Anomalous activation of shallow B+ implants in Ge

The electrical activation of B⁺ implantation at 2 keV to doses of 5.0 × 10¹³–5.0 × 10¹⁵ cm^?2 in crystalline and pre-amorphized Ge following annealing at 400 °C for 1.0 h was studied using micro Hall effect measurements. Preamorphization improved activation for all samples with the samples implanted to a dose of 5.0 × 10¹⁵ cm^?2 displaying an estimated maximum active B concentration of 4.0 × 10²⁰ cm^?3 as compared to 2.0 × 10²⁰ cm^?3 for the crystalline sample. However, incomplete activation was observed for all samples across the investigated dose range. For the sample implanted to a dose of 5.0 × 10¹³ cm^?2, activation values were 7% and 30%, for c-Ge and PA-Ge, respectively. The results suggest the presence of an anomalous clustering phenomenon of shallow B⁺ implants in Ge.     

Front-side metal electrode optimization using fine line double screen printing and nickel plating for large area crystalline silicon solar cells

Industrial applicable fine-line double printing and nickel plating method was applied to single crystalline silicon (c-Si) solar cells. As the finger widths decreased, the efficiency and short circuit current density (J_SC) linearly increased. Although the increase of the J_SC was caused by the reduction of shadowing loss due to the decrease of finger width, the fill factor (FF) was slowly decreased due to increase of contact resistance. The FF of the cells using the fine line was enhanced by using a double printing and nickel plating. c-Si solar cells with the dimensions of 12.5 cm × 12.5 cm, double printed finger width of 50 μm due to spreadability of paste, a finger spacing of 2.4 μm, and aluminum back surface field were fabricated, achieving an increase of J_SC and efficiencies of up to about 0.62 mA/cm² and 0.38% compared to a reference cell at 79.8% of the FF, respectively.     

Reflectance spectra and refractive index of a Nd:YAG laser-oxidized Si surface

The reflectance spectra and refractive index of Nd:YAG laser-oxidized SiO₂ layers with thicknesses from 15 to 75 nm have been investigated with respect to the laser beam energy density and substrate temperature. Thickness and refractive index of films have been determined from reflectance measurements at normal light incidence in the spectral range 300–800 nm. It was found that the oxide-growth conditions at higher substrate temperatures and laser powers greater than 3.36 J cm⁻² provides a better film quality in terms of both optical thickness and refractive index. However, the refractive indices of the films are smaller in the whole spectral range studied as compared to that of conventional thermally grown SiO₂. This might be due to the porous structure formed during the laser-assisted oxidation. The results suggest the need of post-oxidation annealing to improve the refractive indices of the films, suitable for Si-device applications.     

Anodic bonding of silicon onto glass by ion-cut technique and their characterization using high resolution X-ray diffraction studies

Anodic bonding of single crystal silicon wafer with glass and subsequent splitting of the silicon wafer is done by ion-cut technique that involves proton bombardment at desired energies at a dose level > 5 × 10¹⁶ cm^− 2 and then subjected to the bond pair for heat treatment at ∼ 550 °C. Details of the bonding and splitting processes have been discussed in the present study. The high resolution X-ray diffractometry studies have been performed and found that transferred single crystalline thin silicon layer has less crystalline perfection than the original wafer. It suggests that some improvement is still required in the ion-cut technique to improve the crystalline quality of the transferred layer before going to be used for the device applications.     

Effects of LiF/Al back electrode on the amorphous/crystalline silicon heterojunction solar cells

To improve the quantum efficiency (QE) and hence the efficiency of the amorphous/crystalline silicon heterojunction solar cell, we have employed a LiF dielectric layer on the rear side. The high dipole moment of the LiF reduces the aluminum electrode's work–function and then lowers the energy barrier at back contact. This lower energy barrier height helps to enhance both the operating voltage and the QE at longer wavelength region, in turn improves the open-circuit voltage (V_oc), short-circuit current density (J_sc), and then overall cell efficiency. With optimized LiF layer thickness of 20 nm, 1 cm² heterojunction with intrinsic thin layer (HIT) solar cells were produced with industry-compatible process, yielding V_oc of 690 mV, J_sc of 33.62 mA/cm², and cell efficiencies of 17.13%. Therefore LiF/Al electrode on rear side is proposed as an alternate back electrode for high efficiency HIT solar cells.     

Synthesis of nanoporous silicon carbide via the preceramic polymer route

Nanoporous silicon carbide materials were prepared by the pyrolysis of the preceramic polymer, polycarbosilane (PCS), with and without the addition of an inert filler (nano- and micron-sized silicon carbide powders). Hydrosilylation crosslinking of PCS with divinylbenzene prior to pyrolysis appeared to have little influence on the development of micro- and mesoporosity. Maximum micropore volumes were 0.28 cm³ g^?1 for non-crosslinked PCS and 0.25, 0.33 and 0.32 cm³ g^?1 for PCS crosslinked with 2, 6 and 10 wt.% DVB respectively. Micropore volumes decreased under hydrothermal conditions to 0.03 cm³ g^?1 for non-crosslinked and 0 cm³ g^?1 for crosslinked PCS. Porosity was also lost at temperatures above 700 °C. The addition of nano-sized SiC powders to PCS prior to pyrolysis maintained mesoporosity to temperatures of 1200 °C, however, micron-sized SiC powders did not maintain porosity above 800 °C. The modal pore size in pellets formed by compressing micron-sized powders with the preceramic polymer was 5 μm compared to 30 nm when nano-sized powders were used.     

Formation and characterization of Si5C3 type silicon carbide by carbon ion implantation with a MEVVA ion source

A Si₅C₃ type silicon carbon has been prepared via carbon ion implantation into silicon substrate using a MEVVA ion source. Carbon ions were implanted into silicon substrate at a fluence of 5 × 10¹⁷ ions/cm² and then the as-implanted samples were annealed at 1250 °C for 2 h. The thermal annealing produced a silicon carbide layer on the surface of silicon substrate. The results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirm the existence of Si₅C₃, rather than SiC. The results of Fourier transform infrared reflection (FTIR) and Raman spectroscopy analyses show that the Si–C vibration frequency in crystalline Si₅C₃ is slightly less than that in crystalline β-SiC.     

A comparative study of ferroelectric triglycine sulfate (TGS) crystals grown by conventional slow evaporation and unidirectional method

Unidirectional 〈0 1 0〉 TGS single crystal of diameter 35 mm and length 80 mm was grown by Sankaranarayanan–Ramasamy (SR) method. Nearly two times higher d₃₃ value has been obtained for the SR grown TGS crystal compared to conventional grown TGS. The etch pit density of SEST and SR method grown TGS crystal is 2.1 × 10² cm^?2 and 1.5 × 10² cm^?2 respectively. The values of hardness were found to be 152 kg/mm² for SR grown TGS and 108 kg/mm² for SEST grown TGS crystal. The average laser damage threshold obtained on the SEST grown TGS crystal was 29 mJ/cm² whereas a high damage threshold of 39 mJ/cm² was obtained for the SR grown crystal. The SR method grown TGS has 5% higher transmittance as against conventional method grown crystal. Dielectric study showed higher dielectric permittivity and lower dielectric loss in SR grown TGS crystal.     

Effects of grain boundaries on electrical and magnetic properties of melt-processed SmBa2Cu3Ox superconductors

In the present study, we examine the energy dissipation mechanisms and grain boundary effects on the superconducting properties of high-T_c SmBa₂Cu₃O_7?x samples. Sm-123 was synthesized with the top-seeded-melt-growth technique. Grain sizes, as determined by optical microscopy, ranged between 0.5 mm and 1.5 mm. Thus, each specimen, on which the electrical and magnetic measurements were carried out, contained several grains. Some of our findings are as follows: (1) the intragrain T_c is 93.5 K and the intergrain T_c is 87.5 K. Superconducting transition width is narrow and is not affected much by the magnetic field. (2) The intragrain J_c is 110,000 A cm^?2 while the intergrain J_c is 210 A cm^?2 at 10 K. (3) The intergrain J_c shows a secondary peak with the increase in temperature from 10 K to 30 K. The main reasons behind these observations are discussed in detail.     

Synthesis of vertically aligned boron nitride nanosheets using CVD method

Boron nitride nanosheets (BNNSs) protruding from boron nitride (BN) films were synthesized on silicon substrates by chemical vapor deposition technique from a gas mixture of BCl₃–NH₃–H₂–N₂. Parts of the as-grown nanosheets were vertically aligned on the BN films. The morphology and structure of the synthesized BNNSs were characterized by scanning electron microscopy, transmission electron microscopy, and Fourier transformation infrared spectroscopy. The chemical composition was studied by energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Cathodoluminescence spectra revealed that the product emitted strong UV light with a broad band ranging from 250 to 400 nm. Field-emission characteristic of the product shows a low turn-on field of 6.5 V μm^?1.     

Synthesis and characterization of silicon nanowires using tin catalyst for solar cells application

Tin-catalyzed silicon nanowires were synthesized for solar cells application. Voluminous silicon nanowires were fabricated on single crystalline silicon wafer. Optical reflectance and solar cell efficiency of the synthesized silicon nanowires were explored. The reflectance of as-synthesized silicon nanowires was obtained approximately 5% in the short wavelength region (λ < 500 nm). A short circuit current of 2.3 mA/cm² and open circuit voltage of 520 mV for 1 cm² SiNWs solar cell was obtained.     

Low temperature growth of SnO2 nanowires by electron beam evaporation and their application in UV light detection

For the first time, high quality tin oxide (SnO₂) nanowires have been synthesized at a low substrate temperature of 450 °C via vapor–liquid–solid mechanism using an electron beam evaporation technique. The grown nanowires have shown length of 2–4 μm and diameter of 20–60 nm. High resolution transmission electron microscope studies on the grown nanowires have shown the single crystalline nature of the SnO₂ nanowires. We investigated the effect of growth temperature and oxygen partial pressure on SnO₂ nanowires growth. Variation of substrate temperature at a constant oxygen partial pressure of 4 × 10⁻⁴ mbar suggested that a temperature equal to or greater than 450 °C was the best condition for phase pure SnO₂ nanowires growth. The SnO₂ nanowires grown on a SiO₂ substrate were subjected to UV photo detection. The responsivity and quantum efficiency of SnO₂ NWs photo detector (at 10V applied bias) was 12 A/W and 45, respectively, for 12 μW/cm² UV lamp (330 nm) intensity on the photo detector..     

Laser-assisted vibrational control of precursor molecules in diamond synthesis

Control of chemical reactions is the essence of chemistry, producing designed outcomes while suppressing unwanted side products. Laser-assisted molecular vibrational control has been demonstrated to be a potential approach to influencing the outcome of a chemical reaction. In this article, we reviewed recent progress in the laser control of diamond synthesis through vibrational excitation of precursor molecules in a laser-assisted combustion chemical vapor deposition process. Significantly promoted diamond deposition rate (139 μm/h) and crystalline quality were achieved by resonantly exciting the Q-branch (ΔJ = 0) of the CH₂-wagging mode (v₇ mode 949.3 cm⁻¹) of C₂H₄ molecules. Resonant excitation of the fundamental vibrational modes is more effective in promoting diamond growth than random vibrational excitation. Control of diamond crystallographic orientation was also realized by resonantly exciting the R branch (ΔJ = 1) of the CH₂-wagging mode of C₂H₄ molecules and resulted in the preferential growth of {1 0 0}-oriented diamond crystals. Nitrogen-doped diamond films with a nitrogen concentration of 1.5 × 10²⁰ atoms/cm³ were synthesized by resonantly exciting the rotational–vibrational transition (J = 5 → J′ = 6, K = 0) of the N–H wagging mode (v₂ mode) in ammonia molecules. The findings demonstrate the feasibility of laser-assisted vibrational control in steering chemical reactions and controlling reaction outcomes.     

Hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer

We demonstrate hybrid tandem photovoltaic devices with a transparent conductive interconnecting recombination layer. The series-connected hybrid tandem photovoltaic devices were developed by combining hydrogenated amorphous silicon (a-Si:H) and polymer-based organic photovoltaics (OPVs). In order to enhance the interfacial connection between the subcells, we employed highly transparent and conductive indium tin oxide (ITO) thin layer. By using the ITO interconnecting layer, the power conversion efficiency of the hybrid tandem solar cell was enhanced from 1.0% (V_OC = 1.041 V, J_SC = 2.97 mA/cm², FF = 32.3%) to 2.6% (V_OC = 1.336 V, J_SC = 4.65 mA/cm², FF = 41.98%) due to the eliminated interfacial series resistance.     

Annealing effect on the microstructure and photoluminescence of ZnO thin films

Zinc oxide thin films have been obtained by pulsed laser ablation of a ZnO target in O₂ ambient at a pressure of 0.13 Pa using a pulsed Nd:YAG laser. ZnO thin films deposited on Si (1 1 1) substrates were treated at annealing temperatures from 400 °C up to 800 °C after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, resistivity and IR absorption spectra. The results show that the obtained thin films possess good single crystalline with hexagonal structure at annealing temperature 600 °C. Two emission peaks have been observed in photoluminescence spectra. As the post-annealing temperature increase, the UV emission peaks at 368 nm is improved and the intensity of blue emission at 462 nm decreases, which corresponds to the increasing of the optical quality of ZnO film and the decreasing of Zn interstitial defect, respectively. The best optical quality for ZnO thin films emerge at post-annealing temperature 600 °C in our experiment. The measurement of resistivity also proves the decrease of defects of ZnO films. The IR absorption spectra of sample show the typical Zn–O bond bending vibration absorption at wavenumber 418 cm⁻¹.     

Biomolecular urease thin films grown by laser techniques for blood diagnostic applications

Matrix assisted pulsed laser evaporation (MAPLE) was used for growing urease thin films designed for bio-sensor applications in clinical diagnostics. The targets exposed to laser radiation were made from a frozen composite manufactured by dissolving biomaterials in distilled water. We used a UV KrF* (λ = 248 nm, τ_FWHM ? 30 ns, ν = 10 Hz) excimer source for multipulse laser irradiation of the frozen targets cooled with Peltier elements. The laser source was operated at an incident fluence of 0.4 J/cm². Urease activity and kinetics were assayed by the Worthington method that monitors urea hydrolysis by coupling ammonia production to a glutamate dehydrogenase reaction. A decrease in absorbance was measured at 340 nm and correlated with the enzymatic activity of urease. We show that the urease films obtained by MAPLE techniques remain active up to three months after deposition.     

Dislocation density-based modeling of subsurface grain refinement with laser-induced shock compression

Laser shock peening (LSP) is an innovative surface treatment technique applied to improve the mechanical properties and surface microstructures of metallic components. This paper is concerned with prediction of the microstructural evolution of metallic components subjected to single or multiple LSP impacts. A numerical framework is developed to model the evolution of dislocation density and dislocation cell size using a dislocation density-based material model. It is shown that the developed model captures the essential features of the material mechanical behaviors and predicts that the total dislocation density reaches the order of 10¹⁴ m^?2 and a minimum dislocation cell size is below 250 nm for LSP of monocrystalline coppers using the laser energy density on the order of 500 GW/cm². It is further shown that the model is cable of predicting the material strengthening mechanism in terms of residual stress and microhardness of the LY2 aluminum alloy due to grain refinement in a LSP process with less laser energy densities on the order of several GW/cm².     

Ultralow density carbon aerogels with low thermal conductivity up to 2000 °C

Ultralow density (0.052 g cm^?3) carbon aerogels (CAs) were prepared for ultrahigh temperature thermal insulation, and their thermal conductivities were determined by laser flash method. The CAs have a total thermal conductivity as low as 0.601 W m^?1 K^?1, which is only one third of the value for closed-pore carbon foam (CF) with a density of 0.054 g cm^?3, at 2000 °C under 0.15 MPa argon. The solid, gaseous, and radiative conductivities of the CA are all much lower than those of the CF, because of the special nanoporous and pearl-necklace nanoparticle structures of the CA. The ultralow density CA clearly demonstrates its great potentials as thermal insulations for extreme applications.     

Deposition of B4C/BCN/c-BN multilayered thin films by r.f. magnetron sputtering

Thin films of cubic boron nitride (c-BN) and B₄C/BCN/c-BN multilayers, were deposited by r.f. (13.56 MHz) multi-target magnetron sputtering from high-purity (99.99%) h-BN and a (99.5%) B₄C targets, in an Ar (90%)/N₂ (10%) gas mixture. Films were deposited onto silicon substrates with (100) orientations at 300 °C, with r.f. power density near 7 W/cm². In order to obtain the highest fraction of the c-BN phase, an r.f. substrate bias voltage between − 100 and − 300 V was applied during the initial nucleation process and − 50 to − 100 V during the film growth. Additionally, B₄C and BCN films were deposited and analyzed individually. For their deposition, we varied the bias voltage of the B₄C films between − 50 and − 250 V, and for the BCN coatings, the nitrogen gas flow from 3% to 12%. A 300-nm-thick TiN buffer layer was first deposited to improve the adhesion of all samples. X-ray diffraction patterns revealed the presence of c-BN (111) and h-BN phases. FTIR spectroscopy measurements indicate the presence of a peak at 780 cm^− 1 referred to as “out-of-plane” h-BN vibration mode; another peak at 1100 cm^− 1 corresponds to the c-BN TO mode and the “in-plane” vibration mode of the h-BN at 1400 cm^− 1. BN films deposited at 300 °C at a pressure of 4.0 Pa and under − 150 V of nucleation r.f. bias, applied for 35 min, presented the highest c-BN fraction, near 85%. By using 32 layers, it was possible to deposit a 4.6-μm-thick c-BN film with adequate mechanical properties and good adhesion to the substrate.     

Structural,optical, thermal,photoconductivity, laser damage threshold and fluorescence analysis of an organic material: β-P-amino benzoic acid single crystal

β-P-amino benzoic acid, an organic single crystal was grown by slow evaporation technique. Single crystal X-ray diffraction studies show that the grown crystal has β-polymorph of P-amino benzoic acid [β-PABA] form and the lattice parameters are a = 6.30 Å, b = 8.61 Å, c = 12.43 Å α = γ = 90° and β = 100.20°. FTIR analysis confirms that bands at 1588 cm⁻¹, 1415 cm⁻¹ are assigned to ring skeletal vibrations of title compound. The molecular structure of the grown crystal has been identified by Nuclear Magnetic Resonance spectral study. The optical absorbance spectrum from 200 to 1100 nm shows that there is an edge absorbance in UV region. Optical band gap of the crystal has been assessed from the absorbance spectrum. The thermal properties of crystals were evaluated from TG-DTA analysis, it exhibits that there is no weight loss up to 187 °C. Laser damage threshold indicates that the grown crystal has no surface damage up to 35 mJ. Photoconductivity and fluorescence spectral experiments are also carried out and the results are discussed.