Development of an Apparatus for Terahertz Spectroscopy in an Ultrahigh Vacuum - Temperature Dependence of the Spectrum of Vapor-Deposited D<sub>2</sub>O Ice
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2018-01-01 |
| Journal | Vacuum and Surface Science |
| Authors | Genki Shimizu, Natsumi Suzuki, Hirokazu Nasu, Rei Tsuboi, Hiroyuki Kurahashi |
| Institutions | Gakushuin University |
| Citations | 1 |
| Analysis | Full AI Review Included |
6CCVD Technical Documentation: UHV Terahertz Spectroscopy Development
Section titled “6CCVD Technical Documentation: UHV Terahertz Spectroscopy Development”Executive Summary
Section titled “Executive Summary”This research details the successful development and application of a novel Ultra-High Vacuum (UHV) apparatus for reflection-mode Terahertz (THz) Fourier Transform Spectroscopy (FTS). The study leveraged high-performance materials, notably diamond windows, to enable demanding cryogenic surface science investigations of D₂O ice phase transitions.
- System Achievement: Developed a UHV THz FTS system capable of non-destructive, high-sensitivity spectral analysis in the 50-650 cm⁻¹ range (1.5-19.5 THz).
- Material Selection: Diamond optical windows were critical, providing robust pressure isolation, broad THz transparency, and tolerance to high-temperature UHV baking (390 K).
- Vacuum Performance: The system achieved extreme vacuum conditions, reaching a base pressure of 1.7 x 10-9 Pa during liquid helium cooling, necessary for high-purity vapor deposition experiments.
- Phase Transition Detection: Successfully differentiated distinct structural phase changes in vapor-deposited D₂O ice based on unique THz spectral signatures.
- Key Scientific Findings: Confirmed the structural transition from High-Density Amorphous Ice (HD-ASW) to Low-Density Amorphous Ice (LD-ASW) via a sharp increase in absorption strength observed at 45 K.
- Crystalline Analysis: Observed spectral shifts and peak reduction (156 cm⁻¹ peak) associated with the transformation from Cubic Ice (Ic) to Hexagonal Ice (Ih) in the 160 K to 180 K range, providing a non-diffraction method for phase identification.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the development and experimental sections of the research paper:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Spectral Measurement Range | 50-650 | cm⁻¹ | Optimized range for THz FTS |
| Spectral Resolution (Used) | 8.0 | cm⁻¹ | Resolution utilized for background measurements |
| System Base Pressure (Cooled) | 1.7 x 10-9 | Pa | Pressure achieved during cryogenic operation |
| System Base Pressure (Baked) | 1.0 x 10-7 | Pa | Pressure achieved after 390 K bakeout |
| UHV Baking Temperature | 390 | K | Temperature applied for 24 hours during chamber preparation |
| Ice Deposition Temperature | 10 | K | Substrate temperature for initial D₂O vapor deposition |
| HD-ASW to LD-ASW Transition | 45 | K | Temperature of observed abrupt absorption increase |
| LD-ASW to Cubic Ice (Ic) Range | 140-160 | K | Temperature range of amorphous-to-crystalline transition |
| Gold Substrate Dimensions | 15 x 15 x 0.5 | mm | Dimensions of the Au deposition substrate |
| Diamond Window Thickness | 0.5 | mm | Thickness of the SCD windows separating vacuum paths |
| Incidence Angle | 80 | ° | Grazing incidence reflection geometry |
| 156 cm⁻¹ Peak Reduction | 60 | % | Area reduction observed during Ice Ic → Ih transition |
Key Methodologies
Section titled “Key Methodologies”The experimental approach focused on integrating broadband THz optics into a robust, bakeable UHV environment capable of precise cryogenic temperature control:
- Apparatus Design (FTS Integration): A custom reflection-mode THz FTS system was developed utilizing a high-brightness ceramic source, a broadband Mylar beam splitter, and a liquid helium-cooled Si bolometer detector.
- Vacuum Path Construction: The entire optical path was housed in vacuum vessels constructed from SUS316LN stainless steel, evacuated by a series of turbo molecular pumps (TMPs) and dry pumps (DPs).
- UHV Preparation Cycle: To eliminate contaminants, the vacuum chamber and gas introduction system were baked out. The main chamber was baked at 390 K for 24 hours, achieving the necessary UHV base pressure.
- Window Integration: Single Crystal Diamond (SCD) windows (19 mm diameter, 0.5 mm thick) were used to isolate the high vacuum sample chamber from the less critical optical path (OB1/2). The diamond windows were sealed using Viton O-rings under compression.
- Sample Preparation and Control: D₂O vapor was purified using freeze-pump-thaw cycles. The vapor was deposited onto a cooled, highly polished gold substrate (15 mm x 15 mm x 0.5 mm), held at 10 K by a liquid helium continuous-flow cryostat.
- Spectral Measurement: THz absorption spectra were recorded continuously as the substrate temperature was slowly ramped from 10 K to 180 K (rate of 0.05 K/s below 60 K, and 0.2 K/s above 60 K), allowing observation of temperature-dependent phase transformations.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”This research demonstrates a critical need for high-performance, UHV-compatible materials, particularly for optical windows and polished substrates. 6CCVD is uniquely positioned to supply and enhance the materials required for replication and extension of this advanced THz surface science.
Applicable Materials
Section titled “Applicable Materials”The foundation of the UHV apparatus relies on robust optical elements and polished substrates.
- Material Recommendation: Optical Grade Single Crystal Diamond (SCD) Wafers.
- Application: Required for optical windows separating the FTS vacuum from the UHV sample chamber.
- 6CCVD Advantage: Our optical grade SCD provides exceptional broadband transmission, making it ideal for the 50-650 cm⁻¹ range (THz and far-IR), while offering unmatched thermal stability (bakeable well beyond 390 K) and chemical inertness required for UHV environments.
Customization Potential
Section titled “Customization Potential”The experimental setup utilized custom dimensions for the diamond windows and specialized Au substrates. 6CCVD offers direct fulfillment for these specific engineering requirements.
| Research Requirement | 6CCVD Custom Solution | Technical Advantage & Sales Pitch |
|---|---|---|
| Custom Optical Dimensions | Custom Laser Cutting and Shaping Services | We supply SCD plates up to 125 mm diameter. Custom laser cutting ensures precise shaping (e.g., 19 mm diameter windows) and tolerance control necessary for O-ring or brazed sealing in sensitive UHV flanges. |
| Substrate Preparation & Polish | Ultra-Low Roughness Polishing (Ra < 1 nm) | Highly sensitive reflection spectroscopy (80° incidence) demands near-perfect surface quality. We guarantee SCD polish quality of Ra < 1 nm, minimizing scatter and maximizing signal integrity for surface adsorption studies. |
| Substrate Metalization | In-House Metalization Capabilities (Au, Ti/Pt/Au) | The use of custom metal films (e.g., highly reflective gold) is essential for reflection-mode THz experiments. 6CCVD provides internal metalization services (Au, Pt, Ti, Pd, W, Cu) allowing researchers to specify complex adhesion layers directly onto diamond or other customer-supplied substrates. |
| Thickness Control | High-Precision SCD Thickness Control | We offer SCD thicknesses from 0.1 µm up to 500 µm, allowing fine-tuning of window thickness (e.g., 0.5 mm specified in the paper) to optimize mechanical stability, thermal properties, and absorption characteristics in the THz band. |
Engineering Support
Section titled “Engineering Support”This research represents a demanding intersection of vacuum science, cryogenics, and advanced spectroscopy.
6CCVD’s in-house PhD engineering team specializes in the physical and chemical properties of diamond materials under extreme conditions. We offer comprehensive support to assist researchers and technical engineers in optimizing material selection and geometry for similar Cryogenic UHV THz Spectroscopy projects, ensuring reliable performance and maximizing experimental success rates.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
An apparatus for terahertz spectroscopy in an ultrahigh vacuum has been developed. We used broadband Mylar for the beam splitter in a Fourier transform spectrometer, diamond for optical windows, and a liquid-helium-cooled Si bolometer for the terahertz detector to achieve the spectral range of 50-650 cm−1. For the purpose of keeping the ultrahigh vacuum in a sample chamber, we evacuated the whole optical path by turbo molecular pumps and made its pressure down to 10−4 Pa. Using this apparatus, we measured temperature dependence of the terahertz spectrum of D2O ice vapor-deposited at 10 K. The spectral changes due to the structural transformation from amorphous ice to cubic crystalline ice Ic were successfully observed in the range of 140-160 K. We report the spectral difference between low-density and high-density amorphous ice as well as that between hexagonal crystalline ice Ih and cubic one.