Dielectric characterization and dopant profile extraction using scanning capacitance microscopy

Ph.DDOCTOR OF PHILOSOPH

Accurate Modeling of the Effects of Fringing Area Interface Traps on Scanning Capacitance Microscopy Measurement

Scanning capacitance microscopy (SCM) is a dopant profile extraction tool with nanometre spatial resolution. While it is based on the high-frequency MOS capacitor theory, there are crucial second-order effects which make the extraction of dopant profile from SCM data a challenging task. Due to small size of the SCM probe, the trapped charges in the interface traps at the oxide-silicon dioxide interface surrounding the probe significantly affect the measured SCM data through the fringing electric field created by the trapped charges. In this paper, we present numerical simulation results to investigate the nature of SCM dC/dV data in the presence of interface traps. The simulation takes into consideration the traps response to the ac signal used to measure dC/dV as well as the fringing field of the trapped charge surrounding the probe tip. In the study, we present an error estimation of experimental SCM dopant concentration extraction when the interface traps and fringing field are ignored. The trap distribution in a typical SCM sample is also investigated

Synthesis and field emission properties of different ZnO nanostructure arrays

In this article, zinc oxide (ZnO) nanostructures of different shapes were fabricated on silicon substrate. Well-aligned and long ZnO nanowire (NW) arrays, as well as leaf-like ZnO nanostructures (which consist of modulated and single-phase structures), were fabricated by a chemical vapor deposition (CVD) method without the assistance of a catalyst. On the other hand, needle-like ZnO NW arrays were first fabricated with the CVD process followed by chemical etching of the NW arrays. The use of chemical etching provides a low-cost and convenient method of obtaining the needle-like arrays. In addition, the field emission properties of the different ZnO NW arrays were also investigated where some differences in the turn-on field and the field-enhancement factors were observed for the ZnO nanostructures of different lengths and shapes. It was experimentally observed that the leaf-like ZnO nanostructure is most suitable for field emission due to its lowest turn-on and threshold field as well as its high field-enhancement factor among the different synthesized nanostructures

A review on potential of green solvents in hydrothermal liquefaction (HTL) of lignin

One of the greatest challenges in biorefinery is to reduce biomass’ recalcitrance and enable valorization of lignin into higher value compounds. Likewise, green solvents and hydrothermal liquefaction (HTL) with feasible economic viability, functionality, and environmental sustainability have been widely introduced in extraction and conversion of lignin. This review starts with the underscore of disadvantages and limitations of conventional pretreatment approaches and role of green solvents in lignin extraction. Subsequently, the effect of process parameters along with the reaction mechanisms and kinetics on conversion of lignin through HTL were comprehensively reviewed. The limitations of green solvents in extraction and HTL of lignin from biomass were discussed based on the current advancements of the field and future research scopes were also proposed. More details info on HTL of biomass derived lignin which avoid the energy-intensive drying procedures are crucial for the accelerated development and deployment of the advanced lignin biorefinery

Hydrogen sulfide (H2S) conversion to hydrogen (H2) and value-added chemicals : Progress, challenges and outlook

Hydrogen sulfide (H2S) is a toxic gas released from natural occurrences (such as volcanoes, hot springs, municipal waste decomposition) and human economic activities (such as natural gas treatment and biogas production). Even at very low concentrations, H2S can cause adverse health impacts and fatality. As such, the containment and proper management of H2S is of paramount importance. The recovered H2S can then be transformed into hydrogen (H2) and various value-added products as a major step towards sustainability and circular economy. In this review, the state-of-the-art technologies for H2S conversion and utilization are reviewed and discussed. Claus process is an industrially established and matured technology used in converting H2S to sulfur and sulfuric acid. However, the process is energy intensive and emits CO2 and SO2. This calls for more sustainable and energy-efficient H2S conversion technologies. In particular, recent technologies for H2S conversion via thermal, biological, plasma (thermal and non-thermal), electrochemical and photocatalytic routes, are critically reviewed with respect to their strengths and limitations. Besides, the potential of diversified value-added products derived from H2S, such as H2, syngas, carbon disulfide (CS2), ammonium sulphate ((NH4)2SO4), ammonium thiosulfate ((NH4)2S2O3), methyl mercaptan (CH3SH) and ethylene (C2H4) are elucidated in detail with respect to the technology readiness level, market demand of products, technical requirements and environmental impacts. Lastly, the technological gaps and way forward for each technology are also outlined

Characterization, modeling and physical mechanisms of different surface treatment methods at room temperature on the oxide and interfacial quality of the SiO2 film using the spectroscopic scanning capacitance microscopy

In this article, a simple, low cost and combined surface treatment method [pre-oxidation immersion of the p-type silicon (Si) substrate in hydrogen peroxide (H2O2) and post oxidation ultra-violet (UV) irradiation of the silicon-dioxide (SiO2) film] at room temperature is investigated. The interface trap density at midgap [Dit(mg)] of the resulting SiO2 film (denoted as sample 1A) is quantified from the full width at half-maximum of the scanning capacitance microscopy (SCM) differential capacitance (dC/dV) characteristics by utilizing a previously validated theoretical model. The Dit(mg) of sample 1A is significantly lower than the sample without any surface treatments which indicates that it is a viable technique for improving the interfacial quality of the thicker SiO2 films prepared by wet oxidation. Moreover, the proposed combined surface treatment method may possibly complement the commonly used forming gas anneal process to further improve the interfacial quality of the SiO2 films. The positive shift of the flatband voltage due to the overall oxide charges (estimated from the probe tip dc bias at the peak dC/dV spectra) of sample 1A suggests the presence of negative oxide fixed charge density (Nf) in the oxide. In addition, an analytical formula is derived to approximate the difference of the Nf values between the oxide samples that are immersed in H2O2 and UV irradiated from their measured SCM dC/dV spectra. Conversely, some physical mechanisms are proposed that result in the ionization of the SiO− species (which are converted from the neutral SiOH groups that originate from the pre-oxidation immersion in H2O2 and ensuing wet oxidation) during the UV irradiation as well as the UV photo-injected electrons from the Si substrate (which did not interact with the SiOH groups). They constitute the source of mobile electrons which partially passivate the positively charged empty donor-like interface traps at the Si-SiO2 interface. Keywords: Dielectrics, Electronic properties, Oxide defects, Radiation effects, Scanning capacitance microscopy, Surfaces and interfaces, Surface treatment

Chemical stability and defect formation in CaHfO

Defects in CaHfO3 are investigated by ab initio calculations based on density functional theory. Pristine and anion-deficient CaHfO3 are found to be insulating, whereas cation-deficient CaHfO3 is hole-doped. The formation energies of neutral and charged cation and anion vacancies are evaluated to determine the stability in different chemical environments. Moreover, the energies of the partial and full Schottky defect reactions are computed. We show that clustering of anion vacancies in the HfO layers is energetically favorable for sufficiently high defect concentrations and results in metallicity

Specific features investigation of the AE(2)ZnN(2) (AE=Ca, Sr, Ba) compounds from indirect to direct band gap: DFT study

Výpočty prvních zásad jsou prováděny za účelem zkoumání strukturních, elektronických, optických a transportních vlastností ternárních polovodičových sloučenin AE2ZnN2 (AE = Ca, Sr, Ba) v tetragonální krystalové fázi pomocí moderní a vysoce přesné plné potenciální linearizované metody rozšířené rovinné vlny . V tetragonálních ternárních nitridách AE2ZnN2 má Zn neobvyklou lineární koordinaci s dusíkem (N-Zn-N) podél osy c. Hodnoty zakázaného pásma pro sloučeniny AE2ZnN2 se vypočítají metodou modifikovaným modified Becke–Johnson approximation (mBJ).Výpočet zakázaného pásma naznačuje, že tyto materiály jsou extrémně atraktivní pro vynikající termoelektrický výkon. Následně byla pro výpočet termoelektrických vlastností sloučenin AE2ZnN2 (AE = Ca, Sr, Ba) použita poloklasická teorie Boltzmannova transportu. Zakázané pásmo těchto sloučenin kolísá nahrazením kationtového AE a optické parametry závislé na pásmové vzdálenosti jsou předpovězeny pro experimentální perspektivy. Kromě toho optická odezva naznačuje, že materiály AE2ZnN2 jsou užitečné pro optoelektronická zařízení. Dále jsou vypočteny hodnoty tepelného výkonu, účiníku, elektrické a tepelné vodivosti pro každou sloučeninu.First principles calculations are performed to investigate the structural, electronic, optical and transport properties of the ternary semiconducting compounds AE2ZnN2 (AE=Ca, Sr, Ba) in the tetragonal crystal phase by using a modern and highly accurate full potential linearized augmented plane wave method. In the tetragonal ternary nitrides AE2ZnN2, Zn has a unusual linear coordination with nitrogen (N-Zn-N) along the c-axis. The band gap values for the AE2ZnN2 compounds are calculated with the modified Becke–Johnson (mBJ) approximation. The band gap calculation suggests that these materials are extremely attractive for excellent thermoelectric performance. Subsequently, semi-classic Boltzmann transport theory has been utilized to calculate the thermoelectric properties of the AE2ZnN2 (AE=Ca, Sr, Ba) compounds. The band gap of these compounds varies by replacing the cation AE and the band gap dependent optical parameters are predicted for experimental perspectives. In addition, the optical response suggests that the AE2ZnN2 materials are useful for optoelectronic devices. Furthermore, the figures of merit, thermo power, power factor, electrical and thermal conductivity are calculated for each compound

Detrimental effects of oxygen vacancies in electrochromic molybdenum oxide

10.1021/acs.jpcc.5b02609Journal of Physical Chemistry C1191910592-1060