Ahmad Hassan Ahmad

Bio: Ahmad Hassan Ahmad is an academic researcher from Loughborough University. The author has contributed to research in topics: Exchange rate & Ion. The author has an hindex of 10, co-authored 34 publications receiving 350 citations. Previous affiliations of Ahmad Hassan Ahmad include University of Bath & Aix-Marseille University.

Mobile money, financial inclusion and development: a review with reference to african experience

Abstract: We survey literature on mobile money and its contribution in promoting financial inclusion and development, with a focus on sub-Saharan Africa. We use taxonomic, descriptive and analytical methods to evaluate the state of knowledge in the area. We analyse how mobile technology in general may contribute to economic development and financial inclusion in theory and practise. We explain the mechanics of mobile money using Kenya’s M-Pesa as a canonical example; and consider whether the literature has fully established the potential economic impact of mobile money especially its contribution to financial inclusion. We also consider market structure, pricing and regulatory implications of mobile money. We conclude by highlighting issues that require further investigation: the take-up of mobile money; mobile money and financial inclusion; substitutability between mobile money and conventional finance; and regulatory structures for institutions providing mobile money services.

Negative-ion production on carbon materials in hydrogen plasma:influence of the carbon hybridization state and the hydrogen content on H - yield

Abstract: Highly oriented polycrystalline graphite (HOPG), boron-doped diamond (BDD), nanocrystalline diamond, ultra-nanocrystalline diamond and diamond-like carbon surfaces are exposed to low-pressure hydrogen plasma in a 13.56MHz plasma reactor. Relative yields of surface-produced H− ions due to bombardment of positive ions from the plasma are measured by an energy analyser cum quadrupole mass spectrometer. Irrespective of plasma conditions (0.2 and 2 Pa), HOPG surfaces show the highest yield at room temperature (RT), while at high temperature (HT), the highest yield (∼3-5 times compared to HOPG surface at RT) is observed on BDD surfaces. The shapes of ion distribution functions are compared at RT and HT to demonstrate the mechanism of ion generation at the surface. Raman spectroscopy analyses of the plasma-exposed samples reveal surface modifications influencing H− production yields, while further analyses strongly suggest that the hydrogen content of the material and the sp3/sp2 ratio are the key parameters in driving the surface ionization efficiency of carbon materials under the chosen plasma conditions.

Enhanced negative ion yields on diamond surfaces at elevated temperatures

Abstract: Boron-doped polycrystalline diamond (BDD) and highly oriented pyrolytic graphite (HOPG) surfaces were exposed to low pressure hydrogen plasma The relative yields of surface-produced H− ions were measured by an energy analyser quadrupole mass spectrometer The highest H− yield was obtained at 400 °C for a BDD surface and at room temperature for an HOPG surface At low ion bombardment energy, the maximum yield on a BDD surface is about 5 times higher than that on an HOPG surface, which has been the best carbon material so far for surface production of H− ions in caesium-free plasma Raman measurements revealed surface modifications after plasma exposure

Negative-ion surface production in hydrogen plasmas: modeling of negative-ion energy distribution functions and comparison with experiments

Abstract: A negatively biased graphite sample (highly oriented pyrolitic graphite) was placed in a H2 low-pressure plasma. The negative ions were produced on the graphite surface upon positive-ion bombardment. Surface-produced H− negative-ion distribution functions (NIDFs) were measured by means of an energy-resolved mass spectrometer. The shapes of the recorded NIDFs depend not only on the surface production mechanisms but also on the negative-ion trajectories in the plasma and their collection probability by the mass spectrometer. In order to gain an insight into the surface production mechanisms, NIDFs were computed using Stopping and Range of Ions in Matter simulations and calculations of the ion transmission function between the sample and the mass spectrometer detector. The calculations were based on 3D modeling of the sheath potential in the extraction region and 3D modeling of ion transport inside the mass spectrometer. The excellent agreement between experiments and computations led to a better understanding of the experimental NIDFs. The method developed in this work to study H-surface production on graphite can be generalized to any other negative ions and/or surface material.

Theory of double-resonant Raman spectra in graphene: intensity and line shape of defect-induced and two-phonon bands

Abstract: We calculate the double resonant (DR) Raman spectrum of graphene, and determine the lines associated to both phonon-defect processes, and two-phonons ones. Phonon and electronic dispersions reproduce calculations based on density functional theory corrected with GW. Electron-light, -phonon, and -defect scattering matrix elements and the electronic linewidth are explicitly calculated. Defect-induced processes are simulated by considering different kind of idealized defects. For an excitation energy of $\epsilon_L=2.4$ eV, the agreement with measurements is very good and calculations reproduce: the relative intensities among phonon-defect or among two-phonon lines; the measured small widths of the D, $D'$, 2D and $2D'$ lines; the line shapes; the presence of small intensity lines in the 1800, 2000 cm$^{-1}$ range. We determine how the spectra depend on the excitation energy, on the light polarization, on the electronic linewidth, on the kind of defects and on their concentration. According to the present findings, the intensity ratio between the $2D'$ and 2D lines can be used to determine experimentally the electronic linewidth. The intensity ratio between the $D$ and $D'$ lines depends on the kind of model defect, suggesting that this ratio could possibly be used to identify the kind of defects present in actual samples. Charged impurities outside the graphene plane provide an almost undetectable contribution to the Raman signal.

Exchange Rate Regime Durability and Performance in Developing Countries Versus Advanced Economies

Abstract: Drawing on new data and advances in exchange rate regimes' classification, we find that countries appear to benefit by having increasingly flexible exchange rate systems as they become richer and more financially developed. For developing countries with little exposure to international capital markets, pegs are notable for their durability and relatively low inflation. In contrast, for advanced economies, floats are distinctly more durable and also appear to be associated with higher growth. For emerging markets, our results parallel the Baxter and Stockman classic exchange regime neutrality result, though pegs are the least durable and expose countries to higher risk of crisis.

A Guide to and Review of the Use of Multiwavelength Raman Spectroscopy for Characterizing Defective Aromatic Carbon Solids: from Graphene to Amorphous Carbons

Abstract: sp2 hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon They vary from highly ordered to completely disordered solids and detailed knowledge of their internal structure and composition is of utmost importance for the scientific and engineering communities working with these materials Multiwavelength Raman spectroscopy has proven to be a very powerful and non-destructive tool for the characterization of carbons containing both aromatic domains and defects and has been widely used since the 1980s Depending on the material studied, some specific spectroscopic parameters (eg, band position, full width at half maximum, relative intensity ratio between two bands) are used to characterize defects This paper is addressed first to (but not limited to) the newcomer in the field, who needs to be guided due to the vast literature on the subject, in order to understand the physics at play when dealing with Raman spectroscopy of graphene-based solids We also give historical aspects on the development of the Raman spectroscopy technique and on its application to sp2 hybridized carbons, which are generally not presented in the literature We review the way Raman spectroscopy is used for sp2 based carbon samples containing defects As graphene is the building block for all these materials, we try to bridge these two worlds by also reviewing the use of Raman spectroscopy in the characterization of graphene and nanographenes (eg, nanotubes, nanoribbons, nanocones, bombarded graphene) Counterintuitively, because of the Dirac cones in the electronic structure of graphene, Raman spectra are driven by electronic properties: Phonons and electrons being coupled by the double resonance mechanism This justifies the use of multiwavelength Raman spectroscopy to better characterize these materials We conclude with the possible influence of both phonon confinement and curvature of aromatic planes on the shape of Raman spectra, and discuss samples to be studied in the future with some complementary technique (eg, high resolution transmission electron microscopy) in order to disentangle the influence of structure and defects

Negative hydrogen ion production mechanisms

Abstract: Negative hydrogen/deuterium ions can be formed by processes occurring in the plasma volume and on surfaces facing the plasma. The principal mechanisms leading to the formation of these negative ions are dissociative electron attachment to ro-vibrationally excited hydrogen/deuterium molecules when the reaction takes place in the plasma volume, and the direct electron transfer from the low work function metal surface to the hydrogen/deuterium atoms when formation occurs on the surface. The existing theoretical models and reported experimental results on these two mechanisms are summarized. Performance of the negative hydrogen/deuterium ion sources that emerged from studies of these mechanisms is reviewed. Contemporary negative ion sources do not have negative ion production electrodes of original surface type sources but are operated with caesium with their structures nearly identical to volume production type sources. Reasons for enhanced negative ion current due to caesium addition to these sources are discussed.

The mirage of floating exchange rates

Abstract: This note summarizes some of the highlights of my longer paper with Guillermo Calvo”Fear of Floating.” Many emerging market countries have suffered financial crises. One view blames soft pegs for these crises. Adherents to that view suggest that countries move to corner solutions--hard pegs or floating exchange rates. We analyze the behavior of exchange rates, reserves, and interest rates to assess whether there is evidence that country practice is moving toward corner solutions. We focus on whether countries that claim they are floating are indeed doing so. We find that countries that say they allow their exchange rate to float mostly do not--there seems to be an epidemic case of “fear of floating.”