random Flashcards
SAMS
-ordered molecular assemblies formed by the adsorption of an active surfactant on a solid surface.
-Order in these 2D systems produced by a spontaneous chemical synthesis at the interface, as the system approaches equilibrium.
-Prepared by immersing a substrate in the solution containing a ligand that is reactive toward the surface, or by exposing the substrate to the vapor of the reactive species.
materials for SAMS
-Substrate materials for SAMs: Au, Ag, Cu… (it shouldn’t form an oxide surface film that would interfere with the layering process)
-Layering materials for SAMs: thiols, sulfides and disulfides (must be capable of being adsorbed onto the substrate surface)
Aplicações de SAMS
ultra thin resist or etching mask, modification of surface
properties
Guided self-assembly:
basicamente padroes formados por um processo top-down seguidos de um processo bottom up
Guided self-assembly: surface topography
-Processo chato pq as nanoparticulas não “caem” para as cavidades visto que a força gravitica é muito reduzida a esta escala
-Acontece devido as forças de capilaridade do liquido em suspensão
-Uma vez na trap a força eletroestatica da suspensão ou forças de van de waals vão segurar a particula na cavidade
-Tambem pode ser feito por dip coating controlando a velocidade em que a amostra sai da soluçao e taxa de evaporação
random networks
spray coating, drop casting, spin coating or rod-coating of a solution
containing dispersed nanostructures
Atomic layer deposition:
ALD can be seen as “staking of SAM” – flexibility of materials to deposit, precise control of film thickness, pinhole-free films, conformal coatings, highly repeatable and scalable process
Atomic layer deposition (ALD), is a vapor-phase deposition technique for preparing ultrathin films with precise growth control. ALD is currently rapidly evolving, mostly driven by the continuous trend to miniaturize electronic devices.
The need for ALD
Miniaturization, new device functionalities, on flexible substrates or on top of 3D shapes → Requires deposition techniques offering thickness control, uniformity, conformability, low temperature deposition.
How to understand if we are getting good-quality films?
Ellipsometry – refractive index as an indication of film density
TEM
TEM is an analytical tool that allows detailed investigation of the morphology, structure, and local chemistry of metals, ceramics, polymers, biological materials and minerals. It also enables the investigation of crystal structures, crystallographic orientations through electron diffraction, as well as second phase, precipitates and contaminants distribution by x-ray and electron-energy analysis.
Accelerating voltage TEM
Higher accelerating voltages give higher resolution, but less
contrast. High accelerating voltages can also result in greater
specimen damage.
Electromagnetic lenses TEM
These consist of a coil of copper wires inside iron pole pieces. This field acts as a convex lens,
bringing off axis rays back to focus. Focal
length can be changed by changing the
strength of the current.
Condenser lens TEM
Illuminates the specimen.
Objective lens
–Forms initial image further magnified by
other lenses
– Responsible for focus
–The larger the aperture used the more
phase contrast
–The smaller the aperture the more
aperture contrast
Appertures TEM
–The condenser aperture controls the fraction of the beam which is allowed to hit the specimen. It therefore helps to control the intensity of illumination.
–The objective aperture is used to select which beams in the diffraction pattern contribute to the image, thus producing diffraction contrast.
–The selected area aperture is used to selected a region of the specimen from which a diffraction pattern is obtained.
Bright field TEM
Bright-field imaging is used for
examination of most microstructural
imaging
Dark field TEM
In dark field (DF) images, the direct beam is blocked by the
aperture while one or more diffracted beams are allowed to
pass the objective aperture. Since diffracted beams have strongly interacted with the specimen, very useful information is present in DF images, e.g., about planar defects, stacking faults or particle size.
TEM – Diffraction techniques
Spot Patterns-are created when electrons are diffracted in a single crystal region of a given specimen. Used for unknown phase identification and identification of crystal structure and orientation
Ring Patterns-created when electron diffraction occurs simultaneously from many grains with different orientations relative to the incident electron beam. Used to identify
unknown phases or characterize the crystallography of
a material.
TEM imaging – phase or mass contrast
Diffraction contrast/Phase - some grains diffract more strongly than others; defects may affect diffraction
Mass-thickness contrast - absorption/scattering. Thicker areas or materials with higher Z are darker
Bright field (stained polymers) TEM
In the case of polymer and biological samples, due low atomic number and similar electron densities, staining helps to increase the imaging contrast and improves the radiation damage. Staining agents work by selective absorption in one of the phases and tends to stain unsaturated C-C bonds.
Electropolishing
Sample is immersed in an electrolyte
and then subjected to a direct electrical
current.
* The sample is maintained anodic, with
the cathodic connection being made to
a nearby metal conductor.
* Anodic dissolution of sample creates
polished surface.
TEM can:
▪ Image morphology of samples,
▪ Analyze the composition and some bonding differences
▪ Perform several in-situ measurements.
▪ View frozen material
▪ Acquire electron diffraction patterns
TEM can’t
▪ TEM cannot take colour images.
▪ TEM cannot image through thick samples
than 200nm.
▪ A standard TEM cannot image surface information.
TEM vantagens
▪ Highest spatial resolution
▪ Local crystallographic and chemical analysis at very high resolution
▪ Quantitative identification of structural defects
TEM desvantagens
▪ TEM is an expensive instrument
▪ Destructive technique (during sample preparation)
▪ Sample preparation is time consuming
▪ Some materials are sensitive to electron beam radiation, resulting in a loss of crystallinity and mass
▪ Sample dimension is small
Electron backscatter diffraction (EBSD)
analyze the crystallographic structure of materials. It provides detailed information about the crystal orientation, grain size, phase identification, and strain within polycrystalline materials.
-Diffracted electrons create a pattern in the detector, characteristic of the crystalline structure and
orientation. Sub-micron resolution.
EBSD / FIB – 3D
- FIB is used to remove slices of material from the sample. After each slice has been removed EBSD data is collected from the fresh surface. This cycle is repeated and
EBSD maps are collected from the volume of interest. - A 3D data cube is generated and can be reassembled to see the microstructure, measure grain size and phase distribution in volumes, using the 3D viewer software.
AFM: Contact mode
topografia
Forças de adesão fortes
gravada a defleção z do canti
C-AFM Conductive
-Contact mode
current through/on a sample to determine local conductivity variations
Obtem-se:
* Current mappings
* I-V on specific spots
* I profiles
EFM – Electrostatic Force Microscopy
2 pass scanning mode
Ver interações com o campo eletrico
KPFM – Kelvin Probe Force Microscopy
Contact potential difference between tip and sample
-give contrast where topography does not
-measure work function of metals and semiconductors
PFM – Piezoelectric Force Microscopy
Characterization of the electromechanical response of piezoelectric materials.
AFM Local Anodic Oxidation (LAO)
A Bias is applied between the tip and the sample creating an Electric Field that is able of inducing changes
at the surface. (oxidation, electrostatic effects etc)
A voltage pulse is applied between the AFM tip and the sample. The BIAS induces the formation of a water
bridge if the amplitude of the voltage pulse is above a threshold voltage. The liquid medium induces an oxidation reaction, destroying the covalent bonds in H2O molecules.
XPS common usiages
Surface analysis (<5-10 nm)
* Elemental composition and oxidation states
* Reactions at surfaces and interfaces
* Density of states in reciprocal space
* Surface potentials
* Energy band alignments at interfaces
Auger Electron Spectroscopy
fixe para analisar residuos e defeitos
Rutherford Backscattering
Spectrometry (RBS)
Excellent technique to complement XPS in
depth-resolved quantitative elemental analysis
–Quantitative results one order of magnitude
more accurate
–Non-destructive depth resolution
–No chemical information
–Needs H+ or He+ ion source
SIMS
-Não quantitativo
-melhor sensibilidade
-Deteta hidrogenio
diferença SIMS e RBS
SIMS faz bombardeamento de ioes e espetroscopia de massa/nao quantitativo/alta sensibilidade/semicondutores
RBS faz difraçao e analise de energia/quantitativo/moderada sensibilidade/filmes finos
Resolução OL
For improved resolution we should aim for ligth sources with shorter λ, lens with high NA, and processes with low k1
Resistes de EUV vs DUV
higher sensitivity, because of low power of EUV source.
Higher resolution
OL at shorter λ – X-ray
Raios X dificil de focar, mas penetra a maior parte dos materiais
NA e cenas
Accurate image requires higher orders of the sinusoidal wave function – requires higher NA
High NA also means more overall light coming through the lens system → brighter image
For higher NA, DOF drops even more steeply with NA
OL at high NA – immersion OL
Replacing air by a liquid → >n → >NA
Liquid between objective lens and imaging plane reduces theangle of light coming out of the lens
OL at low k1 factor
2 closely adjacent light spots are resolvable when the 1st diffraction minimum of the light spot image coincides with the maximum of another light spot image
Making individual narrow lines is not a major
problem, making closely spaced narrow lines is!
