Doping Of Substrates Research Articles

Regulating the electronic structure of Pt SAs-Ni2P for enhanced hydrogen evolution reaction

The single atom catalysts (SACs) show immense promise as catalytic materials. By doping the single atoms (SAs) of precious metals onto substrates, the atomic utilization of these metals can be maximized, thereby reducing catalyst costs. The electronic structure of precious metal SAs is significantly influenced by compositions of doped substrates. Therefore, optimizing the electronic structure through appropriate doping of substrates can further enhance catalytic activity. Here, Pt single atoms (Pt SAs) are doped onto transition metal sulfide substrate NiS2 (Pt SAs-NiS2) and phosphide substrate Ni2P (Pt SAs-Ni2P) to design and prepare catalysts. Compared to the Pt SAs-NiS2 catalyst, the Pt SAs-Ni2P catalyst exhibits better hydrogen evolution catalytic performance and stability. Under 1 M KOH conditions, the hydrogen evolution mass activity current density of the Pt SAs-Ni2P catalyst reaches 0.225 A mgPt–1 at 50 mV, which is 33 times higher than that of commercial Pt/C catalysts. It requires only 44.9 mV to achieve a current density of 10 mA cm−2. In contrast, for the Pt SAs-NiS2 catalyst, the hydrogen evolution mass activity current density is 0.178 A mgPt–1, requiring 77.8 mV to achieve a current density of 10 mA cm−2. Theoretical calculations indicate that in Pt SAs-Ni2P, the interaction between Pt SAs and the Ni2P substrate causes the Pt d-band center to shift downward, enhancing the H2O desorption and providing optimal H binding sites. Additionally, the hollow octahedral morphology of Ni2P provides a larger surface area, exposing more reactive sites and improving reaction kinetics. This study presents an effective pathway for preparing high-performance hydrogen evolution electrocatalysts by selecting appropriate doped substrates to control the electronic structure of Pt SAs.

Fe-Ti Co-Doped Alumina-Induced Surface Dual Reaction Center for Catalytic Ozonation to Remove Pollutants from Water

Multiphase catalytic ozone oxidation technology has received wide attention for its effectiveness in removing organic pollutants from water. However, the existence of a rate-limiting step in the metal oxide-catalyzed ozonation process based on single-site redox, which inhibits the activity, greatly limits the practical application of the multiphase catalytic ozonation technology. To solve this bottleneck problem, lattice doping of metal oxide γ-Al2O3 substrates with transition metal species Fe and Ti was used to prepare novel dual reaction center catalysts (FT-A-1 DRCs). Characterization of their morphological structures and chemical compositions was conducted by XRD, TEM, XPS, and other techniques, and it was demonstrated that the lattice substitution of Fe and Ti for Al resulted in the formation of surface-poor electron-rich microregions (electron-rich Fe microcenters and electron-deficient Ti microcenters). The FT-A-1 DRCs were used to catalyze the odor oxidation process and exhibited excellent activity and stability for the removal of a range of non-degradable organic pollutants, such as ibuprofen. The interfacial reaction mechanism was revealed using EPR and electrochemical techniques. It was found that in the catalytic odor oxidation process, O3/H2O was directionally reduced at the electron-rich microcenters to produce·OH, whereas the contaminants could be oxidized at the electron-deficient microcenters as electron donors to continuously supply electrons to the reaction system. This reaction process utilizes the pollutant's own energy to achieve two-way degradation of the pollutant (·OH attack and direct electron donor), thereby overcoming the rate-limiting step in the metal-oxide-catalyzed ozone oxidation process.

Precision silicon doping with acceptors by temperature gradient zone melting

We present the results of optimization of the temperature gradient zone melting technique, also known as the thermomigration (ThM) technique, aimed on improvement of the quality of p-layers and formation of p-n junctions with sharper boundaries compared to those obtained by conventional thermal diffusion technique. In addition, ThM allows an expansion of the range of doping of silicon substrates with an acceptor impurity, usually limited by the solidus value. The ternary Al-Ga-Si and Al-Sn-Si melts were used as ligatures. The dependences of the migration rate of the liquid zones on temperature and composition for the Al-Ga and Al-Sn solvent metal are presented. The possibility of changing the acceptor concentration from 2·1019 cm−3 to 6·1019 cm−3 is shown. A threshold temperature of 1400 K was experimentally found for the ThM process with stable migration of triple liquid zones in a crystal. X-ray diffractional rocking curves and projection topography confirmed high structural quality of the Si(Al) p-layer with a thickness of 25 µm, obtained by ThM with stable moving liquid zones. The experimentally measured strain Δd/d=2.3×10−5 for the p-layer and the silicon substrate was used in the substitution model to estimate the Al concentration of 1×1019 cm−3. X-ray topographic images of the layers did not reveal both growth S-defects and misfit dislocations, confirming the high structural perfection of the layers and phase boundaries.

(Invited) Comparison of High Voltage, Vertical Geometry Ga2O3 Rectifiers with GaN and SiC

Ga2O3 is a candidate for power electronics due to its large bandgap, controllable doping and availability of large inexpensive substrates. These include power conditioning systems, pulsed power for avionics and electric ships, solid-state drivers for heavy electric motors and advanced power management and control electronics. There are already cases where the performance exceeds the theoretical values for SiC. Existing Si, SiC (vertical devices), and GaN (lateral devices) enjoy advantages in terms of process maturity, especially for Si, where devices such as super-junctions surpass the unipolar “limit”. Continued development of low defect substrates, optimized epi growth and improved device design and processing methods for Ga2O3 are required to push the experimental results closer to their theoretical values. The actual experimental value of VB is well below the theoretical predictions. Thermal management is a key issue in Ga2O3 power devices and initial studies have appeared on both the experimental and theoretical fronts.

Structure of thermoelectric films of higher manganese silicide on silicon according to electron microscopy data

The structural features of higher manganese-silicide films obtained by the diffusion doping of single-crystal silicon substrates with manganese vapor in a sealed cell and a flow-through quartz reactor with continuous pumping are comparatively analyzed. Scanning electron microscopy and high-resolution transmission electron microscopy show that a single-phase textured film of higher manganese silicide is formed in the evacuated cell. A change in the growth conditions from steady (cell) to quasi-steady-state (reactor) leads to the formation of polycrystalline islands of higher manganese silicide with nanoscale inclusions of the manganese- monosilicide phase.

Liquid-Phase Monolayer Doping of InGaAs with Si-, S-, and Sn-Containing Organic Molecular Layers.

The functionalization and subsequent monolayer doping of InGaAs substrates using a tin-containing molecule and a compound containing both silicon and sulfur was investigated. Epitaxial InGaAs layers were grown on semi-insulating InP wafers and functionalized with both sulfur and silicon using mercaptopropyltriethoxysilane and with tin using allyltributylstannane. The functionalized surfaces were characterized using X-ray photoelectron spectroscopy (XPS). The surfaces were capped and subjected to rapid thermal annealing to cause in-diffusion of dopant atoms. Dopant diffusion was monitored using secondary ion mass spectrometry. Raman scattering was utilized to nondestructively determine the presence of dopant atoms, prior to destructive analysis, by comparison to a blank undoped sample. Additionally, due to the As-dominant surface chemistry, the resistance of the functionalized surfaces to oxidation in ambient conditions over periods of 24 h and 1 week was elucidated using XPS by monitoring the As 3d core level for the presence of oxide components.

Monolayer Doping of Silicon through Grafting a Tailored Molecular Phosphorus Precursor onto Oxide-Passivated Silicon Surfaces

Monolayer doping (MLD) of silicon substrates at the nanoscale is a powerful method to provide controlled doses of dopants and defect-free materials. However, this approach requires the deposition of a thick SiO2 cap layer to limit dopant evaporation during annealing. Here, we describe the controlled surface doping of thin oxide-passivated silicon wafers through a two-step process involving the grafting of a molecular phosphorus precursor containing a polyhedral oligomeric silsesquioxane (POSS) scaffold with silica-like architecture and thermal annealing. We show that the POSS scaffold favors the controlled formation of dopant-containing surface species with up to ∼8 × 1013 P atoms cm–2 and efficiently avoids phosphorus evaporation during annealing for temperatures up to 800 °C. Silicon doping is demonstrated, in particular, by grafting the POSS phosphorus triester on SiO2/Si wafers with optimized surface preparation (thin SiO2 layer of 0.7 nm) and annealing temperature (1000 °C), which provides phosphorus...

Nanoscale nonlinear effects in Erbium-implanted Yttrium Orthosilicate

Doping of substrates at desired locations is a key technology for spin-based quantum memory devices. Focused ion beam implantation is well-suited for this task due to its high spacial resolution. In this work, we investigate ion-beam implanted Erbium ensembles in Yttrium Orthosilicate crystals by means of confocal photoluminescence spectroscopy. The sample temperature and the post-implantation annealing step strongly reverberate in the properties of the implanted ions. We find that hot implantation leads to a higher activation rate of the ions. At high enough fluences, the relation between the fluence and final concentration of ions becomes non-linear. Two models are developed explaining the observed behavior.

CVD Graphene Synthesis on Copper Foils and Doping Effect by Nitric Acid

Graphene was obtained on Cu foil by thermal decomposition method. A gas mixture of H2 and CH4 and an ambient annealing temperature of 1,000℃ were used during the deposition for 30 Min., and for the transfer onto SiO2/Si and Si substrates. The physical properties of graphene were investigated with regard to the effect ofnitrogen atom doping and the various substrates used. The G/2D ratio decreased when the graphene became monolayer graphene. The graphene grown on SiO2/Si substrate showed a low intensity of the G/2D ratio, because the polarity of the SiO2 layer improved the quality of graphene. The intensity of the G/2D ratio of graphene doped with nitrogen atoms increased with the doping time. The quality of graphene depended on the concentration of the nitrogen doping and chemical properties of substrates. High-quality monolayer graphene was obtained with a low G/2D ratio. The increase in the intensity of the G/2D ratios corresponded to a blue shift in the 2D peaks.

Luminescence of broad-band compounds of elements of groups II–VI with a tin impurity

This paper discusses the luminescence properties of films of cadmium and zinc chalcogenides obtained by the diffusion of tin from the vapor phase in a closed volume. It is established that the doping of ZnSe, CdS, and CdSe substrates increases the efficiency of the edge emission, while that of ZnTe causes it to disappear and causes a new band to appear in the energy region 1.8–2.1 eV. The absence of luminescence of CdTe : Sn films in the 0.6–1.6-eV range is explained by band corrugation.

Increasing the speed of solid-state nanopores

In this work, the authors studied the time response of solid-state nanopores to the applied potentials and the corresponding capacitances. They primarily examined the effect of the doping of the silicon substrates as well as the addition of dielectrics above and below the device membrane. For simple silicon nitride membranes on a moderately doped Si, the measured RC time constants in 1M KCl are on the order of hundreds of microseconds or larger. The authors found that the silicon substrate’s doping level has a significant effect on the equivalent circuit of the device and the use of a more lightly doped Si significantly speeds up the device response. They attributed this effect to the reduction of depletion layer capacitance at the Si-electrolyte interfaces. In the best device structure tested, time constants of ∼425 ns were observed in 1M KCl, which is much faster than most DNA translocation times and on the same order of magnitude as the transit time of each base through typical nanopores.

Nanoscale doping of InAs via sulfur monolayers

One of the challenges for the nanoscale device fabrication of III-V semiconductors is controllable postdeposition doping techniques to create ultrashallow junctions. Here, we demonstrate nanoscale, sulfur doping of InAs planar substrates with high dopant areal dose and uniformity by using a self-limiting monolayer doping approach. From transmission electron microscopy and secondary ion mass spectrometry, a dopant profile abruptness of ∼3.5 nm/decade is observed without significant defect density. The n+/p+ junctions fabricated by using this doping scheme exhibit negative differential resistance characteristics, further demonstrating the utility of this approach for device fabrication with high electrically active sulfur concentrations of ∼8×1018 cm−3.

Laser doping of silicon carbide substrates

A direct-write laser conversion technique was used to produce n-type and p-type doped tracks on SiC substrates. Polycrystalline and single-crystal SiC substrates were investigated. The tracks irradiated in an inert gas exhibit a higher electrical resistance than those generated in dopant-containing atmospheres. The effects of various processing parameters, such as the laser-matter interaction time, laser-beam characteristics, number of exposures to the laser beam, and ambient gas in the laser processing chamber, are examined. The laser conversion technique can be used for selective-area doping of silicon carbide substrates to build semiconductor devices for high-temperature applications.

Effects of the Substrate Pretreatments on the Leakage Current in the Low-Temperature Poly-Si TFTs

AbstractPoly-Si TFT’s were fabricated on the glass substrate by the Metal Induced Lateral Crystallization(MILC). Before deposition of the active a-Si thin films(1000 Å), the glass substrate was pretreated in three different ways such as oxidation of a-Si(100 Å), oxide buffer layer deposition(1000 Å), and ion mass doping of the glass substrates. The leakage current at reverse bias could be reduced by one order of magnitude by the substrate pretreatment. Field effect mobility of n-channel TFT’s was 108cm2/Vsec, subthreshold slope and on/off current ratio were 0.7 V/dec. and about 106, respectively.

GaAs doping by rapid thermal diffusion of a laser-deposited elemental Zn source film: Shallow and laterally graded diffusions

We present an excimer-laser-based doping process useful for shallow uniform and laterally graded p-type doping of GaAs substrates. Specifically, low power 248-nm pulses from a KrF excimer laser are used to nonthermally photodeposit thin Zn layers (∼3–300 Å) from a dimethylzinc (DMZn) ambient onto selected GaAs surface regions. Uniform exposure of a sample to the laser pulses produces a source film which is laterally uniform in thickness, whereas variations in exposure time across a sample deposit a source film which is laterally graded in thickness. The surface is subsequently capped, and the Zn source is diffused into the GaAs using rapid thermal annealing. Secondary ion mass spectroscopy and spreading resistance measurements indicate that uniformly thick source depositions result in uniform diffusions with shallow junction depths and high surface concentrations. Alternatively, our measurements show that gradations in the dopant source profile translate into laterally graded doping profiles for appropriately chosen source thicknesses and diffusion parameters.

The catalytic activity of tungsten carbide modified by ion implantation and ion beam mixing

The main problem for the development of fuel cells is the unsatisfactory performance of the catalytically active electrodes. A possibility for the synthesis of active catalysts with interesting properties is the doping of suitable nonmetallic substrates with finely dispersed noble metals. In this study an attempt was made to use ion implantation and ion beam mixing for the doping of tungsten carbide substrates with platinum. The resulting catalysts were tested with respect to their activity for the electrochemical H+-reduction and formic acid and methanol oxidation. The results indicate that the implanted substrates are much more active than the untreated ones, above a dose of 1016 Pt+/cm2 the activity even exceeds the one of smooth platinum metal. Ion beam mixing is less effective. Here the initially high activity of the substrate coated with 25 run Pt decreases with increasing Kr+-dose used for mixing. The long term stability of the implanted WC is excellent and superior to smooth platinum. The results are explained in terms of the size of the platinum clusters resulting from ion implantation and ion beam mixing, and the corresponding tendency for metal-substrate interactions.

Low Temperature Polycrystalline Silicon Thin Film Devices for Large Area Electronics

ABSTRACTA process sequence for polycrystalline silicon NMOS logic circuitry is presented here. The fabrication sequence eliminates ion implantation steps and requires a maximum process temperature of 900°C. Low process temperature and diffusion doping may allow use of high temperature glass as substrates. Diffusion doping of large substrates eliminates expensive modification of an ion implanter. Initial Work utilized ion implantation to dope device channels before oxidation. Phosphorus channel doping is effective in the control of device threshold, based on the observation that both enhancement and depletion mode device behavior can be obtained. Boron doping is not effective because segregation of the boron into SiO2 occurs during subsequent oxidation. The results obtained from ion implantation doping show that functioning NMOS gates can be fabricated. In fact, it was discovered that undoped polycrystalline silicon channels provide suitable enhancement mode devices, while lightly phosphorus doped channels yield depletion mode devices. A process sequence based solely on phosphorus diffusion is then demonstrated.

Reemission of implanted xenon by 100–270 keV helium

Reemission of implanted xenon from silicon due to bombardment with 100–270 keV He + has been investigated at impact angles between 50° and 75° to the surface normal. Doping of the silicon substrates was accomplished by single (1 keV) or double (5 keV +1 keV) implantation of Xe at normal incidence. The depth profiles of Xe and changes thereof were monitored by repeatedly recording backscattering spectra at the same spot of the doped sample. It was found that the areal density of implanted Xe decreases exponentially with increasing He fluence. The cross sections for reemission range from 10 −18 to 10 −17 cm 2 and increase with decreasing He energy, increasing angle of incidence and decreasing distance from the surface. Analysis on the basis of the Rutherford scattering law suggests that the loss of Xe is due to beam induced detrapping followed by outdiffusion.

A slide rule for computing UFand the bulk doping from MIS-capacitor high-frequency C-V curves

A slide rule has been developed for the rapid and accurate calculation of the normalized doping parameter U <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</inf> and the bulk doping of silicon substrates from high-frequency MIS-capacitor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C-V</tex> data. The slide rule can be employed for ambient temperatures from -20 to 100°C, and for a wide range of insulator thicknesses and dielectric constants.