In Neoadjuvant FOLFIRINOX Chemotherapy for Pancreatic Ductal Adenocarcinoma, Which Response is the More Reliable Indicator for Prognosis, Radiologic or Biochemical?

BACKGROUND: In this era of increasing neoadjuvant chemotherapy, methods for evaluating responses to neoadjuvant chemotherapy are still diverse among institutions. Additionally, the efficacy of adjuvant chemotherapy for patients undergoing neoadjuvant chemotherapy remains unclear. Therefore, this retrospective study was performed to evaluate the effectiveness of methods for assessing response to neoadjuvant chemotherapy and the need for adjuvant chemotherapy in treating patients with non-metastatic pancreatic ductal adenocarcinoma. METHODS: The study identified 150 patients who underwent neoadjuvant FOLFIRINOX chemotherapy followed by curative-intent pancreatectomy. The patients were stratified by biochemical response based on the normalization of carbohydrate antigen 19-9 and by radiologic response based on size change at imaging. RESULTS: The patients were classified into the following three groups based on their response to neoadjuvant chemotherapy and prognosis: biochemical responders (BR+), radiology-only responders (BR-/RR+), and non-responders (BR-/RR-). The 3-year overall survival rate was higher for BR+ (71.0%) than for BR-/RR+ (53.6%) or BR-/RR- (33.1%) (P < 0.001). Response to neoadjuvant chemotherapy also was identified as a significant risk factor for recurrence in a comparison between BR-/RR+ and BR+ (hazard ratio [HR], 2.15; 95% confidence interval [CI] 1.19-3.88; P = 0.011) and BR-/RR- (HR, 3.82; 95% CI 2.41-6.08; P < 0.001). Additionally, regardless of the response to neoadjuvant chemotherapy, patients who completed adjuvant chemotherapy had a significantly higher 3-year overall survival rate than those who did not. CONCLUSIONS: This response evaluation criterion for neoadjuvant chemotherapy is feasible and can significantly predict prognosis. Additionally, completion of adjuvant chemotherapy could be helpful to patients who undergo neoadjuvant chemotherapy regardless of their response to neoadjuvant chemotherapy.

Long-Term Outcome of Proximal Gastrectomy for Upper-Third Advanced Gastric and Siewert Type II Esophagogastric Junction Cancer Compared With Total Gastrectomy: A Propensity Score-Matched Analysis.

BACKGROUND: This study aimed to investigate the oncologic long-term safety of proximal gastrectomy for upper-third advanced gastric cancer (AGC) and Siewert type II esophagogastric junction (EGJ) cancer. METHODS: The study enrolled patients who underwent proximal gastrectomy (PG) or total gastrectomy (TG) with standard lymph node (LN) dissection for pathologically proven upper-third AGC and EGJ cancers between January 2007 and December 2018. Propensity score-matching with a 1:1 ratio was performed to reduce the influence of confounding variables such as age, sex, tumor size, T stage, N stage, and tumor-node-metastasis (TNM) stage. Kaplan-Meier survival analysis was performed to analyze oncologic outcome. The prognostic factors of recurrence-free survival (RFS) were analyzed using the Cox proportional hazard analysis. RESULTS: Of the 713 enrolled patients in this study, 60 received PG and 653 received TG. Propensity score-matching yielded 60 patients for each group. The overall survival rates were 61.7 % in the PG group and 68.3 % in the TG group (p = 0.676). The RFS was 86.7 % in the PG group and 83.3 % in the TG group (p = 0.634). The PG group showed eight recurrences (1 anastomosis site, 1 paraaortic LN, 1 liver, 1 spleen, 1 lung, 1 splenic hilar LN, and 2 remnant stomachs). In the multivariate analysis, the operation method was not identified as a prognostic factor of tumor recurrence. CONCLUSION: The patients who underwent PG had a long-term oncologic outcome similar to that for the patients who underwent TG for upper-third AGC and EGJ cancer.

Systematic review on surveillance for non-resected branch-duct intraductal papillary mucinous neoplasms of the pancreas.

BACKGROUND: The management of branch-duct type intraductal papillary mucinous neoplasms (BD-IPMN) varies in existing guidelines. This study investigated the optimal surveillance protocol and safe discontinuation of surveillance considering natural history in non-resected IPMN, by systematically reviewing the published literature. METHODS: This review was guided by PRISMA. Research questions were framed in PICO format "CQ1-1: Is size criteria helpful to determine surveillance period? CQ1-2: How often should surveillance be carried out? CQ1-3: When should surveillance be discontinued? CQ1-4: Is nomogram predicting malignancy useful during surveillance?". PubMed was searched from January-April 2022. RESULTS: The search generated 2373 citations. After screening, 83 articles were included. Among them, 33 studies were identified for CQ1-1, 19 for CQ1-2, 26 for CQ1-3 and 12 for CQ1-4. Cysts <1.5 or 2 cm without worrisome features (WF) were described as more indolent, and most studies advised an initial period of surveillance. The median growth rate of cysts <2 cm ranged from 0.23 to 0.6 mm/year. Patients with cysts <2 cm showing no morphological changes and no WF after 5-years of surveillance have minimal malignancy risk of 0-2%. Two nomograms created with over 1000 patients had AUCs of around 0.8 and appear to be feasible in a real-world practice. CONCLUSIONS: For patients with suspected BD-IPMN <2 cm and no other WF, less frequent surveillance is recommended. Surveillance may be discontinued for cysts that remain stable during 5-year surveillance, with consideration of patient condition and life expectancy. With this updated surveillance strategy, patients with non-worrisome BD-IPMN should expect more streamlined management and decreased healthcare utilization.

Multiple thromboses, including intracardiac thrombi, accompanied by HIT during ECMO successfully treated with NOACs: A case report.

INTRODUCTION: Unfractionated heparin remains the mainstay of anticoagulation therapy during extracorporeal membrane oxygenation (ECMO) maintenance. However, its continued use in clinical practice exposes patients to the risk of developing heparin-induced thrombocytopenia (HIT). CASE REPORT: A 50-year-old male was diagnosed with multiple thromboses, including an intracardiac thrombi, accompanied by HIT during ECMO after cardiogenic shock related to acute myocardial infarction. The patient was successfully treated with new oral anticoagulants (NOAC), without significant complications. DISCUSSION: HIT during ECMO resulting in multiple thromboses is rare. To our knowledge, this is the first reported case of NOAC use in this context. CONCLUSION: Although thrombocytopenia and thrombosis can occur for various reasons during ECMO maintenance, it is important to consider HIT as a potential cause. NOACs can be considered as a therapeutic option.

Inadequacy of the eighth edition of the American Joint Committee on Cancer pancreatic cancer staging system for invasive carcinoma associated with premalignant lesions in the pancreas: an analysis using the National Cancer Database.

BACKGROUND: Invasive carcinomas arising from premalignant lesions are currently staged by the same criteria as conventional pancreatic ductal adenocarcinoma. METHODS: Clinicopathologic information and survival data were extracted through a thorough search of histology codes from National Cancer Database (2006-2016). A total of 723 patients with invasive intraductal papillary mucinous neoplasm and mucinous cystic neoplasm were analyzed. RESULTS: The median age was 67 years, and 351 patients (48.5%) were male. There were 212 (29.3%), 232 (32.1%), 272 (37.6%), and 7 (1.0%) patients with T1, T2, T3, and T4 classification. Extrapancreatic extension (EPE) was present in 284 (39.3%). Age (HR = 1.504, 95% CI 1.196-1.891), R1 or R2 resection (HR = 1.585, 95% CI 1.175-2.140), and EPE (HR = 1.598, 95% CI 1.209-2.113) were independent prognostic factors for overall survival. Size criteria did not significantly affect survival. The median survival was 115.9 months for patients without EPE, compared to 34.2 months for those with EPE. EPE discriminated survival better than tumor size. DISCUSSION: The T classification of the eighth edition AJCC staging system is not adequate for invasive carcinomas associated with premalignant lesions of the pancreas. They merit a separate, dedicated staging system that uses appropriate prognostic factors.

Strain-induced dark exciton generation in rippled monolayer MoS2.

Recently, it has been revealed that dark excitons play a significant role in optically controlled information processing due to their much longer radiative lifetimes than those of bright ones. For the realizable implementation of the features, it is important to understand and manipulate conditions in which dark excitons could exist. We adopt strain-engineered rippling as a new parameter for the modification of the electronic structure of monolayer MoS2 and demonstrate the efficient conversion of bright to dark excitons via a first-principles study. For rippled monolayer MoS2 above a strain of ∼6.8%, we show that the spin order of the conduction band is reversed and the spin forbidden dark exciton then goes below the bright one.

Oncologic safety of robotic extended cholecystectomy for gallbladder cancer.

BACKGROUND: Although laparoscopic cholecystectomy is applicable for the treatment of early gallbladder cancer (GBC), minimally invasive surgery is not widely used for advanced GBC. This is because advanced GBCs necessitate complicated surgical techniques, including lymph node dissection and liver resection. Robotic extended cholecystectomy (REC) is thought to overcome the limitations of laparoscopic surgery, but oncological safety studies are lacking. Therefore, in this study, we aimed to evaluate the oncologic outcomes of REC compared with those of open extended cholecystectomy (OEC). METHODS: A total of 125 patients, who underwent extended cholecystectomy for GBC with tentative T2 or higher stage between 2018 and 2021, were included and stratified by surgical methods. To minimize the confounding factors, 1:1 propensity-score matching was performed between the patients who underwent REC and those who underwent OEC. RESULTS: Regarding short-term outcomes, the REC group showed significantly lower estimated blood loss (382.7 vs. 717.2 mL, P = 0.020) and shorter hospital stay (6.9 vs. 8.5 days, P = 0.042) than the OEC group. In addition, the REC group had significantly lower subjective pain scores than the OEC group from the day of surgery through the 5th postoperative day (P = 0.006). Regarding long-term outcomes, there were no significant differences in the 3-year [5-year] overall survival (OS) and disease-free survival (DFS) rates between the REC group [OS, 92.3% (92.3%); DFS, 84.6% (72.5%)] and the OEC group [OS, 96.8% (96.8%); DFS, 78.2% (78.2%)] (P = 0.807 for OS and 0.991 for DFS). CONCLUSIONS: In this study, REC showed superior short-term outcomes to OEC and no difference in long-term survival outcomes. Additionally, REC was superior to OEC in terms of postoperative pain. Therefore, REC may be a feasible option with early recovery compared with OEC for patients with advanced GBC.

Parallel Analysis of Pre- and Postoperative Circulating Tumor DNA and Matched Tumor Tissues in Resectable Pancreatic Ductal Adenocarcinoma: A Prospective Cohort Study.

BACKGROUND: Circulating tumor DNA (ctDNA) is a promising biomarker for early tumor detection and minimal residual disease (MRD) assessment in early-stage cancer, but quantifying minute amounts of ctDNA is challenging and well-designed studies on ctDNA in early-stage cancer are still lacking. Here, we adapted a sensitive next-generation sequencing (NGS) technology and performed parallel analysis of pre- and postoperative ctDNA and matched tumor tissues in a prospective cohort of patients with resectable pancreatic ductal adenocarcinoma (PDAC). METHODS: In total, 70 consecutive patients undergoing curative resection for resectable PDAC were enrolled. We performed integrated digital error suppression-enhanced cancer personalized profiling by deep sequencing NGS of triple-matched samples (pre/postoperative plasma cell-free DNA [cfDNA], tumor tissue, and genomic DNA) targeting 77 genes. RESULTS: Preoperative ctDNA was detected in 37.7% of the evaluable patients, with a median variant allele frequency of 0.09%. Twelve additional oncogenic mutations were detected exclusively in preoperative ctDNA but not in tissue. When quantitative concentrations of ctDNA were estimated in haploid genome equivalents per milliliter (hGE/mL), the risk of early recurrence was high in patients with postoperative ctDNA >1 hGE/mL. cfDNA variants from 24.5% of patients had features compatible with clonal hematopoiesis. CONCLUSIONS: An optimized NGS approach might add value beyond tissue analysis through the highly sensitive detection of minute amounts of ctDNA in resectable PDAC. Postoperative ctDNA concentration could be a tool for MRD assessment. Moreover, parallel analyses of matched tissues and leukocytes might be required to accurately detect clinically relevant ctDNA.

Thermoelectric performance of novel single-layer ZrTeSe4.

In energy conversion techniques, two-dimensional (2D) thermoelectric materials with high performance are strongly required. This study scrutinizes the electronic and thermoelectric properties of 2D single-layer (1L) ZrTeSe4 based on first-principles calculations combined with Boltzmann transport theory. First-principles molecular dynamics simulations and phonon calculations confirm the thermodynamic stability of 1L-ZrTeSe4. Furthermore, the electron mobility of 1L-ZrTeSe4 is calculated to be ∼5706 cm2 V-1 s-1, which is much higher than that of the typical 2D semiconducting materials. Intriguingly, the calculated lattice thermal conductivity of 1L-ZrTeSe4 is found to be 3.16 W m-1 K-1 at room temperature, which is relatively smaller than that of 2D transition metal dichalcogenides. The maximum figure of merit ZT of 1L-ZrTeSe4 at 900 K is ∼0.8 for both p- and n-type doping at optimal carrier concentrations. As ZT could be improved through the manipulation of its electronic structure, this is an important clue indicating the enormous potential of 1L-ZrTeSe4 in thermoelectric application.

Long-term efficacy and safety of 3D printed implant in patients with nasal septal deformities.

PURPOSE: To investigate the long-term safety and efficacy of a 3D-printed bioresorbable polycaprolactone (PCL) nasal implant for nasal septal deformity reconstruction. METHODS: Fourteen patients who had undergone nasal septum reconstruction surgery using 3D-printed PCL nasal septal implants were enrolled. The primary outcome was the change in total Nasal Obstruction Symptom Evaluation (NOSE) scale scores between postoperative 3 months and current status (3.59 ± 0.51 years). The secondary outcomes were changes in the minimum cross-sectional area (MCA) and volume of both nasal cavities based on acoustic rhinometry, the cross-sectional area of the ostiomeatal unit, and the nasal septum angle of the paranasal sinus (PNS) in computed tomography (CT) images, and a visual analog scale (VAS) of the patients' subjective satisfaction. RESULTS: The results showed no significant changes in the MCAs (Cohen's d:0.09; p = 0.711) or nasal volume (Cohen's d:0.26; p = 0.356), the area of the ostiomeatal unit (Cohen's d:0.49; p = 0.064), septum angles (Cohen's d:0.18; p = 0.831), the NOSE scale (Cohen's d:0.14; p = 0.621), or patients' subjective satisfaction (Cohen's d:0.52; p = 0.076) during the follow-up period. CONCLUSIONS: This homogeneous composite microporous PCL nasal septal implant demonstrated long-term clinical efficacy and safety in human tissues that required maintenance of mechanical strength. Therefore, the indications for this implant could extend to various other craniofacial reconstructions in the future.

Oncological outcome of proximal and middle extrahepatic bile duct cancer according to surgical extent (Is hilar resection oncologically acceptable in proximal and middle extrahepatic bile duct cancer?).

BACKGROUND: For proximal to middle bile duct cancer, it is controversial whether bile duct resection alone is sufficient, or whether hepatic or pancreatic resection should be accompanied by initial planning. This study aimed to determine the optimal surgical extent based on oncological outcomes in patients with proximal to middle bile duct cancer. METHODS: Patients who underwent surgery for proximal to middle extrahepatic bile duct cancer, hilar resection, or combined resection of other organs were included. Clinicopathological characteristics and survival analyses were compared according to operation type. RESULTS: Among 156 patients in total, R0 rate was 56.7% for hilar resection and 82.7% for other organ resection. Although hilar resection was associated with shorter hospital stay and fewer overall complications, operation type did not affect overall survival (p = 0.259) and disease-free-survival (p = 0.774). Overall survival differed according to R status (5YSR 49.8 vs. 27.1%; p = 0.012). CONCLUSION: In proximal to middle extrahepatic bile duct cancer, surgery should be tailored to achieve R0 resection according to the extent of the disease rather than uniformly resecting extensively with other organ resections. Hilar resection could be selected if R0 resection is feasible, considering the lower morbidity with similar long-term survival.

Bone Fracture-Treatment Method: Fixing 3D-Printed Polycaprolactone Scaffolds with Hydrogel Type Bone-Derived Extracellular Matrix and ß-Tricalcium Phosphate as an Osteogenic Promoter.

Bone formation and growth are crucial for treating bone fractures. Improving bone-reconstruction methods using autologous bone and synthetic implants can reduce the recovery time. Here, we investigated three treatments using two different materials, a bone-derived decellularized extracellular matrix (bdECM) and ß-tricalcium phosphate (ß-TCP), individually and in combination, as osteogenic promoter between bone and 3D-printed polycaprolactone scaffold (6-mm diameter) in rat calvarial defects (8-mm critical diameter). The materials were tested with a human pre-osteoblast cell line (MG63) to determine the effects of the osteogenic promoter on bone formation in vitro. A polycaprolactone (PCL) scaffold with a porous structure was placed at the center of the in vivo rat calvarial defects. The gap between the defective bone and PCL scaffold was filled with each material. Animals were sacrificed four weeks post-implantation, and skull samples were preserved for analysis. The preserved samples were scanned by micro-computed tomography and analyzed histologically to examine the clinical benefits of the materials. The bdECM-ß-TCP mixture showed faster bone formation and a lower inflammatory response in the rats. Therefore, our results imply that a bdECM-ß-TCP mixture is an ideal osteogenic promoter for treating fractures.

Optimizing the Aspect Ratio of Nanopatterned Mesoporous TiO2 Thin-Film Layer to Improve Energy Conversion Efficiency of Perovskite Solar Cells.

The energy conversion efficiency (ECE) (η), current density (Jsc), open-circuit voltage (Voc), and fill factor (ff) of perovskite solar cells were studied by using the transmittance of a nanopatterned mesoporous TiO2 (mp-TiO2) thin-film layer. To improve the ECE of perovskite solar cells, a mp-TiO2 thin-film layer was prepared to be used as an electron transport layer (ETL) via the nanoimprinting method for nanopatterning, which was controlled by the aspect ratio. The nanopatterned mp-TiO2 thin-film layer had a uniform and well-designed structure, and the diameter of nanopatterning was 280 nm. The aspect ratio was controlled at the depths of 75, 97, 127, and 167 nm, and the perovskite solar cell was fabricated with different depths. The ECE of the perovskite solar cells with the nanopatterned mp-TiO2 thin-film layer was 14.50%, 15.30%, 15.83%, or 14.24%, which is higher than that of a non-nanopatterned mp-TiO2 thin-film layer (14.07%). The enhancement of ECE was attributed to the transmittance of the nanopatterned mp-TiO2 thin-film layer that is due to the improvement of the electron generation. As a result, better electron generation affected the electron density, and Jsc increased the Voc, and ff of perovskite solar cells.

Osteogenesis of 3D-Printed PCL/TCP/bdECM Scaffold Using Adipose-Derived Stem Cells Aggregates; An Experimental Study in the Canine Mandible.

Three-dimensional (3D) printing is perceived as an innovative tool for change in tissue engineering and regenerative medicine based on research outcomes on the development of artificial organs and tissues. With advances in such technology, research is underway into 3D-printed artificial scaffolds for tissue recovery and regeneration. In this study, we fabricated artificial scaffolds by coating bone demineralized and decellularized extracellular matrix (bdECM) onto existing 3D-printed polycaprolactone/tricalcium phosphate (PCL/TCP) to enhance osteoconductivity and osteoinductivity. After injecting adipose-derived stem cells (ADSCs) in an aggregate form found to be effective in previous studies, we examined the effects of the scaffold on ossification during mandibular reconstruction in beagle dogs. Ten beagles were divided into two groups: group A (PCL/TCP/bdECM + ADSC injection; n = 5) and group B (PCL/TCP/bdECM; n = 5). The results were analyzed four and eight weeks after intervention. Computed tomography (CT) findings showed that group A had more diffuse osteoblast tissue than group B. Evidence of infection or immune rejection was not detected following histological examination. Goldner trichrome (G/T) staining revealed rich ossification in scaffold pores. ColI, Osteocalcin, and Runx2 gene expressions were determined using real-time polymerase chain reaction. Group A showed greater expression of these genes. Through Western blotting, group A showed a greater expression of genes that encode ColI, Osteocalcin, and Runx2 proteins. In conclusion, intervention group A, in which the beagles received the additional ADSC injection together with the 3D-printed PCL/TCP coated with bdECM, showed improved mandibular ossification in and around the pores of the scaffold.

Bioprinting of Multiscaled Hepatic Lobules within a Highly Vascularized Construct.

Highly vascularized complex liver tissue is generally divided into lobes, lobules, hepatocytes, and sinusoids, which can be viewed under different types of lens from the micro- to macro-scale. To engineer multiscaled heterogeneous tissues, a sophisticated and rapid tissue engineering approach is required, such as advanced 3D bioprinting. In this study, a preset extrusion bioprinting technique, which can create heterogeneous, multicellular, and multimaterial structures simultaneously, is utilized for creating a hepatic lobule (≈1 mm) array. The fabricated hepatic lobules include hepatic cells, endothelial cells, and a lumen. The endothelial cells surround the hepatic cells, the exterior of the lobules, the lumen, and finally, become interconnected with each other. Compared to hepatic cell/endothelial cell mixtures, the fabricated hepatic lobule shows higher albumin secretion, urea production, and albumin, MRP2, and CD31 protein levels, as well as, cytochrome P450 enzyme activity. It is found that each cell type with spatial cell patterning in bioink accelerates cellular organization, which could preserve structural integrity and improve cellular functions. In conclusion, preset extruded hepatic lobules within a highly vascularized construct are successfully constructed, enabling both micro- and macro-scale tissue fabrication, which can support the creation of large 3D tissue constructs for multiscale tissue engineering.

Effects of corn particle size on nutrient utilization in pigs evaluated under optimal and heat stress conditions.

The effects of corn particle size on nutrient digestibility and energy utilization in pigs were determined under optimal (experiment 1, 25 ± 1 °C) or heat stress (experiment 2, 37 ± 1 °C) conditions. In Exp. 1 and 2, five experimental diets were tested using a 5 × 5 Latin square design involving five barrows (Landrace × Yorkshire × Duroc, average initial body weight of 30 ± 1 kg and 45.0 ± 1.8 kg, respectively, in individual metabolic cages). Dietary treatments were as follows: 200-, 300-, 400-, 600-, 800-µm corn particle sizes obtained by mesh screens. Under optimal thermal conditions, digestibility of dry matter (DM) and crude fiber (CF) from 200-µm diet was higher (P < 0.05) compared to that from the 300-µm and 400-µm diets. The digestibility of crude protein (CP) and ether extract (EE) was the highest (P < 0.05) at the 200-µm particle size. The apparent total tract digestibility of energy was significantly higher (P < 0.05) on the 200-µm diet. Under heat stress, digestibility of CF when corn was ground to 600 µm was higher (P < 0.05) compared to 300 and 400 µm. Digestibility of NDF and ADF was the highest (P < 0.05) at 600-µm corn particle size. In conclusion, grinding corn to 200-µm corn particles had a positive effect on DM, CP, EE, and CF under optimal thermal condition, while the 600-µm corn particle size had positive effects on digestibility of CF, NDF, and ADF than 200-µm corn particle size under heat stress.

Systems biological approaches to the cardiac signaling network.

Recent systems biological studies of cardiac systems have greatly advanced our understanding of cardiac physiology with a particular focus on the excitation-contraction coupling. With these advancements, there is a growing interest in systems analysis of the cardiac signaling network because its dynamical property is closely associated with cardiac diseases. In this article, we review recent attempts at computational modeling of the cardiac signaling network and provide a system-level perspective on the analysis of the large-scale cardiac signaling network. We discuss why the systems biological approach is useful and what novel insights it can provide for the development of personalized therapeutic strategies for cardiac diseases in the post-genomic era.

Cleft Alveolus Reconstruction Using a Three-Dimensional Printed Bioresorbable Scaffold With Human Bone Marrow Cells.

Bone tissue engineering technology based on scaffold has been applied for cleft lip and palate treatment. However, clinical applications of patient-specific three-dimensional (3D) scaffolds have rarely been performed. In this study, a clinical case using patient-specific 3D-printed bioresorbable scaffold with bone marrow stromal cells collected from iliac crest in the operating room has been introduced. At 6-month after transplantation, the bone volume of the newly regenerated bone was approximately 45% of the total defect volume. Bone mineral density of the newly regenerated bone was about 75% compared to the surrounding bone. The Hounsfield unit value was higher than that of cancellous maxillary alveolar bone and lower than that of the cortical maxillary alveolar bone. Bone-marrow-derived mesenchymal stem cells-seeded 3D-printed patient-specific polycaprolactone scaffolds offer a promising alternative for alveolar cleft reconstruction and other bony defects.

Thickness-Dependent Phonon Renormalization and Enhanced Raman Scattering in Ultrathin Silicon Nanomembranes.

We report on the thickness-dependent Raman spectroscopy of ultrathin silicon (Si) nanomembranes (NMs), whose thicknesses range from 2 to 18 nm, using several excitation energies. We observe that the Raman intensity depends on the thickness and the excitation energy due to the combined effects of interference and resonance from the band-structure modulation. Furthermore, confined acoustic phonon modes in the ultrathin Si NMs were observed in ultralow-frequency Raman spectra, and strong thickness dependence was observed near the quantum limit, which was explained by calculations based on a photoelastic model. Our results provide a reliable method with which to accurately determine the thickness of Si NMs with thicknesses of less than a few nanometers.