THE UCLA POEM MISSION AND RESEARCH SCOPE

The mission of the UCLA Phonon Optimized Engineered Materials (UCLA POEM) Laboratory is the fundamental science investigation of phonons and phonon-related phenomena in advanced materials and the development of innovative methods for controlling phonon transport and phonon interactions with electrons and photons for future electronic and energy conversion technologies. Phonons are quanta of crystal lattice vibrations. Phonons affect materials’ electronic, thermal, optical, and magnetic properties. Acoustic phonons are the main heat carriers in semiconductor and electrically insulating materials. Optical phonons define many optical characteristics of materials. Together, acoustic and optical phonons, scatter electrons, limiting electron mobility and electron coherency in semiconductors. Phonons are essential for forming charge density wave condensate and superconductive phases. The field of phononics or phonon engineering comprises the detailed study and control of phonons, i.e. quanta of crystal lattice vibrations, whose characteristics influence the properties of bulk and nanostructured materials. Phononics of lower-dimensional material systems is particularly interesting, enabling one to elucidate the physics of crystal lattice vibrations and to engineer the phonon spectrum to achieve new properties and functionalities of the materials.

THE UCLA POEM LABORATORY ORGANIZATION

Balandin Group operates the Phonon Optimized Engineered Materials (UCLA POEM) Laboratory, which is located on the ground floor in the Engineering V building. The main POEM Lab hosts electrical, thermal, and low-frequency noise measurement equipment, glove boxes, and transfer systems for van der Waals materials, microscopy, and other equipment. The Raman and Brillouin – Mandelstam Spectroscopy Laboratory (SPECTRA Lab), part of the POEM Laboratory, is in a separate location on the group floor in the Engineering V building. The Cryogenic Brillouin – Mandelstam Spectroscopy (BMS) Facility is located on the ground floor of the California NanoSystems Institute (CNSI). The equipment for chemical exfoliation, processing, and composite preparation is located in the shared research space in the Engineering VI building. The photos below show the POEM MAIN LAB (Figure 1) and POEM SPECTRA LAB (Figure 2).

Figure 1: Views of the Phonon Optimized Engineered Materials (UCLA POEM) Laboratory. The main lab features state-of-the-art equipment that includes Quantum Design PPMS, an in-house-built electronic low-noise measurement setup based on the Lake Shore cryogenic system, a range of the Netzsch thermal measurement systems, advanced VTI Vacuum Technology glove boxes, in-house-built materials transfer systems, microscopes, and other equipment. UCLA POEM Laboratory, Department of Materials Science and Engineering, Engineering V Building, UCLA, December 2024.

Figure 2: Views of Raman and Brillouin – Mandelstam Spectroscopy Laboratory (SPECTRA LAB), a part of the Phonon Optimized Engineered Materials (UCLA POEM) Laboratory. The lab features state-of-the-art Renishaw INVIA and VIRSA systems and an in-house-built Brillouin spectrometer. SPECTRA LAB of the UCLA POEM Laboratory, Department of Materials Science and Engineering, Engineering V Building, UCLA, December 2024.

FACILITIES AND EQUIPMENT IN UCLA POEM LABORATORY 

Electrical Characterization Equipment (POEM LAB): Two in-house-built material transfer systems, including microscopes and micro-manipulators for capturing, moving, and releasing layers of 2D and 1D vdW materials; a thermo-sonic wire bonding machine with a microscope, equipped with ball and wedge bonding; an electron mobility and thermoelectric Seebeck effect measurement system; a Hall mobility measurements system; a cryogenic probe-station with ultra-stable six micro-manipulated probe arms. The sample stage can cover a temperature range from 4 K to 400 K with 3-axis control of probes equipped with flexible tips for soft landing on the device features; critical point dryer; semiconductor device parameter analyzer enabling measurements including I-V, C-V, pulse/dynamic I-V; programmable network analyzer for MHz and GHz frequency ranges. The equipment includes a specially designed, in-house-built low-frequency noise measurement system with a probe station for low-temperature measurements. The in-house built noise measurement system allows one to study electronic current fluctuations, i.e., noise, in electronic materials and devices in a wide range of temperatures from 4.2 K to 400 K. This system consists of a high-performance low-noise preamplifier, variable gain, and differential or single-ended inputs with AC or DC coupling option with line or battery operation. The UCLA POEM Lab features a state-of-the-art Physical Property Measurements System (PPMS), a cryogenic measurement system for controlling temperature, pressure, and magnetic fields to characterize various materials and devices. The system utilizes a single two-stage cooler to cool down the superconducting magnet and the temperature control system. PPMS features a temperature range from 1.8 K to 400 K with continuous low-temperature control, a 9 T magnetic field, precise temperature and field sweep mode, and a built-in cryopump for high-vacuum applications. The PPMS is equipped with an electrical transport option, providing I-V, Hall coefficient, and AC/DC resistance measurements. In addition, the PPMS system features an option for customized experiments using the multi-function probe, enabling an interface with the integrated chamber wiring.

Thermal Characterization Equipment (POEM Lab): A thermal conductivity and thermal diffusivity “laser flash” measurement system, operating in a wide temperature range, with the capability of measuring out-of-plane and in-plane thermal diffusivity. Other equipment includes a transient planar source thermal diffusivity and thermal conductivity “hot-disk” measurement system with an automatic hot-cold bath for temperature control and accessories for varying sample dimensions. A separate heat capacity measurement system operates in the temperature range from ~77 K to ~900 K. Combining specific heat measurements from the DSC with thermal diffusivity measurements from the LFA allows for accurate calculation of thermal conductivity. Thermal resistance and impedance of thermal pastes, e.g., thermal interface materials, are measured with two industry-standard steady-state thermal conductivity testers for the maximum heating temperature of 480 K. The thermal properties of the materials can also be characterized with the available state-of-the-art PPMS.

Optical Characterization Equipment (SPECTRA Lab): The main instrument in SPECTRA Lab is a state-of-the-art micro-Raman spectrometer operating under visible (488 nm; 633 nm) and ultraviolet (325 nm) laser excitation with the spectral resolution of ~0.1 (1/cm). The instrument is equipped with a low-wave-number filter system, allowing the observation of phonons and magnons with minimum energies of ~12 (1/cm) (~360 GHz). The advanced spectrometer system offers full automation and focus tracking technology. It features depth and surface mapping acquisition modulus. It is upgraded with a motorized polarizer accessory for polarization-resolved Raman measurements, enabling detailed studies of anisotropic materials. The polarizer can polarize at 2-degree increments between 0 and 360 degrees. The spectrometer is integrated with an advanced cryostat, allowing for measurements in the temperature range from 3.4 K to 500 K to study temperature-dependent phonon and magnon dynamics. The laboratory has recently acquired an additional Raman system with 785 nm excitation wavelength, 120 mW laser power, and 50 cm-1 to 3200 cm-1 spectral range. This system includes advanced fiber optics for remote measurement capabilities for non-contact and non-destructive analysis of biological and biomedical applications. The system features focus tracking technology, enabling analysis of large and uneven samples. Another major piece of equipment in the SPECTRA Lab is the home-built Brillouin-Mandelstam spectrometer (BMS) and micro-BMS spectrometer, which can probe phonons and magnons with energies in the range of ~1 GHz – 900 GHz. The BMS light source is a solid-state diode-pumped laser with tunable power (0.1 W to 2 W) operating at a wavelength of 532 nm. The BMS system is based on the high-resolution six-pass tandem Fabry-Perot interferometer, which allows one to achieve an exceptional spectral resolution. The system is equipped to perform polarization-resolved measurements, providing insight into the symmetry properties of phonon and magnon modes. The instrument allows one to vary the incident angle of the laser beam, enabling studies of the wave vector dependence of excitations and determining the energy dispersion relations in complex materials. These capabilities make the BMS spectrometer a highly versatile tool for investigating fundamental properties of materials, including elastic moduli, acoustic phonon dispersion, and spin-lattice interactions in a wide range of solid-state systems.

Cryogenic Brillouin – Mandelstam Spectroscopy (BMS) Facility (CNSI B123): The Balandin Group has developed an advanced first-of-its-kind high spatial and frequency resolution cryogenic integrated micro-Raman-Brillouin-Mandelstam spectrometer (CIM-RBMS) with the funding provided by NSF Major Instrumentation Research (MRI) grant. The CIM-RBMS system allows the team to investigate the low-energy acoustic phonon, high-energy optical phonon, and magnon properties in ultra-thin samples with sub-micrometer-lateral dimensions at cryogenic temperatures down to 2 K and under a magnetic field. The unique features of the CIM-RBMS system include rotating microscopy and auto-focus capability to compensate for temperature drift in experiments requiring long accumulation time. The system utilizes a triple-pass tandem Fabry-Perot interferometer with internal polarization optics to achieve high signal-to-noise contrast in solid-state samples. The system is equipped with a 532-nm laser, allowing for high laser powers with low laser linewidth, minimizing broadening of acoustic phonon peaks. The system uses specially designed cryogenic nano-positioners to focus on samples with sub-micrometer lateral dimensions and perform wavevector-dependent surface phonon measurements down to 2 K in a custom-designed helium cryostat. The system features an integrated Raman spectrometer for simultaneous optical and acoustic phonon spectra accumulation near the Brillouin zone center.

Materials Preparation Equipment and Transfer Systems (POEM Lab): This type of equipment includes two fume hoods, allowing for the chemical processing of various materials. The equipment for materials storage includes three vacuum boxes and one oxygen-purged dry nitrogen-filled glovebox to prevent oxidation and deterioration of nanomaterials. The equipment for materials transfer includes two custom-made transfer systems and an optical microscope. The in-house built transfer systems allow one to precisely manipulate the low-dimensional materials and stack van der Waal heterostructures for nanometer-scale device fabrication. One transfer stage resides in ambient conditions and is used for material transfer that is not sensitive to the environment. The other transfer stages are stationed in the glovebox to prevent oxidation while assembling heterostructures. The equipment for material preparation and exfoliation includes three ultrasonic baths, an ultrasonic probe sonicator, a high-temperature vacuum oven with a temperature range of 323 K to 523 K, two centrifuges, a high-speed shear mixer, and a 3D printer.