a wavelenght λ = 1062 nm have been found out providing the synthesis of nanostructured silicon dioxide particles or silicon nanoparticles.

Quantum Mechanical Modeling and Simulation of Monolayer WSe2 Channel Field Effect Transistor

To counter the performance degradation of extremely scaled FETs due to SCEs, ultrathin body channel material with high band gap is essential [1]. In recent years, researchers have been working on Graphene and monolayer transition metal dichalcogenides like MoS2, WSe2 to find the channel material for next generation ultimately scaled transistors. Although, Graphene fulfills the condition of thin body channel and it has excellent carrier mobility, the absence of intrinsic band gap in Graphene sheet made researchers focus on dichalcogenides like MoS2. Despite of showing promise for low power application, MoS2 based transistors are less suitable for high performance operation since monolayer MoS2 has a high electron and hole effective mass and low carrier mobility [2]. In search of high mobility monolayer channel material, many other transition metal dichalcogenides are being explored [3] and as a result of that endeavor monolayer WSe2 based pFET has been fabricated [1] . This experimental device with high band gap (1.6 eV) showed higher carrier mobility (250 cm2/Vs) than monolayer MoS2 based devices. In recent literature methods of n-type and p-type doping of monolayer WSe2 FET are demonstrated [4-5], which led to fabrication of high performance CMOS inverter solely based on monolayer WSe2 channel [6]. Despite of these promising experimental results, rigorous transport and electrostatic study of monolayer WSe2 based FET is yet to appear in the literature. In this work, we have performed a quantum mechanical electrostatics and transport simulation study on monolayer WSe2 FET and calculated different performance parameters. The device structure considered in this work is the nFET version of the device fabricated by Fang et al. [1] which has a 0.7 nm thick monolayer WSe2 channel of length 9.4 μm deposited on a 270 nm thick layer of SiO2. A 17.5 nm thick layer of ZrO2 served as the top oxide of the device (Figure 1). To model the monolayer WSe2 channel FET, we used band structure and material parameters available in the literature from first principle DFT simulations of Monolayer WSe2 sheets which have been listed in table I. In this work, 1D Schrodinger-Poisson equations have been solved self-consistently along the direction perpendicular to the channel to get the C-V characteristics of the device (Figure 2). Then, ballistic transport characteristics were obtained using Launder-Buttiker formulation. Figure 3 and 4 show the Id-Vds and transfer characteristics of the device respectively. The threshold voltage of the device was extracted as 1.1 V (Figure 5). The subthreshold slope was calculated to be 60.913 mV/dec (Figure 6), which is remarkably near to the theoretical lower limit of 60mv/dec. Table II lists some of the performance parameters obtained from the transport simulation. The parameters indicates that monolayer WSe2 FET has a very high on-off current ratio (~108), which makes it suitable for low power applications. The threshold voltage is found to be 1.1V for this undoped monolayer WSe2 channel which can be tuned by changing doping profile and physical dimensions of the device. In this work we have a developed a simulator to study the electrostatics and quantum transport of monolayer WSe2 FET and extracted the performance parameters of that device. The developed simulator can be extended to calculate the ultimate performance limit and study the effects of different physical parameter variation on the performance of the device.

Enhancement of magneto-optical Kerr effect by surface plasmons in trilayer structure consisting of double-layer dielectrics and ferromagnetic metal.

Giant enhancement of the magneto-optical Kerr effect (MOKE) by surface plasmon polaritons (SPPs) is theoretically shown in a trilayer structure consisting of double-layer dielectrics and a ferromagnetic metal (Al2O3/SiO2/Fe). We calculated the resonant enhancement of the transverse MOKE (TMOKE) and polar MOKE (PMOKE) using the attenuated total reflection (ATR) configuration with the transfer matrix method using a 4 × 4 scattering matrix. At a specific film thickness of the low-index SiO2 layer, where confinement of the SPPs on the Fe surface becomes close to the cutoff condition, the incident light from the Al2O3 couples with the SPPs at the SiO2/Fe boundary most efficiently, resulting in resonant enhancement of the MOKE at an incident angle corresponding to the wave vector of the SPPs. The calculated PMOKE showed orthogonal transformation (90°-rotation) and almost full-orbed deformation (44°-ellipticity) of the polarization, and the TMOKE showed a change in reflectance of about 34 dB upon magnetization reversal.

Combination of surface- and interference-enhanced Raman scattering by CuS nanocrystals on nanopatterned Au structures.

We present the results of a Raman study of optical phonons in CuS nanocrystals (NCs) with a low areal density fabricated through the Langmuir–Blodgett technology on nanopatterned Au nanocluster arrays using a combination of surface- and interference-enhanced Raman scattering (SERS and IERS, respectively). Micro-Raman spectra of one monolayer of CuS NCs deposited on a bare Si substrate reveal only features corresponding to crystalline Si. However, a new relatively strong peak occurs in the Raman spectrum of CuS NCs on Au nanocluster arrays at 474 cm−1. This feature is related to the optical phonon mode in CuS NCs and manifests the SERS effect. For CuS NCs deposited on a SiO2 layer this phonon mode is also observed due to the IERS effect. Its intensity changes periodically with increasing SiO2 layer thickness for different laser excitation lines and is enhanced by a factor of about 30. CuS NCs formed on Au nanocluster arrays fabricated on IERS substrates combine the advantages of SERS and IERS and demonstrate stronger SERS enhancement allowing for the observation of Raman signals from CuS NCs with an ultra-low areal density.