Microscopy, nanoscience, synthesis at the nanoscale
Microscopy, nanoscience, synthesis at the nanoscale CHEM 4200
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This 3 page Study Guide was uploaded by Juliana Herran on Thursday September 22, 2016. The Study Guide belongs to CHEM 4200 at University of Northern Iowa taught by Dr. Weeks in Fall 2016. Since its upload, it has received 29 views. For similar materials see Into Nano Fall 2016 in Chemistry and Biochemistry at University of Northern Iowa.
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Date Created: 09/22/16
Scanning Electron Scanning Probe Atomic Force Transmission Possible issues Microscopy (SEM) Microscopy (SPM) Microscopy (AFM) Electron Microscope (TEM) +Uses e- instead of light +Needle scans across +Cantilever flexes +Image appears -Noise: Usually +Max resolution approx. surface and records with surface. darker when it is sinusoidal, does not 1 nm surface structure. +The tip is mounted denser scale. Rotating scan, +W filament used +The tip must be on a cantilever and +Uses very thin changing its speed, size +Measures up to several electrically conductive dragged across samples (100nm or or removing it from nm (e- tunnel from tip to surface less) image are important +Lenses are surface). +Any sample can be +The resolution is measures to ensure you electromagnets +VERY sensitive to tip- measured about 0.1 nm have real data. +Direct e- beam back sample distance +Tips are commercial +In order to increase -Thermal drift: and forth across sample +Voltage used is +Not as sensitive to contrast, the sample Expands from center of +Secondary e-=low approx. 1V electrical noise can be stained with object. Every one energy + weakly +Surface scanned in -Poorer resolution heavy elements (Pb, degree warmer, gets bonded parallel lines than STM Os, U) larger by a factor of -6 -6 +Valence e- of sample +2 usage modes -The bigger the tip, -It-7ses vacuum 10 to 10*10 K (expansion bonded of (Constant distance and the smaller the 10 coefficient). Changes +Elemental composition constant current) resolution -It is necessary to wait by 0.1 degrees/min and can be found using +Good vertical +The angle of for the instrument to moves up and down, emitted x-ray resolution refraction from the come in equilibrium never truly constant. characteristics of the +Probes e- density, not laser reflected in the with its surroundings -Good temperature element atomic density cantilever is before starting control is very -Must be in vacuum -Resolution afected by measured and measurements important for good -Electrons are very sharpness of tip and converted to height in -Wait for instrument to resolution; the reactive surface corrugation order to study the warm up instrument needs to -e- source W filament -Ultimate sharpness of surface -First measurements warm up before data -e- do not penetrate tip: 1 atomic diameter +Lateral resolution 10 will not be really good collection. very far -No lateral resolution nm (things appear -Tunneling does not -Samples must conduct -Exponentially sensitive broader than they see nucleus, only e- electricity (or coated to tip-sample distance really are because of clouds with conductive -Sensitive to vibrations how wide the tip is) material) (since tip is so close to +Vertical resolution -Relies on tunneling sample) about 1 nm current -Sensitive to -Limitations are -Sensitive to electrical contamination (since similar to those of noise only sees the surface) SPM -Small scan area (≤100nm) Applications: Applications: Applications: Applications: *Rough surface *The tip is held just *The heavier the increases the above the surface element the better the electrochemistry: oscillates fast. contrast (because of e- Electrolyte penetration *Imaging resolution scattering) *Stacking and depth can also be controlled *It is possible to do factors with the size of each reactions and check *Energy diference for quantum dot material while it is every orbital is *Contact technique inside the TEM characteristic of every would ruin the sample *Heating nanoparticles element. because of the soft makes the much more *EDX used in order to lipid bilayers (as seen crystalline (Pt find quantum dots in some proteins). example) *K=1 e- replaced *If there is a *Thick samples scatter *L=2 Shell e- replaced uniformity seen in the more e-. Images are membrane (no color harder to see change), molecules *Look for defects at have the same the atomic level orientation. (missing atoms, misalignment of layers, dislocations) Bottom up Synthesis: - Combine atoms to make nanoparticles less than 100 nm in size. - Control of size and shape is big. - Nucleation and size is important. - Same chemical composition and size is important to retain the same properties. - The purity of the sample is very important. - How much do you start with? How long will you have them nucleate? - Use size controls. Number of nuclei controls size, many nuclei, smaller particles. - Particle uniformity is important to avoid nucleation lots of diferent times. - Start, grow, stop. - Growth can be control by amounts of reagents. - Common solvents: Aqueous (water used at industrial scale) and organic (more expensive). - Aqua regia: Nitric acid + Hydrochloric acid Au nanoparticles: Citrate is both the reducing agent and the ligand that coats the particles to prevent a conglomeration into large particles. o In the gold nanoparticles, the surface has a partial positive charge. The positive charges on the surface repel each other which generates an electrostatic repulsion. o Citrate binds to surface. Nanoparticles of Au neutral ~ Van de Waals + Dispersion (London forces). o Clusters remain in solution, Au cluster + citrates = neutral - Viscous forces dominate small particles in a fluid. - All colors are brought up from a combination of red, green and blue. Eyes detect combination of wavelength not absorbed (Complement of absorbed). - Color depends on emission vs. absorption. - Transmittance = I/I 0 - Basic Absorption Spectroscopy is used in physics to study semi-conductive band gaps. The wavenumber is directly proportional to energy (used in vibrational spectroscopy, UV-vis). However, interesting behaviors can be hidden by the light source. - Diferent particles have diferent molar extinction coefficients. - Optical properties depend on surface plasmon (quantum of plasma oscillation). Is produced by incident light. Light cannot penetrate metal nanoparticles. - Electron ripples with particular energy of light (found on surface). Nanoparticles are heavy on surface, light does not enter metals! - The size of electron oscillation will depend on particle size.
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