A new set of tools and techniques are constantly developed and researched in order to assist metrology and lithography into the nano meter and atomic domain that involve nano scale devices and now, more than ever, quantum devices. Those techniques are built to serve a new generation of lithographic and metrology systems with the same goals of the system they came before them: insuring control, precision and confidence in the fabrication process.
Our solution is the design and fabrication of a Multipurpose Atomic Force Microscopy (AFM) probe that integrates UV lithography, field emission lithography and digital lithography in a single system that allows patterning generation with atomic accuracy, real time inspection with atomic resolution and nano meter Raman Spectroscopy.The multifunction probe has shown strong durability, 365 nm laser emission with 1.5 nm FWHM, lithography patterning as low as 7 nm in field emission lithography configuration and 2 atom lithography in scanning tunneling mode.
In this work, Lamb Wave Resonators (LWRs) based on 2 μm thin Y-cut LiNbO3 films have been fabricated using integrated fabrication process that defines IDTs (Inter Digital Transducers) on top surface and a partial Si cavity for a sacrificial layer on the bottom surface. We discuss the etch quality and its effects on the device's performance. For the first time, we present an optimized high-quality etched MEMS (Micro-electromechanical Systems) Resonator with smooth and vertical sidewalls on this material system, reporting the maximum Q-factor of 2500 at 846 MHz frequency. We observed that the resonator system has a Q-factor of 480 over the same frequency range when the etched surface has significant roughness and non-verticality. Q values of the device are greatly diminished by the presence of surface roughness and non-verticality of the etched edges. This truly highlights how important it is to have a high-quality etch profile for a piezoelectric material system like this so that the designed resonators can perform at their best.
KEYWORDS: Lithography, Gallium nitride, Near field scanning optical microscopy, Scanning tunneling microscopy, Field spectroscopy, Scanning probe microscopy, Near field, Emission spectroscopy, Atomic force microscopy, Spectroscopy
We have investigated the potential of wide bandgap nitride tips, specifically GaN NWs as probes tips for AFM, FEL, STM. The use of GaN nanowires as probes creates the possibility of combining AFM and SPL tools, including STM, and NSOM, so that an ‘’universal multi-purpose probe’’ can be used for several lithography and microscopy techniques. We discuss how nanowires have been integrated with Si cantilevers to form the hybrid III-N and Si lithography probe. We have achieved 0.7 nm lithography features in STM mode, sub 7.5 nm lithography in FESPL mode, and optical waveguides into it to allow NSOM measurement and NSOM detection.
The steady advance of nanotechnology from investigation to application and to manufacturing is increasing the demands on nanoscale metrology and lithography and surface chemical analysis. As dimensions shrink to the nano-scale, the available metrologies, necessary for any advanced manufacturing process, become limited. In this seminar we present how we can achieve state of the art results in nano lithography and metrology and possibly NSOM using functionalized III-N nanowires. We will show as, such a single wide-bandgap tip technology offers the functionality and versatility of several incumbent technologies in one single, universal, system.
The steady advance of nanotechnology from investigation to application and to manufacturing is increasing the demands on nanoscale metrology and lithography. As dimensions shrink to the nano-scale, the available metrologies, necessary for any advanced manufacturing process, become limited. Optical metrology faces resolution limits associated with the large size of the photon relative to the nanostructure. Interference techniques offer sub-wavelength resolution, but at the expense of experimental and signal processing complexity. Electron and ion microscopies (SEM, TEM, FIB, etc.) offer resolution but require high vacuum and are generally unavailable for in-line manufacturing applications. Scanning probe techniques such as atomic force microscopy (AFM), scanning tunneling microscopy (STM), and near-field scanning optical microscopy (NSOM) are very attractive, yet, still unreliable to produce ideal results. For example, AFM, commercial tips are often pyramidal, resulting in significant artifacts requiring complex and uncertain deconvolution of the data. For STM and STL (scanning-tunneling lithography), amorphous/polycrystalline metal tips are the dominant commercial technology but are subject to erosion and wear. For NSOM, metal tips require a complex alignment - optical fibers offer an alternative but are difficult to combine with AFM and STM functionality.
To overcome to the above-mentioned problems, we have developed a single nanowire probe systems, based on single crystal III-N semiconductors. Uniform GaN nanowire arrays, formed thought a combination of wet and dry etch of MOCVD GaN films, were achieved over a large area (>105 μm2) with an aspect ratio as large as 50, a radius as small as 17 nm, and atomic-scale sidewall roughness (<1 nm), allowing metrology of vertical structures with no artifact correction. Doping, during MOCVD film growth, controlled the conductivity of the GaN. Studies of the etching mechanism for different doping level are also reported. Optical emission properties of the 65 nm radius and 2 micron length GaN, mounted on an AFM tip shows a lasing at 365 nm with a line width of 0.15 nm and a Q-factor of 1139-2443.
Our results show that fabrication of high-quality GaN nanowire arrays with adaptable aspect ratio and large-area uniformity is feasible through a top-down approach using interferometric lithography and is promising for fabrication of III-nitride-based nanophotonic devices (radial/axial) on the original substrate. Indeed we will also present the state of the art results of these nanowires in AFM and STM metrology as well in field emission and scanning tunneling lithography and NSOM and demonstrate as, such a single wide-bandgap tip technology offers the functionality and versatility of several incumbent technologies in one single, universal, system.
In this study we introduce Gallium Nitride (GaN) nanowire (NW) as high aspect ratio tip with excellent durability for nano-scale metrology. GaN NWs have superior mechanical property and young modulus compare to commercial Si and Carbon tips which results in having less bending issue during measurement. The GaN NWs are prepared via two different methods: i) Catalyst-free selected area growth, using Metal Organic Chemical Vapor Deposition (MOCVD), ii) top-down approach by employing Au nanoparticles as the mask material in dry-etch process. To achieve small diameter tips, the semipolar planes of the NWs grown by MOCVD are etched using AZ400k. The diameter of the NWs fabricated using the top down process is controlled by using different size of nanoparticles and by Inductively Coupled Plasma etching. NWs with various diameters were manipulated on Si cantilevers using Focus Ion Beam (FIB) to make tips for AFM measurement. A Si (110) substrate containing nano-scale grooves with vertical 900 walls were used as a sample for inspection. AFM measurements were carried out in tapping modes for both types of nanowires (top-down and bottom-up grown nanowires) and results are compared with conventional Si and carbon nanotube tips. It is shown our fabricated tips are robust and have improved edge resolution over conventional Si tips. GaN tips made with NW’s fabricated using our top down method are also shown to retain the gold nanoparticle at tip, which showed enhanced field effects in Raman spectroscopy.
We designed and studied a radial junction composed by a photovoltaic and thermoelectric array based on ZnO and CdTe nanowires surrounded by an absorbing organic self assembled in order to efficiently convert UV-visible and IR energy into electricity.
The hot anode of n-type ZnO nanowires was fabricated using a thermal process on pre-seeded layer and results to be crystalline with a transmittance up to 92 % and a bandgap of ~ 3.32 eV. Conductivity measurements reveal diode-like behavior for the ZnO nanowires.
The organic layer was deposited between the anode and cathode at room temperature The organic layer is composed of oppositely charged porphyrin metal (Zn(II) and Sn(IV)(OH)2) derivatives that are separately water soluble, but when combined form a virtually insoluble solid. The electron donor/acceptor properties (energy levels, band gaps) of the solid can be controlled by the choice of metals and the nature of the peripheral substituent groups of the porphyrin ring. A defect free sub nanometer deposition was achieved using a layer-by-layer deposition onto both ZnO and Bi2Te3 nanowires.
The highly thermoelectric structure, which acts as a cold cathode, is composed of p-type Bi2Te3 nanowires with a thermoelectric efficiency (ZT) between ~0.7 to 1, values that are twice that expected for bulk Bi2Te3.
Optoelectronic and structural properties shows that with 6 nm of organic layer it is possible to form a 3% efficient solar device with an enhanced thermo electric effected with a temperature gradient of 300 C.
We propose to utilize confocal Raman spectroscopy combined with high resolution atomic force microscopy (AFM) for nondestructive characterisation of the sidewalls of etched and passivated small pixel (24 μm×24 μm) focal plane arrays (FPA) fabricated using LW/LWIR InAs/GaSb type-II strained layer superlattice (T2SL) detector material. Special high aspect ratio Si and GaAs AFM probes, with tip length of 13 μm and tip aperture less than 7°, allow characterisation of the sidewall morphology. Confocal microscopy enables imaging of the sidewall profile through optical sectioning. Raman spectra measured on etched T2SL FPA single pixels enable us to quantify the non-uniformity of the mesa delineation process.
GaSb thermophotovoltaic cells fabricated using Molecular Beam Epitaxy (MBE) and ion implantation techniques are studied. Challenges including different defect formation mechanisms using MBE and ion-induced defects using ion implantation were investigated by cross-sectional Transmission Electron Microscopy (XTEM), X-Ray Diffraction spectroscopy (XRD) and Scanning Electron Microscopy (SEM). For MBE grown TPVs, several approaches were used to suppress defects, including substrate preparation and using different MBE reactors. For ion-implanted TPVs, different implant doses and energies were tested to minimize the crystal damage and various Rapid Thermal Anneal (RTA) process recipes were studied to maximize the crystal recovery. Large area TPV cells with 1 × 1 cm dimensions were fabricated using these techniques, then electrically and optically characterized. Ideality factors and dark saturation currents were measured and compared for various TPVs.
Damage induced by the implantation of beryllium in n-type GaSb and its removal by Rapid Thermal Annealing (RTA) are studied in detail by Atomic Force Microscopy (AFM), Cross Sectional Transmission Electron Microscopy (XTEM) and Energy Dispersive X-ray Spectroscopy (EDS). RTA has been implemented with different times and temperatures in order to optimize ion activation and to avoid Sb outdiffusion during the process. Results indicate a lattice quality that is close to pristine GaSb for samples annealed at 600 °C for 10s using a thick Si3N4 capping layer. Electrical response of the implanted diodes is measured and characterized as function of different annealing conditions.
An integrated hybrid photovoltaic-thermoelectric system has been developed using multiple layers of organic photosensitizers on inorganic semiconductors in order to efficiently convert UV-visible and IR energy into electricity. The hot anode of n-type ZnO nanowires was fabricated using a thermal process on pre-seeded layer and results to be crystalline with a transmittance up to 92 % and a bandgap of 3.32 eV. The visible-UV light-active organic layer was deposited between the anode and cathode at room temperature using a layer-by-layer deposition onto ITO and ZnO and Bi2Te3 nanowires from aqueous solution. The organic layer, a cooperative binary ionic (CBI) solid is composed of oppositely charged porphyrin metal (Zn(II) and Sn(IV)(OH‑)2) derivatives that are separately water soluble, but when combined form a virtually insoluble solid. The electron donor/acceptor properties (energy levels, band gaps) of the solid can be controlled by the choice of metals and the nature of the peripheral substituent groups of the porphyrin ring. The highly thermoelectric structure, which acts as a cold cathode, is composed of p-type Bi2Te3 nanowires with a thermoelectric efficiency (ZT) between ~0.7 to 1, values that are twice that expected for bulk Bi2Te3. Efficiency of the integrated device, was found to be 35 at 0.2 suns illumination and thermoelectric properties are enhanced by the charge transfer between the CBI and the Bi2Te3 is presented in terms of photo- and thermogenerated current and advantages of the low cost fabrication process is discussed.
Today there is a strong interest in the scientific and industrial community concerning the use of biopolymers for
electronic applications, mainly driven by low-cost and disposable applications. Adding to this interest, we must
recognize the importance of the wireless auto sustained and low energy consumption electronics dream. This dream can
be fulfilled by cellulose paper, the lightest and the cheapest known substrate material, as well as the Earth's major
biopolymer and of tremendous global economic importance. The recent developments of oxide thin film transistors and
in particular the production of paper transistors at room temperature had contributed, as a first step, for the development
of disposable, low cost and flexible electronic devices. To fulfil the wireless demand, it is necessary to prove the concept
of self powered devices. In the case of paper electronics, this implies demonstrating the idea of self regenerated thin film
paper batteries and its integration with other electronic components. Here we demonstrate this possibility by actuating
the gate of paper transistors by paper batteries. We found that when a sheet of cellulose paper is covered in both faces
with thin layers of opposite electrochemical potential materials, a voltage appears between both electrodes -paper
battery, which is also self-regenerated. The value of the potential depends upon the materials used for anode and
cathode. An open circuit voltage of 0.5V and a short-circuit current density of 1μA/cm2 were obtained in the simplest
structure produced (Cu/paper/Al). For actuating the gate of the paper transistor, seven paper batteries were integrated in
the same substrate in series, supplying a voltage of 3.4V. This allows proper ON/OFF control of the paper transistor.
Apart from that transparent conductive oxides can be also used as cathode/anode materials allowing so the production of
thin film batteries with transparent electrodes compatible with flexible, invisible, self powered and wireless electronics.
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