Solution CT3 MPH204 2015 16(Even)

TeerthankerMahaveerUniversity, Moradabad

College of Engineering

CT-3 (Even Semester) Examination 2015-16 For Ist Year/ IInd Semester (

M.Sc. Physics

Subject Code: MPH 204 Duration: 01:45 hr. Course/Branch/Section:M.Sc./Physics/IstYr

(First – 15 Min.are for distribution and reading of the paper & paper writing time 1 Hr 30 Min.) Note: Attempt all questions. Question number 1 is compulsory.

Q1: (A): Discuss following –

(a)Application of nanotechnology in Opto electronic devices. (b)Nanobiotechnology

or [10x2=20] (B): Discuss following –

(a)Use of nanotechnology in Ageless material. (b)Nanomechanics

Q2 (A): How the PVD and CVD technique are used for the synthesis of nanostructures. or [15x1=15]

(B): Explain the principle and working of Transmission Electron microscopy and its application to Nanostructures.

Q3 (A):How miniature hall detector is used in nano magnetism. or [15x1=15]

(B):Explain nanolithography technique for the fabrication of nano devices.

1(A): (a)In the modern communication technology traditional analog electrical devices are increasingly replaced by optical or optoelectronic devices due to their enormous bandwidth and capacity, respectively. Two promising examples are photonic crystals and quantum dots. Photonic crystals are materials with a periodic variation in the refractive index with a lattice constant that is half the wavelength of the light used. They offer a selectable band gap for the propagation of a certain wavelength, thus they resemble a semiconductor, but for light or photons instead of electrons. Quantum dots are nanoscaled objects, which can be used, among many other things, for the construction of lasers. The advantage of a quantum dot laser over the traditional semiconductor laser is that their emitted wavelength depends on the diameter of the dot. Quantum dot lasers are cheaper and offer a higher beam quality than conventional laser diodes.

1(A): (b)Nanobiotechnology: Nanobiotechnology (sometimes referred to as nanobiology) is best described as helping modern medicine progress from treating symptoms to generating cures and regenerating biological tissues. Also, it has been demonstrated in animal studies that a uterus can be grown outside the body and then placed in the body in order to produce a baby. Stem cell treatments have been used to fix diseases that are found in the human heart and are in clinical trials in the United States.

Another example of current nanobiotechnological research involves nanospheres coated with fluorescent polymers. The technology might someday lead to particles which could be introduced into the human body to track down metabolites associated with tumors and other health problems. Another example, from a different perspective, would be evaluation and therapy at the nanoscopic level, i.e. the treatment of Nanobacteria (25-200 nm sized) as is done by NanoBiotechPharma.

While nanobiology is in its infancy, there are a lot of promising methods that will rely on nanobiology in the future. Biological systems are inherently nano in scale; nanoscience must merge with biology in order to deliver biomacromolecules and molecular machines that are similar to nature. Controlling and mimicking the devices and processes that are constructed from molecules is a tremendous challenge to face the converging disciplines of nanotechnology.

1 (B): (a)Applications of nanotechnology are delivering in both expected and unexpected ways on nanotechnology’s promise to benefit society.Nanotechnology is helping to considerably improve, even revolutionize, many technology and industry sectors: information technology, energy, environmental science, medicine, homeland security, food safety, and transportation, among many others. Using nanotechnology, materials can effectively be made to be stronger, lighter, more durable, more reactive, more sieve-like, or better electrical conductors, among many other traits. Thus nanotechnology can be helpful for making future ageless materials.

There already exist over 800 everyday commercial products that rely on nanoscale materials and processes:  Nanoscale additives in polymer composite materials for baseball bats, tennis rackets, motorcycle helmets,

automobile bumpers, luggage, and power tool housings can make them simultaneously lightweight, stiff, durable, and resilient.

 Nanoscale additives to or surface treatments of fabrics help them resist wrinkling, staining, and bacterial growth, and provide lightweight ballistic energy deflection in personal body armor.

 Nanoscale thin films on eyeglasses, computer and camera displays, windows, and other surfaces can make them water-repellent, antireflective, self-cleaning, resistant to ultraviolet or infrared light, antifog, antimicrobial, scratch-resistant, or electrically conductive.

 Nanoscale materials in cosmetic products provide greater clarity or coverage; cleansing; absorption;

personalization; and antioxidant, anti-microbial, and other health properties in sunscreens, cleansers, complexion treatments, creams and lotions, shampoos, and specialized makeup.

 Nano-engineered materials in the food industry include nanocomposites in food containers to minimize carbon dioxide leakage out of carbonated beverages, or reduce oxygen inflow, moisture outflow, or the growth of bacteria in order to keep food fresher and safer, longer. Nanosensors built into plastic packaging can warn against spoiled food. Nanosensors are being developed to detect salmonella, pesticides, and other contaminates on food before packaging and distribution.

 Nanotechnology is improving the efficiency of fuel production from normal and low-grade raw petroleum materials through better catalysis, as well as fuel consumption efficiency in vehicles and power plants through higher-efficiency combustion and decreased friction.

 Nanotechnology has been used in the early diagnosis of atherosclerosis, or the buildup of plaque in arteries. Researchers have developed an imaging technology to measure the amount of an antibody-nanoparticle complex that accumulates specifically in plaque. Clinical scientists are able to monitor the development of plaque as well as its disappearance following treatment

1 (B): (b)Nanomechanics is a branch of nanoscience studying fundamental mechanical (elastic, thermal and kinetic) properties of physical systems at the nanometer scale. Often, nanomechanics is viewed as

a branch of nanotechnology, i.e., an applied area with a focus on the mechanical properties ofengineered nanostructures and nanosystems (systems with nanoscale components of importance). Examples of the latter includenanoparticles, nanopowders, nanowires, nanorods, nanoribbons, nanotubes, including carbon nanotubes (CNT); nanoshells, nanomebranes, nanocoatings, nanocomposite/nanostructured materials, etc.

Some of the well-established fields of nanomechanics are: nanomaterials, nanotribology (friction, wear and contact mechanics at thenanoscale), nanoelectromechanical systems (NEMS), and nanofluidics.Due to smallness of the studied object, nanomechanics also for:

 Discreteness of the object, whose size is comparable with the interatomic distances  Plurality, but finiteness, of degrees of freedom in the object

 Importance of thermal fluctuations

 Importance of entropic effects (see configuration entropy)  Importance of quantum effects (see quantum machine)

These principles serve to provide a basic insight into novel mechanical properties of nanometer objects. Novelty is understood in the sense that these properties are not present in similar macroscale objects or much different from the properties of those (e.g., nanorods vs. usual macroscopic beam structures). In particular, smallness of the subject itself gives rise to various surface effects determined by higher surface-to-volume ratio of nanostructures, and thus affects mechanoenergetic and thermal properties (melting point, heat capacitance, etc.) of nanostructures.

Quantum effects determine forces of interaction between individual atoms in physical objects, which are introduced in nanomechanics by means of some averaged mathematical models called interatomic potentials.

Subsequent utilization of the interatomic potentials within the

classical multibody dynamics provide deterministic mechanical models of nano structures and systems at the atomic scale/resolution. Numerical methods of solution of these models are called molecular dynamics (MD), and sometimes molecular mechanics (especially, in relation to statically equilibrated (still) models).

Quantum effects also determine novel electrical, optical and chemical properties of nanostructures, and therefore they find even greater attention in adjacent areas ofnanoscience and nanotechnology, such as nanoelectronics, advanced energy systems, and nanobiotechnology.

2 (A): Particle precipitation aided CVD:The CVD reaction conditions are so set that particles form by condensation in the gas phase and collect onto a substrate, which is kept under a different condition that allows heterogeneous nucleation. By this method both nanoparticles and particulate films can be prepared. An example of this method has been used to form nanomaterialseg. SnO2, by a method called pyrosol deposition process, where clusters of tin hydroxide are transformed into small aerosol droplets, following which they are reacted onto a heated glass substrate.

CVD technique can be achieved by taking a Process source in the gas phase and using an energy source, such as plasma or a resistively heated coil, to transfer energy to a gaseous molecule. The CVD process uses hydrocarbons as the carbon sources including methane, carbon monoxide and acetylene. CVD involves the reaction or thermal decomposition of gas phase species at elevated temperatures (~500 -1000 oC). The advantages of the CVD process were low power input, lower temperature range, relatively high purity and, most importantly, possibility to scale up the

process.

Physical Vapour Deposition: Thermal evaporation is one of the simplest and most popular

synthesis methods. The basic process of this method is sublimating source material(s) in powder form at high temperature, and a subsequent deposition of the vapor in a certain temperature region to form desired nanostructures.

A typical experimental system is shown in Figure. The synthesis is performed in an alumina or quartz tube, which is located in a horizontal tube furnace. High purity oxide powders contained in an alumina boat are loaded in the middle of the furnace, the highest temperature region. The substrates for collecting the desired nanostructures are usually placed down-stream following the carrier gas. Cooling water flows inside the cover caps to achieve a reasonable temperature gradient in the tube.

During the experiments, the system is first pumped down to around 10-2Torr. Then the furnace is turned on to heat the tube to the reaction temperature at a specific heating rate. An inert carrying gas, such as argon or nitrogen, is then introduced into the system at a constant flow rate to bring the pressure in the tube back to 200-500 Torr (different pressures are required by different source materials and final deposited nanostructures). The reaction temperature and pressure are held for a certain period of time to vaporize the source material and achieve a reasonable amount of deposition.

Source materials can be vaporized at the high temperature and low pressure condition. The vapor is then carried by the innert carrying gas down to the lower temperature region, where the vapor gradually becomes supersaturated. Once it reaches the substrate, nucleation and growth of nanostructures will occur. The growth is terminated when the furnace is turned off. The system is then cooled down to room temperature with flowing inert gas.

2 (B):Transmission Electron Microscopy (TEM) :The transmission electron microscope is a very powerful tool for material science. A high energy beam of electrons is shone through a very thin sample, and the interactions between the electrons and the atoms can be used to observe features such as the crystal structure and features in the structure like dislocations and grain boundaries. Chemical analysis can also be performed. High resolution can be used to analyze the quality, shape, size and density of quantum wells, wires and dots.

The TEM operates on the same basic principles as the light microscope but uses electrons instead of light. Because the wavelength of electrons is much smaller than that of light, the optimal resolution attainable for TEM images is many orders of magnitude better than that from a light microscope. Thus, TEMs can reveal the finest details of internal structure - in some cases as small as individual atoms.

Imaging: The beam of electrons from the electron gun is focused into a small, thin, coherent beam by the use of the condenser lens. This beam is restricted by the condenser aperture, which excludes high angle electrons. The beam then strikes the specimen and parts of it are transmitted depending upon the thickness and electron transparency of the specimen. This transmitted portion is focused by the objective lens into an image on phosphor screen or charge coupled device (CCD) camera. Optional objective apertures can be used to enhance the contrast by blocking out

high-angle diffracted electrons. The image then passed down the column through the intermediate and projector lenses, is enlarged all the way.

The image strikes the phosphor screen and light is generated, allowing the user to see the image. The darker areas of the image represent those areas of the sample that fewer electrons are transmitted through while the lighter areas of the image represent those areas of the sample that more electrons were transmitted through.

Diffraction: Fig2. shows a simple sketch of the path of a beam of electrons in a TEM from just above the specimen and down the column to the phosphor screen. As the electrons pass through the sample, they are scattered by the electrostatic potential set up by the constituent elements in the specimen. After passing through the specimen they pass through the electromagnetic objective lens which focuses all the electrons scattered from one point of the specimen into one point in the image plane.

3 (A):HALL DETECTOR:Micro-Hall sensors are sensitive tools to examine magnetization patterns on a nanoscale. Micro-Hall-magnetometry together with complementary imaging techniques such as, Lorentz- and magnetic force microscopy provide important insights in the magnetic switching process of ‘mesoscopic’ magnets. Miniaturizing the device dimensions is of interest because of the large area of magnetism. In this transition regime the magnetic properties of these so called nanomagnets can be tailored by varying their shape, size, material and structure. This makes them an interesting subject mainly in memory and data storage technology.

Principles of Hall-magnetometry

Micro-Hall-magnetometry, in contrast, imposes only a negligible perturbation on the nanomagnet during the magnetization reversal process. The magnetic field caused by the sensor current is only on the order of 10 µT. An important advantage of this method is that it can be employed over a wide range of temperatures.

The way to provide a sufficiently high Hall coefficient is to reduce the carrier density and low resistivity. An enhancement of the voltage signal by orders of magnitude can be obtained by applying semiconductor Hall devices. Extremely sensitive Hall sensors can be fabricated from GaAs/AlGaAs semiconductor heterostructures providing a two dimensional electron gas (2DEG) only some ten nanometers below the surface. The mobility and the density of 2DEG electrons are typically several 105 cm2/V s and some 1011 cm−2, respectively.

One possible approach to apply the Hall sensors for probing stray fields on a sub-micron scale is Scanning Hall Probe Microscopy (SHPM). A magnetic tip, a micro-Hall sensor is scanned across the surface to probe the local magnetic stray field by measuring the resulting Hall voltage. The guiding of the micro-sensor is accomplished by the scanning unit of a scanning microscope the probe is attached to.The sample sensor distance can be adjusted e. g., by a shear force distance control. Recording the Hall voltage across the scanned area gives a complete map of the magnetic field distribution of a magnetic surface. The highest accessible lateral resolution of nanoscale Hall sensors based on 2DEG systems is estimated to be of order ≈ 50 nm.

The cantilever which is sandwiched between two piezo plates (gray) oscillates at its resonance frequency driven by one of the piezos. The amplitude is detected by the second piezo plate and serves as the control signal for the scanner z-piezo element to maintain constant sensor-sample distance. Instead of moving micro-Hall sensors as scanning probes they can be utilized as miniaturized magnetometers to study magnetization reversal of nanomagnets. The basic idea is to pattern the magnetic particle to be examined directly onto the Hall cross sensor. This technique, which is illustrated by the sketch in Fig. 4, has become a powerful method for the investigation of micron and sub-micron size magnetic particles, as will be demonstrated by several examples in the following sections.Hall sensors might also be used to investigate biological systems.

3 (B):Nanolithography is the branch of nanotechnology concerned with the study and application of fabricating nanometer-scalestructures, meaning patterns with at least one lateral dimension between 1 and 100 nm. Different approaches can be categorized in serial or parallel, mask or maskless/direct-write, top-down or bottom-up, beam or tip-based, resist-based or resist-less methods. As of 2015, nanolithography is a very active area of research in academia and in industry. Applications of nanolithography include among others: Multigate devices such as Field effect transistors (FET), Quantum dots, Nanowires, Gratings, Zone plates andPhotomasks, nanoelectromechanical systems (NEMS), or semiconductor integrated circuits (nanocircuitry). The main lithographic technics are :

Optical lithography, which has been the predominant patterning technique since the advent of the semiconductor age, is capable of producing sub-100-nm patterns with the use of very short optical wavelengths. Several optical lithography techniques require the use of liquid immersion and a host of resolution enhancement technologies like phase-shift masks (PSM) and optical proximity correction (OPC). Multiple patterning is a method of increasing the resolution by printing features in between pre-printed features on the same layer by etching or creating sidewall spacers, and has been used in commercial production of microprocessors since the 32 nm process node e.g. by directed self-assembly (DSA). Extreme ultraviolet lithography (EUVL) uses ultrashort wavelengths (13.5 nm) and as of 2015, is the most popularly considered Next-generation lithography (NGL) technique for mass-fabrication. Electron beam lithography or Electron-Beam Direct-Write Lithography (EBDW) scans a focused beam of electrons on a surface covered with an electron-sensitive film or resist(e.g. PMMA or HSQ) to draw custom shapes. By changing the solubility of the resist and subsequent selective removal of material by immersion in a solvent, sub-10 nm resolutions have been achieved. This form of direct-write, maskless lithography has high resolution and low throughput, limiting single-column e-beams to photomask fabrication, low-volume production of semiconductor devices, and research&development. Multiple-electron beam approaches have as a goal an increase of throughput for semiconductor mass-production.

Nanoimprint lithography (NIL), and its variants, such as Step-and-Flash Imprint Lithography, LISA and LADI are promising nanopattern replication technologies where patterns are created by mechanical deformation of imprint resist, typically a monomer or polymer formulation that is cured by heat or UV light during imprinting. This technique can be combined with contact printing and cold welding.

Multiphoton lithography (also known as direct laser lithography or direct laser writing) patterns surfaces without the use of a photomask, whereby two-photon absorption is utilized to induce a change in the solubility of the resist. Scanning probe lithography (SPL) is a tool for patterning at the nanometer-scale down to individual atoms using scanning probes. Dip-pen nanolithography is an additive, diffusive method, thermochemical nanolithography triggers chemical reactions, thermal scanning probe lithography creates 3D surfaces from polymers, and local oxidation nanolithography employs a local oxidation reaction for patterning purposes.