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Material Characterization
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Profilometer (Dektak 150)
A profilometer measures the vertical depth of a material across a horizontal length.
A diamond stylus is transverse laterally across the sample with a specified distance
and contact force. The stylus moves vertically with the surface variations, and the
displacement can be measured as a function of position. This equipment can be employed
to measure etch depth, deposited film thickness, and surface roughness. TOP OF PAGE
Resistivity and Sheet Resistance (4-point probe)
4-point probe measures the sheet resistance of a thin film. It is an electrical impedance
measuring technique that has a pair of current-carrying (driving force) and voltage-sensing
(sensing) contacts that is more accurate than the traditional two terminal methods,
because it eliminates the impedance contribution of the wiring and the contact resistances.
A current is supplied by a pair of force connections, and a pair of sense connections.
TOP OF PAGE
Solar Simulator (IV Curve System)
Our solar simulator is a Class A Solar Simulator, so it maintains a exceptionally
tight uniformity, output stability, and spectral match. The solar simulator provides
repeatable light conditions, equal to ¡°one sun¡±. The device uses a xenon arc lamp
with an ellipsoidal mirror, filtering, and beam collimation. The cell (or diode) is
connected to a multi-meter and a voltage sweep occurs. That is then plotted verses
the current produced. TOP OF PAGE
External Quantum Efficiency (EQE) System
External Quantum Efficiency (EQE) is known as the ratio of the number of photons (of
a given energy shining on the solar cell) to the number of charge carriers collected.
It reports the response of a photovoltaic cell to the precise wavelengths in the spectrum
of light shining on the cell. For example, if all of the photons of a certain wavelength
were collected, the quantum efficiency would be 100%. TOP OF PAGE
UV-VIS-NIR Spectrophotometer (Lamda 1050)
The Spectrophotometer uses a photometer to measure the intensity of light as a function
of the source wavelength.It evaluates the sample with visible light, near-ultraviolet, and near-infrared (or any combination) and ranges for 190nm
to 3300nm. Our double beam spectrophotometer compares the light intensity between
two paths (one as a reference and the other the test). It measures the transmission
of light through a sample, reflection off of the sample (diffuse and specular), and
pseudo absorption. TOP OF PAGE
Fourier Transform Infrared Spectroscopy (FTIR)
Thermo Scientific Nicolet is FT-IR spectrometer excels at rugged, precise, fast-paced
operation yet simplifies laboratory data collection to its most steps by loading the
sample and generates the spectrum. The Nicolet FT-IR spectrometer is a complete infrared
spectroscopy system for routine analytical needs. The Nicolet delivers the highest
confidence in the verification and identification of materials and is designed for
maximum assurance in its ability to sample and solve challenging problems with a minimal
investment in time. TOP OF PAGE
Ellipsometry (IR-Vase, Mapping, V-Vase) Ellipsometry is a non-destructive optical technique for investigating the dielectric properties of thin films. The technique utilities a beam of polarized light at incident on a sample, and the change in the polarization state and amplitude of that light beam induced by interaction with the sample is determined. Ellipsometry can be used to characterize composition, roughness, thickness (depth), crystalline nature, doping concentration, electrical conductivity and other material properties. It is very sensitive to the change in the optical response of incident radiation that interacts with the material being investigated.
The IR-VASE Ellipsometer is a rotating compensator ellipsometer (RCE) for ex-situ
SE data acquisition in the spectral range of 1.7 to 30 micron ( 333 cm-1 to 6000 cm-1).
A robust instrument to characterize the free carrier behavior in metal and degenerate
semiconductors like TCOs. TOP OF PAGE 
The Mapping Ellipsometer uses M2000 DI ellipsometer which is again RCE type. Spectral
range is quite large, from 0.6 eV to 6.5 eV. Very useful to characterize the inter-band
optical behavior of semiconductors as well as low bandgap dielectrics. TOP OF PAGE 
The V-VASE is a rotating analyzer ellipsometer (RAE), equipped with auto retarder
option which makes superior to other ellipsometers mainly due to its capacity to measure
the ellipsometric parameter "delta" without ambiguity of trouble regions of other
designs. This instrument is also equipped with cryostat which makes possible to measure
samples at temperature ranging from 4.2 to 700 Kelvin. TOP OF PAGE
Atomic Force Microscopy (Veeco NanoScope V)
Atomic force microscopy (AFM) is a very high-resolution type of scanning probe microscopy,
with demonstrated resolution on the order of fractions of a nanometer. The information
is gathered by scanning the surface with a mechanical probe, through which process
a surface morphology picture will be constructed.The AFM consists of a cantilever with a sharp tip (probe) that is used to scan the specimen surface. The cantilever is typically silicon or silicon nitride with a tip radius of curvature on the order of nanometers. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever according to Hooke's law. The deflection is measured using a laser spot reflected from the top surface of the cantilever into an array of photodiodes. TOP OF PAGE
Van der Pauw Hall Effect Measurement System
The MMR Hall Effect Measurement System provides automatic measurements of the electrical
properties of semiconductor materials using the van der Pauw measurement technique.
By measuring the Hall voltage generated by a current-carrying conductor placed in
a magnetic field, properties of the material, such as sheet resistance, doping type,
carrier density, and mobility of majority carrier, can be calculated. The variable
temperature Hall Effect measurement with temperature ranging from 70 K to 500 K is
feasible. TOP OF PAGE
Auger Electron Spectrophotometer (Perkin-Elmer PHI600) The auger electron spectrophotometer (AES) is used specifically to study of surfaces in the area of material science. Measurement is made by analyzing energetic electrons emitted from excited atoms after a series of internal relaxation events. AES is surface sensitive due to electrons having a short mean free path in a solid and is therefore localized to a few nanometers of the target surface. TOP OF PAGE
Thermogravimetric Analysis (Ta Instruments Q600 TGA)
The TA Q600 is capable of simultaneously performing thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC) on small sample up to 1300 C. TGA measures
mass of a sample as it is heated and can be used to determine the decomposition temperature.
DSC measures the energy absorbed/released during heating and can be used to determine
the latent heat of a phase change or the temperature at which it occurs. TOP OF PAGE
Photoluminescence Photoluminescence characterization of semiconducting materials begins with by illuminating the sample with light of energy larger than the material band gap. Should the excited carriers recombine radiatively, the photoluminescence spectra reveals the energy transitions associated with the recombination pathway. Depending on the material, these transitions can be Band-to-Band, Trap-Assisted, or Donor-Acceptor Pair transitions. The Band-to-Band transition indicates the materials band gap while the ratios of photoluminescence intensities are a measure of material quality. TOP OF PAGE
Time-Resolved Photoluminescence
Time-Resolved Photoluminescence (TRPL), also referred to as Time Correlated Single
Photon Counting (TCSPC), provides a non-destructive measurement of the mean carrier
lifetime in a material or thin-film stack. An ultrafast laser pulse is used to excite
the material and while advanced electronics record the time delay between excitation
and the detection of an emitted photon. Longer carrier lifetime is a very important
parameter, as it increases the probability of charges contributing to photo-current
in solar cells. TOP OF PAGE
Raman Spectrophotometer and FT- Photoluminescence Spectrometer
Thermo Scientific Nicolet NXR FT-Raman Spectrometers are the perfect complement to
an FT-IR. The Thermo Scientific family of Nicolet NXR FT-Raman spectrometers are highly
versatile instruments designed to meet the needs of a wide range of applications.
The Nicolet NXR FT-Raman offers fluorescence-free sampling of organic materials enabling
high-quality Raman measurements of many highly fluorescent samples. The Nicolet NXR
FT-Raman spectrometers combine exceptionally high performance with a wide range of
sample accessories to create a system that is capable of running everything from bulk
samples to microscopic samples, either one sample at a time or many at a time. OMNIC
Array provides for automated data collection and analysis of array based sample formats
such as well-plates. The laser used to excite the sample is of wavelength of 976 nm
and able to excite the semiconducting SWNT. It is the important tool for SWNT characterization.The customization of a commercially available FT Raman system allows for development of the FT-PLE apparatus. No commercial FT-based NIR fluorimeters with tunable excitation are available. We utilized a Thermo- Nicolet FT- Raman spectrometer that contains a 1064 nm diode laser for excitation and a liquid nitrogen cooled germanium detector for measuring sample emission from 825 nm to 1700 nm.
The spectrometer is used for detection of SWNTs photoluminescence (PL) with tunable excitation was developed. The instrument offers rapid, robust, and sensitive detection, and was used to perform low-temperature PL measurements and confirm predictions that SWNT recombination kinetics are influenced by multiple excitonic bands, including a dark lower state. Toward the goal of obtaining a single nanotube type, the spectrometer’s speed advantage has allowed for the study the kinetics of PL quenching as isolated nanotubes re-bundle in suspension. TOP OF PAGE
Laser Beam Induced Current (LBIC) and Laser Beam Induced Voltage (LBIV)
Time-Resolved Photoluminescence (TRPL), also referred to as Time Correlated Single
Photon Counting (TCSPC), provides a non-destructive measurement of the mean carrier
lifetime in a material or thin-film stack. An ultrafast laser pulse is used to excite
the material and while advanced electronics record the time delay between excitation
and the detection of an emitted photon. Longer carrier lifetime is a very important
parameter, as it increases the probability of charges contributing to photo-current
in solar cells. TOP OF PAGE
Temperature Programmed Desorption (TPD)
Temperature Programmed Desorption (TPD) involves heating a testing sample while contained
in a vacuum and simultaneously detecting the residual gas in the vacuum by means of
a mass spectrometer. As the temperature rises, certain absorbed species (atoms, molecules,
and etc.) will have enough energy to escape and will be detected as a rise in pressure
for a certain mass. This technique is used for studying surface reactions and molecular
adsorption on the surface. In our lab, quadrupole mass spectrometer (QMS) is used
as the gas analyzer and the whole process is carried out under computer control with
quasi-simultaneous monitoring of a large number of possible products. TOP OF PAGE
PAR 263 Potentiostat/Galvanostat
The PAR 263 is a versatile instrument capable of running many electrochemistry experiments.
UT has coupled it with a three electrode cell for cyclic voltammetry measurements
capable of operating in the laboratory and inside an anaerobic chamber. The system
has also been used for electroplating devices. TOP OF PAGE
Solar Flash Table (Spire SPI-Sun Simulator 4800)
The Spire Solar Flash Table that is able to test large photovoltaic panels by illumination
approximating natural sunlight. This type solar simulator is the flashed simulator
which uses flash tubes with typical durations of several milliseconds. This type of
equipment is often used to prevent unnecessary heat build-up in the device under test.
TOP OF PAGE
Solstice Transient Absorption Laser System
The transient absorption (TA) system consists of a Solstice Laser system from Spectra
Physics. The Solstice output is a ~100 fs laser pulse centered at 798 nm, with a repition
rate of 4 KHz, and pulse energy of 925 μj. This is then sent into a pair of TOPAS
optical parametric amplifiers, so as to tune the wavelengths of the pump and probe
pulses independently. Thus we have TA capabilities from 270 nm to 3 μm for the pump,
and from 300 nm out to 9 μm for the probe. This allows for the investigation of the
ultrafast responses of a wide variety of materials over a wide spectral range. TOP OF PAGE
