Instruments

 

Nanostructure Preparation Instruments

GLANCING ANGLE DEPOSITION (GLAD)

The glancing angle deposition (GLAD) chamber is an in-house built ultra-high vacuum deposition chamber dedicated to the growth of sculptured thin films by electron-beam evaporation. A key part is a three-axis sample manipulator with continuous polar and computer controlled azimuthal sample rotation. Samples are introduced through a load-lock system to allow quick sample exchange procedures and warrant ultra-high vacuum conditions within the deposition chamber. The system is further equipped with a thin film deposition controller, vacuum gauges, ellipsometry ports, and viewports.



PLASMA EXCHANGE

The SPI Plasma Prep II is a tabletop plasma etcher operated at room-temperature. Dry plasma etching is typically used to remove organic contamination from samples without destroying the anorganic parts. Further, most metal oxides can be etched by using argon plasma. The SPI Plasma Prep II is operated at 13.56 MHz and provides an output power up to 100 W. In our lab, it can be used with argon or oxygen.


SPUTTER CHAMBER






DIP COATER

A simple, custom-built dip coating apparatus is available that allows the removal of samples from coating liquids at defined speeds between 1 and 12 mm/min.

 

Nanostructure Characterization Instruments

OPTICAL HALL-EFFECT

The Optical Hall-Effect setup is an in-house built instrument, designed to characterize free-charge carrier properties of bulk or layered samples. This non-contact method can be used in a wide spectral range from the Thz to the NIR (0.1-210THz or 3cm-7000cm-1), with magnetic fields up to 8T and sample temperatures from room temperature down to 1.5K.  The instrument contains three ellipsometers and a closed cycle, superconducting magnet with a VTI sample cooling stage. The magnet can be moved between the MIR ellipsometer (Bruker Vertex 70 FTIR spectrometer 550-7000 cm-1) and the FIR/THz ellipsometer (Bruker Vertex 70 FTIR spectrometer 30-650 cm-1/Backward-Wave-Oscillator 0.1-1.5THz). It is a commercial closed cycle system from Oxford instruments using a dual-stage pulse tube cooler. It is equipped with four optical ports using KBr and PE for the FIR/THz and MIR spectral range as outer and four wedged CVD diamond windows as inner windows. Ideal sample sizes are from 0.5-1inch, but smaller samples can be mounted too.


CONTACT ANGLE IMAGING SYSTEM

The Ramé Hart imaging system utilizes a NRL C.A. goniometer for sample mounting with Ramé Hart 2001 imaging software for precise, digitally calculated contact angle measurements in order to evaluate the hydrophobic and hydrophilic properties of liquid/solid/gas interfaces. Other characterization capabilities are present with the imaging system for measuring acid-base values, surface energy, and the work of adhesion.


M44

The commercial M-44 rotating analyzer ellipsometer (J.A. Woollam, Inc.) is capable of performing standard and generalized ellipsometry measurements. It is equipped with a Xenon arc lamp source for simultaneous measurements of 44 discrete wavelengths between 280 nm and 763 nm. The instrument is mounted on an automated goniometer stage for measurements at variable angles of incidence. A unique feature compared to our other ellipsometers is an automated X-Y translation stage that allows for mapping at lateral distances of 0.1 mm. However, the absence of a compensator might limit the accuracy for measurements on transparent samples.


M-2000VI

The M-2000VI is a commercially available spectroscopic rotating compensator ellipsometer capable of acquiring generalized ellipsometry data from the entire spectral range (590 wavelengths from 370 to 1690 nm) simultaneously. The ellipsometer, manufactured by the J.A. Woollam Company, is mounted on a fully automated translator/rotator/variable angle of incidence stage with an alignment laser and automated z-alignment. Focusing probes are available to measure only defined areas or very small samples.


M-2000

M-2000 The J.A. Woollam Co., Inc., M-2000 multiple wavelength ellipsometer is a versatile instrument operating in the visible spectrum with optional extensions into the near-infrared and near-ultraviolet ranges. The M-2000 measures hundreds of wavelengths simultaneously in seconds, making it useful for quality control or in-situ process monitoring. The M-2000 is a rotating-compensator ellipsometer, allowing it to measure the first three rows of the Mueller matrix. An optional rotation/translation stage allows for sample mapping or rotation measurements for anisotropic samples. Focusing probes can be attached to the instrument for measuring specific locations on inhomogeneous surfaces. M-2000s at the CNFM are used for both ex-situ measurements and in-situ experiments under liquid or vacuum ambient for the observation of dynamic surface modification.


VECTOR-MAGNETO-OPTIC (VMOGE)

The vector-magneto-optic generalized ellipsometry instrument combines a rotating analyzer VASE ellipsometer with autoretarder (J.A. Woollam, Inc.) with an in-house built vector magnet. The specific construction of the vector magnet, four coil pairs along the space diagonals of a cube, allows for magnetic fields of up to 240 mT along an arbitrary direction in space. The sample under investigation, mounted within the center of the vector magnet, can be magnetized by applying a magnetic field. The resulting sample magnetization can be investigated by analyzing the magneto-optic response measured by generalized ellipsometry. The monochromator based ellipsometer is equipped with focusing probes to limit the spot size to the homogeneously magnetized sample area and covers the spectral range from 240 to 1700 nm.

VUV VASE

The J.A.Woollam Co., Inc. VUV-VASE is a monochromator-based variable angle of incidence spectroscopic ellipsometer that covers the wide spectral range from 0.73 eV up to 9.5 eV (147-1700 nm). The nitrogen-purged instrument is equipped with a compensator and allows for standard ellipsometry investigations on isotropic samples as well as generalized ellipsometry characterization of arbitrarily oriented anisotropic samples. This provides incredible versatility to precisely characterize numerous types of materials: semiconductors, dielectrics, polymers, metals, multilayers, even for very thin film thicknesses. The instrument can further be equipped with a liquid prism in order to apply the minimum deviation method for extremely accurate determination of the refractive index n and extinction coefficient k of liquids up to the UV spectral range, e.g. for use as ambient values in in-situ SE measurements.


UHV-ANNEALING CHAMBER WITH VVASE

The custom-built ultra-high vacuum chamber allows for computer-controlled sample annealing up to 600 °C in a controlled environment. Additionally, a rotating analyzer VASE ellipsometer with autoretarder (J.A. Woollam, Inc.) is attached to the chamber for in-situ temperature-depended sample property studies. The sample/heater stage is part of a 5-axes feedthrough which allows for optimal sample alignment for optical investigations.


DIGITAL INSTRUMENTS MULTIMODE AFM

The AFM system available in our lab is an old generation of the DI Multimode AFM (currently Veeco/Bruker) that can be operated in contact mode, STM mode, and tapping mode. Currently only cantilevers for tapping mode measurements are available. Due to the instrument geometry, the maximum sample size should not exceed 1 cm2. Reasonable scan scales are between 0.4 and 20 µm. The precision of the instrument is limited compared to modern versions, but sufficient for fast determination of the surface morphology. The software allows for height and amplitude information, however, phase data is not available. Laser alignment and sample engagement need to be performed manually. For precise measurements on large samples and with very high resolution, the facilities of the Nebraska Center for Materials and Nanoscience (NCMN) are available in the basement of Jorgensen Hall (Room 013), including a DI Dimension D3100 SPM (AFM, STM, STS, LFM, MFM) and a DI EnviroScope AFM for measurements in a controlled environment. The D3100 SPM is further equipped with a camera system with focusing optics allowing one to visually identify and relocate a specific scanning area.


STYLUS PROFILOMETER

The Ambios Technology XP-2 Advanced Stylus Profiling System provides direct contact thickness and roughness measurements for solid thin films.  Using the software, the user controls both the sample mounting platform as well as the diamond tipped stylus which drags across the film’s surface gathering quick and accurate numerical values.  The concurrent line graphs can then be evaluated for film properties with nanoscale accuracy.


Nanostructure Functionalization Instruments

ATOMIC LAYER DEPOSITION - ALD

The atomic layer deposition (ALD) tool Fiji200, purchased from Cambridge Nanotech, Inc., is the state-of-the-art instrument in research. The attached load-lock allows for handling of wafers up to 8” and layer-by-layer growth can be achieved by a thermal, plasma, or ozone process. The available six heated precursor lines, including ‘ALD Vapor Boost’ technology, together with six plasma gas lines, allow for a wide variety of different processes. Attached to the tool is an M-2000U ellipsometer (245 to 1000 nm) for in-situ process control and process development.


QCM-D

The operating principle of a quartz crystal microbalance (QCM) is based around a piezoelectric quartz crystal. The crystal is commonly coated with gold and acts as the substrate surface for molecule attachment studies. An oscillating potential is applied between the top and bottom of the quartz crystal such that the crystal vibrates in a shear mode due to the piezoelectric effect. QCM measures the frequency shifts of the odd harmonic overtones. For mechanically rigid experimental systems, the Sauerbrey equation is often used to provide a linear relationship between mass attachment and frequency shifts. A variant of QCM is the quartz crystal microbalance with dissipation (QCM-D). QCM-D operates in a pulse mode and additionally measures the signal dissipation of the harmonic overtones. Dissipation is an indicator of the experimental system’s viscoelasticity. If viscoelastic effects should not be neglected, a viscoelastic mechanical model is constructed. Relevant properties in the mechanical model, e.g., film thickness and shear, are varied while experimental and model generated frequency and dissipation data are best matched. The Q-Sense E4 QCM-D has capacity for four liquid flow cells, allowing replicate measurements to be acquired simultaneously.


QCM-D/SE

The quartz crystal microbalance with dissipation (QCM-D) QCM-D is sensitive to liquid that is associated with a porous organic film, making the technique ideal for studies on film swelling and collapse. On the other hand, spectroscopic ellipsometry (SE) has been shown to be non-sensitive to the liquid component of a porous film on the order of 10 nm or less. By using both techniques together, one can determine the film’s porosity. Porosity is a quantity that can indicate structure or differences between molecular conformations. The combinatorial QCM-D/SE setup comprises a Q-Sense E1 QCM-D and a J.A. Woollam Co., Inc. M-2000 SE. A liquid cell with windows and beam channels is used to facilitate ellipsometry measurements on the quartz crystal surface.


EC/QCM-D/SE

Adding electrochemical (EC) measurements to a combinatorial quartz crystal microbalance with dissipation (QCM-D) and spectroscopic ellipsometry (SE) experimental setup is currently under development at the CNFM. It is proposed that the additional EC measurements will provide insight to the electrical double layer that forms at the solid-liquid interface and how it relates to organic film structure. A Princeton Applied Research Model 273A potentiostat is implemented with a custom-built liquid flow cell to provide control over reference and counter electrodes and the gold-coated quartz crystal, which acts as the working electrode. The Q-Sense E1 QCM-D and J.A. Woollam, Inc. M-2000 SE are also used.