Copper-doped zinc sulphide (ZnS:Cu) thin films were synthesized through pulsed laser ablation in an inert background gas on stationary and rotating substrates, and a comprehensive opto-electrical characterisation is presented. The... more
Copper-doped zinc sulphide (ZnS:Cu) thin films were synthesized through pulsed laser ablation in an inert background gas on stationary and rotating substrates, and a comprehensive opto-electrical characterisation is presented. The Cu$_x$Zn$_{1-x}$S films demonstrated comparable conductivity and transparency to other leading p-type transparent conducting materials, with a peak conductivity of 49.0 Scm$^{-1}$ and a hole mobility of 1.22 cm$^2$V$^{-1}$s$^{-1}$ for films alloyed with an x = 0.33 copper content. The most conducting films displayed a transparency of 71.8$\%$ over the visible range at a thickness of 100 nm, and band gaps were found in the range 3.22-3.52 eV, which showed a strong negative correlation with copper content. The effects of sulphur-rich rapid thermal annealing on the synthesized compound are reported, with films reliably displaying an increase in conductivity and carrier mobility. Films grown using a stationary substrate possessed large spatial thickness distri...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Electrodeposition of Pb on Au has been of interest for the variety of surface phenomena such as the UnderPotential Deposition (UPD) and surface alloying. Here, we examined the interface between the electrodeposited Pb film on Au, using... more
Electrodeposition of Pb on Au has been of interest for the variety of surface phenomena such as the UnderPotential Deposition (UPD) and surface alloying. Here, we examined the interface between the electrodeposited Pb film on Au, using surface sensitive techniques such as X-ray Photoelectron Spectroscopy (XPS), Ultraviolet Photoelectron Spectroscopy (UPS), Energy-Filtered Photoemission Electron Microscopy (EF-PEEM) and Work Function (WF) mapping. The initially electrodeposited Pb overlayer (~4 ML equivalent thickness) was transferred from the electrochemical cell to the UHV system. The deposited Pb layer was subjected to Argon sputtering cycles to remove oxide formed due to air exposure and gradually thinned down to a monolayer level. Surface science acquisitions showed the existence of a mixed oxide/metallic Pb overlayer at the monolayer level that transformed to a metallic Pb upon high temperature annealing (380 °C for 1 h) and measured changes of the electronic interaction that c...
Research Interests:
Research Interests:
The performance of CuZnSn(S,Se) thin-film solar cells, commonly referred to as kesterite or CZTSSe, is limited by open-circuit voltage (V) values less than 60% of the maximum theoretical limit. In the present study, we employ... more
The performance of CuZnSn(S,Se) thin-film solar cells, commonly referred to as kesterite or CZTSSe, is limited by open-circuit voltage (V) values less than 60% of the maximum theoretical limit. In the present study, we employ energy-filtered photoemission microscopy to visualize nanoscale shunting paths in solution-processed CZTSSe films, which limit the V of cells to approximately 400 mV. These studies unveil areas of local effective work function (LEWF) narrowly distributed around 4.9 eV, whereas other portions show hotspots with LEWF as low as 4.2 eV. Localized valence band spectra and density functional theory calculations allow rationalizing the LEWF maps in terms of the CZTSSe effective work function broadened by potential energy fluctuations and nanoscale Sn(S,Se) phases.
Research Interests:
Research Interests:
In this paper a perspective on the application of spatially- and Angle- Resolved PhotoEmission Spectroscopy (ARPES) for the study of two-dimensional (2D) materials is presented. ARPES allows the direct measurement of the electronic band... more
In this paper a perspective on the application of spatially- and Angle- Resolved PhotoEmission Spectroscopy (ARPES) for the study of two-dimensional (2D) materials is presented. ARPES allows the direct measurement of the electronic band structure of materials generating extremely useful insights into their electronic properties. The possibility to apply this technique to 2D materials is of paramount importance because these ultrathin layers are considered fundamental for future electronic, photonic and spintronic devices. In this review an overview of the technical aspects of spatially localized ARPES is given along with a description of the most advanced setups for laboratory and synchrotron-based equipment. This technique is sensitive to the lateral dimensions of the sample, therefore a discussion on the preparation methods of 2D material is presented. Some of the most interesting results obtained by ARPES are reported in three sections including: graphene, transition metal dichal...
Research Interests:
Substitutional clusters of multiple light element dopants are a promising route to the elusive shallow donor in diamond. To understand the behaviour of co-dopants, this report presents an extensive first principles study of possible... more
Substitutional clusters of multiple light element dopants are a promising route to the elusive shallow donor in diamond. To understand the behaviour of co-dopants, this report presents an extensive first principles study of possible clusters of boron and nitrogen. We use periodic hybrid density functional calculations to predict the geometry, stability and electronic excitation energies of a range of clusters containing up to five N and/or B atoms. Excitation energies from hybrid calculations are compared to those from the empirical marker method, and are in good agreement. When a boron-rich or nitrogen-rich cluster consists of 3 - 5 atoms, the minority dopant element - a nitrogen or boron atom respectively - can be in either a central or peripheral position. We find B-rich clusters are most stable when N sits centrally, whereas N-rich clusters are most stable with B in a peripheral position. In the former case, excitation energies mimic those of the single boron accepto...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests: Engineering, Biochemistry, Physiology, Biophysics, Materials Science, and 15 moreChemistry, Technology, Biotechnology, Ecology, Space Science, Medicine, Surface modification, Semiconductor, Surface, Band Gap, Electronic Structure, Electron Affinity, CHEMICAL SCIENCES, Work Function, and band bending
Research Interests:
ABSTRACT
Research Interests:
Due to its wide band-gap and low or even negative electron affinity (NEA), diamond exhibits high secondary electron emission yields (SEEY) making it suitable for use as a dynode material in devices such as photomultiplier tubes (PMTs). A... more
Due to its wide band-gap and low or even negative electron affinity (NEA), diamond exhibits high secondary electron emission yields (SEEY) making it suitable for use as a dynode material in devices such as photomultiplier tubes (PMTs). A high SEEY allows a reduction in the number of dynode stages required to produce a detectable gain. Moreover, the narrow energy distribution of secondary electrons emitted from the diamond surface can be easily manipulated, improving energy resolution and creating extremely fast response times, coupled with thermal and chemical stability. As a result, diamond-based photomultiplier devices may provide a significant improvement over existing devices. In this paper we describe experiments on the investigation of the reflection yields measured from boron-doped CVD diamond films grown on molybdenum substrates. SEEYs were studied as a function of the incident beam energy, E0 and surface termination.
Research Interests:
Research Interests:
ABSTRACT Amorphic diamond (a-D) films have been grown by pulsed laser deposition using an ArF excimer laser to ablate material from a dense, ultrapure graphite rod. Deposition rates have been investigated as a function of incident pulse... more
ABSTRACT Amorphic diamond (a-D) films have been grown by pulsed laser deposition using an ArF excimer laser to ablate material from a dense, ultrapure graphite rod. Deposition rates have been investigated as a function of incident pulse energy and of time. The resulting films have been analysed by scanning electron microscopy (SEM) and by laser Raman spectroscopy, and their electron emission characteristics tested. We confirm the potential of a-D films for use as a cold cathode material.